chapter organic products from the sea: pharmaceuticals ... · 27 chapter organic products from the...

27

CHAPTER

Organic Products from the Sea:Pharmaceuticals,

Nutraceuticals, FoodAdditives, and

Cosmoceuticals

All figures are available on the companion website in color (if applicable).

27.1 INTRODUCTIONHumans have long used the ocean as a source of food and minerals. The inorganicresources obtained from the sea are primarily salt, sand, and gravel. In coastal regionswhere oysters grow, their shells have been used to formulate a type of concrete calledtabby. Diatomaceous earth is used as an insecticide, a filtration medium, and an abrasive.Although most of the organic materials harvested from the ocean serve as seafood, anincreasing amount is being used for medicinal purposes, as food additives, in cosmetics,and as pesticides. Since the 1970s, much effort has been directed at searching the oceanand its organisms for novel biomolecules. This interest was stimulated by the recogni-tion that marine organisms are likely to have developed unique biosynthetic pathways togenerate compounds that help them survive the environmental conditions found only inthe oceans. Although many unique compounds have been identified, few new productshave yet to be brought to market. Recent advances in biotechnology, such as genomicsand bioinformatics, are now being used to overcome problems associated with the com-mercial development of new marine products. As a result, several marine biomoleculesare now in clinical trials for use in treating cancer, infections, Alzheimer’s disease,and asthma. Others are being tested for use as antifouling agents. These advances aresupported by an interdisciplinary approach involving the expertise of marine biolo-gists, chemical ecologists, synthetic organic chemists, and pharmacologists, along withexperts in genomics, biotechnology, and mariculture.

In this chapter, a description of the marine organic products in current usage isprovided along with a consideration of how the structures of these molecules con-fer predictable physiological activities. This is followed by a discussion of the strategicapproach used to discover and develop marine organic products along with the rea-sons why new products are so hard to bring to market. Finally, some examples of

1

2 CHAPTER 27 Organic Products from the Sea

products now in the development pipeline are presented. These products are beingtargeted for use as biomedicines, nutraceuticals, cosmoceuticals, antifouling agents,pesticides, research probes, and biosensors, and in mariculture and environmental appli-cations.1 The latter include in situ pollutant degradation and removal of toxic heavymetals.

27.2 WHAT ARE MARINE NATURAL PRODUCTS?In this chapter we will focus on the class of organic compounds called naturalproducts or secondary metabolites. These biomolecules do not play a direct role inthe development, growth, or reproduction of organisms. Not all organisms make sec-ondary metabolites. Of those that do, their natural products tend to be quite speciesspecific. The secondary metabolites are generally used by organisms to control ecolog-ical relationships that involve: (1) defense against predation, parasitism, and infection,(2) competition for space and food, (3) intraspecies communication for the purposesof mating, hunting, or quorum signaling, and (4) maintenance of mutualistic symbionts.Some natural products confer UV protection.

Most higher plants and microbes have secondary metabolites whereas most verte-brates do not. Because of the species specificity of these compounds, chemical diversitywithin a phylum is roughly correlated with species diversity. Most of the marine naturalproducts (MNPs) are contributed by the seaweeds, sponges, and cnidarians, reflectingtheir extraordinary species diversity. This high species diversity is part of the reasonwhy the oceans have long been considered as having great potential for new drug dis-coveries. The other reason is inherent in the biological role of natural products—thesebiomolecules help organisms cope with particular ecological challenges. The biochem-ical mechanism responsible for the desirable physiological activity usually involves ahighly specific binding of the secondary metabolite with a target receptor molecule.Fortunately, enough similarity exists among the molecular structures of the targetreceptors in marine organisms and humans that many MNPs exhibit very high phys-iological activity in humans. The kinds of activities most commonly seen are antibiotic,anti-inflammatory, antiviral, antioxidant, anticoagulant, analgesic, and antitumorogenic,giving MNPs great potential in treating bacterial and fungal infections, asthma, immunediseases like HIV/AIDS, pain, and cancer. Other MNPs have light absorption properties,making them excellent candidates for use as sunscreens, dyes, and coloring. Some actas surfactants and, thus, might be useful in preventing biofilm formation, biofouling,

1 A marine nutraceutical is defined as “a marine-derived substance that can be used as a dietary supple-ment or a food ingredient that provides a medicinal or health benefit beyond basic nutrition” [Barrow,C., and F. Shahidi (2008). Marine Nutraceuticals and Functional Foods. CRC Press, 494 pp.] Cos-moceuticals are cosmetic products with druglike benefits conferred by ingredients such as vitamins,phytochemicals, enzymes, antioxidants, and essential oils.

27.3 History of Marine Organic Products 3

and adhesion of microbes to wounds. Others are excellent metal ligands, giving thempotential as water purifying agents.

During the past 30 years, more than 35,000 novel MNPs have been isolated andstructurally identified. Most of these exhibit bioactivity in arenas that suggest theirpotential as a new drug. Many have no terrestrial analog and so represent wholly newclasses of potential drugs. At present, most attention is focused on developing new treat-ments for cancer. Approximately 150 of the MNPs are presently known to be cytotoxicagainst tumor cells, with approximately 35 having a known mechanism(s) of action.Out of these, at least a dozen are now in human clinical trials. As shown in Table 27.1,these include ecteinascidin (Yondelis), bryostatin-1, squalamine, aplidin, dolastatin-10,ILX651, and KRN7000 (�-galactosylceramide). Another very active area of research liesin developing uses for marine biomass leftover from commercial fisheries and maricul-ture operations. In 2000, 100 million tonnes of biomass were harvested, with only halfbeing used. One successful approach to handling seafood “waste” has been developmentof products from Chitosan, a processed form of chitin.

27.3 HISTORY OF MARINE ORGANIC PRODUCTSExtracts from marine organisms have been used for medicinal purposes in China, India,the Near East, and Europe since ancient times. As late as the 1800s, many were a part ofstandard pharmacopoeias. Scientists have since come to appreciate that many of theseremedies contain potent drugs. Substantial efforts are now being directed to the studyof their active agents. For example, various seaweeds have been used to treat dropsy,menstrual difficulties, gastrointestinal disorders, abscesses, and cancer. We now knowthat seaweeds contain a large number of novel, very potent MNPs, many of which arehalogenated compounds. Sponges, which contain high levels of iodine, have been usedto treat tumors, goiter, dysentery, and diarrhea.

Before the invention of synthetic sponges, natural ones were used for absorbentpurposes in medical settings. For example, anesthetics were delivered by impregnatinga sponge with a soporific. Blood flow was stanched with sponges. Contraceptives, suchas lemon juice and quinine, were held in place with sponges.

Hippocrates recorded that juices from various species of mollusks were commonlyused as a laxative. Extracts from the sea hare, Aplysia, have been used as a depilatory.Essences from gastropod opercula have been used in perfume and incense. Severalmarine snails were a source of blue and purple dyes to the Hebrews and Romans duringbiblical times. Given this ancient fund of knowledge, marine scientists have begun a newfield of study called marine ecological anthropology, which seeks to uncover traditionalenvironmental knowledge likely to yield insights into marine organisms with interestingMNPs.

Most MNPs currently in common use are food additives, insecticides, nutraceuti-cals, and ingredients of cosmetics. Some examples are provided in Table 27.2. Productscurrently used as drugs or in drug research are shown in Table 27.3 and discussed next.


Tab

le27

.1M

arine

Natu

ralP

rod

ucts

Curr

ently

inC

linic

alTrials

(Circa

2007).

Phy

lum

Co

mp

oun

dN

ame

Typ

eO

rig

inD

isea

seA

pp

licat

ions

Clin

ical

Pha

se

IPL

57

6,0

92

,

IPL-5

12

,60

2,

and

IPL-5

50

,26

0

Ste

roid

Petr

osia

co

ntig

nata

Infla

mm

atio

n/a

sth

ma

II

E-7

38

9A

nalo

go

fH

alic

ho

nd

rin,

am

acro

lide

Halic

ho

nd

ria

oka

dai

Cancer

III

Talto

bulin

(HT

I-2

86

)&

E7

97

4

Analo

go

ftr

ipep

tid

e

Hem

iaste

rlin

Hem

iaste

rella

min

or

Lung

cancer

I/II

Po

rife

raaLB

H5

89

and

NV

P-L

AQ

28

4

Deriva

tive

of

psam

map

linA

,a

bro

min

ate

daro

matic

am

ino

acid

Psam

map

lysilla

sp

.A

dva

nced

or

meta

sta

tic

NS

CLC

or

malig

nant

ple

ura

lm

eso

thelio

ma

I

KR

N7

00

0G

lyco

sp

hin

go

lipid

,

�-g

ala

cto

syl

cera

mid

e

Ag

ela

sm

auritianus

Pancre

atic

cancer

and

so

lidtu

mo

rs

II

ET-

38

9A

xinella

sp

.C

ancer

I

Zaly

psis

(PM

00

10

4/5

0)

Jo

rum

ycin

and

Renie

ram

ycin

analo

gs

Mo

llusks

and

sp

ong

es

Ad

vanced

so

lidtu

mo

rs

and

lym

pho

ma

I

Cnid

eria

OA

S-1

00

(meth

op

tero

sin

)

Pho

sp

ho

lipid

sP

seud

op

tero

go

rgia

elis

ab

eth

ae

(so

ftco

ral)

Wo

und

healin

g,

anti-infla

mm

ato

ry

I/II


aD

ola

sta

tin

10

and

derv

ative

s,

so

blid

otin

(TZ

T-1

02

7)

and

Syn

thad

otin/T

asid

otin

(ILX

65

1)

Po

lyp

ep

tid

es,

do

lasta

tin

analo

gs

Do

lab

ella

auricula

ria

(sea

hare

)

So

ft-t

issue

sarc

om

as,

meta

sta

tic

mela

no

ma

II

bK

hala

lide

FC

yclic

dep

sip

ep

tid

eE

lysia

rufe

scens

Hep

ato

cellu

lar

carc

ino

ma,

NS

CLC

and

mela

no

ma.

Po

ssib

le

treatm

ent

for

pso

riasis

II

PM

02

73

4K

hala

lide

deriva

tive

Ely

sia

rufe

scens

I

Mo

llusca

Sp

isulo

sin

e(E

S-2

85

)A

min

oalc

oho

lS

pis

ula

(=M

actr

om

eris)

po

lynym

a(A

rctic

surf

cla

m)

Cancer

I

Zaly

psis

(PM

00

10

4/5

0)

Jo

rum

ycin

and

Renie

ram

ycin

analo

gs

Mo

llusks

and

sp

ong

es

Ad

vanced

so

lidtu

mo

rs

and

lym

pho

ma

I

CG

X-1

16

0P

ep

tid

e,

co

no

toxin

deriva

tive

Co

nus

geo

gra

phus

Pain

I

AM

-33

6P

ep

tid

e,

co

no

toxin

deriva

tive

Co

nus

geo

gra

phus

Pain

II

CG

X-1

00

7P

ep

tid

e,

co

no

toxin

deriva

tive

Co

nus

geo

gra

phus

Pain

and

ep

ilep

sy

I

Ecto

pro

cta

Bry

osta

tin

1M

acro

cyc

licla

cto

ne

Bug

ula

neritina

(bry

ozo

an)

Cancer

II

(Continued

)


Tab

le27

.1(C

ontinued

)

Phy

lum

Co

mp

oun

dN

ame

Typ

eO

rig

inD

isea

seA

pp

licat

ions

Clin

ical

Pha

se

Nem

ert

ea

GT

S-2

1,

DM

XB

AA

nab

asein

eanalo

gA

mp

hip

oru

sla

ctiflo

reus

Alz

heim

er’

s/s

chiz

op

hre

nia

I/II

Ap

lidin

e

(dehyd

rod

idem

nin

B)

Dep

sip

ep

tid

e(a

nalo

go

f

did

em

nin

)

Ap

lidiu

malb

icans

(tunic

ate

)

Multip

lem

yelo

ma,

leukem

ia,

mela

no

ma,

renal

and

oth

er

so

lid

tum

ors

I/II

aYo

nd

elis

/Tra

becte

din

(Ecte

inascid

in7

43

)

Tetr

ahyd

rois

oq

uin

olo

ne

alk

alo

id

Ecte

inascid

atu

rbin

ata

(tunic

ate

)

So

ft-t

issue

sarc

om

as,

ova

rian,

pro

sta

te,

bre

ast,

and

so

lidtu

mo

rs

I/II/

III&

Clin

i-

cal

Use

Cho

rdata

Sta

uro

sp

orine,

N-b

enzo

ylate

d(P

KC

41

)

Alk

alo

idE

ud

isto

ma

toeale

nsis

(tunic

ate

)&

its

pre

dato

ryfla

two

rm,

Pseud

ocero

ssp

.

Cancer,

multip

le

mye

lom

a

I

Sq

uala

min

ela

cta

te

(MS

I-1

25

6F)

Am

ino

ste

rol

Sq

ualu

sacanth

ias

(shark

)

Ova

rian

cancer

and

NS

CLC

III

Neo

vasta

t(A

E-9

41

)C

rud

eextr

act

Sq

ualid

e(fis

h)

I-II:

Pro

sta

teC

ancer.

III:

Kid

ney

and

NS

CLC

III

Tectin,

tetr

od

in

(tetr

od

oto

xin

)

Alk

alo

idTetr

ad

ontifo

rmes

(fis

h)

So

diu

mchannel

blo

cker

II/III

Nep

tune

Krill

Oil

Pho

sp

ho

lipid

sK

rill

Pre

menstr

ual

syn

dro

me

II

Mic

rob

es

Salin

osp

ora

mid

eA

(NP

I-0

05

2)

Alk

alo

idM

arine

ob

ligate

actino

myc

ete

Multip

lem

yelo

ma

I

Fung

us

NP

I-2

35

8H

alim

ide

(dik

eto

pip

era

zine)

Asp

erg

illus

sp

.so

lidtu

mo

rsand

lym

pho

mas

I

aP

ossib

leb

acte

rial

so

urc

ebP

ossib

leg

reen

alg

al

so

urc

e

NS

CLC

=no

n-s

mall

cell

lung

cancer


Tab

le27

.2E

xam

ple

sof

Marine

Natu

ral

Pro

ducts

inC

urr

ent

Use

as

either

Pharm

aceuticals

,Food

Ad

ditiv

es,

Insecticid

es,

Nutr

aceuticals

,and

Cosm

oceuticals

.

Pro

duc

tsS

pec

ific

Pro

duc

tS

our

ceU

ses

Trad

eN

ame

or

Pro

duc

tio

nC

om

pan

y

Alg

al

po

lysaccharid

eC

arr

ag

eenans,

ag

ar,

alg

inate

s

Red

alg

ae

Co

sm

etics,

thic

keners

,

antico

ag

ula

nt,

antivi

ral,

pharm

aceuticals

Marine

Co

lloid

s(U

SA

),

Danis

co

(Denm

ark

),

SO

BA

LG

(Fra

nce)

Gly

co

sam

ino

gly

cans

Cho

nd

roitin

sulfa

teFis

hC

osm

etics,

tissue

rep

lacem

ent,

antico

ag

ula

nt

CT

TP

(Fra

nce)

Co

llag

en

Co

sm

etics,

art

ifical

tissue

Chito

san

�-(

1-4

-N-A

cety

l)

glu

co

sam

ine

Cru

sta

cean

shells

,fu

ng

i

Co

sm

etics,

wo

und

dre

ssin

gs,

mic

roencap

sula

tio

n

Lip

ids

Lo

ng

-chain

po

lyunsatu

rate

dfa

tty

acid

s(a

rachid

onic

acid

,

eic

osap

enta

eno

icacid

,

and

do

co

so

hexaeno

ic

acid

[DH

A])

Mic

roalg

ae,

seaw

eed

s,

fish

Pre

ventio

no

fheart

dis

ease,

menta

ld

eve

lop

ment

in

pre

matu

rechild

ren,

antitu

mo

ral,

lipid

meta

bo

lism

BIO

NA

GR

OL

30

00

,

AG

EO

ME

GA

3

(Ark

op

harm

a),

MA

XE

PA

(Pie

rre

Fab

re

Med

icam

ent)

Ho

rmo

nes,

cyc

lic

pep

tid

es

Fis

h

hyd

roly

sate

s

Antio

xid

ant,

imm

uno

stim

ula

nts

,

nutr

aceutical

pro

ducts

Pro

marine

Pep

tid

es

Antifr

eeze

gly

co

pro

tein

sP

ola

rfis

hC

ell

pro

tectio

nd

uring

co

ld

sto

rag

e(a

nim

al

and

hum

an

eg

gs,

blo

od

pla

tele

ts)

and

imp

rove

dq

ualit

yo

ffr

oze

nfo

od

s

A/F

Pro

tein

Caro

teno

ids

Asta

xanth

inK

rill,

alg

ae

Red

-co

lore

dfo

od

ad

ditiv

efo

r

mariculture

dsalm

on

and

shrim

p

used

toenhance

red

co

lor;

antio

xid

ant

Num

ero

us

co

mp

anie

s

mark

eting

und

er

vario

us

trad

enam

es

So

urc

e:

After

Manto

ura

,F.

(ed

.)(2

00

1).

Marine

bio

techno

log

y:A

Euro

pean

str

ate

gy

for

marine

bio

techno

log

y.E

SF

Marine

Bo

ard

Feasib

ility

Stu

dy

Gro

up

Rep

ort

,E

SF

Marine

Bo

ard

Po

sitio

nP

ap

er

4,

p.

8.

Tab

le27

.3M

arine

Natu

ralP

rod

ucts

Curr

ently

Bein

gU

sed

as

Dru

gs

or

inD

rug

Researc

h.

Pro

duc

tTr

ade

Nam

ean

dC

hem

ical

Cla

ssA

pp

licat

ion

Ori

gin

alS

our

ceM

etho

do

fP

rod

ucti

on

Mar

kete

r(Y

ear

of

Co

mm

erci

aliz

atio

n)

Aeq

uo

rin

Bio

lum

inescent

calc

ium

ind

icato

r

Bio

lum

inescent

jelly

fish

Aeq

uo

ravi

cto

ria

Reco

mb

inant

pro

tein

Ara

-AV

idara

bin

eN

ucle

osid

e(a

min

o-6

-

beta

-D-a

rab

ino

-

fura

no

syl

-9,

9h-p

urine)

Antivi

ral

dru

g(h

erp

es

infe

ctio

ns)

Marine

sp

ong

e

Cry

pto

teth

yacry

pta

Mic

rob

ial

ferm

enta

tio

n

of

analo

g

Ara

-CC

yto

sar-

U,

Cyt

ara

bin

e

(19

72

)

Nucle

osid

e

(4-a

min

o-1

-beta

-D-

ara

bin

ofu

rano

syl

-

2(1

H)-

pyr

imid

ino

ne)

Anticancer

dru

g

(leukem

iaand

no

n-H

od

gkin

’s

lym

pho

ma)

Marine

sp

ong

e

Cry

pto

teth

yacry

pta

Chem

ical

syn

thesis

of

analo

g

Caly

culin

AA

GS

cie

ntific

Po

lyketid

eM

ole

cula

rp

rob

e:

sele

ctive

inhib

ito

ro

f

pro

tein

pho

sp

hata

se

1

Sp

ong

eD

isco

derm

ia

caly

x

Extr

acte

dfr

on

the

sp

ong

e

Cep

halo

sp

orins

(19

65

)�

-Lacta

mA

ntib

iotic

(antib

acte

rial

by

inhib

itio

no

f

muco

pep

tid

esyn

thesis

)

Marine

fung

us

Cep

halo

sp

orium

acre

mo

niu

m

Sem

isyn

thetic

antib

iotic

deriva

tive

so

f

cep

halo

sp

orin

C

Fo

rmula

idTM

Mart

ek

Bio

scie

nces

Fatt

yacid

s:

DH

A,

EH

A

Nutr

itio

nal

sup

ple

ments

Marine

mic

roalg

ae

Cell

culture

Gre

en

fluo

rescent

pro

tein

Pro

tein

Rep

ort

er

gene

Bio

lum

inescent

jelly

fish

Aeq

uo

ravi

cto

ria

Reco

mb

inant

pro

tein

Kain

icacid

(early

19

00

s)

Am

ino

acid

Antihelm

intic,

Insecticid

e,

neuro

excitato

ry

and

neuro

toxic

activi

ty

Red

alg

aD

igenea

sim

ple

x

Extr

acte

dfr

om

Dig

enea

sim

ple

x,fo

und

main

ly

near

Jap

an

and

Taiw

an.

Chem

ical

syn

thesis

Lim

ulu

sam

eb

ocyt

e

lysate

Bio

Whitta

ker,

Ert

elA

lso

pD

ete

ctio

no

f

end

oto

xin

s

asso

cia

ted

with

gra

m-n

eg

ative

bacte

ria

Ho

rsesho

ecra

bLim

ulu

s

po

lyp

hem

us

Am

eb

ocyt

es

of

the

ho

rsesho

ecra

b

Mano

alid

eB

IOM

OL

Res.

Lab

.,A

.G.

Scie

ntific

,In

c.,

No

vag

en,

Inc.

No

nste

roid

al

seste

rterp

eno

id

Mo

lecula

rp

rob

e;

pho

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27.4 Chemical Ecology and Structure-Activity Relationships 11

27.4 CHEMICAL ECOLOGY AND STRUCTURE-ACTIVITYRELATIONSHIPS

Secondary metabolites have evolved under the pressure of natural selection for a cer-tain purpose and mode of action. Because of the uniqueness of the marine environment,the necessary adaptations have resulted in novel secondary metabolites that are highlyspecific for their target receptors. Terrestrial plants and microbes have also evolvedunique species-specific natural products. Indeed, evolutionary selection can be viewedas a type of natural drug development process in which structures have become opti-mized for their biological activity. Thus, it is not surprising that about half of the drugsin current use were discovered as natural products.

Marine organisms have long been recognized as likely to contain many potentialnovel drugs because of the environmental conditions that are unique to their habitat.These conditions include high ionic strengths, low light levels, cold temperatures, andhigh pressures. Halides, such as bromine and iodine, are relatively abundant componentsin marine metabolites, reflecting their high concentrations in seawater. Another uniqueadaptation seen in many marine organisms is bioluminescence. Intense competition forspace, light, and nutrients, especially in populous benthic areas such as coral reefs, hasfavored development of a range of chemical mechanisms for warding off competitorsand rapidly assimilating nutrients and light. Most of the lower invertebrates that do nothave hard outer coverings, such as sea cucumbers and sea squirts, tend to have MNPsthat act as chemical deterrents to predation. Thus, the standard rule of thumb amongMNP chemists is that fat, fleshy, slow-moving, and brightly colored animals are likely toharbor MNPs. Finally, reproduction in the marine environment presents challenges thatare quite different from those encountered on land. A common adaption is the use ofMNPs as an attractant to locate a mate or induce spawning.

To date, most marketed marine products have come from shallow and often tropicalmarine organisms, due mainly to the ease of collecting them. But increasing scientificinterest is now being focused on the potential medical uses of organisms found in thedeep sea. These organisms have developed unique adaptations that enable them to sur-vive in dark, cold, and highly pressurized environments. Another relatively unexploredcategory of organisms are marine microbes, which are likely to contain novel substancesdue to their unique metabolic pathways.

MNPs are highly diverse in structure. They include terpenes, halogenated com-pounds, alkaloids (which contain nitrogen), and polyketides. The last are large multien-zyme protein complexes that contain a coordinated group of active sites. Their potentphysiological activity and receptor-binding specificity are the result of a well-defined,complex three-dimensional structure rich in stereochemical centers, concatenated rings,and reactive functional groups. These functional groups enable hydrogen bonding andother intermolecular interactions. MNPs that are involved in enzyme systems tend tohave maximal reactivity between 5 to 12◦C instead of the 30 to 35◦C characteristicof their terrestrial counterparts. (Thermophilic microbes living in hydrothermal ecosys-tems are a likely exception to this.) Because of the complexity of their chemistry, manyof their physiological effects are highly dependent on environmental conditions.


The molecular structures characteristic of MNPs differ from those favored by organicchemists, whose approach toward synthetic drug development focuses on creating low-molecular-weight compounds with few stereochemical centers and a relatively lowdegree of chemical reactivity. The latter confers stability to the drug molecules. Inmany cases, MNPs are too bioactive and have too many negative side effects to beuseful drugs. In these cases, MNP chemists create analogs of the original compoundin which undesirable bioactivity is eliminated, or reduced, through structural modifica-tions. Thus, MNPs are generally used as a starting pointing for development of a newdrug. To accomplish these “redesigns,” MNP chemists must understand structure-activityrelationships.

27.5 THE DISCOVERY AND DEVELOPMENT OF MARINEPHARMACEUTICALS

The process of discovering and developing new pharmaceuticals is a long and arduousprocess. In 2001, the Tufts Center for the Study of Drug Development estimated thatfor the average new drug, this process took 10 to 15 years and $800 million (USA).Much of this time and cost is associated with safety and efficacy testing required bythe U.S. Food and Drug Administration. For every 5000 potential drugs that makeit to the initial stages of required testing, only five undergo clinical trials, with oneeventually being approved for patient use. Compounds derived from terrestrial naturalproducts constitute about half of the pharmaceuticals currently in use, with most ofthe rest being based on completely synthetic structures. Fewer than a dozen drugsnow in use are derived from MNPs. This is partly because a systematic search forbioactive MNPs began only in the 1970s, much later than the search on land. Thelatter was greatly aided by bioethnology in which ancient medical knowledge providedimportant leads on bioactive natural products present in terrestrial plants. In contrast,locating marine organisms most likely to contain useful MNPs requires underwater sur-veys and collections. These activities were greatly limited until development of SCUBAand ROVs.

Because of the costly and risky nature of drug development, few MNPs have made itto market. This situation is likely to change for two reasons: (1) the rate of discovery ofnew terrestrial natural products has slowed and (2) the promise of combinatorial tech-niques in developing synthetic drugs, as promoted in the 1990s, has not been realized.Thus, MNPs are increasingly being recognized as an important source of potential newdrugs. In addition, several technological advances have resolved long-standing problemsassociated with isolation, structure identification, design of better analogs, and syntheticproduction of MNPs. As a result, more than 20 compounds derived from MNPs are nowunder clinical trials (Table 27.1).

The most critical areas of research are targeted at finding natural products fortreatment of the disease targets listed in Table 27.4. As discussed in the following

27.5 The Discovery and Development of Marine Pharmaceuticals 13

Table 27.4 Most Critical Disease Targets for New Drug Development.

Disease Type Example

Infectious Antibiotic-resistant pathogens

Neurological Parkinson’s and Alzheimer’s disease

Cardiovascular Arteriosclerosis

Immunological Lupus and eczema

Antiviral HIV

Anti-inflammatory Arthritis

Oncological Cancer

sections, MNPs have been identified that collectively have the potential to treat all butneurological and cardiovascular diseases, although as regards the latter, antilipemic activ-ity (cholesterol-lowering) is common. Other biomedical applications include repair ofbones and the prevention of biofilm formation. The latter serves to inhibit microbialinfection.

27.5.1 Marine Bioprospecting

The first step in drug discovery is the identification of marine organisms likely to containnovel natural products. This process is termed bioprospecting and relies on insightsfrom the field of marine chemical ecology. The latter seeks to understand how marineorganisms use natural products to: (1) compete for resources, (2) maximize reproductivesuccess, and (3) prevent predation, parasitism, and disease. These compounds includetoxins and attractants. In many cases, the natural products are created by a symbioticmicrobe or prey. The active compound is then concentrated in the tissues of the hostor predator. MNPs tend to be highly species specific because they represent adaptationsto survival in a particular type of environment.

The first step in bioprospecting is observation of species characteristics and behav-iors. For example, slow-moving animals with no hard outer coverings are likely to usetoxins to prevent predation. These include soft-bodied sessile invertebrates, such astunicates, soft coral, and sponges. Some ancient knowledge of these types of bioac-tivity can be found in indigenous populations. Efforts to collate this knowledge arebeing conducted by marine ecological anthropologists. This has led to two concerns:(1) that indigenous cultures benefit from their environment’s genetic resources, and(2) that efforts be made to preserve marine biological diversity. To address this, theUN Convention of Biological Diversity was signed in 1992. It establishes sovereignrights over biological resources. It also seeks to create mechanisms for the sustainableuse of these resources and ensures equitable distribution of the resulting benefits. Inthe case of developing countries, the Convention requires compensation for access


to genetic resources and the provision of assistance in protecting marine biodiver-sity. All marine bioprospecting efforts must now comply with the stipulations of thisConvention.

27.5.2 Isolation and Screening

Once an organism is collected, it is screened for potentially useful natural products.This screening technique has to be fast, as hundreds of organisms can be collectedat a time. Screening typically starts by homogenizing the whole organism or someselected organ in a blender along with a solvent whose polarity can range from polarto nonpolar. Since “like dissolves like,” the polarity of the solvent will determinewhich MNPs are solubilized from the tissues. The resulting “crude extracts” poten-tially contain hundreds or even thousands of compounds. By varying the polarity ofthe solvent, different MNPs can be solubilized and, hence, a family of crude extracts isgenerated.

The crude extracts are subjected to a battery of bioassays designed to detect interest-ing levels and types of biological activity. Bioassays typically involve exposure to intacttissues or cells. For example, bioassays designed to identify cancer drugs use cancercells from humans or rodents. Increasingly, these bioassays are being designed to assessactivity against a specific molecular target involved in treating diseases, such as inhi-bition of mitosis (cell division), promotion of apoptosis (cell death), or inhibition ofspecific enzyme activity (Table 27.5). This approach provides an understanding of thebiochemical basis by which the natural products act. This knowledge enables devel-opment of optimal methods for drug delivery and dosage levels. New bioassays havehad to be developed to accommodate the biochemical mechanisms by which marinenatural products act, as they are quite different from those exhibited by drug moleculesof terrestrial and synthetic origin.

Some bioassays, such as those used to detect antibiotic activity, are so fast andinexpensive that they can be done in the field. Most bioassays require sophisticatedequipment and extended periods of time and, hence, must be done in a laboratory. Byusing robotic technology, systems have been developed to enable performance of thou-sands of bioassays per day. The results are used to identify the crude extracts that havethe highest degrees of interesting bioactivity. Various separation technologies are thenused to fractionate these extracts so as to isolate the bioactive compound(s). Mucheffort is currently being directed at developing bioassays that can identify whether adrug candidate has any potentially harmful biological effects.

Bioassays have demonstrated that more than 10% of marine organisms contain cyto-toxic substances as compared with 2 to 3% of terrestrial species. These toxins occurmore frequently in marine invertebrates than in marine algae, in sessile rather thanmotile species, and in tropical rather than temperate or cold-water animals. Marine tox-ins do not generally make good drugs because they are usually too powerful. Insteadthey are used as model compounds in the study of biochemical mechanisms and forthe synthesis of less toxic analogs.

27.5 The Discovery and Development of Marine Pharmaceuticals 15

Table 27.5 Molecular Targets of Various Bioassays Used in Drug Development.

Disease Molecular Target/Mode of Action MNP Drug Treatment

Proteasome inhibitor NPI-0052

Antimitotic, binds to the minor groove of DNA interfering with

cell division and genetic transcription processes and DNA repair

machinery

Yondelis

Inhibitor of cell proliferation, promotes the disassembly of actin

stress fibers

Spisulosine

Alters the function of the lysosomal membranes inducing cell

death by oncosis

Khalilide

Binds to DNA but does not activate DNA damage checkpoint Zalypsis

Microtubule-stabilizing Discodermolide

Cancer Phospholipase A2 Manoalide

Protein phosphatases Okadaic Acid

Protein kinase Bryostatin I

Inhibits secretion of vascular endothelial growth factor related to

angiogenesis. Arrests cell cycle at the G1 and G2 phases

Aplidine

Immunomodulatory KRN 7000

Depolymerizes microtubules and blocks cell growth HTI-286

Inhibits tumor cell proliferation Halichondrin E789

Anti-neoplastic activity through inhibition of microtubule assembly Dolastatin 10

Inhibitor of growth-factor-mediated endothelial cell proliferation

and migration and angiogenesis

Squalamine

Pain Ion channels Saxitoxin

Nicotinic acetylcholine receptors Conotoxins

27.5.3 Structural Identification and Synthesis

Once a purified extract has been obtained, the next step is structural identification ofthe active compound(s). Typically this requires recollection of a large number of sourceorganisms to provide an adequate supply of material for study. In many cases, this hasproven difficult as a good taxonomic identification is often not possible with inverte-brates such as sponges. In other cases, re-collection of the species does not provideextracts with the same bioactivity as the original set. This is thought to reflect theimportance of bioaccumulation of the active compound from prey or from microbial


symbionts whose growth is controlled by environmental conditions. This variabilityillustrates the importance of developing synthetic means for generating the MNP. With-out a reliable source of the purified compounds, clinical trials are not possible. It alsodemonstrates the importance of field-based screening techniques for the identificationof organisms with promising bioactivity.

Using various chromatographic technologies, individual compounds are isolated fromthe extracts. Most MNPs tend to be unstable at high temperatures, making them una-menable to gas chromatography. In these cases, high-pressure liquid chromatographyis used. The structure of the compounds is then determined by nuclear magneticresonance spectroscopy, mass spectrometry, and x-ray crystallography. This step is chal-lenging as most MNPs are large heteroatomic molecules with complex three-dimensionalfeatures.

With the exception of seaweeds, wild collection is not considered a long-term supplyoption due to high cost, unreliability, and environmental impacts. More feasible optionsinclude: (1) mariculture of organisms or cell lines, (2) chemical synthesis performed onan industrial scale, or (3) production from microbes genetically engineered to synthe-size the compounds. Mariculture is not an easy proposition and, hence, few organismsare currently being grown commercially for the purposes of drug production. No con-tinuous cell lines have been established. Both of these approaches are deemed risky asmicrobial symbionts could be critical to the formation of the MNP and, hence, wouldrequire cultivation along with their host.

More success has been achieved from chemical synthesis, although this has provenchallenging given the large sizes and complicated structures found in MNPs. In somecases, as many as 60 steps have been required to effect a complete synthesis from simplestarting products. In most cases, this is not commercially feasible. One solution has beento identify smaller versions of the MNP that have similar structures and bioactivity,but are easier to produce. These analogs can also be designed to eliminate or reduceundesirable biological side effects. Another synthetic approach is to insert genes intomicrobes to enable them to synthesize the MNP. These microbes are grown on a largescale in purified cultures from which the MNP can easily be extracted.

27.5.4 Clinical Trials, Marketing, and Patents

All substances sold as drugs in the United States must be approved by the federal Foodand Drug Administration. This approval process requires a series of phased drug trialsas illustrated in Figure 27.1. The first phases involve animal testing. If no adverse sideeffects are observed and significant ameliorative effects are found, testing on humansubjects is undertaken. This process can take years because of the need to check forlong-term effects and to optimize methods for drug administration and dosage.

The last stage in drug development is an assessment of the market potential for thedrug. If a manufacturer is not able to realize a large enough profit, the drug will notbe brought to market. Thus, business experts must assess whether the potential marketniche is large enough to provide an acceptable return on investment. This assessmentmust now include the costs of “reimbursing” the country from which the originating

27.6 Examples of Marine Natural Products 17

Review and approval byFood & Drug Administration

Phase III: Confirms effectiveness and monitorsadverse reactions from long-term use in 1,000to 5,000 patient volunteers.

Phase II: Assesses effectivenessand looks for side effects in 100 to500 patient volunteers.

Phase I: Evaluates safety anddosage in 20 to 100 healthyhuman volunteers.

1Compoundapproved

5 Compounds enterclinical trials

Discovery and preclinical testing:Compounds are identified and evaluated inlaboratory and animal studies for safety,biological activity, and formulation.

20 4 6 8Years

10 12 14 16

5,000 Compoundsevaluated

FIGURE 27.1

Clinical drug trials required by the U.S. Food and Drug Administration with estimated time required

for completion. Source: From Brennan, M. B. (2000). Drug discovery: Filtering out failures early in

the game. Chemical and Engineering News, June 5, 2000, pp. 63–73.

marine organism was first collected. In cases where the market return is insufficient,the United States provides resources under the Orphan Drug Act of 1983 to supportfurther commercial development of promising drug candidates.

27.6 EXAMPLES OF MARINE NATURAL PRODUCTSMNPs have been classified by their molecular structure, biosynthetic pathway, andorganismal source. The most common molecular types and their biosynthetic path-ways are shown in Table 27.6. About half of MNPs are generated via the isoprenoidpathway, and most of the remainder are evenly split between the amino acid and aceto-genin pathways. Many important antibiotics and anticancer drugs are polyketides. Theiranabolic formation pathway involves a stepwise polymerization of simple 2-, 3-, and4-carbon functional groups, such as acetyl-CoA, propionyl CoA, and butyryl-CoA. Theother pathways contribute a minor number of MNPs.

Some examples of MNPs that are in current use or are in clinical trials are presentedin the following sections, sorted, for the most part, by phylum. To date, the majorityof MNPs have been isolated from sponges, although this may simply reflect a relativelack of work on microbes and fungi. Other major organismal sources of MNPs are thecoelenterates (soft corals and gorgonians), echinoderms, tunicates, mollusks, and bry-ozoans. Some crustaceans and fish are important sources of nutraceuticals and otherorganic products.


Table 27.6 Biosynthetic Pathways of Natural Products and

Representative Examples.

Biosynthetic Pathway Structural Class

Isoprenoid Terpenes

Steroids

Carotenoids

Quinones

Acetogenin Polyketides

Polyphenols

Fatty acids

Prostaglandins

Amino acid Peptides

Alkaloids

Shikimate Cinnamic acid derivatives

Flavonoids

Coumarines

Nucleic acid Nucleic acids

Nucleo bases

Carbohydrate Sugars

Polysaccharides

Source: From Harper, M. K., T. S. Bugni, B. R. Copp, R. D. James, B. S.

Lindsay, A. D. Richardson, P. C. Schnabel, D. Tasdemir, R. M. Van Wagoner,

S. M. Verbitski, C. M. Ireland (2001). Introduction to the Chemical Ecology of

Marine Natural Products, In Marine Chemical Ecology, J. B. McClintock and

B. J. Baker, eds, CRC Press, p. 3–566 (Table 1.1, p. 5).

27.6.1 Macroalgae: Seaweeds

The macroalgae or seaweeds are classified by their pigments into the Chlorophyta(green algae), the Phaeophyta (brown algae), and the Rhodophyta (red algae). There areapproximately 900 green, 4000 red, and 1500 brown species of seaweed. Red seaweedsare found mostly in subtropical and tropical waters, while brown seaweeds are morecommon in cooler, temperate waters. Around 220 species of seaweed are harvestedcommercially, with about half used for food and the rest for phycocolloid production.

PhycocolloidsPhycocolloids are high-molecular-weight polysaccharides isolated from the cell wallsand mucilage of seaweed as noncrystalline materials or gums. They include agar, car-rageenan, and algin. Agar is obtained from red algae, mostly Gelidium and Gracilaria.It is a variable mixture of several polymers whose most common repeating units areagarose (27.1) and agaropectin (27.2). A significant amount of the agarose also containsacidic residues, primarily sulfate and pyruvate.


CH2OH CH2O

O

OOOH

OHOH

HOHO

Agarose Agaropectin

CH2 CH2OH

OO O

O

OH

OHHO HOHO

Agarose (27.1) and Agaropectin (27.2)

Red algae are also the primary source of carrageenan (27.3), mostly from Kappa-phycus and Betaphycus.

Partial structure of Carrageenan

CH2OH CH2OSO32

OSO32

O

OR

R9O O

O

O

O OH2

2

R9 is usually Hbut can be SO3.R 5 H or SO3.

n

Carrageenan (27.3)

Algins are obtained from the cell walls of the brown seaweed species of Laminaria,known as kelp. Large quantities are harvested off the coast of California by mowingthe fronds. Alginic acid (27.4) is a polymer of two sugar-like units, mannuronic andguluronic acid.

Partial structure of Alginic acid

COOH

COOHO

OO

O

OO

Mannuronic acid L-Guluronic acid

OH OH OHOH

Alginic Acid (27.4)

The phycocolloids are water soluble and have excellent gelling, stabilizing, andemulsifying abilities. Hence, they are widely used in food and cosmetic preparations(Table 27.7). Agar is used as a culture medium for bacteria because it is not readilydecomposed by microbes. According to the Food and Agriculture Organization of theUnited Nations, global production was nearly 10.1 million tons (wet weight) in 2000,with the majority coming from the brown (71%) and red (20%) algae. Most of thisproduction occurs in China. Because of their high iodine content, various seaweeds arealso been used to control and cure goiter. Brown seaweeds are notable as a source ofpotassium-rich fertilizers and soda ash (Na2CO3), which is an important component ofhard soap.

Tab

le27

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of

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d

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s

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pre

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and

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ag

ent

Denta

lad

hesiv

e


Macroalgal Natural ProductsThe natural products discovered in red seaweeds include a large number of uniquepolyketides and mono-, sesqui-, and diterpenoids that are notable for a high degree ofsubstitution by chlorine and bromine atoms. An example of the latter are the halo-genated furanones (27.5) produced by the rhodophyte Delisea pulchra, which appearto prevent bacteria from colonizing the seaweed’s surface. The ability to prevent biofilmformation leads to applications in which antibiofouling activity is needed, such as onmarine structures, contact lenses, medical devices, and bandages. These compoundsappear to disarm bacteria, rather than killing them, by blocking their production ofquorum-sensing compounds, the microbial equivalent of intraspecies chemical commu-nicants. Microbial control via chemicals that prevent biofilm formation is thought to beless likely to induce resistance following repeated usage.

Br

O

O

Br

Furanone

Furanone (27.5)

L-�-Kainic acid (27.6) is another natural product from red algae (Digenea simplex).It has been used in Japan as an antihelmintic (dewormer). Because it is a neurotoxin,kainic acid has also been used to induce brain degeneration in test animals therebysupporting research into Alzheimer’s disease and epilepsy. Kainic acid is producedcommercially from algae specially grown for this purpose.

COOH

H2C

CH2COOH

H3C

C

NH

L-a- Kainic acid

Kainic Acid (27.6)

Although not technically a natural product, inorganic extracts from the red algaeCorallina sp. have been developed to serve as bone-replacement materials. Theseextracts contain porous fluorohydroxyapatite that is applied onto existing bone toserve as a graft. One product currently being marketed for dental applications is FRIOSAlgiporeTM.

Some of the more notable natural products discovered in the brown seaweeds arethe fucoidans and glucans. Interest in their bioactivity stems from the observation thatin Japan, where brown seaweeds are a popular food, the incidence of breast can-cer is about one sixth the rate of that reported for American women. Laminaria


species commonly consumed in Japan include wakame and kombu. Laminaria andSargassum species are used in China as components of traditional herbal medicines forthe treatment of cancer.

The fucoidans are sulfated polysaccharides whose base unit is L-fucose (27.7). Fucoseis a six-carbon sugar whose structure differs from those in Figure 22.9 in having onefewer hydroxyl group. The most abundant disaccharide repeating units in fucoidansisolated from variety of brown algae are shown in (27.8).

OH

OH

OHO

HO

CH3

L - fucose

Fucose (27.7)

Fucoidan preparations have anticoagulant activities making them a suitable sub-stitute for heparin, which is prepared from mammalian mucosa. The algal source ispreferred because the mammalian source can contain infectious agents, such as virusesor prions. Like heparin, the fucoids affect many other biological activities, such asinflammation, cell proliferation and adhesion, viral infection, and fertilization. For exam-ple, fucoidans from wakame (Undaria pinnatifida) exhibit a strong antiviral effect.Commercial preparations from this seaweed are available for treatment of the herpessimplex virus. In vitro clinical tests have demonstrated efficacy as an immune systemstimulant with potential for treatment of breast cancer and HIV/AIDS. Another inter-esting class of polysaccharides in brown algae are the laminarins. They are sulfonatedglucans composed of (1−3)-ß-D-linked glucose and (1−6)-ß-D-linked glucose with man-nitol end groups. The laminarins also exhibit strong heparin-like activity and, thus,could prove useful as anticoagulant, antilipemic, antiviral, or anti-inflammatory agents.

27.6.2 Animals

PoriferaSponges are the most prolific marine invertebrate sources of MNPs. More than 9000species have been described, with many as yet unclassified. The great resistance ofsponges to bacterial decomposition suggests they contain potent antibiotic compounds.Indeed, extracts from more than 100 species have generated antibiotic responses againsta wide spectrum of gram-positive and gram-negative bacteria. The compounds responsi-ble are primarily brominated cyclohexadienes and polyhydroxybrominated phenols. Anexample is the brominated alkaloid, oroidin (27.9).


a. Ascophyllum nodosum/Fucus vesiculosus/Fucus evanescens

HO

O

H

H

H

HCH3

2O3SOHO

HO

O

H

H

H

HCH3

2O3SO

OSO32

HO

O

HOH

H

H

HCH3

2O3SOH

OO

HOH

H

H

HCH3

2O3SO

HO

O

H

H

H

HCH3

R2O

R15 SO32 or H or COCH3

R25 SO32 or H

R35

R1O

HO

O

H

H

H

H

CH3

R2OR3O

HO

O

H

H

H

HCH3

R2O R1O

HO

OH

H

H

H

H

CH3

R2OR2O

HO

O

H

H

H

HCH3

R2OR1O

HO

O

H

H

H

HCH3

R2OR1O

b. Ecklonia kurome

c. Chorda filum

Fucoidans (27.8)

Oroidin

Br

Br NH

CONHCH2CH CH N

NH

NH2

Oroidin (27.9)


As much as 50% of a sponge’s biomass can be composed of bacteria, cyanobacteria,and fungi. The ecological role of these microorganisms is not completely understood,but in some cases appears to include production of natural products that serve as chem-ical defense agents for the host sponge. This presents the possibility that commercialproduction of their MNPs could be achieved via microbial culturing.

Other alkaloids discovered in sponges have given rise to antiviral and anticancerdrugs, namely, Ara-A (Vidarabine) and Ara-C (Cibarine). These are widely considered torepresent the first generation of marine drugs. They are derivatives of the nucleosides,spongouridine (27.10) and spongothymidine (27.11), that were first isolated in 1950from a Caribbean sponge.

Spongouridine Spongothymidine

R RHN CH3HN

N N

O

O

O

O

HOH2C O R

HO

OH

Spongouridine (27.10) and Spongothymidine (27.11)

The base sugar unit in these nucleosides is arabinose, in contrast to DNA and RNA,whose base sugar unit is ribose. Ara-A is currently used in ophthalmic ointments as anantiviral agent. Other analogs of these alkaloid include AZT, the first drug licensed fortreatment of HIV, and acyclovir, used for treating herpes. Ara-C has been approved since1969 for treatment of leukemia.

As shown in Table 27.1, several compounds from sponges are now in clinical tri-als for cancer treatment and control of asthma. Halicondrin B (27.13), a complexpolyketide discovered in the Japanese sponge Halichondria okadai, exhibits tubulin-stabilizing effects. One analog, E789, is currently in Phase I trials for treatment of cancer.Some compounds are too toxic for use as a drug, but have instead found a role as aresearch tool for study of disease processes. An example is manoalide (27.12), whichwas discovered in an Indo-Pacific sponge, Laffariella variabilis. It is a nonsteroidalsesterterpenoid with anti-inflammatory properties. It works by inhibiting phospholipaseA2 (PLA2). This enzyme plays a key role in causing the pain and swelling associated withinflammatory conditions such as arthritis, psoriasis, and poison oak.

CnideriaThe Cnideria include more than 10,000 described species from which over 1500 MNPshave been isolated. Most are terpenoids found in the octocorallia, coral, gorgonians, andzoanthids. As with the sponges, many of these may be synthesized by microbial sym-bionts. An extract from the Caribbean soft coral, Pseudopterogorgia elisabethae (seawhip), is currently marketed in a skin cream (Resilience by Estee Lauder). The activeingredient, pseudopterosin (27.14), is an anti-inflammatory. One analog, methopterosin,is in Phase I and II clinical trials as a topical anti-inflammatory agent.


Manoalide

CH3CH3

CH3 OH

CH3

O

OH

O

O

H

H

H H HH

H

H

H

H

HO

OO

O

O OO

O

O

O O

O

OH OH

OHO

OO

O

CH3

CH2

CH3

CH2

CH3

CH3

Halichondin

Manoalide (27.12) and Halichondrin B (27.13)

CH3

CH3

CH3

CH3

CH3

HO

OH

OHHO

OH

O

Pseudopterosin

Pseudopterosin (27.14)

Prostaglandin hormones were first discovered in the 1960s. These simplelipids were immediately recognized as playing important roles in a great varietyof biological systems, suggesting their potential as a drug for treatment of a widevariety of diseases. The natural production of prostaglandins by land animals istoo limited to provide sufficient quantities for medicinal use. When the Caribbeangorgonian coral, Plexaura homomalla, was discovered in 1969 to be producingextraordinarily high concentrations of prostaglandins (27.15), comprising as much as1.5% of their dry weight, harvesting was considered as an option to meet medicalneeds. Because their prostaglandins lack significant biological activity, they wouldhave had to be chemically modified into mammalian forms (27.16). Fortunately,synthetic techniques have been developed for production of commercial quantitiesof mammalian prostaglandins.

Two photoproteins, aequorin (27.17) and green fluorescent protein (GFP), havebeen isolated from luminescent jellyfish (notably Aequorea victoria) and are now in


O

R1O H(15 R)2PGA2R15 H or CH3CO––R25 H or CH3

(15 S)2PGA2R15 H or HCO ––R25 H or CH3

CH3 CH3

COOR2 COOR2

O

H OR1

Gorgonian Mammalian Prostaglandins

Gorgonian (27.15) and Mammalian Prostaglandins (27.16)

Aequorin

Aequorin (27.17)

Source: From Head, J. F., S. Inouye, K. Teranishi, and O. Shimomura (2000). The crystal

structure of the photoprotein aequorin at 2.3 Å resolution. Nature 405, 372–376.

commercial use. Aequorin is used as a very sensitive bioassay for intracellular calciumbecause the organometallic complex is fluorescent. This has proven useful in diagnosingcardiac irregularities and metastatic carcinoma because both cause subtle changes inserum calcium levels. Aequorin was initially obtained via extraction from jellyfish but isnow produced from microbial cultures using recombinant techniques. GFP is used as aresearch tool in the field of recombinant genetics. Because of its green fluorescence, GFPserves as a highly sensitive molecular marker of gene expression.


EchinodermataAlthough 7000 species of echinoderms have been classified, a relatively small num-ber of MNPs have been isolated from this phylum, probably because these animalshave other means by which to deter predators. Some burrow, some have calcified sur-faces, and many are quite mobile. Some examples of MNPs from this phylum includedihydromarthasterone (27.18) from starfish, and holothurin (27.19) from sea cucumbers.

Dihydromarthasterone

O

OH

HOH

Holothurin

O OO

OH

OSO3NaH

OS1S2S3S4

Variable fatty acid composition is indicated by S1– S4.

Dihydromarthasterone (27.18) and Holothurin (27.19)

A number of steroids isolated from starfish, such as dihydromarthasterone, are toxicto fish and mollusks. They also have anti-inflammatory, antitumoral, and hemolytic activ-ity. Some are used by the Japanese to kill fly larvae. This toxic effect is attributed totheir surfactant nature, which causes a disruption in the molting process. Holothurin isa steroidal saponin that contains sulfate. This compound has been observed to suppresstumor growth and slow amoeboid movement. It also increases leukocyte phagocytosis(the destruction of foreign particles such as bacteria) by white blood cells. Holothurinalso exhibits antifungal and cardiotonic activity.

MolluscaThe phylum Mollusca contains 50,000 species that have yielded a number of interestingMNPs. Murex brandaris and two other species of gastropod snail were a source of theblue dye, indigo, and Tyrian purple (27.20) to the Hebrews and Romans during biblicaltimes. These dyes were highly prized for their deep hues and color-fast nature. As aresult, they were restricted to religious and government use. Only the Roman emperorwas permitted to wear “true” purple as produced by Tyrian purple.

The snails emit precursors of these azo dyes as a clear fluid that also contains severaltoxic compounds, some of which probably repel predators. Upon exposure to O2 andsunlight, enzymatic actions convert the precursors to a white, yellow, green, and finallyblue or purple color. Variations in the color of the final products are related to differ-ences in sex, species, and in situ environmental conditions, as well as the method of dyeprocessing. Knowledge of the latter was lost by 760 AD and subsequently rediscoveredin 1856. The purple gland of the Murex is also a source of urocanylcholine (27.21),


Tyrian purple

H O

HC

C

C

C

CN

H H

H

H

C

C

C CC

C

CC

CBr

BrCC

N

H H

O

Tyrian purple (27.20)

which is sold under the trade name MurexineTM as an insecticide. This compound is astrong paralytic. At low concentrations, it is used as a muscle relaxant, having nicotinicand curariform actions.

Urocanylcholine

N

NH

CH CH CO2CH2CH2N(CH3)31

Urocanylcholine (27.21)

An analog of one molluscan natural product was recently approved for use as apain killer. Ziconotide (27.22), marketed as PrialtTM, is an analog of a conotoxin. These

H2N

H2N

Cys1

Cys25

Lys2 Gly3

Gly5

Cys16 Cys15 Asp14 Tyr13

Met12

Leu11Arg10Ser9

Ser22 Ser19

Cys8Gly18

Cys20Arg21

Lys7Lys24 Thr17

Gly23

Ala6

Lys4

Ziconotide

Ziconotide (27.22)


compounds are peptides composed of 10 to 30 amino acids synthesized by the conesnail, Conus magus. They are used to immobilize prey (worms and fish). Ziconotideappears to suppress pain by targeting and blocking specific ion channels in neurons.This short circuits neurotransmitter release in the nerves that transmit pain signals.While very effectively blocking pain, Ziconotide still allows the rest of the nervoussystem to function properly, unlike other opiates.

Several molluscan natural products are now in clinical trials. They include the dolas-tatins, kahalalide, and ES-285. The dolastatins are polypeptides isolated from the marinemollusk Dolabella auricularia (a sea hare) found in the Indian Ocean. They are pos-sibly of cyanobacterial origin. Two analogs, dolastatin 10 (27.23) and dolastatin 15, arecurrently in Phase I and II clinical trials for cancer. Kahalalide (27.24), a depsipeptide iso-lated from Elysia ruferensces, is in Phase II cancer trials. This bioactive compound mightbe synthesized by algae or Vibrio species. Spisulosine (27.25), from Spisula polynyma,is also presently in cancer trials.

O

O

N(Me)2

NH OMe

OMeN

O

HNS

NO

N

Dolastatin

Me5methyl

Dolastatin (27.23)

MNP chemists are also investigating the potential use of the active compounds inbyssal threads for medical applications such as gluing bones and teeth. Marine musselsuse byssal threads for anchoring to surfaces. The threads are extraordinarily strong.Structurally, they are composed of heavily crosslinked copolymers of collagen and theprotein elastin.

EctoproctaThis phylum includes the bryozoans. One species, Bugula neritina, is a source of bryo-statins, a family of 16 acetogenins. Bryostatin I (27.26) is in Phase II trials for treatmentof cancer. A sustainable supply is currently being produced via mariculture. This is chal-lenging because 14 tons of bryozoans are required to generate an ounce of bryostatin.The acetogenic polyketide structure of bryostatin I suggests that it is probably gener-ated by a symbiotic microbe. If this is the case, genetic engineering could potentiallybe used to insert the active gene into easily culturable bacteria, providing a means bywhich large quantities of bryostatin could be produced.


H2N

NH

NH

HN

HO

HN

NH

NH

HN

NH

NH

HN

ON

HN

OO

O

O

O

O

O

O O

O

O

OO

CH3

CH3

CH3

CH3

NH

CH3

CH3

CH3

CH3

CH3

CH

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

CH3

O

Kahalalide

Kahalalide (27.24)

OH

NH31

2CI2

Spisulosine

Spisulosine (27.25)

O

O

O

O

O

H

H H

H

H

H

H

HOH

OH

HO

O

O

O O

O

O

O

O

OHH

Bryostatin I

Bryostatin I (27.26)


AnnelidaDead annelid worms have long been used to repel and kill flies. The substanceresponsible for this insecticidal activity is nereistoxin (27.27), a disulfide isolated fromthe marine worm, Lumbriconereis heteropoda. A synthetic derivative, padan (27.28),has been marketed under the trade name CartapTM since 1967 as a substitute fordichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (BHC). The insec-ticide works by blocking the ganglionic action of the central nervous system. This isquite unlike the mode of action for the halogenated pesticides, such as DDT. As a result,padan is nontoxic to mammals and decomposes readily, making it an important addi-tion to the antibug arsenal. It is used extensively in Asia and Japan against rice stemborers.

Nereistoxin Padan

CH3 CH3

CH2 CH2

CH2 CH2

CH

CH3CONH2

CONH2

N CHN

CH3S S

S S

Nereistoxin (27.27) and Padan (27.28)

NemerteaNemertines are a phylum of carnivorous marine worms that possess a variety of alka-loidal, peptidic, and proteinaceous toxins. These MNPs serve as chemical defensesagainst potential predators. Anabaseine (27.29) was the first of these alkaloids to beidentified and has insecticidal properties. It also stimulates a wide variety of animalnicotinic acetylcholine receptors. An analog, GTS-21 (27.30), is currently in clinicaltrials for treatment of Alzheimer’s disease and schizophrenia.

ArthropodaThe most important commercial product from this phylum is limulus amebocyte lysate(LAL), which is extracted from the blood of horseshoe crabs, Limulus polyphemus.The most important use of LAL is in a very sensitive bioassay for endotoxins. Thesetoxins are fragments of bacterial cell walls and are the cause of most fevers in humans.Because endotoxins are difficult to degrade, they cannot be destroyed by simple ster-ilization and, hence, must be removed via filtration. LAL is used to verify drug purityand cleanliness of medical products, such as vaccines and intravenous fluids. During thebioassay, endotoxins rapidly react with LAL causing the limulus blood extract to clot.This bioassay has been in use since the 1970s.

LAL is also used to diagnose bacterial infections, including those of the urinarytrack, gonorrhea, endotoxemia, and spinal meningitis. LAL reacts with (1,3)-�-D-glucanin blood sera, making it useful as a diagnostic for invasive fungal infections. Potentialapplications include detection of bacterial contamination in meat, frozen foods, fish,and dairy products.


Anabaseine

N

N

GTS-21

OCH3

OCH3

N

N

Anabaseine (27.29) and GTS-21 (27.30)

LAL is obtained by bleeding wild horseshoe crabs, which are then released withno ill effect. About 300,000 crabs are caught, bled, and released each year, generatingLAL worth $50 million. Research is underway to develop recombinant techniques forgenerating LAL derivatives from microbes so that bleeding of wild horseshoe crabs willno longer be required.

ChordataAscidiansThe ascidians are the largest and most diverse of the four classes of tunicates andthe only one with reported MNPs. Hundreds of novel MNPs have been found in theascidians. Most are thought to be agents of chemical defense. They are considered tohave potential as antifouling, UV protectant and antioxidant agents. The ecteinascidinsare a family of alkaloid compounds produced by sea squirts, Ecteinascidia turbinata.Ecteinascidin 743, also known as trabectedin and Yondelis (27.31), is in Phase II andIII clinical trials for treatment of melanoma. Aplidine (27.32), an analog of a depsipep-tide didemnin isolated from the tunicate Aplidum albicans, is also in Phase II cancertrials. Staurosporine (27.33), an alkaloid discovered in the marine tunicate Eudistomatoealensis, inhibits protein kinases and, hence, has potent antitumor activity. An analog,PKC41, is currently in Phase I trials for treatment of multiple myeloma.

CrustaceansMany insects, crayfish, and other crustaceans synthesize hormones that induce molting.These ecdysones are oxygenated cholestanes, a type of sterol. They have potentialapplications in mariculture as growth regulators and in the control of insect life cycles.Crustecdysone (27.34) is one example of a crustacean ecdysone.


Ecteinascidin 743

O

O

HO

O

N

H

OHO

ONH

H

NS

O

O

HO

O

H HH

Aplidine

O

NO

N O

OHN OH

O

O

O

ONHO

O

O

O

O

N

N

NH

O

H3CO

HO

NHCH3

Staurosporine

N N

NH

O

Ecteinascidin 743 (27.31), Aplidine (27.32), and Staurosporine (27.33)

OH

OH

OH

HO

HOOH

Crustecdysone

OH

Crustecdysone (27.34)

The major commercial products from crustaceans are derivatives of chitin, which is aubiquitous natural polymer composed of amino sugars (Figure 22.11). Because it formsmost of the exoskeletons of crustaceans, chitin is an abundant component of shellfishwastes produced by the seafood industry, amounting to approximately 1 million tons


Table 27.8 Uses of Chitosan.

GeneralApplication

Specific Application Details

Membranes Blood dialysis

Medical product Bandages for wounds

and burns

Hypoallergenic, antibacterial,

antifungal, blood clotting

Agriculture Plant growth enhancer Boosts the ability of plants to

defend against fungal

infections

Removal of phosphorus,

metals, oils and PAHs

Flocculation and scavenging

Water treatment Filtration process Causes the fine sediment par-

ticles to bind together and

is subsequently removed with

the sediment during sand

filtration

Clarification of wine,

mead, and beer

Used in combination with

bentonite, gelatin, silica

gel, isinglass, and other

fining agents

Removes yeast cells, fruit par-

ticles, and other detritus that

causes haze

Fiber In paper; packaging, and

clothing

Yarn, edible food wrap, water-

resistant paper; improves

strength of recycled paper

Nutraceutical Dietary fiber Weight loss, antilipemic

per year. It is a nontoxic, renewable, and biodegradable resource. Controlled deacetylationof chitin produces a water-soluble material called chitosan. Some of the applications of thisproduct are listed in Table 27.8. Many are medical in nature, reflecting chitosan’s ability toefficiently complex metals and natural biomolecules. Another derivative of chitin, calledKylanTM, is used to impart shrink resistance to wool. Chitin is also a source of glucosamineused as a precursor in drug synthesis and as a nutraceutical. Because it is a selective bindingagent, chitin is also used for isolating enzymes.

FishToxinsPotent toxins are found in several marine fish and shellfish. Most appear to be synthe-sized by algae and are concentrated in the animals as a result of bioaccumulation (i.e.,the selective retention of ingested compounds). Because of the large-scale consumptionof fish and shellfish by humans, the resulting toxic effects are a matter of great concern.Such effects include muscle and respiratory paralysis severe enough to cause death. The


majority of the ill effects are experienced from ingestion of coral reef fish leading tociguatera, a “disease” recorded as early as the 1400s by Europeans in the West Indies.The causative agents, ciguatoxin (27.35) and maitotoxin (27.36), are synthesized bydinoflagellates. These are some of the most lethal natural substances known. In mice,the lethal dose of ciguatoxin is 0.45 �g/kg and 0.15 �g/kg for maitotoxin. Oral intakeof as little as 0.1 �g of ciguatoxin can cause illness in a human adult.

OH

OHOH OH

HH H H HH

H HH H H

HH

H HH

HH

H HH

HO

OO

O

O

OO

O

O

O

O

OO

HO

HO

Ciguatoxin

Me 5 methyl

OH

OH

HO

HO

HOHO

HOO

O

O

O

O O O O

OO O O

O OO

O

O

O

O

O

O

OO

OOO

O

OO

OO

O

O

O

O

O

O

OOH

OH

OH

OH

OHOH OH OH

OH

OH OH OH

OH

OH

OH

OHOH

OH OH

OH

OHH

H

H H H H H

S

S

NaO

ONa

H H H H H H

H H

H

H H

HH

H

H

H

H

H

HH

H

Maitotoxin

HH

H

H

HHHHH

H

H H H H H H

H H

Ciguatoxin (27.35) and Maitotoxin (27.36)

Puffers, ocean sunfish, and porcupine fish all contain tetrodotoxin, which is themost toxic low-molecular-weight poison known. Biosynthesis of this toxin appears tobe controlled by symbiotic bacteria of the Vibrio species. In pufferfish, the toxin can befound in their gonads, liver, intestines, and skin. The wild-caught species must be care-fully prepared for consumption as no antidote is known. Farm-raised pufferfish do nothave tetrodotoxin because they do not harbor the bacteria that produce it. Tetrodotoxin(27.37) is commercially available in Japan and the United States. It is used as a molec-ular tool for studying sodium channel conductance. Clinical trials have been proposedto test its use as a pain killer.

Despite their high molecular weights and complex structures, methods for the totalsynthesis of each of these toxins, ciguatoxin, maitotoxin, and tetrodotoxin, have been


Tetrodotoxin

H

HHHN

NH

HHOH

CH2OHHO

OH OO

H2N1O2

Tetrodotoxin (27.37)

developed. This is considered a useful step in creating less toxic analogs with potentiallymore useful physiological effects.

Other Natural Products from FishSeveral omega-3 polyunsaturated fatty acids (PUFA) isolated from marine fish oils havebeen observed to lower blood lipids, such as cholesterol, and have anti-thrombotic andanti-inflammatory activity. The most common long-chain PUFAs are eicosapentaenoicacid (EPA) and docosahexaenoic acid (DHA), both of which are currently marketedas nutraceuticals. Their structures are shown in Table 22.5. Cold-water fish, such asmackerel, salmon, herring, sardines, black cod, anchovies, and albacore tuna, are richsources of DHA and EPA. Some preliminary studies suggest DHA deficiency is a causativefactor in Alzheimer’s disease, schizophrenia, depression, and attention deficit disorder(ADD). This is thought to reflect the important role that DHA plays in brain and nervedevelopment as it helps build membranes around nerve cells. Fish oil is also rich invitamins A (Figure 22.18d) and D, which promote the healing of wounds, burns, andabscesses. Cod and halibut liver oil are also used as laxatives.

A small arginine-rich protein, protamine, has been isolated from some marine fish.Protamine is an antithromboplastic and antiprothrombic agent. It is used as an antidotefor heparin overdosage. By binding with the anticoagulant, protamine inactivates thisdrug. Protamine is also used in the preparation of protamine zinc insulin, which is along-acting antidiabetic drug. Most protamine used in this application is isolated fromtrout and salmon.

Sharks are a source of immunoglobulins, which inhibit cancer lymphocyte activity.Shark liver oil is used as a bactericide and as an intermediate in the manufacture ofpharmaceuticals. It contains the terpene, squalene (Figure 22.18c), which is used as askin lubricant, an ingredient in suppositories, and a carrier of oily drugs. Squalamine,an aminosterol from the dogfish shark, Squalus acanthias, is an inhibitor of tumorcell growth. It is in Phase II clinical trials for treatment of ovarian and lung can-cer. A standardized liquid extract from shark cartilage called Neovastat is in Phase IItrials for kidney, prostate, and lung cancer. This MNP exhibits antiangiogenic activ-ity. Shark cartilage is also a source of chondroitin sulfate used in the treatment ofosteoarthritis.


Some fish species indigenous to the Arctic and Antarctic oceans contain proteinsand glycoproteins that act as an antifreeze by inhibiting the growth of ice crystals atsubzero temperatures. These compounds are large, having molecular weights rangingfrom 3000 to 24,000 daltons. They typically contain the amino acids alanine, threonine,cysteine, and glutamine. Some are being marketed by A/F Protein, Inc. in the UnitedStates for cryoprotection applications, including cold storage of animal and human eggsand blood platelets, as well as improved storage of frozen foods.

27.6.3 Microbes

Marine microbes are widely considered to be the most likely source of new naturalproducts that have potential as drugs. This is based on the fact that they represent themain pool of genetic diversity. As yet, only a small fraction have been cultured. Hence,their biochemistry is still largely unknown. The microbial biota with the greatest poten-tial for new MNPs are the phytoplankton, cyanobacteria, myxobacteria, and fungi. Inmany cases, microbes are the true source of MNPs found in animals. Bacterial symbiontscan serve as sources of the MNP or as precursor molecules that are modified by thehost. Other MNPs are synthesized by free-living microbes, with the bioactive substancesbeing bioaccumulated within food webs.

Another favorable characteristic of microbial natural products is the high likelihoodthat they can be easily produced through culturing of genetically engineered bacteria.Challenges to this approach include a limited knowledge of the optimal growth require-ments for many marine microbes. In addition, the interesting bioactivities exhibited bymicrobial MNPs are, in some cases, the result of community-level interactions. Thus,MNP chemists are working to develop tools that enable characterization of communityassemblages.

PhytoplanktonAs noted earlier, most fish toxins are truly synthesized by dinoflagellates. One of thetoxins responsible for ciguatera, maitotoxin, is produced by Gambierdiscus toxicus.It is the largest natural nonbiopolymer organic molecule known, having 142 carbonatoms. Most red-tide organisms produce potent toxins, including saxitoxin, brevetoxin,and okadaic acid. Diatoms in the genus Pseudo-nitzschia produce domoic acid, whichcauses amnesic shellfish poisoning. Okadaic acid (27.38) is synthesized by Prorocen-trum and Dinophysis and causes diarrheic shellfish poisoning. It is currently marketedas a molecular probe for the study of phosphatases. Dinoflagellate symbionts may beresponsible for the production of the pseudopterins present in the coral, Pseudoptero-gorgia elisabethae. An interesting line of research is directed at developing symbioticcommunities of green algae and bacteria that produce H2 for use as an energy source.

BacteriaActive research is directed at discovering novel products from marine actinomycete bacte-ria. They are among the most common microbes on the planet and are the source of almost


H

H H

H

H HH

O

O O

O

OO

OO

OH

OH

OH

HO

Okadaic acid (27.38)

70% of the world’s naturally occurring antibiotics, all of which come from soil-dwellingstrains. Marine actinomycetes were first discovered in 1969 and are now recognized to bewidespread throughout the oceans. These include a marine-obligate genus, Salinospora,from which more than 2500 strains have been identified. More than 60 natural productshave been isolated from the marine actinomycetes. For example, salinosporamide A is apotent inhibitor of cancer growth, including human colon, lung, and breast cancers. In2005, the first compound isolated from a marine-obligate actinomycete, Salinosporamide A(27.39), entered preclinical trials. It is a highly potent proteasome inhibitor with potentialfor use in the treatment of multiple myelomas.

OH

O

OO

CI

HN

Salinosporamide A (27.39)

Cyanobacteria synthesize toxins such as microcystin and BMAA, �-N-methyl-amino-L-alanine. Given the broad geographic range of cyanobacteria, widespreadexposure to humans is likely. Concern is directed at understanding these expo-sures as eutrophication seems to be causing cyanobacterial numbers to increase(Chapter 28.6.4). BMAA has been implicated in the development of amyotrophic lateralsclerosis(ALS)/Parkinsonism dementia complex in people living in Guam. Cyanobacteriaare also the likely originating source of the dolastatins (27.23), which are in Phase IItrials for cancer treatment.

Another area of research interest is in enzymes and polysaccharides used byextremophile bacteria, especially thermophiles. Microbial exopolysaccharides producedby some mesophilic Vibrio and Alteromonas strains isolated from deep-sea hydrother-mal vents are currently under evaluation for use in tissue regeneration and treatmentof cardiovascular diseases due to their anticoagulant, antithrombotic, and proangiogenicactivity. A polysaccharide isolated from the bacterium Alteromonas macleodii, collected

27.7 Role of Marine Biotechnology 39

near the Galapagos hydrothermal vents, has been shown to reduce the activity ofintercellular adhesion molecules (ICAMs) associated with the acute stages of skininflammation and thereby protect epidermal Langerhans cells. In a clinical setting, it sig-nificantly reduced irritation and repaired damaged skin. It is currently being marketedas Abyssine 657 for use in skin creams.

ArchaeaSome of the extremophiles found living in and around hydrothermal vents are hyperther-mophilic archaea. Since they are surviving and growing at temperatures over 100◦C, theymust have unique enzyme systems that are stable at high temperatures. Thermostableenzymes have potential uses in research and industrial processes. One commercial prod-uct, VentTM DNA polymerase, is currently on the market. This enzyme functions at 95◦C.It was discovered in Thermococcus litoralis, an archaean isolated from hydrothermalvent waters. Commercial production is achieved through recombinant techniques inwhich the genes of the extremophile are expressed in Escherichia coli.

FungiThe first true marine drug, the antibiotic cephalosporin C (27.40), was discovered inthe marine fungus Cephalosporium acremonium. It has been in commercial use since1965 and has proven effective against a variety of bacteria, including penicillin-resistantstrains. The antibiotic effect of this marine fungus was discovered in 1945 as a result ofresearch conducted on the microbial flora living near a sewage outfall in the Mediter-ranean Sea. NPI-2358, an analog developed from a marine fungal extract, began PhaseI trials for treatment of solid tumors and lymphomas in 2006. It is a potent selectivevascular disrupting agent, active against multi-drug-resistant human tumor cell lines.

Cephalosporin C

H3N1

CHCH2CH2CH2COHN2OOC

H HS

ON

COOH

CH2OCOCH3

Cephalosporin C (27.40)

27.7 ROLE OF MARINE BIOTECHNOLOGYInnovations in marine biotechnology are likely to improve the scope, scale, and speed ofMNP development. They are also likely to improve mariculture, management of wild fishstocks, and remediation of marine pollution. New tools represent a blend of molecularbiology and information technology, called genomics and bioinformatics, which can beperformed at the organismal, cellular, and genetic levels.


One of the most promising new directions lies in the use of genetically engineeredbacteria to produce unique biomolecules on a mass scale. The novel metabolismsexhibited by marine bacteria represent microbial factories for concentrating met-als, depositing minerals, harnessing solar energy, decomposing sewage and oil, andexuding anti-biofouling agents. Recombinant techniques, especially those for cloningmetagenomes, should provide the means by which these microbial factories can beharnessed for human use.

In vitro manipulations, such as cloning, are likely to improve mariculture by enablingthe selection of traits such as increased hardiness to environmental stresses and disease,as well as fast growth and maturation rates. Molecular markers, such as mitochon-drial DNA, are now being used to track the populations of commercially importantor endangered species. For example, genetic methods are being used to verify whethersupermarket salmon are farm raised or wild. Evolutionary relationships among speciesare being assessed by genetic mapping of DNA. Exposures to toxins (xenobiotics)induces the production of mixed-function oxygenases, called cytochrome P450, inplants, bacteria, and animals. These compounds are species specific and can be usedas biomarkers of pollution. They are detected by PCR methods (polymerase chainreaction).

Advances in biotechnology have also led to the development of biosensors suchas GFP. Other examples are listed in Table 27.9. The gene for production of GFP iseasily inserted into the nuclear materials of plants, bacteria, and animals. Because bio-luminescence is easily detected at very low levels, expression of the gene for GFPprovides a sensitive marker that can be used to measure cell proliferation, apoptosis,drug metabolism, and kinase activity (antitumor).

Table 27.9 Biosensors Based on Marine Natural Products.

Chemical Source Target End Point Status

Limulus amebocyte

lysate (LAL)

Horseshoe crab,

Limulus polyphemus

Gram-negative

endotoxins

Visual clumping In use

Aequorin Jellyfish, Aequorea

victoria

Ca2+ Bioluminescence In use

Green fluorescent

protein (GFP)

Jellyfish, Aequorea

victoria

Tag proteins and

to follow gene

expression

Bioluminescence In use

Lux genes Bacteria, Vibrio

fischeri

Food-borne

pathogens

Bioluminescence In development

Taq and VentTM

DNA polymerases

Extremophiles:

Thermus aquaticus

and Prococcus

furiosus

DNA Enzymatic activity In use

27.7 Role of Marine Biotechnology 41

27.7.1 Final Remarks

MNPs are most properly viewed as catalysts for the discovery and investigation of newdrugs. In other words, we should expect marine chemicals to inspire new drugs ratherthan to provide them. Our search for potential drugs from the sea has improved ourunderstanding of human physiological processes. It could also play an important role inimproving our understanding of marine chemical ecology at the molecular level. Thisline of research began with great promise in the 1970s, followed by a period of rapiddiscovery of novel compounds. Disappointingly, few have been brought to the com-mercial market. The 2000s have seen a mini-renaissance in the development of newmarine drugs due to improvements in separation technology, bioassay techniques, andthe application of tools from biotechnology and informatics. Other recent changes thathave improved the prospects of new MNP development have been the establishmentof interdisciplinary research teams and centers and the enhanced information exchangeprovided by the Internet. As a result, a respectable number of MNPs are now on themarket with many others in the developmental pipeline. Further successes will dependon the willingness of companies to invest the significant amounts of time and moneyrequired for drug development.

Unfortunately, equal progress has not been made in the arena of biofouling, whereit was hoped that MNPs would be found that would replace the highly toxic tributyltinand copper based paints. The only organic antibiofouling product yet to come to marketis SEA-NINETM. This MNP is an isothiazolone that acts as a broad-spectrum antifoulingagent. It biodegrades rapidly after release into seawater or the sediments.

Given the current rapid rate of loss of biodiversity, great concern exists that weare losing genetic resources before having had a chance to discover their pharmaco-logical potential. As with the denizens of the tropical rain forests, there is no tellingwhich species could hold a cure for diseases such as cancer or AIDS. For this reason,it behooves us to protect these ecosystems.

chapter organic products from the sea: pharmaceuticals ... · 27 chapter organic products from the...

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