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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.
4 CHAPTER 27 Organic Products from the Sea
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
27.3 History of Marine Organic Products 5
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
)
6 CHAPTER 27 Organic Products from the Sea
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
27.3 History of Marine Organic Products 7
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.,
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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.
12 CHAPTER 27 Organic Products from the Sea
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
14 CHAPTER 27 Organic Products from the Sea
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
16 CHAPTER 27 Organic Products from the Sea
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.
18 CHAPTER 27 Organic Products from the Sea
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.
27.6 Examples of Marine Natural Products 19
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
.7C
urr
ent
Uses
of
Marine
Alg
alP
hyc
ocollo
ids.
Phy
coco
lloid
Foo
dA
dd
itiv
eIn
dus
tria
lP
harm
aceu
tica
lP
erso
nal
Car
eP
rod
ucts
Oth
er
Ag
ar
Canned
foo
ds
Laxative
Oin
tments
and
co
sm
etics
Mic
rob
ial
gro
wth
med
ium
Oute
rco
ver
of
cap
sule
s
Cara
geenan
Dairy
pro
ducts
:
co
ttag
echeese,
ice
cre
am
,co
ffee
cre
am
ers
,w
hip
ped
cre
am
s,
cheese,
yog
urt
,cho
co
late
drinks,
dip
s,
pud
din
gs
Fert
ilize
rsand
phyt
ore
med
iatio
n.
Inth
e
textile
ind
ustr
y,it
is
used
as
stiffenin
gand
bin
din
gm
ate
rial
for
a
so
ftfin
ish
Antico
ag
ula
nt,
pre
vents
ulc
ers
and
cho
leste
rol
ab
so
rptio
n,
pre
vents
meta
lad
so
rptio
n,
antivi
ral,
pro
long
sth
eactivi
ties
of
co
mm
on
analg
esic
sand
antico
ug
hm
ed
icin
es
such
as
co
dein
eand
eth
ylm
orp
hin
e,
pro
mo
tes
the
rap
id
dis
inte
gra
tio
no
fd
rug
tab
lets
Lip
sticks,
so
ap
s,
too
thp
aste
,sham
po
os,
lotio
ns,
cre
am
s
Film
,p
ain
t,
varn
ish,
butt
ons
Oth
er:
pie
fillin
gs,
jam
sand
syr
up
,
bab
yfo
od
,sauces,
sala
dd
ressin
gs,
canned
meats
,
shrim
pand
fish
gels
Alg
inD
airy
pro
ducts
,b
eer,
sala
dd
ressin
gs,
cake
mix
es,
and
mering
ues
Pap
er
co
ating
sand
siz
ing
,te
xtile
printing
,
and
weld
ing
-ro
d
co
ating
s
Fo
rmula
tio
ns
of
dru
gta
ble
ts,
denta
lim
pre
ssio
ns,
anta
cid
s,
band
ag
es,
and
deto
xify
ing
ag
ent
Denta
lad
hesiv
e
27.6 Examples of Marine Natural Products 21
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
22 CHAPTER 27 Organic Products from the Sea
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).
27.6 Examples of Marine Natural Products 23
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)
24 CHAPTER 27 Organic Products from the Sea
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.
27.6 Examples of Marine Natural Products 25
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
26 CHAPTER 27 Organic Products from the Sea
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.
27.6 Examples of Marine Natural Products 27
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),
28 CHAPTER 27 Organic Products from the Sea
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)
27.6 Examples of Marine Natural Products 29
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.
30 CHAPTER 27 Organic Products from the Sea
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)
27.6 Examples of Marine Natural Products 31
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.
32 CHAPTER 27 Organic Products from the Sea
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.
27.6 Examples of Marine Natural Products 33
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
34 CHAPTER 27 Organic Products from the Sea
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
27.6 Examples of Marine Natural Products 35
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
36 CHAPTER 27 Organic Products from the Sea
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.
27.6 Examples of Marine Natural Products 37
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
38 CHAPTER 27 Organic Products from the Sea
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.
40 CHAPTER 27 Organic Products from the Sea
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.
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