Reactive Metabolites -

Hints How to Avoid a Drug Safety Hazard Alf Claesson

© 2012 Awametox Consulting, Stockholm, Sweden. Contact: +4670 553 7131, info@awametox.se. LinkedIn

Reactive

Metabolite

Reactions

with DNA

Reactions

with proteins

Drug

The liver is usually

the first casualty

Problems…problems…problems…problems..problems…problems…

2

Modified from Gerry Kenna and Roger

Bonnert, AstraZeneca

Reactive

Metabolite (RM)

Reactions

with DNA

Reactions

with proteins

• An important cause of drug-induced illness

and fatality, e.g. DILI= Drug Induced Liver Injury

• A major concern for drug industry and regulators

• Low-dose drugs cause less/no problems

Mutagenicity

Carcinogenicity

Teratogenicity

- Benzidine

- Safrole

Target organ toxicity

(reproducible or

idiosyncratic)

- Paracetamol

- Diclofenac

Immune

hypersensitivity

reactions

(idiosyncratic)

- Antibacterial sulfon-

amides

- Halothane

Drug

The liver is usually the

first casualty

NH2

NH

S

OO

N

N OH

Br

Cl

F

F

F

3

Slightly modified from Steve Swallow (AZ Drug Safety) at the SCI Conference ”Designing Safer

Medicines in Discovery: Current and Emerging Opportunities to Reduce Attrition”, 25th March 2011

Substructural alerts

Genotox/RM

Reactive cpd

Toxic metabolite

(e.g. forms F-acetic

acid)

logP

Light sens.

Solubility

Stability

+ ADME person

Substance related failures of drugs are of great concern

Drug safety is a major cause of drug attrition.

It will take a very long time before we can predict all hazards

This presentation highlights one factor, i.e. metabolism to reactive

species

– Indeed, we can hope to master this cause of attrition! By

experimentation and increased knowledge

Potency in secondary

test model

Potency in primary test model

Practical

synthesis

Pharmacokinetics

Decreased off-target

I potency

Patent issues

Solubility (for

example)

LeadCD

Decreased off-

target II potency

Not efficient

22%

Toxicology

32% Clinical

safety

12%

DMPK

8%

Portfolio

11%

Other reasons

15%

5

The different fates of reactive species formed by enzymatic action

In the scheme below “I” represents a drug which acts as an irreversible inhibitor of a P450 enzyme

– The general term is Mechanism Based Inhibition (MBI) – also known as suicide inactivation/inhibition.

– Indicated by in vitro experiments where enzymes lose activity by time, Time Dependent Inhibition (TDI)

P= RM Covalent binding to

macromolecules

Reaction with water or

glutathion (inactivation)

Extensive MBI of CYPs by a drug is worrysome since it often

leads to interference with metabolism of other drugs (DDI).

There is good correlation between covalent binding of a drug to

proteins and TDI. Nakayama et al. Drug Met Disp 2011, 54, 1247

Reactions that do not occur in most patients at any dose.

But please don’t call them dose independent; drugs given at a dose of

10 mg/day or less are relatively safe!

Characteristics suggest immune mechanism

Also known as hypersensitivity reactions, allergic reactions, type B

reactions, type II reactions

Idiosyncratic Drug Reactions (Jack Uetrecht’s definition)

6

Some toxicity is reproducible and dose-dependent in animals, e.g. that of paracetamol (acetaminophen). This is referred to as Type A toxicity.

For some drugs toxicitiy in man is unpredictable from animal research and is relatively infrequent. This is referred to as Type B toxicity (truly idiosyncratic).

7

In real life

Picture to the right from a

presentation by Jack

Uetrecht. Skin injuries are

a common sign of allergic

drug reactions.

Etiologies of acute liver failure in

the US (n = 1,321). Data from the

Acute Liver Failure Study Group

registry, 1998–2008 (W. M. Lee).

Abbreviations: AIH = autoimmune

hepatitis; BCS = Budd–Chiari

syndrome; HAV = hepatitis A virus; HBV

= hepatitis B virus; IDR = idiosyncratic

drug reaction.

acetaminophen

Drugs associated with IADRs

Drugs Withdrawn

Aclcofenac (antiinflammatory)

Hepatitis, rash

Alpidem (anxiolytic)

Hepatitis (fatal)

Amodiaquine (antimalarial)

Hepatitis, agranulocytosis

Amineptine (antidepressant)

Hepatitis, cutaneous ADRs

Benoxaprofen (antiinflammatory)

Hepatitis, cutaneous ADRs

Bromfenac (antiinflammatory)

Hepatitis (fatal)

Carbutamide (antidiabetic)

Bone marrow toxicity

Ibufenac (antiinflammatory)

Hepatitis (fatal)

Iproniazid (antidepressant)

Hepatitis (fatal)

Metiamide (antiulcer)

Bone marrow toxicity

Nomifensine (antidepressant)

Hepatitis (fatal), anaemia

Practolol (antiarrhythmic)

Severe cutaneous ADRs

Remoxipride (antipsychotic)

Aplastic anaemia

Sudoxicam (antiinflammatory)

Hepatitis (fatal)

Tienilic Acid (diuretic)

Hepatitis (fatal)

Tolrestat (antidiabetic)

Hepatitis (fatal)

Troglitazone (antidiabetic)

Hepatitis (fatal)

Zomepirac (antiinflammatory)

Hepatitis, cutaneous ADRs

Marketed Drugs

Abacavir (antiretroviral)

Cutaneous ADRs

Acetaminophen (analgesic)

Hepatitis (fatal)

Captopril (antihypertensive)

Cutaneous ADRs, agranulocytosis

Carbamazepine (anticonvulsant)

Hepatitis, agranulocytosis

Clozapine (antipsychotic)

Agranulocytosis

Cyclophosphamide (anticancer)

Agranulocytosis, cutaneous ADRs

Dapsone (antibacterial)

Agranulocytosis, cutaneous ADRs,

aplastic anaemia

Diclofenac (antiinflammatory)

Hepatitis

Felbamate (anticonvulsant)

Hepatitis (fatal), aplastic anaemia

(fatal), severe restriction in use

Furosemide (diurectic)

Agranulocytosis, cutaneous ADRs,

aplastic anaemia

Halothane (anesthetic)

Hepatitis

Imipramine (antidepressant)

Hepatitis

Indomethacin (antiinflammatory)

Hepatitis

Isoniazid (antibacterial)

Hepatitis (can be fatal)

Phenytoin (anticonvulsant)

Agranulocytosis, cutaneous ADRs

Procainamide (antiarrhythmic)

Hepatitis, agranulocytosis

Sulfamethoxazole (antibacterial)

Agranulocytosis, aplastic anaemia

Terbinafine (antifungal)

Hepatitis, cutaneous ADRs

Ticlopidine (antithrombotic)

Agranulocytosis, aplastic anaemia

Tolcapone (antiparkinsons)

Hepatitis (fatal)

Trazodone (antidepressant)

Hepatitis

Trimethoprim (antibacterial)

Agranulocytosis, aplastic anaemia,

cutaneous ADRs

Thalidomide (immunomodulator)

Teratogenicity

Valproic acid (anticonvulsant)

Hepatitis (fatal), teratogenicity

Temp. Withdrawn

or Withdrawn in

other Countries

Aminopyrine (analgesic)

Agranulocytosis

Nefazodone (antidepressant)

Hepatitis (> 200 deaths)

Trovan (antibacterial)

Hepatitis

Zileuton (antiasthma)

Hepatitis

For most of these drugs, bioactivation to reactive metabolites has been demonstrated in vitro or in vivo

Kalgutkar AS and Soglia JR (2005).

Exp. Opin. Drug Metab. & Toxicol. 1:91-141)

Anticancer drugs are visibly absent from the lists.

9

Recent failures of drugs that were on the market

Lumiracoxib (Prexige® from

Novartis) launched 2003-

2004, withdrawn autumn

2007 due to reports of

serious liver adverse

events

NH

O

Cl

F

OH

Sitaxentan (Encysive Pharma) was

withdrawn in 2010 after having been on

the European market for only four years.

This compound has obvious liabilities

regarding hazard for RM formation, yet

no proven link between ADRs and RMs.

C l

ON

N H

S OO

S

O

O

O

S

O

OO

Alkyl

Alkyl halides and sulfonates

[Br,I,Cl]

Electrophilic esters

SNAr electrophiles

N

A

[F,Cl,Br] N

A

OSO2R

Wide variety of structures! (EWG= electronwithdrawing group)

[F,Cl]

EWG

OO

ArO

O

O NH

Oxiranes and aziridines

OSO

2

Michael acceptors

Awareness/avoidance of intrinsic reactivity

[F ,C l]

E W G

Very useful presentation at SCI

Conference, March 25, 2011, on

”Designing Safer Medicines in

Discovery”

Title: ChEMBL & Structural Alerts

By Francis Atkinson

Chemogenomics Group

EMBL – EBI, Hinxton

http://www.soci.org/News/Fine-Safer-Medicines-2011-Papers.aspx

10

11

Shortlived electrophilic intermediates are formed from most drugs during ‘detoxification’

- Imines and iminium ions from alkylamines

- Epoxides from double bonds

- Unsaturated carbonyls

Do not cause a safety problem unless

- Defence mechanisms are overwhelmed

- Key macromolecules are altered - manifested by organ and/or immune toxicity.

RMs can have selective affinity to certain macromolecules

- Genotoxicity vs. other organ tox?

- Structure Reactivity Relationships poorly understood

Reactive metabolites (RMs) from xenobiotics

N+

O

from paracetamol (acetaminophen); not extremely

shortlived. Quinoid species very common as RMs.

Most RM-

forming

reactions are

Phase 1

reactions

Most common RMs

listed at StopRM.org

where references to

reviews are also listed.

12

Phase 1 reactions, i.e. oxidative (cytochromes P-450), reductive (-NO2), and hydrolytic pathways. These are behind most of the RM generation.

Phase 2 reactions, i.e. conjugation reactions like sulfatation and glucuronidation, in general less prone to cause problems by RM generation.

- Important exceptions are formations of nitrene, quinoid and carbenium ion species which are initialized by acetylation, sulfatation, and more

- Formation of acylglucuronides and acyl-CoA thioesters as acylating agents

Metabolic reactions that can generate RMs

All dependent on context - just like organic synthesis…

OOO

O

OH

OH

OH

O

R R= rest of the

drug

R S

O

CoA

Skonberg et al. Exp Op DM Tox 4

(2008) 425

Review

The molecular mechanism of genotoxicity by aromatic amines

Persistent

mutations caused

by intercalated

adducts in hotspots

of DNA lead to

cancer

Repairs

Primary target atom

Nitrenium ion

or nitrene

N H

N N H

N N

O

N H 2

H

N

d R

N N H

N N

O

N H 2

d R

N

+ H + P450

+

+ H +

+

N H 2

N H

N N H

N N

O

N H 2

H

N

d R

N N H

N N

O

N H 2

d R

N

Guanine-rich

DNA motif

CYP1A2 Acetyltransferases

H +

+

• Only 30% of arylamines follow this path

• Rate of HO-N formation and nitrenium ion stability

determine mutagenicity.

Sulfotransferases

N ..N

+ H

N

Reactive nitroso

compounds can also be

formed from anilines

and nitro compounds

DNA products, CRT 2003

See Shamowsky et al. JACS 2011, 133, 16168, and McCarren et al. J

Cheminfo 2011, 3:51

14

Precursors of RMs

Phenyls/benzene – Can form arene oxides and quinoid species

– Problem substituents: nitro, amino (anilines and masked anilines)

– Halo substituents – influence fate of arene oxides

– Alkoxy groups (facilitate hydoxylation and also undergo dealkylation)

– Alkyl groups on aromatics HO-alkyl eliminations to reactive quinomethanes (benzoquinone methides)

Heteroaryls – Thiophenes

– Thiazoles

– Furans, and more…

Other groups – Many, e.g. alkenes ( allylic alcohols), alkynes, alkyl

halides. Also carboxylic acids (form acylglucuronides and thioesters), and more…

Aromatics

Heteroaromatics

Aliphatics

Oxidations by cytochromes P-

450, FMNs, peroxidases

Reduction

15

Epoxides, especially on aromatic rings (‘arene oxides’)

Benzene very frequent group in drug candidates

– Lots of varied substituents and fusions

– Indispensible to medicinal chemists?

RMs formed by epoxidation of the ring

– Labile arene oxides are formed

– As an example, 1,2-naphtalene oxide

was isolated in 1968 by famous NIH

scientists (Daly, Jerina, Witkop et

al. JACS 50 6525)

– Enzymatic inactivation/detoxification

by epoxide hydrolases and/or

GSH S-transferases (also

by direct reaction

with GSH)

GSH is used in vitro to trap RMs and thus indicate/measure their presence

‘NIH shift’ O

More easily formed than

benzene oxide, E =

70.1 and 59.8 kcal/mol,

respectively (Mats

Svensson, AZ).

Glutathione (GSH)

mM conc. in hepato-

cytes

CYP O

R

OH

SG

R

OH

OH

R

OH

R

GSH

H2O

Enzyme

Rearr.

16

Characteristics of dangerous epoxides

Not inactivated fast enough (in relation to

amounts formed)

Toxic quantities able to reach and modify

macromolecules

Learning from experience is possible:

– Polyaromatic oxides are known carcinogens, being

stabilized arene oxides, e.g from benzopyrene

– Other epoxides also have insidious behaviour -

balanced and targeted reactivity towards sensitive

proteins/DNA

O

O

O

‘Stable’ epoxide

from toxic -

naphtoflavone.

Aflatoxins easily form

epoxides on their fused

dihydrofurans (lead to

1,4-dioxo compounds)

O

O

O

O

O O

H

H

NO

NH2

O

‘Stable’ epoxide from

carbamazepine

Lamotrigine is known to form epoxide(s)

NH2

N

NH2

N

N

Cl

Cl

NH2

N

NH2

N

N

Cl

Cl

OCl

N

N

NH2

N

NH2

Cl

GS

NH2

N

NH2

N

N

Cl

Cl

OH

GS

Human

P450 2A6.Rat P4502C11

GSH - H2O

M-I M-II

Maggs et al. (2000) and Chen et al. (2009). Both research groups conclude that

a reactive, but somewhat stabilized, epoxide is formed. Formed in minor

amounts in vivo (reaction products isolated from bile only). Notably, it is also

formed in keratinocytes.

The isomeric analogue irsogladine, a PDE4 inhibitor, is metabolized to an

epoxide via a major pathway. This isomerizes to phenols (Sugiyama et al.

Arzneimittelforschung 1986, 36, 1229)

N

N N

Cl

Cl

NH2

NH2

N

N N

Cl

Cl

NH2

NH2

O

N

N N

Cl

Cl

NH2

NH2

OH

Quinoids comprise a major category of RMs

O

[C,N,O]

R

OH

[C,N,O]

R

OH

[C,N,O]

Nu

RNuP450 or

otherenzyme

In this large group the electrophilic system consists of a quinone, a quinone-

imine, a quinone-diimine, or the corresponding methides, the quinone

methides (quinomethanes) and quinone-imine methides. Only the para isomers

are depicted below.

Testa et al. (Drug Disc Today 2012, 17, 549) have analysed the literature and

conclude: “A markedly greater source of worry and potential toxicity is seen

with redox reactions, most significantly with the formation of quinones,

quinonimines, quinonimides and quinone-diimines, which accounted for 40%

of all toxic and/or reactive metabolites identified in this work.”

In addition, from the abstract of a review (Monks et al. Current Drug Metab

2002): Quinones are ubiquitous in nature and constitute an important class of naturally occurring

compounds found in plants, fungi and bacteria… For example, the quinones of polycyclic aromatic

hydrocarbons are prevalent as environmental contaminants and provide a major source of current

human exposure to quinones. ... . Quinones are oxidants and electrophiles, and the relative

contribution of these properties to quinone toxicity is influenced by chemical structure,

in particular substituent effects.

All roads lead to Rome…or to quinoids (1)

From phenols diphenols quinones

When R= X-H the formation of a phenol or aminophenol is facilitated.

Even more facilitation….

Real drug examples exist NH

F

RO

NH

F

RN

O

R

- HF

O

XH

OH

X

O

X

OH

XH

X = O,N

1,4-elimi-nation

Oxid.Rearr.

O

R OH

ROALK

R

OH

OH

R

O

O

R

OH

OH

Nu R

O

OH

MeR

NuOxid. Oxid.

COMT

19

All roads lead to Rome…or to quinoids (2)

Quinone methides (quinomethanes) and quinone-imine methides.

Thompson et al. studied the phenol below (Toxicology 2001, 160, 197).

OH

OS

O

O

O

[O,N]

H

H

[N,O][O,N]

OH

H

- H2OOxid.

OH OOH

OH

When the benzylic alcohol forms

a sulfate (via SULT enzymes)

the elimination is even faster

The sulfates of the

corresponding 4-

alkoxy-benzylic

alcohols would also

be quite reactive.

O

OS

O

O

O

R

20

All roads lead to Rome…or to quinoids (3)

Spontaneous loss of HF gives rise to a reactive, toxic species (Thompson et al. 2000)

Merck cpd published in 2005.

Decomposes to a carboxylic acid

on standing in a water solution

Order of events can be different (Kalgutkar et al. DMD 2007)

The example also shows that the leaving group can be a ”phenol”

Lefluonomide is a licensed

rheumatoid arthritis drug.

Instability due to isoxazole

ring opening dominates. No

reports of imine-methide

formation.

OH

F

FF

O

FF

- HF

NH

O NO

OH

F

F F

F

N

NH

FO

O

F

NH

N N

N

OCl

N

N

OCl

OH

R

Cl

O

Cyp

N

N

OR

21

22

Paracetamol can be directly oxidised to a reactive acetylated quinoneimine

Massive amounts of NAPQI will

exhaust GSH reserves

N

O

O

N

O

O

S

R

NH

O

OH

S

R

NH

O

OH

R-SHOx. Proton

shifts

NAPQ

Well-known quinoid-forming motifs of real drugs

Kassahun, K. Studies on the Metabolism of Troglitazone to Reactive Intermediates in Vitro and in Vivo. Chem Res Toxicol

2001, 14, 62

O

OH

O

S

NH

O

O

O

O

O

S

NH

O

O

O

OH

GS

R

The thiazolidine ring might also

entail RM problems. But these are

not significant in low-dose

rosiglitazone (Avandia®, GSK) and

pioglitazone (Actos®, Lilly).

Troglitazone - withdrawn from the market.

23

Oxidation of heteroaromatics

Acyl glucuronides (AGs) and acyl-CoA as

RMs

Special case – the antiepileptic felbamate

Formation of acyl halides (halothane)

A few other mechanisms of RM formation are shown on the following four slides

24

Heteroaromatics can also cause problems

Thiophenes form epoxide and/or S-oxides (tienilic acid, a

diuretic drug, is a classic example; withdrawn 1982)

– The epoxide can also hydrolyse and ring-open

– Simple thiophenes largely abandoned within AZ

Thiazoles can also cause problems

S

O

O COOH

Cl

Cl

S+

R

O

S R

Nu

S R

O

S R

Nu

S R

Nu(p450

)

OH

NuH

Add.-Elim.

NuH

Tienilic acid

+

OS

NH

Duloxetine (Cymbalta®)

does not appear to

show RM tox problems.

Daily dose is 60 mg.

Thiabendazole (an

anthelmintic), given

1-3 g/day shortterm

NH

N

S

N

NH

N

O

O S

NH2

H+P450

Invoked mechanisms: – Direct acylation (of amino groups)

– In theory, the acyl glycoside can isomerize by acyl migration to expose a free aldehyde (semiacetal) which can react with amines and rearrange further.

Rare proven cases. Benzoic acids don’t have AG problems whereas aryl acetic acids (many NSAIDs) might have

– Many NSAIDs withdrawn from the market because of hepatotoxicity. Mechanism? Most stuctures have other potential liabilities stemming from aromatic substructures, e.g. zomepirac

25

Reviews: Skonberg et al. Exp Op DM Tox 4

(2008) 425.

Bailey & Dickinson. Chemico-Biological

Interactions 145 (2003) 117/137

Acyl glucuronides (AGs) and acyl-CoA as RMs

From AZ workshop 2007: “The poorly defined link

between acyl glucuronides and toxicity was considered not to reflect evidence of

absence (of such a link), but rather absence of evidence (of such a link).”

Zomepirac,

withdrawn 1984

or O

O H

O H

OH

OO

O

O

R R

O

NH

R 1R 1-N H 2R S

O

CoA

O

R

O

O

NH

OH

OHO

O

Prot

O

N

OH

OCl

O

O

N H2

O

NH2

O

O H

O

NH2

O

O

O

NH2

O

H O H

O

N H

O

O

H

NH

N

Alb

O

N

NAlb

H

E s te ra s e s

A lc o h o ld e h yd ro -g e n a s e

F o rm e d v ia s p o n -ta n e o u s lo s s o f c a rb a m ic a c id

26

Special case – the antiepileptic felbamate

Mechanism

Reaction of the isolated hemiaminal 1 with albumin

(Alb) was studied by Roller et al. in Chem Res Tox

2005, 15, 815. They concluded that conjugate

addition mainly goes via a histidine residue.

1

Within a year of its release in 1993

• 34 cases of aplastic anemia resulting in 13 deaths (Incidence rate 1:4800 – 1:37000)

• 23 cases of hepatotoxicity resulting in 5 deaths (Incidence rate 1:18000 – 1:25000

Black box warning (severe restriction in use)

• thousands of patients estimated to be on drug

Note

No glutathione

conjugates in liver

microsomes and human

hepatocytes.

No covalent binding to

liver microsomes and

human hepatocytes.

27

Volatile anaesthetics and hepatotoxicity

Halothane – introduced1956,

“Delayed” liver injury in ~1: 3000 patients who receive multiple exposures,

and liver failure in ~1: 30,000

Enflurane - introduced in UK in 1981

“Delayed” liver injury in ~1: 100,000 patients who receive multiple exposures

Isoflurane - introduced in UK in 1984

Very rare case reports of “Delayed” liver injury, ~ <1: 100,000 patients who

receive multiple exposures

Sevoflurane - introduced in 1990, initially in Japan

Currently one of the most widely prescribed volatile anaesthetics in developed

nations. Rare case reports of “delayed” liver injury, from Japanese literature;

Desflurane - introduced 1956

Currently one of the most widely prescribed volatile anaesthetics in

developed nations. A few isolated case reports of “delayed” liver injury

F C C

F

F

Br

H

Cl

F C C

F

F

O

Cl

F C C

F

F

O

Protein

CYP 2E1

Halothane TFA-Cl TFA-protein

Mechanism of

halothane

activation

28

Resources on reactive metabolites

Literature reviews (see comprehensive list on stoprm.org), e.g.

– Kalgutkar et al. (Pfizer), have written many reviews; large one from 2005*

– Uetrecht – perspectives

– Baillie – 20 years experience…

Presentations – Some available on the Internet. Also search for presentations at

http://www.slideshare.net.

– A Claesson has collated several presentations at stoprm.org

Databases etc. – SpotRM is a new web application available at spotrm.com

• Structures and text can be searched. Mechanisms of RM formation detailed.

– ’MDL METAB’, now from Accelrys, available to many industrial chemists and

ADMET persons

• Excellent source of metabolite structures

– Mechanism Based Toxicity Database (MBT), from GVK Biosciences

– Lhasa Limited is a resource center that provides info on software and knowledge

– ChEMBLdb (recently added: new drug approvals), Chemspider, and ChemPub

Other resources – Directory of computer-aided Drug Design tools (ADME Toxicity)

* A Comprehensive Listing of Bioactivation Pathways of Organic Functional Groups. 65 pages

Highlighted on next slides

SpotRM is a freely accessible web application that

facilitates learning about how to avoid introducing

RM liabilities into new test compounds

Hits Name and

type of

drug

Market

status

Link to

mechanism

and more info

Link to

mechanistic

context

Clozapine Withdrawn

(largely)

Clozapine M6523

Quetiapin

e

On the

market

(2011)

Clozapine

Mechanism in Context

C l

N

N

N

NH

N

S

N

N

OH

O

These electrophiles (here BQI) are acceptors of nucleophiles in proteins such as amines and

thiols which might lead to antigen formation and to loss of, or impaired, function. They are

also electron acceptors which, in the context of toxicology, could lead to interference with

biochemical processes where electron transport is occurring. For example, quinones are

highly redox active molecules which can redox cycle with their semiquinone radicals, leading

to formation of reactive oxygen species (ROS), including superoxide, hydrogen peroxide, and

ultimately the hydroxyl radical. Production of ROS can cause severe oxidative stress within

cells through the formation of oxidized cellular macromolecules, including lipids, proteins,

and DNA (review by Bolton et al. 2000).

Fig 2. Unsubstituted o- and p-quinoneimines.

O

O

Nu

H

H

H

R

OH

OH

Nu

RO

O

R

NuH

redox cycling oxidative stress

O

NH NH

O

Fig 1. Addition of a nucleophile to a

substituted p-benzoquinone followed

by rearomatization. This can be

followed by a new round of oxidation-

addition. Also, quinones can accept

electrons and generate radicals.

Draw a structure to make a

substructure search

Or type a textword: generic

name or other word (brand

names are not searchable).

Hits are presented in a table con-

taining links to details of current

hypotheses of how a drug forms

reactive metabolites.

The mechanism is also placed in

context of similar reactions .

Hypothesis of

Mechanism

Avoiding reactive metabolites

© 2012 Awametox Consulting, Sweden. Contact: info@awametox.se

Schematics

Avoiding reactive metabolites

© 2012 Awametox Consulting, Sweden. Contact: info@awametox.se

The search results lead to expert reports and to original literature data

Hypothesis of Mechanism

Mechanism in Context (text

document on 3-7 pages)

These electrophiles (here BQI) are acceptors of nucleophiles in proteins such as amines and

thiols which might lead to antigen formation and to loss of, or impaired, function. They are

also electron acceptors which, in the context of toxicology, could lead to interference with

biochemical processes where electron transport is occurring. For example, quinones are

highly redox active molecules which can redox cycle with their semiquinone radicals, leading

to formation of reactive oxygen species (ROS), including superoxide, hydrogen peroxide, and

ultimately the hydroxyl radical. Production of ROS can cause severe oxidative stress within

cells through the formation of oxidized cellular macromolecules, including lipids, proteins,

and DNA (review by Bolton et al. 2000).

Fig 2. Unsubstituted o- and p-quinoneimines.

O

O

Nu

H

H

H

R

OH

OH

Nu

RO

O

R

NuH

redox cycling oxidative stress

O

NH NH

O

Fig 1. Addition of a nucleophile to a

substituted p-benzoquinone followed

by rearomatization. This can be

followed by a new round of oxidation-

addition. Also, quinones can accept

electrons and generate radicals.

Original

literature

Since it is crucially important that drug designers try to avoid

introducing structural elements that have a risk of generating

RMs they have to learn what might represent a hazard

– Mechanisms are grouped in the documents ”Mechanism in Context”

SpotRM facilitates learning in a new way

– Learning directly from the scientific literature is time consuming and

nuances are easily missed

There is no other similar resource available – the

substructure search feature is particularly attractive for

chemists

Further developments of SpotRM are ongoing

– We will add a new modification that will allow mapping of potential

RM liabilities on whole structures

– You are encouraged to forward your views on useful features to add

and other improvements. Go to the SpotRM homepage

Prominent features of SpotRM Avoiding reactive metabolites

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