Ebook Designing multi-target drugs: Part 1

RSC Drug Discovery

Edited by J. Richard Morphy and C. John Harris

Designing Multi-Target Drugs


Designing Multi-Target Drugs


RSC Drug Discovery Series
Editor-in-Chief:
Professor David Thurston, London School of Pharmacy, UK

Series Editors:
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Professor Salvatore Guccione, University of Catania, Italy
Professor Ana Martinez, Instituto de Quimica Medica-CSIC, Spain
Dr David Rotella, Montclair State University, USA

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Titles in the Series:
1: Metabolism, Pharmacokinetics and Toxicity of Functional Groups: Impact
of Chemical Building Blocks on ADMET
2: Emerging Drugs and Targets for Alzheimer’s Disease; Volume 1: BetaAmyloid, Tau Protein and Glucose Metabolism
3: Emerging Drugs and Targets for Alzheimer’s Disease; Volume 2: Neuronal
Plasticity, Neuronal Protection and Other Miscellaneous Strategies
4: Accounts in Drug Discovery: Case Studies in Medicinal Chemistry
5: New Frontiers in Chemical Biology: Enabling Drug Discovery

6: Animal Models for Neurodegenerative Disease
7: Neurodegeneration: Metallostasis and Proteostasis
8: G Protein-Coupled Receptors: From Structure to Function
9: Pharmaceutical Process Development: Current Chemical and Engineering
Challenges
10: Extracellular and Intracellular Signaling
11: New Synthetic Technologies in Medicinal Chemistry
12: New Horizons in Predictive Toxicology: Current Status and Application
13: Drug Design Strategies: Quantitative Approaches
14: Neglected Diseases and Drug Discovery
15: Biomedical Imaging: The Chemistry of Labels, Probes and Contrast Agents
16: Pharmaceutical Salts and Cocrystals
17: Polyamine Drug Discovery
18: Proteinases as Drug Targets
19: Kinase Drug Discovery
20: Drug Design Strategies: Computational Techniques and Applications
21: Designing Multi-Target Drugs

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Designing Multi-Target Drugs

Edited by
J. Richard Morphy
Stirling, UK*

C. John Harris
Eynsford, Kent, UK

*

Current address: Lilly Research Centre, Windlesham Research Centre, Surrey GU20 9PH, UK.


RSC Drug Discovery Series No. 21
ISBN: 978-1-84973-362-5
ISSN: 2041-3203
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Foreword
What is Multi-Targeted Drug Discovery (MTDD)?
This book consists of chapters concerned with a variety of aspects related
to ‘multi-targeted drug discovery’ (MTDD). A good definition of MTDD
is given by Metz and Hajduk1 ‘Multi-targeted drugs are promiscuous and
exhibit activity against a wide range of molecular targets. In fact, it is now
commonly accepted that the polypharmacology of these drugs (i.e. their ability
to modulate the activity of multiple protein targets) is at least partly responsible
for their efficacy’. MTDD is also described by the term ‘designed multiple
ligands’ as described in multiple publications by Morphy.2
The terms ‘promiscuous’ or ‘dirty drug’ may have a pejorative aspect in that
although multiple biological activities can be useful, leading to enhanced
efficacy, they also may not be useful, leading to enhanced undesirable pharmacology (toxicity). Not to be confused with multi-targeting, the term ‘promiscuous’ has also been used in the realm of high throughput screening (HTS)
to denote HTS assay biological activity related to usually undesirable chemical or physicochemical features. This phenomenon may be associated with
covalent bond formation between ligand and target,3 or undesirable in vitro
biophysical effects such as colloidal particle aggregate formation.4 In both
cases, the observed promiscuity is not associated with useful biological
activity. In contrast to the in vitro situation, it should be noted that colloidal
aggregate formation in vivo in the gastrointestinal tract may be beneficial by
enhancing oral absorption.5 There is also a drug discovery viewpoint in favor
of ligands with the potential to form covalent bonds between ligand and
target.6 However, in this author’s opinion, these are minority viewpoints in
dedicated drug discovery.

RSC Drug Discovery Series No. 21
Designing Multi-Target Drugs
Edited by J. Richard Morphy and C. John Harris
r Royal Society of Chemistry 2012
Published by the Royal Society of Chemistry, www.rsc.org

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Foreword

Why is there an Upsurge in Interest in MTDD?
The existence of polypharmacology, which provides the foundation for
MTTD, has been known to medicinal chemists for decades. For example,
the concept of privileged chemistry structures was first described by Evans
et al. in 1988,7 reviewed by Patchett in 2000,8 and discussed in a drug
discovery and library design context in 2010.9 The Merck group’s work on
the use of the benzodiazepine scaffold originally found in anxiolytics provides a rich example of how relatively small structural changes to a scaffold
can lead to a variety of unrelated biological activities. In their words, ‘What
is clear is that certain ‘‘privileged structures’’ are capable of providing useful
ligands for more than one receptor and that judicious modification of such
structures could be a viable alternative in the search for new receptor
agonists and antagonists’. It is clear that in this early work that the concept
of polypharmacology was well understood although it was uncertain if
compounds with polypharmacology might be rare and difficult to find. We
now know that privileged structures (i.e. promiscuous scaffolds) are much
more numerous than previously supposed.10
This work on MTTD is being published in 2012. The reader may well ask

what has changed over the last two decades to bring MTTD to greater
attention. In this author’s opinion, one major change is the gradual realization, especially in this last decade, that the superbly selective single drug with
high affinity for a single biological target coupled with clinical efficacy is,
charitably speaking, ‘the exception’; more critically, some view this as a
‘fundamentally flawed’ approach to drug discovery.11–14 Illustrating the
charitable viewpoint, it is estimated that a complete single point pathway
knockout results in a phenotypic response in only about 10–15% of cases. This
low efficacy of the single-mechanism drug discovery approach is the explanation for the intense interest in target validation. How does one find the
magic 10–15% of potential targets where the single-mechanistic approach has
a chance of working? The low efficacy of the single-mechanism approach
places HTS into context. HTS is only a tool and the HTS approach to drug
discovery is critically dependent on target validation. Explaining the ‘fundamentally flawed’ viewpoint is the genomics-driven ‘drug discovery factory’
approach15 of the early 1990s which wasted hundreds of millions of dollars
and the efforts of many talented scientists.
A second major change is the realization that polypharmacology is the rule
rather than the exception among clinically useful drugs.16,17 Finally, the wealth
of ligand to target database information in the current era allows the exploitation of a more chemo centric as opposed to molecular biology centric view of
drug discovery. This change is well described in the following quote from the
review by Shoichet:18 ‘What is new in the past few years is the quantitative
restatement of classical ideas, allowing formal comparisons among targets and
ligands at a scale not previously attempted. This has suggested unexpected
relationships among receptors, identified targets active in phenotypic screens,
and predicted off-targets and new disease indications for drugs.’


Foreword

vii

Chemical Space, Polypharmacology and MTDD

The distribution of biologically active compounds in chemistry space is
critical to the concepts of polypharmacology and MTDD. If biologically
active compounds are widely or uniformly distributed in chemical space
then one might expect polypharmacology to be rare and MTDD would
likely not work. Conversely, if biologically active compounds are clustered
in chemistry space then polypharmacology should be common and MTTD
should be tractable.
Chemical space is finite but exceedingly large. As discussed in a review by
Reymond et al.19 ‘Is chemical space finite? Yes, if boundaries are defined. For
small molecule drug discovery the natural limit is the molecular weight, which
must be capped at 300–500 Da to ensure reasonable bioavailability. This
chemical space of drug-like molecules has been estimated to be in excess of
1060 molecules.’ The key medicinal chemistry question relevant to MTDD
is whether biologically active compounds are evenly distributed in this
incredibly large chemical space. In this and other authors’ opinion the answer
for synthetic compounds is a resounding ‘no’. Multiple papers in the literature
attest to the very uneven distribution of biologically active synthetic
compounds in chemistry space.20–22 Synthetically made biologically active
compounds (as might be made by medicinal chemists) are most definitely not
evenly distributed in chemical space. In fact, even without consideration of
biological activity, the distribution of chemical structure scaffolds in the
chemical literature is highly biased.23 Screening truly diverse compounds is
the worst way to discover a drug because the current evidence suggests that
most of chemistry space is not populated by biologically active synthetic
compounds.

An Issue of Timing: When is MTDD/Polypharmacology
Undesirable?
Polypharmacology can be undesirable in a chemical biology context as
opposed to a drug discovery context. Broadly speaking, chemical ligands can

be tested in biology assays for two purposes: to discover drugs or to discover
something about a biological process.24 From a drug discovery perspective,
polypharmacology is extremely useful. However, in a chemical biology
context where one may be using a molecule as a tool or probe to learn
something about a biological process,25 perhaps to interrogate a step in a
pathway or to discover a mechanism, selectivity is a key attribute and
polypharmacology is a detriment. This is especially the case in phenotypic
screening where the active chemical ligand becomes the tool or probe that is
the starting point for the detective work to discover mechanism. Even when
the stated screening goal is a chemical biology tool or probe, selectivity is
difficult to achieve. For example, in a crowd sourcing evaluation of the 64
tools and probes resulting from the NIH roadmap HTS screening effort,


viii

Foreword

about one-quarter were judged to be deficient with respect to selectivity.26
The use of chemical biology probes with truly high selectivity can play a key
role in understanding how to rationally design multi-targeted drugs, which is
the key theme of this book.
Christopher Lipinski

References
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J. T. Metz and P. J. Hajduk, Curr. Opin. Chem. Biol., 2010, 14, 498–504.
R. Morphy and Z. Rankovic, Curr. Pharm. Des., 2009, 15, 587–600.
J. B. Baell, Future Med. Chem., 2010, 2, 1529–1546.
A. Jadhav, R. S. Ferreira, C. Klumpp, B. T. Mott, C. P. Austin, J. Inglese,
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Chem., 2010, 53, 37–51.
A. K. Doak, H. Wille, S. B. Prusiner and B. K. Shoichet, J. Med. Chem.,
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D. S. Johnson, E. Weerapana and B. F. Cravatt, Future Med. Chem., 2010,
2, 949–964.

B. E. Evans, K. E. Rittle, M. G. Bock, R. M. DiPardo, R. M. Freidinger,
W. L. Whitter, G. F. Lundell, D. F. Veber and P. S. Anderson, et al.,
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A. A. Patchett and R. P. Nargund (Merck Research Laboratories,
Rahway, NJ, USA), Annu. Rep. Med. Chem., 2000, 35, 289–298.
M. E. Welsch, S. A. Snyder and B. R. Stockwell, Curr. Opin. Chem. Biol.,
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Y. Hu and J. Bajorath, J. Chem. Inf. Model., 2010, 50, 500–510.
R. L. Ho and C. A. Lieu, Drugs in R&D, 2008, 9, 203–216.
H. Kitano, Nat. Rev. Drug Discovery, 2007, 6, 202–210.
D. Brown, Drug Discovery Today, 2007, 12, 1007–1012.
F. Sams-Dodd, Drug Discovery Today, 2006, 11, 465–472.
U. A. K. Betz, R. Farquhar and K. Ziegelbauer, Curr. Opin. Chem. Biol.,
2005, 9, 387–391.
A. L. Hopkins, Nat. Chem. Biol., 2008, 4, 682–690.
Y. Hu and J. Bajorath, J. Chem. Inf. Model., 2010, 50, 2112–2118.
M. J. Keiser, J. J. Irwin and B. K. Shoichet, Biochemistry, 2010, 49,
10267–10276.
J.-L. Reymond, R. van Deursen, L. C. Blum and L. Ruddigkeit, MedChemComm, 2010, 1, 30–38.
J. Hert, J. J. Irwin, C. Laggner, M. J. Keiser and B. K. Shoichet, Nat.
Chem. Biol., 2009, 5, 479–483.
P. Ertl, S. Jelfs, J. Muehlbacher, A. Schuffenhauer and P. Selzer, J. Med.
Chem., 2006, 49, 4568–4573.
C. Lipinski and A. Hopkins, Nature, 2004, 432, 855–861.


Foreword

ix

23. A. H. Lipkus, Q. Yuan, K. A. Lucas, S. A. Funk, W. F. Bartelt, III, R. J.
Schenck and A. J. Trippe, J. Org. Chem., 2008, 73, 4443–4451.
24. T. Kodadek, Nat. Chem. Biol., 2010, 6, 162–165.
25. S. V. Frye, Nat. Chem. Biol., 2010, 6, 159–161.
26. T. I. Oprea, C. G. Bologa, S. Boyer, R. F. Curpan, R. C. Glen, A. L.
Hopkins, C. A. Lipinski, G. R. Marshall, Y. C. Martin, L. OstopoviciHalip, G. Rishton, O. Ursu, R. J. Vaz, C. Waller, H. Waldmann and L. A.
Sklar, Nat. Chem. Biol., 2009, 5, 441–447.



Introduction
Why Design Multi-Target Drugs?
The promiscuity of a drug, that is, its tendency to bind to multiple drug
targets is both a challenge and an opportunity for medicinal chemists. Drug
designers attempt to reduce the ‘off-target’ toxicity liabilities of a compound by
increasing the selectivity of a drug for one target over others. Analysis of the
physicochemical properties of failed and successful drug candidates illustrate
that drug target promiscuity, due to high lipophilicity, is linked to an increased
risked of toxicity and failure in the clinic:1,2 hence the traditional label of
promiscuous compounds as ‘dirty’.3 Guiding the design principle of selectivity
is not only a reduction in potential toxicity but also the assumption that the
direct modulation of single proteins will produce clinical benefits: a reductionist
paradigm summarised as ‘one gene, one disease, one drug’.
Since the completion of the sequencing of the first draft of the human genome, evidence has been accumulating from functional genomics and the new
field of network biology that biological systems are robust to perturbation
of individual genes. The new insights are challenging the dominant assumption
of single target-based drug discovery.4–8 Insights into the robustness of
phenotype to perturbation can be found from understanding the function of
biological networks. The fundamental architecture of networks contributes to
the robustness and redundancy of biological systems. Network analysis of

biological pathways and interactions has revealed that much of the robustness
of biological systems is derived from the structure of biological networks.9,10
The scale-free nature of many biological networks produces systems that are
resilient against random deletion of any one protein (node) but also critically
dependent on a few highly connected hubs. Network biology analysis predicts
that if, in most cases, deletion of individual nodes may have little effect on
disease networks, modulating multiple proteins may be required to perturb
RSC Drug Discovery Series No. 21
Designing Multi-Target Drugs
Edited by J. Richard Morphy and C. John Harris
r Royal Society of Chemistry 2012
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Introduction
6,9,11

12

robust phenotypes.
A network approach to pharmacology suggests two
strategies: targeting highly connected hub proteins, which exhibit pleiotropic
effects (such as the role of HSP90 in cancer) or the targeting of multiple proteins
to increase the perturbation of a network.
The robustness of individual proteins to perturbation is also revealed by
metabolic flux analysis where modulation of single components in a pathway

rarely results in large changes in metabolic flux and therefore phenotype.13–15 A
greater degree of perturbation of phenotype is observed in systems where more
than one gene product is modulated. The emergent phenotype that occurs from
the perturbation of multiple proteins is demonstrated by the systematic
experiments on synthetic lethality. Dual gene deletion experiments in model
systems have shown that, whilst the deletion of any one of two genes by itself
may show no effect, the deletion of both genes can lead to ‘synthetic lethality’ or
‘synthetic sickness’.16 When dual perturbations are introduced, by combining
single gene genetic knock-outs with a second chemical perturbation, the
number of essential genes in yeast is predicted to significantly expand the 18%
of the genes for which singleton gene knockouts are lethal. A large-scale study
by Hillenmeyer et al. demonstrates the extent of synthetic lethality when gene
deletions are augmented by chemical interventions.17 Under ideal conditions
only 34% of single gene deletions result in lethality or sickness. When the whole
genome panel of yeast single gene knock-outs was screened against a diverse,
small molecular library and assayed against a wide range of environment
conditions an additional 63% of gene knock-outs showed a growth phenotype.17 Thus 97% of genes demonstrate a fitness defect when challenged with a
small molecule under at least one environmental condition. The vast majority
of genes may be redundant under any one environmental condition but there
appears to be little redundancy across a spectrum of conditions when a genetic
perturbation is combined with a chemical insult. Genes that may appear dormant and dispensable under one set of specific conditions may prove essential
under other stresses.18,19
The fundamental property of inherent robustness of biological networks has
profound implications for drug discovery; instead of searching for a single
‘disease-modifying’ gene, network biology suggests that the strategy should be
to perturb the disease network.20,21 Hellerstein has argued that the true targets
of drugs are not individual proteins but functionally important biochemical
pathways embedded in larger biological networks.22
The intellectual foundations of network pharmacology challenge deep
assumptions behind target selection and validation. Responding to the new

biological insights into the complexity, robustness and redundancy in
disease phenotype is helping to drive the emergence of a new approach to drug
discovery, that of polypharmacology or multi-target drug discovery
(MTDD).3–6,11,12,23–30 Therefore, understanding the polypharmacology of a
drug and its effect on biological networks and phenotype is essential if we wish
to improve efficacy and understand toxicity.
Over the past decade the assumption of the desirability of single
drug target mechanisms has begun to be questioned.6,12,31 In certain


Introduction

xiii

circumstances, it may be advantageous for a drug to act on multiple drug
targets, deliberately and specifically, rather than be too selective. The
chapters written for this book gather together in one volume the state-ofthe-art of the emerging new field of MTDD. Successes in rational MTDD
have already been reported, such as the approval of lapatinib, discussed in
Chapter 8. Moreover, new tools are now emerging to aid the medicinal
chemists to discover multi-target drugs. We hope this book serves as a
record of the achievements of the field to date and provides inspiration for
the development of rational MTDD as the next paradigm in drug discovery.
Andrew L. Hopkins
Division of Biological Chemistry and Drug Discovery
College of Life Sciences, University of Dundee,
D11 5EH, UK

References
1. P. D. Leeson and B. Springthorpe, Nat. Rev. Drug Discovery, 2007, 6,
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2. J. D. Hughes, et al., Bioorg. Med. Chem. Lett., 2008, 18, 4872–4875.
3. S. Frantz, Nature, 2005, 437, 942–943.
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5. C. G. Wermuth, Drug Discovery Today, 2004, 9, 826–827.
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11. T. Korcsma´ros, M. S. Szalay, C. Bo¨de, I. Kova´cs and P. Csermely, Expert
Opin, Drug Discovery, 2007, 2, 1–10.
12. A. L. Hopkins, Nat. Chem. Biol., 2008, 4, 682–690.
13. J. E. Bailey, Nat. Biotechnol., 1999, 17, 616–618.
14. J. E. Bailey, Metab. Eng., 2001, 3, 111–114.
15. M. K. Hellerstein, J. Pharmacol. Exp. Ther., 2008, 325, 1–9.
16. S. L. Ooi, et al., Trends Genet., 2006, 22, 55–63.
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18. L. M. Blank, L. Kuepfer and U. Sauer, Genome Biol., 2005, 6, R49.
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Introduction

23. S. K. Mencher and L. G. Wang, BMC Clin. Pharma., 2005, 5, 3.
24. A. L. Hopkins, J. S. Mason and J. P. Overington, Curr. Opin. Struct. Biol.,
2006, 16, 127–136.
25. C. S. Flordellis, A. S. Manolis, H. Paris and A. Karabinis, Curr. Top. Med.
Chem., 2006, 6, 1791–1798.
26. N. Dessalew and M. Workalemahu, Curr. Comput.-Aided Drug Design,
2008, 4, 76–90.
27. O. Keskin, A. Gursoy, B. Ma and R. Nussinov, Curr. Topics Med. Chem.,
2007, 7, 943–951.
28. G. R. Zimmermann, J. Leha´r and C. T. Keith, Drug Discovery Today,
2007, 12, 34–42.
29. A. L. Hopkins, Nat. Biotech., 2007, 25, 1110–1111.
30. A. Schrattenholz and V. Soskic, Curr. Med. Chem., 2008, 15, 1520–1528.
31. R. Morphy, C. Kay and Z. Rankovic, Drug Discovery Today, 2004, 9,
641–651.


Preface
Forming part of the Royal Society of Chemistry Drug Discovery Series, this
book is intended to provide an integrated and comprehensive overview of
modern approaches to multi-target drug discovery (MTDD) and the state of
our knowledge in the over-arching field of polypharmacology. Given the
intense current interest in this field, we hope that this book will be of significant interest to medicinal and computational chemists in the commercial
sector and in academia, as well as the wider drug discovery community.
Many readers will already be aware of the serendipitous nature of the discovery of many existing multi-target drugs. In this book we intend to focus on
the rational and practical execution of MTDD. The chapters are written by
widely recognized experts and opinion leaders in the field. The first challenge of
MTDD is to identify biologically validated combinations of targets relevant to

a disease state. However, it is equally important that these disease-relevant
combinations are chemically tractable from a medicinal chemistry perspective.
The book thus follows a natural thread from target identification and validation,
through lead generation and lead optimization, and finally to clinical development. A key feature of the book is a collection of seminal case studies chosen to
illustrate the challenges and opportunities of MTDD. These include compounds
at various stages of development from preclinical to marketed drugs.
In the forward, two eminent proponents of MTDD, Andrew Hopkins and
Chris Lipinski, discuss the motivation and background rationale for designing
multi-target drugs.
Although MTDD has been applied in the context of many diseases, it is
particularly relevant to complex polygenic diseases such as cancer, inflammation and central nervous system (CNS) disorders. In Chapters 1 and 2, Jorrit
Hornberg and Mo Shahid discuss the pathophysiological context of these
diseases that makes the development of multi-target drugs such an attractive
proposition.
RSC Drug Discovery Series No. 21
Designing Multi-Target Drugs
Edited by J. Richard Morphy and C. John Harris
r Royal Society of Chemistry 2012
Published by the Royal Society of Chemistry, www.rsc.org

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A growing area of interest for target identification is network pharmacology.
In Chapter 3, Malcolm Young, Steven Zimmer and Alan Whitmore discuss the
properties of biological networks and how a judicious selection of certain

combinations of targets (or nodes) using network simulation algorithms can
have a disproportionate effect on the robustness of a disease network, thereby
enhancing therapeutic effect.
The chemical tractability of a given target combination has been assessed
using an increasing range of cheminformatics tools, as described by Michael
Keiser and Elisabet Gregori-Puigjane´ in Chapter 4. These predictive polypharmacology methods typically rely upon various measures of chemical
similarity between known ligands for each target and can reveal links between
the binding sites of distant proteins, unrelated by overall sequence or structure
or function. Potentially the same methods can also identify undesired targets
associated with toxicity.
Whilst in silico predictions of polypharmacology are increasingly useful,
currently the most reliable method for exploring the polypharmacology of
compounds is in vitro panel screening using a broad and diverse set of targets.
In Chapter 5, Jonathan Mason explains how these direct readouts of promiscuity and selectivity can be used to select tool compounds for target validation, the best starting compounds for further optimization and to provide
differentiation amongst drug candidates.
The last quarter century has witnessed a seismic change from a world of
drug discovery based upon phenotypic screening in whole organisms to the
reductionist target-centric approach of today. Given the high clinical attrition
seen in recent years, there are signs that this trend is reversing and in Chapter
6, Chris Lipinski describes how phenotypic screening is highly relevant to the
MTDD field and how many active compounds identified in such screens are
likely to display polypharmacology. Whilst it is feasible to optimize and
clinically develop compounds without knowledge of mechanism, if such
knowledge were to be available, then optimization of potency would be more
straightforward. In Chapter 7, Kilian Huber, Giulio Superti-Furga and Georg
Winter describe a range of methods for deconvoluting mechanism of action
for hits from phenotypic screening.
Many different lead generation approaches have been used for MTDD
projects and, given the added complexity of optimizing against multiple targets,
finding high quality starting compounds is critical. Both rational design

and screening approaches are described by Richard Morphy in Chapter 8, and
in silico screening is described in more detail by Yuzong Chen in Chapter 9.
Lead optimization is a pivotal stage in the history of any drug discovery
project and all the more so in the MTDD area, where the simultaneous optimization of multiple parameters must be addressed. In Chapter 10, Richard
Morphy discusses the importance of optimizing the activity ratio, wider
selectivity, physicochemical properties and the pharmacokinetic profile.
There are two possible scenarios for multi-target therapy, drug combinations
and multi-target drugs, which are sometimes seen as competing world views
but which are actually complementary in their value and applicability. In


Preface

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Chapter 11, Janet Dancey and Jose Monzon discuss the challenges of clinical
development of drug combinations in the cancer area and compare and contrast such combinations with multi-target agents such as the multi-kinase
inhibitors like sunitinib.
The storyline of the book then moves to a series of case studies. Continuing
the oncology theme from Chapter 11, Karen Lackey describes how the dual
EGFR/erbB2 kinase inhibitor, lapatinib, was discovered and clinically developed to provide a marketed drug for treating breast cancer. The following three
case studies are also oncology-focussed, illustrating the extent of current
interest in MTDD for this highly complex and heterogeneous disease. Carlos
Garcı´ a-Echeverrı´ a and Andreas Karlsson describe dual PI3K/mTOR inhibitors, Xiong Cai and Changgeng Qian discuss multi-target HDAC/kinase
inhibitors, and Michael Wendt tells the story of how dual inhibitors of Bcl-2
and Bcl-xL were discovered.
The next three case studies describe the discovery of compounds with multiple targets within the CNS. First, John Lowe, one of the inventors of the antischizophrenia drug, ziprasidone, explains how the compound was rationally
designed starting from the structures of dopamine and a serotonin receptor
antagonist. Next, Robert Weikert writes about triple blockers of the serotonin,
noradrenaline and dopamine transporters. Then in Chapter 18, Maria Laura

Bolognesi, Carlo Melchiorre, Cornelis Van der Schyf and Moussa Youdim
discuss a range of multi-target approaches for neurodegenerative diseases, such
as the dual monoamine oxidase/acetylcholinesterase inhibitor, Ladostigil, for
Alzheimer’s disease and Parkinson’s disease.
The book concludes with two final case studies from the cardiovascular and
anti-infective disease areas. The first from Natesan Murugesan describes dual
angiotensin-1/endothelin-A receptor antagonists for treating hypertension and
in the second, Stephen East, Lloyd Czaplewski and David Haydon discuss dual
inhibitors of DNA gyrase/topoisomerase IV as broad-spectrum antibacterial
agents.
This is the first time that a single volume has gathered together in one place
the current state-of-the-art, the achievements and the challenges of the MTDD
field and, importantly, the lessons learned by researchers to date. Through an
intentional focus on the rational and practical execution of MTDD, we hope
that this book will play a significant role in facilitating the future development
of the field.
Richard Morphy and John Harris



Contents
Chapter 1

Simple Drugs Do Not Cure Complex Diseases:
The Need for Multi-Targeted Drugs
Jorrit J. Hornberg
1.1
1.2
1.3
1.4

1.5
1.6

Introduction
The Need for Better and Safer Drugs
Cancer
Rheumatoid Arthritis
Control of Complex Biological Systems
Safety of Multi-Targeted Drugs
1.6.1 Target-Related Toxicity
1.6.2 Off-Target Toxicity
1.6.3 Chemistry-Related Toxicity
1.7 Concluding Remarks
Acknowledgements
References

Chapter 2

Clinical Need and Rationale for Multi-Target Drugs
in Psychiatry
Mohammed Shahid
2.1
2.2
2.3

Introduction
Clinical Need
Rationale For Multi-Target Agents: Multifunctional
Pharmacology and Multi-Therapeutic Application
2.4 New Introductions

2.4.1 Agomelatine
2.4.2 Vilazodone
2.4.3 Asenapine
RSC Drug Discovery Series No. 21
Designing Multi-Target Drugs
Edited by J. Richard Morphy and C. John Harris
r Royal Society of Chemistry 2012
Published by the Royal Society of Chemistry, www.rsc.org

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Chapter 3

Contents

2.4.4 Lurasidone
2.4.5 Iloperidone
2.5 Emerging Promising Compounds in Development
2.5.1 Cariprazine
2.5.2 Lu AA21004 and Zicronapine
2.5.3 LY2140023
2.6 Summary and Future Perspectives
Acknowledgements
References

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24
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24
25
26
27

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28

Drug Molecules and Biology: Network and
Systems Aspects
Malcolm P. Young, Steven Zimmer and Alan V. Whitmore

32

3.1
3.2
3.3
3.4

Chapter 4

Biological Robustness and Therapeutic Discovery
Biological Networks and Their Properties
Multiple Interventions: Expect the Unexpected
Effective Drugs and Multiple Interventions in
Networks
3.5 Drug Discovery Problems in Light of
Network Science
3.6 Network Pharmacology: Exploiting Advances in
Chemical Biology and Network Science
3.7 Prospects for Multi-Target Drug Discovery in Light of
Network Science
Glossary
References

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36

Chemoinformatic Approaches to Target Identification
Elisabet Gregori-Puigjane´ and Michael J. Keiser

50

4.1
4.2

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Introduction
Approaches
4.2.1 Representing Ligands for Similarity
Calculations
4.2.2 Organizing Biological Targets by their
Ligands
4.2.3 Profiling
4.3 Applications
4.3.1 Target Identification
4.3.2 Safety and Target-Specific Toxicity
4.3.3 Applicability
References

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Contents

Chapter 5

Designing Multi-Target Drugs: In Vitro Panel Screening –
Biological Fingerprinting
Jonathan S. Mason
Introduction: Biological Fingerprints – A Biological
View of Compounds
5.2 The Cerep Bioprints Database
5.3 Profiling Concepts and Practice
5.4 Profiling of Drugs: The Multi-Target/
Polypharmacology of Drugs

5.5 Profiling of Project Compounds
5.5.1 Choosing the Best Hit or Lead Compound and
Differentiation
5.5.2 Profiling of Tool Compounds: Target Validation
5.5.3 Selectivity and the Use of the Broad In Vitro
Biological Profile to Predict In Vivo Effects and
Safety Issues
5.5.4 Multi-Target/Polypharmacology of Attrited
Compounds
5.6 Profiling and Clustering of Compounds: In Silico
Descriptors and Similarity Issues
5.7 In Vitro Panel Screening: The Future
References

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5.1

Chapter 6

Phenotypic and In Vivo Screening: Lead Discovery and Drug
Repurposing
Christopher A. Lipinski
6.1
6.2

Changes in Screening Philosophy
Phenotypic Screening: Advantages, Disadvantages,
Ligand Matching and MTDD
6.3 Drug Repurposing: Leveraging Signaling

Network Activities
References

Chapter 7

Target/s Identification Approaches – Experimental
Biological Approaches
Giulio Superti-Furga, Kilian Huber and Georg Winter
7.1
7.2

Introduction
Yeast Genomic Assays
7.2.1 Drug-Induced Haplo-Insufficiency Profiling (HIP)
7.2.2 Homozygous Profiling (HOP)/Haploid Deletion
Chemical Genetic Profiling

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7.3

Genomic Assays in Mammalian Cells
7.3.1 Comparative Gene Expression Profiling
7.3.2 RNA Interference-Based Screens
7.4 Proteomic Approaches
7.4.1 Compound-Centred Chemical Proteomics
(CCCP)
7.4.2 Kinobeads
7.4.3 Activity-Based Protein Profiling (ABPP)

7.4.4 Global Phosphoproteomics
7.4.5 Lysine Acetylation Profiling
7.4.6 Drug Affinity Responsive Target Stability
(DARTS)
7.5 Other Methods
7.5.1 Yeast Three-Hybrid (Y3H)
7.5.2 Protein Microarrays
7.6 Conclusions
References
Chapter 8

Chapter 9

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Historical Strategies for Lead Generation

J. Richard Morphy

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8.1 Introduction
8.2 Historical Approaches
8.2.1 Framework Combination
8.2.2 Screening
8.2.3 Comparing Lead Generation Approaches
8.3 Emerging Approaches
8.3.1 Fragment Approach
8.3.2 Virtual Screening
8.3.3 Structure Guided Approaches
8.3.4 Natural Products
8.4 Chemical Biology
8.5 Factors Influencing the Feasibility of MTDD
8.6 Summary
References

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126

In Silico Lead Generation Approaches in Multi-Target Drug
Discovery
Xiaohou Ma and Yuzong Chen

130

9.1

Introduction to In Silico Screening Methods
9.1.1 Molecular Docking
9.1.2 Pharmacophores
9.1.3 QSAR
9.1.4 Machine Learning Methods

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9.2 Application of In Silico Screening to MTDD

9.3 Perspectives
References

Chapter 10 The Challenges of Multi-Target Lead Optimization
J. Richard Morphy
10.1 Introduction
10.2 Optimization of the Activity Profile
10.3 Wider Selectivity
10.4 Physicochemical Properties
10.5 Summary
References

Chapter 11 Combination Agents Versus Multi-Targeted
Agents – Pros and Cons
Jose G. Monzon and Janet Dancey
11.1
11.2

Introduction
Principles of Combination Chemotherapy for
the Treatment of Cancer
11.2.1 Principle #1: All Drugs Must be Active as
Single Agents
11.2.2 Principle #2: Drugs Should be Chosen for
Non-Overlapping Toxicity
11.2.3 Principle #3: Drugs Should be Chosen for
Different Synergistic Mechanisms of Action
11.2.4 Principle #4: Drugs Should be Chosen That
Have Different Mechanisms or Patterns of
Resistance

11.2.5 Principle #5: Drugs Should be Administered
at the Optimum Dose and Schedule
11.3 Comparison of Combinations of Single Target Drugs
Versus Multi-Targeted Agents – The Pros and Cons
of Each Approach
11.4 Defining which Targeted Agents to Combine
11.4.1 Examples and Rationale Behind Combination
MTTs
11.5 Preclinical Evaluation of Combinations
11.5.1 Factors that Limit the Applicability of In Vitro
Studies
11.5.2 Factors that Limit the Applicability of In Vivo
Studies

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11.6

Challenges in the Clinical Development of Drug
Combinations
11.7 Future Directions
References
Chapter 12 The Discovery of Lapatinib
Karen E. Lackey
Introduction to Inhibition of Kinases for Cancer
Therapeutics

12.2 Developing a Lead Series for Dual Kinase Inhibition
12.3 Performing Multi-Dimensional Data Analysis for
Achieving the Target Profile
12.4 Optimizing Drug Properties whilst Retaining the
Target Profile
12.4.1 Pyridopyrimidines
12.4.2 6-Ether Linked 4-Anilinoquinazolines
12.4.3 6-Heteroaryl Linked 4-Anilinoquinazolines
12.4.4 Alkynylpyrimidine Series
12.5 Understanding the Mode of Inhibition That Makes
Lapatinib Analogs Effective
12.6 Conclusion
Acknowledgements
References

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12.1

Chapter 13 Identification and Optimization of Dual PI3K/mTOR
Inhibitors
Andreas Karlsson and Carlos Garcı´a-Echeverrı´a
13.1
13.2

Introduction
Pyridofuropyrimidine Derivatives: From a Chemical

Tool to a Development Candidate
13.3 Imidazoquinoline: NVP-BEZ235, the First Dual
PI3K/mTOR Inhibitor to Enter Clinical Trials
13.4 Quinoline Derivatives: GSK1059615 and GSK2126458
13.5 Outlook
Acknowledgements
References
Chapter 14 Discovery of HDAC-Inhibiting Multi-Target Inhibitors
Xiong Cai and Changgeng Qian
14.1
14.2

Introduction
CUDC-101: a Potent Multi-Target EGFR, HER2,
and HDAC Inhibitor
14.2.1 Compound Design and Synthesis
14.2.2 In Vitro Potency and Mechanism of Action

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