Trypanosomatid Diseases E-Book

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Serie: Drug Discovery in Infectious Diseases
• Sprache: Englisch

Seitenzahl: 1110

Veröffentlichungsjahr: 2013

Beschreibung

This is the first resource to provide researchers in academia and industry with an urgently needed update on drug intervention against trypanosomatides. As such, it
covers every aspect of the topic from basic research findings, via current treatments to translational approaches in drug development and includes both human and livestock diseases. The outstanding editor and contributor team reads like a Who?s Who of the field, thus guaranteeing the outstanding quality of this ready reference.

Leseprobe

Contents

Cover

Titles of the Series “Drug Discovery in Infectious Diseases”

Title Page

Copyright

Foreword

Acknowledgment

Preface

List of Contributors

Part One: Disease Burden, Current Treatments, Medical Needs, and Strategic Approaches

Chapter 1: Visceral Leishmaniasis – Current Treatments and Needs

Introduction

Current Anti-Leishmanial Drugs and Treatment Options for Visceral Leishmaniasis

PKDL

Open Questions and Needs

References

Chapter 2: Chemotherapy of Leishmaniasis: A Veterinary Perspective

Introduction

Chemotherapy of Canine Leishmaniasis

Exploration of New Anti-Leishmanial Drugs

Concluding Remarks

Acknowledgments

References

Chapter 3: Pharmacological Metabolomics in Trypanosomes

Introduction

Metabolomics – New Technologies Applied to Trypanosomes

Metabolic Affects of Trypanocidal Drugs

Conclusion

Acknowledgments

References

Chapter 4: Drug Design and Screening by In Silico Approaches

Introduction

Computer-Aided Drug Design: General Remarks

Supercomputers and Other Technical Resources

Molecular Modeling and Anti-Kinetoplastida Drug Design

Ligand-Based Approaches Against Trypanosoma Parasites

Structure-Based Drug Design and Screening

Virtual Screening Approaches against Trypanosome Proteins

In Silico Prediction of Protein Druggability

References

Chapter 5: Computational Approaches and Collaborative Drug Discovery for Trypanosomal Diseases

Introduction

CDD Database

Using HTS Data for Machine Learning Models

Discussion

Acknowledgments

References

Part Two: Metabolic Peculiarities in the Trypanosomatid Family Guiding Drug Discovery

Chapter 6: Interaction of Leishmania Parasites with Host Cells and its Functional Consequences

Life Cycle of Leishmania

Host Cells of Leishmania

DCs

Conclusion

References

Chapter 7: Function of Glycosomes in the Metabolism of Trypanosomatid Parasites and the Promise of Glycosomal Proteins as Drug Targets

Introduction

Glycosomes of T. brucei

Glycosomes of T. cruzi

Glycosomes of Leishmania spp.

Essentiality of Controlled Communication Across the Glycosomal Membrane

Essentiality of Correct Integration of Glycosomal Metabolism in the Overall Metabolism – Relation to Life Cycle Differentiation

What Has Been Achieved So Far in Target Characterization?

What Has Been Achieved So Far in the Development of Inhibitors of Glycosomal Enzymes or Processes

Discussion and Conclusions

Acknowledgments

References

Chapter 8: Glyoxalase Enzymes in Trypanosomatids

Glyoxalase Pathway

Glyoxalase I

Glyoxalase II

Glyoxalase Pathway Regulation

Glyoxalase Pathway as a Therapeutic Target

Conclusion

References

Chapter 9: Trypanothione-Based Redox Metabolism of Trypanosomatids

Thiol Redox Metabolism of Trypanosomatids: A Brief Historical Overview

Trypanothione Biosynthesis

Trypanothione Recycling

Trypanothione Utilization

Conclusions

Acknowledgments

References

Chapter 10: Thiol Peroxidases of Trypanosomatids

Thiol-Dependent Peroxidases in Trypanosomatids

Mechanism of Reaction of Thiol Peroxidases

Trypanosomatid PRXs

Trypanosomatid GPXs

Function of Thiol Peroxidases in Trypanosomatids

Conclusions

References

Chapter 11: Peroxynitrite as a Cytotoxic Effector Against Trypanosoma cruzi: Oxidative Killing and Antioxidant Resistance Mechanisms

Introduction

Peroxynitrite Formation During T. cruzi–Mammalian Host Cell Interaction

Peroxynitrite Diffusion and Reactivity with T. cruzi Targets

Peroxynitrite Detoxification Systems

T. cruzi Antioxidant Enzymes as Virulence Mediators

Conclusions

Acknowledgments

References

Chapter 12: Selenoproteome of Kinetoplastids

Introduction

Kinetoplastid Selenoproteome

Selenoproteome is Dispensable

Selenoproteome is Relevant for Long-Term Protection

Conclusions

References

Chapter 13: Replication Machinery of Kinetoplast DNA

Introduction: kDNA Network and its Monomeric Subunits

Replication of kDNA Minicircles, Maxicircles, and Networks

Components of the kDNA Replication Machinery: Replication Proteins and Complexes

Regulation of kDNA Replication

Conclusion: kDNA Replication Machinery as an Anti-Trypanosomal Drug Target

Acknowledgments

References

Chapter 14: Life and Death of Trypanosoma brucei: New Perspectives for Drug Development

Necrosis

Autophagic Cell Death

Apoptosis in Protozoan Parasites

Outlook

References

Part Three: Validation and Selection of Drug Targets in Kinetoplasts

Chapter 15: Rational Selection of Anti-Microbial Drug Targets: Unique or Conserved?

Introduction

Phosphodiesterases

Ergosterol Synthesis

N-Myristoyl Transferase

Proteases

Kinases

Concluding Remarks

References

Chapter 16: Drug Targets in Trypanosomal and Leishmanial Pentose Phosphate Pathway

Pentose Phosphate Pathway in Trypanosomatids: General Considerations and Biological Relevance

Biochemical and Structural Hallmarks of Trypanosomatids PPP Enzymes

Inhibitor Discovery Against PPP Enzymes

Conclusions

Acknowledgments

References

Chapter 17: GDP-Mannose: A Key Point for Target Identification and Drug Design in Kinetoplastids

Introduction

Comparison of Mannosylation Pathways between Mammals and Kinetoplastids

Enzymes and Transporters Involved in Mannosylation in Mammals and Kinetoplastids

Conclusion

References

Chapter 18: Transporters in Anti-Parasitic Drug Development and Resistance

Introduction

“Rule of Five”

Diffusion

Selective Uptake by Protozoan Transporters

Role of Efflux Transporters

Diagnosing Drug Resistance Through Screening of Transporter Mutations: T. congolense as an Example

Concluding Remarks

References

Chapter 19: Peptidases in Autophagy are Therapeutic Targets for Leishmaniasis

Introduction

Molecular Machinery for Autophagosome Biogenesis

ATG4 Regulates the Autophagic Pathway of Leishmania spp.

Leishmania's Cathepsins Regulates Autophagy and Virulence

Other Possible Peptidase Targets

Cysteine Peptidase Inhibitors: Opportunities and Challenges

Conclusions and Future Directions

Acknowledgments

References

Chapter 20: Proteases of Trypanosoma brucei

Introduction

Classes of Proteases

Cellular Functions

Proteases as Drug Targets

Conclusion

References

Part Four: Examples of Target-Based Approaches and Compounds Under Consideration

Chapter 21: Screening Approaches Towards Trypanothione Reductase

Introduction

Unique Thiol Redox Metabolism of Trypanosomatids as a Target Area for Future Drug Development

Screening Approaches Towards TR

Combined In Vitro/In Silico Screening Campaign

Conclusion

References

Chapter 22: Redox-Active Agents in Reactions Involving the Trypanothione/Trypanothione Reductase-based System to Fight Kinetoplastidal Parasites

Introduction

TR as a Drug Target Molecule

Turncoat Inhibitors (Subversive Substrates or Redox Cyclers) of TR as Anti-Trypanosomal Drugs

1,4-NQs as Trypanocidal Agents

Nitrofurans

Other Subversive Substrates

Trypanothione-Reactive Agents (Susceptible to Enter Redox Cycling Following Double Michael Addition) as Anti-Trypanosomal Drugs

Conclusions

Acknowledgments

References

Chapter 23: Inhibition of Trypanothione Synthetase as a Therapeutic Concept

Introduction

Functional and Structural Characteristics of TryS

TryS Inhibitor Design

Conclusions

References

Chapter 24: Targeting the Trypanosomatidic Enzymes Pteridine Reductase and Dihydrofolate Reductase

Introduction

X-Ray Crystal Structures of DHFR and PTR1

Discovery and Development of PTR1 Inhibitors

Inhibition of DHFR

Conclusions and Perspectives

References

Chapter 25: Contribution to New Therapies for Chagas Disease

Introduction

Current Therapy

Targeting the T. cruzi Protease Cruzain

Why is Cruzain a Good Drug Target?

Other Potent Cruzain Inhibitors

Targeting Ergosterol Biosynthesis

Why Multiple Targets?

Development of Drug Screening Methods

Conclusions

Acknowledgements

References

Chapter 26: Ergosterol Biosynthesis for the Specific Treatment of Chagas Disease: From Basic Science to Clinical Trials

Introduction

Currently Available Drugs for the Specific Treatment of Chagas Disease: Limitations and Controversies on their Application

EBIs as Potential New Therapeutic Agents for Chagas Disease

Conclusions

References

Chapter 27: New Developments in the Treatment of Late-Stage Human African Trypanosomiasis

Introduction

Life Cycle of T. b. brucei

Current Chemotherapy

Need for New Chemotherapy

Recent Approaches to New Trypanocidal Agents

Conclusion

References

Index

Titles of the Series “Drug Discovery in Infectious Diseases”

Selzer, P. M. (ed.)

Antiparasitic and Antibacterial Drug Discovery

From Molecular Targets to Drug Candidates

2009

ISBN: 978-3-527-32327-2

Becker, K. (ed.)

Apicomplexan Parasites

Molecular Approaches toward Targeted Drug Development

2011

ISBN: 978-3-527-32731-7

Conor R. Caffrey (ed.)

Parasitic Helminths

Targets, Screens, Drugs and Vaccines

2012

ISBN 978-3-527-33059-1

Forthcoming Topics of the Series

Protein Phosphorylation in Parasites: Novel Targets for Antiparasitic Intervention

Related Titles

Lucius, R., Loos-Frank, B., Grencis, R. K., Striepen, B., Poulin, R. (eds.)

The Biology of Parasites

2014

ISBN: 978-3-527-32848-2

Lamb, T.

Immunity to Parasitic Infections

2013

ISBN: 978-0-470-97247-2

Zajac, A. M., Conboy, G. A. (eds.)

Veterinary Clinical Parasitology

2012

ISBN: 978-0-8138-2053-8

Scott, I., Sutherland, I.

Gastrointestinal Nematodes of Sheep and Cattle

Biology and Control

2009

ISBN: 978-1-4051-8582-0.

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Foreword

Drug Discovery for Neglected Diseases – Past and Present and Future

The kinetoplastid diseases – sleeping sickness, the leishmaniases, and Chagas disease – are “neglected diseases of poverty,” afflicting millions of people and collectively responsible for over 100 000 deaths per annum. No vaccines are available and current insect vector control methods and other public health measures are insufficient to eliminate them. The currently available drug therapies are far from satisfactory due to issues such as poor efficacy, toxicity, the need for hospitalization, the requirement for prolonged parenteral treatment, and high cost. This book is a timely attempt to address some of these unmet medical needs.

It is somewhat ironic that, at the beginning of the twentieth century, many of the ground-breaking developments in drug discovery were driven by economic and colonial expansion in Africa and Asia. The African trypanosome in particular was an early model for experimental chemotherapy along two main lines of investigation: synthetic dyes, and organic arsenicals and antimonials (for further details, see reviews by Williamson [1] and Steverding [2]). Indeed, the first synthetic compound to cure an infectious disease in an animal model was the dye, Trypan red (Ehrlich, 1904), which was a forerunner of suramin (1916–1920), the first effective trypanocidal drug for human African trypanosomiasis (HAT). The demonstration by Thomas and Breinl in 1905 of the trypanocidal activity in mice of atoxyl (p-aminophenylarsonic acid) formed the basis of Ehrlich's pioneering work on organic arsenicals that culminated in the development of arsphenamine (606, Salvarsan) for the treatment of syphilis (Ehrlich and Hata, 1910) and tryparsamide for the treatment of HAT (Jacobs and Heidelberger, 1919). Tryparsamide, which caused blindness in 10–20% of patients, was finally replaced by melarsoprol (Friedheim, 1949). Trivalent antimony, in the form of tartar emetic, was shown to be trypanocidal in mice (Plimmer and Thompson, 1908), but lacked efficacy in humans. However, potassium antimony tartrate was found to have some activity in the treatment of leishmaniasis (Vianna, 1912) and was the forerunner of the pentavalent antimonial drugs, sodium stibogluconate (Pentostam®) and meglumine antimonate (Glucantime®), both introduced in the 1940s. Along with the diamidine, pentamidine (1937), all of these drugs are still in use today.

From the 1950s, subsequent drug treatments have largely been discovered by serendipity through repurposing of existing drugs used for other indications. The nitrofuran, nifurtimox, and the nitroimidazole, benznidazole, used for the treatment of Chagas disease arose from research into nitro-compounds as antibacterial agents. Amphotericin B, isolated in 1953, was originally developed for the treatment of systemic mycoses, but later found use in the treatment of visceral leishmaniasis in the 1990s as the expensive, but highly efficacious liposomal formulation (AmBisome®) or as the cheaper, but more toxic amphotericin B deoxycholate. Both formulations were included in the World Health Organization's Essential Medicines List in 2009. The off-patent aminoglycoside, paromomycin, originally developed as an oral treatment for intestinal infections in the 1960s, finally gained approval as paromomycin intramuscular injection for the treatment of visceral leishmaniasis in India in 2006. Two anticancer agents, the phospholipid analog, miltefosine, registered as the first oral treatment for visceral leishmaniasis in India in 2002, and eflornithine (now in combination with oral nifurtimox as nifurtimox–eflornithine combination therapy (NECT), 2009) for the treatment of HAT caused by Trypanosoma brucei gambiense complete the woefully inadequate treatment options for these diseases. Notably, none of these newer developments have completely displaced their forerunners that were developed prior to the 1950s.

After nearly a century of research, only 10 novel chemical entities for three diseases is a singularly unimpressive output by the pharmaceutical industry. The reason for this lamentable performance is not hard to find. Poor economic return on investment by pharma is a major factor, since these are diseases of poverty. The thalidomide disaster of the late 1950s kick-started regulatory demands for greater patient safety resulting in ever-increasing development costs. Blockbuster drugs were “in;” smaller, less profitable markets were “out.” Ninety percent of research and development was aimed at 10% of the world's unmet medical need – the so-called “10–90 gap.” The drive for greater efficiency and profitability through mergers and acquisitions resulted in the loss of parasitology expertise in most pharma companies. Medicinal chemists were seduced by combinatorial chemistry without due regard for chemical space and drug-likeness. Miniaturization of chemical synthesis restricted the use of animal disease models and shifted emphasis towards target screening. Intellectual property rights were increasingly used as an obstructive, rather than an enabling tool.

At the end of the twentieth century, the situation had become so dire that a radical new approach was required. One of the most encouraging developments was the founding of “public–private partnerships” (PPPs), such as the Drugs for Neglected Diseases initiative (DNDi) and Medicines for Malaria Venture (MMV) – non-profit organizations who strive to forge drug discovery partnerships between multiple academic, biotech, and pharma partners with funding from the governmental and charitable sector [3]. PPPs were initially met with much skepticism, but by 2005, an analysis by Mary Moran and colleagues concluded that PPPs were responsible for three-quarters of an expanded research and development portfolio for neglected diseases [4]. Another important development was the publication of annotated genomes for T. brucei, L. major, and T. cruzi in 2005 [5–7]. As Barry Bloom optimistically prophesized 10 years earlier “Sequencing bacterial and parasitic pathogens . . . could buy the sequence of every virulence determinant, every protein antigen and every drug target . . . for all time” [8]. Certainly, pathogen genomes are proving to be a valuable resource for target discovery, but without a deeper understanding of parasite biology the full potential of these genomes will not be realized. About the same time as genome sequencing was getting underway, C.C. Wang threw down the gauntlet that academics needed genetic evidence of essentiality to justify their claims of the therapeutic potential of their research field [9]. This dogma has now been refined and extended to include chemical evidence of druggability, driven by a defined therapeutic product profile [10]. These challenges have encouraged some academics to move out of their traditional comfort zones to fill the early-stage drug discovery gap in translational medicine not adequately covered by the PPPs [11]. The concept of “one gene, one target, one drug” has been very much at the forefront of current academic (and industry) thinking, with structure-based design an important adjunct in this strategy. Thus, it is timely that much of this book is devoted to the identification of metabolic peculiarities in the kinetoplastids that can be chemically and genetically validated as drug targets.

However, what of the future? Experience in industry and in academia suggests that the rate of validation of new targets is failing to keep pace with the rate of attrition of currently validated targets. Despite initial promise, the target-based approach has yielded disappointing results in anti-bacterial discovery in pharma [12] and lessons need to be learned from this if we are to avoid making the same mistakes. Rapid and robust methods of genetic target validation are still needed for parasites causing visceral leishmaniasis and Chagas disease, and we need a better understanding of basic biology to understand why targets fail. Certainly, not all targets are equal from a medicinal chemistry point of view. Greater attention needs to be paid to drug likeness [13] and ligand efficiency [14] for lead selection. Screening of fragment libraries using biophysical methods should help to weed out “undruggable” targets without recourse to expensive high-throughput screens [15]. From a pharmacology perspective, cytocidal activity is much preferable to cytostatic, so biologists should address this question early in discovery. Likewise, the potential ease for resistance arising as a result of point mutations in a single-target strategy should be a research priority for biologists. Systems biology suggests that exquisitely selective, single-target compounds may exhibit lower than desired clinical efficacy compared with multitarget drugs due to the robustness of biological networks [16]. Thus, polypharmacology (network pharmacology) is undergoing a resurgence of interest. Given the paucity of validated druggable targets, phenotypic screening is undergoing a revival aided by access to large compound collections held by pharma and the development of suitable miniaturized whole-parasite screens and mammalian counter-screens. This approach has the advantage of addressing the key druggability issues of cell permeability, desirable cytocidal activity, and a suitable parasite–host selectivity window. Phenotypic screening can also identify compounds hitting non-protein targets (e.g., amphotericin B) or compounds that act as pro-drugs (e.g., nitroimidazoles). However, the future challenge will be to identify the often complex mode(s) of action of such phenotypic hits (target deconvolution), and to use modern technologies to improve the potency and selectivity of these molecules [17]. Finally, we should ask ourselves whether our compound collections are too “clean” in terms of chemical reactivity. After all, arsenicals, antimonials, nitro-drugs, and eflornithine all undergo reaction with one or more targets, and about one-quarter of all drugs that inhibit enzymes are essentially irreversible reactions [18].

I believe that there is every cause for optimism in the battle against neglected diseases. As long as “donor fatigue” does not set in, and industry continues to engage in a positive and productive manner with academia, future prospects look better than at any time in history. However, we should all remember the dictum by Sir James Black “to first purge your project of wishful thinking” if we are to succeed!

Dundee, UK

Alan Fairlamb

References

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2. Steverding, D. (2010) The development of drugs for treatment of sleeping sickness: a historical review. Parasit. Vectors, 3,e15.

3. Matter, A.. and Keller, T. H. (2008) Impact of non-profit organizations on drug discovery: opportunities, gaps, solutions. Drug Discov. Today, 13, 347–352.

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8. Bloom, B.R. (1995) Genome sequences – a microbial minimalist. Nature, 378, 236.

9. Wang, C.C. (1997) Validating targets for antiparasite chemotherapy. Parasitology, 114, S31–S44.

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Acknowledgment

This publication is supported by COST.

COST – the acronym for European Cooperation in Science and Technology – is the oldest and widest European intergovernmental network for cooperation in research. Established by the Ministerial Conference in November 1971, COST is presently used by the scientific communities of 36 European countries to cooperate in common research projects supported by national funds.

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Preface

Infections caused by parasites of the trypanosomatid family are considered to belong to the most neglected diseases. They comprise the African sleeping sickness (Trypanosoma brucei rhodesiense, T. brucei gambiense), the Chagas' disease in Latin America (T. cruzi), the black fever or Kala-Azar (Leishmania donovani) and other forms of Leishmaniasis (various Leishmania species). They affect about 30 million of people and account for half a million of fatalities per year. Trypanosomatids also cause substantial economic losses by affecting life stock (T. brucei brucei, T. congolense, T. evansi). Available treatments of the diseases are unsatisfactory in terms of safety and efficacy. Industrial commitments to meet the therapeutic needs remain limited because of unfavourable economic perspectives for drugs acting on diseases that prevail in countries with poor socio-economic conditions. In fact, currently used drugs are overwhelmingly those developed many decades ago when the ‘Western World’ had still to be concerned about the health of administrators and soldiers in their tropical colonies.

The present book originates from an interdisciplinary network of academic and industrial researchers devoted to the development of “new drugs for neglected diseases”. The initiative was sponsored by the European Union (COST Action CM0801) and in the beginnings was largely restricted to Europe. Over the four years of its operation, however, the exchange of experience and cooperative projects expanded far beyond its geographical basis, particularly by integrating countries in Latin America, Africa and Asia where the diseases are endemic. The progress achieved by this network is reflected in many of the contributions to the book. The editors, however, took care not just to present a ‘progress report’ but the state-of-the-art in the entire field of drug discovery for trypanosomatid diseases, as reviewed by leading scientists from all over the world. It is hoped that the compiled knowledge will become instrumental to shorten the time from basic discoveries to the urgently needed new drugs for the neglected diseases.

The editor's heartfelt thanks go to the contributing authors for their excellent work, to the series editor Paul M. Selzer for his constructive advice, and to the COST Office in Brussels for financial support.

Braunschweig, Ingelheim, Potsdam, GermanyMarch 2013

Timo JägerOliver KochLeopold Flohé

List of Contributors

José María Alunda1

Universidad Complutense

Department of Animal Health

Faculty of Veterinary Medicine

Avenida Puerta de Hierro s/n

28040 Madrid

Spain

[email protected]

María Noel Alvarez

Departamento de Bioquímica and

Center for Free Radical and

Biomedical Research

Facultad de Medicina

Universidad de la República

Avenida General Flores 2125

11800 Montevideo

Uruguay

Luisana Avilán

Universidad de los Andes

Laboratorio de Fisiología

Facultad de Ciencias

La HechiceraAv. Alberto Carnevalli

Mérida 5101

Venezuela

Cyrus J. Bacchi

Pace University

The Haskins Laboratories

41 Park Row

New York, NY 10038

USA

Michael P. Barrett1

University of Glasgow

Wellcome Trust Centre for Molecular Parasitology

Institute of Infection, Immunity and Inflammation

College of Medical, Veterinary and Life Sciences

120 University Place

Glasgow G12 8TA

UK

[email protected]

Torsten Barth

Eberhard Karls Universität Tübingen

Interfakultäres Institut für Biochemie

Hoppe-Seyler-Strasse 4

72076 Tübingen

Germany

[email protected]

Mathias Beig

MSD Animal Health Innovation GmbH

Zur Propstei

55270 Schwabenheim

Germany

Rachel Bezalel-Buch

The Hebrew University-Hadassah Medical School

Department of Microbiology and Molecular Genetics

Kuvin Center for the Study of Infectious and Tropical Diseases

Institute for Medical Research Israel–Canada

PO Box 12272

Jerusalem 91120

Israel

Maurizio Botta1

University of Siena

Faculty of Pharmacy

Via Aldo Moro 2

53100 Siena

Italy

[email protected]

Barry A. Bunin

Collaborative Drug Discovery, Inc.

1633 Bayshore Highway Suite 342

Burlingame, CA 94010

USA

Ana J. Cáceres

Universidad de los Andes

Laboratorio de Enzimología de Parásitos

Facultad de Ciencias

La HechiceraAv. Alberto Carnevalli

Mérida 5101

Venezuela

Helena Castro1

Universidade do Porto

Instituto de Biologia Molecular e Celular

Rua do Campo Alegre 823

4150-180 Porto

Portugal

[email protected]

Juan José Cazzulo

Universidad Nacional General San Martín/CONICET

Instituto de Investigaciones Biotecnológicas (IIB/INTECH)

Campus Miguelete

Avenida 25 de Mayo y Francia

1650 San Martín

Buenos Aires

Argentina

[email protected]

Marcelo A. Comini1

Institut Pasteur de Montevideo

Group Redox Biology of Trypanosomes

Mataojo 2020

11400 Montevideo

Uruguay

[email protected]

Juan-Luis Concepción

Universidad de los Andes

Laboratorio de Enzimología de Parásitos

Facultad de Ciencias

La Hechicera

Av. Alberto Carnevalli

Mérida 5101

Venezuela

Carlos Cordeiro1

Universidade de Lisboa

Faculdade de Ciências

Departamento de Química e Bioquímica

Centro de Química e Bioquímica

Edifício C8 Campo Grande

1749-016 Lisboa

Portugal

[email protected]

María Jesús Corral-Caridad

Universidad Complutense

Department of Animal Health

Faculty of Veterinary Medicine

Avenida Puerta de Hierro s/n

28040 Madrid

[email protected]

Maria Paola Costi1

University of Modena and Reggio Emilia

Department of Life Science

Via Campi 183

41125 Modena

Italy

[email protected]

Darren J. Creek

University of Glasgow

Wellcome Trust Centre for Molecular Parasitology

Institute of Infection, Immunity and Inflammation

College of Medical, Veterinary and Life Sciences

120 University Place

Glasgow G12 8TA

UK

and

University of Melbourne

Department of Biochemistry and Molecular Biology

Bio21 Molecular Science and Biotechnology Institute

Flemington Road

Parkville

Victoria 3010

Australia

Elisabeth Davioud-Charvet1

UMR CNRS 7509

European School of Chemistry, Polymers and Materials (ECPM)

Bioorganic and Medicinal Chemistry

25 rue Becquerel

67087 Strasbourg Cedex 2

France

[email protected]

Harry P. de Koning1

University of Glasgow

Institute of Infection

Immunity and Inflammation

College of Medical

Veterinary and Life Sciences

120 University Place

Glasgow G12 8TA

UK

[email protected]

Vincent Delespaux

Institute of Tropical Medicine Antwerpen

Department of Biomedical Sciences

Nationalestraat 155

2000 Antwerp

Belgium

Patricia S. Doyle1

University of California San Francisco

Department of Pathology and Sandler Center for Drug Discovery

1700 4th Street 508

San Francisco, CA 94158-2330

USA

[email protected]

Michael Duszenko1

Eberhard Karls Universität Tübingen

Interfakultäres Institut für Biochemie

Hoppe-Seyler-Strasse 4

72076 Tübingen

Germany

[email protected]

Sean Ekins1

Collaborative Drug Discovery, Inc.

1633 Bayshore Highway Suite 342

Burlingame, CA 94010

USA

[email protected]

and

Collaborations in Chemistry

5616 Hilltop Needmore Road

Fuquay Varina, NC 27526

USA

and

University of Maryland

Department of Pharmaceutical Sciences

20 North Pine Street

Baltimore, MD 21201

USA

and

University of Medicine & Dentistry of New Jersey (UMDNJ)

Robert Wood Johnson Medical School

Department of Pharmacology

675 Hoes lane

Piscataway, NJ 08854

USA

Juan C. Engel

University of California San Francisco

Department of Pathology and Sandler Center for Drug Discovery

1700 4th Street 508

San Francisco, CA 94158-2330

USA

[email protected]

Alan Fairlamb1

Division of Biological Chemistry & Drug Discovery

College of Life Sciences

University of Dundee

Dundee DD1 5EH

UK

[email protected]

Stefania Ferrari

University of Modena and Reggio Emilia

Department of Life Science

Via Campi 183

41125 Modena

Italy

António E.N. Ferreira

Universidade de Lisboa

Faculdade de Ciências

Departamento de Química e Bioquímica

Centro de Química e Bioquímica

Edifício C8 Campo Grande

1749-016 Lisboa

Portugal

Leopold Flohé

Otto-von-Guericke-Universität Magdeburg

Chemisches Institut

Universitätsplatz 2

39106 Magdeburg

Germany

Thibault Gendron

UMR CNRS 7509

European School of Chemistry, Polymers and Materials (ECPM)

Bioorganic and Medicinal Chemistry

25 rue Becquerel

67087 Strasbourg Cedex 2

France

Vadim N. Gladyshev1

Harvard Medical School

Division of Genetics

Department of Medicine

Brigham and Women's Hospital

75 Francis Street

Boston, MA 02115

USA

[email protected]

Ricardo Gomes

Universidade de Lisboa

Faculdade de Ciências

Departamento de Química e Bioquímica

Centro de Química e Bioquímica

Edifício C8 Campo Grande

1749-016 Lisboa

Portugal

Melisa Gualdrón-López

Université catholique de Louvain

Research Unit for Tropical Diseases

de Duve Institute

Avenue Hippocrate 74

La Hechicera

Av. Alberto Carnevalli

1200 Brussels

Belgium

Martín Hugo

Departamento de Bioquímica and

Center for Free Radical and Biomedical Research

Facultad de Medicina

Universidad de la República

Avenida General Flores 2125

11800 Montevideo

Uruguay

Robert T. Jacobs

Scynexis, Inc.

PO Box 12878

Research Triangle Park NC 27709-2878

USA

Timo Jäger

German Centre for Infection Research (DZIF)

Inhoffenstraße 7

38124 Braunschweig

Germany

[email protected]

Oliver Koch1

Junior Research Group Leader “Medicinal Chemistry”

Chemical Biology – Faculty of Chemistry

Technische Universität Dortmund

Otto-Hahn-Straße 6

44227 Dortmund

[email protected]

R. Luise Krauth-Siegel

Heidelberg University

Biochemistry Center

Im Neuenheimer Feld 328

69120 Heidelberg

Germany

Bruno K. Kubata

Research for Health Africa & Pharma Innovation

AU/NEPAD Agency Regional Office in Nairobi

C/o the AU/Inter African Bureau for Animal Resources

P.O. BOX 13601-00800

Kenya

[email protected]

Don Antoine Lanfranchi

UMR CNRS 7509

European School of Chemistry, Polymers and Materials (ECPM)

Bioorganic and Medicinal Chemistry

25 rue Becquerel

67087 Strasbourg Cedex 2

France

Alexei V. Lobanov

Harvard Medical School

Division of Genetics

Department of Medicine

Brigham and Women's Hospital

75 Francis Street

Boston, MA 02115

USA

Philippe M. Loiseau

Université Paris-Sud 11

Faculté de Pharmacie

UMR 8076 CNRS

Chimiothérapie Antiparasitaire

5 rue Jean-Baptiste Clément

92290 Châtenay-Malabry

France

Valeria Losasso

University of Modena and Reggio Emilia

Department of Life Science

Via Campi 183

41125 Modena

Italy

and

Scientific Computing Department, Science and Technology Facilities Council

Daresbury Laboratory

Keckwick Lane

Warrington WA4 4AD

UK

Anita Masic

University of Würzburg

Institute for Molecular Infection Biology

Josef-Schneider-Strasse 2/D15

97080 Würzburg

Germany

Paul A.M. Michels1

Université catholique de Louvain

Research Unit for Tropical Diseases

de Duve Institute

Avenue Hippocrate 74

1200 Brussels

Belgium

[email protected]

Stefan Mogk

Eberhard Karls Universität Tübingen

Interfakultäres Institut für Biochemie

Hoppe-Seyler-Strasse 4

72076 Tübingen

Germany

[email protected]

Heidrun Moll1

University of Würzburg

Institute for Molecular Infection Biology

Josef-Schneider-Strasse 2/D15

97080 Würzburg

Germany

[email protected]

Mattia Mori

University of Siena

Faculty of Pharmacy

Via Aldo Moro 2

53100 Siena

Italy

Frank Oellien

MSD Animal Health Innovation GmbH

Zur Propstei

55270 Schwabenheim

Germany

Cecilia Ortíz

Institut Pasteur de Montevideo

Group Redox Biology of Trypanosomes

Mataojo 2020

11400 Montevideo

Uruguay

[email protected]

Gonzalo Peluffo

Departamento de Bioquímica and

Center for Free Radical and Biomedical Research

Facultad de Medicina

Universidad de la República

Avenida General Flores 2125

11800 Montevideo

Uruguay

Lucía Piacenza

Departamento de Bioquímica and

Center for Free Radical and Biomedical Research

Facultad de Medicina

Universidad de la República

Avenida General Flores 2125

11800 Montevideo

Uruguay

Sébastien Pomel1

Université Paris-Sud 11

Faculté de Pharmacie

UMR 8076 CNRS

Chimiothérapie Antiparasitaire

5 rue Jean-Baptiste Clément

92290 Châtenay-Malabry

France

[email protected]

Ana Ponces Freire

Universidade de Lisboa

Faculdade de Ciências

Departamento de Química e Bioquímica

Centro de Química e Bioquímica

Edifício C8 Campo Grande

1749-016 Lisboa

Portugal

Wilfredo Quiñones

Universidad de los Andes

Laboratorio de Enzimología de Parásitos

Facultad de Ciencias

La Hechicera

Av. Alberto Carnevalli

Mérida 5101

Venezuela

Rafael Radi1

Departamento de Bioquímica and

Center for Free Radical and Biomedical Research

Facultad de Medicina

Universidad de la República

Avenida General Flores 2125

11800 Montevideo

Uruguay

[email protected]

Boris Rodenko

University of Glasgow

Institute of Infection, Immunity and Inflammation

College of Medical, Veterinary and Life Sciences

120 University Place

Glasgow G12 8TA

[email protected]

and

The Netherlands Cancer Institute

Department of Chemical Biology

Division of Cell Biology

Plesmanlaan 121

1066 CX Amsterdam

The Netherlands

Poonam Salotra

National Institute of Pathology (ICMR)

Safdarjung Hospital Campus

Post Box 4909

New Delhi 110029

India

Puneet Saxena

University of Modena and Reggio Emilia

Department of Life Science

Via Campi 183

41125 Modena

Italy

Caroline Schönfeld

Eberhard Karls Universität Tübingen

Interfakultäres Institut für Biochemie

Hoppe-Seyler-Strasse 4

72076 Tübingen

Germany

[email protected]

Uta Schurigt

University of Würzburg

Institute for Molecular Infection Biology

Josef-Schneider-Strasse 2/D15

97080 Würzburg

Germany

Karin Seifert1

London School of Hygiene & Tropical Medicine

Faculty of Infectious and Tropical Diseases

Keppel Street

London WC1E 7HT

UK

[email protected]

Paul M. Selzer1

MSD Animal Health Innovation GmbH

Zur Propstei

55270 Schwabenheim

Germany

[email protected]

and

University of Tübingen

Interfaculty Institute of Biochemistry

Hoppe-Seyler-Strasse 4

72076 Tübingen

Germany

and

University of Glasgow

Institute of Infection, Immunity and Inflammation

120 University Place

Glasgow G12 8TA

UK

Joseph Shlomai1

The Hebrew University-Hadassah Medical School

Department of Microbiology and Molecular Genetics

Kuvin Center for the Study of Infectious and Tropical Diseases

Institute for Medical Research

Israel–Canada

PO Box 12272

Jerusalem 91120

Israel

[email protected]

Ruchi Singh

National Institute of Pathology (ICMR)

Safdarjung Hospital Campus

Post Box 4909

New Delhi 110029

India

Marta Sousa Silva

Universidade de Lisboa

Faculdade de Ciências

Departamento de Química e Bioquímica

Centro de Química e Bioquímica

Edifício C8 Campo Grande

1749-016 Lisboa

Portugal

Jasmin Stein

Eberhard Karls Universität Tübingen

Interfakultäres Institut für Biochemie

Hoppe-Seyler-Strasse 4

72076 Tübingen

Germany

[email protected]

Dietmar Steverding1

University of East Anglia

BioMedical Research Centre

Norwich Medical School

Norwich Research Park

Norwich NR4 7TJ

UK

[email protected]

Ana M. Tomás

Universidade do Porto

Instituto de Biologia Molecular e Celular

Rua do Campo Alegre 823

4150-180 Porto

Portugal

and

Universidade do Porto

Instituto de Ciências Biomédicas Abel Salazar

Rua de Jorge Viterbo Ferreira 228

4050-313 Porto

Portugal

and

Faculdade de Ciências

Departamento de Química e Bioquímica

Centro de Química e Bioquímica

Edifício C8 Campo Grande

1749-016 Lisboa

Portugal

Madia Trujillo

Departamento de Bioquímica and

Center for Free Radical and Biomedical Research

Facultad de Medicina

Universidad de la República

Avenida General Flores 2125

11800 Montevideo

Uruguay

Julio A. Urbina1

Instituto Venezolano de Investigaciones Científicas

Centro de Biofisica y Bioquimica

Apartado 21827

Caracas 1020A

Venezuela

and

200 Lakeside Drive No. 503

Oakland, CA 94612-3503

United States

[email protected]

Isabel M. Vincent

University of Glasgow

Wellcome Trust Centre for Molecular Parasitology

Institute of Infection, Immunity and Inflammation

College of Medical, Veterinary and Life Sciences

120 University Place

Glasgow G12 8TA

UK

and

Université Laval

Centre de Recherche en Infectiologie du CHUL

2705 Boulevard Laurier

Québec G1V 4G2

Canada

Roderick A.M. Williams1

University of Strathclyde

Strathclyde Institute for Pharmacy and Biological Sciences

161 Cathedral Street

Glasgow G4 0RE

UK

[email protected]

and

University of the West of Scotland School of Science

High Street

Paisley PA1 2BE

UK

[email protected]

Nurit Yaffe

The Hebrew University-Hadassah Medical School

Department of Microbiology and Molecular Genetics

Kuvin Center for the Study of Infectious and Tropical Diseases

Institute for Medical Research

Israel–Canada

PO Box 12272

Jerusalem 91120

Israel

Nigel Yarlett1

Pace University

The Haskins Laboratories and Chemistry and Physical Sciences

41 Park Row

New York, NY 10038

USA

[email protected]

Note

1. Corresponding Author

Part One

Disease Burden, Current Treatments, Medical Needs, and Strategic Approaches

1

Visceral Leishmaniasis – Current Treatments and Needs

Poonam Salotra, Ruchi Singh, and Karin Seifert1

Abstract

The last decade has seen significant advances in the treatment of visceral leishmaniasis. Two new drugs (miltefosine and paromomycin) have been registered for the treatment of visceral leishmaniasis since 2002. Multidrug treatments have been investigated in systematic clinical studies and are now recommended as a new treatment approach for visceral leishmaniasis. However, the range of available drugs is still limited. Regional differences in response rates to anti-leishmanial available drugs as well as treatment of post-kala-azar dermal leishmaniasis, a complication of visceral leishmaniasis, are examples of the continued need for improved treatments for visceral leishmaniasis. In this chapter we discuss current treatments for visceral leishmaniasis and needs for drug discovery and development and translation to the clinic.

Introduction

Visceral leishmaniasis belongs to the group of neglected tropical diseases (NTDs), a group of chronic parasitic and related bacterial and viral infections that promote poverty [1]. Visceral leishmaniasis is caused by different species of the intracellular protozoan parasite Leishmania; predominantly by L. donovani in Asia and Africa, L. infantum in Europe and Latin America, and to a lesser extent in Africa [1–4]. Parasites, promastigotes as the insect stage, are transmitted by the bite of female phlebotomine sandflies to mammalian hosts [5]. Transmission can be zoonotic (transmission from animal to vector to human) or anthroponotic (transmission from human to vector to human). Inside the host the parasites invade monocytes and macrophages of the mononuclear phagocyte system and transform to the mammalian stage, intracellular amastigotes, which survive and multiply within host cell phagolysosomes. Parasite dissemination occurs through lymphatic and vascular systems. Clinical features of established visceral leishmaniasis include fever, abdominal pain, weight loss, splenomegaly, hepatomegaly, and lymphadenopathy [6]. It should be noted that infection can remain subclinical or develop into clinical disease. The latter displays fatality rates of 100% if untreated. Risk factors to develop clinical disease include malnutrition and immune suppression, and are often linked to the overarching factor of poverty [7–9]. Visceral leishmaniasis is also an important infection associated with HIV/AIDS [10].

Major geographical areas affected are South Asia, which carries around 60% of cases worldwide [1], East Africa [4], North Africa and the Middle East [11], Latin America [2], and Southern Europe [3]. There are an estimated 50 000 new visceral leishmaniasis cases and 59 000 deaths per year [12]. However, under-reporting, misdiagnosis, and forced human migration obscure the establishment of exact numbers [4, 6, 12]. Importantly 90% of cases occur in only six countries: India, Bangladesh, Sudan, Brazil, Nepal, and Ethiopia [13].

Post-kala-azar dermal leishmaniasis (PKDL) is a complication of visceral leishmaniasis characterized by a spectrum of skin lesions following a visceral leishmaniasis episode mainly in areas where L. donovani is endemic. Reported incidence and time of onset of PKDL vary between countries; from 50 to 60% of cured visceral leishmaniasis cases within weeks to few months in Sudan to 5–10% generally after 2–4 years in India. There are sporadic reports of PKDL cases with no previous recorded history of visceral leishmaniasis. PKDL lesions contain parasites and are seen as an important reservoir for transmission [14].

In the following sections we will address (i) treatment options for visceral leishmaniasis and geographical differences in treatment response (see the “Current Anti-Leishmanial Drugs and Treatment Options for Visceral Leishmaniasis” section), and (ii) pathology, immunopathology, and treatment options for PKDL (see the “PKDL” section).

Current Anti-Leishmanial Drugs and Treatment Options for Visceral Leishmaniasis

Available Drugs

Pentavalent antimonials (sodium stibogluconate (SSG), generic sodium antimony gluconate, and meglumine antimoniate depending on country and region) have been the standard drugs for the last 60 years. Due to high rates of clinical unresponsiveness their use has been largely abandoned in Bihar state, India [15], but they continue to be used in other endemic areas [16, 17]. SSG is still used to a wide extent in Africa, where limited availability of other drugs persists. Toxicity, lot-to-lot variations and need for hospitalization are severe limitations of antimonial treatment [16]. The polyene antibiotic amphotericin B is highly effective. It is used as amphotericin B deoxycholate, which suffers from toxicity [16], and as a liposomal formulation (AmBisome®) approved for the treatment of visceral leishmaniasis [18]. Notably, liposomal amphotericin B is the safest and most effective drug available [19]. Recently, a preferential pricing agreement for developing countries has reduced the cost of liposomal amphotericin B from US$200 to 20 per 50 mg vial [20]. Following this agreement a single infusion of liposomal amphotericin B at a dose of 10 mg/kg body weight was shown to be non-inferior and less expensive than treatment with conventional amphotericin B deoxycholate [21]. A single infusion of 10 mg/kg liposomal amphotericin B is now recommended as first-line treatment for anthroponotic visceral leishmaniasis in the Indian subcontinent [22] and one component in recently trialed short-course multidrug treatment regimes [23, 24]. Sadly, despite the price reduction, cost is still an inhibiting factor for use of liposomal amphotericin B in some endemic areas. Another limitation is temperature stability as temperatures above 25 °C and below 0 °C can alter liposome characteristics, and impact on drug efficacy and toxicity [19]. Miltefosine, an alkylphosphocholine, was the first oral anti-leishmanial drug registered for visceral leishmaniasis in India in 2002 following clinical trials with 94% cure rates [25]. It is used as a potential tool in the visceral leishmaniasis elimination program in India, Bangladesh, and Nepal [16, 17]. The gastrointestinal tract is the main target organ for side-effects [26] and gastrointestinal symptoms were recognized as the most common adverse effect in clinical trials [27]. The major limitation of miltefosine is its contraindication in pregnancy, and mandatory contraception for women in child-bearing age for the duration of therapy and 2–3 months beyond. This restriction is based on a teratogenic effect seen in one species (rat) in preclinical studies and the pharmacokinetic profile of miltefosine [26]. Paromomycin, an aminoglycoside antibiotic, is the latest drug registered for visceral leishmaniasis in India in 2006. Non-inferiority of paromomycin to amphotericin B was shown in a phase III trial in India [28]. Safety and efficacy of both miltefosine [27] and paromomycin [29] were confirmed in phase IV studies in an outpatient setting.

Current drugs and treatment regimes are summarized in Table 1.1.

Table 1.1 Current drugs for visceral leishmaniasis and treatment regimes in Europe, Middle East, Latin America, South Asia, and East Africa.

New Treatment Regimes

Treatment courses for visceral leishmaniasis have been long (3–4 weeks) with a negative impact on compliance and cost. Experimental resistance to the new drugs, miltefosine [30–33] and paromomycin [34, 35], was easily generated in the laboratory. Antimony-resistant Indian visceral leishmaniasis parasites show increased tolerance to miltefosine and amphotericin B, but not to paromomycin [36, 37]. In addition, miltefosine has a long terminal half-life and concerns have been raised about the emergence of resistance when used as monotherapy [38]. Drug combinations and multidrug treatment regimes are in practice for infectious diseases such as malaria and tuberculosis. The rational for use of combination chemotherapy or multidrug treatments is reduction of treatment duration and total drug doses (resulting in decreased toxicity, higher compliance, and less burden on health systems), and delay of emergence of resistance (and hence an increase of a drug's lifespan) [39, 40].

Multidrug treatments against visceral leishmaniasis have been trialed earlier on smaller scales with a limited number of drugs available. Examples are SSG plus paromomycin in Sudan (which became standard treatment used by Médecins Sans Frontières) and India [41, 42], and SSG plus allopurinol in Kenya [43] in the 1990s and 1980s. With the registration of new drugs and the efficacy of single-dose treatment of liposomal amphotericin B, multidrug treatment regimes became a real possibility for systematic use in visceral leishmaniasis. Non-overlapping drug toxicities and matching half-lives are important considerations in the design of drug combinations [44] as is the relationship between drug concentrations, drug resistance, and tolerance [45]. These questions have been explored in the field of anti-malarial drug combinations. The issues related to drug combinations for visceral leishmaniasis have recently been summarized [39]. Importantly, there are no drugs available for fixed-dose combinations for visceral leishmaniasis and the arsenal of drugs to chose from for coadministration or sequential administration is still limited. Hence, experimental studies [46] and clinical trials [23, 24, 47, 48] are focused on coadministration of available drugs in a pragmatic approach. This approach in visceral leishmaniasis is not yet fully guided by a pharmacological or biological evidence base since our understanding of the pharmacokinetic/pharmacodynamic profiles of visceral leishmaniasis drugs, combination treatment regimes, and evolution of drug resistance in the field is still limited. Based on the different modes of action of current anti-leishmanial drugs [49, 50] mutual protection against resistance may be achieved, but ultimately (experimental) proof-of-concept and integrated pharmacokinetic/pharmacodynamic studies are still to be carried out. The need for increased knowledge of parasite biology and pharmacology has been voiced [39]. Assessment of pharmacodynamic properties of three treatment arms (single-dose liposomal amphotericin B plus SSG, single-dose liposomal amphotericin B plus miltefosine, and miltefosine alone), pharmacokinetic properties of miltefosine alone and in combination with liposomal amphotericin B, and subsequent modeling of pharmacokinetic/pharmacodynamic relationships for miltefosine are planned for a phase II study for treatment of visceral leishmaniasis in East Africa [47]. This integrated approach will provide highly valuable information. The significant advantage that multidrug treatment regimens in visceral leishmaniasis have shown so far over monotherapy is reduction of treatment duration, cost, and frequency of adverse events [23]. This treatment approach is expected to be the strategy for visceral leishmaniasis in the future.

Recent clinical trials have been reviewed and summarized elsewhere [39, 40]. Further information on ongoing trials may be found at www.dndi.org and www.clinicaltrials.gov.

Another combination approach discussed for PKDL [51] and HIV coinfected individuals is the combination of an immunotherapy or therapeutic vaccine with drug treatment. One rational for this approach is to decrease the parasite burden with an effective (preferentially fast killing) drug used at low dose or as a short-course treatment and boost the effector immune response with an immunostimulatory agent [52]. This approach has been tried with first-generation vaccines, recombinant proteins, adjuvant, and cytokines, but lacked availability of defined products suitable for registration. With defined vaccines and immunotherapies currently in development this approach is set to gain future attention.

Regional Differences in Clinical Drug Efficacy

Regional differences in clinical drug efficacy have been reported between and within countries. The most recent example is the finding for paromomycin in East Africa. A dose of 15 mg/kg/day paromomycin sulfate for 21 days was efficacious in a phase III trial in India with a 94.6% cure rate, but gave an unacceptable low overall cure rate of 63.8% in East African countries [8]. The pharmacological and/or biological basis, patient or parasite factor, for this difference still needs to be established. Differences in treatment response to liposomal amphotericin B between Indian, Kenyan, and Brazilian patients have also been reported earlier in a phase II study [53]. A recent report addressed the question of differences in visceral leishmaniasis patient (demographic and nutritional) profiles in Brazil, East Africa, and South Asia [9], highlighting potential requirements of distinct strategies between geographical settings. These may be based on differences at the level of parasite, host or parasite host interactions.

PKDL

Pathology and Immunopathology of PKDL

PKDL, predominantly observed in the Indian subcontinent and East Africa, is a dermal manifestation in a fraction of treated visceral leishmaniasis patients caused by L. donovani [54]. Sporadic cases of PKDL have been reported due to L. infantum, especially in HIV–visceral leishmaniasis coinfection [55]. The clinical spectrum of disease ranges from hypopigmented macular lesions to infiltrated plaques to the chronic and most aggravated nodular form. Most patients present with a combination of lesions described as polymorphic form [54, 56, 57].

Dermal infiltration of lymphocytes, macrophages, and plasma cells in varying proportion is observed in granuloma of Indian PKDL in contrast to Sudanese PKDL, where plasma cells are virtually absent [54, 57, 58]. The parasites are mainly present in the superficial epidermis, and easily detected in nodular lesion compared to macular and papular lesions [59]. Neuritis in small cutaneous nerves indicating peripheral nerve involvement, mucosal lesions with destructive complication in oro-nasal regions, and ocular lesions have been described in Sudanese PKDL, but appear rare in Indian PKDL with a sole report of neuritis [54, 57, 60].

Immunosuppression, reactivation of residual parasite, or reinfection in a viscerally immune person is thought to be the underlying mechanism in the development of PKDL [54, 58, 61]. Mechanisms of parasite persistence in the host are not yet well established. However, increasing evidence indicates the involvement of host as well as parasite factors.

Predominantly, CD8+ T cells are observed in dermal lesions as well as in lymph nodes of Indian PKDL, unlike in Sudanese PKDL patients where a preponderance of CD4+ T cells is observed [57, 62]. Increased production of interleukin (IL)-10 by keratinocytes and high levels of IL-10 in plasma and peripheral blood mononuclear cell cultures as well as elevated C-reactive proteins predicted the development of PKDL in Sudan [57]. Persistence of parasites in Indian PKDL despite high interferon (IFN)-γ and tumor necrosis factor (TNF)-α expression has been accounted to the presence of counteracting cytokines and minimal expression of IFN-γ receptor 1, and the TNF receptors TNFR1 and R2 [63, 64]. Ample evidence is available to conclude that an IL-10-rich milieu promotes Leishmania parasite persistence and reactivation in skin.

In the Sudanese population, PKDL susceptibility has been associated with polymorphism observed at promoter regions of IFN-γ receptor 1 and IL-10 genes. However, confirmatory experimental analysis to demonstrate a regulatory role of this polymorphism is awaited [65, 66]. Such studies are yet to be performed in Indian PKDL.

In addition to immunological mechanisms, Leishmania genetic determinants also contribute to alterations of the host–parasite equilibrium in favor of the parasite, resulting in the persistence in the human host for up to 20 years in Indian PKDL. It is well established that parasites isolated from visceral leishmaniasis and PKDL patients are essentially the same [67], although polymorphism is observed at the 28S rRNA locus and β-tubulin locus [68, 69]. Transient changes such as preferential expression of surface proteases in parasites isolated from PKDL lesions are suggestive of altered interaction with macrophages and may be responsible for the predilection of parasite to the dermis [69].

Current Treatment Options for PKDL

Treating PKDL patients is an important aspect of visceral leishmaniasis control programs as PKDL patients are deemed as the major reservoir in anthroponotic transmission settings. High incidence of refractoriness to antimony has been attributed to anthroponotic transmission via PKDL in India [70]. Three to four times longer treatment regimens than for visceral leishmaniasis, increasing antimony resistance, and poor patient compliance pose major challenges for treatment of PKDL. In Sudan, most of the PKDL patients self heal, and only severe and chronic patients are treated, while in Indian PKDL treatment is always required. In India, SSG is extensively used at a dose of 20 mg/kg/day for 120 days with cure rates of 64–92% [57, 71]. As an alternative, various drugs including allopurinol, ketoconazole, and rifampicin alone or in combination with pentavalent antimonials have been tried in Indian PKDL with variable cure rates [72]. Amphotericin B and miltefosine, the frontline drugs for visceral leishmaniasis, have potential benefits for PKDL patients. Amphotericin B deoxycholate at a dose of 1 mg/kg/day by infusion for 60–80 doses over a period of 120 days was found 100% effective [73]. Miltefosine at a dose of 100 mg/day in divided doses for 12 weeks has been found effective in Indian PKDL [74]. However, a shorter regimen of 150 mg/day in three doses for 60 days was also found curative and advocated in patients capable of tolerating gastrointestinal symptoms caused by the drug [75].

Non-healing Sudanese PKDL patients with severe lesions are best treated with SSG at a dose of 20 mg/kg/day for 30 days, which may be prolonged to 2–3 months if necessary [57]. Liposomal amphotericin B at 2.5 mg/kg/day by infusion for 20 days has been effective with a cure rate of 83% without side-effects in Sudan [76]. Novel immunochemotherapy using alum-precipitated autoclaved L. major (Alum/ALM) vaccine plus Bacille Calmette-Guerin (BCG) and SSG was found safe and effective with a cure rate of 87% by day 60 in Sudanese PKDL [77].

However, systematic studies on larger sets of patients to evaluate drugs for treatment of PKDL are urgently needed to accomplish improved, effective, and shortened treatments.

Open Questions and Needs

Without doubt real progress has been made in the treatment of visceral leishmaniasis over the last decade. However, this progress was also driven by the repurposing of drugs initially developed for other indications and pragmatic approaches. A new chemical entity (NCE) dedicated to visceral leishmaniasis has yet to be identified along with candidates for fixed-dose combinations. Screening campaigns over the last 5 years have focused on high-throughput and high-content screening formats, yet the complexity of the Leishmania parasite and its lifestyle do not make it an easy candidate for this approach. Consideration has to be given to crucial aspects of parasite biology in order to identify compounds that hold potential to progress into treatments for visceral leishmaniasis [78]. There is also a strong need for refined models and approaches for preclinical candidate selection, optimal drug use, and dosing regimes with inclusion of pharmacokinetic/pharmacodynamic relationships in anti-leishmanial drug development.

Understanding of pathogenesis, host factors, host–parasite interactions, and regional differences in clinical treatment response require continued research efforts and are crucial to design optimal treatments for visceral leishmaniasis and PKDL. Lastly, the importance of access to treatment has to be emphasized for the effort of all disciplines involved in the drug discovery and development process to yield long-lasting fruits. Poor access to care for leishmaniasis remains a major barrier to control. Factors that determine access to drugs (drug affordability, drug availability, forecasting, distribution and storage, drug quality, drug legislation and pharmacovigilance, user-friendliness, etc.) have recently been reviewed and the importance of a concerted effort by all stakeholders emphasized [13].

Promising directions and strategies have been set and are ongoing. Now research efforts have to continue to support further progress in treatment of visceral leishmaniasis and PKDL.

Note

1 Corresponding Author

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