Drug discovery and human African trypanosomiasis: a disease less neglected?

Benzophenone Glucosides and B-Type Proanthocyanidin Dimers from Zambian Cassia abbreviata and Their Trypanocidal Activities

Two benzophenone glucosides (1 and 2), five flavan-3-ol dimers (5-9), and 17 known compounds (3, 4, and 10-24) were identified from the bark extract of Cassia abbreviata. The chemical structures display two points of interest. First, as an unusual characteristic feature of the ¹H NMR spectra of 1 and 2, the signals for the protons on glucosidic carbons C-2 are shielded as compared to those generally observed for glucosyl moieties. The geometrically optimized 3D structures derived from conformational analysis and density functional theory (DFT) calculations revealed that this shielding effect originates from intramolecular hydrogen bonds in 1 and 2. Additionally, 3-15 were identified as dimeric B-type proanthocyanidins, which have 2R,3S-absolute-configured C-rings and C-4-C-8″ linkages, as evidenced by X-ray crystallography and by NMR and ECD spectroscopy. These results suggest the structure-determining procedures for some reported dimers need to be reconsidered. The trypanocidal activities of the isolated compounds against Trypanosoma brucei brucei, T. b. gambiense, T. b. rhodesiense, T. congolense, and T. evansi were evaluated, and the active compounds were identified.

Recent Progress in the Discovery and Development of 2-Nitroimidazooxazines and 6-Nitroimidazooxazoles to Treat Tuberculosis and Neglected Tropical Diseases

Nitroimidazole drugs have a long history as therapeutic agents to treat bacterial and parasitic diseases. The discovery in 1989 of a bicyclic nitroimidazole lead, displaying in vitro and in vivo antitubercular activity, spurred intensive exploration of this and related scaffolds, which led to the regulatory approval of pretomanid and delamanid as a new class of tuberculosis drugs. Much of the discovery work related to this took place over a 20-year period ending in 2010, which is covered in a number of cited reviews. This review highlights subsequent research published over the 2011–August 2020 timeframe, and captures detailed structure–activity relationship studies and synthetic strategies directed towards uncovering newer generation drugs for both tuberculosis and selected neglected tropical diseases. Additionally, this review presents in silico calculations relating to the drug-like properties of lead compounds and clinical agents, as well as chemical development and manufacturing processes toward providing bulk drug supplies.

Spiro-containing derivatives show antiparasitic activity against Trypanosoma brucei through inhibition of the trypanothione reductase enzyme

Trypanothione reductase (TR) is a key enzyme that catalyzes the reduction of trypanothione, an antioxidant dithiol that protects Trypanosomatid parasites from oxidative stress induced by mammalian host defense systems. TR is considered an attractive target for the development of novel anti-parasitic agents as it is essential for parasite survival but has no close homologue in humans. We report here the identification of spiro-containing derivatives as inhibitors of TR from Trypanosoma brucei (TbTR), the parasite responsible for Human African Trypanosomiasis. The hit series, identified by high throughput screening, was shown to bind TbTR reversibly and to compete with the trypanothione (TS₂) substrate. The prototype compound 1 from this series was also found to impede the growth of Trypanosoma brucei parasites in vitro. The X-ray crystal structure of TbTR in complex with compound 1 solved at 1.98 Å allowed the identification of the hydrophobic pocket where the inhibitor binds, placed close to the catalytic histidine (His 461’) and lined by Trp21, Val53, Ile106, Tyr110 and Met113. This new inhibitor is specific for TbTR and no activity was detected against the structurally similar human glutathione reductase (hGR). The central spiro scaffold is known to be suitable for brain active compounds in humans thus representing an attractive starting point for the future treatment of the central nervous system stage of T. brucei infections.

Trypanosoma brucei is a parasite responsible for neglected pathologies such as human African trypanosomiasis, also known as sleeping sickness. This disease is endemic in sub-Saharan Africa, with 70 million people at risk of infection. Current treatments for this type of disease are limited by their toxicity, administration in endemic countries and treatment resistance. Therapies against infectious diseases typically rely on targeting one or more components of the parasite that are not present in humans to ensure the best possible therapeutic window. In this case we aimed at targeting the Trypanosoma brucei trypanothione reductase (TR), one enzyme that synthesize the reduced trypanothione a key molecule for preserving the parasite redox balance. This enzyme does not exist in humans that have glutathione instead of trypanothione. Past attempts to identify novel inhibitors of this target has failed to generate drug-like molecules. To overcome this limitation we employed a recent, higher quality, TR activity assay to test a collection of compounds previously reported to be active against these parasites. This approach led to the identification and validation of a new chemotype with a unique mode of inhibition of TR. This chemical series is a drug-like starting point, in fact its core (spiro) is present in drugs approved for human use.

Metabolic and Pharmaceutical Aspects of Fluorinated Compounds

The applications of fluorine in drug design continue to expand, facilitated by an improved understanding of its effects on physicochemical properties and the development of synthetic methodologies that are providing access to new fluorinated motifs. In turn, studies of fluorinated molecules are providing deeper insights into the effects of fluorine on metabolic pathways, distribution, and disposition. Despite the high strength of the C-F bond, the departure of fluoride from metabolic intermediates can be facile. This reactivity has been leveraged in the design of mechanism-based enzyme inhibitors and has influenced the metabolic fate of fluorinated compounds. In this Perspective, we summarize the literature associated with the metabolism of fluorinated molecules, focusing on examples where the presence of fluorine influences the metabolic profile. These studies have revealed potentially problematic outcomes with some fluorinated motifs and are enhancing our understanding of how fluorine should be deployed.

Applications of fluorine-containing amino acids for drug design

Fluorine-containing amino acids are becoming increasingly prominent in new drugs due to two general trends in the modern pharmaceutical industry. Firstly, the growing acceptance of peptides and modified peptides as drugs; and secondly, fluorine editing has become a prevalent protocol in drug-candidate optimization. Accordingly, fluorine-containing amino acids represent one of the more promising and rapidly developing areas of research in organic, bio-organic and medicinal chemistry. The goal of this Review article is to highlight the current state-of-the-art in this area by profiling 42 selected compounds that combine fluorine and amino acid structural elements. The compounds under discussion represent pharmaceutical drugs currently on the market, or in clinical trials as well as examples of drug-candidates that although withdrawn from development had a significant impact on the progress of medicinal chemistry and/or provided a deeper understanding of the nature and mechanism of biological action. For each compound, we present features of biological activity, a brief history of the design principles and the development of the synthetic approach, focusing on the source of tailor-made amino acid structures and fluorination methods. General aspects of the medicinal chemistry of fluorine-containing amino acids and synthetic methodology are briefly discussed.

N-substituted noscapine derivatives as new antiprotozoal agents: Synthesis, antiparasitic activity and molecular docking study

Novel N-substituted noscapine derivatives were synthesized by a three-component Strecker reaction of cyclic ether of N-nornoscapine with varied aldehydes, in the presence of cyanide ion. Moreover, the corresponding amides were synthesized by the oxidation of cyanide moieties in good yields. The in vitro antiprotozoal activity of the products was also investigated. Interestingly, some analogues did put on display promising antiparasitic activity against Trypanosoma brucei rhodesiense with IC₅₀ values between 2.5 and 10.0 µM and selectivity index (SI) ranged from 0.8 to 13.2. Eight compounds exhibited activity against Plasmodium falciparum K1 strain with IC₅₀ ranging 1.7-6.4 µM, and SI values between 2.8 and 10.5 against L6 rat myoblast cell lines. Molecular docking was carried out on trypanothione reductase (TbTR, PDB ID: 2WOW) and UDP-galactose 4' epimerase (TbUDPGE PDB: 1GY8) as targets for studying the envisaged mechanism of action. Compounds 6j₂ and 6b₂ displayed excellent docking scores with -8.59 and -8.86 kcal/mol for TbTR and TbUDPGE, respectively.

Anilinoquinoline based inhibitors of trypanosomatid proliferation

We recently reported the medicinal chemistry re-optimization of a series of compounds derived from the human tyrosine kinase inhibitor, lapatinib, for activity against Plasmodium falciparum. From this same library of compounds, we now report potent compounds against Trypanosoma brucei brucei (which causes human African trypanosomiasis), T. cruzi (the pathogen that causes Chagas disease), and Leishmania spp. (which cause leishmaniasis). In addition, sub-micromolar compounds were identified that inhibit proliferation of the parasites that cause African animal trypanosomiasis, T. congolense and T. vivax. We have found that this set of compounds display acceptable physicochemical properties and represent progress towards identification of lead compounds to combat several neglected tropical diseases.

As part of our efforts to identify compounds that are active against the parasite that causes malaria (P. falciparum), we employed a “parasite hopping” approach in our drug discovery efforts. This involved screening a library of demonstrated antiparasitic agents against other parasites responsible for a host of neglected tropical diseases (NTDs) including Chagas disease (T. cruzi), human African trypanosomiasis (T. brucei) and cutaneous leishmaniasis (L. major). The compounds we identified generally show improved selectivity for the parasite of interest over the mammalian cell lines tested and, from this work, we have made progress towards the identification of lead compounds against multiple NTDs.

Assessment of a pretomanid analogue library for African trypanosomiasis: Hit-to-lead studies on 6-substituted 2-nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazine 8-oxides

A 900 compound nitroimidazole-based library derived from our pretomanid backup program with TB Alliance was screened for utility against human African trypanosomiasis (HAT) by the Drugs for Neglected Diseases initiative. Potent hits included 2-nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]thiazine 8-oxides, which surprisingly displayed good metabolic stability and excellent cell permeability. Following comprehensive mouse pharmacokinetic assessments on four hits and determination of the most active chiral form, a thiazine oxide counterpart of pretomanid (24) was identified as the best lead. With once daily oral dosing, this compound delivered complete cures in an acute infection mouse model of HAT and increased survival times in a stage 2 model, implying the need for more prolonged CNS exposure. In preliminary SAR findings, antitrypanosomal activity was reduced by removal of the benzylic methylene but enhanced through a phenylpyridine-based side chain, providing important direction for future studies.

Bistacrines as potential antitrypanosomal agents

Human African Trypanosomiasis (HAT) is caused by two subspecies of the genus Trypanosoma, namely Trypanosoma brucei rhodesiense and Trypanosoma brucei gambiense. The disease is fatal if left untreated and therapy is limited due to only five non-adequate drugs currently available. In preliminary studies, dimeric tacrine derivatives were found to inhibit parasite growth with IC₅₀-values in the nanomolar concentration range. This prompted the synthesis of a small, but smart library of monomeric and dimeric tacrine-type compounds and their evaluation of antiprotozoal activity. Rhodesain, a lysosomal cathepsin-L like cysteine protease of T. brucei rhodesiense is essential for parasite survival and likely target of the tacrine derivatives. In addition, the inhibition of trypanothione reductase by bistacrines was found. This flavoprotein oxidoreductase is the main defense against oxidative stress in the thiol redox system unique for protozoa.

CSF in acute and chronic infectious diseases

Infections of the nervous system are an important and challenging aspect of clinical neurology. Immediate correct diagnosis enables to introduce effective therapy, in conditions that without diagnosis may leave the patient with severe neurological incapacitation and sometimes even death. The cerebrospinal fluid (CSF) is a mirror that reflects nervous system pathology and can promote early diagnosis and therapy. The present chapter focuses on the CSF findings in neuro-infections, mainly viral and bacterial. Opening pressure, protein and glucose levels, presence of cells and type of the cellular reaction should be monitored. Other tests can also shed light on the causative agent: serology, culture, staining, molecular techniques such as polymerase chain reaction. Specific examination such as panbacterial and panfungal examinations should be examined when relevant. Our chapter is a guide-text that combines clinical presentation and course with CSF findings as a usuaful tool in diagnosis of neuroinfections.

24-Methylenecyclopropane steroidal inhibitors: A Trojan horse in ergosterol biosynthesis that prevents growth of Trypanosoma brucei

A new class of steroidal therapeutics based on phylogenetic-guided design of covalent inhibitors that target parasite-specific enzymes of ergosterol biosynthesis is shown to prevent growth of the protozoan-Trypanosoma brucei, responsible for sleeping sickness. In the presence of approximately 15±5μM 26,27-dehydrolanosterol, T. brucei procyclic or blood stream form growth is inhibited by 50%. This compound is actively converted by the parasite to an acceptable substrate of sterol C24-methyl transferase (SMT) that upon position-specific side chain methylation at C26 inactivates the enzyme. Treated cells show dose-dependent depletion of ergosterol and other 24β-methyl sterols with no accumulation of intermediates in contradistinction to profiles typical of tight binding inhibitor treatments to azoles showing loss of ergosterol accompanied by accumulation of toxic 14-methyl sterols. HEK cells accumulate 26,27-dehydrolanosterol without effect on cholesterol biosynthesis. During exposure of cloned TbSMT to 26,27-dehydrozymosterol, the enzyme is gradually inactivated (k_cat/k_inact=0.13min^-1/0.08min^-1; partition ratio of 1.6) while 26,27-dehydrolanosterol binds nonproductively. GC-MS analysis of the turnover product and bound intermediate released as a C26-methylated diol (C3-OH and C24-OH) confirmed substrate recognition and covalent binding to TbSMT. This study has potential implications for design of a novel class of chemotherapeutic leads functioning as mechanism-based inhibitors of ergosterol biosynthesis to treat neglected tropical diseases.

Targeting the HSP60/10 chaperonin systems of Trypanosoma brucei as a strategy for treating African sleeping sickness

Trypanosoma brucei are protozoan parasites that cause African sleeping sickness in humans (also known as Human African Trypanosomiasis-HAT). Without treatment, T. brucei infections are fatal. There is an urgent need for new therapeutic strategies as current drugs are toxic, have complex treatment regimens, and are becoming less effective owing to rising antibiotic resistance in parasites. We hypothesize that targeting the HSP60/10 chaperonin systems in T. brucei is a viable anti-trypanosomal strategy as parasites rely on these stress response elements for their development and survival. We recently discovered several hundred inhibitors of the prototypical HSP60/10 chaperonin system from Escherichia coli, termed GroEL/ES. One of the most potent GroEL/ES inhibitors we discovered was compound 1. While examining the PubChem database, we found that a related analog, 2e-p, exhibited cytotoxicity to Leishmania major promastigotes, which are trypanosomatids highly related to Trypanosoma brucei. Through initial counter-screening, we found that compounds 1 and 2e-p were also cytotoxic to Trypanosoma brucei parasites (EC₅₀=7.9 and 3.1μM, respectively). These encouraging initial results prompted us to develop a library of inhibitor analogs and examine their anti-parasitic potential in vitro. Of the 49 new chaperonin inhibitors developed, 39% exhibit greater cytotoxicity to T. brucei parasites than parent compound 1. While many analogs exhibit moderate cytotoxicity to human liver and kidney cells, we identified molecular substructures to pursue for further medicinal chemistry optimization to increase the therapeutic windows of this novel class of chaperonin-targeting anti-parasitic candidates. An intriguing finding from this study is that suramin, the first-line drug for treating early stage T. brucei infections, is also a potent inhibitor of GroEL/ES and HSP60/10 chaperonin systems.

Fluorinated Sterols Are Suicide Inhibitors of Ergosterol Biosynthesis and Growth in Trypanosoma brucei

Trypanosoma brucei, the causal agent for sleeping sickness, depends on ergosterol for growth. Here, we describe the effects of a mechanism-based inhibitor, 26-fluorolanosterol (26FL), which converts in vivo to a fluorinated substrate of the sterol C24-methyltransferase essential for sterol methylation and function of ergosterol, and missing from the human host. 26FL showed potent inhibition of ergosterol biosynthesis and growth of procyclic and bloodstream forms while having no effect on cholesterol biosynthesis or growth of human epithelial kidney cells. During exposure of cloned TbSMT to 26-fluorocholesta-5,7,24-trienol, the enzyme is gradually killed as a consequence of the covalent binding of the intermediate C25 cation to the active site (kcat/kinact = 0.26 min(-1)/0.24 min(-1); partition ratio of 1.08), whereas 26FL is non-productively bound. These results demonstrate that poisoning of ergosterol biosynthesis by a 26-fluorinated Δ(24)-sterol is a promising strategy for developing a new treatment for trypanosomiasis.

Phenolic Constituents of Medicinal Plants with Activity against Trypanosoma brucei

Neglected tropical diseases (NTDs) affect over one billion people all over the world. These diseases are classified as neglected because they impact populations in areas with poor financial conditions and hence do not attract sufficient research investment. Human African Trypanosomiasis (HAT or sleeping sickness), caused by the parasite Trypanosoma brucei, is one of the NTDs. The current therapeutic interventions for T. brucei infections often have toxic side effects or require hospitalization so that they are not available in the rural environments where HAT occurs. Furthermore, parasite resistance is increasing, so that there is an urgent need to identify novel lead compounds against this infection. Recognizing the wide structural diversity of natural products, we desired to explore and identify novel antitrypanosomal chemotypes from a collection of natural products obtained from plants. In this study, 440 pure compounds from various medicinal plants were tested against T. brucei by in a screening using whole cell in vitro assays. As the result, twenty-two phenolic compounds exhibited potent activity against cultures of T. brucei. Among them, eight compounds—4, 7, 11, 14, 15, 18, 20, and 21—showed inhibitory activity against T. brucei, with IC₅₀ values below 5 µM, ranging from 0.52 to 4.70 μM. Based on these results, we attempt to establish some general trends with respect to structure-activity relationships, which indicate that further investigation and optimization of these derivatives might enable the preparation of potentially useful compounds for treating HAT.

Focus on PAINS: false friends in the quest for selective anti-protozoal lead structures from Nature?

Pan-assay interference compounds (PAINS) are molecules showing promising but deceptive activities in various biochemical screenings mainly due to unselective interactions with the target.

Multicomponent reaction-based synthesis and biological evaluation of tricyclic heterofused quinolines with multi-trypanosomatid activity

Human African trypanosomiasis (HAT), Chagas disease and leishmaniasis, which are caused by the trypanosomatids Trypanosoma brucei, Trypanosoma cruzi and Leishmania species, are among the most deadly neglected tropical diseases. The development of drugs that are active against several trypanosomatids is appealing from a clinical and economic viewpoint, and seems feasible, as these parasites share metabolic pathways and hence might be treatable by common drugs. From benzonapthyridine 1, an inhibitor of acetylcholinesterase (AChE) for which we have found a remarkable trypanocidal activity, we have designed and synthesized novel benzo[h][1,6]naphthyridines, pyrrolo[3,2-c]quinolines, azepino[3,2-c]quinolines, and pyrano[3,2-c]quinolines through 2–4-step sequences featuring an initial multicomponent Povarov reaction as the key step. To assess the therapeutic potential of the novel compounds, we have evaluated their in vitro activity against T. brucei, T. cruzi, and Leishmania infantum, as well as their brain permeability, which is of specific interest for the treatment of late-stage HAT. To assess their potential toxicity, we have determined their cytotoxicity against rat myoblast L6 cells and their AChE inhibitory activity. Several tricyclic heterofused quinoline derivatives were found to display an interesting multi-trypanosomatid profile, with one-digit micromolar potencies against two of these parasites and two-digit micromolar potency against the other. Pyranoquinoline 39, which displays IC₅₀ values of 1.5 μM, 6.1 μM and 29.2 μM against T. brucei, L. infantum and T. cruzi, respectively, brain permeability, better drug-like properties (lower lipophilicity and molecular weight and higher CNS MPO desirability score) than hit 1, and the lowest AChE inhibitory activity of the series (IC₅₀ > 30 μM), emerges as an interesting multi-trypanosomatid lead, amenable to further optimization particularly in terms of its selectivity index over mammalian cells.

•

Novel classes of tricyclic heterofused quinolines have been synthesized.

•

Their 2–4-step syntheses involve a multicomponent Povarov reaction as the key step.

•

Some compounds exhibit single digit micromolar potencies against 2 trypanosomatids.

•

All compounds with multi-trypanosomatid activity can cross the blood–brain barrier.

•

Most compounds with multi-trypanosomatid activity have drug like properties.

In Vitro and In Vivo Investigation of the Inhibition of Trypanosoma brucei Cell Growth by Lipophilic Bisphosphonates

We report the results of a screen of a library of 925 potential prenyl synthase inhibitors against Trypanosoma brucei farnesyl diphosphate synthase (TbFPPS) and against T. brucei, the causative agent of human African trypanosomiasis. The most potent compounds were lipophilic analogs of the bone resorption drug zoledronate, some of which had submicromolar to low micromolar activity against bloodstream form T. brucei and selectivity indices of up to ∼ 300. We evaluated the effects of two such inhibitors on survival and parasitemia in a T. brucei mouse model of infection and found that survival increased by up to 16 days. We also investigated the binding of three lipophilic bisphosphonates to an expressed TbFPPS using crystallography and investigated the thermodynamics of binding using isothermal titration calorimetry.

6-Arylpyrazine-2-carboxamides: A New Core for Trypanosoma brucei Inhibitors

From a whole-organism high throughput screen of approximately 87000 compounds against Trypanosoma brucei brucei, we recently identified eight new unique compounds for the treatment of human African trypanosomiasis. In an effort to understand the structure-activity relationships around these compounds, we report for the first time our results on a new class of trypanocides, the pyrazine carboxamides. Attracted by the low molecular weight (270 g·mol(-1)) of our starting hit (9) and its potency (0.49 μM), the SAR around the core was explored, leading to compounds having an EC50 as low as 25 nM against T. b. brucei and being more than 1500 times less toxic against mammalian L6 and HEK293 cell lines. The most potent compounds in the series were exquisitely selective for T. brucei over a panel of other protozoan parasites, showing an excellent correlation with the human infective parasite Trypanosoma brucei rhodesiense, the most potent compound (65) having an EC50 of 24 nM. The compounds are highly drug-like and are able to penetrate the CNS, their only limitation currently being their rate of microsomal metabolism. To that effect, efforts to identify potential metabolites of selected compounds are also reported.

Synthesis, biological profiling and mechanistic studies of 4-aminoquinoline-based heterodimeric compounds with dual trypanocidal-antiplasmodial activity

Dual submicromolar trypanocidal-antiplasmodial compounds have been identified by screening and chemical synthesis of 4-aminoquinoline-based heterodimeric compounds of three different structural classes. In Trypanosoma brucei, inhibition of the enzyme trypanothione reductase seems to be involved in the potent trypanocidal activity of these heterodimers, although it is probably not the main biological target. Regarding antiplasmodial activity, the heterodimers seem to share the mode of action of the antimalarial drug chloroquine, which involves inhibition of the haem detoxification process. Interestingly, all of these heterodimers display good brain permeabilities, thereby being potentially useful for late stage human African trypanosomiasis. Future optimization of these compounds should focus mainly on decreasing cytotoxicity and acetylcholinesterase inhibitory activity.

Discovery of an ergosterol-signaling factor that regulates Trypanosoma brucei growth

Ergosterol biosynthesis and homeostasis in the parasitic protozoan Trypanosoma brucei was analyzed by RNAi silencing and inhibition of sterol C24β-methyltransferase (TbSMT) and sterol 14α-demethylase [TbSDM (TbCYP51)] to explore the functions of sterols in T. brucei growth. Inhibition of the amount or activity of these enzymes depletes ergosterol from cells at <6 fg/cell for procyclic form (PCF) cells or <0.01 fg/cell for bloodstream form (BSF) cells and reduces infectivity in a mouse model of infection. Silencing of TbSMT expression by RNAi in PCF or BSF in combination with 25-azalanosterol (AZA) inhibited parasite growth and this inhibition was restored completely by adding synergistic cholesterol (7.8 μM from lipid-depleted media) with small amounts of ergosterol (1.2 μM) to the medium. These observations are consistent with the proposed requirement for ergosterol as a signaling factor to spark cell proliferation while imported cholesterol or the endogenously formed cholesta-5,7,24-trienol act as bulk membrane components. To test the potential chemotherapeutic importance of disrupting ergosterol biosynthesis using pairs of mechanism-based inhibitors that block two enzymes in the post-squalene segment, parasites were treated with AZA and itraconazole at 1 μM each (ED50 values) resulting in parasite death. Taken together, our results demonstrate that the ergosterol pathway is a prime drug target for intervention in T. brucei infection.

Emerging and reemerging neglected tropical diseases: a review of key characteristics, risk factors, and the policy and innovation environment

In global health, critical challenges have arisen from infectious diseases, including the emergence and reemergence of old and new infectious diseases. Emergence and reemergence are accelerated by rapid human development, including numerous changes in demographics, populations, and the environment. This has also led to zoonoses in the changing human-animal ecosystem, which are impacted by a growing globalized society where pathogens do not recognize geopolitical borders. Within this context, neglected tropical infectious diseases have historically lacked adequate attention in international public health efforts, leading to insufficient prevention and treatment options. This subset of 17 infectious tropical diseases disproportionately impacts the world's poorest, represents a significant and underappreciated global disease burden, and is a major barrier to development efforts to alleviate poverty and improve human health. Neglected tropical diseases that are also categorized as emerging or reemerging infectious diseases are an even more serious threat and have not been adequately examined or discussed in terms of their unique risk characteristics. This review sets out to identify emerging and reemerging neglected tropical diseases and explore the policy and innovation environment that could hamper or enable control efforts. Through this examination, we hope to raise awareness and guide potential approaches to addressing this global health concern.