Safety and efficacy of oral fexinidazole in children with gambiense human African trypanosomiasis: a multicentre, single-arm, open-label, phase 2–3 trial

Transforming the chemotherapy of human African trypanosomiasis

SUMMARYPrior to 2019, when the orally available drug fexinidazole began its clinical use, the treatment of human African trypanosomiasis (HAT) was complex and unsatisfactory for many reasons. Two sub-species of the Trypanosoma brucei parasite are responsible for HAT, namely the rhodesiense form found in East and Southern Africa and the gambiense form found in Central and West Africa. Diseases caused by both forms manifest in two stages: stage 1 before and stage 2 after central nervous system involvement. Prior to 2019, different drugs were required for each of the two parasite sub-species at each stage. Gambiense disease required pentamidine or nifurtimox-eflornithine combination therapy, while for rhodesiense disease, suramin or melarsoprol was given for stages 1 and 2, respectively. These drugs all suffered complications including protracted administration regimens involving multiple injections with drug-induced adverse effects common. Today, a single drug, fexinidazole, can be given orally in most cases for both diseases at either stage. Another compound, acoziborole, effective in both stages 1 and 2 gambiense disease with a single dosing is anticipated to become available within a few years. Moreover, the recent engagement of multilateral organizations in seeking other compounds that could be used in HAT therapy has also been successful, and a rich vein of new trypanocides has been discovered. Here, the clinical use, modes of action, and resistance risks for drugs used against HAT are discussed.

Pass the boron: benzoxaboroles as antiparasite drugs

The development of new drug modalities has been facilitated recently by the introduction of boron as a component of organic compounds, and specifically within a benzoxaborale scaffold. This has enabled exploration of new chemical space and the development of effective compounds targeting a broad range of morbidities, including infections by protozoa, fungi, worms, and bacteria. Most notable is the recent demonstration of a single oral dose cure using acoziborole against African trypanosomiasis. Common and species-/structure-specific interactions between benzoxaboroles and parasite species have emerged and provide vital insights into the mechanisms of cidality, as well as potential challenges in terms of resistance and/or side effects. Here, we discuss the literature specific to benzoxaborole studies in parasitic protists and consider unanswered questions concerning this important new drug class.

The evolving spectrum of human African trypanosomiasis

Human African trypanosomiasis (HAT), or sleeping sickness, continues to be a major threat to human health in 36 countries throughout sub-Saharan Africa with up to 60 million people at risk. Over the last decade, there have been several advances in this area, some of which are discussed in this overview. Due to the concerted efforts of several bodies, including better identification and treatment of cases and improved tsetse fly vector control, the number of cases of HAT has declined dramatically. The clinical heterogeneity of HAT has also been increasingly recognized, and the disease, while usually fatal if untreated or inadequately treated, does not always have a uniformly fatal outcome. Improved methods of HAT diagnosis have now been developed including rapid diagnostic tests. Novel drug treatment of HAT has also been developed, notably nifurtimox-eflornithine combination therapy (NECT) for late-stage Trypanosoma brucei gambiense, oral fexinidazole for early and the early component of the late-stage of T.b. gambiense, and the new oral compounds of the oxaborole group, which have shown considerable promise in field trials. Advances in HAT neuropathogenesis have been steady, though largely incremental, with a particular focus on the role of the blood-brain barrier in parasite entry into the central nervous system and the relevant importance of both innate and adaptive immunity. While the World Health Organization goal of elimination of HAT as a public health problem by 2020 has probably been achieved, it remains to be seen whether the second more ambitious goal of interruption of transmission of HAT by 2030 will be attained.

Emerging compounds and therapeutic strategies to treat infections from Trypanosoma brucei: an overhaul of the last 5-years patents

INTRODUCTION

Human African Trypanosomiasis is a neglected disease caused by infection from parasites belonging to the Trypanosoma brucei species. Only six drugs are currently available and employed depending on the stage of the infection: pentamidine, suramin, melarsoprol, eflornithine, nifurtimox, and fexinidazole. Joint research projects were launched in an attempt to find new therapeutic options for this severe and often lethal disease.

AREAS COVERED

After a brief description of the recent literature on the parasite and the disease, we searched for patents dealing with the proposal of new anti-trypanosomiasis agents and, following the PRISMA guidelines, we filtered the results to those published from 2018onwards returning suitable entries, which represent the contemporary landscape of compounds/strategies against Trypanosoma brucei. In addition, some relevant publications from the overall scientific literature were also discussed.

EXPERT OPINION

This review comprehensively covers and analyzes the most recent advances not only in the discovery of new inhibitors and their structure-activity relationships but also in the assessment of innovative biological targets opening new scenarios in the MedChem field. Lastly, also new vaccines and formulations recently patented were described. However, natural and synthetic compounds were analyzed in terms of inhibitory activity and selective toxicity against human cells.

Screening the Pathogen Box to Discover and Characterize New Cruzain and TbrCatL Inhibitors

Chagas disease and Human African Trypanosomiasis, caused by Trypanosoma cruzi and T. brucei, respectively, pose relevant health challenges throughout the world, placing 65 to 70 million people at risk each. Given the limited efficacy and severe side effects associated with current chemotherapy, new drugs are urgently needed for both diseases. Here, we report the screening of the Pathogen Box collection against cruzain and TbrCatL, validated targets for Chagas disease and Human African Trypanosomiasis, respectively. Enzymatic assays were applied to screen 400 compounds, validate hits, determine IC₅₀ values and, when possible, mechanisms of inhibition. In this case, 12 initial hits were obtained and ten were prioritized for follow-up. IC₅₀ values were obtained for six of them (hit rate = 1.5%) and ranged from 0.46 ± 0.03 to 27 ± 3 µM. MMV687246 was found to be a mixed inhibitor of cruzain (K_i = 57 ± 6 µM) while MMV688179 was found to be a competitive inhibitor of cruzain with a nanomolar potency (K_i = 165 ± 63 nM). A putative binding mode for MMV688179 was obtained by docking. The six hits discovered against cruzain and TbrCatL are of great interest for further optimization by the medicinal chemistry community.

Trypanosome spliced leader RNA for diagnosis of acoziborole treatment outcome in gambiense human African trypanosomiasis: A longitudinal follow-up study

BACKGROUND

Detection of spliced leader (SL)-RNA allows sensitive diagnosis of gambiense human African trypanosomiasis (HAT). We investigated its diagnostic performance for treatment outcome assessment.

METHODS

Blood and cerebrospinal fluid (CSF) from a consecutive series of 97 HAT patients, originating from the Democratic Republic of the Congo, were prospectively collected before treatment with acoziborole, and during 18 months of longitudinal follow-up after treatment. For treatment outcome assessment, SL-RNA detection was compared with microscopic trypanosome detection and CSF white blood cell count. The trial was registered under NCT03112655 in clinicaltrials.gov.

FINDINGS

Before treatment, respectively 94.9% (92/97; CI 88.5-97.8%) and 67.7% (65/96; CI 57.8-76.2%) HAT patients were SL-RNA positive in blood or CSF. During follow-up, one patient relapsed with trypanosomes observed at 18 months, and was SL-RNA positive in blood and CSF at 12 months, and CSF positive at 18 months. Among cured patients, one individual tested SL-RNA positive in blood at month 12 (Specificity 98.9%; 90/91; CI 94.0-99.8%) and 18 (Specificity 98.9%; 88/89; CI 93.9-99.8%).

INTERPRETATION

SL-RNA detection for HAT treatment outcome assessment shows ≥98.9% specificity in blood and 100% in CSF, and may detect relapses without lumbar puncture.

FUNDING

The DiTECT-HAT project is part of the EDCTP2 programme, supported by Horizon 2020, the European Union Funding for Research and Innovation (grant number DRIA-2014-306-DiTECT-HAT).

Fexinidazole for Human African Trypanosomiasis, the Fruit of a Successful Public-Private Partnership

After 100 years of chemotherapy with impractical and toxic drugs, an oral cure for human African trypanosomiasis (HAT) is available: Fexinidazole. In this case, we review the history of drug discovery for HAT with special emphasis on the discovery, pre-clinical development, and operational challenges of the clinical trials of fexinidazole. The screening of the Drugs for Neglected Diseases initiative (DNDi) HAT-library by the Swiss TPH had singled out fexinidazole, originally developed by Hoechst (now Sanofi), as the most promising of a series of over 800 nitroimidazoles and related molecules. In cell culture, fexinidazole has an IC50 of around 1 µM against Trypanosoma brucei and is more than 100-fold less toxic to mammalian cells. In the mouse model, fexinidazole cures both the first, haemolymphatic, and the second, meningoencephalitic stage of the infection, the latter at 100 mg/kg twice daily for 5 days. In patients, the clinical trials managed by DNDi and supported by Swiss TPH mainly conducted in the Democratic Republic of the Congo demonstrated that oral fexinidazole is safe and effective for use against first- and early second-stage sleeping sickness. Based on the positive opinion issued by the European Medicines Agency in 2018, the WHO has released new interim guidelines for the treatment of HAT including fexinidazole as the new therapy for first-stage and non-severe second-stage sleeping sickness caused by Trypanosoma brucei gambiense (gHAT). This greatly facilitates the diagnosis and treatment algorithm for gHAT, increasing the attainable coverage and paving the way towards the envisaged goal of zero transmission by 2030.