Assay development in leishmaniasis drug discovery: a comprehensive review

ABSTRACT

Introduction

Cutaneous, muco-cutaneous and visceral leishmaniasis occur due to an infection with the protozoan parasite Leishmania. The current therapeutic options are limited mainly due to extensive toxicity, emerging resistance and variation in efficacy based on species and strain of the Leishmania parasite. There exists a high unmet medical need to identify new chemical starting points for drug discovery to tackle the disease.

Areas covered

The authors have highlighted the recent progress, limitations and successes achieved in assay development for leishmaniasis drug discovery.

Expert opinion

It is true that sophisticated and robust phenotypic in vitro assays have been developed during the last decade, however limitations and challenges remain with respect to variation in activity reported between different research groups and success in translating in vitro outcomes in vivo. The variability is not only due to strain and species differences but also a lack of well-defined criteria and assay conditions, e.g. culture media, host cell type, assay formats, parasite form used, multiplicity of infection and incubation periods. Thus, there is an urgent need for more physiologically relevant assays that encompass multi-species phenotypic approaches to identify new chemical starting points for leishmaniasis drug discovery.

KEYWORDS:

• Leishmania
• leishmaniasis
• high-throughput screening
• high content imaging
• assay
• neglected tropical diseases
• drug discovery

Article highlights

• Leishmaniasis is a global health problem that disproportionally affects the poorest people, living in remote, isolated communities with limited access to medical care.

• Current drugs are toxic, consist of prolonged and complicated administration schedules and resistance are an increasing problem. The predictive value for identifying promising anti-leishmanial compounds for development using promastigote or axenic amastigote assays is highly debatable when compared to intracellular amastigote assays.

• HCI assays have revolutionized drug discovery efforts for leishmaniasis; they are highly sensitive, mimicking the pathophysiological properties of the disease more accurately, providing multiplexing of different parameters/measurements, such as infectivity ratio, cellular morphology, protein expression and reduced artifact interference.

• The key differences in available HCI assays include variations in host cell type and activation, parasite species and strains, metacyclic promastigotes isolation methods, whether promastigotes or axenic amastigotes used to infect cells, incubation times and detection markers for the intracellular amastigotes.

• The biodiversity of the different species, strains and different parasite stages is a contributing factor in in vitro data variation observed between different research groups, resulting in a lack of in vivo and clinical translation.

• Increased understanding of the parasite–host relationship, and the impact on compound efficacy, is essential for improved translation of drug discovery efforts.

This box summarizes key points contained in the article.

Declaration of interest

B Zulfiqar and VM Avery undertake Leishmania based drug discovery research funded by the Drugs for Neglected Diseases Initiative (DNDi), which is independent of their personal views conveyed here. The authors also perform support work for Griffith University within the Discovery Biology laboratories. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This paper was not funded.