Comparative in vitro Susceptibility of Clinical Leishmania Isolates to Miltefosine and Oleylphosphocholine

Ali Khamesipour¹minoo Tasbihi¹Akram Mir Amin Mohammadi¹Jodie Dixon²David J Clark³Henry M Staines³Sanjeev Krishna^3,4,5,6Vanessa Yardley⁷Simon L Croft⁷Neal Alexander⁸Katrien Van Bocxlaer^2*

• ¹Tehran University of Medical Sciences Center for Research and Training in Skin Diseases and Leprosy, Tehran, Iran
• ²Hull York Medical School, York, United Kingdom
• ³City St George's University of London Institute for Infection and Immunity, London, United Kingdom
• ⁴St George's University Hospitals NHS Foundation Trust, London, United Kingdom
• ⁵Institut für Tropenmedizin, Universitätsklinikum Tübingen, Tübingen, Germany
• ⁶Centre de Recherches Medicales de Lambarene, Lambarene, Gabon
• ⁷London School of Hygiene & Tropical Medicine Department of Infection Biology, London, United Kingdom
• ⁸London School of Hygiene & Tropical Medicine Faculty of Epidemiology and Population Health, London, United Kingdom

Cutaneous leishmaniasis (CL) is a neglected tropical disease caused by protozoan parasites of the genus Leishmania. It poses a significant global health burden particularly because treatment options are limited. More effective and safe treatments are urgently needed. In previous studies, oleylphosphocholine (OlPC), a novel investigational compound structurally related to miltefosine, exhibited comparable activity to miltefosine in intramacrophage assays across various CL-causing laboratory strains and demonstrated superior efficacy in an experimental CL model. This study investigated the in vitro activity of OlPC against clinical isolates of Leishmania spp., comparing its activity to standard antileishmanial drugs including miltefosine, amphotericin B and pentavalent antimonial agents. Seventy ex vivo isolates (L. major and L. tropica), directly obtained from CL patients before any treatment, were used to capture the diversity of drug susceptibilities in circulating parasite populations. Dose-response curves were fitted using a four-parameter log-logistic model to estimate EC50 and EC90 values. Additionally, a linear mixed-effects model was applied to examine the influence of drug type and species on EC50 values while accounting for within-isolate variability. Our findings indicate that OlPC exhibits potent in vitro antileishmanial activity, exceeding that of miltefosine using our in vitro intramacrophage model. To facilitate this analysis for others, we provide a dedicated wrapper function in R, designed to simplify curve fitting and parameter estimation, making the process more accessible to researchers.