Photodynamic therapy towards inactivation of miltefosine-resistant Leishmania amazonensis

Abstract

INTRODUCTION: Cutaneous leishmaniasis (CL) is a chronic disease developed by Leishmania parasites that promotes destructive lesions. The emergence of drug-resistant parasites has been related to the misuse of drugs, being a major threat to global health. Although antimicrobial photodynamic therapy (APDT) has been reported as an attractive treatment against a broad spectrum of drug-resistant pathogens, the use of APDT against drug-resistant Leishmania parasites has never been explored. OBJECTIVES: This study aimed to explore the effects of methylene blue-mediated APDT (MB-APDT) on promastigotes and intracellular amastigotes of two different strains of Leishmania amazonensis, a wild-type (WT) and a miltefosine-resistant cell line (MFR). MATERIALS AND METHODS: Promastigotes and intracellular amastigotes were treated at different concentrations of miltefosine. Regarding APDT, we used a red LED (λ= 660±22 nm) at 20 mW/cm 2 and two MB concentrations. Parasites were exposed to radiant exposures of 0 to 25 J/cm 2 .DISCUSSION AND RESULTS: The miltefosine concentration necessary to reduce 50% (EC50) MFR promastigotes was found to be 5.6-fold higher than that of the WT strain. Amastigotes were even more resistant, and the concentration needed to effectively kill MFR was not able to be calculated once it was toxic to health macrophages. Differently, both promastigotes and intracellular amastigotes were susceptible to MB-APDT. Indeed, promastigotes were equally susceptible to treatment regardless of the MB concentration. EC50 calculated for the light dose delivered was nearly 3 J/cm2, which corresponds to an exposure time of 150 s. Surprisingly, amastigotes of MFR were more susceptible to MB-APDT at 50 μM MB concentration, and the light dose necessary to reduce 50% of resistant parasites was half of that of the WT strain (2.3 J/cm 2 and 4.7 J/cm 2 , respectively). CONCLUSION: These results indicate that MB-APDT could be a promising treatment to overcome the global issue of antileishmanial drug resistance in CL.