# Nucleoside Analogue with Thymidine Nucleobase Inhibits Leishmania infantum and Depolarizes the Plasma Membrane Potential In Vitro

## TL;DR

A new nucleoside analogue shows promise as a potential treatment for leishmaniasis by targeting the parasite's plasma membrane.

## Contribution

A thymidine nucleoside analogue (compound 5) was identified as a selective and effective antileishmanial agent with low cytotoxicity.

## Key findings

- Compound 5 inhibited Leishmania infantum amastigotes with an EC50 of 8.02 μM.
- Compound 5 depolarized the plasma membrane potential of Leishmania parasites without causing membrane damage.
- Compound 5 showed low cytotoxicity and nonhemolytic activity in mammalian cells.

## Abstract

Visceral leishmaniasis,
caused by the protozoan parasites Leishmania infantum or L. donovani, remains a lethal
neglected tropical disease without effective therapy.
Current drugs available are toxic, leading to severe side effects,
treatment abandonment, and resistance, underscoring the urgent need
for new therapeutic options. As Leishmania spp. are auxotrophic for purines, they rely on the purine salvage
pathway for their nucleotide biosynthesis. Consequently, nucleoside
analogues (NAs) represent a promising class of compounds for the design
of antiparasitic agents. This study aimed to investigate the in vitro
antileishmanial activity of NA compounds and the cellular alterations
induced by treatment. Twelve NA compounds were screened for antileishmanial
activity against promastigote and amastigote forms of L. infantum and cytotoxic effects in mammalian cells.
Among all compounds evaluated, six of them demonstrated antipromastigote
activity, exhibiting 50% effective concentration (EC50)
values ranging from 9.29 to 76.74 μM. As for amastigote activity,
two compounds, 5 and 10, were effective,
with values of EC50 of 8.02 and 31.95 μM, respectively.
Only compound 1 maintained cellular viability at the
maximum concentration tested (>200 μM). The selective index
for the derivatives investigated ranges from 0.5 to 4.2. Compound 5, a tritylated thymidine NA, the most active, was further
subjected to analysis of cellular alterations using fluorescent-based
approaches. This analogue demonstrated a lack of cytotoxicity against
murine peritoneal macrophages up to 50 μM and nonhemolytic activity
up to 100 μM. When applied at EC50, it did not cause
damage to plasma membrane permeability, the integrity of the genetic
material, acidocalcisomes, intracellular Ca2+, and ROS
levels of treated Leishmania parasites. However,
it caused depolarization of the plasma membrane potential, leading
to cell death. Further studies are also necessary to understand the
enzymatic action of this most active compound, and optimization is
required to develop more effective and safer antileishmanial lead
compounds. In conclusion, compound 5 might be a suitable
candidate for the development of antileishmanial agents.