Chagas disease, caused by Trypanosoma cruzi (T. cruzi), is a serious public health problem. Current treatment is restricted to two drugs, benznidazole and nifurtimox, displaying serious efficacy and safety drawbacks. Nucleoside analogues represent a promising alternative as protozoans do not biosynthesize purines and rely on purine salvage from the hosts. Protozoan transporters often present different substrate specificities from mammalian transporters, justifying the exploration of nucleoside analogues as therapeutic agents. Previous reports identified nucleosides with potent trypanocidal activity; therefore, two 7-derivatized tubercidins (FH11706, FH10714) and a 3′-deoxytubercidin (FH8513) were assayed against T. cruzi. They were highly potent and selective, and the uptake of the tubercidin analogues appeared to be mediated by the nucleoside transporter TcrNT2. At 10 μM, the analogues reduced parasitemia >90% in 2D and 3D cardiac cultures. The washout assays showed that FH10714 sterilized the infected cultures. Given orally, the compounds did not induce noticeable mouse toxicity (50 mg/kg), suppressed the parasitemia of T. cruzi-infected Swiss mice (25 mg/kg, 5 days) and presented DNA amplification below the limit of detection. These findings justify further studies with longer treatment regimens, as well as evaluations in combination with nitro drugs, aiming to identify more effective and safer therapies for Chagas disease.

Chemotherapy for cutaneous leishmaniasis is hindered by high toxicity, adverse effects, and increasing drug resistance. Thus, safer and more selective therapies are urgently required. Here, we evaluated the antiparasitic efficacy of methylene blue (MB) and new MB, as well as novel ruthenium complex derivatives (NMB-B and NMB-P) against promastigote and amastigote forms of Leishmania amazonensis. Their cytotoxicity and selectivity on L929, HepG2, VERO, J774.G8 cells, and murine peritoneal macrophages were measured. Mechanisms of action were explored via flow cytometry, assessing morphological changes, mitochondrial depolarization, ROS production, and cell death. The compounds inhibited parasite proliferation in a dose and time-dependent manner, achieving submicromolar efficacy against amastigotes (NMB-P = 0.46 μM). No cytotoxicity was observed on L929, J774.G8, and VERO cells (except NMB), while HepG2 and murine peritoneal macrophages showed low to moderate toxicity. Selective indexes reached 84 for promastigotes and over 500 for amastigotes. The compounds induced mitochondrial depolarization by up to 61% and a five-fold increase in ROS levels, leading to structural damage and parasite death via late apoptosis/necrosis-like mechanisms. These findings indicate that the compounds act selectively and trigger the release of oxidative species, exerting leishmanicidal activity and warranting further investigation.