New Insights into the Mechanism of Action of the Cyclopalladated Complex (CP2) in Leishmania: Calcium Dysregulation, Mitochondrial Dysfunction, and Cell Death.

The current treatment of leishmaniasis is based on a few drugs that present several drawbacks, such as high toxicity, difficult administration route, and low efficacy. These disadvantages raise the necessity to develop novel antileishmanial compounds allied with a comprehensive understanding of their mechanisms of action. Here, we elucidate the probable mechanism of action of the antileishmanial binuclear cyclopalladated complex [Pd(dmba)(µ-N3)]2 (CP2) in Leishmania amazonensis. CP2 causes oxidative stress in the parasite, resulting in disruption of mitochondrial Ca2+ homeostasis, cell cycle arrest at the S-phase, increasing the reactive oxygen species (ROS) production and overexpression of stress-related and cell detoxification proteins, and collapsing the Leishmania mitochondrial membrane potential, and promotes apoptotic-like features in promastigotes, leading to necrosis, or directs programmed cell death (PCD)-committed cells toward necrotic-like destruction. Moreover, CP2 reduces the parasite load in both liver and spleen in Leishmania infantum-infected hamsters when treated for 15 days with 1.5 mg/kg body weight/day CP2, expanding its potential application in addition to the already known effectiveness on cutaneous leishmaniasis for the treatment of visceral leishmaniasis, showing the broad spectrum of action of this cyclopalladated complex. The data presented here bring new insights into the CP2 molecular mechanisms of action, assisting the promotion of its rational modification to improve both safety and efficacy.

Antileishmanial activity of tetra-cationic porphyrins with peripheral Pt(II) and Pd(II) complexes mediated by photodynamic therapy.

Leishmaniasis is a neglected disease that impacts more than one billion people in endemic areas of the globe. Several drawbacks are associated with the currently existing drugs for treatment such as low effectiveness, toxicity, and the emergence of resistant strains that demonstrate the importance of looking for novel therapeutic alternatives. Photodynamic therapy (PDT) is a promising novel alternative for cutaneous leishmaniasis treatment because its topical application avoids potential side effects generally associated with oral/parenteral application. A light-sensitive compound known as photosensitizer (PS) interacts with light and molecular oxygen to generate reactive oxygen species (ROS), which promote cell death by oxidative stress through PDT approaches. Here, for the first time, we demonstrate the antileishmanial effect of tetra-cationic porphyrins with peripheral Pt(II)- and Pd(II)-polypyridyl complexes using PDT. The isomeric tetra-cationic porphyrins in the meta positions, 3-PtTPyP, and 3-PdTPyP, exhibited the highest antiparasitic activity against promastigote (IC50-pro = 41.8 nM and 46.1 nM, respectively) and intracellular amastigote forms (IC50-ama = 27.6 nM and 38.8 nM, respectively) of L. amazonensis under white light irradiation (72 J cm-2) with high selectivity (SI > 50) for both forms of parasites regarding mammalian cells. In addition, these PS induced the cell death of parasites principally by a necrotic process in the presence of white light by mitochondrial and acidic compartments accumulation. This study showed that porphyrins 3-PtTPyP and 3-PdTPyP displayed a promising antileishmanial-PDT activity with potential application for cutaneous leishmaniasis treatment.

Antileishmanial activity of amphiphilic chlorin derivatives mediated by photodynamic therapy.

Leishmaniasis is a serious and neglected disease that affects 14 million people around the World. The currently available drugs for treatment present several drawbacks such as low efficacy and severe side effects, contributing to patients' low compliance. Photodynamic therapy (PDT) is rising as a promising treatment of cutaneous leishmaniasis, mainly considering its topical administration that circumvents any potential adverse effects commonly related to oral/parenteral administration. PDT depends on the interaction between a light-sensitive compound (photosensitizer - PS), light and molecular oxygen. The reaction generates reactive oxygen species (ROS) which induce cell death by oxidative stress. The main goal of this study is to demonstrate the antileishmanial effect of three chlorin derivatives (CHL-OH-A, CHL-OH-B, CHL-TRISMA) using PDT, as well as to investigate their cell death pathway on Leishmania amazonensis promastigote forms after chlorin-PDT application. The chlorin derivatives herein studied did not exhibit aggregates in aqueous medium and showed fast accumulation in Leishmania acidic compartments. CHL-OH-A exhibited the highest antiparasitic activity at 24 h (0.33 µmol L-1) and 48 h (0.14 µmol L-1) after irradiation at 660 nm (6.0 Jcm-2). CHL-OH-A, CHL-OH-B and CHL-TRISMA molecules induced the cell death of parasites mainly by an apoptotic-like process in the presence of light. These chlorin derivatives are 80-fold more active against Leishmania when compared to other PSs reported in the literature. In this study, we have shown that these amphiphilic chlorins, and in particular, CHL-OH-A, exert an interesting leishmanicidal activity suggesting that the use of these PSs associated with PDT could be a promising strategy for treatment of cutaneous leishmaniasis.

New drugs with antiprotozoal activity from marine algae: a review

The use of indigenous or remote popular knowledge to identify new drugs against diseases or infections is a well-known approach in medicine. The inhabitants of coastal regions are known to prepare algae extracts for the treatment of disorders and ailments such as wounds, fever and stomach aches, as for the prevention of arrhythmia. Recent trends in drug research from natural sources have indicated that marine algae are a promising source of novel biochemically active compounds, especially with antiprotozoal activity. Algae survive in a competitive environment and, therefore, developed defense strategies that have resulted in a significant level of chemical structural diversity in various metabolic pathways. The exploration of these organisms for pharmaceutical and medical purposes has provided important chemical candidates for the discovery of new agents against neglected tropical diseases, stimulating the use of sophisticated physical techniques. This current review describes the main substances biosynthesized by benthic marine algae with activity against Leishmania spp., Trypanosoma cruzi and Trypanosoma brucei; the causative agents of leishmaniasis, Chagas disease and African trypanosomiasis, respectively. Emphasis is given to secondary metabolites and crude extracts prepared from marine algae.