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Tafenoquine (TFQ), an 8-aminoquinoline analogue of primaquine, which is currently under clinical trial (phase IIb/III) for the treatment and prevention of malaria, may represent an alternative treatment for leishmaniasis. In this work, we have studied the mechanism of action of TFQ against Leishmania parasites. TFQ impaired the overall bioenergetic metabolism of Leishmania promastigotes, causing a rapid drop in intracellular ATP levels without affecting plasma membrane permeability. TFQ induced mitochondrial dysfunction through the inhibition of cytochrome c reductase (respiratory complex III) with a decrease in the oxygen consumption rate and depolarization of mitochondrial membrane potential. This was accompanied by ROS production, elevation of intracellular Ca 2؉ levels and concomitant nuclear DNA fragmentation. We conclude that TFQ targets Leishmania mitochondria, leading to an apoptosis-like death process.Leishmaniasis includes a wide variety of clinical manifestations caused by the protozoan parasite Leishmania. Visceral leishmaniasis is the most severe form of the disease and is usually fatal if not treated (http://www.who.int/leishmaniasis /burden/en/). In the absence of a reliable vaccine, leishmaniasis treatment relies exclusively on chemotherapy. Resistance to organic pentavalent antimonials (until recently considered to be the standard treatment) in northeast India (4), together with the severe side effects associated with their use, has led to the use of alternative treatments based on the incorporation of drugs such as amphotericin B, miltefosine, and paromomycin into the arsenal of antileishmanial drugs (8). Nevertheless, the limited number of active drugs has prompted the WHO to recommend a combined therapy in order to extend the life expectancy of these compounds.Among the new drugs under development, sitamaquine (WR6026; GlaxoSmithKline), an 8-aminoquinoline, currently under phase IIb clinical trials, represents a promising drug for the oral treatment of leishmaniasis (35). In addition, another 8-aminoquinolines have been synthesized and evaluated for their leishmanicidal activity (29, 36). However, the leishmanicidal mechanism of 8-aminoquinolines is still unknown. Sitamaquine, for example, accumulates in the acidocalcisomes, but this organelle has been ruled out as its final target (17). The collapse of mitochondrial potential in digitonized Leishmania donovani promastigotes has also been reported (39). Tafenoquine (TFQ), formerly known as WR238605, is an analogue of primaquine with much lower toxicity than the parental drug. It has demonstrated significant leishmanicidal activity in the mouse experimental model (41) and may represent an alternative treatment for leishmaniasis.In the present study, we have shown that TFQ inhibits the mitochondrial cytochrome c reductase of Leishmania promastigotes. This inhibition causes a drop in the intracellular ATP levels of the parasite and the loss of mitochondrial membrane potential. TFQ induces ROS production and deregulation of Ca 2ϩ homeostasis, fol...

Miltefosine (hexadecylphosphocholine, MLF) is the first oral drug with recognized efficacy against both visceral and cutaneous leishmaniasis. However, some clinical studies have suggested that MLF shows significantly less efficiency against the cutaneous leishmaniasis caused by Leishmania braziliensis. In this work, we have determined the cellular and molecular basis for the natural MLF resistance observed in L. braziliensis. Four independent L. braziliensis clinical isolates showed a marked decrease in MLF sensitivity that was due to their inability to internalize the drug. MLF internalization in the highly sensitive L. donovani species requires at least two proteins in the plasma membrane, LdMT, a P-type ATPase involved in phospholipid translocation, and its ␤ subunit, LdRos3. Strikingly, L. braziliensis parasites showed highly reduced levels of this MLF translocation machinery at the plasma membrane, mainly because of the low expression levels of the ␤ subunit, LbRos3. Overexpression of LbRos3 induces increased MLF sensitivity not only in L. braziliensis promastigotes but also in intracellular amastigotes. These results further highlight the importance of the MLF translocation machinery in determining MLF potency and point toward the development of protocols to routinely monitor MLF susceptibility in geographic areas where L. braziliensis might be prevalent.Pentavalent antimonials have been the first-line treatment for both visceral leishmaniasis (VL) and cutaneous leishmaniasis (CL); however, the drugs' toxicity and the emergence of resistance in VL strains in India limit their use. Lipid amphotericin B formulations are used as the second line of treatment of VL (4). Miltefosine (hexadecylphosphocholine, MLF), registered as Impavido, has become the first oral drug with recognized efficacy for the treatment of VL and CL (16,20,21), although sensitivity to MLF and other alkyl-lysophospholipids is known to vary between Leishmania species (3,5,22). Among the different clinically relevant species studied so far, Leishmania donovani and Leishmania braziliensis seem to be the most sensitive and one of the less sensitive, respectively, at least in in vitro studies. This intrinsic MLF resistance observed in L. braziliensis has also been demonstrated in a number of clinical studies (8,(16)(17)(18). While MLF induced a rapid clinical and parasitological cure in 94% of the VL cases caused by L. donovani (2), its efficacy against CL caused by L. braziliensis was only 33% in Guatemala (16) and 58 to 88% in Bolivia (18,19).The mechanisms of action of MLF are not properly understood, but a clear correlation between the accumulation of the drug within the parasite and its toxic effects has already been described (13). Consequently, the variation in the abilities of different Leishmania species to internalize the drug seems to correlate with MLF susceptibility, as observed in different eukaryotic cells (9,15,23). MLF is primarily taken up by specific protein translocation machinery present at the plasma membrane (PM) in Leish...

Two series of novel thermally stable second-order nonlinear optical (NLO) and photochromic chromophores have been designed and synthesized. The two series of compounds were based on different combinations of donor groups (pyrrole or thienylpyrrole) which act simultaneously as -conjugated bridges, together with diazoaryl or diazothiazolyl as acceptor moieties. Their photochromic and electrochemical behavior were characterized, while hyper-Rayleigh scattering (HRS) was employed to evaluate their second-order nonlinear optical properties. The results of these studies have been critically analyzed together with two other related compounds reported earlier from our laboratories in which the thienylpyrrole system was used as the donor group keeping the functionalized diazoaryl as acceptor moiety.The measured molecular first hyperpolarizabilities and the observed photochromic behavior showed strong variations for the different donor systems used (pyrrole or thienylpyrrole) and were also sensitive to the acceptor strength of the diazenehetero(aryl) moiety.The thienylpyrrole based compounds endowed with extended -conjugated bridges and stronger donor auxiliary effects in comparison to the pyrrole compounds, when coupled to the stronger acceptor diazo(hetero)aryl groups gave rise to significantly larger hyperpolarizabilities ( = 274 -415 x 10 -30 esu) for an incident wavelength of 1064nm). These compounds also displayed improved photochromic behavior with very fast response to the visible light stimulus (1.5 s) and fast thermal return to the original forms (2-3 s).