Nifurtimox in the treatment of South American leishmaniasis

Advances in Development of New Treatment for Leishmaniasis

Leishmaniasis is a neglected infectious disease caused by several different species of protozoan parasites of the genus Leishmania. Current strategies to control this disease are mainly based on chemotherapy. Despite being available for the last 70 years, leishmanial chemotherapy has lack of efficiency, since its route of administration is difficult and it can cause serious side effects, which results in the emergence of resistant cases. The medical-scientific community is facing difficulties to overcome these problems with new suitable and efficient drugs, as well as the identification of new drug targets. The availability of the complete genome sequence of Leishmania has given the scientific community the possibility of large-scale analysis, which may lead to better understanding of parasite biology and consequent identification of novel drug targets. In this review we focus on how high-throughput analysis is helping us and other groups to identify novel targets for chemotherapeutic interventions. We further discuss recent data produced by our group regarding the use of the high-throughput techniques and how this helped us to identify and assess the potential of new identified targets.

Identification of potent chemotypes targeting Leishmania major using a high-throughput, low-stringency, computationally enhanced, small molecule screen

Patients with clinical manifestations of leishmaniasis, including cutaneous leishmaniasis, have limited treatment options, and existing therapies frequently have significant untoward liabilities. Rapid expansion in the diversity of available cutaneous leishmanicidal chemotypes is the initial step in finding alternative efficacious treatments. To this end, we combined a low-stringency Leishmania major promastigote growth inhibition assay with a structural computational filtering algorithm. After a rigorous assay validation process, we interrogated ∼200,000 unique compounds for L. major promastigote growth inhibition. Using iterative computational filtering of the compounds exhibiting >50% inhibition, we identified 553 structural clusters and 640 compound singletons. Secondary confirmation assays yielded 93 compounds with EC₅₀s ≤ 1 µM, with none of the identified chemotypes being structurally similar to known leishmanicidals and most having favorable in silico predicted bioavailability characteristics. The leishmanicidal activity of a representative subset of 15 chemotypes was confirmed in two independent assay formats, and L. major parasite specificity was demonstrated by assaying against a panel of human cell lines. Thirteen chemotypes inhibited the growth of a L. major axenic amastigote-like population. Murine in vivo efficacy studies using one of the new chemotypes document inhibition of footpad lesion development. These results authenticate that low stringency, large-scale compound screening combined with computational structure filtering can rapidly expand the chemotypes targeting in vitro and in vivo Leishmania growth and viability.

Leishmaniasis is a parasitic disease with cutaneous, mucocutaneous and visceral clinical manifestations, depending on the Leishmania spp. and human host. Globally, there are 350 million people at risk of leishmaniasis, but current treatment options rely predominantly on ancient pentavalent antimonials, which have the potential to cause serious systemic toxicity. Our research focuses on the rapid expansion of potential anti-leishmanial compounds that could function as novel chemical structures for future drug development and offer additional therapeutic options to patients with leishmaniasis. We combined high throughput screening methodologies with computational algorithms and multiple confirmatory assay formats to identify and characterize new potent L. major promastigote growth inhibitors, including one that displays in vivo activity without toxicity to human cells. Our use of a large, broadly distributed compound library enabled the identification of these new chemotypes. In addition, since this chemical library is publicly available and annotated, we were able to cross-query archived bioassays and to identify new molecular targets that may be involved in L. major growth and viability as well as identify new protein targets for future leishmanicidal drug discovery.

Treatment of cutaneous leishmaniasis

The World Health Organization estimates that approximately 400,000 new cases of leishmaniasis occur worldwide each year. Cutaneous leishmaniasis is being encountered more frequently in the United States because of increasing travel and immigration from endemic areas. The indications for treatment and recommended treatment regimens reported in the infectious disease and dermatology literature vary widely. We examine both classic and newly developed therapeutic agents and modalities for cutaneous leishmaniasis. Proper therapy depends on species identification. New World leishmaniasis, in general, requires more aggressive therapy; parenteral antimonials are the drugs of choice. Physical modalities may suffice in most cases of Old World leishmaniasis because of its strong tendency toward spontaneous resolution.

Efficacy of ketoconazole against Leishmania braziliensis panamensis cutaneous leishmaniasis

PURPOSE, PATIENTS, AND METHODS

The classic agent for cutaneous leishmaniasis is pentavalent antimony. However, there are no reports of the efficacy of antimony versus placebo or of the efficacy of any alternative therapy versus either antimony or placebo. In the present report, the oral antifungal agent ketoconazole (600 mg/day for 28 days) was compared to a recommended regimen of intramuscular Pentostam (20 mg antimony/kg, with a maximum of 850 mg antimony/day, for 20 days) in a randomized study of the treatment of Panamanian cutaneous leishmaniasis due to Leishmania braziliensis panamensis. A separate group of patients with this disease was administered placebo.

RESULTS

Ketoconazole clinically cured 16 of 21 (76%) patients. The lesions on nine patients healed by 1 month after therapy, and the lesions healed by 3 months after therapy on the other seven patients. Side effects were limited to a 27% incidence of mild, reversible hepatocellular enzyme elevation and an asymptomatic, reversible, approximately 70% decrease in serum testosterone in all patients. Pentostam cured 13 of 19 (68%) patients; the lesions on seven patients healed by the end of therapy, and the lesions on four other patients healed by 1 month after the end of therapy. Side effects were a 47% incidence of mild, reversible hepatocellular enzyme elevation and the morbidity due to 20 intramuscular injections in almost all patients. The placebo group of 11 patients had a 0% cure rate. By 1 month after therapy, all placebo-treated patients demonstrated new lesions or one lesion that was 23% to 875% larger than before therapy.

CONCLUSION

Both ketoconazole and Pentostam were more effective than placebo against L. braziliensis panamensis cutaneous leishmaniasis. Oral ketoconazole is comparable in efficacy to this parenteral Pentostam regimen and can be recommended as initial treatment for this disease.

Long-term follow-up of patients with Leishmania (Viannia) braziliensis infection and treated with Glucantime

Seventy-nine patients with cutaneous (62) or mucosal (17) infection with Leishmania (Viannia) braziliensis in Três Braços, Bahia, Brazil, were followed for at least 4 years after initiating treatment with antimony. Cutaneous relapses occurred in 6/62 (10%), mucosal relapse after cutaneous infection in 2/62 (3%), and mucosal relapse after mucosal disease in 2/17 (17%). It is concluded that relapse (cutaneous and mucosal) is rare after adequate antimony therapy and that no definite prediction of relapse (clinical, serological or by skin reaction) is possible.

Karyotype analysis of Leishmania species and its use in classification and clinical diagnosis

Chromosomes of four species of Leishmania represented by ten different geographic isolates were analyzed by pulsed field gradient gel electrophoresis (PFG) to assess chromosome stability in these parasitic protozoans. Among different geographic isolates of the same subspecies, more than two-thirds of chromosomes had similar sizes, ethidium bromide staining intensities, and locations of alpha,beta-tubulin genes. However, among New World Leishmania, members of different species or subspecies have fewer than one-third of their chromosomes in common. Therefore, PFG karyotypes of Leishmania exhibit intraspecific variability similar to that reported for other parasitic protozoans. The greater similarities of the karyotypes of members of the same Leishmania subspecies may indicate that they represent valid taxa. These similarities also allowed the use of PFG in clinical diagnosis for rapid and accurate typing of patient isolates.

Mucosal leishmaniasis ("espundia" Escomel, 1911)

One of the more serious clinical forms of leishmaniasis occurs in espundia when the mucosae of the upper respiratory passages are inflamed. This complication is a metastasis from a skin lesion caused by Leishmania braziliensis braziliensis (Lbb) although cases have been described associated with other leishmanial species. Epidemiological data suggest that a detectable mucosal metastasis occurs in fewer than 5% of patients infected with Lbb in our study area. The determinants of this complication are still largely obscure. The granuloma usually commences on the nasal septum. In about two-thirds of our patients the lesion remained restricted to the nose. In the rest the pharynx, palate, larynx and lips were involved, in this order. It is often difficult to isolate the parasite and for routine diagnosis the leishmanin skin reaction and serological tests are helpful. Although a serious condition, with possible mutilation and even death as subsequent complications, treatment is still mainly with pentavalent antimonials, introduced 40 years ago. These are most unsatisfactory for field use, being given parenterally and relatively toxic. In mucosal leishmaniasis, if sufficient antimony can be administered in a regular daily dose, the relapse rate is small (3 of 42 patients followed for a mean of 5 years). Also, antimony treatment of the initial skin ulcer due to Lbb followed for a mean of 4 years of 83 patients resulted in subsequent mucosal metastasis in only 2. Since espundia is relatively rare, specific treatment targeted to this specific problem is the efficient short term solution. At present there is no satisfactory alternative drug to those in current use.

A common major surface antigen on amastigotes and promastigotes of Leishmania species

Enzymatic surface iodination and biosynthetic labeling with [35S]methionine, combined with immunoprecipitation by sera from patients with different forms of Leishmaniasis revealed a 65,000 Mr glycoprotein as the immunodominant moiety in promastigotes and amastigotes of the nine Leishmania species and isolates examined. Sera from patients with one form of Leishmaniasis recognized this component strongly, not only in the homologous, but also in the heterologous species. In addition to the crossreactivity displayed by immune sera, the 65,000 Mr glycoprotein (gp) common to all Leishmania species presented a characteristic shift to Mr 50,000 when samples were run in sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. These results are in agreement with our previous studies (7), where a simple and similar profile was obtained for several geographic isolates of L. donovani, with a major surface glycoprotein of 65,000 Mr displaying the same characteristics described here. The structural similarity of the major 65,000 Mr gp of the six Leishmania species was demonstrated by Cleveland mapping. It is suggested that immunological specificities may be contributed by minor differences in glycosylation of this molecule. In keeping with recent data (13-15), where strong cross protection among different Leishmania species has been obtained by prophylactic immunization with irradiated whole promastigotes, this glycoprotein may be a good candidate for an antigen to be used for immunoprophylaxis of all forms of Leishmaniasis.

A focus of mucocutaneous leishmaniasis in Três Braços, Bahia, Brazil: characterization and identification of Leishmania stocks isolated from man and dogs

The characterization and identification to species and subspecies of 20 stocks of Leishmania isolated from the region of Três Braços, Bahia, Brazil, are described: 17 stocks were from patients and three from dogs. The following techniques were used (i) biological (growth in culture, hamster tissues and phlebotomine gut), (ii) biochemical (isoenzyme and kinetoplast DNA analysis) and (iii) immunological (using monoclonal antibodies). All except two stocks belong to the L. braziliensis complex. One of these two corresponded to L. mexicana amazonensis but the other, while clearly in the mexicana complex, showed slight differences from the L. mexicana amazonensis reference strain on isoenzyme analysis. Two stocks from different lesions in the same patient and with different growth characteristics in hamster tissues were both identified as L. braziliensis braziliensis. All the fully characterized stocks of the L. braziliensis complex were identified as L. braziliensis braziliensis. L. braziliensis guyanensis was not identified. Dog and human stocks of L. braziliensis braziliensis were indistinguishable. From these findings and other evidence, L. braziliensis braziliensis seems to be the predominant species transmitted in Três Braços.

Leishmaniose mucocutânea humana em Três Braços, Bahia - Brasil: uma área de transmissão de Leishmania braziliensis braziliensis. III. Comprometimento mucoso e evolução inicial

Numa análise de 57 pacientes o acometimento da mucosa foi mais comumente observado em homens (77%) na terceira década de vida, embora fosse grande a variação das idades e ocorrendo mesmo o acometimento de duas crianças. Com a exceção de nove pacientes (16%) todos os outros tinham sinais de leishmaniose cutânea sendo que em somente oito (14%) de lesão era ativa. O acometimento do nariz foi observado em 100% de 19 pacientes que apresentavam lesões múltiplas e em 92% de 38 pacientes apresentando uma única lesão. A faringe, palato, laringe e lábio superior foram afetados nesta experiência. 42% dos pacientes com lesões múltiplas apresentavam acometimento da laringe sendo que em dois pacientes a única lesão existente apresentava-se neste ponto. Não foi observada qualquer diferença relacionada com a idade no que se referia à existencia de lesões únicas ou múltiplas. A duração do acometimento da mucosa variou de menos de 4 até 264 meses. Somente 7% desenvolveram o acometimento da mucosa após mais de dez anos o desenvolvimento da lesão cutânea. Os pacientes usualmente responderam ao tra-tamento adequado por antimonial embora em algumas exceções fosse usada amphotericina B. Morreram três pacientes que se recusaram a colaborar no tratamento. Dois anos após o tratamento observou-se positividade de anticorpos fluorescentes em somente 18% dos pacientes entre aqueles acompanhados.

Human mucocutaneous leishmaniasis in Três Braços, Bahia - Brazil: an area of Leishmania braziliensis braziliensis transmission. II. Cutaneous disease. Presentation and evolution

The clinical records of 182 patients with cutaneous leishmaniasis probably due to Leishmania braziliensis braziliensis are analysed. 68% had a single lesion which was usually an ulceron the lower anterior tibial third. Many had short histories of one to two months and all age groups were represented 13% had closed lesions of a verrucose or plaque like nature. Evolution of these skin lesions after treatment was related to the regularity of antimony therapy. Although healing usually occurred in three months, the time to scarring after commencing treatment was variable and related to the size ofthe lesion (p < 0.01). Usually if sufficient antimony treatment was given the lesion closed. Seven of the ten patients with initially negative leishmanin skin tests converted to positive after treatment. A significant decline of indirect fluorescent antibody titres occurred in patients followed, during and after therapy.

Further trials of nifurtimox in mucocutaneous leishmaniasis

At a dosage level of 8 to 10 mg/kg body-weight daily for 120 days nifurtimox was associated with clinical healing of cutaneous leishmaniasis in five of eight patients. At a dosage level of 20 mg/kg body-weight daily for 10 days in six of 10 patients the skin ulcer healed. Results and the reasons why both schemes are impracticable are briefly discussed.

A histological classification of mucocutaneous leishmaniasis in Brazil and its clinical evaluation

Biopsies of skin and mucosal lesions were made on 60 well documented Brazilian patients with untreated cutaneous or mucocutaneous leishmaniasis, whose response to treatment was subsequently evaluated in 38 cases. The biopsies were examined with a view to classification after correlation with clinical and immunological findings. Although there was no simple or unified spectrum, five histological groups were defined and found to have some clinico-prognostic significance. In two groups the cases were all cutaneous with a relatively good prognosis. In another two groups they were evolving as mucocutaneous with a poor prognosis. The fifth group showed mixed characteristics with a tendency to relapse. There was no strong correlation with serum antibodies or Montenegro skin test, which were usually positive, or with parasite load, which was always low. The tissue response was distinguished from that in oriental sore by the degree of connective tissue involvement in all groups. It was the primary response in two groups, and subsidiary to a mono-nuclear response in the others. It suggested damage due to extra-cellular parasites or immune complexes. It did not correlate with the distinction between cutaneous and mucocutaneous disease. The single, most favourable, prognostic feature in either the cellular or connective tissue component was necrosis with a reactive response.