Refractoriness to the treatment of sodium stibogluconate in Indian kala-azar field isolates persist in in vitro and in vivo experimental models

Ever since their discovery about 60 years ago as therapeutic agent for visceral leishmaniasis (VL) or kala-azar, pentavalent antimonials (Sb-v) have remained the first line treatment of choice all over the world including India. But recently, the number of kala-azar patients unresponsive to sodium stibogluconate (SSG) therapy, is steadily increasing in India. In this study, three clinical isolates, of which two were from SSG unresponsive and one from SSG responsive patients were evaluated for their infectivity and for their chemotherapeutic responses in vitro (macrophage-amastigote system) and in vivo (in hamsters). Persistence of SSG resistance was also checked by repeated passages in vitro as well as in vivo. The drug resistant strains (2039 and 2041) did not respond to SSG therapy both in vitro as well as in vivo but strains 2001 and Dd8 showed full sensitivity to SSG treatment. All the four strains responded well to amphotericin B and miltefosine treatment both in macrophages and in hamsters. The specific chemotherapeutic responses of all the strains to SSG were consistently persistent after repeated passages in cultures and in vivo, which indicates that these isolates are truly refractory to SSG treatment in field conditions. Two isolates were also transfected with green fluorescent protein (GFP) for the development of in vitro assay for studying antileishmanial activities of new and reference drugs in macrophages by flow cytometry.