Preparation and characterisation of amphotericin B-copolymer complex for the treatment of leishmaniasis

Abstract

A copolymer was used as a platform for solubilisation of an anti-leishmanial agent. A non-covalent complex of amphotericin B (AmB) and poly(vinylpyrrolidone-co-methacrylic acid) (PVM) sodium salt was prepared from a N-hydroxysuccinimide (NHS) active ester precursor polymer in an effort to improve the therapeutic index of AmB. Leishmaniasis is a neglected disease that can be effectively treated with AmB. Unfortunately AmB is poorly soluble and highly prone to aggregation and degradation. It is also toxic and the lipid formulations of AmB that can mediate this toxicity are too expensive and unstable to use in resource-limited regions of the world. We hypothesised that replacement of the lipids with an appropriate water-soluble polymer would be a viable strategy to address the issues of AmB solubility, toxicity and cost of the final medicine. Copolymer precursors of PVM were prepared using different ratios of the monomers, N-1-vinyl-2-pyrrolidone and N-methacryloxysuccinimide. Complexation of AmB was achieved by hydrolysis of the NHS moiety as a DMSO solution of the copolymer precursor and AmB was diluted with sodium hydroxide and water. The free AmB was removed from the AmB–PVM complex, and then freeze dried to give water-soluble (2 mg mL⁻¹ AmB equivalents) complexes with AmB loadings ranging from 20 to 30 wt%. The AmB–PVM complex reduced the toxicity of AmB towards mammalian cells (THP-1 and KB cells) while retaining its activity against intracellular L. major amastigotes in macrophages derived from THP-1 cells. The EC₅₀ of the complex ranged between 0.08 and 0.18 μg mL⁻¹ which is quite similar to clinical AmB (Fungizone®) (0.06 ± 0.01 μg ml⁻¹). Our results show that there is potential to develop safe and effective AmB–polymer complexes to treat leishmaniasis.