Microbial-catalysed derivatization of anti-cancer drug exemestane and cytotoxicity of resulting metabolites against human breast adenocarcinoma cell line (MCF-7) in vitro.

Structural transformation of anticancer drug exemestane (1) with fungi Cunninghamella blakesleeana (ATCC 8688A), Curvularia lunata (ATCC 12017), Aspergillus niger (ATCC 10549), and Gibberella fujikuroi (ATCC 10704) yielded eleven metabolites 2-12, in which 2 and 8 were identified as new. Their structures were characterized as 6-methylene-5α-androstane-3β,16β,17β-triol (2), 17β-hydroxy-6-methyleneandrosta-4-ene-3-one (3), 6α-spiroxirandrost-4-ene-3,17-dione (4), 6-methyleneandrosta-4-ene-3,17-dione (5), 6β,17β-dihydroxyandrost-4-en-3-one (6), 17β-hydroxy-6α-spiroxirandrost-1,4-diene-3-one (7), 17β-hydroxy-6α-hydroxymethylandrosta-1,4-dien-3-one (8), 6α-hydroxymethylandrosta-1,4-diene-3,17-dione (9), 17β-hydroxy-6-methyleneandrosta-1,4-diene-3,16-dione (10), 6α-hydroxy-4-androstene-3,17-dione (11), and 6α-hydroxymethylandrost-4-ene-3,17-dione (12). Substrate 1, and its transformed products were evaluated for their cytotoxicity against breast cancer cell line (MCF-7). Compound 3 was found to be moderately active with an IC50 of 33.43±4.01μM, in comparison to the standard anti-cancer drug, doxorubicin (IC50 =0.92±0.1μM).