The cytotoxic effect of P4 does not require metabolization. SK-N-AS cells were repeatedly exposed to either three higher cytotoxic concentrations (10, 20 and 40 µmol/L) of P4 alone or combined with different concentrations of finasteride for 3 and 6 d by replacing the culture medium daily containing drugs. Cell death was measured by MTT assay. Data are expressed as means ± SD of three independent experiments. Finasteride (F) could not block the cytotoxic effect of P4 (P) at any concentration.