Branched alkyl of phenyl 4-(2-oxo-3-alkylimidazolidin-1-yl)benzenesulfonates as unique cytochrome P450 1A1-activated antimitotic prodrugs: Biological evaluation and mechanism of bioactivation.

We recently discovered a new family of prodrugs deriving from phenyl 4-(2-oxo-3-imidazolidin-1-yl)benzenesulfonates (PIB-SOs) bioactivatable by cytochrome P450 1A1 (CYP1A1) into potent antimitotics referred to as phenyl 4-(2-oxo-3-alkylimidazolidin-1-yl)benzenesulfonates (PAIB-SOs). PAIB-SOs display significant selectivity toward human breast cancer cells based on the N-dealkylation of PAIB-SOs into their corresponding PIB-SOs by CYP1A1. In this study, we have evaluated the molecular mechanism of the bioactivation of PAIB-SOs into PIB-SOs by branching the linear alkyl chain on the imidazolidin-2-one (IMZ) moiety of PAIB-SOs by branched alkyl groups such as isopropyl, isobutyl and sec-butyl. Our results show that PAIB-SOs bearing an isobutyl group on the IMZ moiety and either a methoxy, a chloro or a bromo group at positions 3, 3,5 or 3,4,5 on the aromatic ring B exhibit antiproliferative activity ranging from 0.13 to 6.9 μM and selectivity toward MCF7 and MDA-MB-468 mammary cancer cells comparatively to other cell lines tested. Moreover, the most potent and selective PAIB-SOs bearing an isobutyl group and either a 3,5-Cl (44), 3,5-Br (45) or a 3,4,5-OMe (46) on the IMZ moiety exhibit antiproliferative activity in the sub-micromolar range and high selectivity ratios toward mammary cancer cells. They stop the cell cycle of MCF7 cells in the G2/M phase and disrupt their cytoskeleton. Furthermore, our studies evidenced that PAIB-SOs bearing either an isopropyl, a sec-butyl or an isobutyl group are hydroxylated on the carbon atom adjacent to the IMZ (Cα-OH) but only PAIB-SOs bearing an isobutyl group are bioactivated into PIB-SOs. Finally, PAIB-SOs 45 and 46 exhibit low toxicity toward normal cells and chick embryos and are thus promising antimitotic prodrugs highly selective toward CYP1A1-expressing breast cancer cells.