To reduce the pervasive toxicity of natural shikonin, alkannin, and their synthetic analogues and to enhance the selectivity of these chemotherapeutics toward cancer cells, a novel 5,8-dimethyl alkannin oxime derivative (DMAKO-20) was designed, synthesized, and evaluated for its strong antitumor activity both in vitro and in vivo. It showed potent growth inhibitory effects against HCT-15, HCT-116, and K562 cells (IC50 < 1 μM), moderate antiproliferative activity toward MDA-MB-231, HepG2, PANC, Bel7402, and MGC803 cancer cells (IC50 < 10 μM), and was nontoxic to the human normal VEC and HSF cells. In vivo efficacy studies demonstrated that DMAKO-20 (10 mg/kg, i.v. on every the other day, 8 times in 14 days) resulted in 59.3% reduction in HCT-15 xenograft volume. It was as effective as the toxic antimetabolite 5-FU but revealed neither toxicity nor death in mice. The mechanistic investigations indicated that DMAKO-20 underwent the tumor-specific CYP1B1-catalyzed bioactivation to afford nitric oxide and active naphthoquinone mono-oximes, which exhibited combined anticancer effects. It was defined as a representative of the "Multi-target Anticancer Prodrugs Activated by Specific Enzymes in cancer cells". The produced active metabolites exerted anticancer effects by the direct nucleophilic alkylation and the induction of the apoptosis of cancer cells through activation of the mitochondrial pathway. The discovery of DMAKO-20 and the illustration of its molecular mechanisms may provide a new strategy to overcome the nonselective toxicity of the current chemotherapeutics.
Keywords: CYP1B1; DMAKO-20; anticancer prodrugs; in vivo efficacy; shikonin derivatives.