Cytotoxicity and Biotransformation of the Anticancer Drug Perillyl Alcohol in PC12 Cells and in the Rat

Abstract

The cytotoxic monoterpene perillyl alcohol (POH) has anticancer properties. We investigated its cytotoxicity in PC12 cells in relation to its biotransformation. POH is oxidized by alcohol dehydrogenase and aldehyde dehydrogenase to perillaldehyde (PCO) and perillic acid (PCOOH), respectively. Apoptosis was determined by cell cycle (subG0G1) analysis and AnnexinV staining followed by flow cytometry. PCO caused apoptosis at 200 μM, POH caused apoptosis from 500 μM on, while PCOOH had no effect. The caspase inhibitor zVAD prevented apoptosis. Inhibition of POH oxidation by 4-methylpyrazol did not prevent the apoptotic effect of POH indicating that POH itself is also apoptotic. To find out to what extent POH is metabolized to PCO, the metabolism of POH, PCO, and PCOOH was determined after intravenous injection in the rat and in isolated hepatocytes. Although PCO can form a glutathione conjugate(s), no indication of the formation of GSH conjugates was found either in vivo or in hepatocytes. About 70% of the dose was recovered as glucuronides in bile and urine. PCOOH generated only the acyl glucuronide, while POH and PCO formed both acyl and ether glucuronides. These results indicate that PCO is a major intermediary metabolite of POH in the rat in vivo and suggest that PCO may contribute to the anticancer effect of POH.