Screening of Drug Metabolizing Enzymes for the Ginsenoside Compound K In Vitro: An Efficient Anti-Cancer Substance Originating from Panax Ginseng

Ginsenoside compound K (CK), a rare ginsenoside originating from Panax Ginseng, has been found to possess unique pharmacological activities specifically as anti-cancers. However, the role of cytochrome P450s (CYPs) in the metabolism of CK is unclear. In this study, we screened the CYPs for the metabolism of CK in vitro using human liver microsomes (HLMs) or human recombinant CYPs. The results showed that CK inhibited the enzyme activities of CYP2C9 and CYP3A4 in the HLMs. The K-m and V-max values of CK were 84.20+/-21.92 mu M and 0.28+/-0.04 nmol/mg protein/min, respectively, for the HLMs; 34.63+/-10.48 mu M and 0.45+/-0.05 nmol/nmol P450/min, respectively, for CYP2C9; and 27.03+/-5.04 mu M and 0.68+/-0.04 nmol/nmol P450/min, respectively, for CYP3A4. The IC50 values were 16.00 mu M and 9.83 mu M, and K-i values were 14.92 mu M and 11.42 mu M for CYP2C9 and CYP3A4, respectively. Other human CYP isoforms, including CYP1A2, CYP2A6, CYP2D6, CYP2E1, and CYP2C19, showed minimal or no effect on CK metabolism. The results suggested that CK was a substrate and also inhibitors for both CYP2C9 and CYP3A4. Patients using CK in combination with therapeutic drugs that are substrates of CYP2C9 and CYP3A4 for different reasons should be careful, although the inhibiting potency of CK is much poorer than that of enzyme-specific inhibitors.