In Vitro characterization of narciclasine: solubility, metabolic stability, and P-glycoprotein substrate status

Background Narciclasine has demonstrated anticancer activity at low nanomolar concentrations in various preclinical cancer models, but no clinical data in cancer patients are available. Although its biological activity and structure-activity relationships are relatively well characterized, the pharmacological properties of narciclasine have not been reported. This information will benefit the research to further develop narciclasine. The goal of the current study is to characterize the physicochemical properties, metabolic stability, and P-glycoprotein substrate status of narciclasine. Methods We first developed a robust HPLC-tandem mass spectrometry assay to measure narciclasine in mouse plasma. Then, we assessed the stability, metabolic pathways, and cytochrome P450 inhibitory effect of narciclasine. We also evaluated narciclasine for its P-glycoprotein substrate status using two methods: 1) Caco-2 permeability assay, and 2) cytotoxicity assay in human cancer cells with exogenous expression of P-glycoprotein. Results Narciclasine was stable in the plasma of the four species tested. It showed metabolic stability in human liver microsomes and hepatocytes, but in other species, metabolic clearance was higher than in humans, indicating that humans may metabolize narciclasine minimally. Further studies to identify the metabolic pathway of narciclasine detected trace amounts of reduction and glucuronidation in human liver microsomes. Narciclasine was highly soluble under both thermodynamic and kinetic conditions over a range of pH values, with a lipophilicity value of 0.40, indicating it is hydrophilic. P-glycoprotein (P-gp) overexpression reduced the in vitro cytotoxicity of narciclasine less than that of another known P-gp substrate, vincristine. Conclusion Narciclasine demonstrates metabolic stability in human liver microsomes and hepatocyts, and its cancer cell penetration is minimally affected by P-glycoprotein. These data will inform future development of narciclasine as a cancer therapeutic agent.