P-glycoprotein (P-gp) is one of the highly expressed
cancer cell efflux transporters that cause the failure of
chemotherapy. To reverse P-gp induced multidrug resistance, we employed a flaxseed-derived
lignan;
secoisolariciresinol (SECO) that acts as an inhibitor of
breast cancer resistance
protein; another efflux transporter that shares some substrate/inhibitor specificity with P-gp. Molecular dynamics (MD) simulation identified SECO as a possible P-gp inhibitor. Comparing root mean square deviation (RMSD) of P-gp bound with SECO with that bound to its standard inhibitor
verapamil showed that fluctuations in RMSD were lower in P-gp bound to SECO demonstrating higher stability of the complex of P-gp with SECO. In addition, the superimposition of P-gp structures after MD simulation showed that the
nucleotide-binding domains of P-gp bound to SECO undertook a more central closer position compared with that bound to
verapamil. Using
rhodamine efflux assay on NCI/ADR-RES
cancer cells, SECO was confirmed as a P-gp inhibitor, where cells treated with 25 or 50 µM of SECO showed significantly higher fluorescence intensity compared to control. Using MTT assay, SECO alone showed dose-dependent cytotoxicity, where 25 or 50 µM of SECO caused significantly less NCI/ADR-RES cellular viability compared to control. Furthermore, when 50 µM of SECO was added to
doxorubicin (DOX), an anticancer drug, SECO significantly enhanced DOX-induced cytotoxicity compared to DOX alone. The combination index calculated by CompuSyn software indicated synergism between DOX and SECO. Our results suggest SECO as a novel P-gp inhibitor that can re-sensitize
cancer cells during DOX
chemotherapy.