The aim of the present study was to evaluate the inhibitory potency of β-carotene on the ABC efflux transporters, as well as the reversal effect of β-carotene toward MDR cancers. The underlying molecular mechanisms and inhibitory kinetics of β-carotene on the major ABC efflux transporter, P-glycoprotein, were further investigated.
The human P-gp (ABCB1/Flp-InTM-293), MRP1 (ABCC1/Flp-InTM-293) and BCRP (ABCG2/Flp-InTM-293) stable expression cells were established by using the Flp-InTM system. The cytotoxicity of β-carotene was evaluated by MTT assay in the established cell lines, sensitive cancer cell lines (HeLaS3 and NCI-H460) and resistant cancer cell lines (KB-vin and NCI-H460/MX20). Surface protein detection assay and eFluxx-ID Green Dye assay were applied for confirmation of surface expression and function of the transporters. The transporter inhibition potency of β-carotene was evaluated by calcein-AM uptake assay and mitoxantrone accumulation assay. Further interaction kinetics between β-carotene and P-gp were analyzed by rhodamine123 and doxorubicin efflux assay. The influence of β-carotene on ATPase activity was evaluated by Pgp-GloTM Assay System.
Among the tested ABC efflux transporters, β-carotene significantly inhibited human P-gp efflux function without altering ABCB1 mRNA expression. Furthermore, β-carotene stimulated both P-gp basal ATPase activity and the verapamil-stimulated P-gp ATPase activity. In addition, β-carotene exerted partially inhibitory effect on BCRP efflux function. The combination of β-carotene and chemotherapeutic agents significantly potentiated their cytotoxicity in both cell stably expressed human P-gp (ABCB1/Flp-InTM-293) and MDR cancer cells (KB-vin and NCI-H460/MX20).
The present study indicated that β-carotene may be considered as a chemo-sensitizer and regarded as an adjuvant therapy in MDR cancer treatment.