Phytochemical mediated modulation of breast cancer resistance protein at the blood brain barrier and blood cerebrospinal fluid barrier

Abstract

Drug delivery to the central nervous system (CNS) is significantly hindered by thepresence of the blood brain barrier (BBB) and blood cerebrospinal fluid barrier(BCSFB) and associated drug efflux transporter proteins. The aim of this work was to modulate the expression of breast cancer resistance protein (BCRP) at each barrier site using phytochemical modulators. In-vitro cellular models of both the BBB (PBMEC/C1-2) and BCSFB (Z310) were utilised and 18 phytochemical modulators screened for their cellular toxicity with IC50 values for the majority of phytochemicals being in excess of 100 μM. Intracellular accumulation of H33342 was assessed in each barrier cell line to determine short-term modulation of BCRP efflux or long-term modulation of protein expression. Incubations with modulators demonstrated significant inhibition of BCRP efflux activity for a range of modulators in both cell lines with TMF (1-100 μM) demonstrating a > 6 fold increase in intracellular accumulation.Similarly, many modulators demonstrated proposed protein-level modulation of BCRP resulting in increases or decreases in H33342 accumulation following a 24 hour exposure. Western blotting subsequently confirmed that quercetin and naringin for PBMEC/C1-2 and baiclain and flavone for Z310 induced BCRP expression (to 2-3 fold of control) whereas curcumin and 17-β-estradiol for PBMEC/C1-2 and silymarin, quercetin and 17-β-estradiol for Z310 down-regulated BCRP expression (to 0.24-0.4 fold of control). This was further confirmed in substrate transport studies using permeable insert models which demonstrated functional changes in the permeabilityof BCRP substrates across both barrier models.Subsequently the regulation of BCRP by AhR was confirmed through siRNAknockdown of AhR, which resulted in a significant decrease in BCRP geneexpression in both cell lines. Furthermore the induction/down-regulation effects on BCRP were, in general, diminished following AhR knockdown, suggesting AhR plays an important role in mediating the genomic/proteomic alterations in BCRP expression when exposed to phytochemicals.