Phytoestrogens Modulate Breast Cancer Resistance Protein Expression and Function at the Blood-Cerebrospinal Fluid Barrier

Abstract

-PURPOSE: Breast cancer resistance protein (BCRP/ABCG2) is a drug efflux transporter expressed at the blood cerebrospinal fluid barrier (BCSFB), and influences distribution of drugs into the central nervous systems (CNS). Current inhibitors have failed clinically due to neurotoxicity. Novel approaches are needed to identify new modulators to enhance CNS delivery. This study examines 18 compounds (mainly phytoestrogens) as modulators of the expression/function of BCRP in an in vitro rat choroid plexus BCSFB model. METHODS: Modulators were initially subject to cytotoxicity (MTT) assessment to determine optimal non-toxic concentrations. Reverse-transcriptase PCR and confocal microscopy were used to identify the presence of BCRP in Z310 cells. Thereafter modulation of the intracellular accumulation of the fluorescent BCRP probe substrate Hoechst 33342 (H33342), changes in protein expression of BCRP (western blotting) and the functional activity of BCRP (membrane insert model) were assessed under modulator exposure. RESULTS: A 24 hour cytotoxicity assay (0.001 µM-1000 µM) demonstrated the majority of modulators possessed a cellular viability IC50 > 148 µM. Intracellular accumulation of H33342 was significantly increased in the presence of the known BCRP inhibitor Ko143 and, following a 24 hour pre-incubation, all modulators demonstrated statistically significant increases in H33342 accumulation (P < 0.001), when compared to control and Ko143. After a 24 hour pre-incubation with modulators alone, a 0.16-2.5 -fold change in BCRP expression was observed for test compounds. The functional consequences of this were confirmed in a permeable insert model of the BCSFB which demonstrated that 17-β-estradiol, naringin and silymarin (down-regulators) and baicalin (up-regulator) can modulate BCRP-mediated transport function at the BCSFB. CONCLUSION: We have successfully confirmed the gene and protein expression of BCRP in Z310 cells and demonstrated the potential for phytoestrogen modulators to influence the functionality of BCRP at the BCSFB and thereby potentially allowing manipulation of CNS drug disposition.

MED23 in endocrinotherapy for breast cancer

“…The present study indicates that the mutual regulation between HER2 and MED23 plays a critical role in the formation of drug resistance of everolimus in human breast cancer cells (23). Effects on ER may be an important molecular mechanism of MED23 in the participation in inducing drug resistance to everolimus (24).…”

Phytoestrogens: The current state of research emphasizing breast pathophysiology

“…This study points out to the potential use of glabridin and tamoxifen in estrogen replacement therapy while negating the side effect of tamoxifen to cause endometrial cancer (Jen, Wei, & Yin, ). Further, apigenin, naringenin, quercetin, biochanin A, hesperitin, silymarin, and fistein have all reported to influence the expression of breast cancer resistance protein (Kaur & Badhan, ). Although available data show that phytoestrogens could be used as an alternative to synthetic SERMs, whether the use of phytoestrogens as SERMs is entirely beneficial remains a question.…”

Effect of Disease Pathologies on Transporter Expression and Function

“…Several transporters are present in the BBB (Figure ) to restrict access of drugs primarily to the brain . The blood–cerebrospinal‐fluid barrier (BCSFB), which lines the choroid plexus, has also been evaluated for specific transporter expression and function (Figure ) . Anatomically, the fenestrated character and lack of permeation barriers on the BCSFB make their contribution to drug resistance nominal compared with the BBB .…”

“…102 The blood-cerebrospinal-fluid barrier (BCSFB), which lines the choroid plexus, has also been evaluated for specific transporter expression and function ( Figure 3). 104,105 Anatomically, the fenestrated character and lack of permeation barriers on the BCSFB make their contribution to drug resistance nominal compared with the BBB. 106 This section of the review will discuss published findings relevant to variations in transporter expression and function across brain diseases including brain tumors, epilepsy, amyotrophic lateral sclerosis (ALS), and stroke (Table 3).…”