Therapeutic drugs at clinically relevant levels significantly inhibit active efflux in blood brain barrier endothelial cells

M. H. Shubbar, J. I. Penny. Pharmacy and optometry, University of Manchester, Manchester, United Kingdom.

Introduction: The Food and Drug Administration have highlighted the increasing importance of interactions between therapeutic drugs and transporters, including ATP-binding cassette (ABC) efflux transporters [1]. Modulation (inhibition or induction) of ABC transporters can dramatically alter pharmacokinetics leading to unexpected toxicities or sub-optimal treatment. Blood-brain barrier endothelial cells express high levels of ABCB1 and ABCG2 that are protective in function. However, many widely prescribed therapeutic drugs are ABCB1 and ABCG2 substrates, and modulation of their activities may influence CNS drug penetration of ABCB1 and ABCG2 substrates [2].

Methods: Primary porcine brain endothelial cells (PBECs) were isolated and maintained as described previously [3]. The effect of 1.5 μM telmisartan, 5.5 μM pantoprazole, 7 μM quinidine, 2.5 μM sulfasalazine and 4 μM nefazodone, i.e. reported plasma concentrations, on cell viability was measured using the Neutral Red assay. The impact of drugs on ABCB1 and ABCG2 transporter activity was determined by measuring intracellular calcein and Hoechst 33342 accumulation, respectively, in cells pre-treated with these drugs.

Results: At the concentrations used, no drug significantly affected the viability of PBECs. Significant increases in intracellular accumulation of calcein, indicating significant (*p<0.05) inhibition of ABCB1, were observed when PBECs were treated with telmisartan, quinidine, and nefazodone by 276, 580 and 488 % RFU.μg protein^-1, respectively. Whilst treatment with telmisartan, pantoprazole, quinidine, sulfasalazine and nefazodone significantly (*p<0.05) increased intracellular accumulation of Hoechst 33342, indicative of ABCG2 inhibition by 189, 204, 160, 240 and 244 % RFU.μg protein^-1, respectively.

Conclusion: These are the first studies to demonstrate clinically-relevant levels of therapeutic drugs significantly inhibit ABCB1 and ABCG2 in PBECs. The findings suggest the above drugs, which are widely used in patient treatment regimes, could influence CNS penetration of co-administered therapeutics that are ABCB1 and ABCG2 substrates.

References

1. Huang, S.M., et al.(2007). Clinical Pharmacology & Therapeutics 81 : 298-304.

2. Marchetti, S., et al.(2007). The Oncologist 12: 927-941.

3. Cantrill, C.A., et al..(2012). Brain research 1479: 17-30.