Multidrug resistance (MDR) is a major cause of chemotherapy failure. Overexpression of ATP‐binding cassette (ABC) transporters, P‐glycoprotein (P‐gp) and breast cancer resistance protein (BCRP) are two well‐studied drug transporters which are associated with MDR. These two transporters also act as a major functional unit of the blood brain barrier to protect the brain from xenobiotics and toxins. Lack of clinically approved P‐gp and BCRP inhibitors renders chemotherapy treatments of many MDR cancers ineffective and obstructs drug uptake into the brain. Using computational methods, we previously identified a novel class of P‐gp inhibitors that were not transport substrates of the pump. Here we describe the effects of chemical variants of the previously identified P‐gp inhibitor, SMU‐29. The variants were generated using computational approaches or by structure‐based design to improve protein binding interactions. All variants showed improved efficacy in reversing paclitaxel resistance in the P‐gp over‐expressing DU145 TXR prostate cancer cell line and their ability of increasing P‐gp substrate calcein in these cells. Five of these variants were not transported by P‐gp and three of them were substrates of the pump. Four variants only affected P‐gp, but not BCRP function, making them more selective than the parental compound, SMU 29. The three variants that affected BCRP reversed MDR in a BCRP over‐expressing breast cancer cell line, MCF‐7 M100, and increased accumulation of BCRP substrates such as Hoechst 33342, mitoxantrone and daunorubicin in these cells, indicating the potential to be used as BCRP inhibitors. The variants that affected both P‐gp and BCRP also showed higher accumulation of P‐gp and BCRP substrates in a blood brain barrier model cell line, hCMEC/D3, showing the potential to open the blood brain barrier for increased drug uptake into the brain.Support or Funding InformationThis work was supported by NIH NIGMS [R15GM094771‐02] to PVD and JGW, SMU University Research Council, the SMU Center for Drug Discovery, Design and Delivery, the Communities Foundation of Texas, and a private gift from Ms. Suzy Ruff of Dallas, Texas.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The overexpression of breast cancer resistance protein (BCRP) is associated with multidrug resistance (MDR) in specific cancers. BCRP is an ATP‐binding cassette (ABC) transporter that is also functionally important in the blood brain barrier. The ability of BCRP to export cancer chemotherapeutics to sub‐therapeutic concentrations renders chemotherapy treatment ineffective in cancers that overexpress BCRP. BCRP can also be problematic in its ability to inhibit the delivery of drugs to the brain. There are currently no clinically approved inhibitors of BCRP. The identification of inhibitors of BCRP that have the potential for clinical use would therefore greatly improve drug delivery systems to both cancers and the brain.Using computational approaches, we have identified a number of small, drug‐like molecules that have been predicted to inhibit BCRP. We report here the results of testing these small molecules in vitro in a BCRP‐overexpressing breast cancer cell line (MCF‐7 M100). The compound, Hoechst 33342, is known to be a transport substrate of BCRP, and was used here in assays that attempted to identify BCRP inhibition. Since Hoechst 33342 can be pumped out of the cells by BCRP, inhibition of BCRP leads to its intracellular accumulation. The BCRP activity assay used here takes advantage of the fact that accumulated Hoechst 33342 binds to DNA in the nucleus where it becomes highly fluorescent. The fluorescence of cells treated with putative inhibitors was compared with vehicle treated cells as an indication of BCRP inhibition. Nearly 100 experimental compounds were assayed at 10 μM in this study and compounds that exhibited three‐fold or greater accumulation over the vehicle treated control group were tested for inhibition of BCRP activity at lower concentrations. Five compounds have been identified so far that have demonstrated effective BCRP inhibition at nM concentrations. These compounds are currently being tested for the ability to reverse MDR in the BCRP‐overexpressing MCF‐7 M100 cell line.Support or Funding InformationThis work was supported by NIH NIGMS [R15GM09477102] to John G. Wise, SMU University Research Council, the SMU Center for Drug Discovery, Design and Delivery, the Communities Foundation of Texas, the Hamilton Undergraduate Research Scholars Program, and a private gift from Ms. Suzy Ruff of Dallas, Texas.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.