In silico identified inhibitors of ABC transporters increase chemotherapy efficacy in multidrug resistant cancer cell culture models
Authors: Nanayakkara Amila K. , Aljowni Maha , Chen Gang , Williams Noelle S. , Lippert Alexander R. , Vogel Pia D. , Wise John G. 
Published: June 2021

Overexpression of ATP‐binding cassette (ABC) transporters, P‐glycoprotein (P‐gp) and breast cancer resistance protein (BCRP), is associated with multidrug resistance (MDR) in cancers. These two transporters are also major functional units of the blood brain barrier. Lack of clinically approved P‐gp and BCRP inhibitors renders chemotherapy treatments of many MDR cancers ineffective and obstructs drug delivery into the brain. Using computational methods, we have identified several compounds that inhibited P‐gp (Brewer et al., Mol. Pharmacol. 86, 716–726, 2014 and Follit et al., Pharmacol. Res. Perspect. 3, e00170, 2015). Here, we show that co‐administration of the initially identified P‐gp inhibitors, SMU‐29, 34 and 45 with paclitaxel led to increased apoptosis in a P‐gp overexpressing cancer cell line (DU145TXR), and that these compounds directly affected P‐gp function. Western blot analyses confirmed that these inhibitors did not influence the expression of P‐gp. Treatment of P‐gp overexpressing DU145TXR cells with the known P‐gp inhibitor, tariquidar, led to significant intracellular accumulation of the P‐gp substrate, daunorubicin, while the presence or absence of tariquidar had no influence on accumulation of SMU‐29, 34 and 45, indicating that these inhibitors are not P‐gp transport substrates. P‐gp inhibitors 34 and 45 did not appear to affect BCRP transport activities, while compound 29 affected both P‐gp and BCRP catalyzed transport. The experimental compounds 29, 34 and 45 therefore appear to be promising candidates for further development into cotherapeutics to treat cancers that are multidrug resistant due to P‐gp overexpression. Additional experiments showed that chemical variants of SMU‐29 showed higher efficacy in cell viability assays and led to increased accumulation of P‐gp substrates compared to the parental compound.We assessed several in silico identified BCRP inhibitors for their potential to inhibit BCRP using a BCRP‐overexpressing breast cancer cell line (MCF‐7 M100). We have identified several compounds that potentiated the accumulation of the BCRP substrate, Hoechst 33342, in MCF‐7 M100 cells suggesting that these compounds inhibited BCRP. One of these compounds, SMU‐53, reversed the mitoxantrone resistance in MCF‐7 M100 cells and increased the accumulation of BCRP substrate chemotherapeutics, mitoxantrone and daunorubicin. Using the intrinsic fluorescence of SMU‐53, we have confirmed that the presence of a BCRP inhibitor (Ko143) or BCRP substrates did not affect the accumulation of SMU‐53 suggesting that the BCRP inhibitor was not a transport substrate of BCRP.Support or Funding InformationThis work was supported by NIH NIGMS [R15GM094771‐02] to John G. Wise, 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 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.