Therefore, this work aims to elevate our previous findings by employing the strong carboranyl quinazoline inhibitors that were shown to reverse MDR in human ABCG2-overexpressing Madin-Darby canine kidney cells (MDCKII-hABCG2) [32,33], in co-administration with the BCRP substrate and chemotherapeutic agent doxorubicin on ABCG2-overexpressing cancer cell lines. Here, ABCG2 is linked to cancer.