Date of Award


Document Type


Degree Name

Philosophy (Ph.D)


Pharmaceutical Sciences

First Advisor

Zhe-Sheng ZC Chen

Second Advisor

Sabesan SY Yoganathan

Third Advisor

John JW Wurpel


Accumulating evidence has suggested that multi-drug resistance (MDR) in cancer cells is a phenotype whereby cancer cells have attenuated sensitivity to drugs. ATP-binding cassette super-family G member 2 (ABCG2/BCRP) and ATP-binding cassette sub-family B member 1 (ABCB1/P-gp) are members of the ATP-binding cassette (ABC) transporter family and involved in MDR. OTS964 is a potent inhibitor targeting to PDZ-binding kinase (PBK)/T-lymphokine-activated killer cell-originated protein kinase (TOPK). Herein, we aimed to explore the relationship between MDR-associated ABC transporters, including ABCG2 and ABCB1, and the regulation of OTS964 efficacy. PBK/TOPK inhibitor OTS964 resistance is mediated by ABCG2-dependent transport function in cancer: in vitro study The efficacy of OTS964 is limited in drug-selected and drug resistant gene-transfected cells, which overexpress ABCG2, compared to those of corresponding drug-sensitive cells. Also, a verified ABCG2 inhibitor Ko143 can re-sensitize the acquired resistance to OTS964. In mechanism-based studies, OTS964 shows inhibitory effect on the efflux function mediated by ABCG2. Furthermore, OTS964 stimulates ATPase activity of ABCG2 and upregulates ABCG2 expression, resulting in enhanced resistance to substrate-drugs transported by ABCG2. The in silico molecular docking analysis suggested that OTS964 interacts with drug-binding pocket of ABCG2. PBK/TOPK inhibitor OTS964 resistance is mediated by ABCB1-dependent transport function in cancer: in vitro and in vivo study The overexpression of ABCB1 significantly desensitizes both drug-selected and gene-transfected cell lines, which overexpress ABCB1, to OTS964 and that this drug resistance can be antagonized by a verified ABCB1 inhibitor verapamil. Also, a similar trend was observed in tumor-bearing mouse model. In mechanistic studies, OTS964 inhibits the efflux function mediated by ABCB1. Moreover, OTS964 stimulates ATPase activity and expression levels of ABCB1, leading to induced resistance to substrate-drugs transported by ABCB1. OTS964 receives a comparable affinity score and can dock into the substrate-binding site of human ABCB1 protein. Altogether, OTS964 is susceptible to ABCG2- and ABCB1-mediated drug resistance, and that this effect can be antagonized by known inhibitors. Our findings strongly support the importance of monitoring the level of ABCG2 and ABCB1 in cancer patients under OTS964 treatment. These findings may also serve as a valuable indication for follow-up clinical investigation on potential use of OTS964.