Date of Award

2021

Document Type

Dissertation

Degree Name

Philosophy (Ph.D)

Department

Pharmaceutical Sciences

First Advisor

John N.D. Wurpel

Second Advisor

Zhe-Sheng Chen,

Third Advisor

Sandra Reznik

Abstract

Multidrug resistance (MDR) is a major challenge in colon cancer chemotherapy, which is typically mediated by the overexpression of ATP-binding cassette (ABC) transporters, particularly ABCB1 (P-gp, MDR1). The application of ABCB1 inhibitors to overcome ABCB1-mediated MDR has been disappointing in the clinical settings. As an alternative approach, a synthetic analog of survivin inhibitor MX106, MX106-4C, was identified as a potent collateral sensitivity (CS) agent that selectively exerted more than 10-fold cytotoxicity on ABCB1 positive MDR colon cancer cell lines compared to cell lines with low ABCB1 expression. Biochemical assays revealed that MX106-4C did not affect the ATPase activity or the efflux function of ABCB1. Short-term (up to 72 h) incubation with MX106-4C significantly downregulated ABCB1 expression at the transcriptional level but not protein level, whereas long-term (14 d) incubation with MX106-4C significantly downregulated ABCB1 protein expression. These findings suggest an indirect interaction and regulation between MX106-4C and ABCB1. However, the selective toxicity of MX106-4C could be reversed by an ABCB1 inhibitor, knockout of ABCB1, or ABCB1 mutation with impaired function, indicating that the selective cytotoxicity was ABCB1 expression and function dependent. Therefore, MX106-4C may interact with an ABCB1-dependent downstream event. Further studies demonstrated that the selective cytotoxic effects of MX106-4C were associated with cell cycle arrest at G0/G1 phase and apoptosis, possibly via survivin inhibition and activation of caspases-3/7. Bioinformatic analysis indicated potential involvement of the p21-CDK6-pRb phosphorylation pathway in MX106-4C-induced cell cycle arrest. Anti-cancer efficacy and safety tests demonstrated that MX106-4C had good selectivity against ABCB1 positive colon cancer cells compared to normal colon cells. The selective toxicity of MX106-4C to ABCB1 positive colon cancer could be retained in multicellular tumor spheroids that mimicked in vitro settings. Besides, MX106-4C could exert a cytotoxic effect synergistically with doxorubicin on ABCB1 overexpressing colon cancer cells, and re-sensitize ABCB1 positive cells to doxorubicin by reducing ABCB1 expression in cell population via long term exposure. Overall, this study demonstrates that MX106-4C selectively kills ABCB1 positive MDR colon cancer cells and indirectly interacts with ABCB1, which provides a clue for CS compound design and a novel strategy to obviate ABCB1-mediated colon cancer MDR.

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