Novel therapeutic strategy to inhibit growth of pancreatic cancer organoids using a rational combination of drugs to induce mitotic arrest and apoptosis.

Abstract

322 Background: The ability of cancer cells to suppress apoptosis is critical for carcinogenesis. The Bcl-2-family of regulator proteins, including the anti-apoptotic members Bcl-2, Bcl-xL and Mcl-1, contributes to a complex network in control of apoptosis. BH3-mimetics (e.g. ABT-263) can inhibit anti-apoptotic Bcl-2 proteins and therefore have been developed as potential cancer therapeutics. Aurora Kinase A (AKA) is over-expressed in pancreatic cancer (PC) and is expressed to regulate G2-M transition during mitosis, making it an attractive target for PC. In this study we hypothesized that a combination of mitotic arrest using an AKA inhibitor (e.g. MLN8237) would sensitize PC to induction of apoptosis by a BH3-mimetic. Methods: Pancreatic cell lines (AsPC-1, PANC-1, MIA PaCa-2, HPAF-II) and patient-derived pancreatic cancer organoids (PDO) were treated with a BH3-mimetic (ABT-263) alone, an AKA inhibitor (MLN8237) alone, or the combination in comparison to untreated controls. Cell viability was measured using the CellTiter-Fluor (Promega) assay. Apoptosis was evaluated by Western blot (WB) for cleaved PARP, caspase 3 or caspase 7, and flow cytometry. Nude mice were implanted with pancreatic cancer cells to generate PC xenografts which were then treated with the same 4 treatment groups as in the in vitro studies. Results: ABT-263 combined with MLN8237 showed greater potency than either single drug alone, demonstrating synergy in inhibiting the growth of PC cells and PDOs. Combined treatment with MLN8237 and ABT-263 in PDOs suppressed organoid formation and proliferation by inducing apoptosis. Mechanistically, MLN8237 enhanced the activity of ABT-263 through reduction of Bcl-xL and Mcl-1 in pancreatic cancer cell lines and PDOs. The combination therapy also showed greater suppression of the growth of xenograft tumors, as compared with control treatments with single drug alone or vehicle. Conclusions: The combination of ABT-263 and MLN8237 appears to synergistically induce apoptosis via reduction of Bcl-2 family proteins in PC and should be further explored.