Abstract
316 Background: BH3-mimetics were designed to inhibit the anti-apoptotic members of the Bcl-2 family of proteins. BH3-mimetics in clinical development do not inhibit the Bcl-2 protein Mcl1, which is often active in pancreatic cancer. However, Mcl1 level can be decreased by mitotic arrest. Therefore, drugs that cause mitotic arrest may augment apoptosis induced by BH3-mimetics. Aurora Kinase A (AKA), also commonly overexpressed in pancreatic cancer, regulates mitotic spindle assembly and centrosome maturation and its inhibition leads to M-phase arrest. We hypothesized that inhibiting AKA would increase sensitivity of pancreatic cancer cells to BH3-mimetic-induced apoptosis. Methods: Pancreatic cancer cell lines (AsPC-1, PANC-1, MIA PaCa-2, HPAF-II) were evaluated for AKA protein expression by Western blot (WB). Baseline cell cycle distribution was evaluated by flow cytometry. All four cell lines 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 assay. Apoptosis was evaluated by WB for cleaved PARP and caspase 3. Percentage of cells undergoing apoptosis was quantitated using flow cytometry of annexin V and propidium iodide stained cells. Results: AKA expression varied between cell lines but correlated with percentage of cells in G2/M. Level of AKA expression did not appear to correlate with response to MLN8237. However, MLN8237 did induce mitotic arrest resulting in an increase in the G2/M fraction. Cell viability assays revealed limited sensitivity to MLN8237 or ABT-263 alone. MIA PaCa-2 cells were the most sensitive to MLN8237 with IC50 ~0.09µM and HPAF-II cells were the most sensitive to ABT-263 with IC50 0.6µM. MLN8237 lowered the IC50of ABT-263 in all 4 cell lines. Chou-Talalay plots exhibited a combination index < 1 in each cell line, confirming synergy. WB for cleaved PARP and caspase 3 showed increased apoptosis with the combination. The percentage of cells undergoing apoptosis also increased with the combination in each cell line. Conclusions: Inhibition of AKA synergistically augments BH3-mimetic-induced apoptosis in pancreatic cancer cells.
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