Targeting of AKT and Inhibitor of Apoptosis Proteins (IAP) in the treatment of pancreatic ductal adenocarcinoma (PDAC)


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Swati Kumar1, Leanne Stevenson1, Richard C Turkington1
1Queen’s University Belfast

Abstract

Background

PDAC is a lethal malignancy having a 5 year survival rate of 3%. There is a need to develop novel drug combinations as chemoresistance is a common cause of treatment failure contributing to poor prognosis. Our previous work showed promising results by combined targeting of AKT with an Inhibitor of apoptosis (IAP) antagonist BV6 in oesophageal adenocarcinoma. Since PDAC is a KRAS driven cancer, we hypothesized that targeting its downstream effector AKT in combination with chemotherapy or the IAP antagonist BV6 may enhance treatment efficacy.

Method

A novel allosteric AKT inhibitor AKTi was used to target AKT and BV6 was used to target IAPs. Cell viability was assessed by MTT assay following treatment with AKTi alone or in combination with chemotherapy or the IAP antagonist BV6. Synergy was assessed by Combination Index (CI) values. Western blots were used to examine AKT, IAPs and cleaved PARP after drug treatments. Total cell counts were used to measure proliferation rates and cells were treated with the caspase inhibitor ZVAD to study the mechanism of drug interactions. 

Results

MTT assays showed reduced cell viability in chemo/AKTi treatments when compared to either treatment alone. AKTi synergized with Oxaliplatin, 5FU and gemcitabine in the PDAC cell lines. Western blots showed no increase in cleaved PARP in the chemo/AKTi combinations, however, a reduction in the proliferation rates was observed. The AKTi/BV6 combination was highly synergistic and showed a marked reduction in cell viability in 72h MTT assays. This was also accompanied by a small increase in cleaved PARP with the loss of full-length PARP. ZVAD partially rescued the combination in the cell line PANC1 but no rescue was seen in MIAPACA indicating the role of both caspase dependent and independent mechanisms of cell death. Treatment of the gemcitabine-resistant line with the AKTi/BV6 combination also significantly reduced cell viability.

Conclusion

Combined inhibition of AKT and IAPs synergistically reduced cell viability in parental and chemo-resistant PDAC cell lines, suggesting that this combination could be used as a second line therapy in chemorefractory PDAC. 

Impact statement

Our results suggest that the dual targeting of AKT and IAPs could be an effective therapeutic combination in PDAC.