Abstract P5-03-14: MLN0128 regulates survival signaling by AKT and its downstream effectors in HER2+ breast cancer model

Evading apoptosis is considered to be a hallmark of cancers including breast cancer, since mutations in apoptotic regulators invariably accompany tumorigenesis. Chemotherapeutic agents induce apoptosis, and hence disruption of apoptosis during tumor progression may promote drug resistance. AKT is an apoptotic regulator that is activated in HER2+ breast tumor cells and promotes anti-HER2 therapy resistance in vitro . Nevertheless, how mTORC1/C2-AKT signaling disables apoptosis and its contribution to clinical drug resistance are not clear yet. Using HER2 amplified breast cancer cells [BT474 ( HER2+/ Trastuzumab-sensitive), BT474HerR ( HER2+/ Trastuzumab-resistant), HCC1954 and MDA-MB453 (both are HER2 +/ PIK3CA kinase domain mutated)], we show that mTORC1/C2 inhibitor; MLN0128 abrogates AKT (Ser473), Survivin and controls its downstream effectors of apoptotic signaling molecules (e.g. cleaved Caspase 3/9, cleaved PARP, MCL and BIM). MLN0128 also induces annexinV positive cells and regulates cellular proliferation (ON-TOP 3D colony formation and real-time proliferation assay). Additionally, increased cleaved Caspase 3 and decreased MCL1 expression were also observed following MLN0128 treatment in HER2+ xenograft model along with tumor growth inhibition. Our studies provide strong experimental evidence that high apoptotic signaling –specifically reduced MCL1 and increased cleaved-CASPASE3 expression expedite the response of targeted therapy that directly inhibits mTORC1/C2-AKT signaling. Citation Format: De PK, Carlson JH, Sun Y, Lin X, Williams C, Dey N, Leyland-Jones BR. MLN0128 regulates survival signaling by AKT and its downstream effectors in HER2+ breast cancer model. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P5-03-14.