Dual mTORC1/2 inhibition in a preclinical xenograft tumor model of endometrial cancer.

OBJECTIVES: Up to 70% of endometrioid endometrial cancers carry PTEN gene deletions that can upregulate mTOR activity. Investigational mTOR kinase inhibitors may provide a novel therapeutic approach for these tumors. Using a xenograft tumor model of endometrial cancer, we assessed the activity of mTOR and downstream effector proteins in the mTOR translational control pathway after treatment with a dual mTOR complex 1 and 2 (mTORC1/2) catalytic inhibitor (PP242) compared to that of an allosteric mTOR complex 1 (mTORC1) inhibitor (everolimus, RAD001).
METHODS: Grade 3 endometrioid endometrial cancer cells (AN3CA) were xenografted into nude mice. Animals were treated with PP242, PP242 and carboplatin, carboplatin, RAD001, and RAD001 and carboplatin. Mean tumor volume was compared across groups by ANOVA. Immunoblot analysis was performed to assess mTORC1/2 activity using P-Akt, P-S6 and P-4E-BP1.
RESULTS: The mean tumor volume of PP242+carboplatin was significantly lower than in all other treatment groups, P < 0.001 (89% smaller). The RAD001+carboplatin group was also smaller, but this did not reach statistical significance (P = 0.097). Immunoblot analysis of tumor lysates treated with PP242 demonstrated inhibition of activated P-Akt.
CONCLUSIONS: Catalytic mTORC1/2 inhibition demonstrates clear efficacy in tumor growth control that is enhanced by the addition of a DNA damage agent, carboplatin. Targeting mTORC1/2 leads to inhibition of Akt activation and strong downregulation of effectors of mTORC1, resulting in downregulation of protein synthesis. Based on this study, mTORC1/2 kinase inhibitors warrant further investigation as a potential treatment for endometrial cancer.