Abstract 676: Effect of novel mTOR-PI3K dual inhibitors on neuroendocrine tumor cell proliferation and apoptosis

Introduction: Neuroendocrine tumors (NETs) are a heterogeneous group of neoplasms arising from multiple organs. The mammalian Target of Rapamycin (mTOR) and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway has a well-established role in NETs that was supported by the clinical efficacy, shown by the rapamycin analog, Everolimus. However, treatment with everolimus results in activation of Akt as an escape mechanism for cancer cells. Novel dual mTOR/PI3K inhibitors, PF-04691502 and PKI-402, were shown to have superior antineoplastic effect, however, not have been tested in NETs. The purpose of our current study was to test the effects of PF-04691502 and PKI-402 on proliferation, apoptosis and Akt activation of NET cells in vitro. Methods: For these studies, we utilized two human NET cell lines: BON, a pancreatic carcinoid tumor, and QGP-1, a somatostatinoma. (i) BON and QGP-1 cells were treated with increasing concentrations of PF-04691502 (100nM – 10,000nM) and PKI-402 (50nM – 1,000nM) at 72, 96 and 120 h to determine half maximal inhibitory concentration (IC-50) by sulforhodamine B (SRB) assay. (ii) BON and QGP-1 cells were then treated with and harvested 24 h later to further examine expression of cyclin D1 and PARP by Western blot. In addition, phospho-Akt (S473), phospho-S6 (S235/236), and phospho-4E-BP1(Thr37/46) expression was evaluated by Western blot to assess the effect of PI3K/mTOR inhibition on downstream signaling proteins in NET cells. Results: (i) SRB assays demonstrated that IC-50 was 74nM for PF-04691502 in BON cells, 196nM for PF-04691502 in QGP-1 cells, 40nM for PKI-402 in BON cells, and 45nM for PKI-402 in QGP-1 cells at 96 h. (ii) Cyclin D1 expression was decreased in a dose-dependent fashion in both BON and QGP-1 cells. PARP expression was increased in QGP-1 cells treated with PF-04691502 (500nM). In contrast, we did not observe a significant increase in PARP expression in BON cells following PF-04691502 treatment or with PKI-402 treatment of either cell line. (iii) A dose-dependent decrease in p-AKT (S473) and p-6S (S235/236) expression was noted in cells treated with PF-04691502 at 24 h and with PKI-402 at 4 h. We did not observe significant difference in p4E-BP1(Thr37/46) expression in QGP-1 cells after treatment with PF-04691502 at 24h and PKI-402 at 4h. Conclusion: Our results demonstrate that both PF-04691502 and PKI-402 have a cytostatic inhibitory effect on proliferation in both BON and QGP-1 cells. In addition, treatment with PF-04691502 causes cytotoxic induction of apoptosis in QGP-1 cells, but not in BON cells. Our results suggest that PI3K/mTOR inhibition with PF-04691502 could be a novel therapeutic approach to the treatment of NETs. Citation Format: Zeta Chow, Courtney Townsend, B. Mark Evers, Piotr Rychahou. Effect of novel mTOR-PI3K dual inhibitors on neuroendocrine tumor cell proliferation and apoptosis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 676.