Abstract 4490: INK128, a novel TORC1/2 inhibitor, demonstrates potent oral antitumor activity in a VEGF-reinforced murine model of breast cancer and enhances efficacy of bevacizumab
Authors: Gökmen-Polar Yesim , Liu Yi , Toroni Rachel A. , Sanders Kerry L. , Zaheer Narjis A. , Mehta Rutika , Badve Sunil , Rommel Christian , Sledge George W. 
Published: February 2011

Background: Aberrant activation of the mammalian target of rapamycin (mTOR) signaling plays an important role in breast cancer progression and represents a potential therapeutic target for breast cancer. mTOR, existing in two distinct multi-protein complexes, TORC1 and TORC2, plays a key role in several signaling pathways controlling tumor growth, hypoxia, metabolism as well as angiogenesis. Through rational drug design we have identified INK128, a potent and selective small molecule active-site TORC1/2 kinase inhibitor, with excellent drug-like properties. In this study, we evaluated the potential therapeutic impact of INK128 alone or in combination with bevacizumab, the recombinant humanized VEGF targeting antibody, on tumor growth and angiogenesis using a genetically engineered xenograft model of breast cancer.

Methods: MCF-7 cells transfected with vector (ML20) or VEGF (MV165) were implanted into mammary fat pads of athymic mice. Treatment of INK128 alone (0.3 mg/kg or 1 mg/kg/daily to 3 mg/kg thrice weekly for 4 weeks) or vehicle control was started when tumors were palpable. Target proteins of PI3K/Akt/ mTORC1/2 signaling were analyzed by immunoblotting, while Ki-67, VEGF, VEGFR2, and carbonic anhydrase IX (CA IX) were assessed by immunohistochemistry (IHC). The potential of INK128 in combination with bevacizumab was also evaluated in this model.

Results: INK128 inhibited primary tumor growth significantly in MV165 xenografts in all doses tested (p=0.014), compared with vehicle control, while the impact of INK128 on ML20 xenografts was only significant at 3 mg/kg dose (p=0.05). Treatment with INK128 decreased the phosphorylation of AktS473, pS6S240/244, and p4EBP1T37/45 in both ML20 and MV165 xenograft tumors. Inhibition of the PRAS40T246 phosphorylation is more prominent in MV165 tumors in a dose-dependent manner. INK128 blocked phosphorylation of NDRG1 potently. Among the markers analyzed by IHC, only CA IX cytoplasmic expression in MV165 tumors was significantly reduced in the 3 mg/kg group as compared to control (p=0.008). Combination therapy with INK128 and bevacizumab reduced the tumor growth in both ML20 (p=0.040) and MV165 (p=0.002) xenografts significantly, when compared to vehicle groups, while the impact of inhibition was greater in MV165 than in ML20. Combination therapy was superior to INK128 alone in MV165 (p=0.009) but not in ML20 (p=0.145); in contrast, combination therapy was superior to bevacizumab in both ML20 (p=0.043) and MV165 (0.005).

Conclusions: INK128 inhibits TORC1 and TORC2-dependent signaling in VEGF-overexpressing xenograft model. Addition of INK128 to bevacizumab, a VEGF-targeting antibody, provided further benefit in xenograft models, even with transgenically elevated levels of VEGF, suggesting a promising approach in breast cancer therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4490.