Abstract 2584: Tandutinib inhibits the PI3 Kinase/Akt/mTOR signaling pathway to inhibit colon cancer growth.

Background: Despite therapeutic advances, colon cancer remains the second leading cause of death in the United States. The c-Kit receptor can activate distinct signaling pathways including phosphatidylinositol-3- kinase (PI3K)/Akt and mammalian target of rapamycin (mTOR). Aberrant c-Kit activation protects cells from apoptosis and enhances invasion of colon carcinoma cells. Tandutinib is a novel quinazoline-based inhibitor of the type III receptor tyrosine kinases including c-Kit and PDGFR. The current study is designed to determine the effect of tandutinib on colon cancer growth and identified a mechanism of action. Method: Colon cancer cell lines HCT116, HT-29 and SW480 and normal colon epithelial cells were used in the study. Cell growth was measured by hexoseaminidase and clonogenicity assays. Apoptosis was determined by measuring caspase 3/7 activities. Cell cycle analysis was measured by Flow cytometry. Signaling proteins were quantified by western blot analysis. For in vivo effects, HCT116 xenografts were developed in the flanks of nude mice. Immunohistochemistry was performed for CD31 and Akt/mTOR signaling proteins. Results: Tandutinib treatment resulted in a dose and time dependent inhibition of proliferation and colony formation in all three cell lines but did not affect normal colonic epithelial cells. Treatment also induced colon cancer cells to undergo apoptosis and G0/G1 arrest. Apoptosis was further confirmed by increased levels of activated caspase 3 and Bax/Bcl2 ratio, coupled with a reduction in cyclin D1. There was also a downregulation of cyclooxygenase 2 (COX-2), vascular endothelial growth factor (VEGF) and interleukin-8 expression suggesting effects on cancer promoting genes. Moreover, tandutinib inhibited phosphorylation of c-Kit, Akt, mTOR, p70S6 Kinase and 4EBP1. Overexpression of constitutively active Akt1 overcame this inhibitory effect suggesting a critical role for this pathway. To determine the effect of tandutinib on tumor growth in vivo, nude mice harboring HCT116 tumor xenografts in their flanks were administered the compound intraperitoneally every day for 21 days. Tandutinib treatment significantly suppressed tumor xenograft growth, with notably lower tumor volume and weight. Microvessel density, based on CD31 staining was also significantly lower in the tumors following tandutinib treatment when compared to controls suggesting inhibition of angiogenesis. Western blot and immunohistochemistry analyses demonstrated significant inhibition in the expression cancer promoting genes COX-2 and VEGF, and suppressed the activation of Akt/mTOR signaling proteins in the tandutinib-treated xenograft tissues. Conclusion: Together, these data suggest that tandutinib is a novel potent therapeutic agent that can target the Akt/mTOR/p70S6K signaling pathway to inhibit tumor growth and angiogenesis. Citation Format: Dharmalingam Subramaniam, Sivapriya Ponnurangam, David Standing, Parthasarathy Rangarajan. Tandutinib inhibits the PI3 Kinase/Akt/mTOR signaling pathway to inhibit colon cancer growth. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2584. doi:10.1158/1538-7445.AM2013-2584