Abstract 5654: Docetaxel followed by temsirolimus suppresses mTOR pathway and can overcome PI3K / AKT over activation mechanism of resistance in lung cancer cell line.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Background: Mammalian target of rapamycin (mTOR) is a downstream regulatory protein of PI3K/AKT signal transduction pathway. The activation of cell surface receptors including IGF-1R (Insulin-Growth Factor-1Receptor) and EGFR (Epidermal Growth Factor Receptor) signals through PI3K/AKT pathway and is essential in cell proliferation, angiogenesis and anti-apoptosis process. Over activation of PI3K/AKT is a potential mechanism of resistance to mTOR inhibitors. mTOR inhibition could be a potential novel strategy in the treatment of lung cancer. Docetaxel (D) is commonly used in lung cancer treatment. Previously, we demonstrated that the sequence of D followed by mTOR inhibitor temsirolimus (T) in lung cancer cell lines (LCCL) had increased suppression of cell proliferation as compared to reverse sequence of T→D. The reason for this difference in decrease in proliferation effect is unclear. We hypothesized that D→T sequence can suppress the over activation of PI3K/AKT mechanism of resistance. We studied the expression of pmTOR, AKT and PI3K expression in lung cancer cell lines treated with different sequences of D and T and at different time points. Methods: Adenocarcinoma LCCL H2122 and H1437 were treated with T 1000nM or D 100nM for 24, 48 and 72h. We then treated both LCCL with D exposed for 24h followed by addition of T and the reverse sequence in both LCCL and prepared cell lysate at 24, 48 and 72h time points. We determined the expression of pmTOR, pAKT and PI3K by western blot using antibody from Cell Signaling. Results: T alone suppressed pmTOR after 24h but not at 48 and 72h in both LCCL. AKT was not suppressed. PI3K increased after 48h in both LCCL. The sequence of D→T suppressed expression of pmTOR and decreased expression of pAKT and PI3K at 48 and 72h in the H1437. We observed suppression of mTOR and PI3K but not AKT in the H2122. The opposite sequence of T→D did not suppress the expression of pmTOR and did not suppress the expression of pAKT and PI3K. Conclusion: The combination of D → T has synergistic inhibition of mTOR and it is able to suppress the over activation of AKT/PI3K pathway when compared with reverse sequence. This suggests that sequence of D→T can overcome the over activation of PI3K/AKT mechanism of resistance and it would be the ideal treatment sequence when using D in combination with mTOR inhibitor in the treatment of lung cancer. Expression of AKT/PI3K could be used as a biomarker of response to this regimen. Citation Format: Chao H. Huang, Peter J. VanVeldhuizen, Stephen K. Williamson, Ayten Gadashova, Faris Farassati. Docetaxel followed by temsirolimus suppresses mTOR pathway and can overcome PI3K / AKT over activation mechanism of resistance in lung cancer cell line. [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 5654. doi:10.1158/1538-7445.AM2013-5654