Docetaxel followed by temsirolimus in suppression of mTOR pathway.

Abstract

e13535 Background: Mammalian target of rapamicin(mTOR) is a downstream regulatory protein of the PI3K/Akt signal transduction pathway. This is a common pathway for a several cell surface receptors including IGFR (Insulin-like Growth Factor Receptor) and EGFR (Epidermal Growth Factor Receptor). The activation of these receptors through PI3K/Akt pathway is essential in cell proliferation, angiogenesis and anti-apoptosis process. Several therapeutic agents that inhibit these receptors have shown to be active in the treatment of diverse types of cancers. Docetaxel (D) is commonly used in the treatment of lung cancer. We demonstrated previously that the sequence of D followed by mTOR inhibition using temsirolimus (T) in lung cancer cell lines (LCCL) had synergistic effect in suppressing cell proliferation compared with T→D. The exact mechanism of this effect is unknown. We studied the expression of mTOR, Raptor and PI3K in these cell lines treated in different time points to investigate the activity of this pathway when using these sequences of drug treatment. Methods: Adenocarcinoma LCCL H2122 and H1437 were plated and exposed to temsirolimus 1000nM and docetaxel 100nM. The cell viability was measured by optical density (OD) at 24, 48 and 72h. We tested the sequence of D treated for 24h followed by addition of T and the reverse in both LCCL. We then prepared cell lysate at 24h, 48h and 72h time points and studied the expression of mTOR, Raptor and PI3K by western blot using antibody obtained from Cell Signaling. Results: The sequence of D→T had increased suppression of mTOR, Raptor and PI3K at 48 and 72 hours compared with the opposite sequence of T→D. Conclusions: The combination of D → T seems to have synergistic suppression of mTOR and PI3K pathway in 2 LCCL compared with opposite sequence. Further studies in animal models using this sequence and confirmation of mTOR suppression may help determine if this is a feasible combination in the treatment of lung cancer.