Preclinical study of cytotoxicity and predictive markers of response to dual inhibition of PI3K and mTORC1/2 signaling by NVP-BEZ235 with or without paclitaxel or nab-paclitaxel as a new therapeutic strategy in pancreatic cancer cell lines.

e15007 Background: Targeting the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) (PI3K-AKT-mTOR) pathway could arrest tumor growth and induce cell death in cancers that are resistant to currently available therapies. NVP-BEZ235 is an oral, targeted anticancer agent which exerts its potential activity through PI3K/mTOR dual inhibition. The paradoxical feedback activation of the PI3K/Akt pathway may compromise the efficacy of TORC1 inhibitors and provide the rationale for generating dual inhibitors in human pancreatic cancer. Methods: Kras mutant and wild-type human pancreatic cell lines were treated in vitro with BEZ235 and its combination with nab-paclitaxel. Antiproliferative effect per WST-1 assay was measured. Western blot analysis of S235/S236P-RPS6 and Akt (S473P-Akt, T308P-Akt) after exposure to BEZ235 was also performed. The potential synergistic and time-dependent effect at different concentrations of experimental agents was measured at different intervals. Results: BEZ235 reduced S473P-Akt, T308P-Akt and S235/S236P-RPS6 levels in a dose-dependent manner. Nab-paclitaxel at higher concentration exerts significant antiproliferative effects in a time-dependent fashion in pancreatic cell lines irrespective of Kras mutation status. BEZ235 in combination with nab-paclitaxel showed significant synergistic effect in a time and dose-dependent manner compared with the corresponding single drug treatments in pancreatic cancer cell lines with wild-type Kras (BxPC-3) but not in cell lines with mutant Kras (MIA PaCa-2 and PANC-1), the latter leading to a paradoxical increase in proliferation in comparison with controls, suggesting an escape pathway. Conclusions: These results provide the preclinical rationale for studies examining the synthetic lethality and escape pathways of PI3K/mTOR dual inhibition in particular subtypes of pancreatic cancer cell lines. Kras may be studied as a potential predictive biomarker of response to these agents and their combination with standard chemotherapy.