We previously performed a multi-step genomic study in almost 100 resected SQLC patients dichotomized according to the prognosis. Among the pathways with a biological impact on SQLC oncogenesis, PI3K/mTOR-Rictor emerged as a crucial axis [Pilotto WCLC 2016]. In order to explore the potentiality of mTOR inhibition, we present a set of in vitro experiments in RICTOR-aberrant SQLC preclinical models.
Next-generation sequencing (NGS), fluorescence in situ hybridization (FISH) and Western Blot were performed in 3 SQLC cell lines (H-1703, SK-Mes-1, Calu-1) for detecting CNG/protein profile of the PI3K/mTOR-Rictor components. The activity of PI3K/mTOR pathway targeted inhibitors in the SQLC cell lines was examined in short- (72 hours) and long-term (1 week) cell viability assays.
NGS analysis revealed a different amount of RICTOR CNG among SQLC cell lines. FISH confirmed that H-1703 harbors the highest number of RICTOR copies (6) followed by SK-Mes-1 (4) and Calu-1 (3.5), suggesting polysomy of the short arm of chromosome 5 as the main mechanism of RICTOR gain. Although Rictor protein levels were similar among the cell lines, p-mTOR S2448 (active form of mTOR complexes) was higher in H-1703 than SK-Mes-1 and Calu-1. PI3K/mTOR inhibition proved more effective in H-1703, with lower IC50 values in short term treatment (Table). Similar findings were confirmed in long-term assays.Table: 1879P
|PF-05212384 (PI3K/mTOR inhibitor)||18||26||335|
|AZD-2014 (Dual mTORC1/C2 inhibitor)||145||217||215|
|Everolimus (mTORC1 inhibitor)||Unable determine IC50||Unable determine IC50||Unable determine IC50|
|MK-2206 (pan-Akt inhibitor)||Unable determine IC50||Unable determine IC50||Unable determine IC50|
Overall, the results of our study suggest the potential implication of PI3K/mTOR-Rictor pathway in SQLC oncogenesis, thus rendering it a promising target for a targeted approach. Among the mTOR components, RICTOR CNG seems to predict a higher sensitivity to PI3K/mTOR inhibition and might represent a potential biomarker to be explored as a stratification tool in clinical trials. Confirmatory RICTOR silencing experiments are currently ongoing.
Clinical trial identification
Legal entity responsible for the study
AIRC (Associazione Italiana per la Ricerca sul Cancro).
All authors have declared no conflicts of interest.