RICTOR amplification identifies a subgroup in small cell lung cancer and predicts response to drugs targeting mTOR

// Nneha Sakre 1, 2 , Gary Wildey 1, 2 , Mohadese Behtaj 3 , Adam Kresak 1, 3 , Michael Yang 3 , Pingfu Fu 4 , Afshin Dowlati 1, 2 1 Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, Ohio, 44106 USA 2 Division of Hematology and Oncology, University Hospitals Cleveland Medical Center, Cleveland, Ohio, 44106 USA 3 Department of Pathology, University Hospitals Cleveland Medical Center, Cleveland, Ohio, 44106 USA 4 Epidemiology and Biostatistics, Case Western Reserve University, Cleveland, Ohio, 44106 USA Correspondence to: Afshin Dowlati, email: afshin.dowlati@case.edu Keywords: RICTOR, mTORC1/2 inhibitors, CNV, amplification, small cell lung cancer Received: May 27, 2016 Accepted: October 26, 2016 Published: November 15, 2016 ABSTRACT Small cell lung cancer (SCLC) is an aggressive cancer that represents ~15% of all lung cancers. Currently there are no targeted therapies to treat SCLC. Our genomic analysis of a metastatic SCLC cohort identified recurrent RICTOR amplification. Here, we examine the translational potential of this observation. RICTOR was the most frequently amplified gene observed (~14% patients), and co-amplified with FGF10 and IL7R on chromosome 5p13. RICTOR copy number variation correlated with RICTOR protein expression in SCLC cells. In parallel, cells with RICTOR copy number (CN) gain showed increased sensitivity to three mTOR inhibitors, AZD8055, AZD2014 and INK128 in cell growth assays, with AZD2014 demonstrating the best inhibition of downstream signaling. SCLC cells with RICTOR CN gain also migrated more rapidly in chemotaxis and scratch wound assays and were again more sensitive to mTOR inhibitors. The overall survival in SCLC patients with RICTOR amplification was significantly decreased (p = 0.021). Taken together, our results suggest that SCLC patients with RICTOR amplification may constitute a clinically important subgroup because of their potential response to mTORC1/2 inhibitors.