Abstract 3576: Rictor alterations elicit non-canonical signaling mechanisms contributing to tumorigenicity and therapeutic resistance in non-small cell lung cancer (NSCLC)

Abstract

Background: Rictor (RPTOR independent companion of MTOR, complex 2) is a highly conserved protein and is a critical component for proper assembly and functionality of the mTORC2 complex. The goal of our current study is to characterize the functional consequences of genomic alterations of RICTOR in advanced refractory NSCLC. Our preliminary data suggest that Rictor alterations have the potential to not only signal canonically through AKT, but also provide cancer cells with alternate, more advantageous oncogenic signaling via non-canonical mechanisms.

Methods: We correlated genomic data (DNA hybrid capture based next generation sequencing (NGS), Foundation Medicine, Inc.), gene expression profiling, and clinical outcome in the context of the ongoing BATTLE-2 clinical trial of targeted therapies in chemo-refractory NSCLC (198 cases). We further (1) surveyed early stage NSCLC (230 cases) in The Cancer Genome Atlas (TCGA) database and performed two-way hierarchical clustering comparing gene expression profiling in amplified vs. diploid cases; (2) utilized a single-nucleotide polymorphism array to select RICTOR amplified and diploid NSCLC cell lines; (3) assessed Rictor protein and RNA expression by Western blot and qRT-PCR, respectively; and (4) performed RICTOR knockdown using siRNA followed by migration, invasion, and clonogenic assays.

Results: In the BATTLE-2 cases, we identified 15% of RICTOR alterations (9% amplifications, 6% mutations, mutually exclusive) preferentially associated with resistance to all therapies (AKTi+MEKi, erlotinib+AKTi, sorafenib, or erlotinib). In the TCGA we found: (1) 10% of RICTOR amplifications and 3% mutations; (2) significant correlation between amplification and elevated RICTOR gene expression; and (3) a putative functional gene expression signature associated with RICTOR amplification. In diploid cell lines we found concordance between AKT phosphorylation and activation of other downstream mTORC2 targets (i.e. SGK1 and PKCα), but in RICTOR amplified cell lines we witnessed a discordant activation of these pathways, and thus were able to define unique signaling class systems in our cell lines harboring RICTOR alterations. Furthermore, following RICTOR knockdown in our amplified cell lines, a reduction in clonogenic, migratory, and invasive capacity was seen, suggesting that RICTOR amplification may provide a survival advantage in select cancer cells by tipping the signaling balance toward a non-canonical oncogenic pathway (AKT-independent).

Conclusion: Rictor alterations may define a new molecular NSCLC subtype with distinct biology that expose unique avenues for therapeutic intervention. Ongoing studies are underway to explore specific therapeutic strategies, non-canonical signaling and Rictor mutations.

Supported by: NHI-NCI CA155196 & 2P50CA070907-16A1

Citation Format: Dennis Ruder, Vassiliki Papadimitrakopoulou, Kazuhiko Shien, Neda Kalhor, J. Jack Lee, Waun K. Hong, Ximing Tang, Luc Girard, John D. Minna, Lixia Diao, Jing Wang, Nana E. Hanson, James Sun, Vincent Miller, Garrett Frampton, Roy S. Herbst, Ignacio I. Wistuba, Julie G. Izzo. Rictor alterations elicit non-canonical signaling mechanisms contributing to tumorigenicity and therapeutic resistance in non-small cell lung cancer (NSCLC). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3576. doi:10.1158/1538-7445.AM2015-3576