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ORAL 42 - Drug Resistance (ID 160)
- Event: WCLC 2015
- Type: Oral Session
- Track: Biology, Pathology, and Molecular Testing
- Presentations: 1
- Moderators:R.C. Doebele, J.V. DeGregori
- Coordinates: 9/09/2015, 18:30 - 20:00, Mile High Ballroom 4a-4f
ORAL42.04 - Rictor Alterations Elicit Mechanisms of Survival Advantage and Resistance to Targeted Therapy in Non-Small Cell Lung Cancer (NCSLC) (ID 2991)
18:30 - 20:00 | Author(s): D. Ruder
Rictor (RPTOR independent companion of MTOR, complex 2) is a highly conserved protein and is a critical component for assembly and functionality of the mTORC2 complex. Alterations of the PI3K/mTOR/AKT pathway are hallmark of many cancer types, underscoring the potential important role of Rictor. The goal of our current study was 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 (via activation of AKT), but also provide cancer cells with alternate, more advantageous oncogenic signaling via non-canonical mechanisms.
We correlated genomic data (DNA 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 cases(230 cases) in The Cancer Genome Atlas (TCGA) database to perform 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; (4) performed Rictor knockdown (siRNA), and (5) performed drug sensitivity to targeted therapies by MTS assay.
In the Battle-2 cases, we identified 15% of Rictor alterations (9% gene amplifications, 6.6% mutations, non-concomitant). Among the mutations, 1 was mapped to an N-terminal phosphorylation site, while all others are of unknown significance to date. Rictor alterations were significantly associated with lack of 8-week disease control in the AKTi+MEKi therapeutic arm. In the TCGA we found: (1) 10% Rictor amplifications and 3% mutations; (2) significant correlation between amplification and elevated Rictor gene expression; (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. Furthermore, following Rictor knockdown in our amplified cell lines, a significant reduction of colony formation, migratory, and invasive potential was seen in a pathway-differential manner. Thus, suggesting that Rictor amplifications may provide survival advantage in select cancer cells by tipping the signaling balance toward a non-canonical oncogenic pathway (AKT-independent[I1] ).Also in a differential pathway manner, Rictor gene amplification and overexpression contributed to resistance to a number of targeted therapies
Rictor alterations may constitute a potential novel mechanism of targeted therapy resistance via the activation of non-canonical signaling pathways. These alterations could define new molecular NSCLC subtypes with distinct biology that expose unique avenues for therapeutic implication. Ongoing studies are exploring therapeutic vulnerabilities, non-canonical signaling and Rictor mutations.