RICTOR amplification as a novel therapeutic target for lung cancer brain metastases.

Abstract

3597 Background: Approximately 20% to 50% of patients with advanced lung cancer develop brain metastases, which are associated with debilitating neurologic impairment and a dismal prognosis. There have been very limited studies investigating the genomics of brain metastases in lung cancer. Methods: We comprehensively investigated the frequency of PI3K/AKT/RICTOR/mTOR pathway aberrations in primary and metastatic sites using an extensive database of 11845 cases of lung adenocarcinoma by NGS (FoundationOne). The potential roles of RICTOR amplification in the development of brain metastases were studied both in vitro and in vivo in orthotopic mouse models. Results: Compared to the primary tumor, PI3K/AKT/mTOR gene alterations were more frequent in metastatic sites, with particular enrichment noted in brain metastases. RICTOR amplification alone accounted for the observed higher frequency both in brain metastases (brain vs. primary: 9.73% vs 3.50%, P = 2.6E-14; brain vs. other mets: 9.73% vs. 7.3%, P = 0.03) and other metastatic sites (other mets vs. primary: 7.3% vs.3.5%, P = 10E-15), whereas the frequency of PTEN, AKT1, PK3CA or mTOR genetic alterations was not different in the primary tumor, brain and other metastatic sites. In vitro, inducible RICTOR knockdown in H23 lung cancer cells (parental line with RICTOR amplification) was associated with reduced cell migration and invasion, whereas upregulation of RICTOR in HCC827 lung cancer cells (parental line with normal RICTOR copy numbers) was associated with an increase of both processes. These results were confirmed with pharmacological inhibition using mTOR1/2 inhibitors with known CNS penetration. In vivo, both inducible ablation of RICTOR and the mTOR1/2 inhibitor TAK228 (Sapanisertinib) significantly inhibited lung cancer H23-R4-Luc tumor growth in the brain, including a number of near complete responses. Mechanistic studies suggest that RICTOR may regulate the brain metastasis process through AKT and CXCL12 chemokine-CXCR4 axis. Conclusions: RICTOR amplification is the first identified actionable target that is markedly enriched in brain metastases. Our study provides a strong rationale for the development of RICTOR-targeted therapeutic strategies for the treatment and/or prevention of these major causes of lung cancer morbidity and mortality.