Co-targeting Translation Initiation and the RAS/ERK Pathway for the Treatment of KRAS-mutant Lung Cancer

Abstract

Lung cancer is the leading cause of cancer-related death worldwide with non-small cell lung cancer (NSCLC) being the most frequent subtype. Among the genetic alterations associated with NSCLC, activating mutations in the KRAS oncogene account for approximately 30% of cases. Despite extensive research efforts spanning several decades, the development of effective therapies for KRAS-mutant NSCLCs remains limited. While KRAS G12C inhibitors have recently been developed, responses are temporary and are restricted to a subset of patients. In addition, these agents are not relevant for the ~60% of KRAS-mutant NSCLCs that harbor other KRAS mutations. Therapeutic combinations that co- target components of the two major RAS effector pathways (ERK and mTOR) have been shown exert robust anti-tumor effects in animal models. Nonetheless, their clinical application has been limited by toxicity. Therefore, we sought to identify more refined therapeutic targets within these pathways that might selectively affect cancer cells while minimizing damage to normal tissues.

In this dissertation we present compelling evidence supporting the cap-dependent eucaryotic initiation factor 4F (eIF4F) complex as a promising therapeutic target in NSCLC. Importantly, eIF4F is commonly hyperactivated in human cancers due to the convergence of multiple oncogenic pathways on this complex, including RAS/ERK, PI3K/mTOR, and MYC. Its aberrant activation culminates in the increased translation of mRNAs harboring long and highly structured 5’-UTRs, many of which encode proteins that promote tumor growth, development, and drug resistance. Therefore, we hypothesized that suppressing the enhanced translation of pro-tumorigenic mRNAs through inhibition of the eIF4F complex activity might enhance the effects of RAS/ERK pathway inhibitors and selectively kill KRAS-mutant lung cancer cells. Importantly, we found that targeting the eIF4F’s RNA helicase component eIF4A dramatically enhances the effects of KRAS G12C or MEK inhibitors in NSCLCs and induces potent and durable tumor regression in vivo. Moreover, by screening a broad panel of eIF4F targets, we identified pro-survival BCL-2 family proteins as the key translational targets, among many, that mediate the therapeutic response. Finally, we found that concurrent MYC amplification or overexpression dictates sensitivity to these combinations by creating a dependency on eIF4A/F-mediated translation for the expression of the BCL-2 family proteins. Preliminary evidence further suggests that these eIF4A inhibitor- based combinations may exhibit efficacy also against other RAS pathway-driven tumors.

In a separate series of studies, we also found that suppressing the eIF4F complex activity either by targeting the cap-binding protein eIF4E, or by blocking its phosphorylation at Ser209 through the inhibition of MNK1/2 kinases, dramatically enhances the effects of RAS/ERK pathway inhibitors in KRAS- mutant NSCLC cells. These findings further highlight the importance of the eIF4F complex in KRAS- mutant NSCLCs and demonstrate that multiple approaches can be used to inhibit the translation initiation machinery in this tumor type. Interestingly however, while eIF4A and MNK1/2 inhibitors both potentiate the effects of RAS pathway inhibitors, these agents are effective in non-overlapping sets of NSCLC models, suggesting that different signals are responsible for dictating sensitivity to each of these combinations.

Taken together, these findings reveal the potential of targeting cap-dependent translation using diverse strategies to enhance the efficacy of RAS/ERK pathway inhibitors in KRAS-mutant NSCLCs and potentially other RAS pathway-driven tumors. In addition to inspiring the development of specific clinical trials, these findings should encourage further mechanistic investigations into the role of each component of the eIF4F complex in modulating the cell translatome of lung cancer cells. Finally, we hope that our work will fuel additional studies aimed at targeting cap-dependent translation in human cancers, ultimately increasing our understanding of this process in tumor development and the discovery of successful cancer treatments.