MNK Inhibition Sensitizes KRAS-Mutant Colorectal Cancer to mTORC1 Inhibition by Reducing eIF4E Phosphorylation and c-MYC Expression

Abstract

KRAS-mutant colorectal cancers (CRC) are resistant to therapeutics, presenting a significant problem for ~40% of cases. Rapalogs, which inhibit mTORC1 and thus protein synthesis, are significantly less potent in KRAS-mutant CRC. Using Kras-mutant mouse models and mouse-and patient-derived organoids we demonstrate that KRAS with G12D mutation fundamentally rewires translation to increase both bulk and mRNA-specific translation initiation. This occurs via the MNK/eIF4E pathway culminating in sustained expression of c-MYC. By genetic and small molecule targeting of this pathway, we acutely sensitize KRAS G12D models to rapamycin via suppression of c-MYC. We show that 45% of CRCs have high signaling through mTORC1 and the MNKs, with this signature correlating with a 3.5-year shorter cancer-specific survival in a subset of patients. This work provides a c-MYCdependent co-targeting strategy with remarkable potency in multiple Kras-mutant mouse models and metastatic human organoids and identifies a patient population who may benefit from its clinical application.

Rpl24Bst mutation suppresses colorectal cancer by promoting eEF2 phosphorylation via eEF2K

“…In the short-term hyperproliferation model, the inactivation of Eef2k completely reversed the suppression of proliferation seen in Apc fl/fl Kras G12D/+ Rpl24 Bst/+ small intestines ( Figure 5A–C ), and the medial colon ( Figure 5—figure supplement 1A ). The kinase inactive Eef2k allele resulted in P-eEF2 being undetectable ( Figure 5C and Figure 2—figure supplement 1 ), and we previously reported no difference in hyperproliferation between Apc fl/fl Kras G12D/+ and Apc fl/fl Kras G12D/+ Eef2k D273A/D273A models ( Knight et al, 2020a ). The reversal in proliferation rate with Eef2k and Rpl24 Bst mutations was also seen in intestinal organoid growth after 3 days ( Figure 5D ).…”

“…Evidence suggests that targeting translation in KRAS -mutant CRC can be effective. As well as our recent study re-sensitising Kras -mutant CRCs to rapamycin by targeting translation initiation ( Knight et al, 2020a ), we have demonstrated that Kras -mutant models of CRC depend upon the transporter SLC7A5 to maintain protein synthesis by facilitating the influx of amino acids ( Najumudeen et al, 2021 ). These data support protein synthesis as a tractable target in CRC, with the discovery of additional factors regulating these pathways only improving the potential to target protein synthesis in the clinic ( Knight and Sansom, 2021 ).…”

“…As well as exploiting protein synthesis to drive cell division, cancers use translation to selectively synthesise a proteome geared towards proliferation, survival, and immune evasion. For example, in colorectal cancer (CRC) translation of the mRNA encoding the proto-oncogene c-MYC is selectively upregulated by eIF4E and mTORC1 signalling ( Knight et al, 2020a ). Likewise, independent reports have shown that the expression of the immune suppressive ligand PD-L1 is maintained on tumour cells by the activity of the translation factors eIF4A and eIF5B as well as phosphorylation of eIF4E and eIF2α ( Suresh et al, 2020 ; Xu et al, 2019 ; Cerezo et al, 2018 ).…”

“…However, the regulation of translation elongation in CRC is complex, notably being influenced by specific cancer-associated mutations. We have shown that mutation of Kras drives resistance to rapamycin in Apc -deficient models both in terms of its effect on elongation and on proliferation ( Knight et al, 2020a ). This is consistent with KRAS -mutant CRCs being resistant to rapalogues, and other therapeutics ( Ng et al, 2013 ; Spindler et al, 2013 ; DeStefanis et al, 2019 ) and highlights the unmet need for effective therapies against KRAS -mutant cancers.…”

High-Throughput Translational Profiling with riboPLATE-seq

“…Furthermore, while rapamycin rapidly reduces phospho-eIF4E, MNK1-dependent eIF4E phosphorylation demonstrably occurs under prolonged treatment 13 . MNK1 blockade has additionally been demonstrated to sensitize rapalog-resistant glioma to inhibition of mTORC1 14,15 .…”