RAF dimer inhibition enhances the antitumor activity of MEK inhibitors in K‐RAS mutant tumors

Abstract

The mutation of K-RAS represents one of the most frequent genetic alterations in cancer. Targeting of downstream effectors of RAS, including of MEK and ERK, has limited clinical success in cancer patients with K-RAS mutations. The reduced sensitivity of K-RAS-mutated cells to certain MEK inhibitors (MEKi) is associated with the feedback phosphorylation of MEK by C-RAF and with the reactivation of mitogen-activated protein kinase (MAPK) signaling. Here, we report that the RAF dimer inhibitors lifirafenib (BGB-283) and compound C show a strong synergistic effect with MEKi, including mirdametinib (PD-0325901) and selumetinib, in suppressing the proliferation of K-RAS-mutated non-small-cell lung cancer and colorectal cancer (CRC) cell lines. This synergistic effect was not observed with the B-RAF V600E selective inhibitor vemurafenib. Our mechanistic analysis revealed that RAF dimer inhibition suppresses RAF-dependent MEK reactivation and leads to the sustained inhibition of MAPK signaling in K-RAS-mutated cells. This synergistic effect was also observed in several K-RAS mutant mouse xenograft models. A pharmacodynamic analysis supported a role for the synergistic phospho-ERK blockade in enhancing the antitumor activity observed in the K-RAS mutant models. These findings support a vertical inhibition strategy in which RAF dimer and MEKi are combined to target K-RAS-mutated cancers, and have led to a Phase 1b/2 combination therapy study of lifirafenib and mirdametinib in solid tumor patients with K-RAS mutations and other MAPK pathway aberrations.Abbreviations CR, complete regression; CRC, colorectal cancer; EOHSA, excess over highest single agent; MAPK, mitogen-activated protein kinase; MEKi, MEK inhibitors; NFA, negative feedback amplified; NSCLC, non-small-cell lung cancer; PR, partial regression; TGI, tumor growth inhibition; WT, wild-type.

Evaluation of the RAS signaling network in response to MEK inhibition using organoids derived from a familial adenomatous polyposis patient

“…3 C). As previously reported in studies using two-dimensional cell lines, phosphorylation of MEK was increased by MEK inhibition in a time-dependent manner 34 , 38 , 39 . Phosphorylation of MEK was shown to be induced by the allosteric inhibition of MEK in RAS-activated cells 34 .…”

A systematic analysis of signaling reactivation and drug resistance

“…For several type II RAF inhibitors, such as LY3009120, AZ-628, TAK-632, TAK-580, or lifirafenib, which have low apparent dissociation constants and a narrow range of paradoxical activation, synergy with MEK inhibitors has been observed ( Yen et al, 2018 ; Yuan et al, 2020 ). However, our calculations suggest that the zone where antagonism prevails can still be substantial, and sufficiently high doses of type II RAF inhibitors are required to remain in the synergy zone ( Figure 6A ).…”

Recent Updates on the Significance of KRAS Mutations in Colorectal Cancer Biology

“…Notably, in CRC cells, it has been demonstrated that KRAS mutations lead to aberrantly elevated MAPK signalling [ 15 , 16 ]. Therefore, many attempts have been made to target and inhibit molecules downstream of KRAS, although breakthrough success in therapeutic applications has not been realised [ 17 ].…”