ETX-929, a potential best-In-class, oral, highly potent and selective dual ON / OFF state Pan-KRAS small molecule inhibitor for the treatment of KRAS mutant and wild-type amplified cancers

Oncogenic KRAS alterations occur in approximately 23% of all human cancers. The most common oncogenic KRAS alterations are G12D (~31%), G12V (~24%), and G12C (~15%) mutations. In addition, ~10% of KRAS-altered cancers have wild-type (WT) KRAS amplification or harbor multiple oncogenic KRAS alterations, including co-occurring KRAS mutations and amplifications. While there have been drug approvals for KRAS G12C targeting covalent inhibitors, there are currently no approved targeted therapies against other oncogenic KRAS alterations. Pan-KRAS inhibitors that target multiple oncogenic KRAS alterations while sparing other RAS isoforms have the potential to treat broad patient populations and address resistance to mutant selective KRAS inhibition while avoiding the on-target toxicities associated with pan-RAS inhibition. ETX-929 is an orally bioavailable, potent, dual GTP (ON)- and GDP (OFF)-state pan-KRAS inhibitor with excellent selectivity over other RAS isoforms. ETX-929 binds WT and mutant KRAS in active (ON) and inactive (OFF) conformations with high affinity [K D (ON-state) = single digit nanomolar; K D (OFF-state) = picomolar] and >100-fold selectivity over NRAS and HRAS. In the KRAS-RAF1 RAS-binding domain biochemical assay, ETX-929 potently inhibited complex formation when KRAS (WT / mutant) was either in the active GMPPNP-bound state (single digit nM IC 50 ) or inactive GDP-bound state (pM IC 50 ). In cells, ETX-929's dual ON / OFF-state inhibitory activity potently inhibits KRAS mutants that rapidly cycle between GTP- and GDP-bound states ( KRAS WTamp , KRAS G12C ) as well as slow cycling mutants ( KRAS G12V and KRAS Q61H ) that predominantly reside in the ON state. In a broad panel of KRAS mutant (G12X, G13D, Q61H) and WT amplified cancer cell lines, ETX-929 potently inhibited the KRAS pathway (pERK median IC 50 = 0.9 nM) and cell proliferation (median IC 50 = 6.23 nM), while showing no viability effects on low copy number WT KRAS or mutant NRAS / HRAS cells. Oral ETX-929 showed dose-dependent exposures with concordant sustained tumor pERK reductions, inducing tumor stasis or regression in colorectal, stomach, and lung cancer cell line-derived xenograft models harboring KRAS alterations (G12D, G12V, G12C, and WT amplified). ETX-929 also shows good cross-species pharmacokinetics including higher species, excellent pre-clinical tolerability, and no meaningful off-target activity or in vitro safety signals, supporting its advancement toward clinical development. Overall, ETX-929 is a potential best-in-class, pan-KRAS inhibitor with superior potency, selectivity over NRAS / HRAS, excellent efficacy and favorable drug-like properties that could improve outcomes for KRAS-driven cancers that currently lack targeted therapeutic options.