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Preprint WatchMildOctober 2nd, 2026

High-resolution measurement of ERK activation state reveals determinants of BRAF regulation and drug sensitivity

Adebanjo, A. F.; Simon, J. J.; Banales Mejia, F.; Fowler, D.; Maly, D. J.

A sequencing-based ERK activation assay profiled about 1,600 BRAF variants, separating residues that stabilise autoinhibition from those required for active dimer formation, identifying a class of dominant negative variants, and mapping hinge and activation-loop positions that confer resistance to the RAF inhibitor LXH254. The authors report that disrupting the BRAF to MEK interface is broadly sensitising across variants.

Mild contradiction

1 prior failure

One documented clinical failure (Phase 1 or 2) overlaps with the claimed mechanism.

The sensitising result points at exactly the combination the Claidex graph already records as stopped. Brimarafenib with the MEK inhibitor mirdametinib in BRAF and NRAS-mutant melanoma ended on tolerability rather than on activity (brimarafenib-mirdametinib-braf-melanoma-phase1-2-tolerability-termination). Reading the two together sharpens the problem for RAF and MEK co-targeting: the mechanistic case for breaking the BRAF to MEK interface is strengthening while the recorded clinical obstacle is the tolerability of combined pathway blockade, not its potency. The variant-resolved resistance map is the more immediately usable output, because it offers a way to select patients whose hinge and activation-loop residues predict response and so to pursue activity at doses that a combination schedule can sustain.

Abstract excerpt

High-resolution measurements of pathway activity make it possible to characterize how signaling responds to changing cellular conditions, to evaluate pathway-targeted inhibitors, and to dissect how sequence variation shapes signaling output. Here, we describe a sequencing-based assay that uses engineered, phospho-state-selective affinity reagents to quantify ERK activation state as a high-resolution, ratiometric readout of RAS/ERK MAPK pathway activity. Profiling ~1,600 BRAF variants at basal and elevated RAS-GTP levels allowed us to assign activity scores to somatic cancer and germline RASopathy variants and to distinguish residues that stabilize autoinhibition from those required for active dimer formation. We identified a large class of dominant negative variants that suppress signaling below endogenous levels through enhanced RAS engagement and an inability to form productive RAF dimers. Measuring the intracellular potency of the RAF inhibitor LXH254 against ~1,000 variants in parallel revealed hinge and activation-loop positions conferring resistance and showed that disrupting the BRAF-MEK interface is broadly sensitizing.

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This is an automated contradiction flag, not an editorial judgment on the preprint's quality. Flags identify where the preclinical literature and the clinical failure record diverge.