Molecular Frameworks for ERK1/2 Inhibition: Lessons from Synthetic and SAR Explorations

The mitogen-activated protein kinase (MAPK) cascade, specifically the extracellular signal-regulated kinases 1 and 2 (ERK1/2), orchestrates a broad spectrum of cellular responses, including proliferation, differentiation, and survival. Dysregulation of ERK signaling is inherently linked to the pathogenesis of several cancers and other chronic diseases, rendering ERK1/2 as a pivotal therapeutic target. Over the past two decades, diverse classes of small-molecule ERK1/2 inhibitors have been developed, progressing from reversible ATP-competitive agents to selective covalent inhibitors with clinical relevance. Despite extensive preclinical progress, the development of selective ERK1/2 inhibitors continues to pose significant challenges, primarily because of the high level of structural conservation across MAPKs such as p38 and JNK and the frequent emergence of resistance that limits sustained clinical efficacy. This review provides a consolidated perspective on the molecular frameworks that underpin ERK1/2 inhibition, emphasizing scaffold evolution, synthetic strategies, and structure-activity relationship (SAR) analyses. Special attention is given to key pharmacophores such as pyrazolopyridines, imidazopyrazinone, pyridopyrimidine, etc. among others, with a discussion on synthetic complexity and modularity. Furthermore, we delineate the clinical trajectory of advanced ERK inhibitors, highlighting challenges in resistance, target selectivity, and combinatorial therapy. By integrating chemical innovation with biological insight, this review offers a holistic map of the current landscape and future potential of ERK1/2-targeted anticancer therapeutics.