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Ref Type Journal Article
PMID (37916956)
Authors Varkaris A, Pazolli E, Gunaydin H, Wang Q, Pierce L, Boezio AA, Bulku A, DiPietro L, Fridrich C, Frost A, Giordanetto F, Hamilton EP, Harris K, Holliday M, Hunter TL, Iskandar A, Ji Y, Larivée A, LaRochelle JR, Lescarbeau A, Llambi F, Lormil B, Mader MM, Mar BG, Martin I, McLean TH, Michelsen K, Pechersky Y, Puente-Poushnejad E, Raynor K, Rogala D, Samadani R, Schram AM, Shortsleeves K, Swaminathan S, Tajmir S, Tan G, Tang Y, Valverde R, Wehrenberg B, Wilbur J, Williams BR, Zeng H, Zhang H, Walters WP, Wolf BB, Shaw DE, Bergstrom DA, Watters J, Fraser JS, Fortin PD, Kipp DR
Title Discovery and Clinical Proof-of-Concept of RLY-2608, a First-in-Class Mutant-Selective Allosteric PI3Kα Inhibitor That Decouples Antitumor Activity from Hyperinsulinemia.
URL
Abstract Text PIK3CA (PI3Kα) is a lipid kinase commonly mutated in cancer, including ∼40% of hormone receptor-positive breast cancer. The most frequently observed mutants occur in the kinase and helical domains. Orthosteric PI3Kα inhibitors suffer from poor selectivity leading to undesirable side effects, most prominently hyperglycemia due to inhibition of wild-type (WT) PI3Kα. Here, we used molecular dynamics simulations and cryo-electron microscopy to identify an allosteric network that provides an explanation for how mutations favor PI3Kα activation. A DNA-encoded library screen leveraging electron microscopy-optimized constructs, differential enrichment, and an orthosteric-blocking compound led to the identification of RLY-2608, a first-in-class allosteric mutant-selective inhibitor of PI3Kα. RLY-2608 inhibited tumor growth in PIK3CA-mutant xenograft models with minimal impact on insulin, a marker of dysregulated glucose homeostasis. RLY-2608 elicited objective tumor responses in two patients diagnosed with advanced hormone receptor-positive breast cancer with kinase or helical domain PIK3CA mutations, with no observed WT PI3Kα-related toxicities.Treatments for PIK3CA-mutant cancers are limited by toxicities associated with the inhibition of WT PI3Kα. Molecular dynamics, cryo-electron microscopy, and DNA-encoded libraries were used to develop RLY-2608, a first-in-class inhibitor that demonstrates mutant selectivity in patients. This marks the advance of clinical mutant-selective inhibition that overcomes limitations of orthosteric PI3Kα inhibitors. See related commentary by Gong and Vanhaesebroeck, p. 204 . See related article by Varkaris et al., p. 227 . This article is featured in Selected Articles from This Issue, p. 201.

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Molecular Profile Treatment Approach
Gene Name Source Synonyms Protein Domains Gene Description Gene Role
Therapy Name Drugs Efficacy Evidence Clinical Trials
Drug Name Trade Name Synonyms Drug Classes Drug Description
Gene Variant Impact Protein Effect Variant Description Associated with drug Resistance
Molecular Profile Indication/Tumor Type Response Type Therapy Name Approval Status Evidence Type Efficacy Evidence References
PIK3CA H1047R breast cancer sensitive RLY-2608 Preclinical - Cell line xenograft Actionable In a preclinical study, RLY-2608 inhibited viability of hormone receptor-positive breast cancer cells harboring PIK3CA H1047R in culture, and inhibited tumor growth in a cell line xenograft model (PMID: 37916956). 37916956
PIK3CA E545K breast cancer sensitive RLY-2608 Preclinical - Cell line xenograft Actionable In a preclinical study, RLY-2608 inhibited proliferation of hormone receptor-positive breast cancer cells harboring PIK3CA E545K in culture, and led to tumor regression in a cell line xenograft model (PMID: 37916956). 37916956
PIK3CA E542K estrogen-receptor positive breast cancer predicted - sensitive RLY-2608 Case Reports/Case Series Actionable In a clinical case study, treatment with RLY-2608 resulted in a partial response with disappearance of the soft tissue target lesion, which was ongoing at day 141, in a patient with ESR1/PGR-positive, ERBB2 (HER2)-negative breast cancer harboring PIK3CA E542K (PMID: 37916956; NCT05216432). 37916956
PIK3CA E453K PIK3CA H1047R estrogen-receptor positive breast cancer predicted - sensitive RLY-2608 Case Reports/Case Series Actionable In a clinical case study, treatment with RLY-2608 resulted in a partial response with a reduction in liver, lung, and soft tissue target lesions in a patient with ESR1/PGR-positive, ERBB2 (HER2)-low breast cancer harboring PIK3CA H1047R and PIK3CA E453K (PMID: 37916956; NCT05216432). 37916956