RLY-2608

Moreover, we show that in the H1047R mutant, the cavity, where the allosteric ligands STX-478 and RLY-2608 bind, is more accessible contrary to the WT. This study provides insights into the molecular mechanisms underlying activation of oncogenic PI3Kα by C-terminal mutations and represents a valuable resource for continued efforts in the development of mutant selective inhibitors as therapeutics.

P1, N=400, Recruiting, Relay Therapeutics, Inc. | Trial completion date: Aug 2025 --> Aug 2026 | Trial primary completion date: Jan 2025 --> Dec 2025

Background: PIK3CA mutations occur in ~40% of HR-positive breast cancers, where alpelisib, an orthosteric PI3Kα inhibitor, is FDA-approved in combination with fulvestrant... To identify on-target and off-target alterations potentially mediating resistance to PI3Kα inhibitors, we used a targeted next-generation sequencing assay (Guardant360; Guardant Health) to analyze ctDNA in serially collected plasma samples from 32 patients with PIK3CA-mutated advanced HR-positive, HER2-negative breast cancer treated with alpelisib and inavolisib...Some mutations had differential effects on PI3Kaselective vs. pan-PI3K inhibitors, but resistance induced by all mutations could be overcome by the novel allosteric pan-mutant-selective PI3Ka-inhibitor RLY-2608... In one of the largest patient cohorts analyzed to date, this study defines the clinical landscape of acquired resistance to PI3Ka inhibitors. Genomic alterations within the PI3K pathway represent a major mode of resistance and identify a novel class of secondary PIK3CA resistance mutations that can be overcome by an allosteric PI3Ka inhibitor. Together, these findings provide insights to guide strategies to overcome resistance in PIK3CA-mutated cancers.

P1, N=400, Recruiting, Relay Therapeutics, Inc. | N=235 --> 400

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 PI3Ka-related toxicities.

PIK3CA mutations occur in ~8% of cancers, including ~40% of HR-positive breast cancers, where the PI3K-alpha (PI3Ka)-selective inhibitor alpelisib is FDA-approved in combination with fulvestrant. Some mutations had differential effects on PI3Ka-selective vs. pan-PI3K inhibitors, but resistance induced by all mutations could be overcome by the novel allosteric pan-mutant-selective PI3Ka-inhibitor RLY-2608. Together, these findings provide insights to guide strategies to overcome resistance in PIK3CA-mutated cancers.

Alpelisib, a non-mutant selective PI3Kα inhibitor, is effective in ER+ breast cancer thus validating PI3Kα as a therapeutic target. ReDiscover (NCT05216432) is enrolling worldwide. For further information, contact clinicaltrials@relaytx.com.

Alpelisib, a non-selective orthosteric PI3Kα inhibitor, is approved in combination with fulvestrant for patients with PIK3CA-mutant, ER+, HER2– advanced breast cancer...It is molecularly distinct with differentiated pharmaceutical properties compared to RLY-2608...This study (NCT05759949) is enrolling in the United States. For further information, please contact clinicaltrials@relaytx.com.

Background: PIK3CA mutations occur in ~40% of HR-positive breast cancers, where alpelisib, an orthosteric PI3Kα inhibitor, is FDA-approved in combination with fulvestrant... To identify on-target and off-target alterations potentially mediating resistance to PI3Kα inhibitors, we used a targeted next-generation sequencing assay (Guardant360; Guardant Health) to analyze ctDNA in serially collected plasma samples from 32 patients with PIK3CA-mutated advanced HR-positive, HER2-negative breast cancer treated with alpelisib and inavolisib...Some mutations had differential effects on PI3Ka-selective vs. pan-PI3K inhibitors, but resistance induced by all mutations could be overcome by the novel allosteric pan-mutant-selective PI3Ka-inhibitor RLY-2608... In one of the largest patient cohorts analyzed to date, this study defines the clinical landscape of acquired resistance to PI3Ka inhibitors. Genomic alterations within the PI3K pathway represent a major mode of resistance and identify a novel class of secondary PIK3CA resistance mutations that can be overcome by an allosteric PI3Ka inhibitor. Together, these findings provide insights to guide strategies to overcome resistance in PIK3CA-mutated cancers.

Alpelisib, an orthosteric inhibitor, validated mutant-PI3Kα as a therapeutic target; however, toxicity from non-selective inhibition of WT PI3Kα (hyperglycemia) and other PI3K isoforms limits its clinical activity...We initiated a first-in-human study (NCT05216432) to define the MTD, safety, pharmacokinetics (PK), and anti-tumor activity of RLY-2608 in PIK3CA-mutant solid tumor patients (pts) and of RLY-2608 plus fulvestrant (combo) in pts with PIK3CA-mutant, HR+HER2-BC, who had received prior CDK4/6 inhibitor and endocrine therapy. Adult pts with no prior PI3Ki/mTORi therapy received RLY-2608 QD or BID on a 4-week (wk) cycle following a Bayesian Optimal Interval dose escalation... Across PIK3CA genotypes, RLY-2608 demonstrated target inhibition and anti-tumor activity with minimal impact on glucose homeostasis. These proof-of-mechanism data indicate that RLY-2608 is the first allosteric, pan-mutant selective PI3Kα inhibitor and that RLY-2608 has broad therapeutic potential in PIK3CA-driven cancers.

Toxicity related to non- selective inhibition of WT PI3Kα (hyperglycemia) and other PI3K isoforms limits the tolerability, dosing and efficacy of the orthosteric inhibitor, alpelisib, the only approved solid tumor PI3K inhibitor. The primary endpoints are MTD/RP2D and AE profile for single agent and combination; key secondary endpoints are PI3KCA genotype in blood and tumor, PK, biomarkers, and overall response rate. US enrollment began December 2021 and ex-USA startup is under way.

Toxicity related to non-selective inhibition of WT PI3Kα (hyperglycemia) and other PI3K isoforms limits the tolerability, dosing and efficacy of the orthosteric inhibitor, alpelisib, the only approved solid tumor PI3K inhibitor...The primary endpoints are MTD/RP2D and AE profile for single agent and combination; key secondary endpoints are PI3KCA genotype in blood and tumor, PK, biomarkers, and overall response rate. US enrollment began December 2021 and ex-USA startup is underway.

P1, N=190, Recruiting, Relay Therapeutics, Inc.

Alpelisib, the only approved orthosteric PI3Kα inhibitor, is emblematic of the class with toxicity related to inhibition of wild type PI3Kα and other PI3K isoforms resulting in sub-optimal inhibition of mutant PI3Kα, frequent discontinuation, and challenges in combining with CDK4/6 inhibitors...In addition, in vivo combination efficacy with fulvestrant and CDK4/6 inhibitors (palbociclib or abemaciclib) was assessed in patient-derived xenografts harboring the PIK3CA H1047R or E545K mutation along with a second site PIK3CA minor mutation...RLY-2608 can be combined with fulvestrant and CDK4/6 inhibitors in vivo with tumor regressions observed in both cell- and patient-derived xenograft models. The pre-clinical profile of RLY-2608 supports the clinical development of RLY-2608 both in single agent and combination clinical trials in patients with PIK3CA mutant tumors, including HR+/ PIK3CA mutant breast cancer.