Relay Therapeutics (Nasdaq: RLAY), based in Cambridge, Massachusetts, has opened a first-in-human study of RLY-8161, a small molecule the company describes as a potential first NRAS-selective inhibitor, in patients with advanced NRAS-mutant melanoma and other solid tumors — entering a target space where no approved direct inhibitor currently exists.
The Phase I trial (NCT07584226) enrolled its first participants in March 2026 across four US sites, including Massachusetts General Hospital and Memorial Sloan Kettering Cancer Center. The study is structured in two sequential parts: dose escalation in any NRAS-mutant solid tumor, followed by expansion at the recommended Phase II dose in a population enriched for NRAS-mutant disease. Enrollment is planned for approximately 35 participants. The primary completion date is set for December 2027, according to the trial record.
Eligibility is restricted to adults with unresectable Stage III or IV melanoma or other solid tumors bearing a documented primary oncogenic NRAS mutation, an ECOG performance status of 0 or 1, and measurable disease by RECIST v1.1. Notably, the protocol excludes patients with known activating KRAS, HRAS, or BRAF mutations and anyone who has received prior therapy targeting the RAS-MAPK pathway — including MEK, ERK, RAF, or RAS inhibitors. That exclusion criterion defines the intended treatment population as RAS-MAPK pathway-naïve, which has implications both for the scientific interpretation of early efficacy signals and for the eventual commercial positioning of the asset.
The science behind NRAS selectivity
NRAS mutations drive oncogenesis primarily through constitutive activation of the MAPK and PI3K signaling cascades. In melanoma, NRAS mutations — most commonly at codon 61 (Q61R, Q61K, Q61L, Q61H) — are present in approximately 15%–20% of cases and have historically been associated with aggressive disease and limited targeted therapy options. BRAF-mutant melanoma has been addressed by a well-established class of BRAF and MEK inhibitors, but NRAS-mutant melanoma has remained without a direct targeted agent. Attempts to inhibit the pathway downstream through MEK inhibition alone have produced limited and transient responses in clinical trials.
RLY-8161 is designed to inhibit NRAS selectively, sparing KRAS and HRAS. Relay Therapeutics has stated publicly that this isoform selectivity is intended to address a core liability of pan-RAS inhibitors: on-target toxicity arising from inhibition of wild-type KRAS, which plays essential roles in normal tissue homeostasis. The precise binding mechanism of RLY-8161 — including whether it engages the GDP-bound or GTP-bound state of NRAS, and whether it acts covalently or non-covalently — has not been disclosed in public sources to date. NRAS Q61 mutations impair intrinsic GTPase activity, leaving the protein constitutively loaded with GTP and active; how RLY-8161 engages this state remains a key mechanistic question that early pharmacodynamic data from the trial may begin to address.