Urocortin-2 Peptide: Genentech's $2.3B Muscle-Sparing Obesity Bet

Genentech, the Roche subsidiary, has licensed HM17321 — an experimental urocortin-2 peptide analog designed to burn fat while preserving muscle — from South Korea’s Hanmi Pharm in a deal worth up to $2.3 billion, the companies announced August 24. The agreement targets the single biggest clinical complaint about GLP-1 weight-loss drugs: the lean mass patients lose alongside the weight.

What Is HM17321?

HM17321 is a proprietary analog of urocortin-2 (UCN2), a naturally occurring signaling peptide in the corticotropin-releasing factor family. Unlike GLP-1 drugs, which work through receptors in the gut and brain to suppress appetite, HM17321 acts through the CRHR2 receptor, which is highly expressed in skeletal muscle. Activation triggers the mTOR protein-synthesis pathway — a primary switch for muscle growth — while simultaneously inducing fat breakdown in adipose tissue and suppressing fat storage.

The dual action is why the mechanism is drawing attention: more muscle, less fat, at the same time. Because HM17321 is a peptide, it can be delivered by subcutaneous injection, the same route as GLP-1 drugs, and Hanmi says the compound may have future potential in fixed-dose combination products alongside incretin-based treatments.

Why Muscle Preservation Is the GLP-1 Blind Spot

Published data cited in TechTimes’ coverage estimate that lean body mass accounts for roughly 25 to 39 percent of total weight lost on GLP-1 therapies — about 25 percent with tirzepatide and up to 39 percent with semaglutide. The clinical significance of that loss is actively debated. At the ADA 2026 Scientific Sessions, Dr. Samuel Klein of Washington University argued the loss is proportional to total weight loss and not linked to frailty, while Dr. Eric Ravussin of Louisiana State University countered that older patients with low muscle reserves face real exposure.

Roughly 40 percent of GLP-1 users are over 60, a population with lower baseline muscle mass and higher frailty risk. Published data also indicate up to two-thirds of patients discontinue GLP-1 therapy within a year, and weight regain typically follows — often including the muscle that was lost. A drug that actively maintains or rebuilds muscle would change the risk calculus of that stop-start pattern.

The Deal

Under the agreement, Genentech receives exclusive worldwide rights to develop, manufacture, and commercialize HM17321 for obesity and associated conditions including type 2 diabetes and cardiovascular disease, with South Korea excluded — Hanmi retains rights in its home market. Hanmi receives $190 million upfront and is eligible for development, regulatory, and commercial milestone payments that bring the potential total to approximately $2.3 billion, plus tiered royalties on future sales.

The U.S. FDA cleared Hanmi’s investigational new drug application in November 2025. An ongoing Phase 1 trial is evaluating safety, tolerability, pharmacokinetics, and pharmacodynamics in healthy volunteers and people with obesity. Hanmi will complete Phase 1; Genentech takes over development starting with Phase 2, as Korea JoongAng Daily reported.

In preclinical studies, Hanmi says HM17321 produced fat-selective weight reduction with preserved lean mass in Rhesus monkeys — data presented at the 2025 European Association for the Study of Diabetes meeting — and body-composition improvements that improved further when combined with semaglutide, presented at the 2025 ADA Scientific Sessions.

What the Companies Say

In-Young Choi, Senior Executive Vice President and Head of Hanmi’s R&D Division, framed the deal as a shift in how obesity treatment is evaluated. “The paradigm of obesity treatment is evolving beyond simple weight reduction toward improving body composition and restoring metabolic health,” Choi said. “We are very pleased that the differentiated scientific mechanism and development potential of HM17321 have been recognized by the global market.”

Boris L. Zaitra, head of Roche Corporate Business Development, said the compound fits Roche’s broader cardiometabolic strategy. “By licensing this next-generation investigational therapy with first-in-class potential from Hanmi, Roche and Genentech will pursue a differentiated approach to selectively reduce fat mass while improving both muscle mass and muscle function,” Zaitra said.

A Race Is Forming

Hanmi is not alone in pursuing UCN2. Denmark’s Gubra initiated its own Phase 1/2 trial of a competing UCN2 analog, GUB-UCN2, in July 2026, and Pfizer has published mechanistic research on the target without advancing a candidate to clinical trials. Hanmi’s November 2025 IND clearance gives the Hanmi-Genentech program roughly an eight-month head start.

For Roche, HM17321 adds a non-incretin mechanism to an obesity portfolio that already includes enicepatide, a dual GLP-1/GIP agonist in Phase 3, an oral GLP-1 candidate, and petrelintide, an amylin analog partnered with Zealand Pharma.

Why This Matters

The deal is a validation of peptide-based mechanisms beyond the GLP-1 class and a signal that the industry is treating muscle preservation as the next competitive battleground in obesity medicine. If HM17321 or a rival clears early human studies, the UCN2/CRHR2 pathway could attract a wave of entrants — the same pattern PeptidesBeat has tracked in the fat-loss-without-muscle-loss research and the evidence on GLP-1 body composition. For a broader view of the evolving metabolic peptide landscape, see our oral GLP-1 comparison and the MOTS-c compound guide.

HM17321 remains investigational. It has not been approved by any regulator, and no efficacy data from the ongoing Phase 1 trial have been published.

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