8-K: Rhythm Pharma's Setmelanotide Shows Promise in PWS Trial

Rhythm Pharmaceuticals announced positive preliminary Phase 2 results for setmelanotide in Prader-Willi syndrome, showing reductions in BMI and hyperphagia, and plans to advance to a Phase 3 trial.

Summary

• Preliminary results from an exploratory Phase 2 trial of setmelanotide in patients with Prader-Willi syndrome (PWS) were announced.
• The 52-week trial enrolled 18 PWS patients aged 6-65 years with a BMI ≥ 30 kg/m2 for adults or BMI ≥ 95th percentile for age and sex for patients younger than 18.
• At Month 3 (n=8), 6 out of 8 patients achieved BMI reductions from baseline.
• At Month 6 (n=5), 3 out of 5 patients achieved BMI reductions, with two seeing deeper reductions versus Month 3 and one unchanged.
• 6 out of 7 evaluable patients at Month 3 achieved meaningful reductions in Hyperphagia Questionnaire for Clinical Trials (HQ-CT) scores; one patient's baseline and Month 3 HQ-CT score was 0, therefore not evaluable.
• 17 of the 18 patients enrolled remain on active setmelanotide therapy.
• Safety and tolerability results have been consistent with setmelanotide's well-established clinical profile, with no deaths, serious adverse events, or drug withdrawals reported.
• The company plans to advance setmelanotide into a Phase 3 registrational trial for PWS, pending successful completion of this Phase 2 trial.
• A Phase 1, Part D study for the weekly MC4R agonist RM-718 in up to 20 PWS patients has been initiated, with first patient screening anticipated in December 2025.

Sentiment

Score: 8

Explanation: The preliminary Phase 2 results for setmelanotide in Prader-Willi syndrome are positive, showing reductions in BMI and hyperphagia, and are strong enough to warrant progression to a Phase 3 registrational trial. High patient retention and a consistent safety profile further bolster confidence. The initiation of a new Phase 1 study for RM-718 also indicates a robust pipeline. While preliminary, these are very encouraging signs for a rare disease with significant unmet needs.

Positives

• Setmelanotide demonstrated potential therapeutic benefit with BMI reductions in 6 of 8 patients at Month 3 and 3 of 5 patients at Month 6.
• Meaningful hyperphagia reductions were observed in 6 of 7 evaluable patients at Month 3.
• High patient retention, with 17 of 18 enrolled patients remaining on active therapy.
• Safety and tolerability results are consistent with setmelanotide's well-established clinical profile, with no deaths, serious adverse events, or drug withdrawals reported.
• The positive preliminary results support advancing setmelanotide into a Phase 3 registrational trial for PWS.
• Initiation of a Phase 1, Part D study for the weekly MC4R agonist RM-718 in PWS expands the potential treatment pipeline.

Negatives

• One patient at Month 3 and two patients at Month 6 did not show BMI reductions, with one patient's BMI unchanged at Month 6.
• One patient's HQ-CT score was not evaluable at Month 3 due to a baseline score of 0.
• One patient experienced worsened diabetes control after 13 weeks and started on insulin.
• One patient was non-compliant after initial response.
• One patient discontinued prior to Month 6 visit.
• One patient had poorly controlled diabetes, lipohypertrophy, and severe lower extremity lymph edema.

Risks

• Ability to enroll patients in clinical trials.
• Design and outcome of clinical trials.
• Impact of competition.
• Ability to achieve or obtain necessary regulatory approvals.
• Risks associated with data analysis and reporting.
• Ability to successfully commercialize setmelanotide.
• Liquidity and expenses.
• Ability to retain key employees and consultants, and to attract, retain and motivate qualified personnel.
• General economic conditions.
• Setmelanotide is not indicated for obesity due to suspected POMC, PCSK1 or LEPR deficiency with variants classified as benign or likely benign, or other types of obesity not related to these deficiencies or BBS.
• Potential for skin hyperpigmentation, darkening of pre-existing nevi, and development of new melanocytic nevi.
• Potential for disturbance in sexual arousal (spontaneous penile erections in males, sexual adverse reactions in females).
• Potential for depression and suicidal ideation.
• Risk of serious hypersensitivity reactions (e.g., anaphylaxis).
• In growing children, the impact of weight loss on growth and maturation should be evaluated.
• Risk of serious adverse reactions due to benzyl alcohol preservative in neonates and low birth weight infants (IMCIVREE is not approved for this use).
• Treatment with IMCIVREE is not recommended when breastfeeding; discontinue IMCIVREE when pregnancy is recognized unless the benefits of therapy outweigh the potential risks to the fetus.

Future Outlook

Rhythm Pharmaceuticals plans to advance setmelanotide into a Phase 3 registrational trial for Prader-Willi syndrome (PWS) based on these promising preliminary Phase 2 results. The company anticipates a complete six-month data readout in the first half of 2026 and plans to submit the data for presentation at a medical conference in 2026. Additionally, the company has initiated a Phase 1, Part D study for its weekly MC4R agonist RM-718 in PWS, with the first patient screening expected in December 2025.

Management Comments

• Jennifer Miller, M.D., Principal Investigator: "There remains a profound unmet need in the PWS patient population. Hyperphagia and severe obesity associated with PWS present serious challenges for patients and often lead to significant health complications over time. These interim data offer meaningful insight into the potential for a future treatment option that could help address the unique and critical needs of patients living with PWS."
• David Meeker, M.D., Chairman, CEO and President of Rhythm: "We are encouraged by these preliminary results, which give us confidence to advance setmelanotide into a registrational Phase 3 trial for PWS. We look forward to additional data in the first half of 2026 and remain committed to exploring the potential of MC4R agonism for this patient population, for whom there are very few treatment options available. In parallel, we look forward to evaluating our weekly MC4R agonist RM-718 in PWS, and we expect the first patient with PWS to enter screening for this study in December."

Industry Context

Prader-Willi syndrome (PWS) is a rare genetic disorder affecting approximately 400,000 people worldwide and 20,000 in the U.S., characterized by extreme hyperphagia and severe obesity. There are currently limited effective therapeutic options for PWS, making the development of new treatments like setmelanotide and RM-718 critical for addressing this significant unmet medical need. Rhythm Pharmaceuticals' focus on MC4R agonism positions it within the rare neuroendocrine disease space, where targeted therapies can have a substantial impact.

Comparison to Industry Standards

• The prior setmelanotide trial in PWS in 2016 had a maximum dose of 2.5 mg for 8 weeks in 4 patients, showing individual patients demonstrated promising weight loss after 8 weeks. This current trial uses a higher dose (up to 5 mg/day) and longer duration (52 weeks), potentially leading to more robust results.
• Beloranib trial results in PWS showed mean % change in body weight from baseline to Week 26, providing a benchmark for weight loss efficacy in PWS trials. While specific comparative numbers are not provided for setmelanotide against beloranib, the positive preliminary results suggest setmelanotide is showing a similar therapeutic direction.
• The HQ-CT (Hyperphagia Questionnaire for Clinical Trials) is a standardized, observer-reported outcome measure used in PWS clinical trials, indicating adherence to industry-accepted methods for assessing hyperphagia.

Stakeholder Impact

• Shareholders: Positive preliminary clinical data and progression to Phase 3 could increase investor confidence and potentially the company's valuation.
• Patients with PWS: The potential for setmelanotide to reduce BMI and hyperphagia offers hope for a new treatment option for a disease with limited therapies.
• Healthcare Providers: Successful development could provide a new tool for managing the complex challenges of PWS.
• Employees: Positive clinical progress can boost morale and job security, potentially attracting new talent.

Next Steps

• Complete six-month data readout for setmelanotide PWS trial in the first half of 2026.
• Submit setmelanotide PWS data for presentation at a medical conference in 2026.
• Begin planning for a Phase 3 registrational trial for setmelanotide in PWS.
• Screen the first patient for the Phase 1, Part D study of RM-718 in PWS in December 2025.

Key Dates

Recommendation

The preliminary Phase 2 results for setmelanotide in Prader-Willi syndrome are highly encouraging, demonstrating reductions in BMI and hyperphagia in a significant portion of patients with a favorable safety profile. The company's decision to advance setmelanotide to a Phase 3 registrational trial, coupled with high patient retention in the ongoing Phase 2 study, signals strong confidence in the drug's potential. Given the profound unmet medical need in PWS and the limited existing therapeutic options, a successful Phase 3 trial and subsequent approval could represent a significant market opportunity for Rhythm Pharmaceuticals. The initiation of the RM-718 study further strengthens the long-term pipeline. These factors collectively suggest a strong upside potential for the stock.

Keywords

Prader-Willi Syndrome, PWS, Setmelanotide, MC4R Agonist, Obesity, Hyperphagia, Clinical Trial, Phase 2, Phase 3, RM-718, Biopharmaceutical, Rare Disease, Rhythm Pharmaceuticals