MBX Biosciences, Inc. (NASDAQ:MBX), a clinical-stage biopharmaceutical company focused on the discovery and development of novel precision peptide therapies for the treatment of endocrine and metabolic disorders, today announced dosing of the first participant in its Phase 1 trial of MBX 4291, the Company's Precision Endocrine Peptide™ (PEP™) glucagon-like peptide-1 (GLP-1)/ glucose-dependent insulinotropic polypeptide (GIP) co-agonist prodrug candidate for the treatment of obesity.

"Initiation of our first clinical trial in obesity is a significant milestone for the Company and an important step in addressing this global public health issue," said Kent Hawryluk, President and Chief Executive Officer of MBX Biosciences. "MBX 4291 has demonstrated positive preclinical results and is designed to be a best-in-class weight loss prodrug, with the potential for convenient once-monthly administration, improved weight loss, and better gastrointestinal tolerability compared to currently available treatment options. We look forward to topline results anticipated in 2027."

The Phase 1 trial is a randomized, double-blind, placebo-controlled first-in-human study to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple ascending doses of MBX 4291 in adult participants with obesity. The Phase 1 trial will include:

Part A Single Ascending Dose (SAD): single ascending doses of MBX 4291 or matching placebo will be administered in 5 cohorts consisting of 8 participants each. Participants will be randomized on Study Day 1 to receive MBX 4291 or matching placebo in a 3:1 ratio. Participants in each cohort will be followed for 63 days after the single study intervention administration.

Part B Multiple Ascending Dose (MAD) (4 weeks): multiple ascending doses of MBX 4291 or matching placebo will be administered in 3 cohorts consisting of 8 participants each. Participants will be randomized on Study Day 1 to receive MBX 4291 or matching placebo in a 3:1 ratio. Participants in each cohort will receive a total of 4 study intervention administrations one week apart and will be followed for 71 days after the first study intervention administration.

Following completion of Parts A and B, the Company plans to evaluate multiple ascending doses of MBX 4291, or matching placebo, administered over 12 weeks in up to two cohorts consisting of 30 participants each in a 2:1 randomization ratio. Participants are expected to receive up to a total of 12 study intervention administrations one week or one week and one month apart with increasing doses of MBX 4291 and will be followed for 120 days after the first dose.