MBX Biosciences Announces First Patient Dosed in Phase 3 Trial

What Happened

• On August 27, 2026 MBX Biosciences, Inc. (MBX) announced via press release (furnished as Exhibit 99.1) that the first patient has been dosed in its pivotal Phase 3 oPTimize trial of once-weekly canvuparatide for adults with chronic hypoparathyroidism (HP). The filing was made on Form 8-K.

Key Details

• Trial design: global, multicenter, randomized, double-blind, placebo-controlled study with a 26-week double-blind period followed by a 78-week open-label extension. (ClinicalTrials.gov identifier NCT07699471.)
• Enrollment and randomization: approximately 160 patients, randomized 3:1 to canvuparatide vs. placebo.
• Dosing schedule: 4-week fixed dose at 600 µg once weekly, then an 18-week individualized titration period (up to 1,600 µg weekly), then a 4-week maintenance period through Week 26; the device intended for commercial use will be used in the trial.
• Primary endpoint: proportion of patients achieving a composite responder outcome at Week 26 — normal albumin‑adjusted serum calcium, independence from active vitamin D, reduction of calcium supplementation to ≤600 mg/day, and no dose increases during the four weeks before the Week 26 assessment. Key secondary endpoints include normalization of urinary calcium for those with elevated baseline urinary calcium and improvement in physical functioning and hypocalcemia-related symptoms.

Why It Matters

• This filing confirms MBX has advanced canvuparatide into a pivotal Phase 3 study, a key clinical milestone toward potential regulatory approval and commercialization for treating chronic hypoparathyroidism. The trial’s size, randomized placebo control, and prespecified composite primary endpoint are material to assessing the drug’s efficacy and potential marketability.
• The 8-K also reiterates standard forward-looking statements and risk factors (clinical, regulatory, financial and third‑party dependencies) that could affect development timelines and outcomes — information investors should consider when evaluating MBX’s prospects.