---
schema_version: "secwatch.filing_event.v1"
accession: "0001776111-25-000007"
form_type: "8-K"
ticker: "MBX"
cik: "0001776111"
company_name: "MBX Biosciences, Inc."
filed_at: "2025-09-04T23:59:59+00:00"
generated_at: "2026-05-17T08:20:27.663896+00:00"
event_type: "other_material"
sentiment: "neutral"
materiality_score: 0.35
calibrated_materiality_score: 0.35
confidence: "high"
source: SEC EDGAR
---

# MBX Biosciences doses first participant in Phase 1 trial of obesity drug MBX 4291

## Summary
- Phase 1 trial is randomized, double-blind, placebo-controlled; Part A: 5 SAD cohorts (8 each, 3:1 randomization).
- Part B: 3 MAD cohorts (4 weekly doses, 8 each, 3:1 randomization); plus optional 12-week MAD cohorts (30 each, 2:1).
- Topline results anticipated in 2027; preclinical data support once-monthly dosing and improved GI tolerability.
- MBX 4291 is a long-acting GLP-1/GIP co-agonist prodrug for obesity, designed for best-in-class weight loss.

## SEC filing metadata
- accession: 0001776111-25-000007
- form_type: 8-K
- ticker: MBX
- cik: 0001776111
- company_name: MBX Biosciences, Inc.
- filed_at: 2025-09-04T23:59:59+00:00
- event_type: other_material
- sentiment: neutral
- materiality_score: 0.35
- calibrated_materiality_score: 0.35
- confidence: high
- sec_items: 7.01, 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1776111/000177611125000007/0001776111-25-000007-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1776111/000177611125000007/mbx-20250904.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001776111-25-000007
- JSON: https://secwatch.observer/filing/0001776111-25-000007.json
- Plain text: https://secwatch.observer/filing/0001776111-25-000007.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.