MBX: Obesity Day Adds Confidence that MBX 4291 Can Achieve a Once-Monthly; Broader Obesity Platform Poised to Accelerate

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MBX: Obesity Day Adds Confidence that MBX 4291 Can Achieve a Once-Monthly; Broader Obesity Platform Poised to Accelerate

FLASH NOTE

May 12, 2026

Seamus Fernandez seamus.fernandez@guggenheimpartners.com MBX: Obesity Day Adds Confidence that MBX 4291

617 859 4637 Can Achieve a Once-Monthly; Broader Obesity

Zach Dunn, Ph.D.

zach.dunn@guggenheimpartners.com Platform Poised to Accelerate

617 859 4603

Evan Wang Key Message: We came away away from yesterday's Obesity Day in NYC with increased

evan.wang@guggenheimpartners.com confidence that MBX 4291 (GLP-1/GIP dual agonst) has the potential to achieve a 212 651 9756

competitive tolerability and weight loss profile with once-monthly dosing in MBX's 12-

Alana Lelo, Ph.D. week unblinded 4Q26 data release. Importantly, we confirmed that the full tolerability

alana.lelo@guggenheimpartners.com profile for 4291, including injection site reactions (ISR), raised no concerns. Early 212 518 9955 PoC for once-monthly MBX 4291 offers positive readthrough (again, albeit early) to the

Colleen Garvey, Ph.D. asset's 4Q26 update, justifying investment in the obesity PEP platform, with amycretin

colleen.garvey@guggenheimpartners.com (DC nominated) and triple G (DC nomination expected by mgmt in 3Q26) advancing to

617 859 4664 IND. We continue to believe 4291's 4Q26 update holds significant upside potential should

MBX's early data continue to perform in line with this initial result. Select details below.

MBX Overall,in our datawe previewhighlight:(HERE),(1) in whileline withrecognizingour firstthistakeis (seeblindedHERE)data,and-7%outlinedweight

MBX Biosciences, Inc. loss at week 8 clearly indicates 4291 is active; (2) The dose-dependent, on-

Sector: Biotechnology mechanism SAD adverse events and 12.5% (n=1/8) nausea/vomiting/diarrhea rate