GTB-5550 TriKE (Sponsored (IST) protocol)

September 15, 2026: GT Biopharma (NASDAQ: GTBP) said the FDA cleared a new IND for GTB-5550 in multiple myeloma, enabling an investigator-sponsored Phase 1a/1b trial; initiation is contingent on timing and receipt of non-dilutive grant funding. GTB-5550 is described as the first-in-human B7-H3-targeted TriKE in multiple myeloma and will use subcutaneous administration.

The Phase 1a dose-escalation portion will enroll 4th-line-and-later multiple myeloma patients across up to 6 dose cohorts to determine the maximum tolerated dose. The Phase 1b expansion will enroll 25 patients at the MTD to further assess safety, tolerability, and preliminary anti-tumor activity. Dosing is planned on 3 non-consecutive days per week during Weeks 1 and 2 of each 4-week cycle, with disease reassessment on Day 28; patients with partial response or better may continue up to 1 year, with 12-month follow-up for PFS and OS.

Separately, the company said its Phase 1 dose-escalation basket trial of GTB-5550 in solid tumors is actively enrolling, with an update anticipated in Q4 2026. It also noted ongoing Phase 1 enrollment for GTB-3650. Unaudited pro forma cash as of September 15, 2026 was about $11 million, expected to fund operations into Q3 2027.