GT Biopharma Inc. (GTBP) announced Thursday that it submitted an investigational new drug (IND) application to the U.S. Food and Drug Administration in December 2025 for GTB-5550 TriKE, a treatment designed to tackle solid tumors.

The therapy is a B7-H3-targeted natural killer (NK) cell engager, which essentially recruits the immune system's NK cells to attack cancer cells expressing the B7-H3 protein. Think of it as giving your immune system better targeting instructions.

"The IND for GTB-5550 represents the third NK cell engager we plan to move into clinical development and a tremendous accomplishment for the company," said Michael Breen, Executive Chairman and CEO of GT Biopharma.

The company plans to launch a Phase 1 basket trial in 2026 that will test GTB-5550 across multiple solid tumor types. Breen noted that the global market for B7-H3-expressing solid tumor cancers represents a slice of the estimated $362 billion global solid tumor cancer market.

GT Biopharma expects to apply lessons learned from its GTB-3650 study, which is currently enrolling patients in a Phase 1 trial for myeloid blood cancer. The company anticipates the next data readout from that trial in the first half of 2026, potentially showing evidence of clinical activity.

How the Trial Will Work

The Phase 1a dose escalation portion will test up to seven dose levels to identify the maximum tolerated dose (MTD). Once that's established, the Phase 1b expansion phase will confirm the MTD across seven distinct metastatic disease cohorts while evaluating tolerability, assuming toxicity rates remain consistent across groups.

Treatment administration follows a structured schedule: GTB-5550 will be delivered via subcutaneous injection in the abdominal area for five consecutive days during Week 1 and Week 2, followed by two weeks off. Each treatment cycle lasts four weeks.

Patients will undergo at least two cycles, with disease reassessment performed after two cycles and every 8-12 weeks thereafter. Treatment continues until disease progression, unacceptable toxicity, patient refusal, or if continuing is no longer in the patient's best interest. Patients will be followed for 12 months to determine progression-free survival and overall survival.

Price Action: GTBP stock jumped 12.92% to $0.75 during Thursday's premarket session.