GT Biopharma Advances GTB-5550 TriKE to Clinical Trials Targeting Solid Tumors in 2026

GT Biopharma Inc. (NASDAQ: GTBP) is advancing its oncology pipeline with the submission of an investigational new drug (IND) application to the U.S. Food and Drug Administration (FDA) for its investigational therapy GTB-5550 TriKE. This submission, completed in December 2025, marks a critical milestone in the company’s development of immunotherapies targeting solid tumors that express the B7-H3 protein. GTB-5550 represents the company's third natural killer (NK) cell engager entering the clinical development phase. GTB-5550 TriKE is engineered to engage natural killer cells by targeting the B7-H3 antigen, which is expressed on a range of solid tumor cancers. This therapeutic strategy leverages the immune system’s innate ability to identify and destroy cancer cells, focusing specifically on tumors with B7-H3 expression. The development of this candidate underscores GT Biopharma's commitment to harnessing NK cell biology for cancer treatment. Michael Breen, Executive Chairman and CEO of GT Biopharma, highlighted the significance of the IND submission, describing it as a "tremendous accomplishment for the company," especially as it expands its NK cell engager portfolio. He emphasized that the company intends to initiate a Phase 1 basket trial in 2026 that will evaluate GTB-5550 across various solid tumor types. This broad approach is intended to assess the drug's efficacy and safety across multiple cancer indications characterized by B7-H3 expression. The upcoming Phase 1 trial design incorporates both dose-escalation and dose-expansion components. In the Phase 1a portion, GT Biopharma plans to test up to seven different dose levels to establish the maximum tolerated dose (MTD). Following dose determination, the Phase 1b dose-expansion will administer the MTD across seven metastatic disease cohorts. This structure aims to confirm tolerability and further investigate safety profiles, assuming that toxicity rates remain consistent across the cohorts. Treatment administration will involve subcutaneous injections into the abdominal area. The dosing schedule is set for five consecutive days during both Week 1 and Week 2, followed by a two-week treatment hiatus—constituting a four-week cycle. Patients will undergo at least two cycles of treatment, with subsequent disease reassessments planned after every two cycles and continuing on intervals of eight to twelve weeks. Treatment duration may extend until disease progression, unacceptable toxicity, patient choice to discontinue, or when continuation ceases to be in the patient’s best interest. Importantly, patients enrolled in the trial will be monitored for progression-free survival (PFS) and overall survival (OS) over a 12-month follow-up period, providing key clinical endpoints to evaluate treatment efficacy. GT Biopharma is concurrently advancing the clinical development of GTB-3650, another NK cell engager focused on myeloid blood cancers. This ongoing Phase 1 trial is actively enrolling patients, with results anticipated in the first half of 2026. Data from the GTB-3650 study are expected to inform the clinical development pathway for GTB-5550, helping to refine dosing, safety, and efficacy signals in its targeted patient population. Regarding market potential, Breen noted that cancers expressing B7-H3 contribute to a segment of the global solid tumor market, which is valued at an estimated $362 billion worldwide. This substantial market size elucidates the potential commercial impact of successful therapies targeting this antigen. In financial markets, GT Biopharma’s stock price responded positively to the announcement, gaining 12.92% in premarket trading to $0.75 as of the latest check on Thursday. GT Biopharma’s strategic expansion into solid tumor immunotherapy via GTB-5550 demonstrates a focused effort to apply natural killer cell engager technology beyond hematologic malignancies, aiming to address significant unmet needs in oncology. The planned Phase 1 basket trial in 2026 will serve as a pivotal step in assessing this investigational agent's therapeutic utility across diverse solid tumor indications expressing B7-H3.