GT Biopharma Submits IND To FDA For GTB-5550 TriKE, A B7-H3-Targeted NK Cell Engager For Treating B7-H3–Expressing Solid Tumor Cancers

GT Biopharma, Inc., a clinical-stage immuno-oncology company developing novel cancer treatments using its proprietary TriKE natural killer (NK) cell engager platform, has announced the submission of an Investigational New Drug (IND) application to the U.S. Food and Drug Administration (FDA) in December 2025. The IND is for GTB-5550 TriKE, a B7-H3-targeted NK cell engager intended for the treatment of solid tumors that express the B7-H3 antigen.

According to Michael Breen, Executive Chairman and Chief Executive Officer of GT Biopharma, the IND submission marks an important achievement for the company, as GTB-5550 becomes another NK cell engager candidate progressing toward clinical testing. He explained that while the company continues enrolling patients in its Phase 1 trial of GTB-3650 for myeloid blood cancers, new clinical data expected in the first half of 2026 may provide early signs of activity. 

GT Biopharma also plans to initiate a Phase 1 basket study of GTB-5550 in 2026, which will include patients across several types of solid tumors. Breen added that insights from the GTB-3650 program are expected to guide development of GTB-5550, particularly since B7-H3-expressing solid tumor cancers represent a significantly larger patient population than myeloid blood cancers. Globally, B7-H3-positive solid tumors form a substantial segment of the solid tumor market, which is valued at approximately $362 billion, according to Data Bridge Market Research.

GTB-5550 is a tri-specific natural killer cell engager built with camelid nanobody technology. It consists of three linked components: a nanobody that binds to the CD16 activating receptor on NK cells, a wild-type IL-15 linker that supports NK cell growth, priming, and survival, and a nanobody that targets the B7-H3 antigen commonly expressed on tumor cells. Together, these elements are designed to activate NK cells, stimulate their expansion, and direct them toward B7-H3-positive cancer cells.

The planned Phase 1 clinical trial for GTB-5550 will be the first to test a dual-nanobody TriKE using subcutaneous administration, which is expected to be more convenient for patients. The Phase 1a dose-escalation portion will evaluate up to seven dose levels to determine the maximum tolerated dose. The Phase 1b expansion phase will then test this selected dose across seven metastatic solid tumor groups, including castration-resistant prostate cancer, ovarian cancer, breast cancer, head and neck cancer, non-small cell lung cancer, pancreatic cancer, and bladder cancer. This stage of the study will focus on confirming safety and tolerability across different cancer types.

GTB-5550 will be administered as a subcutaneous injection in the abdominal area for five consecutive days in Week 1 and Week 2, followed by two weeks without treatment, forming a four-week cycle. Patients will receive at least two cycles of therapy, after which their disease status will be reassessed. Follow-up evaluations will occur every eight to twelve weeks. Treatment may continue as long as patients are benefiting and not experiencing unacceptable side effects, or until disease progression or a clinical decision is made to stop therapy. After completing treatment, all patients will be monitored for twelve months to assess progression-free survival and overall survival.