Phase 1 Trial: GTB-5550, Another B7-H3 NK-targeted Therapy for mCRPC

GTB-5550 has begun Phase 1 clinical testing in solid tumors, marking the first patient dosing in a dose-escalation basket study. The trial is starting with prostate cancer, a setting where B7-H3 is reportedly highly expressed and where treatment options remain limited in the metastatic castration-resistant stage.

The therapy is being delivered subcutaneously, which is notable because it could make administration more convenient than many infused therapies if the drug continues to show promise. The study will examine multiple dose levels before moving into expansion cohorts that include ovarian, breast, head and neck, non-small cell lung, pancreatic, and bladder cancers.

GTB-5550 is designed to recruit natural killer cells against tumor cells through the B7-H3 target, while also incorporating the TriKE platform’s immune-stimulating features. In a difficult disease like metastatic castration-resistant prostate cancer, that kind of mechanism is worth watching closely, especially if early PSA changes suggest biological activity.

Preclinical studies of GTB‑5550 in prostate cancer showed that the construct substantially boosts NK‑cell function against prostate tumor cells, including difficult settings such as enzalutamide‑resistant lines and hypoxic conditions.
NK cells from both healthy donors and prostate cancer patients displayed stronger, antigen‑specific degranulation and higher cytotoxic activity against prostate cancer cell lines when exposed to GTB‑5550, and this activity was maintained even in the presence of myeloid‑derived suppressor cells, a key immunosuppressive component of the prostate tumor microenvironment. In xenograft mouse models of prostate cancer, GTB‑5550 treatment translated this immune activation into improved tumor control compared with IL‑15 alone or no treatment, supporting the move into first‑in‑human trials in metastatic castration‑resistant disease.

For now, the main question is whether the drug can combine tolerability with enough signal to justify further development. The beginning of dosing does not answer that question, but it does move the program from concept to clinic, which is always an important milestone.

Source.

Clinical trial.