GT Biopharma's Pivot: FDA Clears Myeloma Trial for B7-H3 Engager GTB-5550

SAN FRANCISCO, CA – September 15, 2026 – GT Biopharma has secured a critical green light from the U.S. Food and Drug Administration (FDA) for its Investigational New Drug (IND) application, clearing the path for GTB-5550 to be studied in multiple myeloma. The move marks a significant strategic diversification for the company's proprietary TriKE® platform, extending its reach from solid tumors into the challenging arena of hematological malignancies. However, the initiation of this new Phase 1 trial comes with a major caveat: it is entirely contingent on the firm's ability to secure non-dilutive grant funding, a detail that underscores the financial tightrope many clinical-stage biotechs walk.

“Today’s IND to expand the potential indications for GTB-5550 highlights the diverse utility of our Trike® platform,” said Michael Breen, Executive Chairman and Chief Executive Officer of GT Biopharma. “The company remains focused on its two ongoing Phase 1 trials with GTB-5550 and GTB-3650, both of which are actively enrolling, and we look forward to the potential initiation of a third Phase 1 trial, pending receipt of non-dilutive grant funding.”

A New Weapon for a Stubborn Disease

Multiple myeloma remains an incurable blood cancer characterized by cycles of remission and relapse. For patients who have progressed through multiple lines of therapy, the prognosis is often bleak, with treatment options dwindling and their effectiveness diminishing over time. This creates a desperate and persistent unmet medical need for novel therapeutic approaches that can offer new hope to a heavily pre-treated population.

GT Biopharma aims to address this gap by targeting B7-H3, a protein that has garnered significant interest in the oncology community. While B7-H3 is minimally expressed on healthy tissues, it is overexpressed on a wide array of cancer cells, including, according to recent research, the plasma cells of a majority of multiple myeloma patients. Its presence is often linked to immune evasion and a poorer prognosis, making it an attractive bullseye for targeted therapies.

“Targeting B7-H3 remains an active area for clinical development of new anti-cancer drugs, yet most competitive efforts are focused on solid tumors,” noted Dr. Aimee Merino, Assistant Professor of Medicine at the University of Minnesota, whose institution licensed the TriKE® technology to GT Biopharma. “Based on our findings of high levels of B7-H3 expression within the bone marrow of newly diagnosed multiple myeloma patients, we have begun a dedicated effort for this novel approach in later-line patients, which continues to be an area of unmet need.” Dr. Merino also pointed to encouraging preclinical results showing high levels of NK cell-mediated anti-tumor activity in the presence of GTB-5550.

The TriKE® Engine and a Crowded Field

At the heart of GT Biopharma’s strategy is its Tri-specific Killer Engager (TriKE®) platform. These complex molecules are engineered to perform a three-part mission. GTB-5550, for instance, uses one arm to bind to the CD16 receptor on the surface of Natural Killer (NK) cells—the immune system's rapid-response assassins. A second arm grabs onto the B7-H3 protein on the tumor cell, effectively handcuffing the killer to its target. The third component, a built-in interleukin-15 (IL-15) fragment, acts as a powerful stimulant, promoting the survival and proliferation of the NK cells directly at the tumor site, turning them into a more potent and durable fighting force.

This expansion into multiple myeloma is a calculated diversification. While the B7-H3 target is being pursued by other companies, most of those efforts are concentrated in solid tumors. By applying its technology to a hematologic cancer, GT Biopharma is carving out a potentially less crowded niche. Furthermore, the planned trial will utilize a patient-friendly subcutaneous injection, a significant quality-of-life improvement over intravenous infusions and a formulation designed to extend the drug's half-life.

However, the company is not operating in a vacuum. The multiple myeloma landscape is fiercely competitive, with powerful incumbents and a pipeline of innovative therapies, including BCMA-targeting CAR-T cells and bispecific antibodies. GTB-5550's NK cell-based mechanism offers a distinct immunological approach that could prove effective where others have failed, particularly in overcoming antigen escape, but it will need to deliver compelling clinical data to stand out.

The High-Stakes Funding Gambit

For a clinical-stage company, progress is measured in data, but it is fueled by capital. GT Biopharma's announcement puts its financial strategy in sharp relief. The company reported an unaudited proforma cash balance of approximately $11 million, which it anticipates will fund operations into the third quarter of 2027. This runway provides a buffer for its two currently active trials but makes the explicit dependency on external, non-dilutive funding for the new myeloma trial a critical variable for investors.

Securing a grant from an organization like the National Cancer Institute or the Multiple Myeloma Research Foundation would be a significant validation of the science behind GTB-5550. It would also allow the company to advance this promising program without diluting the value of its stock by issuing new shares—a constant concern for shareholders of development-stage firms. This funding contingency introduces an element of uncertainty into the clinical timeline but also reflects a fiscally prudent approach to pipeline expansion. This financial balancing act is further highlighted by the company's recent 1-for-25 reverse stock split, a common maneuver to maintain NASDAQ listing compliance that can also signal underlying market pressure.

Charting the Clinical Course

The proposed first-in-human trial of a B7-H3 TriKE® in multiple myeloma is meticulously designed. The initial Phase 1a dose-escalation stage will enroll patients who have already failed at least three prior lines of therapy, targeting the population with the most urgent need. Researchers will evaluate up to six dose levels to determine the maximum tolerated dose (MTD). Once the MTD is established, a Phase 1b expansion cohort will enroll 25 patients to further assess safety, tolerability, and preliminary signs of anti-tumor activity.

Patients will receive subcutaneous injections three times a week for the first two weeks of a four-week cycle. Disease activity will be monitored at the end of each cycle, with pathways for patients to continue treatment for up to a year if they show a response. This study runs parallel to the company’s other clinical endeavors, including a Phase 1 trial of GTB-5550 in solid tumor patients, which is expected to have an update in the fourth quarter of 2026, and an ongoing Phase 1 trial for GTB-3650 in patients with acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Together, these trials represent a broad and ambitious effort to validate the TriKE® platform across multiple cancers and targets, with the new myeloma study representing a pivotal next chapter in the company's story.