<p><strong>GT Biopharma Inc.</strong> (NASDAQ:GTBP) on Thursday dosed the first patient on a Phase 1 dose-escalation basket trial evaluating GTB-5550, its B7-H3-targeted NK cell engager for solid tumors expressing B7-H3.</p>



<h2>GT Biopharma Advances TriKE Platform Into Solid Tumors</h2>



<p>&#34;The ongoing Phase 1 progress with GTB-3650 in hematologic malignancies now gives us the confidence to advance the platform with GTB-5550 to target B7-H3, which is broadly expressed across many of the most common and difficult-to-treat solid tumor cancers. We look forward to providing updates on the trial's progress throughout the second half of 2026&#34;, said <strong>Michael Breen</strong>, Executive Chairman and CEO of GT Biopharma.</p>



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<h2>Phase 1 Trial To Focus Initially On Prostate Cancer Patients</h2>



<p>The Phase 1 trial of GTB-5550 will be the first nanobody TriKE tested using subcutaneous dosing. The Phase 1a dose-escalation portion will primarily enroll prostate cancer patients and evaluate up to six dose levels to identify the maximum tolerated dose (MTD).</p>



<p>Following dose escalation, the Phase 1b expansion phase will enroll patients across up to seven tumor types, including castration-resistant prostate cancer, ovarian cancer, breast cancer, head and neck cancer, non-small cell lung cancer, pancreatic cancer, and bladder cancer, while further evaluating safety, tolerability, and preliminary anti-tumor activity.</p>



<h2>GTB-5550 Dosing Schedule And Patient Monitoring Details</h2>



<p>GTB-5550 will be administered through subcutaneous injection in the abdominal area for five consecutive days during Week 1 and Week 2, followed by two weeks without treatment. Each treatment cycle lasts four weeks.</p>



<p>Subsequent cycles will include treatment three times weekly for two weeks, followed by two weeks off treatment. A minimum of two cycles is planned, with disease reassessment scheduled after two cycles and every 8-12 weeks thereafter.</p>



<p>Treatment may continue until disease progression, unacceptable toxicity, patient refusal, or when treatment is no longer considered in the patient's best interest.</p>



<p>Patients will be followed for 12 months to evaluate progression-free survival (PFS) and overall survival (OS).</p>



<p>The immuno-oncology company had cash and cash equivalents of approximately $7 million as of December 31, 2025, and an unaudited pro-forma cash balance as of January 31, 2026, of approximately $9 million, which is anticipated to provide cash runway through the fourth quarter of 2026.</p>



<p><strong>GTBP Price Action:</strong> GT Biopharma shares were up 13.94% at $0.35 during premarket trading on Thursday. The stock is trading near its 52-week low of $0.26, according to Benzinga Pro data.</p>



<p><em>Photo via Shutterstock</em></p>

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<p>GT Biopharma has initiated a Phase 1 trial for its drug candidate GTB-5550, targeting B7-H3-positive solid tumors. The trial will initially focus on prostate cancer patients, with plans to expand to seven tumor types. The treatment involves subcutaneous injections over a four-week cycle, with patient monitoring for up to 12 months. The company reported a cash balance of approximately $9 million, expected to last through Q4 2026. GT Biopharma shares rose 13.94% to $0.35 during premarket trading.</p>

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EXCLUSIVE: GT Biopharma Begins Testing Of Lead Solid Tumor Drug Candidate Across Multiple Cancer Types