GT Biopharma, Inc.

We are a clinical stage biopharmaceutical company focused on the development and commercialization of novel immuno-oncology products based on our proprietary Tri-specific Killer Engager (“TriKE®”), and Tetra-specific Killer Engager (“Dual Targeting TriKE®”) fusion protein immune cell engager technology platforms. Our TriKE® and Dual Targeting TriKE® platforms generate proprietary therapeutics designed to harness and enhance the cancer killing abilities of a patient’s own natural killer cells (“NK cells”). Once bound to an NK cell, our moieties are designed to activate the NK cell to direct it to one or more specifically targeted proteins expressed on a specific type of cancer cell or virus infected cell, resulting in the targeted cell’s death. TriKE®s can be designed to target any number of tumor antigens, including B7-H3, HER2, CD33 and PDL1, on hematologic malignancies or solid tumors and do not require patient-specific customization. We believe our TriKE® and Dual Targeting TriKE® platforms that activate endogenous NK cells are potentially safer than T-cell immunotherapy because there is less cytokine release syndrome (“CRS”) and fewer neurological complications. Our preclinical data suggests that this is explained by the TriKE® dependent, CD16 directed, IL-15 proliferation of NK cells, with little effect endogenous T cells.

We are using our TriKE® platform with the intent to bring to market immuno-oncology products that can treat a range of hematologic malignancies, solid tumors, and potentially autoimmune disorders. The platform is scalable, and we are implementing processes to produce investigational new drug (“IND”) ready moieties in a timely manner after a specific TriKE® conceptual design. Specific drug candidates can then be advanced into the clinic on our own or through potential collaborations with partnering companies. We believe our TriKE®s may have the ability, if approved for marketing, to be used as both monotherapy and in combination with other standard-of-care therapies.

Our initial work was conducted in collaboration with the Masonic Cancer Center at the University of Minnesota under a program led by Dr. Jeffrey Miller, Professor of Medicine, and the Interim Director at the Masonic Cancer Center. Dr. Miller, who also serves as our Consulting Senior Medical Director, is a recognized key opinion leader in the field of NK cell and IL-15 biology and their therapeutic potential. We have exclusive rights to the TriKE® platform and are generating additional intellectual property for specific moieties.

Product Pipeline

Our current TriKE® product candidate pipeline (as of February 23, 2026) is summarized in the table below:

GTB-3550

GTB-3550 was our first TriKE® product candidate and its clinical development was suspended so that we could focus resources on second-generation TriKEs®. GTB-3550 is a tri-specific killer engager, or TriKE, comprised of two single-chain variable fragments (“scFv”) composed of the variable regions of the heavy and light chains of anti-CD16 and anti-CD33 antibodies and a modified form of IL-15. We studied this anti-CD16-IL-15-anti-CD33 TriKE® in CD33 positive leukemias, a marker expressed on tumor cells in acute myelogenous leukemia (“AML”), and myelodysplastic syndrome (“MDS”). The anti-CD33 antibody fragment in GTB-3550 was derived from the M195 humanized anti-CD33 scFv. We believe the approval of the antibody-drug conjugate gemtuzumab validates the targeting of CD33.

We previously announced the interim clinical trial results for GTB-3550, which showed significantly reduced CD 33+ bone marrow blast levels by 33.3%, 61.7%, 63.6%, 50% in Patient 5 (25 µg/kg/day), Patient 7 (50 µg/kg/day), Patient 9 (100 µg/kg/day), and Patient 11 (150 µg/kg/day), respectively. After the end of infusion, GTB-3550 and IL-15 concentrations declined rapidly with overall geometric mean terminal phase elimination half-life (T1/2) of 2.2 and 2.52 hours, respectively. There was minimal CRS resulting from hyperactivation of patient’s T-cell population at doses 5–150 µg/kg/day.

Despite the positive interim clinical trial results, GTB-3550 was replaced by a more potent next-generation camelid nanobody TriKE®, GTB-3650, that similarly targets CD33 on relapsed/refractory AML and high-risk MDS. A key difference between GTB-3550 and GTB-3650 is the incorporation of camelid antibody technology instead of a scFv; our preclinical experience showed markedly enhanced potency of TriKEs® comprised of camelid components. This is illustrated below by better tumor control of AML bearing animals with GTB-3650 (purple dots) compared to GTB-3550 (blue dots). This provided the rationale for pausing further development of GTB-3550 and moving over to solely develop the second-generation, camelid-based TriKE® platform.

Second Generation TriKE®s Utilize Camelid Nanobody Technology

Our goal is to be a leader in immuno-oncology therapies targeting a broad range of indications including hematological malignancies and solid tumors. A key element of our strategy includes introducing a next-generation camelid nanobody platform. Camelid antibodies (often referred to as nanobodies) are smaller than human immunoglobulin, consisting of two heavy chains instead of two heavy and two light chains. These nanobodies have the potential to have greater affinity to target antigens, potentially resulting in greater potency. We are utilizing this camelid antibody structure for all of our new TriKE® product candidates.

To develop second generation TriKE®s, we designed a new humanized CD16 engager derived from a single-domain antibody. While scFvs consist of a heavy and a light variable chain joined by a linker, single-domain antibodies consist of a single variable heavy chain capable of engaging without the need of a light chain counterpart (see figure below).

These single-domain antibodies are thought to have certain attractive features for antibody engineering, including physical stability, ability to bind deep grooves, and increased production yields, amongst others. Pre-clinical studies demonstrated increased NK cell activation against CD33+ targets including enhanced NK cell degranulation (% CD107a+) and IFNγ with the single-domain CD16 TriKE® (cam 16-wt15-33; GTB-3650) compared to the original TriKE® (scFv16-m 15-33; GTB-3550) (see figure below). This data was published by Dr. Felices M et al (2020) in Cancer Immunol Res.

CD33+ HL60 Targets in Killing Assays

The purple line represents the GTB-3650 and the blue line represents GTB-3550.

GTB-3650

GTB-3650 is a TriKE® which targets CD33 on the surface of myeloid leukemias and an agonistic camelid engager to the potent activating receptor on NK cells, CD16. Use of this engager enhances the activity of wild type IL-15 included in GTB-3650. The TriKE® approach provides a novel way to specifically target these tumors by leveraging NK cells, which have been shown to mediate relapse protection in this setting, in an anti-CD33-targeted fashion. We are advancing GTB-3650 to clinical studies based on pre-clinical data showing a marked increase in potency compared to GTB-3550, which we anticipate could lead to an enhanced efficacy signal in AML and MDS. We advanced GTB-3650 through requisite preclinical studies and filed an IND application with the U.S. Food and Drug Administration (the “FDA”) in December 2023. In late June 2024, the FDA cleared our IND Application for GTB-3650. We started study enrollment targeting patients with relapsed/refractory AML and high grade MDS on January 21, 2025. This initial study is testing GTB-3650 as monotherapy testing administration 2 weeks on and two weeks off (to prevent NK cell exhaustion) for at least 2 cycles of therapy, as agreed on with the FDA.

GTB-5550

GTB-5550 is a B7-H3 targeted TriKE® which targets B7-H3 on the surface of advanced solid tumors (figure above). GTB-5550 is our first dual camelid TriKE®. B7-H3 is expressed on a broad spectrum of solid tumor malignancies, allowing our team to target these malignancies through GTB-5550. Pre-clinical work has shown that this molecule has NK-cell targeted activity against a variety of solid tumors, including head and neck cancer squamous cell carcinoma (figure below), prostate cancer, breast cancer, ovarian cancer, glioblastoma, and lung cancer (amongst others).

We advanced GTB-5550 through requisite preclinical studies and filed an IND application with the FDA in October 2023 with a written response from the FDA in December 2023. The main question from the FDA was regarding pre-clinical toxicology and a pivot to subcutaneous dosing. In early January 2026, the FDA cleared our IND Application for GTB-5550. We anticipate starting study enrollment in mid-year 2026. The initial trial is designed as a basket trial for patients with B7-H3+ solid tumors using Monday through Friday dosing (2 weeks on and 2 weeks off to prevent immune exhaustion).

GTB-7550

GTB-7550 TriKE® is a product candidate in development for the treatment of lupus and other autoimmune disorders. GTB-7550 TriKE® is a tri-specific molecule composed of a camelid nanobody that binds the CD16 receptor on NK cells, a scFv engager against CD19 on malignant and normal B cells, and a human IL-15 sequence between them.

Published data shows that GTB-7550 effectively targets CD19+ malignant cell lines and primary chronic lymphocytic leukemia. Preliminary data shows that GTB-7550 can target and eliminate normal B cells, which we are continuing to test in mice. We are currently exploring and assessing potential manufacturers of GTB-7550.

Oncology Markets

Acute Myeloid Leukemia and Myelodysplastic Syndromes

AML is a heterogeneous hematologic stem cell malignancy in adults with an incidence rate of 4.3% per 100,000 populations. The median age at the time of diagnosis is 68 years. AML is an aggressive disease and is fatal without anti-leukemic treatment. AML is the most common form of adult leukemia in the U.S. These patients will require frontline therapy, usually chemotherapy including cytarabine and an anthracycline, a therapy that has not changed in over 40 years. Myelodysplastic syndromes are a heterogeneous group of myeloid neoplasms characterized by dysplastic features of erythroid/myeloid/megakaryocytic lineages, progressive bone marrow failure, a varying percentage of blast cells, and enhanced risk to evolve into acute myeloid leukemia. It is estimated that over 10,000 new cases of MDS are diagnosed each year and there are minimal treatment options; other estimates have put this number higher. In addition, the incidence of MDS is rising for unknown reasons.

B7-H3 Positive Solid Tumors

The B7-H3 protein, which functions as a checkpoint inhibitor, has been identified in many of the most common solid tumor cancers, including but not limited to bladder, breast, cervical, colorectal, endometrial, esophageal, gastric, glioma, kidney, liver, lung, pancreatic, prostate, head and neck cancer, and melanoma. In recent studies, B7-H3 has been identified as a critical promoter of tumor cell proliferation, migration, invasion, epithelial-to-mesenchymal transition, cancer stemness and drug resistance. Because this protein does not seem to be expressed in normal cells, this makes it an attractive target for therapeutic intervention.

Manufacturing

We do not currently own or operate manufacturing facilities for the production of clinical or commercial quantities of any of our product candidates. We rely on third-party contract manufacturing operations, including Cytovance Biologics, Inc. (“Cytovance”), a related party as of the year ended December 31, 2024, but not as of the year ended December 31, 2025, to produce and/or test our compounds and expect to continue to do so to meet the preclinical and clinical requirements of our potential product candidates as well as for our future commercial needs. We require in our manufacturing and processing agreements that third-party product manufacturers produce intermediates, active pharmaceutical ingredients (“API”), and finished products in accordance with the FDA’s current Good Manufacturing Practices (“cGMP”), and all other applicable laws and regulations. We maintain confidentiality agreements with potential and existing manufacturers to protect our proprietary rights related to our drug candidates.

Competition

The market for therapeutic immuno-oncology products is highly competitive. Our therapeutic immuno-oncology (“IO”) development programs face, and will continue to face, intense competition from pharmaceutical, biopharmaceutical and biotechnology companies, as well as numerous academic and research institutions and governmental agencies engaged in drug discovery activities or funding, both in the United States and abroad. Some of these competitors are pursuing the development of drugs and other therapies that target the same diseases and conditions that we are targeting with our product candidates.

As a general matter, we also face competition from many companies that are researching and developing cell therapies. Many of these companies have financial and other resources substantially greater than ours. In addition, many of these competitors have significantly greater experience in testing pharmaceutical and other therapeutic products, obtaining FDA and other regulatory approvals, and marketing and selling. If we obtain regulatory approval for any of our product candidates, we also will be competing with respect to manufacturing efficiency and marketing capabilities, areas in which we have limited or no commercial-scale experience. Mergers and acquisitions in the pharmaceutical and biotechnology industries may result in even more resources’ being concentrated by our competitors. Competition may increase further as a result of advances made in the commercial applicability of our technologies and greater availability of capital for investment in these fields.

TriKE®Patents and Trademarks

On August 24, 2021, two patents were issued by the US Patent Office covering our pipeline of clinical and non-clinical product candidates consisting of tri-specific killer engagers, or TriKE®s, designed to target natural killer, or NK, cells and tumor or virus infected cells forming an immune synapse between the NK cell and the tumor cell thereby inducing NK cell activation at that site. The patents broadly include TriKE®s that target the CD16 receptor, which includes the more potent camelid nanobody sequence, an IL-15 activating domain, and any targeting domain.

2023 Sponsored Research Agreement

On May 20, 2024, the Company entered into a sponsored research agreement (the “2023 Sponsored Research Agreement”) with the Regents of the University of Minnesota (the “University of Minnesota”), effective July 1, 2023. Payments totaling approximately $1.7 million were initially due over the life of the agreement. The purpose of the agreement was for the University of Minnesota to continue work with the Company with three major goals in mind: (1) support the Company’s TriKE® product development and commercial GMP manufacturing efforts; (2) TriKE® pharmacokinetics optimization in humans and investigation of effects of altering the route of administration; and (3) research and development of TriKE® platform. The major deliverables proposed were: (1) creation of IND enabling data for TriKE® constructs in support of the Company’s product development and commercial GMP manufacturing efforts outside of the University of Minnesota; (2) TriKE® platform drug delivery changes to allow transition from intravenous (IV) continuous infusion to alternative drug delivery administration (IV bolus, intraperitoneal [IP], subcutaneous [SQ]) and extended PK in humans and gain an increased understanding of changes in the patient’s native NK cell population as a result of alteration of TriKE® administration; and (3) research and development of TriKE® platform combination with other FDA approved (or soon to be approved) therapeutics and alterations to TriKE® platform through formation of immune complexes. Most studies used TriKE® DNA/amino acid sequences created by the Company under existing licensing terms.

On June 18, 2025, the 2023 Sponsored Research Agreement was amended to expire on December 31, 2025. In addition, payments amounting to $216,000 were added bringing the total payments due over the life of the agreement to approximately $1.9 million.

The Company recorded an expense classified as research and development of approximately $863,000 and $1,078,000, pursuant to the 2023 Sponsored Research Agreement, for the years ended December 31, 2025 and 2024, respectively.

As of December 31, 2025, there were no outstanding commitments in relation to unbilled and unaccrued amounts from the University of Minnesota pursuant to the 2023 Sponsored Research Agreement for services that have not yet been rendered as of December 31, 2025.

2016 Exclusive Patent License Agreement

Effective July 18, 2016, the Company entered into an exclusive patent license agreement with the University of Minnesota (as amended, the “2016 Exclusive Patent License Agreement”), to further develop and commercialize cancer therapies using TriKE® technology developed by researchers at the University of Minnesota to target NK cells to cancer. Under the terms of the agreement, the Company receives exclusive rights to conduct research and to develop, make, use, sell, and import TriKE® technology worldwide for the treatment of any disease, state, or condition in humans. The Company is responsible for obtaining all permits, licenses, authorizations, registrations, and regulatory approvals required or granted by any governmental authority anywhere in the world that is responsible for the regulation of products such as the TriKE® technology, including without limitation the FDA and the European Agency for the Evaluation of Medicinal Products in the European Union. The agreement requires an upfront payment of $200,000, and license maintenance fees of $200,000 for years 2017 through 2020, and $100,000 per year beginning in year 2021 and each year thereafter. The agreement also includes 4% royalty fees on the net sales of licensed products, not to exceed 6% under subsequent license agreements or amendments to this agreement, and minimum royalty payments due upon the commencement of commercial sales of licensed product is $250,000 beginning in 2022, $2 million beginning in 2025, and $5 million beginning in 2027 throughout the remainder of the term. The agreement also includes numerous performance milestone payments including clinical development milestone payments totaling $3.1 million, and one-time sales milestone payments of $1 million upon reaching $250 million in cumulative gross sales, and $5 million upon reaching $500 million in cumulative gross sales of licensed products.

Effective May 13, 2024, the Company entered into an amended and restated exclusive patent license agreement with the University of Minnesota (the “A&R 2016 Exclusive Patent License Agreement”). The amendment requires an upfront payment of $145,000 and amends the license maintenance fees to $50,000 in 2025, and $100,000 per year beginning in year 2026 and each year thereafter. The amendment also includes 1% to 5% royalty fees on the net sales of licensed products, not to exceed 6% under subsequent license agreements or amendments, and minimum royalty payments due upon the commencement of commercial sales of licensed product is $250,000 in year one, $2 million in years two through five, and $5 million in year six throughout the remainder of the term. The amendment also includes numerous performance milestone payments including clinical development milestone payments totaling $3.1 million, and one-time sales milestone, and one-time sales milestone payments of $1 million upon reaching $250 million in cumulative gross sales, and $5 million upon reaching $500 million in cumulative gross sales of licensed products.

The Company recorded an expense classified as research and development of $50,000 and $145,000, pursuant to the A&R 2016 Exclusive Patent License Agreement, for the years ended December 31, 2025 and 2024, respectively.

2021 Exclusive License Agreement

Effective March 26, 2021, the Company entered into an exclusive license agreement with the University of Minnesota (the “2021 Exclusive Patent License Agreement”), specific to the B7H3 targeted TriKE®. The agreement requires an upfront payment of $20,000, and license maintenance fees of $5,000 per year beginning in year 2022 and each year thereafter. The agreement also includes 2.5% to 5% royalty fees on the net sales of licensed products, and minimum royalty payments due upon the commencement of commercial sales of licensed product of $250,000 in year one though four, and $2 million beginning in year five and throughout the remainder of the term. The agreement also includes numerous performance milestone payments including clinical development milestone payments totaling $3.1 million, and one-time sales milestone payments of $1 million upon reaching $250 million in cumulative gross sales, and $5 million upon reaching $500 million in cumulative gross sales of licensed products. There is no double payment intended; if one of the milestone payments has been paid under the A&R 2016 Exclusive Patent License Agreement no further payment is due for the corresponding milestone.

The Company recorded an expense classified as research and development of $5,000 and $0, pursuant to the 2021 Exclusive License Agreement, for years ended December 31, 2025 and 2024, respectively.

2024 GTB-3650 Clinical Trial Agreement

On November 18, 2024, the Company entered into an investigator initiated clinical trial agreement (the “2024 Clinical Trial Agreement”) with the University of Minnesota, pursuant to which, the University of Minnesota shall sponsor an IND application for IND 165546 GTB-3650 (the “Research Program”) and shall serve as a sponsor investigator for a phase 1 clinical trial entitled, “GTB-3650 (CD16/IL-15/CD33) Tri-Specific Killer Engager (TriKE) for the Treatment of High Risk Myelodysplastic Syndromes (MDS), Refractory/Relapsed Acute Myeloid Leukemia (AML), and Minimal Residual Disease in AML,” designed by the University of Minnesota (the “Study”). The Research Program is being conducted for clinical research use. The budget for the Study, including without limitations, funding and resources, provides for up to approximately $2 million over the course of three years borne by the Company. The Study data will be owned by the University of Minnesota, however, the Company may use the Study data subject to any applicable signed informed consent documents and authorization forms, applicable law and terms of the 2024 Clinical Trial Agreement. The University of Minnesota and the Company will each have the right to publish the Study results. The 2024 Clinical Trial Agreement may be terminated by the Company or the University of Minnesota at any time upon thirty days’ written notice to the other party, by the University of Minnesota immediately for health, welfare and safety reasons, or by either party if the other party materially breaches the 2024 Clinical Trial Agreement, provided that the breaching party fails to cure such breach within thirty days.

The Company recorded an expense classified as research and development of approximately $750,000 and $190,000, pursuant to the 2024 Clinical Trial Agreement, for the years ended December 31, 2025 and 2024, respectively.

As of December 31, 2025, the Company’s commitments in relation to unbilled and unaccrued amounts from the University of Minnesota pursuant to the 2024 Clinical Trial Agreement for services that have not yet been rendered as of December 31, 2025, amounted to approximately $1.1 million.

Common Stock (February 2024 Reverse Stock-Split)

On February 2, 2024, the Company effectuated a reverse stock-split of its common stock, at a ratio of 1 for 30. The Company’s common stock began trading on a reverse stock-split-adjusted basis on The Nasdaq Capital Market on February 5, 2024, under the existing trading symbol “GTBP.”

As a result of the reverse stock-split, every thirty (30) shares of issued and outstanding common stock were automatically combined into one issued and outstanding share of common stock, without any change in the par value per share. The reverse stock-split reduced the number of shares of common stock outstanding on the effective date of the reverse stock-split from 41,419,000 shares to 1,380,633 shares, subject to minor adjustments due to the treatment of fractional shares.

Proportionate adjustments were made to the per share exercise price and the number of shares of common stock that could be purchased upon exercise of outstanding stock options and warrants for the Company’s common stock, and to the number of shares of common stock reserved for future issuance pursuant to the Company’s 2022 Omnibus Incentive Plan.

All share and per share information within this report have been adjusted to retroactively reflect the reverse stock-split as of the earliest period presented.

The Committed Equity Facility

On May 14, 2025, the Company entered into the common shares purchase agreement (as amended, the “Common Shares Purchase Agreement”) with Bristol Capital, LLC, a Delaware limited liability company (“Bristol”), and Five Narrow Lane, L.P., a Delaware limited partnership (“5NL”), relating to a committed equity facility (the “Committed Equity Facility”), whereby we have the right from time to time at our option to sell to the Facility Investors (as defined below) up to $20 million of our common stock subject to certain conditions and limitations set forth in the Common Shares Purchase Agreement. Bristol subsequently assigned all of its all of its right, title, interest and obligations in the Common Shares Purchase Agreement to its affiliate, Hailstone Peak Funding, LLC, a Delaware limited liability company (“Hailstone,” and together with 5NL, the “Facility Investors”). Sales of the shares of common stock to the Facility Investors under the Common Shares Purchase Agreement, and the timing of any sales, are determined by the Company from time to time in its sole discretion and depend on a variety of factors, including, among other things, market conditions, the trading price of the common stock and determinations by the Company regarding the use of proceeds of such shares of common stock. The net proceeds from any sales under the Common Shares Purchase Agreement will depend on the frequency with, and prices at, which the shares of common stock are sold to the Facility Investors. The purchase price of the shares of common stock that the Company elects to sell to the Facility Investors pursuant to the Common Shares Purchase Agreement are equal to 93% of the volume weighted average price of the shares of Common Stock during the applicable purchase date on which the Company has timely delivered written notice to the Facility Investors directing it to purchase shares of common stock under the Common Shares Purchase Agreement.

Employees and Human Capital Resources

At the date of this Annual Report, we have one full-time employee and numerous consultants to carry on our operations. Many of our activities are outsourced to consultants who provide services to us on a project basis. As business activities require and capital resources permit, we will hire additional employees and consultants to fulfill our Company’s needs.

Available Information

We post our annual report on Form 10-K, quarterly reports on Form 10-Q, current reports on Form 8-K, and any amendments to those reports filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange Act, free of charge, on the Investors section of our public website (www.gtbiopharma.com) as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC . In addition, you can read our SEC filings over the Internet at the SEC’s website at www.sec.gov. The contents of these websites are not incorporated into this annual report on Form 10-K. Further, our references to the URLs for these websites are intended to be inactive textual references only.