GT Biopharma (GTBP) Announces Updated Interim GTB-3550 Trike Clinical Trial Results

GT Biopharma, Inc. (NASDAQ: GTBP) a clinical stage immuno-oncology company focused on developing innovative therapeutics based on the Company's proprietary NK cell engager (TriKE™) protein biologic technology platform is pleased to announce updated interim Phase I/II clinical trial results for the Company's lead therapeutic candidate, GTB-3550, being evaluated for the treatment of high-risk myelodysplastic syndromes (MDS) and refractory/relapsed acute myeloid leukemia (AML).

Reduction in Bone Marrow Blast Levels Achieved

To date, 9 patients have been enrolled in the Phase I/II Expansion clinical trial. Patients enrolled early in the Study (patients 1-4) were treated with doses of GTB-3550 below the anticipated therapeutic dose (RP2D) and maximum tolerated dose (MTD) to address possible safety concerns. All patients treated at the lower doses exhibited no signs of toxicity, and did not experience any Grade of Cytokine Release Syndrome (CRS).

Patients 5-9 were treated with increasing doses of GTB-3550 (25mcg/kg/day, 50mcg/kg/day and 100mcg/kg/day, respectively). Three of the five patients (60%) experienced reduction in bone marrow blasts with two patients (one patient treated at the 50mcg/kg/day dose level and one patient treated at the 100mcg/kg/day dose level) experiencing significant reductions in bone marrow blast levels. As previously reported, Patient 7 treated at the 50mcg/kg/day dose level achieved a 61.7% reduction in bone marrow blast levels from 12% before therapy to 4.6% after GTB-3550 therapy. Patient 9 treated at the 100mcg/kg/day dose level achieved a 63.7% reduction in bone marrow blast levels from 22% before therapy to 8% after therapy. All patients treated at these higher doses of GTB-3550 did not experience any Grade of Cytokine Release Syndrome (CRS).

No Cytokine Release Syndrome (CRS) Observed

All patients treated to date with GTB-3550 TriKE displayed no signs of any Grade of cytokine release syndrome (CRS). Of particular note, GTB-3550 is currently being administered to patients at doses significantly higher than the reported MTD (Maximum Tolerated Dose) for continuous infusion of recombinant human IL-15 (Interleukin-15) (Waldmann, TA et al, Clin Cancer Res. (2019) 25:4945–54). GTB-3550 is a single-chain, tri-specific scFv recombinant fusion protein conjugate 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.

Improved NK Cell Function, Proliferation & Persistence

Correlative studies have shown reproducible endogenous ("native") NK cell activity in all patients. NK cell activation increases early during treatment. This finding correlated with an increase proportion and absolute number of NK cells during treatment. Targeted delivery of IL-15 to NK cells via GTB-3550 TriKE showed preferential proliferation of NK cells and significantly less effect on CD8+ and CD4+ T-cells. We also observed no CD16 shedding by patients' NK cells, and saw enhanced HL-60 AML target cell killing. This data indicates GTB-3550 TriKE™ rescues the patient's exhausted/inhibited endogenous NK cells resulting in their activation, proliferation and persistence.

Mr. Anthony Cataldo, the Chairman and Chief Executive Officer of GT Biopharma commented: "We are pleased with the continued clinical performance of our lead GTB-3550 TriKE™ product candidate as we continue dose escalation." Mr. Cataldo further stated "this early data indicates GTB-3550 therapy demonstrates significant bone marrow blast level reductions in AML and MDS patients without the need for expensive progenitor-derived or autologous/allogenic cell therapies. We believe as we continue to dose escalate GTB-3550 TriKE™, more patients will experience greater clinical efficacy. TriKE's ability to work in the patient without outside supplemental engineered NK cells or the need for any combination drugs, sets TriKE apart from other cancer therapies. This is also the reason why TriKE™ therapy will be significantly less expensive than other treatments, opening the door to an off-the-shelf therapeutic."

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