On May 30, 2019 GT Biopharma, Inc. (OTCQB: GTBP) (GTBP.PA) an immuno-oncology company focused on innovative treatments based on the Company’s proprietary NK cell engager (TriKE) platform and Multi-Target Directed Bispecific Drug Conjugate (MTBDC) platform, reported an update with respect to the further clinical development of GTB-1550 (Press release, GT Biopharma , MAY 30, 2019, View Source [SID1234539513]).

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GTB-1550 (DT2219) is a novel multi-target directed therapy for the treatment of chemotherapy-refractory B-cell malignancies, including Non Hodgkins Lymphoma and Leukemia. To date, GT Biopharma has completed one dose escalation Phase I-II expansion clinical trial, and one fixed dose Phase I-II expansion clinical trial which collectively enrolled a combined 43 patients.

Top-line Consolidated Results:

Two patients exhibited a Complete Remission (CR) with one patient currently disease-free at 50 months post treatment.
Five patients exhibited Stable Disease (SD), cancers that are neither increasing or decreasing in severity, with the longest response lasting 12 months post treatment.
Two patients with transformed lymphoma showed transient tumor shrinkage, however, therapy was discontinued due to dose-limiting toxicities after the 1st cycle.
Greater than 50% of evaluable patients, (patients where response to treatment can be measured because enough data has been collected), receiving 60 mg/kg dose had positive clinical response defined as stable disease, partial remission, or complete remission.
Dr. Veronika Bachanova, Associate Professor of Medicine, Division of Hematology, Oncology and Transplantation at the University of Minnesota and the Principal Investigator for both clinical trials commented: "We are pleased the patient who experienced a complete remission following treatment with GTB-1550 is doing well, and we are excited about moving forward with a GTB-1550 Phase II clinical trial for the treatment of chemotherapy-refractive B-cell malignancies."

Mr. Anthony Cataldo, the Chairman and Chief Executive Officer of GT Biopharma commented: "GTB-1550 has shown positive results in its two Phase I-II clinical trials in advanced cancer patients who have failed all other therapies, and we are now planning to proceed with a Phase II clinical trial."

The initial Phase I-II expansion clinical trial ( NCT 00889408; Clin Cancer Res 21(6) pgs 1267–72) demonstrated decreased tumor mass in one patient, and a complete response in a second patient that remains on-going at 50 months post treatment. After a single course of GTB-1550 (DT2219) at dose level 40 mg/kg/day x 4, a 77-year-old patient with chemotherapy-refractory CD19+/CD22- chronic lymphocytic leukemia (CLL) experienced a 40% reduction in cervical and axillary adenopathy with decrease of an abdominal tumor mass at day 28 after treatment, which was sustained for 2 months. The second clinical response occurred in a 53-year-old patient with relapsed CD19+/CD22+ diffuse large B cell lymphoma (dose level 60 mg/kg) who experienced a 75% reduction in size of lymphoma lesion after a single course complicated by a grade 3 capillary leak syndrome. Eight weeks later after FDA approval, this patient received a second DT2219 course at a reduced dose of 40 mg/kg/dose for 4 days, which resulted in a complete resolution of a subcutaneous mass and pelvic lymphadenopathy. The patient is alive and in complete remission with no neutralizing antibodies, currently at 50 months after therapy.

The results of the second GTB-1550 Phase I-II expansion trial ( NCT02370160; J Clin Oncology 37, 2019 suppl; abstract e19066) targeting CD22 and CD19 for treatment of refractory B-cell malignancies showed treatment was well tolerated at 60 mg/kg x 8 doses. The most common adverse events included capillary leak syndrome, elevated AST/ALT, low albumin, weight gain and leukopenia. All were Grade 1-2 and resolved after 3-5 days allowing day 15 GTB-1550 administration. There were no neutropenic fever or immune mediated adverse events. Four patients experienced dose limiting toxicity (DLT) at dose 80 μg/kg/day: Grade 4 capillary leak syndrome (n=1), Grade 3 liver function test (LFT) abnormalities (n=2) and Grade 4 thrombocytopenia >7 days duration (n=1). Thirteen patients were evaluable for response, and 3 experienced objective clinical benefit. One patient with primary refractory pre-B acute lymphoblastic leukemia achieved complete remission after 1st cycle. Two patients with transformed lymphoma demonstrated transient tumor shrinkage, however, GTB-1550 therapy was discontinued due to DLT and increased neutralizing antibody titer after 1st cycle (pre C1 28%, pre C2 108%). Correlative studies showed a low incidence of neutralizing antibody in Non-Hodgkin Lymphoma (NHL) patients recently exposed to Rituximab.