On June 13, 2019 GT Biopharma, Inc. (OTCQB: GTBP) (GTBP.PA) an immuno-oncology company reported that developing GTB-1550, a novel multi-target bispecific drug conjugate therapy for the treatment of chemotherapy-refractory B-cell malignancies (Press release, GT Biopharma , JUN 13, 2019, View Source [SID1234539511]).

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Today, Bloomberg discussed antibody-drug conjugates (ADC) as effective cancer therapies having the potential to replace traditional chemotherapy. ADCs are essentially a "trojan horse" therapeutics which have several advantages over traditional chemotherapy including less toxicity and higher efficacy due to a more precise targeting of cancer cells compared to non-cancer cells.

An ADC is composed of an antibody which specifically identifies cancer cells and a cytotoxic agent (the payload) which has been grafted onto the antibody. When injected into patients, the ADC traffics through the patient’s body to find the targeted cancer cells. Upon binding to the cancer cell, the ADC is internalized by the cancer cell, and the cytotoxic payload kills the cancer cell.

Anthony Cataldo (CEO GT Biopharma, Inc.) said, "The Bloomberg article points out the excitement that big pharma is now realizing as the potential for ADC’s as a realistic alternative to Chemo Therapies. What differentiates our ADC Bispecific GTB-1550, is the ability for our drug to hit multiple target sites of B-cell malignancies as opposed to the one target ADC’s represented in the Bloomberg article. We are happy to see the attention of the large pharmaceuticals moving in this direction."

GTB-1550 is a novel, multi-target bispecific cytotoxic therapeutic agent consisting of diphtheria toxin and bispecific single-chain variable fragments (scFV) of antibodies targeting human CD19 and CD22. By simultaneously targeting cancer cells that express either CD19 or CD22 or both, GTB-1550 is capable of killing a broader variety of hematological malignancies than either a traditional a CD19 antibody drug conjugate or a CD19 CAR-T immunotherapy which are only able to target and attack CD19 expressing hematological malignancies. Simultaneously targeting multiple cancer targets such as CD19 and CD22 using a single therapeutic agent potentially makes GT Biopharma’s multi-target bispecific drug conjugate therapy the next generation of advanced cancer therapies.

To date, GTB-1550 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) 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 receiving 60 mg/kg dose had positive clinical response defined as stable disease, partial remission, or complete remission.