Four lymphoma and leukemia patients have completed treatment with the cancer therapy OXS-1550 (DT2219ARL) in a Phase 2 clinical trial being run by GT Biopharma and the University of Minnesota. "We are pleased with the progress of our four patients in the Phase 2 trial as we continue to move forward with this promising technology," Anthony Cataldo, GT Biopharma's executive chairman, said in a press release. The University of Minnesota developed OSX-1550, which is an antibody drug conjugate, or ADC. This class of drug is designed to kill cancer cells only, an approach that's more targeted than treatments such as chemotherapy. Scientists who create ADCs achieve precision targeting by linking a cancer drug to an antibody, a protein the immune system uses to kill invaders. The combination of the drug and antibody means an ADC will hone in only on cancer cells, avoiding damage to healthy tissue. GT Biopharma partnered with the University of Minnesota to advance OXS-1550's development as a treatment for blood cancers. It delivers a diphtheria toxin to cancer cells that have CD19 protein receptors, CD22 protein receptors, or both, on their surface. The drug showed promise in earlier trials of patients with relapsed or refractory B-cell lymphoma or leukemia. The primary objective of the Phase 2 trial (NCT02370160), which started in April 2017, is to determine patients' overall response rate to eight intravenous injections of OXS-1550. An overall response rate covers both complete and partial responses. Patients may receive two additional doses unless their disease progresses or they experience unacceptable toxicity. The main results of the study are expected in early 2018. The Phase 2 trial follows a Phase 1 study (NCT00889408) in which researchers determined the highest tolerated dose of OXS-1550. The therapy "performed well in Phase 1 studies of blood cancers," said Dr. Kathleen Clarence-Smith, GT Biopharma's chief executive officer. "Enrollment in the Phase 2 study is advancing rapidly, and we look forward to providing a targeted immunotherapy product that has the capability of treating a number of different liquid tumors." Dr. Daniel Vallera, director of the Molecular Cancer Therapeutics program at the University of Minnesota's Masonic Cancer Center, who helped develop OXS-1550, said the start of "Phase 2 patient treatment is a key opportunity to demonstrate the effectiveness of this promising cancer therapy."