OXS-1550 is an immunotherapy being developed by Oxis Biotech to treat patients with B-cell leukemia or lymphoma who have not responded well to other treatments. OXC-1550 uses a combination of antibodies and a toxin to kill cancer cells.
How OXS-1550 works
OXS-1550 consists of antibodies that target CD19 and CD22, proteins commonly found on the surface of B-cell lymphomas and leukemias, and a modified form of diphtheria toxin. When OXS-1550 binds to either CD19 or CD22, or, in some cases, to both — if both are expressed on the same cell — the cell takes in the diphtheria toxin. Once inside the cells, the toxin, referred to as the drug’s “cytotoxic payload,” essentially poisons the cells to shrink the tumor.
OXS-1550 is called a bispecific ligand-directed toxin (BLT) because it can bind to two targets, and in doing so direct the toxin to the cancer cells.
OXS-1550 in clinical trials
The first Phase 1 trial of OXS-1550 (NCT00889408) included 25 patients, ages 12 and older, with refractory or relapsed B-cell lymphoma or leukemia. All the patients had been treated with several rounds of chemotherapy, and many had received stem cell transplants. They had either not responded to treatment at all — that is, they were refractory — or their cancer returned after successful treatment — that is, they had relapsed. Only patients with cancers that expressed CD19, CD22 or both were included in the study.
The primary purpose of the trial was to establish an ideal dose range by giving patients different doses and watching for adverse effects. Patients received one intravenous infusion of the drug every other day, for a total of four doses.
In an article published in the March 2015 issue of Clinical Cancer Research, investigators reported they have determined a safe dose and a dosing schedule.
A Phase 1/Phase 2 trial of OXS-1550 (NCT02370160) in patients with refractory or relapsed B-cell lymphomas and leukemias began in December 2015 and is ongoing. The Phase 1 portion of the trial will use the single infusion dose established in the earlier Phase 1 trial but add more doses. The Phase 2 portion of the latest trial will be an extension study to assess the safety and activity of OXS-1550 at the dose level and dose schedule determined in Phase 1, as well as patients’ response to the therapy.
The trial’s estimated completion date is June 2019. Oxis, which expects to enroll 44 patients in the study, is still recruiting participants. In April 2017, the U.S. Food and Drug Administration cleared the way for OXS-1550 to go to Phase 2 clinical trials.
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