Blinatumomab Shows BiTE in Relapsed/Refractory ALL



LONDON – The investigational agent blinatumomab could help more patients with relapsed or refractory acute lymphoblastic leukemia achieve remission, compared with conventional treatment strategies, interim findings of an exploratory phase II trial suggest.

Although a small study – just 12 patients were included in the analysis – "we saw a response rate of 75%," principal study investigator Dr. Max S. Topp said in an interview at the annual European Hematology Association congress.

"Obviously it’s a very small number of patients," Dr. Topp, a professor of medicine and consultant in hematology at the University of Wurzburg in Munich, conceded. "Nevertheless it’s basically more than double what you would expect."

The outlook for patients with relapsed or refractory B-precursor acute lymphoblastic leukemia (ALL) is often grim, Dr. Topp noted, with low response rates to intensive chemotherapy (17%-45%), and a high chance of further relapse with a median duration of 4-5 months for complete remission (CR).There is also a high rate of treatment-related mortality, with up to a quarter of patients dying during their treatment.

"Blinatumomab is a new kind of drug. It’s not actually an antibody in the classical sense, which is more passive. This is actually something that is actively looking for the tumor, as it uses the T cells to exert its action," Dr. Topp explained.

According to Micromet, the company developing the novel agent, blinatumomab is the most advanced of a new class of agents called BiTE (bispecific T-cell engager) antibodies. These agents are designed to direct cytotoxic T-cells to CD19-expressing cancer cells (Science 2008;321:974-7).

Data from a phase I study have already shown that blinatumomab is active in the treatment of relapsed or refractory B-cell non-Hodgkin’s lymphoma (American Society of Hematology annual meeting, abstract 2880). Dr. Topp and team have also demonstrated its tolerability and activity in patients with ALL who had minimal residual disease (MRD) (J. Clin. Oncol. 2011;29:2493-8).

"We then asked the question if you can actually treat full-blown relapse, and it looks like we can make a difference here," Dr. Topp observed.

The ongoing, open-label phase II study currently involves seven patients aged a median of 37 years who are being treated with blinatumomab at a dose of 15 mcg/m2 per day over three cycles and for maintenance treatment. Another five patients, with a median age of 60 years, are receiving the drug at an initial dose of 5 mcg/m2 per day, then at a dose of 15 or 30 mcg/m2 per day (cohort 2). Blinatumomab is delivered via continuous intravenous infusion for 2 weeks, with a 2-week treatment-free period.

Although the agent is in its very early days, results show that it has great promise in the treatment of relapsed or refractory ALL. The overall CR rate was 75%, and 71% in patients given the steady 15-mcg dose of blinatumomab and 80% in those whose dose was increased in subsequent cycles.

The increasing dosing regimen appears to be associated with better tolerability. "Adapting the system to have a slow start with 5 mcg and going up to 15 mcg we have had no severe adverse events ... and that is great news," Dr. Topp observed.

Some of the most common side effects seen in the trial to date include raised gamma-glutamyltransferase and C-reactive protein, peripheral edema, fatigue, pyrexia. Blood fibrinogen and fibrin d-dimer have also been increased, suggesting that thrombotic complications could be a future concern.

The bottom line, said Dr. Topp, is that "we have a non-chemotherapy, immunotherapy-based, effective treatment for patients with relapsed ALL, with very good safety profile."

Research is ongoing and a further 10 patients are likely to be included in the current trial. "We’re looking at the safety issues. We have to find the most likely regimen which we would like to use," Dr. Topp said.

The study was funded by Micromet AG. Dr. Topp is the principal investigator for the trial and disclosed acting as a consultant to the company.

Next Article: