April 6 (Reuters) - An experimental drug being developed by Agios Pharmaceuticals Inc showed promising anti-cancer activity in a tiny Phase I study of patients with relapsed acute myeloid leukemia (AML), according to data presented on Sunday.
Of seven patients available to be evaluated following a 28-day cycle of treatment with the drug, AG-221, six had what researchers deemed objective responses to the medicine.
Three of them achieved complete remission and two achieved complete remission with incomplete platelet recovery, meaning that the leukemia had exited their bone marrow but the blood platelet count had not yet returned to normal levels.
"I'm very excited about what has happened with those patients so far who have responded," the study's lead investigator, Dr. Eytan Stein of Memorial Sloan Kettering Cancer Center in New York, said in a telephone interview.
AML, the most common type of acute leukemia in adults, is a cancer of the blood and bone marrow that progresses quickly if left untreated. AG-221 targets a gene mutation that is present in 10 percent to 15 percent of AML patients, Stein explained.
Stein, who presented the results at the American Association for Cancer Research (AACR) meeting in San Diego, cautioned that this was very preliminary data.
"If the results are confirmed (in upcoming larger trials) that would be a remarkably exciting result," Stein said of the first-in-class drug.
Patients in the study had AML that had progressed after, or failed to respond to, up to four other therapies.
They all had the specific genetic mutation in the leukemic cells that the drug is designed to impact, called isocitrate dehydrogenase-2, or IDH2. The treatment led to substantially lower levels of a cancer metabolite in the blood called 2HG that researchers believe reprograms white blood cells, stripping their ability to become infection fighters.
Stein noted that in the tiny group of patients there were no observable side effects that appear related to the drug itself, "which is very different from chemotherapy."
Patients in the study received either 30 milligrams or 50 mg of AG-221 twice a day. Another arm of the trial was studying two higher doses, but that data was not yet available.
Stein said researchers were not expecting the impact seen with the lowest doses in the first handful of patients.
"We were actually kind of surprised that at the first dose level we're seeing dramatic clinical activity. That usually doesn't happen," he said. (Reporting by Bill Berkrot; Editing by Raissa Kasolowsky)