Blocking enzyme could help in rare blood cancer

By Julie Steenhuysen

CHICAGO (Reuters) - An enzyme that fights some kinds of cancers may foster the growth of a rare type of leukemia that affects babies, U.S. researchers said on Wednesday in a finding that may lead to new drugs for the hard-to-treat cancer.

They said drugs that blocked the enzyme glycogen synthase kinase, or GSK3, helped mice with mixed-lineage leukemia, or MLL, live far longer than untreated mice.

The finding is a surprise because prior studies have found GSK3 helped suppress unchecked cell growth in other cancers.

"GSK3 has never been implicated in promoting cancer," said Dr. Michael Cleary of Stanford University in California, whose research appears in the journal Nature.

Cleary's team found that blocking GSK3 fights leukemias caused by mutations in the MLL gene, which accounts for 5 percent to 10 percent of child and adult leukemias and more than three-quarters of leukemias diagnosed in infants.

Cleary said only a few hundred people in the United States get MLL each year, but when babies get leukemia, they tend to get this form, although it is not clear why.

While most leukemias get their start in either lymph nodes or bone marrow, MLL cancer cells can originate from both.

"These patients don't typically respond well to chemotherapy. There is a real need for better treatments," Cleary said in a telephone interview.

His team first got a hint that blocking GSK3 might fight MLL through routine screening tests in the lab.

The researchers gave the mice with MLL lithium, a drug used to treat bipolar disease in humans.

"It is not the best GSK3 inhibitor, but it is one that could be administered long-term in mice," Cleary said.

Mice treated with the lithium lived significantly longer than the untreated mice. Cleary's team also used a different GSK3 inhibitor in MLL cells and found it stopped them from growing.

"I think where we need to go in the future is to come up with better inhibitors that can be administered long-term," Cleary said.

That may come through research of the drug in other diseases. Cleary said drug companies are developing GSK3 inhibitors as treatments for diabetes and Alzheimer's disease.

(Editing by Maggie Fox)