An experimental drug from Merck & Co. showed effectiveness in treating certain types of leukemia that have proven resistant to both Novartis AG’s Gleevec medicine and Bristol-Myers Squibb Co.‘s recently launched Sprycel, according to researchers at the M.D. Anderson Cancer Center.

Data presented on Monday at the annual meeting of the American Society of Hematology indicated the experimental MK-0457 drug showed activity against several genetic mutations found in chronic myeloid leukemia, or CML, and acute lymphocytic leukemia, or ALL.

The trial involving 44 patients showed the first clinical activity of the drug, which Merck is developing with Vertex Pharmaceuticals Inc.

The drug is of interest to investors because it has the potential to be effective in patients with certain genetic mutations who are resistant to Gleevec, a $2.5 billion drug, and Sprycel, which is approved to treat CML patients who have developed resistance to Gleevec and works in many cases.

Merck’s drug also showed activity against a genetic mutation sometimes present in myeloproliferative disorders, or MPD, a group of blood diseases that can evolve into leukemia, the research showed.

While still early in development, the drug could be important as it addresses patient populations - about 10 percent of those diagnosed with each of the three conditions - for which no drug is effective.

“This is a relatively small population that can potentially benefit from the drug, but for those who have these mutations, this research opens the door to a tremendous option for them,” said Francis Giles, professor in the department of leukemia at M.D. Anderson Cancer Center, who reported the data. “At present there is nothing to offer them.”

Patients with CML who have a genetic mutation known as T3151 Bcr-Abl, are resistant Gleevec, Sprycel and to an experimental drug under development by Novartis called Tasigna. Sprycel and Tasigna are affective in treating other mutations that cause resistance to Gleevec.

Patients with myeloproliferative disorders who carry a mutation known as JAK-2 are similarly resistant.

According to the study, 35 leukemia patients had at least four prior types of therapy, and nine MPD patients’ treatments ranged from one to seven.

The drug, which was given intravenously, led to a response in nearly all the patients, prompting the investigators to move forward with additional trials faster than expected.

According to the American Cancer Society, there are about 4,000 new cases of ALL, about 4,500 new cases of CML and about 10,000 cases of MPD diagnosed each year.