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) -- An early look at a pivotal study of

Ariad Pharmaceuticals'


experimental leukemia pill ponatinib yielded a response rate of 46% in heavily pre-treated patients with a markedly lower incidence of pancreatitis, a key measure of the drug's safety.

The new ponatinib data, which exceed investor expectations, are contained in a research abstract for next month's American Society of Hematology (ASH) annual meeting released Monday morning.

Ariad shares were down 11 cents to $11.90 in early Monday trading ahead of the ponatinib abstract release.

The pivotal study of ponatinib won't be completed until the first half of next year, but Ariad chief executive Harvey Berger said early patient responses and the drug's low 3.7% incidence of pancreatitis were "striking," particularly since leukemia patients in the study were no longer responsive to currently approved therapies.

"If these data were our submission to the FDA, ponatinib is approvable," said Berger in a phone interview Friday.

Ponatinib is being developed to treat chronic myeloid leukemia (CML) and so-called Philadelphia-positive acute lymphoblastic leukemia (ALL). Both forms of cancer cause excessive and unregulated production of white blood cells by the bone marrow due to a genetic abnormality that produces excessive quantities of a protein known as BCR-ABL.

In 2001,


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Gleevec was approved as one of the first "targeted" drugs capable of repairing the genetic error in CML and ALL patients. Gleevec became a multi-billion dollar blockbuster drug for Novartis, which went on to develop and market a successor drug, Tasigna.

Bristol-Myers Squibb

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markets a similar drug known as Sprycel.

Ariad views ponatinib as the next step in the evolution of targeted leukemia drugs because the drug is engineered to inhibit the production of BCR-ABL protein even in patients who no longer respond to Tasigna and Sprycel.

The pivotal study of ponatinib, dubbed PACE, enrolled 450 CML and ALL patients, all of whom are either resistant to Tasigna or Sprycel, or who have a specific genetic mutation known as T315I that makes the leukemia resistant to current therapies.

Among 83 patients enrolled in the PACE study with at least three months of treatment, 38 patients overall, or 46%, reported a major cytogenic, or cellular, response, meaning a reduction in the number mutated cells to less than 35%. In the subgroup of patients with the T315I mutation, the major cytogenic response rate was 57%.

The early ponatinib response rates in the PACE study are in line with results from a phase I study of ponatinib and are also similar to the response rates that convinced FDA to approve Tasigna and Sprycel, although both those drugs treated earlier-stage patients.

Patients in the PACE study are assessed for response every three months. When the study is completed, all patients will be assessed for at least six months, many for longer. Ariad's Berger says response to ponatinib is expected to grow over time based on prior clinical experience with the drug.

The initial safety analysis of the PACE study incorporates data from 159 patients. The 3.7% incidence of pancreatitis, or inflammation of the pancreas, is well below the 12% rate observed in the previous phase I study. Pancreatitis was seen as a potential worrisome side effect of ponatinib.

"Pancreatitis appears to be a non-event" in the PACE study, said Berger.

Additional data from the PACE study of ponatinib, including updates on response rates in a greater number of patients, will be presented at the ASH meeting in early December.

Ariad own full rights to ponatinib, and if approved, the company will market the drug on its own in the U.S. Ariad may license ex-U.S. rights to a partner, Berger said.

Novartis reported almost $4 billion in sales from Gleevec and Tasigna through nine months of 2011. Bristol's Sprycel sales totaled $576 million in the same period.

--Written by Adam Feuerstein in Boston.

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Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback;

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