Targeted Plexxikon drug helps ease pain from rare joint disease

CHICAGO (Reuters) - An experimental cancer drug being developed by Plexxikon, a unit of Daiichi Sankyo, appears to ease pain and swelling in patients with a rare joint disease caused by a genetic mutation, researchers said on Wednesday.

The finding, borne out of recent advances in understanding the genetic underpinnings of cancer, shows how greater knowledge of individual mutations can lead to more specific treatments.

The disease, called recurrent pigmented villonodular synovitis, or PVNS, is caused by a glitch in a single gene that instructs cells to overproduce a molecule called colony stimulating factor 1. It causes immune cells to collect in the soft tissue of joints, gradually destroying them.

Plexxikon’s drug, PLX3397, is a new cancer drug that acts on this same pathway, blocking the abnormality that drives PVNS.

Researchers at Memorial Sloan-Kettering Cancer Center in New York tested the drug in people with this rare disease, which affects about 600 people in the United States.

Like cancer, the disorder is marked by the overgrowth of abnormal cells, but it does not spread to other parts of the body.

Results of an early-stage trial of the treatment, released on Wednesday, look promising. Eleven of 14 patients had a partial response to the drug, meaning the tumor shrank at least by half, and three patients had stable disease. On average, tumors among this sample of 14 patients shrank by 61 percent.

“These results are a shining example of how patients can experience a meaningful clinical benefit when we are able to match the right treatment with the right target,” said Dr William Tap of Memorial Sloan-Kettering, who led the study.

Tap said patients often reported a marked decrease in swelling and pain “even very early in their treatment course.”

More testing is needed to determine whether the treatment works in a larger population of patients. A late-stage study of the treatment is planned.

Dr Clifford Hudis, president of American Society of Clinical Oncology, said the study “offers an exciting glimpse” at future treatments that will become possible as a result of efforts to better match patients’ tumors with targeted drugs.

“The research shows what’s possible when we unravel the molecular drivers of a disease and identify a drug that directly targets these defects.”

Full results of the study will be presented at the ASCO meeting in Chicago starting on May 30 and running through June 3.

Reporting by Julie Steenhuysen; Editing by Dan Grebler