New drugs target hard-to-treat breast cancers

* BiPar/Sanofi drug boosts survival 60 pct

* AstraZeneca's olaparib shrinks tumors in 1/3 of patients

By Deena Beasley

ORLANDO, Fla., May 31 (Reuters) - Drugs targeting an enzyme known as PARP show promise as treatments for some of the most aggressive and difficult-to-treat forms of breast cancer, according to new research.

Mid-stage results from a PARP inhibitor developed by BiPar Sciences Inc show that it improved survival by 60 percent compared with chemotherapy alone for women with "triple negative breast cancer."

And a small trial of AstraZeneca Plc's (AZN.L) olaparib in women with advanced breast cancer linked to genetic mutations showed that it shrank tumors in a third of patients.

The findings were presented on Sunday at the annual meeting of the American Society of Clinical Oncology.

PARP is short for "poly (ADP-ribose) polymerase," which is used by cancer cells to repair DNA damage, including the damage inflicted by chemotherapy drugs.

Breast cancer was the one of first types of cancer that scientists have been able to dissect into subgroups based on biological markers.

Back in the 1970s they identified women whose tumors contained estrogen receptors -- paving the way for the development of hormonal therapies, like tamoxifen and aromatase inhibitors.

That breakthrough was followed by the launch in 1998 of Herceptin, an antibody-based drug designed to target the HER-2 protein, which is generated by around 25 percent of breast cancer patients.

NEXT BREAST CANCER BREAKTHROUGH

"The third breakthrough is this one," said Dr. Barry Sherman, head of development at BiPar, which presented results from a 116-patient trial of its intravenous PARP inhibitor, known as BSI-201.

Privately held BiPar agreed in April to be purchased by French drugmaker Sanofi Aventis SA (SASY.PA) for up to $500 million.

BSI-201 is being studied in women with "triple negative" metastatic breast cancer, meaning their tumors do not express the hormones estrogen or progesterone as well as HER-2.

These women, accounting for 15 to 20 percent of breast cancer patients, have a very aggressive form of the disease and there are currently no treatments beyond chemotherapy, Sherman said.