Clinical benefit from use of a novel histone deacetylase inhibitor drug may be determined by examining blood cells days after a patient receives treatment. The drug, entinostat, is the first histone deacetylase inhibitor successfully tested in a randomized, placebo-controlled study in metastatic breast cancer — and is the first to show that clinical outcome can be predicted shortly after administration.

The findings, reported at the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics, held Nov. 12-16, 2011, represent an advance in the goal to offer patients only those therapies that will help treat cancer effectively, the researchers said.

“The ability to have a marker of benefit within the first several weeks of using this drug represents an exciting advance in personalized medicine,” said lead researcher Peter Ordentlich, Ph.D., executive director of translational science and a founder of Syndax Pharmaceuticals Inc. in Waltham, Mass. Syndax Pharmaceuticals developed entinostat, an oral small-molecule drug that inhibits enzymes that alter the packaging of DNA inside the nucleus, which controls gene expression.

“The goal of entinostat in breast cancer is to extend the benefit of hormone therapy and delay the time that patients will need to use chemotherapy,” said Ordentlich. More than 160,000 women are diagnosed each year with estrogen receptor (ER)-positive invasive breast cancer, and many are treated with agents that block the hormone. But most women become resistant to these therapies, and entinostat, combined with antihormone agents, is meant to extend their benefit, he said.

To test that strategy in ER-positive metastatic breast cancer, Syndax Pharmaceuticals conducted ENCORE-301, a randomized, placebo-controlled, phase 2 study (n=130) testing the use of exemestane, an aromatase inhibitor, with either entinostat or placebo.

Results of the clinical trial, released in September, showed that the combination therapy delayed cancer progression by 27 percent (4.3 vs. 2.3 months) compared with exemestane treatment alone. At a median follow-up of 18 months, overall survival was also significantly longer with exemestane plus entinostat than with exemestane plus placebo (26.9 vs. 20.3 months).

In this subset analysis, researchers examined blood samples from 49 patients (27 received combination therapy) to evaluate whether changes in circulating blood cells that reflected the activity of the histone deacetylase (HDAC) inhibitor could be detected. Researchers measured protein lysine acetylation, a biological marker of entinostat activity, in B cells, T cells and monocytes in blood samples taken at pretreatment and one, eight and 15 days after therapy with entinostat, which is taken once a week.

While levels of lysine acetylation after one day were not linked to clinical benefit, levels measured eight and 15 days after therapy were related to clinical benefit, Ordentlich said. Researchers found that patients with elevated levels of protein lysine acetylation had a 68 percent reduced risk for disease progression compared with those patients who did not have sustained elevated levels.

Researchers found that hyperacetylation was also associated with longer median progression-free survival across cell lines: B cells, 8.5 vs. 1.9 months; T cells, 6.6 vs. 1.8 months; and monocytes, 6.2 vs. 1.9 months. “Those patients who were able to maintain acetylation did well,” Ordentlich said.

He added that entinostat’s long half-life and unique pharmacology allow researchers to quickly gauge the agent’s activity. In this way, “we gain insight into how to use HDAC inhibitors, as a class of cancer drugs, in a variety of solid tumors,” he said.

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The study was funded by Syndax Pharmaceuticals. Co-authors include investigators from the National Cancer Institute, who developed the assay used to test protein lysine acetylation in patient blood samples.

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The mission of the American Association for Cancer Research is to prevent and cure cancer. Founded in 1907, the AACR is the world’s oldest and largest professional organization dedicated to advancing cancer research. The membership includes 33,000 laboratory, translational and clinical researchers; health care professionals; and cancer survivors and advocates in the United States and more than 90 other countries. The AACR marshals the full spectrum of expertise from the cancer community to accelerate progress in the prevention, diagnosis and treatment of cancer through high-quality scientific and educational programs. It funds innovative, meritorious research grants, research fellowships and career development awards to young investigators, and it also funds cutting-edge research projects conducted by senior researchers. The AACR has numerous fruitful collaborations with organizations and foundations in the U.S. and abroad, and functions as the Scientific Partner of Stand Up To Cancer, a charitable initiative that supports groundbreaking research aimed at getting new cancer treatments to patients in an accelerated time frame. The AACR Annual Meeting attracts more than 17,000 participants who share the latest discoveries and developments in the field. Special Conferences throughout the year present novel data across a wide variety of topics in cancer research, treatment and patient care, and Educational Workshops are held for the training of young cancer investigators. The AACR publishes seven major peer-reviewed journals: Cancer Discovery; Cancer Research; Clinical Cancer Research; Cancer Epidemiology, Biomarkers & Prevention; Molecular Cancer Therapeutics; Molecular Cancer Research; and Cancer Prevention Research. In 2010, AACR journals received 20 percent of the total number of citations given to oncology journals. The AACR also publishes Cancer Today, a magazine for cancer patients, survivors and their caregivers, which provides practical knowledge and new hope for cancer survivors. A major goal of the AACR is to educate the general public and policymakers about the value of cancer research in improving public health, the vital importance of increases in sustained funding for cancer research and biomedical science, and the need for national policies that foster innovation and the acceleration of progress against the 200 diseases we call cancer.

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Jeremy Moore
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American Association for Cancer Research