Polaris Group’s ADI‑PEG 20 Shows Robust Clinical Activity in Malignant Plural Mesothelioma When Combined with Standard First-Line Chemotherapy Regimen

SAN DIEGO, May 5, 2016 – Polaris Group announced results from an ongoing phase 1 study that combines its lead therapeutic ADI‑PEG 20 (pegylated arginine deiminase) with the standard first-line chemotherapy (cisplatin + pemetrexed doublet) in malignant pleural mesothelioma (MPM) demonstrating promising response rates. Dr. Peter Szlosarek from Barts Cancer Institute, London, England the lead investigator on the study, presented the results at a plenary session of the 13th International Conference of the International Mesothelioma Interest Group (IMIG) in Birmingham, England.

MPM patients with tumor cells deficient in the enzyme argininosuccinate synthetase (ASS1) enrolled in the study received standard dose cisplatin + pemetrexed, and increasing doses of ADI‑PEG 20 treatment. ASS1 plays an important role in the synthesis of the amino acid arginine, which is required for cell growth and function. Polaris Group believes that ASS1 deficiency in certain cancer cells requires these cells to obtain arginine from the circulation in order to survive.  ADI‑PEG 20 is designed to deplete arginine in the circulation and cause cancer cells to die while leaving patients’ normal cells unharmed.

Twenty ASS1-deficient MPM patients have been enrolled, with five patients in the dose escalating cohorts and 15 patients in the expansion cohort. Of those patients, 17 were eligible for toxicity and response assessment.  The enrolled population is heavily skewed toward non-epithelioid histologies (six biphasic and seven sarcomatoid), which have worse prognosis than epithelioid MPM patients.  Nine patients (53%) had a partial response (PR) as measured by modified RECIST and eight patients (47%) had stable disease (SD) as best response, yielding a 100% disease control rate.  The combination of ADI‑PEG 20 + cisplatin + pemetrexed has been well-tolerated.  The expansion phase of the study is currently ongoing and is expected to enroll up to 30 MPM patients in total.

“We are excited by the tolerability and high response rate seen in a patient population enriched for non-epithelioid histologies, patients who are in dire need of effective therapeutic intervention”, said John Bomalaski, M.D., Executive Vice President, Medical Affairs, of Polaris Pharmaceuticals, Inc. “We look forward to investigating ADI‑PEG 20’s therapeutic benefit in further studies of MPM patients in the near future.”

About ADI‑PEG 20

ADI‑PEG 20 is a biologic developed by Polaris Group to treat cancers, especially those carrying a major metabolic defect that renders such cancer cells, unlike normal cells, unable to internally synthesize arginine. Because arginine is one of the 20 amino acids that are essential for protein synthesis and survival of cells, it is believed these cancer cells become dependent upon the external supply of arginine to survive and grow. ADI‑PEG 20 is designed to deplete the external supply of arginine, which causes arginine-dependent cancer cells to die while leaving the patient’s normal cells unharmed. Multiple cancers have been reported to have a high degree of arginine-dependency.

About Polaris Group

Polaris Group, a multinational biopharmaceutical drug company, specializes in the research and development of protein drugs to treat cancer and other debilitating diseases. Polaris Group is investigating ADI‑PEG 20 as a treatment for a number of cancers, such as leukemia, lymphoma, melanoma, mesothelioma, non-small cell lung cancers, sarcoma, breast, ovarian, pancreatic cancer and hepatocellular carcinoma. In addition to the ADI‑PEG 20 program, Polaris Group is researching and developing other biotherapeutic agents and is advancing a small molecule drug program that utilizes a rational structure-based approach to design novel compounds that inhibit the biological function of cancer-related protein targets.

For additional information please visit www.polarispharma.com.