ChemGenex Launches Multi-Centre Phase 2 Clinical Trial of Ceflatonin® in Combination with Gleevec® in Patients with Chronic Myelogenous Leukemia

MELBOURNE, Australia, and MENLO PARK, California U.S.A.

April 07, 2005

ChemGenex Pharmaceuticals Limited (ASX: CXS) announced today that it has launched a multi-centre Phase 2 study evaluating the use of Ceflatonin® (homoharringtonine or HHT) in combination with Gleevec® (imatinib mesylate), in patients with chronic myelogenous leukemia (CML) who have developed resistance to Gleevec®. Dr. Jorge Cortes, Professor of Leukemia at the M.D. Anderson Cancer Center in Houston, Texas, is the principal investigator for the study.

Gleevec® is a targeted therapeutic with global sales in excess of US$1.6 billion in 2004. Gleevec® was first approved in 2001 for the treatment of advanced-stage CML patients, and it remains the dominant therapy for CML globally. Despite Gleevec®'s effectiveness in early stage CML, responses in late (blastic) phase patients are usually short-lived (3-6 months median duration), with only 15% of patients experiencing a durable response. When used in earlier (chronic) stages of the disease, approximately 20% of patients have primary resistance to Gleevec® and a further 20% of patients develop resistance after 14 months.

While Gleevec® and other investigational tyrosine kinase inhibitors have generated excellent results, there is still a need to improve therapy in CML. Agents with novel mechanisms of action are needed to treat patients who fail or develop resistance to tyrosine kinase inhibitors like Gleevec®. Moreover, agents with synergistic mechanisms of action are needed for use in-combination with tyrosine kinase inhibitors to limit resistance and increase the chances of a cure.

"Ceflatonin® is an attractive agent to combine with Gleevec® because it has confirmed Phase 2 single agent activity in refractory CML. We also know that it has a complementary mechanism of action that can reduce Bcr-Abl protein expression associated with Gleevec® resistance," said Greg Collier, Ph.D., Chief Executive Officer and Managing Director of ChemGenex. "Our objective in this study is to induce a good patient response while at the same time reducing the Bcr-Abl proteins associated with resistance to Gleevec® and CML disease progression."

Ceflatonin® Clinical and Preclinical Activity

Laboratory and human studies have demonstrated that HHT is active in patients with CML who have become resistant to Gleevec®:

• In a recent Phase 1 safety study sponsored by the National Cancer Institute (NCI) at the M.D. Anderson Cancer Center in Houston, Texas, 10 patients in the advanced stages of CML who no longer responded to Gleevec® were treated with HHT. The investigators observed no significant toxicities and five (50%) of the patients responded to HHT therapy.
• In preclinical studies, HHT showed synergistic activity with Gleevec® as measured by a reduction in the marker (Bcr-Abl protein expression) that is a hallmark of Gleevec® resistance in CML.

These studies confirm that Ceflatonin® shows promise against CML, both as a single agent therapy in advanced stages of the disease and in combination with Gleevec® for earlier stage disease.

Clinical Trial Details

The trial will be an open-label, multi-center study for patients with CML, whose disease is in chronic, accelerated, or blast phase. Patients will receive 2.5 mg/m2 Ceflatonin® by continuous 24-hour intravenous infusion, daily for 5 days (days 1 - 5 of each treatment cycle) every 4 weeks. They will also receive Gleevec® 400 mg daily for CML patients in chronic phase, and 600 mg daily for CML patients in accelerated and blast phases.

About ChemGenex Pharmaceuticals Limited (www.chemgenex.com)

ChemGenex Pharmaceuticals is a gene-based pharmaceutical company dedicated to improving the lives of patients by developing therapeutics in the areas of oncology, diabetes, obesity, and depression. ChemGenex currently has two compounds in Phase 2 clinical trials, Ceflatonin® for leukemia and Quinamed® for solid tumors, and has a significant portfolio of anti-cancer, diabetes, obesity and depression programs. The company's diabetes and obesity program is partnered with Merck KGaA and the depression program is partnered with Vernalis plc. ChemGenex currently trades on the Australian Stock Exchange under the symbol "CXS".

Gleevec® is a registered trade-mark of Novartis AG.

Contacts

Dr. Greg Collier (CEO and Managing Director)	Australia +61 3 5227 2752 USA +1 650 474 9800 ext 103
Dr. Dennis Brown (President and Director)	USA +1 650 474 9800 ext 108 Australia +61 3 5227 2703

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