ChemGenex Presents Positive Clinical Trial Data on Anticancer Compound, Quinamed, at U.S. Cancer Conference.

MELBOURNE, Australia & MENLO PARK, Calif. -- ChemGenex Pharmaceuticals Limited (ASX:CXS) announced today updated positive data from a Phase I/II clinical study of its investigational drug, Quinamed(R) (amonafide dihydrochloride), and new pre-clinical data showing the drug's ability to significantly enhance the activity of other standard anticancer drugs. The data was presented at the American Association for Cancer Research (AACR) Oncogenomics 2005: Dissecting Cancer Through Genome Research conference in San Diego, California. Quinamed is currently in a Phase II clinical trial for hormone refractory prostate cancer.

In June 2004, ChemGenex investigators reported results from a 32-patient Phase I/II study of Quinamed, showing some preliminary responses to treatment with Quinamed in patients with advanced prostate, ovarian and gastric cancers. At AACR, the investigators updated that data and reported that four of the responding patients have continued to benefit from treatment with Quinamed:

--One patient with hormone refractory prostate cancer had a 40% reduction in tumor volume and a 50% reduction in a key prostate cancer marker, the prostate-specific antigen (PSA) count.

--Two other patients with refractory metastatic ovarian cancer experienced a stabilization in the growth of their tumors, with one of those patients also experiencing a declining count in CA125, a molecular marker for ovarian cancer.

--Another patient with metastatic gastrointestinal stromal cancer (GIST) who had failed previous treatment with surgery, Gleevec(R) and chemotherapy continues to respond to Quinamed after 16 months of therapy.

Data from pre-clinical studies also presented at the AACR conference demonstrated the ability of Quinamed to significantly enhance, or chemopotentiate, the effects of standard chemotherapeutic agents such as 5-FU, cisplatin and camptothecin in experimental animal models. ChemGenex researchers observed the chemopotentiation activity independent of whether the drug was administered orally or systemically.

"We are very encouraged by these prolonged clinical responses in a Phase I study with heavily pre-treated patients and are continuing to explore the use of Quinamed and its dosing based on NAT-2 genotype in a variety of solid tumors," said Greg Collier, Ph.D., chief executive officer and managing director of ChemGenex Pharmaceuticals. "We believe this use of genotyping to tailor dosing for safer, more effective therapy clearly illustrates the potential of targeted, gene-based medicine for improving the treatment of cancer."

A patient's NAT-2 genotype correlates to how quickly they will metabolize the drug, which may be slow, intermediate or fast. By determining the most appropriate dose for each patient based on their NAT-2 genotype, ChemGenex believes it may maximize effectiveness of that anticancer therapy while minimizing the risk of serious drug side-effects.

About Quinamed(R)

Quinamed is a novel naphthalimide analog currently in Phase II clinical trials for hormone refractory prostate cancer.

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 II clinical trials, Ceflatonin(R) for leukemia and Quinamed(R) 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. ChemGenex currently trades on the Australian Stock Exchange under the symbol "CXS."

Safe Harbor Statement

Certain statements made herein that use the words "estimate," 'project," "intend," "expect," "believe," and similar expressions are intended to identify forward-looking statements within the meaning of the US Private Securities Litigation Reform Act of 1995. These forward-looking statements involve known and unknown risks and uncertainties which could cause the actual results, performance or achievements of the company to be materially different from those which may be expressed or implied by such statements, including, among others, risks or uncertainties associated with the development of the company's technology, the ability to successfully market products in the clinical pipeline, the ability to advance promising therapeutics through clinical trials, the ability to establish our fully integrated technologies, the ability to enter into additional collaborations and strategic alliances and expand current collaborations and obtain milestone payments, the suitability of internally discovered genes for drug development, the ability of the company to meet its financial requirements, the ability of the company to protect its proprietary technology, potential limitations on the company's technology, the market for the company's products, government regulation in Australia and the United States, changes in tax and other laws, changes in competition and the loss of key personnel. These statements are based on our management's current expectations and are subject to a number of uncertainties that could change the results described in the forward-looking statements. Investors should be aware that there are no assurances that results will not differ from those projected.