Independent Publication Confirms Growing Therapeutic Challenge of T315I Mutation in Patients with CML, Notes ChemGenex

MELBOURNE, Australia, and MENLO PARK, California U.S.A. (May 21, 2007): ChemGenex Pharmaceuticals (ASX: CXS, NASDAQ: CXSP) notes the publication of new clinical data relevant to the development strategy for Ceflatonin® (homoharringtonine). The paper "Targeted therapy and the T315I mutation in Philadelphia-positive leukemias" by researchers Simona Soverini and colleagues at the University of Bologna, Italy (Haematologica Volume 92, pages 401-404) offers insight into the growing therapeutic challenge presented by the T315I Bcr-Abl point mutation in patients with chronic myeloid leukemia (CML). The T315I Bcr-Abl mutation is associated with the development of resistance to tyrosine kinase inhibitor drugs such as imatinib (Gleevec®).

The paper describes the clinical progress of Gleevec-resistant CML patients who were treated with dasatinib (Sprycel®).

Key points of the publication are as follows:

• The study followed 45 Philadelphia-positive CML and acute lymphoblastic leukemia (ALL) patients who had failed Gleevec, and who were migrated to dasatinib therapy.

• Eight of the 45 patients (17.7%) had primary resistance to dasatinib, and showed no response. Seven of these 8 patients harboured the T315I point mutation.

• A further 13 patients (28.8%) acquired resistance to dasatinib after a median of 7 months, and seven (15.6%) of these patients were T315I positive.

• In summary the T315I mutation was associated with resistance to dasatinib in 31% of patients, and the total number of patients who were resistant to therapy was 46.7%.

• This incidence of T315I-associated resistance is higher than has previously been reported and reflects, in the words of Soverini et al., that the T315I mutation "is likely to become the prevalent mutation in those who fail to benefit from second-line treatment with dasatinib".

Data from this publication support ChemGenex’s two-pronged phase 2/3 clinical approach for Ceflatonin, targeting Gleevec-resistant CML patients who harbour the T315I mutation, as well as CML patients who have failed two tyrosine kinase inhibitors (usually Gleevec and Sprycel).

Gleevec®/Glivec® is a registered trademark of Novartis AG.

Sprycel® is a registered trademark of the Bristol-Myers Squibb Company.

Ceflatonin® is a registered trademark of ChemGenex Pharmaceuticals Limited.

About ChemGenex Pharmaceuticals Limited (www.chemgenex.com)

ChemGenex Pharmaceuticals is a pharmaceutical development company dedicated to improving the lives of patients by developing therapeutics in the areas of oncology, diabetes, obesity, and depression. ChemGenex harnesses the power of genomics for target discovery and validation, and in clinical trials to develop more individualized therapeutic outcomes. ChemGenex’s lead compound, Ceflatonin®, is currently in phase 2/3 clinical trials for chronic myeloid leukemia (CML) and Quinamed® is in phase 2 clinical development for prostate, breast and ovarian cancers. The company has a significant portfolio of anti-cancer, diabetes, obesity and depression programs, several of which have been partnered with international pharmaceutical companies. ChemGenex currently trades on the Australian Stock Exchange under the symbol "CXS" and on NASDAQ under the symbol "CXSP".

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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PO Box 1069, Grovedale Victoria 3216, Australia Telephone: +61 3 5227 2752 Facsimile: +61 3 5227 1322 Email: chemgenex@chemgenex.com ABN 79 000 248 304

Posted: May 2007

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