( MELBOURNE Australia and MENLO PARK ...)Independent Publication Confirms Growing Therapeutic Challenge of,T315I Mutation in Patients with CML, Notes ChemGenex,Health

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 benefi
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