Multi=center Phase II trial for Ceflatonin in combo with IM

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ChemGenex Launches Multi-Center Phase 2 Clinical Trial of Ceflatonin in

Combination with Gleevec in Patients with Chronic Myelogenous Leukemia

MELBOURNE, Australia & MENLO PARK, Calif.--(BUSINESS WIRE)--April 7,

2005--ChemGenex Pharmaceuticals Limited (ASX:CXS) announced today that it

has launched a multi-center 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. Cortes, Professor of

Leukemia at the M.D. 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. 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 milligrams per meter squared 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 ( <http://www.chemgenex.com/>

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.