Antisoma presents positive PSA data from AS1404 phase II trial in prostate cancer

London, UK and Boston, Mass: 18 September 2006 - Cancer drug developer Antisoma plc (LSE: ASM, US OTC: ATSMY) announces the presentation of the first findings from its ongoing phase II trial of AS1404 in hormone-refractory prostate cancer. These show a markedly higher rate of PSA responses among men receiving AS1404. Preliminary data from the first 64 of 74 patients in the trial show a PSA response rate of 57% in those receiving AS1404 plus docetaxel chemotherapy compared with 35% in those receiving docetaxel alone. In addition, the proportion of men showing disease progression by PSA was almost halved in the AS1404 group (17% versus 29% with docetaxel alone). The findings were presented yesterday at the Tumor Microenvironment meeting in Boston by Dr Gary Acton, Antisoma’s Chief Medical Officer.

PSA is a protein, prostate-specific antigen. Levels of PSA in the blood are used in the diagnosis of prostate cancer and the tracking of responses to its treatment. PSA is one of the most widely recognised disease markers in oncology, and PSA responses have been related to clinical outcomes in numerous studies.

As well as the PSA data, Dr Acton reviewed safety findings to date from the trial. These show that addition of AS1404 to docetaxel chemotherapy has been generally well-tolerated, without exacerbation of chemotherapy side-effects.

Commenting, Glyn Edwards, CEO of Antisoma, said: “These positive data from our phase II prostate cancer trial of AS1404 are a further important demonstration of the drug’s effects. They complement the positive survival, progression and response data already presented from our lung cancer trial, and show that the potential of AS1404 extends to two of the big four cancer indications. The findings underline again our leading position in the development of vascular disrupting agents and reinforce our confidence that we are well placed to strike a partnering deal for AS1404.”

Antisoma disclaimer

Certain matters discussed in this statement are forward looking statements that are subject to a number of risks and uncertainties that could cause actual results to differ materially from results, performance or achievements expressed or implied by such statements. These risks and uncertainties may be associated with product discovery and development, including statements regarding the company’s clinical development programmes, the expected timing of clinical trials and regulatory filings. Such statements are based on management’s current expectations, but actual results may differ materially.



Details of the PSA findings

Data are currently available from 64 of the 74 men participating in the trial. PSA response is defined as a 50% or greater reduction in PSA level from baseline, in accordance with the Bubley criteria (Eligibility and response guidelines for phase II clinical trials in androgen-independent prostate cancer: recommendations from the Prostate-Specific Antigen Working Group. Journal of Clinical Oncology 1999, Volume 17, pp 3461-67). On this measure, of the 64 men currently evaluable, 17/30 in the AS1404 + docetaxel group and 12/34 in the docetaxel alone group, had PSA responses. Of these, all but three in each group have already been confirmed by a second reading 6 weeks after the initial result. The other three responses in each group are unconfirmed pending data from further tests. Progression by PSA is defined as a 25% or greater increase. Among the first 64 patients, five in the AS1404 + docetaxel group and ten in the docetaxel alone group showed progressive disease by this measure.



Background on AS1404

AS1404 (DMXAA) is a small-molecule vascular disrupting agent which targets the blood vessels that nourish tumours . The drug was discovered by Professors Bruce Baguley and William Denny and their teams at the Auckland Cancer Society Research Centre, University of Auckland, New Zealand. It was in-licensed by Antisoma from Cancer Research Ventures Limited (now Cancer Research Technology) in August 2001.



Background on Antisoma

Based in London, UK, Antisoma is a biopharmaceutical company that develops novel products for the treatment of cancer. Antisoma fills its development pipeline by acquiring promising new product candidates from internationally recognised academic or cancer research institutions. Its core activity is the preclinical and clinical development of these drug candidates. Please visit www.antisoma.com for further information.

Contact Information

Daniel Elger

Director of Communications

Antisoma plc

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