Antisoma's AS1409 shows anti-cancer activity in phase I trial

London, UK, and Cambridge, MA: 31 May 2009 - Antisoma plc (LSE: ASM; USOTC: ATSMY) today announces positive findings from a phase I trial of its antibody-cytokine fusion drug, AS1409. The trial identified a well-tolerated dose of AS1409 at which biomarker activation, clinical improvement and objective radiological evidence of anti-cancer activity were seen. Two patients with malignant melanoma showed substantial tumour shrinkage. These findings are presented today at the American Society of Clinical Oncology (ASCO) meeting in Orlando by Dr James Spicer of Guys and St Thomas' Hospital, London, UK, a leading investigator in the trial. AS1409 is a fusion protein that combines the anti-tumour cytokine IL-12 with a tumour-targeting antibody. Systemic IL-12 has shown promising signs of activity in renal cancer and melanoma, but in the absence of a targeting strategy it has significant, treatment-limiting side-effects. The aim in developing AS1409 is to focus the activity of IL-12 at tumour sites whilst minimising effects on other tissues. Dr Spicer said: "The phase I findings provide validation for the idea of targeting the delivery of IL-12 to tumours using an antibody. AS1409 has shown evidence of anti-cancer activity without the serious side-effects seen with untargeted IL-12." Dr Gary Acton, Antisoma's Chief Medical Officer, added: "AS1409 is a highly innovative drug, which warrants further evaluation to build on these initial promising findings in patients with advanced cancer." Additional details of the findings are available in the poster presented at ASCO, which can be found at www.antisoma.com/asm/products/as1409 Enquiries: Glyn Edwards, CEO Daniel Elger, Director of Communications Antisoma plc +44 (0)7909 915 068 Mark Court/Lisa Baderoon/Rebecca Skye Dietrich Buchanan Communications +44 (0)20 7466 5000 Brian Korb The Trout Group +1 646 378 2923 Except for the historical information presented, certain matters discussed in this announcement 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. About the phase I trial of AS1409 The phase I trial of AS1409 was a dose-escalating study that enrolled eleven patients with malignant melanoma and two with renal cell carcinoma (kidney cancer). The main side-effects seen were flu-like symptoms. The maximum tolerated dose was identified as 15 µg/kg. Dose-limiting toxicities were observed at 25 µg/kg: these were transaminase elevation, fatigue and haemolytic anaemia. Severe interleukin-related side effects like those seen with untargeted IL-12 were not recorded. One patient with melanoma treated at 15 µg/kg experienced a partial response as measured by RECIST (Response Evaluation Criteria in Solid Tumors). Four melanoma patients experienced disease stabilisation, one of whom went on to experience tumour reduction that continued ten months later. In total, five out of nine evaluable patients with melanoma experienced some decrease in tumour burden (sum of largest diameters of target lesions) during the study. About AS1409 AS1409 was originally developed through a collaboration between Antisoma and EMD-Lexigen, now a part of Merck-Serono. The tumour-targeting antibody used in AS1409 binds to a protein found around blood vessels in many types of cancer, including breast, colorectal, lung, and prostate, as well as renal cancer and melanoma. The drug therefore has potential in a variety of cancer settings. About Antisoma Antisoma is a London Stock Exchange-listed biopharmaceutical company that develops novel products for the treatment of cancer. The Company has operations in the UK and the US. Please visit www.antisoma.com for further information about Antisoma. This announcement was originally distributed by Hugin. The issuer is solely responsible for the content of this announcement.