Antisoma to advance AS1411 in AML based on positive phase II data presented at ASCO

London, UK, Cambridge, MA, and Orlando, FL: 29 May 2009 - Antisoma plc (LSE: ASM; USOTC: ATSMY) announces that it plans to advance the development of AS1411 in AML (acute myeloid leukaemia) based on positive data from a phase II study in relapsed and refractory AML presented today at the American Society of Clinical Oncology (ASCO) meeting in Orlando. AS1411 belongs to a new type of drug called aptamers. These drugs are short pieces of DNA or RNA that fold into three-dimensional structures capable of targeting particular proteins. AS1411 is a DNA aptamer that targets nucleolin, a protein found on the surface of cancer cells. The AS1411 phase II study in AML was the first randomised controlled trial to test an aptamer as a treatment for cancer. A broad spectrum of AML patients were allowed to participate in the trial, but all had disease that had proved non-responsive (refractory) to prior treatments or had relapsed after one or more previous therapies. Given these requirements, many of the patients had a very poor prognosis. Patients were assigned randomly to three treatment groups. A control group was treated with high-dose cytarabine, a standard chemotherapy treatment for relapsed and refractory AML. The other two groups received high-dose cytarabine combined with either 10 or 40 mg/kg/day AS1411. The response rate in the cytarabine control group was 5% (1/19) patients. By contrast, response rates in the groups receiving 10 or 40 mg/kg/day AS1411 with cytarabine were 21% (4/19 patients) and 19% (4/21) patients, respectively. Addition of AS1411 to high-dose cytarabine was well tolerated at both the 10 and 40 mg/kg/day doses. Most of the side-effects observed were those typically associated with cytarabine treatment. Commenting on the findings, Dr Robert Stuart of the Medical University of South Carolina, Principal Investigator in the phase II trial and presenter of the data at the ASCO meeting, said: "These findings, seen in a very poor prognosis group of leukaemia patients, are very promising, and encourage us to go forward and further define the potential for AS1411 as a new treatment option for patients with AML." Glyn Edwards, Antisoma's CEO added: "With these positive results, we have a good basis on which to progress AS1411 in AML. We are working with leading experts in the field to identify the best approach to further development and ensure we make the most of this exciting opportunity." It is anticipated that Antisoma will carry out a programme of phase IIb trials to optimise the choice of patient population and design for future pivotal studies of AS1411 in AML. A separate phase II trial of AS1411 in renal cancer recently completed patient recruitment and is expected to report initial data later this year. A copy of the poster presented at the ASCO meeting is available on the Antisoma website at Enquiries: Antisoma plc: Glyn Edwards, CEO Daniel Elger, VP Marketing & Communications (In Orlando) +44 (0) 7909 915 068 Mark Court/Lisa Baderoon/Rebecca Skye +44 (0)20 7466 5000 Dietrich Buchanan Communications Brian Korb +1 646 378 2923 The Trout Group 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 AML (acute myeloid leukaemia) AML is a type of cancer in which the bone marrow makes abnormal and immature blood cells, eventually leading to bone marrow failure. The American Cancer Society estimates that there will be over 13,000 new cases of AML diagnosed this year in the US alone. About AS1411 AS1411 was originally developed by Dr Paula Bates, Dr John Trent and Prof. Donald Miller at the University of Alabama and then at the University of Louisville. Antisoma added AS1411 to its pipeline when it acquired the Louisville-based company Aptamera Inc. in 2005. AS1411 belongs to a new type of drugs called aptamers. These are short pieces of DNA or RNA that fold into three-dimensional structures capable of targeting particular proteins. AS1411 is a DNA aptamer that binds to nucleolin, a protein expressed in the nucleus of all cells but which in cancer cells is also exposed on the cell surface, providing a basis for specific targeting by AS1411. When AS1411 binds to nucleolin on cancer cells, it is internalised and causes apoptosis through interference with various functions of nucleolin. A 30-patient phase I trial provided evidence for activity of AS1411 monotherapy. Among 12 patients with renal cancer, two showed objective responses and nine had a best overall response of stable disease. No serious adverse events related to treatment were observed. Two phase II trials have been conducted with AS1411: the AML study described here and a study in renal cancer, which is ongoing. 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 for further information about Antisoma. ---END OF MESSAGE--- This announcement was originally distributed by Hugin. The issuer is solely responsible for the content of this announcement.