(ASTX) Topline Results SGI-110 AML Phase 2 Myeloid Leukemia Study

DUBLIN, Calif., Aug. 28, 2013 — Astex Pharmaceuticals, Inc. (Nasdaq:ASTX) today announced topline results from the ongoing phase 2 of SGI-110 in patients with AML and MDS. The Phase 2 study is a randomized study of SGI-110 given either as 60 or 90 mg/m2 daily for 5 days in a 28-day course. As of end of June data cutoff, 67 AML patients had a minimum follow up of 3 months (50 patients representing the complete cohort of relapsed/refractory AML, and 17 patients in the treatment-naive elderly AML not suitable for induction chemotherapy cohort). The primary endpoint is overall remission rate (Complete Remission or CR; Complete Remission with Incomplete hematologic recovery or CRi/CRp). There were 8 remissions in relapsed/refractory AML and 9 remissions in treatment-naive elderly AML for an overall complete remission rate (CR, CRi/CRp) of 17/67 or 25%. The detailed results have been submitted for presentation to the American Society of Hematology (ASH) meeting to be held later this year during December 7-10 in New Orleans, LA.

About SGI-110

SGI-110 is a novel small molecule, DNA-hypomethylating agent administered as a single low volume subcutaneous injection. SGI-110 demonstrated activity in restoring silenced tumor suppressor gene expression in cancer cells by reversal of DNA methylation and inducing responses in previously treated MDS and AML patients. SGI-110 is wholly owned by Astex Pharmaceuticals.

About Astex Pharmaceuticals

Astex Pharmaceuticals is dedicated to the discovery and development of novel small molecule therapeutics with a focus on oncology. The Company is developing a proprietary pipeline of novel therapies and is creating de-risked products for partnership with leading pharmaceutical companies. Astex Pharmaceuticals developed and out-licensed DACOGEN® (decitabine) for Injection and receives significant royalties on global sales.

For more information about Astex Pharmaceuticals, Inc., please visit http://www.astx.com.

CONTACT: Timothy L. Enns
         Astex Pharmaceuticals, Inc.
         Senior Vice President
         Corporate Communications & Marketing
         Tel: +1 (925) 560-2810
         E-mail: tim.enns@astx.com

         Susanna Chau
         Astex Pharmaceuticals, Inc.
         Manager
         Investor Relations
         Tel: +1 (925) 560-2845
         E-mail: susanna.chau@astx.com

         Alan Roemer
         The Trout Group
         Managing Director
         Tel: +1 (646) 378-2945
         E-mail: aroemer@troutgroup.com