Callisto Pharmaceuticals Announces Plan to Evaluate Atiprimod in Myelodysplastic Syndrome Patients

NEW YORK, NY – May 23, 2005 – Callisto Pharmaceuticals, Inc. (AMEX: KAL), a biopharmaceutical company primarily focused on the development of drugs to treat cancer, announced today that it intends to evaluate Atiprimod in patients with myelodysplastic syndrome (MDS). Atiprimod is currently in a Phase I/IIa clinical trial in refractory or relapsed multiple myeloma patients at 4 clinical sites in the U. S., and in a Phase I/IIa clinical trial in advanced cancer patients at the University of Texas M.D. Anderson Cancer Center. The protocol for the anticipated trial in MDS patients is currently being finalized, and is expected to be submitted to the institutional review board (IRB) at M.D. Anderson Cancer Center in the near future.


About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company primarily focused on the development of drugs to treat cancer. Callisto has two lead drugs in clinical development, Annamycin to treat relapsed leukemia, and Atiprimod to treat relapsed multiple myeloma. Callisto intends to initiate a clinical trial of Annamycin in relapsed acute lymphoblastic leukemia patients in mid 2005. Annamycin, a drug from the anthracycline family, has a novel therapeutic profile, including activity against resistant diseases and significantly reduced cardiotoxicity. Callisto’s second drug, Atiprimod, is in a Phase I/IIa clinical trial in relapsed multiple myeloma patients, and is a small-molecule, orally available drug with antiproliferative and antiangiogenic activity. Callisto also has drugs in preclinical development for melanoma, gastrointestinal inflammation, and a program focused on the development of a drug to protect against staphylococcus and streptococcus biowarfare agents. Callisto has exclusive worldwide licenses from AnorMED Inc. and M.D. Anderson Cancer Center to develop, manufacture, use and sell Atiprimod and Annamycin, respectively. For additional information, visit www.callistopharma.com.


Investor Relations:
Marty Tullio or Mark Tullio
McCloud Communications, LLC
949.553.9748
marty@McCloudCommunications.com
mark@McCloudCommunications.com

Company Contact:
Dan D’Agostino
Callisto Pharmaceuticals, Inc.
212.297.0010 x227
dagostino@callistopharma.com