New York, New York – September 24, 2003 – Callisto Pharmaceuticals, Inc. (OTCBB: CLSP) today announced the filing of an Investigational New Drug (IND) application with the U.S. Food and Drug Administration (FDA) for its cancer drug Atiprimod. The planned Phase I/IIa clinical trial is an open label study of the safety and efficacy of drug treatment for patients with refractory or relapsed multiple myeloma. This clinical trial will be conducted at leading cancer hospitals in the United States. One site will be The University of Texas M.D. Anderson Cancer Center and will be coordinated by a leading cancer clinician and investigator, Dr. Moshe Talpaz. The primary objectives of this clinical trial are to identify the maximum tolerated dose (MTD) and safety of Atiprimod in multiple myeloma patients. The secondary objectives are to evaluate the response of relapsed multiple myeloma patients, measure the drug pharmacokinetics and evaluate a wide variety of surrogate markers to better define the mechanisms of action for Atiprimod. “The filing of this IND is a significant milestone for Callisto. We are very excited about the potential of Atiprimod to treat multiple myeloma patients,” says Dr. Gary S. Jacob, CEO of Callisto Pharmaceuticals, Inc.

Multiple myeloma is a common hematological malignancy (10% of all hematological cancers) and represents 1% of all cancer malignancies. There are currently approximately 50,000 patients in the U.S. with approximately 15,000 newly diagnosed patients yearly. Despite 3 decades of clinical trial research involving thousands of patients with multiple myeloma and the recent approval of new drugs, the disease continues to be fatal to the majority of patients.

Atiprimod is a drug that has completed a Phase I/IIa clinical trial in rheumatoid arthritis patients with patient dosing as long as 1 year. The drug is now entering clinical trials in multiple myeloma based on a wide range of compelling preclinical data for this particular cancer. Atiprimod has also shown potent activity against a wide range of solid tumors in in-vitro screens and will be evaluated in animal models of solid tumors to expand Atiprimod’s clinical trial indications. Callisto has an exclusive worldwide license from AnorMED Inc. to develop, manufacture, use and sell Atiprimod.

About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company primarily focused on the development of drugs to treat multiple myeloma, other cancers and osteolytic bone disease. Callisto’s lead drug candidate, Atiprimod, is a small-molecule, orally available drug with antiproliferative and antiangiogenic activity. Callisto’s second anticancer program is focused on the development of an analog of the human intestinal hormone, uroguanylin, to treat colon cancer. Callisto has two operating subsidiaries, Callisto Research Labs, LLC and Synergy Pharmaceuticals Inc.

Included in this release are “forward-looking: statements. Such statements are indicated by words such as “expect,” “should,” “anticipate” and similar words indicating uncertainty in facts and figures. Although Callisto believes that the expectations reflected in such forward-looking statements are reasonable, it can give no assurance that such expectations reflected in such forward-looking statements will prove to have been correct. Callisto’s actual results could differ materially from those anticipated in the forward-looking statements as a result of various factors.