Callisto Pharmaceuticals Announces Presentation on SP-304 at the 3rd International Congress on Natural Peptides to Drugs.

NEW YORK -- Callisto Pharmaceuticals, Inc. (AMEX: KAL; FWB: CA4), a developer of new drug treatments in the fight against cancer and gastrointestinal disorders, announced today that Dr. Kunwar Shailubhai, Sr. VP Discovery Research, will give a plenary talk covering therapeutic applications of guanylate cyclase C agonist peptides at the 3rd International Congress on "Natural Peptides to Drugs (NP2D)", to be held April 14-17, 2008 in Zermatt, Switzerland. Dr. Shailubhai's presentation entitled "GC-C receptor peptides: new class of oral drug candidates" is scheduled for 11:00 am on April 16, 2008. The 3(rd) International Congress NP2D (www.np2D.com) is a leading forum gathering top researchers from academia and major pharmaceutical and biotechnology companies.

SP-304 (previously called Guanilib) is a patented oral drug candidate to treat gastrointestinal disorders. The drug is presently being developed for the treatment of chronic constipation and constipation-predominant irritable bowel syndrome (IBS-C), and is scheduled to enter clinical trials in May 2008.

"SP-304 is an analog of the human hormone uroguanylin with superior properties to the natural molecule, and which acts primarily by promoting water secretion into the lumen of the GI-tract to facilitate bowel movement, said Dr. Shailubhai, Sr. VP of Callisto. "An Investigational New Drug (IND) application was recently filed for SP-304, and we hope to initiate clinical trials shortly."

About SP-304

SP-304 (also called Guanilib) is an analog (synthetic molecule) of uroguanylin, a natural gastro-intestinal hormone produced in the gut that is a key regulator of intestinal function. SP-304 works by activating a unique receptor on intestinal cells. The receptor, called the guanylate cyclase C (GC-C) receptor, promotes fluid and ion transport in the gastro-intestinal (GI) tract. Under normal conditions, the receptor is activated by the natural hormones uroguanylin and guanylin. Activation of the receptor leads to the transport of chloride and bicarbonate into the intestine, and water is carried with these ions into the lumen of the intestine, thereby producing a looser stool. SP-304 has been demonstrated to be superior to uroguanylin, in its biological activity, protease stability and pH characteristics. The compound is not absorbed systemically and demonstrates a very good safety profile. An IND was filed for SP-304 on April 2, 2008, and a phase 1 clinical trial is expected to start with the compound in May 2008.

About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company focused on the development of new drugs to treat various forms of gastrointestinal diseases and cancer. Callisto's drug candidates include a SP-304 for gastrointestinal disorders that is currently being developed by its wholly-owned subsidiary, Synergy Pharmaceuticals, as well as two anti-cancer agents. The Company's lead drug in the clinic, Atiprimod, is presently in a Phase II clinical trial in advanced carcinoid cancer, a neuroendocrine tumor, and in a Phase II extension trial in advanced carcinoid cancer patients. Callisto's second drug in the clinic, L-Annamycin, is currently in a Phase I/II clinical trial in adult relapsed or refractory acute lymphocytic leukemia, and in a Phase I clinical trial in children and young adults with refractory or relapsed acute lymphocytic leukemia or acute myelogenous leukemia. Callisto has exclusive worldwide licenses from Genzyme Inc. and M.D. Anderson Cancer Center to develop, manufacture, use and sell Atiprimod and L-Annamycin, respectively. Callisto is also listed on the Frankfurt Stock Exchange under the ticker symbol CA4. More information is available at http://www.callistopharma.com.

Forward-Looking Statements

Certain statements made in this press release are forward-looking. 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 be correct. As discussed in the Callisto Pharmaceuticals Annual Report on Form 10-K for the year ended December 31, 2007, and other periodic reports, as filed with the Securities and Exchange Commission, actual results could differ materially from those projected in the forward-looking statements as a result of the following factors, among others: uncertainties associated with product development, the risk that products that appeared promising in early clinical trials do not demonstrate efficacy in larger-scale clinical trials, the risk that Callisto will not obtain approval to market its products, the risks associated with dependence upon key personnel and the need for additional financing.