Callisto Announces Guanilib Presentation at the 5th Annual Meeting of Cancer Drugs Research and Development.

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 an oral presentation covering preclinical data on Guanilib at the 5th Cancer Drugs Research and Development conference, to be held February 21-22, 2008 in Phoenix, Arizona. Dr. Shailubhai's presentation entitled "Guanilib, a guanylate cyclase-C (GC-C) agonist, is a new class of oral drug candidate for GI disorders and colon cancer" is scheduled for 1:00 pm on February 21, 2008. The 5th Cancer Drugs R&D conference is a leading forum gathering top researchers from academia and major pharmaceutical and biotechnology companies.

Guanilib is Callisto's patented oral drug candidate to treat gastrointestinal disorders. The drug is presently being developed for treatment of chronic constipation and constipation-predominant irritable bowel syndrome (IBS-C), and is scheduled to enter clinical trials in early 2008. "Guanilib 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. In addition, Guanilib also downregulates key pro-inflammatory cytokines, including IL-4, IL-5, IL-23, and TNF," said Dr. Shailubhai.

"Callisto presently has a major effort underway to bring Guanilib into the clinic," said Dr. Gary S. Jacob, Chief Executive Officer of Callisto Pharmaceuticals. "We plan to file an Investigational New Drug (IND) application in early 2008 and to initiate clinical trials shortly thereafter."

About Guanilib

Guanilib (also called SP-304) is a potent analog (synthetic molecule) of uroguanylin developed by Callisto scientists, and is proprietary to Callisto. Guanilib is a targeted therapy, acting specifically by binding to and activating a specific receptor on epithelial cells of the gut. The drug is orally administered, and acts in the lumen of the gut, demonstrating virtually no systemic absorption and an excellent safety profile in animal models. The drug has been shown to be superior to the natural hormone, uroguanylin, in its biological activity, protease stability and pH characteristics.

More details are available at http://www.callistopharma.com/content/pipeline/guanilib/science.jsp.

About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company focused on the development of new drugs to treat various forms of cancer and gastrointestinal diseases. Callisto's drug candidates include two anti-cancer agents as well as a drug for gastrointestinal disorders. One of the Company's lead drug candidates, Atiprimod is presently in a Phase II clinical trial in advanced carcinoid cancer patients, a neuroendocrine tumor, and in a Phase I/IIa human clinical trial in relapsed or refractory multiple myeloma patients. Another anti-cancer drug, L-Annamycin, is being developed as a treatment for forms of relapsed or refractory acute leukemia, a currently incurable blood cancer. L-Annamycin is currently in a Phase I 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. L-Annamycin, a member of the anthracycline family of proven anti-cancer drugs, has a novel therapeutic profile, including potential activity against multi-drug resistant tumors and significantly reduced cardiotoxicity, or damage to the heart, compared to currently available drug alternatives. Callisto also has a proprietary drug Guanilib in preclinical development for gastro-intestinal disorders. 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, 2006, 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.