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Callisto Pharmaceuticals' Interim Phase II Data of Atiprimod inAdvanced Carcinoid Cancer to be presented at ASCO Conference

NEW YORK--(BUSINESS WIRE)--Apr 14, 2008 - Callisto Pharmaceuticals, Inc. (AMEX: KAL; FWB: CA4), a developer of new drug treatments in the fight against cancer and gastrointestinal disorders, announced today that interim data from the company's ongoing open-label Phase II clinical trial of Atiprimod in advanced carcinoid cancer, will be presented at the 44th annual meeting of the American Society of Clinical Oncology (ASCO), which will be held in Chicago May 30-June 3, 2008.

The study is an open-label Phase II trial designed to evaluate the anti-tumor efficacy, effect on symptoms, and safety and tolerability of Atiprimod in patients with low to intermediate grade neuroendocrine carcinoma (also called carcinoid cancer) who have metastatic or unresectable cancer and who have progression of their disease despite standard therapy (octreotide and others). Forty-six patients have been enrolled in the study, all of whom had progressing disease in the six months preceding enrollment. In addition, patients were required to complete two weeks of a symptoms diary to establish their symptoms baseline before commencing Atiprimod dosing. Atiprimod has been given orphan drug designation to treat carcinoid cancer.

"We had previously hoped to release the interim data from this trial during the first quarter 2008, but this is not possible due to ASCO media embargo rules," said Dr. Gary S. Jacob, CEO of Callisto. "We are of course pleased that ASCO views these data to be important enough for inclusion in the scientific program at the conference. We are continuing to collect considerable clinical data from a number of patients participating in the study, and believe these additional data collected during the next few months are particularly important. Advanced carcinoid cancer, although aggressive, is a relatively slow growing cancer, and evaluating patients who have been on drug for over 6 months is extremely useful in further assessing Atiprimod's potential."

Callisto has begun to plan for a pivotal phase III study for Atiprimod, and for an end of Phase II meeting with FDA at the appropriate time. The Company also continues to assess the potential of Atiprimod to treat other cancers, such as cancer of the liver and mantle cell lymphoma.

About Carcinoid cancer

Carcinoid tumors, or carcinoids, originate in hormone-producing cells of the gastrointestinal (GI) tract, the respiratory tract, the hepatobiliary (liver) system and the reproductive glands. The most common site of origin is the GI tract, especially the small bowel. There are about 37,000 patients with carcinoid cancer. About 7,000 new cases are diagnosed annually with the number increasing over the past 20-30 years. Carcinoid tumors that metastasize to the liver have a poor prognosis. Traditionally, chemotherapy relieves symptoms in less than 30% of cases of metastatic carcinoid tumors, usually for less than 1 year. Very few drugs that have been tested in this cancer have shown clinically meaningful efficacy. Carcinoid tumors often produce a condition called "carcinoid syndrome" which is caused by the release of hormones from the tumors into the blood stream. The symptoms vary depending on which hormones are released by the tumors, but typically include diarrhea, facial flushing, wheezing, abdominal pain and valvular heart disease.

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 drug for gastrointestinal disorders that is currently being developed by its wholly-owned subsidiary, Synergy Pharmaceuticals, as well as two anti-cancer agents. Synergy's proprietary drug SP-304 (Guanilib) is planned to begin clinical development in 2Q2008 for gastro-intestinal disorders. SP-304 is a synthetic analog of the human gastrointestinal hormone uroguanylin, and acts by activating the guanylate cyclase C (GC-C) receptor on epithelial cells of the colon. 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.

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

Posted: April 2008