Research Agreement to Support Biological Studies on New Tumor-Fighting Class of Drugs NEW YORK, June 15 /PRNewswire-FirstCall/ -- Callisto Pharmaceuticals, Inc. (Amex: KAL; FWB: CA4), a developer of new drug treatments in the fight against cancer and other major health threats, announced today that a sponsored laboratory study agreement has been executed with The University of Texas M. D. Anderson Cancer Center to support development of the Company's Degrasyn class of cancer-fighting compounds. The two-year agreement is intended to support in-vitro and animal model studies to be performed by a group of research scientists at M. D. Anderson, who will focus on evaluating Degrasyn analogs being synthesized under the auspices of a separate executed sponsored laboratory study agreement with M. D. Anderson. Callisto recently licensed the Degrasyn class of compounds, formerly referred to as tyrphostins, from The University of Texas M. D. Anderson Cancer Center, a leading center devoted to cancer patient care and research. The novel anti-cancer activity of Degrasyns relates to their ability to selectively promote degradation of key proteins involved in tumor growth and survival. "The planned research by M. D. Anderson scientists, where the Degrasyn class of drugs was initially developed, provides an exciting opportunity to advance the Degrasyn program towards the clinic," said Dr. Donald Picker, Callisto's Executive Vice President of Research and Development. "This program is a high priority activity at Callisto which we hope could yield an important new tumor-fighting drug to treat a variety of cancers." Dr. Nicholas J. Donato, associate professor in the Department of Experimental Therapeutics, at M. D. Anderson will serve as principal investigator on the program, formally titled, "Analysis of the Anti-Tumor Activity and Mechanism of Action of WP1130 and its Analogs." "We are working closely with Callisto and with my colleague at M. D. Anderson, Dr. William Bornmann and his associates, to evaluate a library of synthesized Degrasyn analogs utilizing state-of-the-art biological assays," said Dr. Donato. "We also are continuing to explore the unique mechanism-of- action elicited by this interesting class of compounds." About Callisto Pharmaceuticals, Inc. Callisto is a biopharmaceutical company focused on the development of new drugs to treat various forms of cancer and other serious afflictions. Callisto's drug candidates in development currently include anti-cancer agents in clinical development, in addition to drugs for other significant health care markets, including ulcerative colitis and biodefense. One of the Company's lead drug candidates, L-Annamycin, is being developed as a treatment for forms of relapsed acute leukemia, a currently incurable blood cancer. Callisto initiated a clinical trial of L-Annamycin in adult relapsed acute lymphocytic leukemia patients in 4Q 2005. L-Annamycin, a new compound from the anthracycline family of proven anti-cancer drugs, has a novel therapeutic profile, including activity against resistant diseases and significantly reduced cardiotoxicity, or damage to the heart, compared to currently available drug alternatives. Another anti-cancer drug, Atiprimod, is in development to treat relapsed multiple myeloma, a blood cancer, and advanced carcinoid cancer. Atiprimod is presently in Phase I/IIa human clinical trials in relapsed multiple myeloma patients, and advanced cancer patients, respectively. Callisto also has drugs in preclinical development for gastro- intestinal 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 The University of Texas 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. For additional information, visit 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/A for the year ended December 31, 2005, 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. DATASOURCE: Callisto Pharmaceuticals, Inc. CONTACT: Dan D'Agostino of Callisto Pharmaceuticals, Inc., +1-212-297- 0010 ext. 227, Web site: http://www.callistopharma.com/

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