Company Cites Continuing Progress on Clinical and Preclinical Programs NEW YORK, Aug. 8 /PRNewswire-FirstCall/ -- Callisto Pharmaceuticals, Inc. (Amex: KAL; FWB: CA4), a developer of new drug treatments in the fight against cancer and gastrointestinal diseases, is pleased to provide an update covering its strategic and drug development activities for the second quarter of 2007. "Callisto has made substantial progress with our clinical and preclinical programs in 2007," stated Gary S. Jacob, CEO of Callisto Pharmaceuticals. "In particular, the pace of our Phase II clinical trial of Atiprimod in neuroendocrine cancer patients continues to go well, and we expect to have full enrollment accomplished by the third quarter of 2007. " The Atiprimod Phase II clinical trial in neuroendocrine carcinoma is a multiple-center, open-label study of the safety and efficacy of Atiprimod in low to intermediate grade neuroendocrine carcinoma patients. The trial, designed to enroll 40 patients, presently has 29 patients on study, and Callisto anticipates achieving the total enrollment of 40 patients in the third quarter of 2007. The trial was opened in November, 2006 and there are presently 5 clinical sites in the U.S. that are enrolling patients. The Company plans to have discussions with FDA some time in the fourth quarter of 2007 regarding the design of a pivotal trial in this disease indication. Dr. Jacob continued, "We also have implemented a plan to develop Guanilib, Callisto's guanylyl cyclase C receptor agonist, to treat gastrointestinal disorders such as chronic constipation and irritable bowel syndrome. We plan to file an Investigational New Drug application with FDA in early 2008, and evaluate its potential initially in gastrointestinal disorders where there is a critical need for new drugs to treat the millions of patients currently suffering from these maladies." 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 has been demonstrated to be superior to uroguanylin in its biological activity, protease stability and pH characteristics, and is currently undergoing pre-clinical animal studies as a treatment for gastrointestinal (GI) diseases and GI inflammation. Animal model data on Guanilib previously demonstrated anti-inflammatory activity in a number of mouse-models of ulcerative colitis, and the drug is currently being evaluated in animal models of GI disorders. Callisto plans to initiate clinical trials of Guanilib in early 2008. About Atiprimod Atiprimod is an orally bio-available small molecule drug that displays multiple mechanisms of action. The drug has been shown to be antiangiogenic, inhibit secretion of VEGF and IL-6, elicit an apoptotic response (programmed cellular death), and inhibit phosphorylation of key kinases involved in tumor progression and survival including Akt and STAT3. The drug is presently in two clinical trials: a Phase II trial in advanced carcinoid cancer patients, and a Phase I/IIa human clinical trial in relapsed or refractory multiple myeloma patients. 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 in development currently include anti-cancer agents in clinical development, in addition to drugs in pre-clinical development for other significant health care markets, including 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. CONTACT: Gary Jacob of Callisto Pharmaceuticals, Inc., +1-212-297-0010, Web site: http://www.callistopharma.com/ Barretto Pacific Corporation John Baldissera 800-368-1217 DATASOURCE: Callisto Pharmaceuticals, Inc. CONTACT: Gary Jacob of Callisto Pharmaceuticals, Inc., +1-212-297-0010, ; or John Baldissera of Barretto Pacific Corporation, 1-800-368-1217, for Callisto Pharmaceuticals, Inc. Web site: http://www.callistopharma.com/

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