March 3, 2007

Callisto Pharmaceuticals Announces Publication Of Research Paper On Atiprimod

Callisto Pharmaceuticals, Inc. (Amex: KAL) (Frankfurt: CA4), a developer of new drug treatments in the fight against cancer and other major health threats, today announced a recent publication of a research paper on Atiprimod in Molecular Cancer Therapeutics, a journal published by the American Association of Cancer ( The publication, jointly authored by scientists from Callisto and the Institute of Hepatitis Virus Research, describes preclinical data suggesting that Atiprimod inhibited growth of liver carcinoma cells to a greater degree when cells expressed hepatitis B (HBV) and hepatitis C (HCV) viruses than for those cells not expressing these viruses.

According to Dr. Kunwar Shailubhai, Sr. VP Discovery Research, the senior author of the article, Atiprimod has unique properties centering on its ability to selectively inhibit activation of PI-3 kinase/Akt and Jak/STAT3 pathways which are overexpressed in a majority of human cancers.

The research paper entitled "Deactivation of Akt and STAT3 signaling promotes apoptosis, inhibits proliferation, and enhances the sensitivity of hepatocellular carcinoma cells to an anticancer agent, Atiprimod" was published in the January 2007 issue of Molecular Cancer Therapeutics (Volume 6, pages 112-121).

"We are particularly focused on evaluating Atiprimod in advanced carcinoid patients," notes Dr. Gary S. Jacob, Chief Executive Officer of Callisto. "These patients oftentimes exhibit the spread of their carcinoid tumors to their liver, and have proven to be very difficult to treat effectively using approved chemotherapies. Accordingly there are very few options available that offer hope to patients with this cancer."

Atiprimod is presently in a Phase II clinical trial in advanced carcinoid cancer patients, and a Phase I/IIa clinical trial in relapsed or refractory multiple myeloma patients. Callisto earlier announced in June 2006 interim data from a Phase I trial of Atiprimod in advanced cancer patients. The patients who were entered into this trial had growing tumors and symptoms that were no longer controlled by the standard therapies utilized. During treatment, three of the five advanced carcinoid patients had measurable tumor regressions and loss of many of the debilitating symptoms of this disease.

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 in pre-clinical development for other significant health care markets, including ulcerative colitis. One of the Company's lead drug candidates, Atiprimod, is in development to treat advanced carcinoid cancer, a neuroendocrine tumor, and relapsed multiple myeloma, a blood cancer. Atiprimod is presently in a Phase II clinical trial in advanced carcinoid cancer patients, and in Phase I/IIa human clinical trials in relapsed or refractory multiple myeloma patients, and advanced cancer patients, respectively. 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. Callisto initiated a clinical trial of L-Annamycin in adult relapsed or refractory 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. Callisto also has drugs in preclinical development for gastro-intestinal inflammation, and cancer. Callisto has exclusive worldwide licenses from AnorMED 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

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.

Callisto Pharmaceuticals, Inc.

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