NEW YORK, April 11 /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 the publication of a research article on Atiprimod, Callisto’s drug currently in clinical trials in carcinoid cancer and multiple myeloma patients, in the February 2007 issue of Blood, a peer-reviewed scientific journal that publishes original research articles related to hematological malignancies.

The article authored by Dr. Michael Wang and Dr. Qing Yi, from the University of Texas M.D. Anderson Cancer Center, focuses on Atiprimod’s ability to inhibit proliferation of mantle cell lymphoma (MCL) cells in vitro and to inhibit growth of MCL tumors in tumor-bearing mice. The animal data demonstrated that Atiprimod significantly inhibited tumor growth in vivo and prolonged survival of tumor-bearing mice. Atiprimod was shown to enhance release of apoptosis-inducing factor (AIF) from cellular mitochondria, and the authors suggest that this is the mechanism of Atiprimod’s apoptotic (programmed cellular death) activity.

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.

The publication appeared in Blood First Edition Paper, prepublished online February 22, 2007 DOI 10.1182/Blood-2006-12-063958 and is titled: “Atiprimod inhibits the growth of mantle cell lymphoma in vitro and in vivo and induces apoptosis via activating the mitochondrial pathways” by M. Wang, L. Zhang, X. Han, J. Yang, J. Qian, S. Hong, F. Samaniego, J. Romaguera and Q. Yi.

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 pediatric acute leukemia patients in 1Q 2007 and initiated a trial in adult relapsed or refractory acute lymphoblastic 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 http://www.callistopharma.com.

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 Form S-3/A declared effective on February 15, 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.