SOURCE: Callisto Pharmaceuticals, Inc.

July 07, 2005 09:45 ET

MD Anderson Cancer Researchers Publish Manuscript on Callisto Pharmaceuticals' Atiprimod in British Cancer Journal

Atiprimod's Anti-Cancer Mechanisms of Action Highlighted in British Journal of Cancer

NEW YORK, NY -- (MARKET WIRE) -- July 7, 2005 -- Callisto Pharmaceuticals, Inc. (AMEX: KAL), a biopharmaceutical company primarily focused on the development of drugs to treat cancer, announced the publication of a paper in the British Journal of Cancer on Atiprimod's anti-multiple myeloma activity. The paper, entitled "Atiprimod Blocks STAT3 Phosphorylation and Induces Apoptosis in Multiple Myeloma Cells," appeared in the British Journal of Cancer, Volume 92, Number 13, pp.1-11 (2005.), and was authored by a team of scientists and clinicians from the University of Texas M.D. Anderson Cancer Center, highly regarded experts in multiple myeloma, blood cancers and bioimmunotherapy. The publication provides further evidence that Atiprimod has anti-neoplastic effects on human myeloma cells in culture, and further elucidated the biological mechanisms by which Atiprimod exerts these anti-neoplastic effects.

"The team of scientists and clinicians who participated in this study has an impressive record of advancements in the basic science of blood cancers, as well as a proven record of success in the clinic," said Dr. Gary S. Jacob, Chief Executive Officer of Callisto Pharmaceuticals. "Atiprimod is currently being evaluated at M.D. Anderson in a Phase I/IIa clinical trial in patients with relapsed multiple myeloma, as well as in a single agent trial in advanced cancer patients."

In the present work, Atiprimod's effects on proliferation of myeloma cells, and on the key signaling pathways in myeloma cells were evaluated. Atiprimod was shown to inhibit proliferation in a time- and dose-dependent manner, and to arrest myeloma cell growth, preventing cell cycle progression. Furthermore, Atiprimod inhibited STAT 3 activation, blocking the signaling pathway of interleukin-6, which contributes to myeloma cell proliferation and survival. Incubation of myeloma cells with Atiprimod induced apoptosis (cell death) through the activation of caspase 3, leading to deactivation of the DNA repair enzyme PARP.

In separate experiments, Atiprimod suppressed myeloma colony-forming cell proliferation of fresh marrow cells from five patients with newly diagnosed MM in a dose-dependent fashion.

Atiprimod is currently being evaluated in a Phase I clinical trial in relapsed or refractory multiple myeloma patients at four clinical sites in the United States -- the Dana-Farber Cancer Institute (Boston, MA), the M.D. Anderson Cancer Center (Houston, TX), the St. Vincent's Comprehensive Cancer Center (New York, NY) and the Roswell Park Cancer Institute (Buffalo, NY). On May 4, 2005 Callisto announced that three patient cohorts had completed dosing at 30, 60 and 90 mg, respectively, and a fourth dosing cohort was underway at 120 mg. No dose limiting toxicities had been observed, and a fifth dose cohort at 180 mg was anticipated to begin in the following 6-8 weeks.

About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company focused on the development of drugs to treat cancer. Callisto has two lead drugs in clinical development, Annamycin to treat relapsed leukemia, and Atiprimod to treat relapsed multiple myeloma. Callisto intends to initiate a clinical trial of Annamycin in relapsed acute lymphoblastic leukemia patients in mid 2005. Annamycin, a drug from the anthracycline family, has a novel therapeutic profile, including activity against resistant diseases and significantly reduced cardiotoxicity. Callisto's second drug, Atiprimod, is in a Phase I/IIa clinical trial in relapsed multiple myeloma patients, and is a small-molecule, orally available drug with antiproliferative and antiangiogenic activity. Callisto also has drugs in preclinical development for melanoma, gastrointestinal 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 M.D. Anderson Cancer Center to develop, manufacture, use and sell Atiprimod and Annamycin, respectively. For additional information, visit 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, 2004,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.

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