SOURCE: Callisto Pharmaceuticals, Inc.

June 10, 2005 08:30 ET

Dana-Farber Cancer Researchers Show Callisto Pharmaceuticals' Atiprimod Inhibits Tumor Growth in an Animal Model of Multiple Myeloma

Atiprimod's Anti-Cancer Mechanisms of Action Highlighted in American Society of Hematology Journal

NEW YORK, NY -- (MARKET WIRE) -- June 10, 2005 -- Callisto Pharmaceuticals, Inc. (AMEX: KAL), a biopharmaceutical company primarily focused on the development of drugs to treat cancer, today announced the publication of a manuscript on Atiprimod, Callisto's drug candidate for multiple myeloma in the June issue of the American Society of Hematology's journal Blood, Volume 105, Number 11, pp. 4470-4476 (2005). The article entitled "Azaspirane (N-N-diethyl-8,8-diropyl-2-azaspiro[4.5] decance-2-propanamine) inhibits human multiple myeloma cell growth in the bone marrow milieu in vitro and in vivo" was authored by a team of scientists at Dana-Farber Cancer Institute (Boston, MA) and scientists at Callisto Pharmaceuticals, Inc.

"The Dana-Farber research team, led by Dr. Ken Anderson, Director of the Jerome Lipper Multiple Myeloma Center, is at the forefront of cutting-edge research on the development of new drugs to treat multiple myeloma," said Dr. Gary S. Jacob, Chief Executive Officer, Callisto Pharmaceuticals. "We are pleased to be collaborating with this world-class team to learn more about how Atiprimod exerts its effect against multiple myeloma."

The manuscript presented the first demonstration of Atiprimod's ability to inhibit growth of multiple myeloma in an animal model of this human disease. Importantly, Atiprimod demonstrated in vivo anti-tumor activity against human multiple myeloma tumor growth in severe combined immunodeficient (SCID) mice. This indicates that Atiprimod can similarly target human MM cells in the bone marrow microenvironment of an animal. Approved drugs such as Velcade® and Thalidomid® used for therapy also exhibit activity in similar animal models.

In studies directed at understanding how Atiprimod works, Atiprimod was shown to significantly inhibit growth and induce programmed cell death (apoptosis) in drug-sensitive and drug-resistant human multiple myeloma (MM) cell lines, as well as in human MM cells. Atiprimod was shown to inhibit key signaling enzymes in MM cells -- inhibiting STAT3 phosphorylation and Akt phosphorylation -- and to inhibit both IL-6 and VEGF secretion in bone marrow stem cells triggered by MM cell binding.

Atiprimod is currently being evaluated in a Phase I/IIa 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). Three patient cohorts have now completed dosing at 30, 60 and 90 mg, respectively, and a fourth dosing cohort is currently underway at 120 mg. No dose limiting toxicities have been observed, to date. A fifth dose cohort at 180 mg is anticipated to begin in the next 6-8 weeks.

About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company focused on the development of drugs to treat cancer and osteolytic bone disease. 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-KSB 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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