Callisto Cites New Research Data on Cancer Drug Atiprimod in Presentations at American Society of Hematology Meeting; Company Announces Plan for Next Phase of Trial Following Release of Additional Clinical and Pre-Clinical Data.

NEW YORK -- Callisto Pharmaceuticals, Inc. (AMEX:KAL) (FWB:CA4), a developer of new drug technologies in the fight against cancer and other serious healthcare threats, has released additional clinical research data on its cancer drug candidate Atiprimod, and further announced plans to extend the present Phase I/IIa clinical trial in multiple myeloma patients to higher drug dosages to obtain a maximum tolerated dose (MTD), and further evaluate patients for drug efficacy.

Callisto's drug candidate Atiprimod is currently being evaluated to treat multiple myeloma, a serious and ultimately invariably fatal blood cancer that creates devastating complications including bone resorption and skeletal compression fractures.

New clinical and pre-clinical research data on Atiprimod was delivered on Dec. 11 and Dec.12 during two invited presentations at this year's American Society of Hematology (ASH) annual meeting, in Atlanta, GA. The ASH meeting is widely recognized as the leading scientific conference in the field of medical and clinical research relating to research and diseases of the blood. Research of particular significance is selected for oral presentation at the annual gathering. Notably, two abstracts on Callisto's drug candidate Atiprimod were selected for oral presentation.

Approximately a thousand ASH meeting-goers attended the two Atiprimod presentations, according to Callisto's estimates.

"The large attendance at this multiple myeloma session at which we presented demonstrates the high level of interest among the hematology and cancer research community for new drug candidates such as Atiprimod," said Dr. Donald Picker, Executive Vice President of R&D for Callisto. "So far, the Atiprimod research has demonstrated encouraging indications and we are looking forward to additional clinical data to further evaluate its efficacy. Continued clinical development of Atiprimod is a major strategic focus for Callisto."

The clinical presentation at the ASH conference on the Phase I/IIa clinical trial of Atiprimod in relapsed or refractory multiple myeloma patients provided additional data on the 15 patients treated with drug, including the 3 patients at the highest dose level of 180 mg/day. The presentation disclosed that two patients exhibited stable disease, with one patient having a 34% decrease in M protein over 3 months of treatment. It was also noted that two patients reported a subjective decrease in bone pain.

Callisto plans to continue this trial at higher dose levels until a maximum tolerated dose is reached and then treat 10 additional patients at that level. The Company and investigators are encouraged by the initial results and hope to see greater activity at higher dose levels.

About the American Society of Hematology

The mission of the American Society of Hematology (ASH) is to further the understanding, diagnosis, treatment, and prevention of disorders affecting the blood, bone marrow, and the immunologic, hemostatic and vascular systems, by promoting research, clinical care, education, training, and advocacy in hematology. For the past four decades, ASH has sponsored its annual meeting, the premier annual education and scientific event in the field of hematology, and has published Blood, the Journal of the American Society of Hematology, which is the most cited peer-reviewed publication in the field. Each December, the Society's annual meeting provides hematologists from around the world a forum for discussing critical issues in hematology. Nearly 20,000 clinicians, scientists, and others attend the four-day meeting, which consists of a superb educational program and cutting-edge scientific sessions. Oral and poster presentations, which are chosen by peer-reviewers from abstracts submitted prior to the annual meeting, are featured at the annual meeting and contain the latest and most exciting developments in scientific research. For more information, please visit http://www.hematology.org.

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 for a range of other significant health care market segments, including biodefense. One of the Company's lead drug candidates, L-Annamycin, is being developed as a treatment for forms of relapsed 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. Another anti-cancer drug, Atiprimod, is in development to treat relapsed multiple myeloma, a blood cancer. Atiprimod has entered Phase I/IIa human clinical trials in relapsed multiple myeloma patients. Callisto also has drugs in preclinical development for 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 L-Annamycin, respectively. For investor-specific information about Callisto, including recent news and stock price data, please visit http://www.trilogy-capital.com/tcp/callisto/. For an Investor Fact Sheet about Callisto, please visit http://www.trilogy-capital.com/tcp/callisto/factsheet.html. To view an informational presentation of the Company's development pipeline of drug candidates, visit http://www.trilogy-capital.com/tcp/callisto/powerpoint.html. Callisto is also listed on the Frankfurt Stock Exchange under the ticker symbol CA4. 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.