Company Cites Progress with Clinical and Preclinical Programs NEW YORK, April 16 /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, provided an update covering its strategic and drug development activities for the period of 2006 and first quarter of 2007. Achievements from Jan. 2006 to the present include: 1. Initiated a Phase II clinical trial of Atiprimod in low to intermediate grade neuroendocrine cancer (including advanced carcinoid cancer) 2. Announced data on cohort of advanced carcinoid patients in Phase I clinical trial suggesting potential of Atiprimod to treat advanced carcinoid cancer 3. Received Orphan Drug Designation for Atiprimod to treat carcinoid cancer 4. Initiated a Phase I clinical trial of L-Annamycin in relapsed or refractory pediatric ALL or AML 5. Announced patent on Guanilib, Callisto's first-in-class drug candidate to treat ulcerative colitis, issued on May 9, 2006 6. Acquired exclusive rights from the University of Texas M. D. Anderson Cancer Center on a novel class of anti-cancer drugs called Degrasyns 7. Announced intention to move Guanilib into clinical trial to treat ulcerative colitis 8. Completed two financings totaling $11.8 M "Callisto made significant progress during this past year in moving forward with our clinical and preclinical program," stated Gary S. Jacob, CEO of Callisto Pharmaceuticals. "In particular, the start of the Phase II clinical trial of Atiprimod in neuroendocrine cancer patients is an important step forward in determining the potential of this drug to treat this underserved cancer indication. We have also recently announced our intention to move Guanilib, Callisto's first-in-class drug to treat inflammatory bowel disease, from preclinical development to the clinic." ATIPRIMOD CLINICAL TRIALS Phase I Clinical Trial in Relapsed or Refractory Multiple Myeloma Multi-center, dose-escalation, open-label study of safety and efficacy of Atiprimod. Initial protocol permitted patient dosing to 180 mg treatment cycle (each treatment cycle consists of 14 consecutive days on drug, followed by 14 days off drug). The protocol was amended in 2006 to enable combination of ursodiol. Patients are presently being treated at 180 mg Atiprimod dose plus Ursodiol. The protocol requires 3 cycles of treatment to assess safety, before dose escalation. To date, 25 subjects have been enrolled in this trial. Phase I Clinical Trial in Advanced Cancer Patients Single-center, dose-escalation, open-label study in advanced cancer patients. Patient enrollment totaled 24 subjects. Patients were dosed up to the 150 mg/day treatment cycle. Cohort of 6 subjects with advanced carcinoid cancer provided basis for Company's decision to open clinical trial in this particular indication. Enrollment for the Phase I trial in Advanced Cancer Patients was closed in November, 2006. Phase II Clinical Trial in Low to Intermediate Grade Neuroendocrine Carcinoma Multiple-center, open-label study of safety and efficacy of Atiprimod. The trial was opened in November, 2006 and there are presently 3 clinical sites in the U.S. enrolling patients. The trial is designed to enroll 40 patients. Currently 13 patients are enrolled in the trial. Callisto plans to have additional sites opened in the next 1-2 months. L-ANNAMYCIN CLINICAL TRIALS Phase I Clinical Trial in Adult Relapsed or Refractory Acute Lymphocytic Leukemia (ALL) Callisto has been conducting a well-controlled study using single-agent L- Annamycin in the treatment of adults with relapsed or refractory acute ALL to confirm the maximum tolerated dose (MTD) reported from the previous sponsor. The clinical data from our studies indicate that the MTD reported by the previous sponsor - suggesting that patients could be dosed as high as 280 mg/m2/day for 3 consecutive days - in ALL patients was too high. Callisto utilizes a uniform validated reconstitution method that we believe delivers a more uniform liposomal drug product when infused into patients. This infusion methodology is being utilized across all study sites and we are continuing to enroll patients in this study at lower doses until the MTD is confirmed. Once the MTD has been established, the company plans to move to the fixed-dose portion of the trial. Although the MTD has not yet been determined, preliminary data suggests that the use of L-Annamycin gives promising decreased peripheral blood and bone marrow blasts in the small number of patients treated to date. Phase I Clinical Trial in Pediatric Relapsed or Refractory ALL or Pediatric Relapsed or Refractory Acute Myeloid Leukemia (AML) Callisto opened a Phase I trial in pediatric relapsed or refractory ALL or AML patients in February, 2006. Based on the information from the adult trial, we initiated this trial at 130 mg/m2/day for three consecutive days. The trial is a multi-center, open-label, single-agent, dose-escalation study that is utilizing POETIC - a consortium of ten pediatric cancer centers located in the U.S. and Canada. The trial is presently open at four sites, and the Company expects to have additional sites opening in the next few months. GUANILIB PRE-CLINICAL PROGRAM In May 2006, Callisto was notified by the USPTO that its patent covering Guanilib to treat inflammatory diseases of the bowel issued on May 9, 2006. Guanilib is an orally deliverable analog of the human intestinal hormone uroguanylin which is normally produced in the body's intestinal tract. Encouraging animal data and mechanistic studies on Guanilib in models of ulcerative colitis were recently announced, and the Company is planning to move Guanilib into a clinical trial to treat ulcerative colitis. 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 in relapsed or refractory multiple myeloma, a blood cancer. Atiprimod is currently 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, respectively. A second anti-cancer drug, L-Annamycin, is being developed as a treatment for forms of relapsed or refractory acute leukemia, a currently incurable blood cancer. 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. Guanilib is the lead candidate of our Guanylate Cyclase Receptor Agonist (GCRA) platform. Callisto own worldwide patent coverage for therapeutic applications of Guanilib in cancer and GI inflammatory diseases. Guanilib is expected to enter clinical trial in inflammatory bowel disease in 2008. 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/. 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 Form S-3/A declared effective on February 15, 2007, and its 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. DATASOURCE: Callisto Pharmaceuticals, Inc. CONTACT: Dan D'Agostino of Callisto Pharmaceuticals, Inc., +1-212-297-0010, ext. 227, Web site: http://www.callistopharma.com/

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