NEW YORK, September 20 /PRNewswire/ --

Callisto Pharmaceuticals, Inc. (Amex: KAL; FWB: CA4), a developer of new
drug treatments in the fight against cancer and gastrointestinal disorders
and diseases, announced today that complete enrollment of its Phase II
clinical trial of Atiprimod to treat low to intermediate grade neuroendocrine
carcinoma (advanced carcinoid cancer) was accomplished ahead of schedule. The
trial, designed to enroll 40 patients, presently has patients enrolled at
seven clinical sites in the U.S., and was closed to further enrollment with
the addition of the 40th patient.

"This Atiprimod trial was initiated in November, 2006 and we are pleased
with the tremendous pace of enrollment that we experienced," said Dr. Gary S.
Jacob, Chief Executive Officer of Callisto. "We have patients who have now
been on our drug for as long as 11 months, and we expect that by January of
2008 the bulk of patients will have been treated for 6 months or more on our
drug. We anticipate at that time releasing interim data from the trial as
well as planning for a meeting with FDA on the design of a registration
trial."

The primary objective of the Phase II clinical trial was to evaluate
efficacy of Atiprimod in patients with low to intermediate grade
neuroendocrine carcinoma who have metastatic or unresectable cancer and who
have progression of their disease despite standard therapy (octreotide).
Patients, after signing an informed consent, were required to complete two
weeks of a symptoms diary to establish their symptoms baseline before
commencing Atiprimod dosing. Efficacy evaluations include the measure of
target lesions (per RECIST), and the quantization of symptom relief. Further
details of this trial can be found at http://www.clinicaltrials.gov.

About Atiprimod

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. Callisto earlier announced in June, 2006 interim data from
a Phase I trial of Atiprimod in advanced cancer patients. The patients who
were entered into this trial had growing tumors and symptoms that were no
longer controlled by the standard therapies utilized. During treatment, three
of the five advanced carcinoid patients had measurable tumor regressions and
loss of many of the debilitating symptoms of this disease.

About Carcinoid Cancer

Carcinoid tumors, or carcinoids, originate in hormone-producing cells of
the gastrointestinal (GI) tract, the respiratory tract, the hepatobiliary
(liver) system and the reproductive glands. The most common site of origin is
the GI tract, with tumors often developing in the rectum, and other sections
of the small intestine. Approximately 7,000 cases of carcinoid cancer are
diagnosed in the U.S. annually, with the number increasing over the past
20-30 years. Carcinoid tumors that metastasize to the liver have a poor
prognosis. Traditionally, chemotherapy relieves symptoms in less than 30% of
cases of metastatic carcinoid tumors, usually for less than 1 year. Carcinoid
tumors typically produce a condition called "carcinoid syndrome" which is
caused by the release of hormones by the tumors into the blood stream. The
symptoms vary depending on which hormones are released by the tumors, but
typically include diarrhea, facial flushing, wheezing, abdominal pain and
valvular heart disease.

About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company focused on the development of new
drugs to treat various forms of cancer and gastrointestinal diseases.
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
gastrointestinal disorders. One of the Company's lead drug candidates,
Atiprimod is presently in a Phase II clinical trial in advanced carcinoid
cancer patients, a neuroendocrine tumor, and in a Phase I/IIa human clinical
trial in relapsed or refractory multiple myeloma patients. 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.
L-Annamycin is currently in a Phase I clinical trial in adult relapsed or
refractory acute lymphocytic leukemia, and in a Phase I clinical trial in
children and young adults with refractory or relapsed acute lymphocytic
leukemia or acute myelogenous leukemia. L-Annamycin, a member of the
anthracycline family of proven anti-cancer drugs, has a novel therapeutic
profile, including potential activity against multi-drug resistant tumors and
significantly reduced cardiotoxicity, or damage to the heart, compared to
currently available drug alternatives. Callisto also has a proprietary drug
Guanilib in preclinical development for gastro-intestinal disorders. Callisto
has exclusive worldwide licenses from Genzyme 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 Annual Report on Form 10-K for the
year ended December 31, 2006, 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.

CONTACT: Gary Jacob of Callisto Pharmaceuticals, Inc., +1-212-297-0010

Web site: http://www.callistopharma.com
              http://www.clinicaltrials.gov