Callisto Pharmaceuticals Announces Presentation on SP-304 at the 3rd International Congress on Natural Peptides to Drugs

Callisto Pharmaceuticals, Inc. (AMEX: KAL; FWB: CA4), a developer
of new drug treatments in the fight against cancer and
gastrointestinal disorders, announced today that Dr. Kunwar
Shailubhai, Sr. VP Discovery Research, will give a plenary talk
covering therapeutic applications of guanylate cyclase C agonist
peptides at the 3rd International Congress on "Natural Peptides to
Drugs (NP2D)", to be held April 14-17, 2008 in Zermatt, Switzerland.
Dr. Shailubhai´s presentation entitled "GC-C receptor peptides: new
class of oral drug candidates" is scheduled for 11:00 am on April 16

2008. The 3rd International Congress NP2D (www.np2D.com) is a leading
forum gathering top researchers from academia and major pharmaceutical
and biotechnology companies.

SP-304 (previously called Guanilib) is a patented oral drug
candidate to treat gastrointestinal disorders. The drug is presently
being developed for the treatment of chronic constipation and
constipation-predominant irritable bowel syndrome (IBS-C), and is
scheduled to enter clinical trials in May 2008.

"SP-304 is an analog of the human hormone uroguanylin with
superior properties to the natural molecule, and which acts primarily
by promoting water secretion into the lumen of the GI-tract to
facilitate bowel movement, said Dr. Shailubhai, Sr. VP of Callisto.
"An Investigational New Drug (IND) application was recently filed for
SP-304, and we hope to initiate clinical trials shortly."

About SP-304

SP-304 (also called Guanilib) is an analog (synthetic molecule) of
uroguanylin, a natural gastro-intestinal hormone produced in the gut
that is a key regulator of intestinal function. SP-304 works by
activating a unique receptor on intestinal cells. The receptor, called
the guanylate cyclase C (GC-C) receptor, promotes fluid and ion
transport in the gastro-intestinal (GI) tract. Under normal
conditions, the receptor is activated by the natural hormones
uroguanylin and guanylin. Activation of the receptor leads to the
transport of chloride and bicarbonate into the intestine, and water is
carried with these ions into the lumen of the intestine, thereby
producing a looser stool. SP-304 has been demonstrated to be superior
to uroguanylin, in its biological activity, protease stability and pH
characteristics. The compound is not absorbed systemically and
demonstrates a very good safety profile. An IND was filed for SP-304
on April 2, 2008, and a phase 1 clinical trial is expected to start
with the compound in May 2008.

About Callisto Pharmaceuticals, Inc.

Callisto is a biopharmaceutical company focused on the development
of new drugs to treat various forms of gastrointestinal diseases and
cancer. Callisto´s drug candidates include a SP-304 for
gastrointestinal disorders that is currently being developed by its
wholly-owned subsidiary, Synergy Pharmaceuticals, as well as two
anti-cancer agents. The Company´s lead drug in the clinic, Atiprimod

is presently in a Phase II clinical trial in advanced carcinoid
cancer, a neuroendocrine tumor, and in a Phase II extension trial in
advanced carcinoid cancer patients. Callisto´s second drug in the
clinic, L-Annamycin, is currently in a Phase I/II 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.
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, 2007, 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.