Callisto Pharmaceuticals Announces Investor Conference Call to Provide Details on Guanilib Strategic Initiative in GI Disorders

Callisto Pharmaceuticals, Inc. (Amex: KAL; FWB: CA4), a developer
of new drugs against gastrointestinal disorders and cancer announced
today that it will hold an investor teleconference on January 14, 2008
at 10:00 AM EST to provide additional details regarding its strategic
initiative to develop Guanilib for gastrointestinal disorders.

On October 3, 2007 Callisto announced plans to develop Guanilib,
its guanylate cyclase C (GC-C) receptor agonist, for chronic
constipation (CC) and constipation-predominant irritable bowel
syndrome (IBS-C). Guanilib is an analog of uroguanylin, the natural
hormone produced by the intestine and a key regulator of intestine
function. The teleconference will provide additional details on the
company´s plans for development of Guanilib as well as the large
upside potential that this drug is capable of generating for the
company.

"We have very high hopes for the development of Guanilib," said
Dr. Gary S. Jacob, Chief Executive Officer of Callisto. "Guanilib acts
locally on receptors in the lining of the intestine and is not
absorbed into the rest of the body. The FDA and the public are
particularly focused on the issue of drug safety, and we believe that
Guanilib´s safety profile should be a major advantage as we move this
drug forward into the clinic."

The value potential of GC-C receptor agonists to treat CC and
IBS-C was recently set with the announced partnership between
Microbia, Inc. and Forest Laboratories, Inc., with an upfront payment
to Microbia of $70 million and milestone payments totaling $260
million for 50/50 co-development and promotion rights in the US, as
well as rights for Canada and Mexico. Linaclotide showed promising
data in a set of Phase IIa clinical trials in CC and IBS-C. Callisto
plans to file an IND for Guanilib in the first quarter of 2008, and to
initiate a Phase I trial shortly thereafter. The Company also plans to
open a Phase Ib trial of Guanilib in CC in the second half of 2008.

"We believe that the value of Guanilib to Callisto has not yet
been fully appreciated by Wall Street, and that Callisto is
significantly undervalued," noted Dr. Jacob. "The planned investor
conference call is the first step in addressing this issue."

The teleconference will be held at 10:00 AM Eastern Standard Time
on January 14, 2008. The conference can be accessed by calling
866-202-3109, or +1-617-213-8844 from outside the US. The participant
code is 61516766. To see the presentation slides and hear the
teleconference via the web, please go to

http://phx.corporate-ir.net/
phoenix.zhtml?p=irol-eventDetails&c=120912&eventID=1720743. (Due to
its length, this URL may need to be copied/pasted into your Internet
browser´s address field. Remove the extra space if one exists.)

Note that you will only be able to ask questions after the
presentation via telephone. The presentation material and the
teleconference will also be recorded and accessible later via the
Callisto website at www.callistopharma.com.

About Guanilib

Guanilib (also called SP-304) is an analog (synthetic molecule) of
uroguanylin, a natural gastro-intestinal hormone produced in the gut
that is a key regulator of intestinal function. Guanilib 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. Guanilib, developed by Callisto scientists,
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.
Guanilib has also been found to be effective in reducing inflammation
in animal models of ulcerative colitis. Callisto plans to initiate
clinical trials of Guanilib in early 2008.

About Chronic Constipation and Irritable Bowel Syndrome

Chronic constipation is a very common condition. Up to 26 million
Americans suffer from the condition and of these about 5 million have
a severe problem. The prevalence is similar in other developed
countries. Patients with chronic constipation often experience hard
stools, straining during bowel movements and not enough bowel
movements during the week. People with chronic constipation can
experience serious discomfort which adversely affects their ability to
work and their quality of life. Up to one sixth of adults experience
Inflammatory Bowel Syndrome (IBS), a condition marked by disturbed
bowel function and abdominal pain. IBS patients can have three
different sets of symptoms; diarrhea-predominant (IBS-D),
constipation-predominant (IBS-C) and mixed or alternating disorder
(IBS-M). About 35% of patients suffer from IBS-C. IBS accounts for 12%
of adult visits to primary care physicians in the US.

There are currently few therapies available for chronic
constipation or IBS-C. The main product in this market, Zelnorm from
Novartis Pharmaceuticals (NYSE: NVS), was withdrawn due to
cardiotoxicity in April 2007 in the US. In 2006 Zelnorm sold about
$561 million with about a 30% growth rate at the time of withdrawal.

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 drug for gastrointestinal
disorders as well as two anti-cancer agents. Callisto´s proprietary
drug Guanilib in late preclinical development for gastro-intestinal
disorders. Guanilib is a synthetic analog of the human
gastrointestinal hormone uroguanylin, and acts by activating the
guanylate cyclase C (GC-C) receptor on epithelial cells of the colon.
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 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.