NEW YORK--(BUSINESS WIRE)--May 3, 2006--Callisto Pharmaceuticals, Inc. (AMEX:KAL - News; FWB:CA4), a developer of new drug treatments in the fight against cancer and other major health threats, announced that the U.S. Patent and Trademark Office (USPTO) has notified Callisto that on May 9, 2006 its patent will be issued covering a novel drug candidate Guanilib developed by Callisto scientists to treat and prevent a variety of inflammatory diseases of the bowel. The drug candidate is first-in-class of a new category of compounds with the potential to treat gastro-intestinal diseases such as ulcerative colitis.