Cell Pathways Receives Patent for the Company's Second Investigational Anti-cancer Drug.

HORSHAM, Pa.--(BW HealthWire)--Sept. 8, 1999--

Cell Pathways, Inc. (Nasdaq: CLPA) today announced it has been granted U.S. patent number 5,948,779 covering its second investigational drug, CP461 and related compounds. A Phase IB clinical study with CP461 as a potential treatment for cancer is currently underway.

"This patent for CP461 further strengthens the growing intellectual property position covering our selective apoptotic anti-neoplastic drugs (SAANDs)," said Robert J. Towarnicki, president and chief executive officer of Cell Pathways. "CP461 is the second of this unique class of compounds to enter clinical trials. We have designed these SAAND compounds to specifically exploit a novel apoptotic pathway unique to cancerous and precancerous conditions. As a result, these drug candidates are not expected to demonstrate the adverse side-effects common to drugs which have been developed for other indications and are now being tested in cancer."

In a Phase IA human safety study in which the drug was taken orally, CP461 produced no significant side effects at any dose, including doses above the level predicted to be necessary to produce anti-cancer effects.

Preclinical studies of CP461 have demonstrated that this compound has a potent anticancer effect in a broad range of human cancer cells including prostate, breast, colon, lung, ovarian, pancreatic, leukemia, lymphoma and multiple myeloma cell lines. In addition, the agent is not toxic to normal healthy cells and demonstrated a wide safety margin in preclinical toxicological tests in animals.

SAAND compounds inhibit a particular cyclic GMP phosphodiesterase and induce apoptosis (programmed cell death) in abnormally growing precancerous and cancerous cells. Because SAANDs do not induce apoptosis in normal cells, they do not produce the serious side effects normally associated with traditional chemotherapeutic agents. Nor do they inhibit cyclooxygenase (COX) and therefore do not produce the gastric and renal toxicities reported to be associated with non-steroidal anti-inflammatory drugs (NSAIDs) including the COX II inhibitors.

Cell Pathways, headquartered in Horsham, Pennsylvania, is a development stage pharmaceutical company focused on the research, development and commercialization of products to prevent and treat cancer. The company recently filed a New Drug Application for its lead SAANDs compound, Aptosyn(TM) (exisulind) for the treatment of adenomatous polyposis coli (APC). Additional human clinical studies of that compound continue in trials involving prostate, breast and lung cancers, Barrett's Esophagus and sporadic colonic polyps.

For additional information on Cell Pathways, Inc., visit the Company's website at http://www.cellpathways.com.

Note: Certain statements made herein, and oral statements made in respect hereof, constitute "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995. Such statements are those which express plan, anticipation, intent, contingency or future development and/or otherwise are not statements of historical fact. These statements are subject to risks and uncertainties, known and unknown, which could cause actual results and developments to differ materially from those expressed or implied in such statements. Such risks and uncertainties relate to, among other factors, the absence of approved products; history of operating losses; early stage of development; the costs, delays and uncertainties inherent in basic pharmaceutical research, drug development, clinical trials and the regulatory approval process, with respect to both the Company's current product candidates and its future product candidates, if any; dependence on development of exisulind; the limitations on, or absence of, the predictive value of data obtained in laboratory tests, animal models and human clinical trials when planning additional steps in product development; the uncertainty of obtaining regulatory approval, including uncertainty of approval of the NDA submitted for exisulind for APC; the timing and scope of any approval which might be received for any compound for any indication in the future; acceptance by providers of healthcare reimbursement; the validity, scope and enforceability of patents; the actions of competitors; dependence upon third parties; product liability; the need for further financing; and other risks detailed in Cell Pathways, Inc. reports filed from time to time under the Securities Act of 1933 and/or the Securities Exchange Act of 1934, including the sections entitled "Business" and "Risk Factors" in the Company's report on Form 10-K for the year ended December 31, 1998. Given these uncertainties, current and prospective investors are cautioned not to place undue reliance on any such forward-looking statements. The Company undertakes no obligation to update or revise the statements made herein or the factors which may relate thereto.