Cell Pathways Presents Research Supporting the Broad Applicability of Aptosyn and Other SAANDs in the Treatment of Cancer and Precancerous Conditions.

Business Editors & Health/Medical Writers

SAN DIEGO--(BW HealthWire)--May 23, 2000

Colonic tumor cells marked by hereditary defects different from the APC gene mutation that characterizes familial adenomatous polyposis (FAP) also undergo apoptosis when treated with Aptosyn(TM) (exisulind) or other selective apoptotic antineoplastic drugs (SAANDs), according to researchers from Cell Pathways, Inc. (Nasdaq:CLPA).

Aptosyn(TM) is the company's lead drug candidate which is currently being reviewed by the Food and Drug Administration for approval for familial adenomatous polyposis (FAP), a precancerous disease of the colon. The scientists presented their findings today at the annual meeting of the American Gastroenterological Association (AGA). They also reported laboratory findings that the cyclic GMP phosphodiesterase targeted by Aptosyn(TM) and other SAANDs is over-expressed in precancerous colonic polyps and colon cancer relative to normal colonic mucosal tissue. This observation may explain in part the selectivity of SAANDs for precancerous and cancerous cells and not for normal tissue.

"While research has demonstrated the ability of Aptosyn(TM) to trigger apoptosis (programmed cell death) in a wide variety of cancer cells, our past studies of colon tumor cells have chiefly focused on cells containing APC mutations," said W. Joseph Thompson, Ph.D., Cell Pathways vice president of research. "Through our research, we have shown that Aptosyn(TM) and other SAANDs also trigger apoptosis in colon cancer cells marked by a different gene defect, which causes a more common disease than FAP, hereditary nonpolyposis colorectal cancer (HNPCC). This finding further supports our theory that SAANDs act on a common pathway found in precancerous and cancer cells and so may have broad applicability to these diseases."

The company's research showed that in both colorectal cancer cells with an APC mutation and those with a HNPCC mutation, Aptosyn(TM) and other SAANDs triggered apoptosis by inhibiting cyclic GMP phosphodiesterase (cGMP-PDE), resulting in an increase in cGMP. This rise in cGMP activates cyclic GMP-dependent protein kinase (PKG), which in turn reduces beta-catenin, triggering apoptosis. Beta-catenin is believed to be an important regulator of cell growth in a number of human cancers. They also showed that the cGMP PDE targeted by Aptosyn(TM) and other SAANDs was overexpressed in colonic adenomas and adenocarcinomas compared to normal proliferating colon epithelium, demonstrating the specificity of the cGMP PDE target in cancer and precancerous conditions.

Aptosyn(TM) is currently undergoing advanced clinical trials for the treatment and prevention of a variety of cancer types, both on its own and in combination with currently marketed chemotherapeutic agents. A second Cell Pathways' SAAND compound, CP461, is completing Phase 1b human clinical safety studies in cancer patients. CP461 works through the same mechanism of action as Aptosyn(TM), but has been shown in laboratory studies to be 100 to 1000 times more potent. The company has also generated a portfolio of over 500 additional SAAND compounds, some of which are at the preclinical stages of development.

Cell Pathways, Inc., headquartered in Horsham, Pennsylvania, is a development stage pharmaceutical company focused on the research, development and commercialization of novel and unique medications to prevent and treat cancer. For additional information on Cell Pathways, Inc., visit the Company's website at http://www.cellpathways.com.

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 Aptosyn(TM) (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 New Drug Application submitted for Aptosyn(TM) (exisulind) for familial adenomatous polyposis (a rare disease that puts those afflicted at high risk of developing colon cancer), whether in connection with the adequacy of the data generated in the clinical trials of Aptosyn(TM) (exisulind) or otherwise; the uncertainty of the effect of product approval, if achieved, on the market price of the Common Stock; 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; and the need for further financing. These and other risks are detailed in the Company's 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," "Risk Factors," "Management's Discussion and Analysis of Financial Condition and Results of Operations" and "Other Events" in the Company's reports on Form 10-K for the year ended December 31, 1999, Form 10-Q for each of the first three quarters of 2000, Form 8-K for the month of August 1999, and Form S-3 filed in December 1999. You are encouraged to read these filings as they are made from time to time. They are available over the Internet from the SEC in its EDGAR database. Given the uncertainties affecting pharmaceutical companies in the development stage, current and prospective investors are cautioned not to place undue reliance on any such forward-looking statements, any of which may turn out to be wrong due to inaccurate assumptions, unknown risks, uncertainties or other factors. The Company undertakes no obligation to update or revise the statements made herein or the factors which may relate thereto.