Clinical Trial of Cell Pathways' Aptosyn -- Exisulin -- in Children With Familial Adenomatous Polyposis Completes Enrollment.

Business Editors/Health & Medical Writers

HORSHAM, Pa.--(BW HealthWire)--March 29, 2000

Cell Pathways, Inc. (Nasdaq:CLPA) today announced that it has completed enrollment in an open-label Phase II clinical study of Aptosyn(TM) as a treatment for precancerous colon polyps in children with familial adenomatous polyposis (FAP).

The study will investigate whether Aptosyn(TM) reduces the number of polyps in these children after one year of treatment. All participants receive a baseline colonoscopy at enrollment, and a second colonoscopy following one year of therapy with Aptosyn(TM). Following the one-year trial, all participants are eligible to continue on treatment as part of extension studies.

"After obtaining initial safety data from a small number of pediatric patients, we expanded enrollment in this study to include a total of twenty children with FAP, each of whom has colon polyps," commented Rifat Pamukcu, M.D., chief scientific officer and senior vice president of research and development. "Normally, these patients require surgical removal of most of their colon as teenagers or young adults to reduce their risk of colon cancer. We hope to see a stabilization in polyp formation followed by a reduction in the number of polyps in these young patients, with the subsequent goal of preventing or delaying the need for surgery. We are also considering additional clinical trials in this pediatric population. The search for an effective medical treatment for these young patients was the impetus for the founding of Cell Pathways over a decade ago."

About FAP

FAP is a relatively rare hereditary condition characterized by the development of hundreds to thousands of adenomatous polyps in the colon and rectum during adolescence and early adulthood. Experts consider adenomatous polyps to be precursor lesions to colorectal cancer. Left untreated, virtually all patients with FAP develop colorectal cancer by age 40-50. There are currently no drugs approved for prevention of polyps in FAP, and these patients have very few disease management options.

Aptosyn

Aptosyn(TM) (exisulind) is the first product candidate from a novel class of compounds under development by Cell Pathways, called selective apoptotic anti-neoplastic drugs (SAANDs). SAANDs inhibit cyclic GMP phosphodiesterase and selectively 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. SAANDs also do not inhibit cyclooxygenase (COX I or COX II) and have not exhibited the gastric and renal toxicities reported to be associated with non-steroidal anti-inflammatory drugs (NSAIDs), including the COX II inhibitors.

A New Drug Application for Apotsyn(TM) as a treatment for patients with familial adenomatous polyposis, a precancerous condition that often leads to colon cancer, is currently under review by the U.S. Food and Drug Agency (FDA). The compound is also undergoing further clinical evaluation in a variety of additional precancer and cancer indications.

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 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 1999, Form 8-K in the month of August 1999, and Form S-3 filed in December 1999. Given these uncertainties, 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.