Cell Pathways Announces Positive One-Year Data from Extension Trial of Aptosyn --Exisulind-- in FAP Patients; NDA Review Period Extended.

Business Editors/Health and Medical Writers

HORSHAM, Pa.--(BW HEALTHWIRE)--June 27, 2000

Cell Pathways today announced positive new data from a one-year extension of a 1997-1999 Phase III trial which show that the long-term use of Aptosyn(TM) (exisulind) significantly reduces the formation of precancerous colorectal adenomatous polyps in patients with familial adenomatous polyposis ("FAP"). These clinically meaningful and statistically significant findings further support and extend the results of previous studies of Aptosyn(TM) in FAP patients.

"These new findings are consistent with the data from our prior trials of Aptosyn(TM)," said Robert J. Towarnicki, president and chief executive officer of Cell Pathways. "As required by FDA regulation we have submitted ten volumes of additional data and analyses as an amendment to the NDA currently under review by the Food and Drug Administration (FDA). We submitted the NDA on August 25, 1999. As a result of the amendment just submitted, the FDA has informed us that they are extending the NDA review period: the primary user fee goal date is September 25, 2000, with a secondary user fee goal date of November 25, 2000. Our understanding is that it is the goal of the FDA to complete their review by the primary date of September 25; however, they reserve the right to continue the review process through November 25 if necessary."

Results of the Trial

Of the 65 FAP patients who completed the one-year Phase III trial, 55 patients elected to enter and 47 patients completed the one-year extension study. In the 25 patients who had received placebo during the Phase III trial and subsequently crossed-over to active drug and completed the second year, a clinically meaningful 49% reduction in polyp formation was seen. This reduction was statistically significant (p=0.001). Twenty-two patients who received Aptosyn(TM) during the Phase III trial continued on active drug throughout the one-year extension. These patients experienced a further clinically significant decline in the rate of polyp formation of 54% below the already reduced rate that they had experienced across the entire colorectum during the first year on drug. This additional decline was also statistically significant (p=0.004).

A separate, more stringent analysis of all 55 patients who entered the extension trial, including eight patients who did not complete the trial, was also undertaken and demonstrated clinically meaningful and statistically significant results. All patients who entered the study were included in the analysis. Patients who dropped out were assumed to have no improvement in their polyp formation rate when compared to the prior year, even though they may have otherwise shown a drug effect. In the 30 patients who received placebo for the first year and then crossed-over and received drug for the second year, a 32% reduction in polyp formation was seen. The results were statistically significant (p=0.001). In the 25 patients who had received drug in the initial study and elected to continue in the extension study, a 54% decrease in polyp formation was seen. These results were also statistically significant (p=0.004).

"These new data demonstrate the ability of Aptosyn(TM) to significantly decrease the formation of new adenomatous polyps in a broad range of patients afflicted with FAP, including those patients forming polyps at historically low and high rates," commented Rifat Pamukcu, M.D., chief scientific officer and senior vice president of research and development at Cell Pathways. "The continued durable effect of Aptosyn(TM) now shown in the two-year prevention study parallels the sustained effect in polyp regression and prevention demonstrated in the Phase I/II extension studies which we commenced in 1995 and are continuing. The durability of clinical effect is one of the most important characteristics of any drug intended to be used for the lifelong treatment and prevention of precancerous lesions."

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 the prevention of polyps in FAP, and these patients have very few disease management options.

A Phase I/II study of Aptosyn(TM) in FAP, commenced with National Cancer Institute funding in 1995, demonstrated a statistically significant dose-dependent response in polyp regression. A Phase III trial, which ended in January 1999, demonstrated a statistically significant reduction in new polyp formation among patients meeting protocol-specified eligibility requirements. The results of the extension study announced today extend these clinically and statistically significant findings.

SAANDs Technology

Aptosyn(TM) (exisulind) is Cell Pathways' lead drug candidate from a new class of compounds called selective apoptotic anti-neoplastic drugs (SAANDs). Cell Pathways research has shown that its SAANDs compounds inhibit a novel pattern of over-expressed cyclic GMP phosphodiesterases in cancerous and precanerous cells. Inhibition of cGMP-PDE results in an increase in cGMP which activates PKG, a downstream regulator of apoptosis (programmed cell death). This activation allows the apoptotic pathway to proceed and selectively induce apoptosis 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. They 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.

Additional human clinical studies of Aptosyn(TM) as single agent therapy are underway. Aptosyn(TM) is also entering combination therapy trials with established chemotherapeutic agents of Aventis, Roche Laboratories and Eli Lilly and Company.

A second SAANDs compound, CP 461, is currently concluding Phase IB safety studies in cancer patients and is intended to enter one or more Phase II cancer trials later this year.

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. 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. Both forward-looking statements and statements of historic fact must be understood in the context of the risks referred to above which characterize the Company's development stage business. The Company undertakes no obligation to update or revise the statements made herein or the factors which may relate thereto.