Cell Pathways Announces Positive Results of Additional Trials of Aptosyn -- Exisulind -- for the Prevention of Precancerous Colon Polyps.

HORSHAM, Pa.--(BW HealthWire)--Oct. 27, 1999--

Cell Pathways (Nasdaq:CLPA) today announced that new data from three additional trials reinforces that the long-term use of Aptosyn(TM) (exisulind) prevents the formation of precancerous colorectal adenomatous polyps in patients with familial adenomatous polyposis ("FAP").

These clinically significant findings support and extend the results of previous studies of Aptosyn in FAP patients.

"These findings are quite consistent with the results from our previous pivotal Phase I/II and Phase II/III trials. We are submitting these additional clinical data to the U.S. Food and Drug Administration in support of our New Drug Application for Aptosyn, which was submitted on August 25, 1999," said Robert J. Towarnicki, president and chief executive officer of Cell Pathways. "We also plan to submit the results for publication in a peer-reviewed journal."

Results From These Additional Trials

The first of the three trials involved 48 of the patients who completed the Phase II/III study of Aptosyn reported earlier this year. Twenty-five of the 48 patients had received placebo for one year as part of the blinded Phase II/III trial, and then received Aptosyn on an open-label basis for an additional six months.

After the six months on Aptosyn, those 25 patients experienced a 50% reduction in their polyp formation rate across the entire colorectum; the reduction was statistically significant and clinically meaningful.

The remaining 23 patients, who had received Aptosyn for one year during the earlier study, continued on drug treatment for an additional six months. At the end of this period, these patients demonstrated further declines in their polyp formation rate, to 50% below the already reduced rate they had experienced across the entire colorectum during the first year on drug.

These additional declines were also clinically and statistically significant. Cell Pathways plans to continue monitoring the 48 patients as they continue to receive drug for at least another six months.

The second study was an extension study of 11 patients who participated in the company's six-month open-label Phase I/II dose-ranging, safety and efficacy trial of Aptosyn. These patients are still on therapy and have been receiving Aptosyn for 36 to 50 months. During the first two years of therapy, Aptosyn taken at optimal doses achieved statistically significant reductions in polyp formation rates. These patients' polyp formation rates remained at these reduced levels during their third year of therapy.

The third study was a double-blind, placebo-controlled safety study of 26 patients. The trend in the data, including all patients, supports the previously seen results that Aptosyn reduces new polyp formation in FAP patients when compared to placebo.

"As we observed in earlier studies, the FAP patients in these studies experienced a significant reduction in precancerous colon polyp formation while maintaining this effect over long periods of time. The durability of the 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," commented Rifat Pamukcu, M.D., chief scientific officer and senior vice president of research and development at Cell Pathways.

"In addition, Aptosyn was generally well tolerated by patients during the course of all three studies."

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 no drugs approved for use in the care of FAP, and these patients have very few disease management options.

Aptosyn(TM) (Exisulind)

Aptosyn is Cell Pathways' lead drug candidate from a new class of compounds called selective apoptotic anti-neoplastic drugs (SAANDs). These compounds inhibit a cyclic GMP phosphodiesterase and selectively induce apoptosis (programmed cell death) in abnormally growing precancerous and cancerous cells but not in normal cells.

Because SAANDs do not affect 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 are underway that target prostate, breast and lung cancers, Barrett's Esophagus and sporadic colonic polyps. A one-year trial of Aptosyn in children with FAP is nearing full enrollment.

Cell Pathways, headquartered in Horsham, 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.

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 that 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, 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; 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 Dec. 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.