Cell Pathways Aptosyn and CP461 Show Synergy With Herceptin and Taxotere, as well as Activity Against Breast Cancers Resistant to Those Drugs.

Business Editors/Medical Writers

HORSHAM, Penn.--(BW HealthWire)--Dec. 8, 2000

New research reported today at the annual San Antonio Breast Cancer meeting by Drs. Li Liu and W. Joseph Thompson from Cell Pathways (Nasdaq:CLPA) and their collaborators, Drs. Mark Pegram and Dennis Slamon at the University of California, Los Angeles, Jonsson Cancer Center shows that exisulind (Aptosyn(TM)) and CP461 inhibit cell growth and trigger apoptosis in human breast cancer cell lines, including cells lacking HER-2/neu or estrogen receptors. Moreover, in breast cancer lines that over-express HER-2/neu or estrogen receptors, exisulind and CP461 each demonstrate synergistic anticancer activity in combination with Herceptin(R) and Taxotere(R).

"Herceptin(R) and Taxotere(R) have been shown to be effective in treating some breast cancers," said Mark Pegram, M.D., assistant professor, Division of Hematology-Oncology, Jonsson Comprehensive Cancer Center, University of California, Los Angeles School of Medicine. "In particular, Herceptin(R), which targets HER-2/neu receptors, has been effective in tumors where these receptors are over-expressed. We know that not all breast cancers express the HER-2/neu receptor or respond to Taxotere(R). The research presented today suggests that exisulind and CP461 may have potential for development as treatments for breast cancers unresponsive to Herceptin(R) and Taxotere(R). It also suggests that combining exisulind or CP461 with either of these drugs may provide greater anticancer benefit than can be achieved by Herceptin(R) or Taxotere(R) alone."

"Based on these exciting data as well as other laboratory and preclinical findings of synergy, Cell Pathways is pursuing the clinical development of Aptosyn(TM) in combination with other systemic therapies in breast cancer patients with advanced disease. In a Phase I trial of Aptosyn(TM) in combination with weekly Taxotere(R) full doses of each agent have been given to patients without unexpected toxicity," said Rifat Pamukcu, M.D., executive vice president of research and development at Cell Pathways. "In addition, a Phase I/II breast cancer trial of Aptosyn(TM) and Taxotere(R) that includes patients receiving Herceptin(R) as well as a Phase I/II breast cancer trial with Aptosyn(TM) and Xeloda(R) are planned for early 2001."

Exisulind (Aptosyn(TM)) and CP461 are the first members of a new class of potential therapeutic agents called selective apoptotic antineoplastic drugs, or SAANDs, which have been discovered and are under development by Cell Pathways, Inc. SAANDs inhibit cyclic GMP phosphodiesterases that show unique patterns of expression in tumors and selectively induce apoptosis (programmed cell death) in abnormally growing precancerous and cancerous cells. Cell Pathways is conducting clinical studies with Aptosyn(TM) as a single agent and in combination with conventional chemotherapeutic drugs in a variety of cancer and precancerous indications. The company is also preparing to initiate Phase II clinical trials of CP461 in cancer patients. Preclinical and clinical research to date suggests that drugs that target the cyclic GMP phosphodiesterases, as SAANDs do, may lead to the development of new therapeutics with broad-based activity.

Cell Pathways, Inc., headquartered in Horsham, Penn., is a development stage pharmaceutical company focused on the research, development and commercialization of novel and unique compounds 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 the development and market acceptance of Aptosyn(TM) (exisulind) for one or more significant disease indications; 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 of any compound for any disease indication; the delay, uncertainty and adversity arising from the recent action of the FDA in issuing a "not approvable" letter with respect to the New Drug Application ("NDA") submitted for Aptosyn(TM) (exisulind) for the orphan drug condition of familial adenomatous polyposis, a rare disease that puts those afflicted at high risk of developing colon cancer; 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 and Forms 10-Q and 8-K during 2000 and in such registration statements on Form S-3 as may be filed from time to time. You are encouraged to read these filings as they are made. 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. No forward-looking statement can be guaranteed; actual future results may vary materially. 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.

Note to Editors: Aptosyn(TM) is a trademark of Cell Pathways, Herceptin(R) is a registered trademark of Genentech, Inc., Xeloda is a registered trademark of Roche Laboratories, Inc. and Taxotere(R) is a registered trademark of Aventis.