Cell Pathways Advances Second SAAND Compound, CP461, to Phase II Testing.

Business Editors/Health & Medical Writers

BIOWIRE2K

HORSHAM, Pa.--(BW HealthWire)--Aug. 6, 2001

Cell Pathways, Inc., (Nasdaq:CLPA) today announced it has initiated three pilot Phase II studies of CP461, the Company's second selective apoptotic anti-neoplastic drug (SAAND). These Phase IIa human clinical trials will investigate the safety and efficacy of CP461 as a single agent in patients with chronic lymphocytic leukemia (CLL), renal cell (kidney) carcinoma, and hormone-refractory prostate cancer. In each of these open-label studies, fourteen to nineteen patients will be evaluated for an objective response to CP461 treatment by measuring tumor size or tumor burden. Patients will be tracked for a minimum of three months. Assuming positive results from one or more of these Phase IIa studies, the Company plans to expand enrollment into larger Phase IIb trial(s).

"These studies mark the start of our Phase II clinical development program for CP461, which plans to include studies investigating the compound as both a single agent for the treatment of cancer and in combination with other leading chemotherapeutic drugs," said Robert E. Bellet, M.D., Cell Pathways' senior vice president of clinical and regulatory affairs. "The preclinical results with CP461 have been very encouraging. Cell culture and animal studies have suggested that CP461 may have substantial potency as an anti-cancer agent. Also, CP461's pro-apoptotic effects in cell culture (or the triggering of programmed cell death in tumor cells by inhibiting certain cyclic GMP phosphodiesterases) are rapid in onset.

"We plan to investigate CP461 in a number of clinical cancer indications," Dr. Bellet continued. "We chose CLL, renal cancer and hormone-refractory prostate cancer based on earlier observations that these tumor types either over-express the cyclic GMP phosphodiesterases targeted by CP461, or demonstrate evidence of tumor cell sensitivity to CP461 in cultured cancer cell lines, animals studies, or primary cultures of cancer cells from affected patients."

"CLL, renal cancer and hormone refractory prostate cancer are all cancers where the current treatment options are limited and new therapies are sorely needed. Positive results from studies in any of these diseases may present opportunities for the accelerated clinical development of CP461," said Robert Towarnicki, chairman and chief executive officer of Cell Pathways.

CP461 is a second-generation SAAND compound, designed to treat cancer by selectively triggering programmed cell death, or apoptosis, in precancerous and cancer cells but not normal cells. Data from a Phase I safety study of CP461 presented earlier this year showed that the drug was rapidly absorbed when orally administered and was well tolerated by patients.

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 web site at http://www.cellpathways.com.

Certain statements in this release, and oral statements made with respect to this release, 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, 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; uncertainty of obtaining regulatory approval of any compound for any disease indication; the risks that clinical studies are not positive or even if positive do not result in the safety and efficacy necessary to obtain regulatory approvals; the risk that a positive result does not present an opportunity for accelerated development of CP461; the risk that the company's drug development plans change; the risks of conducting clinical trials of our drugs in combination with other drug therapies; the absence of approved products; history of operating losses and the need for further financing; early stage of development; the costs, delays and uncertainties inherent in scientific research, basic pharmaceutical research, drug development, clinical trials and the regulatory approval process, with respect to both our current product candidates and our future product candidates, if any; dependence on the development and market acceptance of Aptosyn(TM) (exisulind) for one or more significant disease indications; uncertainty and adversity arising from the action of the U.S. Food and Drug Administration, or FDA, in issuing a "not approvable" letter with respect to the New Drug Application, or NDA, submitted for Aptosyn(TM) (exisulind) for the orphan drug condition of familial adenomatous polyposis; the timing and scope of any approval which might be received, or any failure to receive approval, for any compound for any indication in the future; the volatility of the market price of our common stock; our ability to sell securities registered under the shelf registration statement; acceptance of any product candidates by physicians and providers of healthcare reimbursement; the actions of competitors; the pace of technological changes in the biopharmaceutical industry; dependence upon third parties; the validity, scope and enforceability of patents; the risk of our pending class action securities litigations; potential product liability claims; and availability and adequacy of insurance. These and other risks are detailed in our reports filed from time to time under the Securities Act and/or the Securities Exchange Act, including the sections entitled "Business," "Risk Factors," "Management's Discussion and Analysis of Financial Condition and Results of Operations" and "Other Events" in our annual reports on Form 10-K, quarterly reports on Form 10-Q and periodic reports on Form 8-K and in such registration statements on Form S-3 as we may file 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 at http://www.sec.gov and from the Company. Given the uncertainties affecting pharmaceutical companies in the development stage, you 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 our development-stage business. We undertake no obligation to update or revise the statements made herein or the risk factors that may relate thereto.