Cell pathways' SAANDs compounds enhance antitumor effects of Taxol™ in rodent models of breast cancer

April 02, 2000

HORSHAM, PA (April 3, 2000) -- CP461, a second generation selective apoptotic antineoplastic drug (SAAND) compound, under development by Cell Pathways, Inc. (Nasdaq: CLPA), significantly enhanced the anti-tumor activity of Taxol™ (paclitaxel) in a classic mouse model of human breast cancer, according to a presentation by company scientists this week at the annual meeting of the American Association for Cancer Research (AACR).

Cell Pathways researchers implanted human breast tumor cell lines in immunosuppressed (nude) mice and divided them into treatment and control groups. The treated mice were divided into multiple groups receiving either (1) five days of intravenous paclitaxel alone, (2) 14 days of oral CP461 at a subtherapeutic dose based on previous single agent studies, or (3) the drugs in combination. The researchers then observed the mice for 45 days. The mice tolerated the drug treatments well, whether they received the single agents or combination therapy, and there were no differences in unscheduled deaths or weight loss between the groups. The researchers observed that the reduction in the size of the tumors achieved by the combination of paclitaxel and CP461 was significantly greater (p=0.03) than that achieved with paclitaxel alone during treatment and during the month after discontinuation of treatment.

"This research suggests that CP461, given in combination with paclitaxel, may potentially increase paclitaxel1s efficacy in breast cancer without adding any additional side-effects," said Rifat Pamukcu, M.D., chief scientific officer of Cell Pathways. "CP461 is nearing completion of a Phase Ib safety study as a single agent in cancer patients. Based on these preclinical results, we plan to investigate CP461 as a single agent cancer therapy and in combination cancer chemotherapeutic studies in the near future."

CP461 is a second generation SAAND based on the mechanism of action of Aptosynä (exisulind). Aptosyn™ 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 specific inhibitors. A New Drug Application for Aptosyn™ 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 Company1s website at http://www.cellpathways.com.
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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 Company1s current product candidates and its future product candidates, if any; dependence on development of Aptosyn™ 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™ (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*™ (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 Company1s 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.

Kureczka/Martin Associates

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