Fas/FasL expression in tumor biopsies: a prognostic response factor to fluoropyrimidines? * K. Bezulier*, F. Fina PhD, M. 2 Roussel* PhD, S.-S. Bun* PharmD PhD, J. Ciccolini* PharmD PhD, P.-M. Martin MD PhD, G. Milanoà PhD, C. Aubert* PhD and Y. Barra§ PhD *Toxicokinetics & Pharmacokinetics – UPRES EA3286, Faculty of Pharmacy, Marseille, France,  Experimental Oncology Department, North Faculty of Medicine, Marseille, France, àOncopharmacology Department, Centre Antoine Lacassagne, Nice, France and §UMR-CNRS6032, Faculty of Pharmacy, Marseille, France SUMMARY Various studies suggested that cytotoxicity induced by 5-fluorouracil (5-FU) is an apoptotic mechanism possibly mediated by the Fas/FasL system. In this preliminary work, we studied retrospectively the role the Fas/FasL expression as a predictive response factor with fluoropyrimi- dine-based chemotherapies. We developed a real- time PCR method for measuring Fas and FasL expression in various biopsies from patients treated with a FUFOL-like protocol. No correla- tion was found between Fas or FasL expression and overall survival or partial response. However, the PCR assay was simple and convenient to use for quantitation of Fas/FasL in tumor biopsies. Keywords: Fas, FasL, 5-fluorouracil, real-time quantitative PCR, response factor INTRODUCTION Apoptosis is the name given to programmed cell death, and this process plays an important role in the modulation of the development, morphogen- esis and maintenance of homeostasis in normal tissues (1). Moreover, apoptosis has a crucial role in the proliferation and turnover of cells in a wide range of tumors (2). Tumor progression is now more usually consid- ered as the result of suppressed apoptosis, rather than simply cell proliferation. This has led to a reconsideration of the pharmacology of most anti- cancer agents. Therefore, chemotherapies, inclu- ding the fluoropyrimidines, are now evaluated not only for their cytotoxic properties but also for their ability to induce or restore a weak apoptotic response. Forty years after its synthesis, 5-fluor- ouracil (5-FU) is still a mainstay in the treatment of metastatic colorectal cancer (3). Because of its analogy with uracil, 5-FU follows the pyrimidines metabolic pathway eventually leading to triphos- phorylatted nucleotides, which are incorporated into nucleic acids (4, 5). 5-FU is now known to have several mechanisms of action, including thymidylate synthase (TS) inhibition, and DNA and RNA incorporation. Which mechanism underlies the predominant anti- proliferative effect seems to be tumor- and administration-dependent (6, 7) 3 . Cytotoxic drugs and radiation have been found to modulate Fas and FasL expression. Many pub- lished in vitro and in vivo studies suggest that the Fas/FasL system could be implicated in the antit- umoral activity of 5-FU (8–11). TS inhibition seems to be the mechanism through which Fas could be triggered in cells exposed to 5-FU (12,13). More interestingly, we demonstrated in our laboratory that cell lines deficient in Fas were resistant to 5-FU, compared with cell lines with functionnal Fas receptor (14). This prompted us to determine whether basal Fas levels could be considered as a response predictor for fluoropyrimidines. We report on the development of a quantita- tive real-time PCR method for analysis of the Received 27 August 2002, Accepted 19 September 2002 Correspondence: Yves Barra, Faculty of Pharmacy, 27 Bd Jean Moulin 13385 Marseille cedex 05, France. E-mail: yves.barra@ pharmacie.univ-mrs.fr *This work has been presented, in part, at the AACR 93th Meeting, 2002, San Francisco, CA, USA. Journal of Clinical Pharmacy and Therapeutics (2003) 28, 403–408 Ó 2003 Blackwell Publishing Ltd 403