title: Retinoic Acid Enhances Drug-Induced Cell Death in Anticancer Drug-Resistant Cell Lines.
abstract: OBJECTIVE
  Retinoids (RA), a group of vitamin A derivatives, is known to be important for regulation of normal cellular growth and differentiation. RA treatment of various cancers resulted in cell growth inhibition and apoptosis. Therefore, the chemotherapeutic and chemopreventative activities of various types of tumor have been examined. Biological actions of RA are mediated through nuclear receptors, including the retinoic acid receptors (RARs) and retinoid X receptors (RXRs). In this study, we examined the effect of all-trans-retinoic acid (atRA) as an anticancer drug-sensitiser in cancer cell lines and in its drug- resistant cancer cell lines MATERIALS AND METGODS: Cells were maintained by RPMI 1640 medium containing 10% fetal bovine serum. Cells were treated with 1 micro M atRA for 48 h, then with the desired concentration of anticancer drug for 24 h. Cell viability was measured spectrophotometrically at 540 nm using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. Western blot analyses were performed with the desired antibodies.
  
  
  RESULTS
  We investigated if pre-treatment with atRA enhanced the drug-sensitivity of various cancer cell lines to either 5-fluorouracil, adriamycin, or cisplatin. 5-FU (SNU638-F2) and CDDP-resistant cell (SNU638-Cis) lines, from a Korean gastric cancer cell line (SNU638) and the ADR-resistant cells (AD600) was established from a colon cancer cell line (SW620). Treatment of each cell line, with 1 micro M atRA, prior to drug exposure resulted in enhanced cell death in these cell lines. Furthermore, the effect of atRA on growth inhibition, in each drug-resistant cell line, was more obvious than in their parent cell lines. Increased activity of Transglutaminase II (TgaseII) and cleavage of Poly (ADP-ribose) polymerase (PARP) were also observed (western blot analysis.
  
  
  CONCLUSIONS
  Based on our data, we suggest that atRA enhances anticancer drug-induced cell death and reverses the drug-sensitivity of the drug-resistant cancer cell lines.
authors.forename: Young Mi
authors.initials: YM
authors.lastname: Whang
authors.forename: Yeul Hong
authors.initials: YH
authors.lastname: Kim
authors.forename: Sang Won
authors.initials: SW
authors.lastname: Shin
authors.forename: Byung Soo
authors.initials: BS
authors.lastname: Kim
authors.forename: Jun Suk
authors.initials: JS
authors.lastname: Kim
authors.forename: Young Do
authors.initials: YD
authors.lastname: Yoo
authors.forename: Sun Hee
authors.initials: SH
authors.lastname: Park
keywords: 5-fluorouracil; Adriamycin; Cisplatin; Drug-resistant cancer cell lines; Retinoic acid