STOMACH

Effect of peroxisome proliferator activated receptor ligands on growth and gene expression profiles of gastric cancer cells

W K Leung¹, A H C Bai¹, V Y W Chan¹, J Yu¹, M W Y Chan¹, K-F To², J-R Wu³, K-K Chan¹, Y-G Fu¹, F K L Chan¹, J J Y Sung¹

¹ Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong
² Department of Anatomical and Cellular Pathology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong
³ Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China

Correspondence to:
Correspondence to:
Dr W K Leung
Department of Medicine and Therapeutics, Prince of Wales Hospital, Shatin, Hong Kong; wkleung{at}cuhk.edu.hk

Background and aims: Although peroxisome proliferator activated receptor (PPAR) agonists have been implicated in differentiation and growth inhibition of cancer cells, the potential therapeutic and chemopreventive effects on gastric cancer are poorly defined. We examined the in vitro and in vivo effects of PPAR ligands on growth of gastric cancer, and the effect of PPAR activation on expression of cyclooxygenase 2 (COX-2) and cancer related genes.

Methods: Gastric cell lines (MKN28 and MKN45) were treated with two specific PPAR ligands: ciglitazone and 15-deoxy-^12,14-prostaglandin J₂. Cell growth was determined by bromodeoxyuridine incorporation assay and apoptosis was measured by DNA fragmentation. Expression of COX-2 was determined by western blot and real time quantitative polymerase chain reaction (PCR). Expression profiles of cancer related genes were screened with cDNA array. In vivo growth of implanted MKN45 cells in nude mice was monitored after oral treatment with rosiglitazone.

Results: PPAR ligands suppressed the in vitro growth of MKN45 cells in a dose dependent manner whereas prostacyclin, a PPAR agonist, had no growth inhibitory effect. Growth inhibition was more pronounced in MKN45 cells, which was accompanied by DNA fragmentation and downregulation of COX-2. Screening by cDNA microarray showed that PPAR ligand treatment was associated with upregulation of bad and p53, and downregulation of bcl-2, bcl-xl, and cyclin E1 in MKN45 cells, which was confirmed by quantitative real time PCR. In contrast, MKN28 cells with lower PPAR and COX-2 expression levels had lower growth inhibitory responses to PPAR ligands. Microarray experiments only showed induction of the bad gene in MKN28 cells. In vivo growth of MKN45 cells in nude mice was retarded by rosiglitazone. Mean tumour volume in rosiglitazone treated mice was significantly lower than controls at six weeks (p = 0.019) and seven weeks (p = 0.001) after treatment.

Conclusions: PPAR ligands suppress both in vitro and in vivo growth of gastric cancer and may play a major role in cancer therapy and prevention.

Keywords: peroxisome proliferator activated receptor; apoptosis; cyclooxygenase; gene expression; gastric cancer

Abbreviations: PPAR, peroxisome proliferator activated receptor ; COX, cyclooxygenase; PGJ₂, prostaglandin J₂; PGI₂, carbaprostacyclin; FBS, fetal bovine serum; BrdU, bromodeoxyuridine; RT-PCR, reverse transcription-polymerase chain reaction

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