• Disulfiram-mediated inhibition of NF-kappaB activity enhances cytotoxicity of 5-fluorouracil in human colorectal cancer cell lines.

      Wang, Weiguang; McLeod, Howard; Cassidy, James (Wiley InterScience, 2003)
      5-Fluorouracil (5-FU) is the major chemotherapeutic component for colorectal cancer (CRC) and other types of solid tumours. Resistance of cancer cells to 5-FU is considered the major obstacle for successful chemotherapy. NF-kappaB is a transcription factor. Cancer cells with high NF-kappaB nuclear activity demonstrate robust chemo- and radio-resistance. We demonstrated that nuclear NF-kappaB activity in CRC cell lines, DLD-1 and RKO(WT), was significantly induced by 5-FU in a concentration- and time-dependent manner. 5-FU induced IkappaBalpha degradation and promoted both NF-kappaB nuclear translocation and its DNA binding activity. 5-FU treatment did not influence the activities of AP-1, AP-2, Oct-1, SP-1, CRE-B and TFIID. Disulfiram (DS), a clinically used anti-alcoholism drug, strongly inhibited constitutive and 5-FU-induced NF-kappaB activity in a dose-dependent manner. DS inhibited both NF-kappaB nuclear translocation and DNA binding activity but had no effect on 5-FU-induced IkappaBalpha degradation. Used in combination, DS significantly enhanced the apoptotic effect of 5-FU on DLD-1 and RKO(WT) cell lines and synergistically potentiated the cytotoxicity of 5-FU to both cell lines. DS also effectively abolished 5-FU chemoresistance in a 5-FU resistant cell line H630(5-FU) in vitro. As DS has extensive preclinical and clinical experience, translating its anticancer usage from in vitro study to clinical trials is relatively straightforward.
    • In vitro evaluation of cancer-specific NF-kappaB-CEA enhancer-promoter system for 5-fluorouracil prodrug gene therapy in colon cancer cell lines.

      Guo, X.; Evans, T.R.J.; Somanath, S.; Armesilla, Angel; Darling, John L.; Schatzlein, A.; Cassidy, James; Wang, Weiguang (Nature Publishing Group, 2007)
      Nuclear factor-kappa B (NF-kappaB) is a transcription factor with high transcriptional activity in cancer cells. In this study, we developed a novel enhancer-promoter system, kappaB4-CEA205, in which the basal carcinoembryonic antigen (CEA) promoter sequence (CEA205) was placed downstream of the four tandem-linked NF-kappaB DNA-binding sites (kappaB4). In combination with a kappaB4 enhancer, the transcriptional activity of the CEA promoter was significantly enhanced (three- to eight-fold) in cancer cell lines but not in normal cells. In cancer cell lines, the transcriptional activity of kappaB4-CEA205 was comparable with that of the SV40 promoter. We also constructed vectors in which the thymidine phosphorylase (TP) cDNA was under the control of CEA205, kappaB4, kappaB4-CEA205 and CMV promoters, respectively. TP protein and enzyme activity were detected at comparable levels in kappaB4-CEA205- and CMV-driven TP cDNA-transfected cancer cell lines (H630 and RKO). The kappaB4-TP and CEA205-TP-transfected cell lines, respectively, only demonstrated negligible and low levels of TP protein and enzyme activity. Both CMV- and kappaB4-CEA205-driven TP cDNA transiently transfected cells were 8- to 10-fold sensitised to 5-fluorouracil (5-FU) prodrug, 5'-deoxy-5-fluorouradine (5'-DFUR), in contrast to only 1.5- to 2-fold sensitised by the kappaB4- and CEA205-driven TP cDNA-transfected cells. The bystander killing effect of CMV- and kappaB4-CEA205-driven TP cDNA-transfected cells was comparable. This is the first report that indicates that the NF-kappaB DNA-binding site could be used as a novel cancer-specific enhancer to improve cancer-specific promoter activity in gene-directed enzyme prodrug therapy.
    • Mechanistic and predictive profiling of 5-Fluorouracil resistance in human cancer cells.

      Wang, Weiguang; Cassidy, James; O'Brien, Vincent; Ryan, Kevin; Collie-Duguid, Elaina (American Association for Cancer Research, 2004)
      Gene expression was analyzed in five pairs of 5-fluorouracil (5-FU) resistant and parental cancer cell lines on DNA microarrays. In unsupervised analysis, a prediction rule was built from the expression profiles of 29 genes, and 5-FU sensitivity class was predicted with 100% accuracy and high predictive strength. In supervised analysis of key 5-FU pathways, expression of 91 genes was associated with 5-FU sensitivity phenotype and segregated samples accordingly in hierarchical analysis. Key genes involved in 5-FU activation were significantly down-regulated (thymidine kinase, 2.9-fold; orotate phosphoribosyltransferase, 2.3-fold; uridine monophosphate kinase, 3.2-fold; pyrimidine nucleoside phosphorylase 3.6-fold) in resistant cells. Overexpression of thymidylate synthase and its adjacent gene, c-Yes, was detected in the resistant cell lines. The mRNA and protein overexpression of nuclear factor kappaB (NFkappaB) p65 and related antiapoptotic c-Flip gene was detected in resistant cells. The 5-FU-resistant cell lines also showed high NFkappaB DNA-binding activity. Cotransfection of NFkappaB p50 and p65 cDNA induced 5-FU resistance in MCF-7 cells. Both NFkappaB- and 5-FU-induced resistant cell lines manifested reduced expression of genes governing G(1)-S and S-phase transition. Expression of genes involved in DNA replication was also down-regulated in resistant cell lines. These findings were highly consistent with the slower growth rate, higher proportion of G(1), and lower proportion of S-phase cells in the resistant cell lines. This phenotype may protect resistant cells from cell death induced by incorporation of 5-FU into DNA chains, by allowing time to repair 5-FU-induced damage. Our findings may provide novel targets for tackling 5-FU resistance.
    • Pharmacogenomic dissection of resistance to thymidylate synthase inhibitors.

      Wang, Weiguang; Marsh, S.; Cassidy, James; McLeod, Howard (American Association for Cancer Research, 2001)
      Chemoresistance is a major obstacle for successful cancer treatment. Gene amplification and altered expression are the main genetic mechanisms of tumor chemoresistance. Previously, only a limited number of genes were analyzed in each individual study using traditional molecular methods such as Northern and Southern blotting. In this study, the global gene expression patterns of 1176 genes in a panel of five thymidylate synthase (TS) inhibitor [raltitrexed (TDX) and 5-fluorouracil (5-FU)] resistant and sensitive parent cell lines were investigated using cDNA array technology. Only 28 of 1176 genes were altered >1.5-fold among resistant cells, with 2 genes (TS and YES1) consistently higher in the panel. TS mRNA and protein were consistently overexpressed in all drug-resistant tumor cell lines compared with the sensitive parent cell lines. Southern blot and FISH analysis demonstrated that the TS gene was amplified in 5-FU- and TDX-resistant cell lines. YES1 mRNA and protein were overexpressed in four drug-resistant tumor cell lines but were not overexpressed in the lymphoblast cell line W1L2(TDX), although the YES1 gene was highly amplified in these cells. The fact that W1L2 has high level (>10-fold) resistance to TS inhibitor in the absence of high YES1 expression leads to a conclusion that YES1 has no direct role in this drug resistance process. By narrowing the search from 1176 to 2 genes, the analysis of in vitro TDX and 5-FU resistance becomes more straightforward for confirmatory studies. These data provide encouragement that comprehensive transcript analysis will aid the quest for more enlightened therapeutics.