Quantitation of cytosine deaminase mRNA by real-time reverse transcription polymerase chain reaction: a sensitive method for assessing 5-fluorocytosine toxicity in vitro

Suppression of thymidine phosphorylase expression by promoter methylation in human cancer cells lacking enzyme activity

PURPOSE

Thymidine phosphorylase (TP, EC 2.4.2.4) activity varies in different human cancer cell lines. Nevertheless, little is known about the regulatory mechanisms of TP expression in such cancers. Promoter methylation of dinucleotide cytosine-guanine (CpG) sites is a known mechanism of reversible gene expression silencing.

METHODS

TP promoter methylation was investigated in five cancer cell lines (SKBR-3, 786-O, HT-29, MDA-231, DLD-1). TP mRNA levels were determined by real-time quantitative PCR. The degree of methylation was identified by bisulfite sequencing. Minimal TP promoter activity was determined by Luciferase reporter assays. DNA-protein interactions were evaluated by electrophoretic mobility shift assays.

RESULTS

SKBR-3 cells exhibited the highest TP expression, 786-O, HT-29, and MDA-231 cells exhibited intermediate TP expression, while DLD-1 cells did not express TP as demonstrated by TP mRNA, protein, and enzyme activity levels. SKBR-3 lacked methylation in the TP promoter, intron 1 and exon 1 regions, while DLD-1 showed extensive methylation. Treatment of DLD-1 and SKBR-3 with the methylation-inhibitor, 5-aza-2'-deoxycytidine (5-aza-2dC), resulted in a concentration-dependent increase in TP mRNA and protein levels in DLD-1 but not SKBR-3 cells. Trichostatin-A treatment, a histone deacetylase inhibitor, improved the 5-aza-2dC-induced TP re-activation. Electrophoretic mobility shift assays demonstrated that methylation significantly inhibits transcription factor binding. Supershift analyses suggest that the Sp1 and Sp3 (to a lesser degree) transcription factors have a role in the regulation of TP expression.

CONCLUSIONS

These findings suggest that TP promoter methylation is a mechanism for down-regulation of TP expression in cancer cells and may have implications in modulating prognosis of cancer patients.

Antitumor effect of cytosine deaminase/5-fluorocytosine suicide gene therapy system mediated by Bifidobacterium infantis on melanoma

AIM

To construct a Bifidobacterium infantis/CD targeting gene therapy system and observe the antitumor effect of cytosine deaminase/5-fluorocytosine (CD/5-FC) suicide gene therapy system mediated by Bifidobacterium infantis on melanoma in vitro and in vivo.

METHODS

A recombinant CD/pGEX-1LamdaT plasmid was transfected into Bifidobacterium infantis by electroporation. Bifidobacterium infantis transfected by recombinant CD/pGEX-1LamdaT plasmid was incubated with 5-FC anaerobically. Then the supernatant fluid was collected and added to melanoma B16-F10 cells to observe the killing effect for B16-F10 cells. Mice were inoculated with melanoma B16-F10 cells to establish animal models. The mice were then injected with 5-FC and Bifidobacterium infantis transfected by recombinant CD/pGEX-1LamdaT plasmid.

RESULTS

Two segments of approximate 4.9 kb and 1.3 kb were extracted from the 6.2 kb recombinant plasmid, which were equal to the size of the pGEX-1LamdaT plasmid and CD gene, respectively. Sequencing results showed that the full length and sequence of nucleotide acid of the inserted gene in extracted recombinant plasmid was completely identical to the CD gene. In vitro, B16-F10 cells treated by supernatant fluid were remarkably damaged morphologically, and the cell growth was significantly inhibited. Experiments on the mice melanoma model showed that after treatment with a combination of transfected Bifidobacterium infantis and 5-FC, the tumor volume was significantly inhibited compared with controls.

CONCLUSION

The foreign gene, CD gene, was correctly inserted into pGEX-1LambdaT plasmid and transferred into Bifidobacterium infantis. CD/5-FC suicide gene therapy system mediated by Bifidobacterium infantis demonstrated a good antitumor effect on melanoma in vitro and in vivo.

Expression of CEA, Tag-72, and Lewis-Y antigen in primary and metastatic lesions of ovarian carcinoma

Ovarian carcinoma has a high mortality rate, because most ovarian carcinomas are detected at a late stage. Traditional therapies, such as surgical debulking and chemotherapy, have not been successful in improving the long-term survival of these patients. Alternative therapies targeting various biomarkers, such as carcinoembryonic antigen (CEA), Tag-72, and Lewis-Y antigen, have been developed to treat patients with advanced ovarian cancers. To ensure that therapies targeting these biomarkers are effective, it is imperative to determine whether there is any differential expression of these targeted biomarkers between primary and metastatic ovarian carcinomas. In the present study, primary and metastatic lesions from 68 and 58 patients, respectively, including primary and matched metastatic lesions from 31 patients, were evaluated for cytoplasmic and membranous expression of CEA (clone Col-1), Tag-72 (clone CC-49), and Lewis-Y antigen (clone BR-96) by immunohistochemistry. No significant differences were observed with cytoplasmic and membranous expression of Tag-72 (CC-49) and Lewis-Y antigen (BR-96) in the primary and metastatic, matched and unmatched lesions (Wilcoxon signed-rank test). Although there was no statistically significant difference in the scores of CEA (Col-1) between primary and metastatic lesions, 5 of 11 (45%) cases with positive staining with CEA (Col-1) demonstrated discordant results between primary and metastatic lesions. There was a moderate positive correlation of the cytoplasmic and membranous expression of Tag-72 (CC-49), as well as cytoplasmic expression of BR-96 between primary and metastatic ovarian carcinomas. There was a weak negative correlation between the membranous expression of CEA (Col-1) and that of Lewis-Y antigen (BR-96); however, the difference was not statistically significant. No correlation was observed with other combinations of biomarkers. Our findings suggest that samples from either primary or metastatic ovarian carcinomas can be used for the evaluation of the expression of Tag-72 (CC-49) and Lewis-Y antigen (BR-96) to identify targets for novel therapies in patients with disseminated ovarian carcinomas. CEA (Col-1), due to its low expression and variation in phenotypic expression between primary and metastatic lesions, should be evaluated carefully in metastatic lesions before targeting the CEA antigen with CEA (Col-1)-like antibodies.