Induction of metallothionein isoforms in rat hepatoma cells by various anticancer drugs

Identification of carbonic anhydrase 9 as a contributor to pingyangmycin-induced drug resistance in human tongue cancer cells

Drug resistance is the major obstacle to successful cancer treatment. To understand the mechanisms responsible for drug resistance in tongue cancer, Tca8113 cells derived from moderately differentiated human tongue squamous cell carcinoma were exposed to stepwise escalated concentrations of pingyangmycin (PYM) to develop the resistant cell line called Tca8113/PYM, which showed over 18.78-fold increased resistance to PYM as compared with Tca8113 cells, and cross-resistance to cisplatin, pirarubicin, paclitaxel, adriamycin, and mitomycin. We found that the resistance was not associated with multidrug resistance transporter 1 (p170, p-gp), multidrug resistance-associated protein 1 and breast cancer resistance protein overexpression, so we hypothesized that Tca8113/PYM cells must have some other resistance mechanism selected by PYM. To test this hypothesis, the global gene expression profiles between Tca8113 and Tca8113/PYM cells were compared by cDNA microarray. Eighty-nine genes and thirteen expressed sequence tags with differential expression levels between the two cell lines were identified. Some differential expression levels were validated with real-time PCR and western blot. Furthermore, the functional validation showed that both carbonic anhydrase (CA) inhibitor acetazolamide application and CA9 silencing with CA9 antisense oligonucleotides contribute to the medium pH increase of Tca8113/PYM cells and enhanced PYM chemosensitivity. Moreover, both acetazolamide and CA9 antisense oligonucleotides significantly increased PYM-induced caspase 3 activation in Tca8113/PYM cells. Thus, our study suggests that the resistance of Tca8113/PYM cells is probably associated with CA9 and other differential expression molecules, and that CA9 may be an important marker for prediction of PYM responsiveness in tongue cancer chemotherapy.

Increased Expression of Metallothionein Is Associated with Irinotecan Resistance in Gastric Cancer

To gain insight into clinically relevant mechanisms of irinotecan resistance, we undertook oligonucleotide microarray analyses on paired malignant effusion samples obtained from eight gastric cancer patients treated with weekly irinotecan. Pretreatment and posttreatment (48 h) effusion samples were obtained for each patient, and the change in expression profile was compared between clinical responders and nonresponders. When differences in the expression of genes were examined using SAM (Significance Analysis of Microarrays) software, five isoforms of the metallothionein family were identified to have significantly higher signal log ratios in five nonresponders, compared with three responders. Compared with control cells, metallothionein 1X (MT1X)-transfected AGS cells showed a 1.4-fold higher irinotecan IC(50) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and tended to form more colonies. These findings collectively suggest that irinotecan-induced up-regulation of metallothionein might be associated with irinotecan resistance in patients with gastric cancer, although it remains to be confirmed in a larger data set.

Metallothionein expression in hepatocellular carcinoma

AIM: To investigate the expression of metallothioneins (MTs), which were recently thought to have close relationship with tumors, in human hepatocellular carcinoma.

METHODS: Histological specimens of 35 cases of primary human hepatocellular carcinoma with para-neoplastic liver tissue and 5 cases of normal liver were stained for MTs with monoclonal mouse anti-MTs serum (E9) by the immunohistochemical ABC technique.

RESULTS: MTs were stained in the 35 cases of HCC, including 6 cases negative (17.1%), 23 weakly positive (65.7%), and 6 strongly positive (17.1%). But MTs were stained strongly positive in all the five cases of normal liver and 35 cases of para-neoplastic liver tissue. The differences of MTs expression between HCC and normal liver tissue or para-neoplastic liver tissue were highly significant (P < 0.01). The rate of MTs expression in HCC grade I was 100 percent, higher than that in grade II (81%) and grade III and IV (78%). But the differences were not significant (P > 0.05). No obvious correlations between MTs expression in HCC and tumor size, clinical stage or serum alpha fetoprotein concentration were found (P > 0.05).

CONCLUSION: Decrease of MTs expression in HCC may play a role in carcinogenesis of HCC. MTs are stained heterogenously in HCC. We can choose the anticancer agents according to the MTs concentration in HCC, which may improve the results of chemotherapy for HCC.