Analysis of various mRNA potentially involved in cisplatin resistance of murine leukemia L1210 cells

Single nucleotide polymorphisms and expression of ERCC1 and ERCC2 vis-à-vis chemotherapy drug cytotoxicity in human glioma

ERCC1 and ERCC2 have been known to belong to the nucleotide excision repair (NER) pathway and are essential to the repair of cisplatin DNA adducts. In the present study, we have examined the potential correlation of ERCC1, ERCC2 mRNA expression and single nucleotide polymorphism (SNP) to chemotherapy drug cytotoxicity from 49 human gliomas. Fresh human glioma specimens were obtained during surgery. SNPs of ERCC1 and ERCC2 was determined by single strand conformation polymorphism (SSCP) and sequencing. ERCC1 and ERCC2 expression was quantified using real-time quantitative reverse transcription-PCR. Chemotherapy drug cytotoxicity was determined by the tetrazolium (MTT) assay for cisplatin (CDDP), 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU), vincristine (VCR) and teniposide (VM26). The results show that there was no statistically significant association between the C8092A polymorphism of ERCC1 or codon 312 and codon 751 polymorphisms of ERCC2 and the chemotherapy drug cytotoxicity. However there was a strong correlation between ERCC1 and ERCC2 mRNA expression levels (Spearman r = 0.42; P < 0.003). Further more, tumor samples with low ERCC1 mRNA expression levels showed enhanced CDDP cytotoxicity (P = 0.0001) while ERCC2 expression was reversely correlated with BCNU cytotoxicity (P = 0.004). In sum, Our results indicated that ERCC1 mRNA expression is associated with CDDP cytotoxicity and ERCC2 mRNA levels is related with BCNU cytotoxicity, while there was no correlation between SNP of ERCC1, ERCC2 and in vitro cytotoxicity of four anticancer drugs, CDDP, BCNU, VCR and VM26.

Preferential platination of an activated cellular promoter by cis-diamminedichloroplatinum

This study examines how accessibility to cisplatin on various genomic regions in T47D breast cancer cells, including the retinoic acid receptor beta gene promoter and coding region and the dihydrofolate reductase gene promoter and coding region, is affected by treatment of the cells with 9-cis retinoic acid, a treatment that activates the retinoic acid receptor beta gene promoter in these cells. A PCR-based assay was used to measure cisplatin adduct density based on the inhibition of PCR amplification of templates from cisplatin treated versus untreated cells. Treatment of cells with 9-cis retinoic acid enhanced accessibility to cisplatin on the retinoic acid receptor beta gene promoter region, but not on the coding regions of that gene nor on the dihydrofolate reductase gene promoter or coding regions, where accessibilities to cisplatin remained 2-4 times lower than on the activated retinoic acid receptor beta gene promoter. Examination of smaller regions within this promoter region showed a repression of platination in the 500 bp region surrounding the TATA box in cells prior to 9-cis retinoic acid treatment, which was abolished following promoter activation. Differences in sequence composition between the various regions could not fully account for differences in platination, suggesting that structural features such as bends in retinoic acid receptor beta gene promoter DNA following gene activation, create energetically favorable sites for platination, and contribute to the cytotoxicity of the drug.

An XPG DNA repair defect causing mutagen hypersensitivity in mouse leukemia L1210 cells

One of the most widely used antitumor drugs is cis-diamminedichloroplatinum(II) (cisplatin), and mechanisms of cisplatin resistance have been investigated in numerous model systems. Many studies have used mouse leukemia L1210/0 as a reference wild-type cell line, and cisplatin-resistant subclones have been derived from it. Increased DNA excision repair capacity is thought to play a key role in the acquired cisplatin resistance, and this has influenced development of drugs for clinical trials. We report here that the L1210/0 line is in fact severely deficient in nucleotide excision repair of damaged DNA in vivo and in vitro. L1210/0 cell extracts could be complemented by extracts from repair-defective human xeroderma pigmentosum (XP) or rodent excision repair cross-complementing (ERCC) mutant cells, except for XPG/ERCC5 mutants. Purified XPG protein could restore repair proficiency to L1210/0 extracts. Expression of mouse XPG mRNA was similar in all L1210 lines studied, suggesting a point mutation or small alteration of XPG in L1210/0 cells. The DNA repair capacity of a cisplatin-resistant subline, L1210/DDP10, is similar to that of type culture collection L1210 cells and to those of other normal mammalian cell lines. Nucleotide excision repair of DNA is thus clearly important in the intrinsic cellular defense against cisplatin. However, in contrast to what is generally believed, enhancement of DNA repair above the normal level in these rodent cells does not appear to be a mechanism of acquired resistance to the drug.

DNA excision-repair synthesis is enhanced in a murine leukemia L1210 cell line resistant to cisplatin

Among various molecular mechanisms of cell resistance to antitumor agents such as cisplatin, it has recently been suggested that enhanced DNA-repair activity might be involved in the resistant phenotype of cell lines. Mouse leukemia-cisplatin-resistant cell lines L1210/10 (adapted in vitro) and L1210/DDP (adapted in vivo) have been reported to exhibit an increase DNA-repair activity, as determined by host-cell reactivation after transformation with damaged plasmids. In this paper, excision-repair activity was monitored by an in-vitro assay allowing quantification of DNA-repair synthesis in cell extracts from resistant and sensitive parental cells (L1210/10 versus L1210/0 and L1210/DDP versus L1210/S). Experimental conditions for optimal repair-synthesis activity were found to be different from these reported with human cell-line extracts. L1210/S sensitive cell line, grown in vivo by a weekly intraperitoneal graft in mice, displayed a repair activity about fourfold lower than the same cell line maintained in vitro or than L1210/0 cell grown in vitro. The repair activity was found similar in a L1210/10 and L1210/0 cell lines, but it was enhanced in L1210/DDP resistant cell line when compared with its parental line.

Differential effects of cisplatin on the expression of chimeric marker genes in CV-1 cells

The effect of the antitumor drug cisplatin on marker gene expression in CV-1 monkey cells was measured. When non-replicating test genes were introduced by transient transfection, there was strong differential inhibition caused by the drug. Expression of certain genes was relatively insensitive, but expression of others was inhibited as strongly as was DNA replication. Stronger promoters led to stronger inhibition. This selective inhibition was not observed with the pharmacologically inactive isomer transplatin. The results raise the possibility that inhibition of strongly expressed genes by cisplatin may contribute to the antitumor activity of the drug.

Cisplatin resistance in human cancers

Cancer chemotherapeutic agents primarily act by damaging cellular DNA directly or indirectly. Tumor cells, in contrast to normal cells, respond to cisplatin with transient gene expression to protect and/or repair their chromosomes. Repeated cisplatin treatments results in a stable resistant cell line with enhanced gene expression but lacking gene amplification for the proteins that will limit cisplatin cytotoxicity. Recently, several new human cell lines have been characterized for cisplatin resistance. These cell lines have led to a better understanding of the molecular and biochemical basis of cisplatin resistance. The c-fos proto-oncogene, a master switch for turning on other genes in response to a wide range of stimuli, has been shown to play an important role in cisplatin resistance both in vitro and in patients. Based on these studies, new strategies have been developed to circumvent and/or exploit clinical cisplatin resistance.