Reversion of Multidrug-Resistance by Proteasome Inhibitor Bortezomib in K562/DNR Cell Line

OBJECTIVE

To observe the reversion of multi-drug resistance by proteasome inhibitor bortezomib in K562/DNR cell line and to analyze the possible mechanism of reversion of multidrug-resistance.

METHODS

MTT method was used to determine the drug resistance of K562/DNR cells and the cellular toxicity of bortezomib. K562/DNR cells were cultured for 12 hours, 24 hours and 36 hours with 100 μg/ml DNR only or plus 4 μg/L bortezomib. The expressions of NF-κB, IκB and P-gp of K562/DNR were detected with Western blot method, the activity of NF-κB was tested by ELISA method and the apoptosis rate was observed in each group respectively.

RESULTS

The IC50 of DNR on cells of K562/S and K562/DNR groups were 1.16 μg/ml and 50.43 μg/mL, respectively. The drug-resistant fold was 43.47. The IC10 of PS-341 on Cell strain K562/DNR was 4 μg/L. Therefore, 4 μg/L was selected as the concentration for PS-341 to reverse drug-resistance in this study. DNR induced down-regulation of IκB expression, up-regulation of NF-κB and P-gp expression. After treatment with PS-341, a proteasome inhibitor, the IκB degradation was inhibited, IκB expression increased, NF-κB and P-gp expression decreased in a time dependent manner. Compared to DNR group, the NF-κB p65 activity of DNR+PS-341 group was decreased. Compared to corresponding DNR group, DNR induced apoptosis rate increases after addition of PS-341 in a time dependent manner.

CONCLUSION

Proteasome inhibitor bortezomib can convert the leukemia cell drug resistance. The mechanism may be that bortezomib decreases the degradation of IκB and the expression of NF-κB and P-gp, therefore induces the apoptosis of multi-drug resistant cells.

Frequency of C3435T single nucleotide MDR1 genetic polymorphism in an Asian population: phenotypic-genotypic correlates

AIMS

To investigate the frequency of the single nucleotide polymorphism C3435T in exon 26 of the MDR1 gene in Asians and to determine the functional significance of this SNP with the clinical pharmacokinetics of oral cyclosporin (Neoral) in 10 stable heart transplant patients.

METHODS

The MDR1 C3435T polymorphism was investigated in 290 healthy Asian subjects (98 Chinese, 99 Malays and 93 Indians). We also compared the MDR1 polymorphism between the Asian population studied here and the published data on Africans and Caucasians. The clinical relevance of this SNP on oral bioavailability of a known P-gp substrate, cyclosporin, was assessed in 10 stable Chinese heart transplant patients.

RESULTS

The homozygous TT genotype was observed in 32%, 28% and 43% of Chinese, Malays and Indians. The homozygous CC genotype was found in 25% of Chinese and Malays compared with 18% of Indians. The Indians had a lower frequency of the C allele [0.38 (0.31-0.45)] compared with the Chinese [0.46 (0.39-0.53)] and Malays [0.48 (0.42-0.55)]. Chi-squared test showed that the distribution of allele frequencies between the Malays and Indians differed significantly (P = 0.04). In this Asian population, the overall distribution of genotypes (CC, CT and TT) and allele frequencies were significantly different from those in Africans (P < 0.001). The results were also significant when the Chinese, Malays and Indians were compared separately with the African group (P < 0.001). Compared with the Caucasian data, the overall distribution of genotype and allele frequencies in the Asian population were also significantly different (P < or = 0.05). However, when each Asian ethnic group was compared separately with the Caucasians, only the Indians were found to be significantly different (P < or = 0.004). Genotypic-phenotypic correlations of this SNP were assessed in 10 stable Chinese heart transplant patients. The median AUC(0,4 h) was 11% lower in patients with CC genotype compared with subjects with TT genotype. However, the interpatient variability in AUC(0,4 h) was high in patients, especially in those with CC genotype.

CONCLUSIONS

The distribution of the SNP C3435T in exon 26 in the Chinese and Malay population was found to be similar to the Caucasians whereas the Indians were different. The Asian population also differed significantly from the African and Caucasian population in the distribution of the C3435T SNP. The low frequency of the T allele in the Indian population implies lower expression of P-gp and may have important therapeutic and prognostic implications for use of P-gp dependent drugs in individuals of Indian origin.

Immunohistochemical localization of P-glycoprotein and expression of the multidrug resistance-1 gene in human pancreatic cancer: relevance to indicator of better prognosis

We investigated immunohistochemical localization of P-glycoprotein (P-gp) on paraffin-embedded sections from 103 cases of previously untreated pancreatic tumors and also analyzed multidrug resistance-1 (MDR1) gene expression by polymerase chain reaction after reverse transcription in 35 cases. High positive staining for P-gp was observed in 72.8% of pancreatic tumors and in 73.2% of ductal adenocarcinoma. In ductal adenocarcinoma, immunoreactivity of P-gp was inversely correlated with biological aggressiveness of tumors determined by histologic grading (P<0.01), tumor size (P < 0.01), retroperitoneal invasion (P < 0.01) and portal invasion (P < 0.05). Expression of the MDR1 gene was detected in all the pancreatic tumors examined and was significantly higher than that in normal pancreas (P < 0.05). The levels of MDR1 mRNA showed a moderate correlation with those of P-gp (r=0.62, P<0.0001). Higher expression levels of MDR1/P-gp significantly correlated with better prognosis of patients with ductal carcinoma (P < 0.05). Among patients with ductal carcinoma, the high staining group for P-gp revealed a 3.5-fold better prognosis compared with the low staining group (HR=3.47, 95% CI=1.62, 7.45; P=0.0016). In conclusion, MDR1 gene/P-gp expression in pancreatic cancer without chemotherapy inversely correlates with biological aggressiveness and is an independent indicator of favorable prognosis.

Purification and characterization of NF-R2 that regulates the expression of the human multidrug resistance (MDR1) gene

NF-R2 is a DNA-binding protein that interacts with the MDR1 gene proximal promoter sequence. We previously reported that NF-R2 binds within the promoter's -126 and -102 regions, which contain the ATTCAGTCA motif. In the present study, we have purified NF-R2 from the nuclear extract of K562/ADM cells, a multidrug-resistant cell line derived from human myelogenous leukemia K562 cells, using sequential chromatography on Sephacryl S-300, DEAE-Sepharose, heparin-Sepharose and a DNA affinity column consisting of a repetitive synthetic ATTCAGTCA motif coupled to Sepharose. NF-R2 runs as a single protein of 75 kDa on SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis). CAT (chloramphenicol acetyltransferase) expression assay and gel mobility shift competition assay with mutated promoters revealed that the ATTCAGTCA motif is a positive regulatory element of MDR1 gene and that the motif is important for NF-R2 binding. These results suggest that NF-R2 may be involved in the positive regulation of the MDR1 gene transcription.

In situ localization of the human multidrug-resistance gene mRNA using thymine-thymine dimerized single-stranded cDNA

In order to detect the mRNA transcribed from the multidrug-resistance gene (MDR1), thymine-thymine (T-T) dimerized single-stranded DNA probes have been utilized for hybridization with mRNA either on nitrocellulose filters or in cells and tissues. S1 nuclease digestion rather than sonication was used to obtain short T-T dimerized single-stranded DNA (300-400 bases) so that they could penetrate well into the cytoplasm. The hybridized T-T DNA was detected immunohistochemically using rabbit anti-T-T DNA antibody (Ab) and peroxidase-labeled goat anti-rabbit IgG Ab. Employing this system, MDR1 mRNA could be localized clearly in the human multidrug-resistant cell lines K562/ADM, CEM/VLB, 2780AD, and KBC4 cells as well as in human fetal kidney and gastric carcinoma. Furthermore, our system successfully detected the expression of MDR1 mRNA in cell lines of increasing resistance. These results paralleled results obtained at the protein level by immunohistochemistry. The analysis of MDR1 RNA expression by this in situ hybridization technique should be useful in the study of normal human tissues and tumor samples expressing the MDR1 gene.