Maintenance of hypomethylation status and preferential expression of exogenous human MDR1/PGY1 gene in mouse L cells by YAC mediated transfer

Outcomes after induction chemotherapy in patients with acute myeloid leukemia arising from myelodysplastic syndrome

BACKGROUND

Secondary acute myeloid leukemia (AML) from an antecedent myelodysplastic syndrome (MDS)/myeloproliferative neoplasm is associated with a poor prognosis. The authors evaluated predictive factors in patients with secondary AML treated with anthracycline-based induction therapy.

METHODS

This was a retrospective review of secondary AML patients treated with induction therapy. Age, International Prognostic Scoring System, Eastern Cooperative Oncology Group performance status, cytogenetics, duration of MDS/myeloproliferative neoplasm, and prior MDS/myeloproliferative neoplasm treatment were evaluated for their impact on complete response (CR), CR with low platelets, and overall survival (OS).

RESULTS

The authors evaluated 61 secondary AML patients who received induction chemotherapy; 59% (36 patients) achieved CR/CR with low platelets (95% confidence interval [CI], 46%-71%), and median OS was 6.5 (95% CI, 3.9-8.1) months. Three factors were associated with lower CR/CR with low platelets and OS: poor risk cytogenetics, prior treatment with hypomethylating agents or lenalidomide, and longer time to transformation to AML. Of those treated with hypomethylating agents or lenalidomide, 32% achieved CR/CR with low platelets versus 78% in the group not treated with a hypomethylating agent or lenalidomide (odds ratio [OR], 0.13; 95% CI, 0.04-0.42). Median OS for those treated with a hypomethylating agent or lenalidomide was 3.7 versus 10.5 months for those not treated with a hypomethylating agent or lenalidomide (P < .0001). The CR/CR with low platelets rate for those with intermediate risk cytogenetics was 70% versus 35% for those with poor risk (OR, 4.33; 95% CI, 1.38-13.6). Those with poor risk cytogenetics had a median OS of 2.8 versus 7.5 months for those with intermediate risk (P = .01).

CONCLUSIONS

Prior treatment with hypomethylating agents or lenalidomide, poor risk cytogenetics, and longer time to transformation to AML are independent negative predictive factors for response and OS in patients with secondary AML after induction therapy.

Epigenetic regulation of WTH3 in primary and cultured drug-resistant breast cancer cells

Previous studies showed that the WTH3 gene functioned as a negative regulator during multidrug resistance (MDR) development in vitro. To understand whether this gene is also involved in clinical drug resistance, hypermethylation at its promoter region observed in cultured MDR MCF7/AdrR cells was examined in primary drug-resistant breast cancer epithelial cells isolated from effusions of breast cancer patients. The results showed that this event also occurred in drug-resistant breast cancer epithelial cells and a newly induced drug-resistant cell line, MCF7/inR. Interestingly, we found that a CpG (CpG 23) that was close to the TATA-like box was constantly methylated in the WTH3 promoter of drug-resistant breast cancer epithelial and cultured MDR cells. Mutagenic study suggested that this CpG site had a functional effect on promoter activity. We also discovered that MCF7/AdrR cells treated with trichostatin A, a histone deacetylase inhibitor, exhibited higher WTH3, but lower MDR1, expression. A reverse correlation between WTH3 and MDR1 gene expression was also observed in MCF7/AdrR, and its non-MDR parental cell line, MCF7/WT. This result indicated that both DNA methylation and histone deacetylase could act in concert to inhibit WTH3 and consequently stimulate MDR1 expression. This hypothesis was supported by data obtained from introducing the WTH3 transgene into MDR cell lines, which reduced endogenous MDR1 expression. Therefore, our studies suggested that the behavior of WTH3 in primary drug-resistant breast cancer epithelial cells was similar to that in a model system where epigenetic regulation of the WTH3 gene was linked to the MDR phenotype.

WTH3, which encodes a small G protein, is differentially regulated in multidrug-resistant and sensitive MCF7 cells

The WTH3 gene's biological characteristics and relationship to multidrug resistance (MDR) were investigated further. Results showed that WTH3 was mainly located in the cytosol and capable of binding to GTP. In addition, WTH3's promoter function was significantly attenuated in MDR (MFC7/AdrR) relative to non-MDR (MCF7/WT) cells. Advanced analyses indicated that two mechanisms could be involved in WTH3's down-regulation: DNA methylation and trans-element modulations. It was found that the 5' end portion of a CpG island in WTH3's promoter was hypermethylated in MCF7/AdrR but not MCF7/WT cells, which could have a negative effect on the WTH3 promoter. This idea was supported by the observation that a 45-bp sequence (DMR45) in this differentially methylated region positively influenced promoter activity. We also discovered that different nuclear proteins in MCF7/AdrR and MCF7/WT cells bound to methylated or nonmethylated DMR45. Moreover, a sequence containing a unique repeat that was also a positive cis-element for the promoter was attached by different transcription factors depending on whether they were prepared from MCF7/AdrR or MCF7/WT cells. These molecular changes, apparently induced by drug treatment, resulted in WTH3's down regulation in MDR cells. Therefore, present studies support previous observations that WTH3, as a negative regulator, participates in MDR development in MCF7/AdrR cells.

The rise of DNA methylation and the importance of chromatin on multidrug resistance in cancer

In recent years, the different classes of drugs and regimens used clinically have provided an improvement in tumour management. However, treatment is often palliative for the majority of cancer patients. Transformed cells respond poorly to chemotherapy mainly due to the development of the multidrug resistance (MDR) phenotype. Response to treatment does not generally result in complete remission and disease cure is uncommon for patients presenting with advanced stage cancer. Successful treatment of cancer requires a clearer understanding of chemotherapeutic resistance. Here, we examine what is known of one of the most extensively studied mechanisms of cellular drug resistance. The human multidrug resistance gene 1 (MDR1) is associated with expression of p-glycoprotein (Pgp). A transmembrane protein, Pgp acts as an efflux pump and reduces intracellular drug levels and thus its effectiveness as an antitumor agent. The precise mechanism of transcriptional regulation has been unclear due to the complex regulatory nature of the gene. It has become increasingly apparent that trans-activation or genetic amplification is by no means the only mechanism of activation. Consequently, alternative pathways have received more attention in the area of epigenetics to help explain transcriptional competence at a higher level of organization. The goal of this article is to highlight important findings in the field of methylation and explain how they impinge on MDR1 gene regulation. In this review, we cover the current information and postulate that epigenetic modification of MDR1 chromatin influences gene transcription in leukaemia. Finally, we explore transcriptional regulation and highlight recent progress with engineered ZFP's (zinc finger proteins).

The basic and clinical implications of ABC transporters, Y-box-binding protein-1 (YB-1) and angiogenesis-related factors in human malignancies

In our laboratories, we have been studying molecular targets which might be advantageous for novel cancer therapeutics. In this review, we focus on how ATP-binding cassette (ABC) transporter superfamily genes, Y-box-binding protein-1 (YB-1), and tumor angiogenesis-associated factors could contribute to the development of novel strategies for molecular cancer therapeutics. ABC transporters such as P-glycoprotein/MDR1 and several MRP family proteins function to protect cells from xenobiotics, drugs and poisons, suggesting that ABC transporters are a double-edged sword. In this regard, P-glycoprotein/MDR1 is a representative ABC transporter which plays a critical role in the efflux of a wide range of drugs. We have reported that gene amplification, gene rearrangements, transcription factor YB-1 and CpG methylation on the promoter are involved in MDR1 gene overexpression in cultured cancer cells. Among them, two mechanisms appear to be relevant to the up-regulation of MDR1 gene in human malignancies. We first reported that MDR1 gene promoter is activated in response to environmental stimuli, and is modulated by methylation/demethylation of CpG sites on the MDR1 promoter. We also demonstrated that YB-1 modulates not only transcription of various genes associated with cell growth, drug resistance and DNA synthesis, but also translation, mRNA stabilization and DNA repair/self-defense processes. Angiogenesis is also involved in tumor growth, invasion and metastasis of various malignancies, and so angiogenesis-related molecules also offer novel molecular targets for anticancer therapeutics.

WTH3, a new member of the Rab6 gene family, and multidrug resistance

The WTH3 gene was obtained by a DNA fragment isolated by the methylation-sensitive representational difference analysis technique due to its hypermethylation in the human multidrug resistant (MDR) breast cancer cell line MCF7/AdrR. The WTH3 gene product is 89% and 91% identical to the human Rab6 and Rab6c proteins, but possesses an elongated C-terminal region which contains 46 extra amino acids. Nevertheless, we consider the WTH3 gene a new member of the Rab6 gene family. Semi-quantitative reverse transcriptase-polymerase chain reaction results showed that WTH3 was 15 and 4 times downregulated in MCF7/AdrR and MES-SA/Dx5, a human MDR uterine sarcoma cell line, as compared to their non-MDR parental cell lines. Permanent expression of the WTH3 transgene in MDR cell lines increased to varying degrees their sensitivity to several anticancer drugs, which included doxorubicin, taxol, vinblastine, vincristine, and etoposide, as compared to the control sublines transfected with the empty vector. Flow cytometry and fluorescence microscope experiments suggest that the WTH3 transgene stimulated the host's uptake and retention of DOX. Our results imply that the WTH3 gene plays a role(s) in MDR phenotype development in vitro.

Retrovirus insertion and transcriptional activation of the multidrug-resistance gene in leukemias treated by a chemotherapeutic agent in vivo

To understand the molecular basis for multidrug-resistant (MDR) cancer cells in vivo, this study analyzed molecular changes of the mdr1a gene region in leukemia cells in mice during continuous treatment with vincristine. An inverse insertion of murine leukemia retrovirus (MuLV) into the 5'-flanking region of the mdr1a gene was found. This insertion was concomitantly accompanied by up-regulation of the mdr1a gene and the loss of chemosensitivity. Deletion of long-terminal repeat (LTR) sequences dramatically decreased the mdr1a promoter-driven reporter activity. The MuLV LTR insertion appears to exert its enhancer activity on mdr1a transcription during the appearance of MDR leukemia cells. Two mechanisms were postulated to explain the mdr1a gene activation by retrovirus insertion during in vivo chemotreatment: de novo insertion of MuLV induced by vincristine treatment and selection of a small fraction of pre-existing cells carrying MuLV insertion during vincristine treatment. No rearranged sequence was detected by polymerase chain reaction in parental cells. This result argued for the first mechanism. The randomly altered distribution of MuLV during repetitive chemotreatment might also be consistent with this hypothesis. On the other hand, the retrovirus insertion was detected at the same site of the mdr1a promoter region in 2 independent experiments, which suggests the second mechanism. It should be noted that in vivo chemotreatment using vincristine could generate the mdr1a-overexpressing cells through retrovirus insertion and the enhancer effect of the LTR.

Regulation of MDR1 gene expression: emerging concepts

Drug resistance genes, such as MDR1, involved in drug efflux, and their regulation have been the subject of intense research efforts in the past 10 years. Many factors and cellular signalling pathways play a role in the regulation of MDR1 gene expression. Commonly used chemotherapeutic agents activate in vitro and in vivo general stress response pathways, potential targets of which include MDR1 and other drug resistance genes. The contribution of these agents to the emergence of drug-resistant tumour cells is of concern. Recent evidence points to a role for the epigenetic regulation of MDR1 gene expression. The identification of key components in the DNA methylation/chromatin system of gene regulation may in time lead to more informed and targeted approaches to treating drug-resistant tumours. Copyright 2000 Harcourt Publishers Ltd.

Association of 5' CpG demethylation and altered chromatin structure in the promoter region with transcriptional activation of the multidrug resistance 1 gene in human cancer cells

Selection of human cells for resistance to vincristine or doxorubicin often induces overexpression of the multidrug resistance 1 gene (MDR1), which encodes the cell surface P-glycoprotein, as a result of gene amplification or transcriptional activation. However, the precise mechanism underlying such transcriptional activation of MDR1 remains unclear. The relation between methylation status of CpG sites in the MDR1 promoter region and transcriptional activation of MDR1 has now been investigated. The P-glycoprotein-overexpressing, multidrug-resistant KB/VJ300 and KB-C1 cells, which were established from human cancer KB3-1 cells, were examined; MDR1 is transcriptionally activated but not amplified in KB/VJ300 cells, whereas it is amplified in KB-C1 cells. Determination of the methylation status revealed that the MDR1 promoter region was hypomethylated in KB/VJ300 and KB-C1 cells, but hypermethylated in KB3-1 cells. Prior treatment of KB3-1 cells with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine resulted in a 90-fold increase in the frequency of vincristine-resistance. Of three lines, KB/CdR-1, KB/CdR-2, and KB/CdR-3, established from KB3-1 cells after exposure to 5-aza-2'-deoxycytidine, MspI/HpaII sites in the MDR1 promoter region were hypomethylated in KB/CdR-1 and KB/CdR-2 cells, but not in KB/CdR-3 cells. MDR1 mRNA expression was detected in KB/CdR-1 and KB/CdR-2 cells, but not in KB/CdR-3 cells. The binding of YB-1 and Sp1, transcription factors implicated in MDR1 expression, in the MDR1 promoter was not affected by the methylation status of a neighboring CpG sites. The MDR1 promoter region in KB/VJ300 cells showed an increased sensitivity to DNase I compared with that in KB3-1 cells, suggesting an altered chromatin structure. The methylation status of the promoter region may plays an important role in MDR1 overexpression and in acquisition of the P-glycoprotein-mediated multidrug resistance phenotype.

Hypomethylation Status of CpG Sites at the Promoter Region and Overexpression of the Human MDR1 Gene in Acute Myeloid Leukemias

Selection of human cells for resistance to vincristine or doxorubicin often induces overexpression of the multidrug resistance 1 gene (MDR1), which encodes the cell surface P-glycoprotein, as a result of gene amplification or transcriptional activation. Moreover, overexpression of the MDR1 gene has been shown to be associated closely with clinical outcome in various hematological malignancies, including acute myeloid leukemia (AML). However, the precise mechanism underlying overexpression of the MDR1 gene during acquisition of drug resistance remains unclear. We recently described an inverse correlation between the methylation status of CpG sites at the promoter region and expression of the MDR1 gene in malignant cell lines. In this study, we expanded this analysis to 42 clinical AML samples. We adapted a quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay for gene expression and a quantitative PCR after digestion by Hpa II for methylation status of the MDR1gene. We observed a statistically significant inverse correlation between methylation and MDR1 expression in clinical samples. The hypomethylation status of the MDR1 promoter region might be a necessary condition for MDR1 gene overexpression and establishment of P-glycoprotein–mediated multidrug resistance in AML patients.

Hypomethylation Status of CpG Sites at the Promoter Region and Overexpression of the Human MDR1 Gene in Acute Myeloid Leukemias

Selection of human cells for resistance to vincristine or doxorubicin often induces overexpression of the multidrug resistance 1 gene (MDR1), which encodes the cell surface P-glycoprotein, as a result of gene amplification or transcriptional activation. Moreover, overexpression of the MDR1 gene has been shown to be associated closely with clinical outcome in various hematological malignancies, including acute myeloid leukemia (AML). However, the precise mechanism underlying overexpression of the MDR1 gene during acquisition of drug resistance remains unclear. We recently described an inverse correlation between the methylation status of CpG sites at the promoter region and expression of the MDR1 gene in malignant cell lines. In this study, we expanded this analysis to 42 clinical AML samples. We adapted a quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay for gene expression and a quantitative PCR after digestion by Hpa II for methylation status of the MDR1gene. We observed a statistically significant inverse correlation between methylation and MDR1 expression in clinical samples. The hypomethylation status of the MDR1 promoter region might be a necessary condition for MDR1 gene overexpression and establishment of P-glycoprotein–mediated multidrug resistance in AML patients.

Localization of 67 exons on a YAC contig spanning 1.5 Mb around the multidrug resistance gene region of human chromosome 7q21.1

A contig of 21 nonchimeric yeast artificial chromosomes (YACs) was previously assembled across 1.5 Mb of the multidrug resistance (MDR) gene (PGY1 and PGY3) region of human chromosome 7q21.1. This region of the human genome has now been subjected to exon amplification to detect the presence of additional genes. Exon trapping was performed directly on the YACs. Sixty-seven gene fragments were isolated and characterized by sequence analysis and comparison with public databases. The localization of these exons in the 1.5-Mb region was determined by hybridization to YAC clones, and they were localized in 11 subregions of YAC contigs. The exon collection includes 21 exons that were identical to known cDNA sequences of PGY1, PGY3, sorcin (SRI), the cDNA similar to the delta subunit of the human amiloride-sensitive Na- channel (SCNED), and 4 cDNAs with unknown function; 43 exons that showed homology/similarity to known cDNA sequences of mouse DMP1, rat COT, mouse and human NADHD, human MDC, 3 cDNAs encoding possible membrane proteins, and 21 other cDNAs; and 3 exons that shared no homology/similarity with any sequence in public databases. The nucleotide sequences of all the PGY1 and PGY3 exons were identical to the corresponding cDNA sequences previously determined, and these exons were localized to the expected positions on the appropriate YAC clones. No other member of the MDR gene family thus appeared to be present in the 1.5-Mb region. The integrated physical and exon maps should prove valuable for both fine mapping and determination of a complete gene map of this segment of the genome.