Pgp-positive leukaemic cells have increased mtDNA but no increased rate of proliferation

Quantitative analysis of mitochondrial DNA 4977-bp deletion in sporadic breast cancer and benign breast diseases

The mitochondrial DNA (mtDNA) 4977-bp deletion (DeltamtDNA(4977) mutation) is one of the most frequently observed mtDNA mutations in human tissues and may play a role in carcinogenesis. Only a few studies have evaluated DeltamtDNA(4977) mutation in breast cancer tissue, and the findings have been inconsistent, which may be due to methodological differences. In this study, we developed a quantitative real-time PCR assay to assess the level of the DeltamtDNA(4977) mutation in tumor tissue samples from 55 primary breast cancer patients and 21 patients with benign breast disease (BBD). The DeltamtDNA(4977) mutation was detected in all of the samples with levels varying from 0.000149% to 7.0%. The DeltamtDNA(4977) mutation levels were lower in tumor tissues than in adjacent normal tissues in both breast cancer and BBD subjects. The differences, however, were not statistically significant. No significant difference between breast cancer and BBD patients was found in the DeltamtDNA(4977) mutation levels of tumor tissues and adjacent normal tissues. The DeltamtDNA(4977) mutation levels were not significantly associated with clinicopathological characteristics (age, histology, tumor stage, and ER/PR status) in breast cancer or BBD patients. These results do not support the notion that the mitochondrial DNA 4977-bp deletion plays a major role in breast carcinogenesis.

Application of mitochondrial genome information in cancer epidemiology

Two genomes, nuclear and mitochondrial, exist in humans although information contained in the mitochondrial genome has not been fully utilized in cancer epidemiology. Over the last few years, a variety of approaches have been developed to improve results of conventional cancer screening by detecting molecular markers in different populations. Mitochondrial DNA alterations (mutations, deletions and instability) are emerging as new molecular markers for detecting a variety of cancers in tissue samples and biofluids which can be included in population screening studies. Since mitochondrial genome is small (16.6 kb) and high-throughput assays have been developed for sequencing whole mitochondrial genome, it can be adopted by most of the laboratories conducting epidemiological studies. Applications of mitochondrial DNA markers to identify high risk populations and future challenges are discussed in this article.

Mitochondrial DNA sequence variation in single cells from leukemia patients

A high frequency of mtDNA somatic mutation has been observed in many tumors as well as in aging tissues. In this study, we analyzed the mtDNA control region sequence variation in 3534 single normal cells and individual blasts from 18 patients with leukemia and 10 healthy donors, to address the mutation process in leukemic cells. We found significant differences in mtDNA sequence, as represented by the number of haplotypes and the mean number of cells with each nonaggregate haplotype in a population of cells, in patients compared to controls. Patients with similar clinical leukemia types, particularly acute myeloid leukemia (AML), did not show a uniform pattern of sequence variation in single blasts. Some patients at relapse presented a complex shift of major haplotypes in single cells. Four patients showed high frequencies of cells containing mutations 189, 260, 16150, and 16488, respectively, as a result of clonal expansion and could be considered as potential markers for their respective disease progression. To our knowledge, this is the first large-scale study of mtDNA variation in single malignant cells. Our results suggest that the somatic mutation process in leukemia is complex, leading to diverse levels of genetic alterations due to either intrinsic aspects of leukemia pathophysiology or chemotherapy effects.

Non-irradiation-derived reactive oxygen species (ROS) and cancer: therapeutic implications

Owing to their chemical reactivity, radicals have cytocidal properties. Destruction of cells by irradiation-induced radical formation is one of the most frequent interventions in cancer therapy. An alternative to irradiation-induced radical formation is in principle drug-induced formation of radicals, and the formation of toxic metabolites by enzyme catalysed reactions. Although these developments are currently still in their infancy, they nevertheless deserve consideration. There are now numerous examples known of conventional anti-cancer drugs that may at least in part exert cytotoxicity by induction of radical formation. Some drugs, such as arsenic trioxide and 2-methoxy-estradiol, were shown to induce programmed cell death due to radical formation. Enzyme-catalysed radical formation has the advantage that cytotoxic products are produced continuously over an extended period of time in the vicinity of tumour cells. Up to now the enzymatic formation of toxic metabolites has nearly exclusively been investigated using bovine serum amine oxidase (BSAO), and spermine as substrate. The metabolites of this reaction, hydrogen peroxide and aldehydes are cytotoxic. The combination of BSAO and spermine is not only able to prevent tumour cell growth, but prevents also tumour growth, particularly well if the enzyme has been conjugated with a biocompatible gel. Since the tumour cells release substrates of BSAO, the administration of spermine is not required. Combination with cytotoxic drugs, and elevation of temperature improves the cytocidal effect of spermine metabolites. The fact that multidrug resistant cells are more sensitive to spermine metabolites than their wild type counterparts makes this new approach especially attractive, since the development of multidrug resistance is one of the major problems of conventional cancer therapy.

P-glycoprotein-mediated multidrug resistance phenotype of L1210/VCR cells is associated with decreases of oligo- and/or polysaccharide contents

Multidrug resistance of murine leukaemic cell line L1210/VCR (obtained by adaptation of parental drug-sensitive L1210 cells to vincristine) is associated with overexpression of mdr1 gene product P-glycoprotein (Pgp)-the ATP-dependent drug efflux pump. 31P-NMR spectra of L1210 and L1210/VCR cells (the latter in the presence of vincristine) revealed, besides the decrease of ATP level, a considerable lower level of UDP-saccharides in L1210/VCR cells. Histochemical staining of negatively charged cell surface binding sites (mostly sialic acid) by ruthenium red (RR) revealed a compact layer of RR bound to the external coat of sensitive cells. In resistant cells cultivated in the absence or presence of vincristine, the RR layer is either reduced or absent. Consistently, resistant cells were found to be less sensitive to Concanavalin A (ConA). Moreover, differences in the amount and spectrum of glycoproteins interacting with ConA-Sepharose were demonstrated between sensitive and resistant cells. Finally, the content of glycogen in resistant cells is lower than in sensitive cells. All the above facts indicate that multidrug resistance of L1210/VCR cells mediated predominantly by drug efflux activity of Pgp is accompanied by a considerable depression of oligo- and/or polysaccharides biosynthesis.

Mitochondrial defects in cancer

Mitochondria play important roles in cellular energy metabolism, free radical generation, and apoptosis. Defects in mitochondrial function have long been suspected to contribute to the development and progression of cancer. In this review article, we aim to provide a brief summary of our current understanding of mitochondrial genetics and biology, review the mtDNA alterations reported in various types of cancer, and offer some perspective as to the emergence of mtDNA mutations, their functional consequences in cancer development, and therapeutic implications.

Enzymatic oxidation products of spermine induce greater cytotoxic effects on human multidrug-resistant colon carcinoma cells (LoVo) than on their wild-type counterparts

The occurrence of resistance to cytotoxic agents in tumor cells, associated with several phenotypic alterations, is one of the major obstacles to successful anticancer chemotherapy. A new strategy to overcome MDR of human cancer cells was studied, using BSAO, which generates cytotoxic products from spermine, H(2)O(2) and aldehyde(s). The involvement of these products in causing cytotoxicity was investigated in both drug-sensitive (LoVo WT) and drug-resistant (LoVo DX) colon adenocarcinoma cells. Evaluation of clonogenic cell survival showed that LoVo DX cells are more sensitive than LoVo WT cells. Fluorometric assay and treatments performed in the presence of catalase demonstrated that the cytotoxicity was due mainly to the presence of H(2)O(2). Cytotoxicity was eliminated in the presence of both catalase and ALDH. Transmission electron microscopic observations showed more pronounced mitochondrial modifications in drug-resistant than in drug-sensitive cells. Mitochondrial functionality studies performed by flow cytometry after JC-1 labeling revealed basal hyperpolarization of the mitochondrial membrane in LoVo DX cells. After treatment with BSAO and spermine, earlier and higher mitochondrial membrane depolarization was found in LoVo DX cells than in drug-sensitive cells. In addition, higher basal ROS production in LoVo DX cells than in drug-sensitive cells was detected by flow-cytometric analysis, suggesting increased mitochondrial activity in drug-resistant cells. Our results support the hypothesis that mitochondrial functionality affects the sensitivity of cells to the cytotoxic enzymatic oxidation products of spermine, which might be promising anticancer agents, mainly against drug-resistant tumor cells.

Generation of reactive oxygen species is not involved in idarubicin-induced apoptosis in human leukaemic cells

The anthracycline antibiotic idarubicin (IDA) induces double-stranded DNA breaks, the generation of reactive oxygen species (ROS) and apoptosis in human leukaemic cells. It is unclear whether the generation of ROS is associated with the apoptotic process. Using the T-lymphoblastic leukaemic CEM cell line, we found that IDA-induced DNA breaks were correlated with final cell death. The reduction in mitochondrial membrane potential (Deltapsim) and the generation of ROS occurred simultaneously with IDA-induced activation of caspase-9 and caspase-3. Inhibition of caspases by a pan-caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-fmk) completely blocked IDA-induced reduction of Deltapsim, apoptosis and final cell death. Interestingly, ROS generation was significantly enhanced by Z-VAD-fmk. ROS generation was neither caspase dependent nor part of the apoptotic process. IDA-mediated reduction in Deltapsim is caspase dependent and is not a consequence of the generation of ROS. These results indicate that IDA-induced generation of ROS and apoptosis are separate events. Inhibition of caspases facilitates IDA-mediated generation of ROS.

Expression of P-170 glycoprotein sensitizes lymphoblastoid CEM cells to mitochondria-mediated apoptosis

Multidrug resistance caused by P-glycoprotein (P-170) is a phenomenon by which cells exposed to a single drug acquire resistance to other structurally and functionally unrelated drugs. This is a widespread phenomenon described in vivo in the management of infectious as well as non-infectious diseases. Several in vitro models have been developed in order to evaluate physiopathological properties of P-170. Among these are P-170-expressing variants of the human T-lymphoblastoid CEM cell line called VBL100. As a general rule, drug resistance normally results in resistance to apoptosis induction. By contrast, a paradoxical activity is exerted in this cell model by the cytokine tumour necrosis factor-alpha (TNF-alpha), which is capable of inducing apoptosis in P-170-expressing variants better than in wild-type (wt) cells. In the present study we partially address the mechanisms underlying this activity. In fact, the susceptibility of VBL100 cells to TNF-alpha appears to be specifically due to the depolarization of their mitochondrial membrane, a key factor for apoptotic induction. The same was observed with staurosporine, a specific mitochondrion-mediated proapoptotic chemical probe. Conversely, other proapoptotic stimuli, such as Fas/CD95 or the anti-cancer drug etoposide, did induce significant cell death in wild type cells only. Thus, schematically, mitochondrially dependent stimuli appeared to be more effective in VBL100-cell killing, while 'physiological' stimuli showed the opposite behaviour. Importantly, under steady-state conditions, VBL100 cells displayed per se a mitochondrial membrane hyperpolarization that appeared strictly related to their high susceptibility to specific apoptotic stimuli. In conclusion, the study of a well-established cell model such as that represented by the wt/VBL CEM lymphoid cell line seems to suggest that the multidrug resistance phenotype can specifically sensitize cells towards 'unphysiological', mitochondria-associated cell death cascade or, in the same fashion, it could shift cells from type I (mainly plasma membrane-associated) towards type II (mainly mitochondrial membrane-associated) phenotype.

Multidrug resistance in tumour cells: characterization of the multidrug resistant cell line K562-Lucena 1

Multidrug resistance to chemotherapy is a major obstacle in the treatment of cancer patients. The best characterised mechanism responsible for multidrug resistance involves the expression of the MDR-1 gene product, P-glycoprotein. However, the resistance process is multifactorial. Studies of multidrug resistance mechanisms have relied on the analysis of cancer cell lines that have been selected and present cross-reactivity to a broad range of anticancer agents. This work characterises a multidrug resistant cell line, originally selected for resistance to the Vinca alkaloid vincristine and derived from the human erythroleukaemia cell K562. This cell line, named Lucena 1, overexpresses P-glycoprotein and have its resistance reversed by the chemosensitisers verapamil, trifluoperazine and cyclosporins A, D and G. Furthermore, we demonstrated that methylene blue was capable of partially reversing the resistance in this cell line. On the contrary, the use of 5-fluorouracil increased the resistance of Lucena 1. In addition to chemotherapics, Lucena 1 cells were resistant to ultraviolet A radiation and hydrogen peroxide and failed to mobilise intracellular calcium when thapsigargin was used. Changes in the cytoskeleton of this cell line were also observed.