Recent developments in drug resistance and apoptosis research

Label-Free Quantitative Proteomics Analysis of Adriamycin Selected Multidrug Resistant Human Lung Cancer Cells

The development of drug resistance in lung cancer is a major clinical challenge, leading to a 5-year survival rate of only 18%. Therefore, unravelling the mechanisms of drug resistance and developing novel therapeutic strategies is of crucial importance. This study systematically explores the novel biomarkers of drug resistance using a lung cancer model (DLKP) with a series of drug-resistant variants. In-depth label-free quantitative mass spectrometry-based proteomics and gene ontology analysis shows that parental DLKP cells significantly differ from drug-resistant variants, and the cellular proteome changes even among the drug-resistant subpopulations. Overall, ABC transporter proteins and lipid metabolism were determined to play a significant role in the formation of drug resistance in DKLP cells. A series of membrane-related proteins such as HMOX1, TMB1, EPHX2 and NEU1 were identified to be correlated with levels of drug resistance in the DLKP subpopulations. The study also showed enrichment in biological processes and molecular functions such as drug metabolism, cellular response to the drug and drug binding. In gene ontology analysis, 18 proteins were determined to be positively or negatively correlated with resistance levels. Overall, 34 proteins which potentially have a therapeutic and diagnostic value were identified.

Cucurbita ficifolia Fruit Extract Induces Tp53/Caspase-Mediated Apoptosis in MCF-7 Breast Cancer Cells

The second most biggest cancer worldwide is breast cancer. There is an increasing need for safer, effective, and affordable drug candidates from natural sources to treat breast cancer. In the present investigation, the anticancer effect of Cucurbita ficifolia Bouché (C. ficifolia) fruit extract was tested on the human breast cancer cells such as MCF-7. The cells were exposed with different doses of C. ficifolia, for the assessment of IC₅₀ concentrations on the MCF-7 cell lines for 24 hs. The effect of C. ficifolia fruit extract on morphological and apoptotic changes were evaluated by specific fluorescence staining techniques and real-time PCR in a time-dependent manner for 24 hs and 48 hs. The IC₅₀ value for C. ficifolia fruit extract was found to be 90 μg/mL. Morphological alteration and apoptotic distinctiveness aspect like chromatin condensation and nuclear fragmentation were noticed in C. ficifolia extract exposed breast cancer cells. Further, we observed that C. ficifolia extract-induced programmed cell death in the MCF-7 cells were mediated with the elevated expression of the tumor suppressor gene such as p53 and apoptotic markers such as caspase-8, caspase-9, caspase-3, fatty acid synthase (FAS), Fas-associated protein with death domain (FADD), Bcl-2 homologous antagonist/killer (BAK), and Bcl-2-associated X protein (BAX). These observations established that C. ficifolia significantly concealed the cell division and provoked p53/caspase-mediated programmed cell death. Further, we noticed that this cell death in MCF-7 cells is concentration and time dependent. As evaluated through the comet assay, C. ficifolia induced DNA damage; further upon increasing the duration of the treatment, the DNA damage was higher than before. Thus, our study concludes that C. ficifolia could serve as an effective anticancer agent through vital gene modulation.

Identification of proteins responsible for adriamycin resistance in breast cancer cells using proteomics analysis

Chemoresistance is a poor prognostic factor in breast cancer and is a major obstacle to the successful treatment of patients receiving chemotherapy. However, the precise mechanism of resistance remains unclear. In this study, a pair of breast cancer cell lines, MCF-7 and its adriamycin-resistant counterpart MCF-7/ADR was used to examine resistance-dependent cellular responses and to identify potential therapeutic targets. We applied nanoflow liquid chromatography (nLC) and tandem mass tags (TmT) quantitative mass spectrometry to distinguish the differentially expressed proteins (DEPs) between the two cell lines. Bioinformatics analyses were used to identify functionally active proteins and networks. 80 DEPs were identified with either up- or down-regulation. Basing on the human protein-protein interactions (PPI), we have retrieved the associated functional interaction networks for the DEPs and analyzed the biological functions. Six different signaling pathways and most of the DEPs strongly linked to chemoresistance, invasion, metastasis development, proliferation, and apoptosis. The identified proteins in biological networks served to resistant drug and to select critical candidates for validation analyses by western blot. The glucose-6-phosphate dehydrogenase (G6PD), gamma-glutamyl cyclotransferase (GGCT), isocitrate dehydrogenase 1 (NADP+,soluble)(IDH1), isocitrate dehydrogenase 2 (NADP+,mitochondrial) (IDH2) and glutathione S-transferase pi 1(GSTP1), five of the critical components of GSH pathway, contribute to chemoresistance.

Molecular markers of multiple drug resistance in breast cancer

Breast cancer is a significant health problem in terms of both morbidity and mortality, with approximately 12% of women directly affected by this disease. Chemotherapy, given to patients with earlier stage disease, has a good survival impact and may contribute to cure. The failure of chemotherapeutic drugs to eradicate cancer cells in more advanced disease states may be due to intrinsic or acquired drug resistance, including multiple drug resistance. The drug resistance observed in breast cancer patients is likely to be multifactorial, involving mechanisms such as altered expression and/or activity of drug efflux pumps, nuclear DNA-binding enzymes, metabolizing and conjugating enzymes, and mismatch repair deficiency. More extensive transcriptomic and proteomic analyses of breast tumour and normal biopsies, followed by functional genomic studies in relevant cell line models, should increase our understanding of this phenomenon and lead to therapies being individualized for identifiable subgroups of breast cancer patients.

Inhibition of P-glycoprotein activity and reversal of cancer multidrug resistance by Momordica charantia extract

PURPOSE

Multidrug resistance (MDR) is known as a problem limiting the success of therapy in patients treated long term with chemotherapeutic drugs. The drug resistance is mainly due to the overexpression of the 170 kDa P-glycoprotein (Pgp), which causes a reduction in drug accumulation in the cancer cells. In this study, novel chemical modulator(s) from bitter melon (Momordica charantia L.) extracts obtained from leaves, fruits and tendrils were tested for their abilities to modulate the function of Pgp and the MDR phenotype in the multidrug-resistant human cervical carcinoma KB-V1 cells (high Pgp expression) in comparison with wildtype drug-sensitive KB-3-1 cells (lacking Pgp).

METHODS

The KB-V1 and KB-3-1 cells were exposed to bitter melon extracts in the presence of various concentrations of vinblastine, and cytotoxicity was assessed by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. Relative resistance was calculated as the ratio of the IC50 value of the KB-V1 cells to the IC50 value of the KB-3-1 cells. Accumulation and efflux of vinblastine in KB-V1 and KB-3-1 cells were measured using a [3H]-vinblastine incorporation assay.

RESULTS

The leaf extracts increased the intracellular accumulation of [3H]-vinblastine in KB-V1 cells in a dose-dependent manner, but extracts from the fruits and tendrils had no effect. By modulating Pgp-mediated vinblastine efflux, the leaf extracts decreased the [3H]-vinblastine efflux in KB-V1 cells in a dose-dependent manner, but not in KB-3-1 cells. Treatment of drug-resistant KB-V1 cells with bitter melon leaf extracts increased their sensitivity to vinblastine, but similar treatment of KB-3-1 cells showed no modulating effect. The fruit and tendril extracts did not affect the MDR phenotype in either cell line.

CONCLUSION

The leaf extracts from bitter melon were able to reverse the MDR phenotype, which is consistent with an increase in intracellular accumulation of the drug. The exact nature of the active components of bitter melon leaf extracts remains to be identified.

NMR studies of the relationship between the changes of membrane lipids and the cisplatin-resistance of A549/DDP cells

Changes of membrane lipids in cisplatin-sensitive A549 and cisplatin-resistant A549/DDP cells during the apoptotic process induced by a clinical dose of cisplatin (30 &mgr;M) were detected by 1H and 31P-NMR spectroscopy and by membrane fluidity measurement. The apoptotic phenotypes of the two cell lines were monitored with flow cytometry. The assays of apoptosis showed that significant apoptotic characteristics of the A549 cells were induced when the cells were cultured for 24 hours after treatment with cisplatin, while no apoptotic characteristic could be detected for the resistant A549/DDP cells even after 48 hours. The results of 1H-NMR spectroscopy demonstrated that the CH2/CH3 and Glu/Ct ratios of the membrane of A549 cells increased significantly, but those in A549/DDP cell membranes decreased. In addition, the Chol/CH3 and Eth/Ct ratios decreased for the former but increased for the latter cells under the same conditions. 31P-NMR spectroscopy indicated levels of phosphomonoesters (PME) and ATP decreased in A549 but increased in A549/DDP cells after being treated with cisplatin. These results were supported with the data obtained from 1H-NMR measurements. The results clearly indicated that components and properties of membrane phospholipids of the two cell lines were significantly different during the apoptotic process when they were treated with a clinical dose of cisplatin. Plasma membrane fluidity changes during cisplatin treatment as detected with the fluorescence probe TMA-DPH also indicate marked difference between the two cell lines. We provided evidence that there are significant differences in plasma membrane changes during treatment of cisplatin sensitive A549 and resistant A549/DDP cells.

A new monoclonal antibody, P2A8(6), that specifically recognizes a novel epitope on the multidrug resistance-associated protein 1 (MRP1), but not on MRP2 nor MRP3

Multidrug resistance (MDR) is a major problem in the chemotherapeutic treatment of cancer. Overexpression of the multidrug resistance-associated protein 1 (MRP1), is associated with MDR in certain tumors. A number of MRP1-specific MAbs, which facilitate both clinical and experimental investigations of this protein, are available. To add to this panel of existing antibodies, we have now generated an additional MRP1-specific monoclonal antibody (MAb), P2A8(6), which detects a unique heat stable epitope on the MRP1 molecule. Female Wistar rats were immunized via footpad injections with a combination of two short synthetic peptides corresponding to amino acids 235-246 (peptide A) and 246-260 (peptide B) of the MRP1 protein. Immune reactive B cells were then isolated from the popliteal lymph nodes for fusion with SP2/O-Ag14 myeloma cells. Resultant hybridoma supernatants were screened for MRP1-specific antibody production. Antibody P2A8(6) was characterized by Western blotting and immunocytochemistry on paired multidrug resistant (MRP1 overexpressing) and sensitive parental cell lines. The antibody detects a protein of 190 kDa in MRP1-expressing cell lines but not in MRP2- or MRP3-transfected cell lines. P2A8(6) stains drug-selected and MRP1-transfected cell lines homogeneously by immunocytochemistry and recognizes MRP1 by immunohistochemistry on formalin-fixed paraffin wax-embedded tissue sections. Peptide inhibition studies confirm that P2A8(6) reacts with peptide B (amino acids 246-260), therefore recognizing a different epitope from that of all currently available MRP1 MAbs. This new MAb, chosen for its specificity to the MRP1 protein, may be a useful addition to the currently available range of MRP1-specific MAbs.

Gamma-tocopheryl quinone stimulates apoptosis in drug-sensitive and multidrug-resistant cancer cells

Chemotherapy-induced cell death is linked to apoptosis, and there is increasing evidence that multidrug-resistance in cancer cells may be the result of a decrease in the ability of a cell to initiate apoptosis in response to cytotoxic agents. In previous studies, we synthesized two classes of electrophilic tocopheryl quinones (TQ), nonarylating alpha-TQ and arylating gamma- and delta-TQ, and found that gamma- and delta-TQ, but not alpha-TQ, were highly cytotoxic in human acute lymphoblastic leukemia cells (CEM) and multidrug-resistant (MDR) CEM/VLB100. We have now extended these studies on tumor biology with CEM, HL60 and MDR HL60/MX2 human promyelocytic leukemia, U937 human monocytic leukemia, and ZR-75-1 breast adenocarcinoma cells. gamma-TQ, but not alpha-TQ or tocopherols, showed concentration and incubation time-dependent effects on loss of plasma membrane integrity, diminished viable cell number, and stimulation of apoptosis. Its cytotoxicity exceeded that of doxorubicin in HL60/MX2 cells, which express MRP, an MDR-associated protein. Apoptosis was confirmed by TEM, TUNEL, and DNA gel electrophoresis. Kinetic studies showed that an induction period was required to initiate an irreversible multiphase process. Gamma-TQ released mitochondrial cytochrome c to the cytosol, induced the cleavage of poly(ADP-ribose)polymerase, and depleted intracellular glutathione. Unlike xenobiotic electrophiles, gamma-TQ is a highly cytotoxic arylating electrophile that stimulates apoptosis in several cancer cell lines including cells that express MDR through both P-glycoprotein and MRP-associated proteins. The biological properties of arylating TQ electrophiles are closely associated with cytotoxicity and may contribute to other biological effects of these highly active agents.

Bcl-2 expression identifies patients with advanced bladder cancer treated by radiotherapy who benefit from neoadjuvant chemotherapy

OBJECTIVE

To assess the prognostic significance of Bcl-2 expression on the clinical outcome after radiotherapy for muscle-invasive bladder cancer, and to determine if it is possible to identify a subgroup of patients to whom neoadjuvant chemotherapy can be targeted to improve survival.

PATIENTS AND METHODS

Immunohistochemical staining for Bcl-2 and p53 was performed on the tumours of 51 patients with stage T2-T4a NXM0 transitional cell carcinoma of the bladder who had been included in a randomized clinical trial of radiotherapy with or without neoadjuvant cisplatin. The association between positive staining and salvage cystectomy rate and overall survival was examined, with a median follow-up of 12 years.

RESULTS

Bcl-2 and p53 expression was positive in 31 (61%) and 39 (76%) of the tumours, with no association between either, or with tumour stage or grade. There was no difference according to Bcl-2 positivity in the salvage cystectomy rate (P = 0.83) or survival (P = 0.68) for the 51 patients as a whole, but Bcl-2-negative patients receiving neoadjuvant cisplatin had a significantly better prognosis, with a median survival of 72 months compared to 17 months in Bcl-2-positive patients, and a 5-year survival rate of 55% (P = 0.03).

CONCLUSIONS

Quantifying Bcl-2 in patients undergoing radiotherapy for advanced bladder cancer identifies those who may benefit from neoadjuvant chemotherapy. Further studies of other members of the Bcl-2 family and other proteins controlling both cell proliferation and apoptosis are warranted, to define the roles and the interactions between them that may contribute to oncogenesis and resistance to standard treatments. This may allow the targeting of specific treatments to patients known to be sensitive to them, and aid the future development of novel therapies for bladder cancer.

Altered expression of mRNAs for apoptosis-modulating proteins in a low level multidrug resistant variant of a human lung carcinoma cell line that also expresses mdr1 mRNA

An in vitro model that might be relevant to cancer cell chemoresistance in vivo was generated by exposing the human lung carcinoma clonal cell line DLKP-SQ to 10 sequential pulses of pharmacologically attainable doses of doxorubicin. The resistant variant, DLKP-SQ/10p, was found to be cross-resistant to doxorubicin (10x), vincristine (43x), etoposide (3x), sodium arsenate (3x), paclitaxel (38x) [which could imply overexpression of P-glycoprotein (P-gp) and possibly increased multidrug resistance-associated protein activity] and 5-fluorouracil (4x), but slightly sensitized to carboplatin. Analysis of mRNA levels in the resistant variant revealed overexpression of mdr1 mRNA without significant alteration in mrp, Topo. IIalpha, GSTpi, dhfr or thymidylate synthase mRNA levels. Overexpression of the anti-apoptotic bcl-xL transcript and the pro-apoptotic bax mRNA was also detected but no alterations in bcl-2 or bag-1 mRNA levels were observed. Resistance to a P-gp-associated drug, doxorubicin, could be reversed with P-gp circumventing agents such as cyclosporin A and verapamil, but these substances had no effect on resistance to 5-fluorouracil. Overexpression of the pro-apoptotic bcl-xS gene in the DLKP-SQ/10p line partially reversed resistance not only to P-gp-associated drugs but also to 5-fluorouracil, indicating that the ratio of bcl family members may be important in determining sensitivity to chemotherapeutic drug-induced apoptosis.