Modulation of cisplatin sensitivity and growth rate of an ovarian carcinoma cell line by bombesin and tumor necrosis factor-alpha

Cisplatin resistance in human cervical, ovarian and lung cancer cells

PURPOSE

This study was performed to determine whether or not in cervical, ovarian and lung cancer cell lines, free radicals (ROS) play a role in cisplatin cytotoxicity and activation of the mitochondrial and JNK/p38 pathways. The role of the enzyme, dihydrodiol dehydrogenase (DDH1), in the activation/deactivation of this pathway and how this may be related to the development of resistance was also investigated.

METHODS

Mitochondrial membrane potential and ROS analysis were performed by flow cytometry, P-JNK and P-p38 by western blotting and mRNA by RT-PCR. Dihydrodiol dehydrogenase (DDH1) and thioredoxin knockdowns were prepared by standard techniques.

RESULTS

Cisplatin treatment of a cervical cancer cell line resulted in ROS production with mitochondrial membrane depolarization and phosphorylation of JNK and p38. N-acetyl-cysteine, a free radical scavenger, ameliorated these effects. Treatment of the sensitive cells with H2O2 produced similar effects but at shorter incubation times. Similar results were observed with an ovarian cell line. Downregulation of dihydrodiol dehydrogenase in the cisplatin-resistant cervical and lung cancer cell lines resulted in increased drug sensitivity with detectable production of ROS and activation of the JNK/p38 pathways; however, downregulation of thioredoxin in the cervical cells had minimal effect.

CONCLUSION

Dihydrodiol dehydrogenase appears to play a role in cisplatin resistance in cervical, ovarian and lung cancer cells which includes mitochondrial membrane depolarization, ROS production and activation of the JNK pathway. However, its mode of action cannot be mimicked by an ROS scavenger so its mechanism of action is more complex (a not unexpected finding considering its role in xenobiotic activation/countering oxidative stress).

Resistance to platinum-based chemotherapy in lung cancer cell lines

PURPOSE

A series of six lung cancer cell lines of different cell origin (including small cell and mesothelioma) were characterized immunohistochemically and the role of a series of protein candidates previously implicated in drug resistance were investigated.

METHODS

These include colony-forming and cell growth assays, immunohistochemistry, siRNA knockouts, real-time PCR and western blots.

RESULTS

No correlation was found with AKT, HO-1, HO-2, GRP78, 14-3-3zeta and ERCC1 levels and cisplatin nor oxaliplatin cytotoxicity, but an association was observed with levels of the enzyme, dihydrodiol dehydrogenase (DDH); an enzyme previously implicated in the development of platinum resistance. The relationship appeared to hold true for those cell lines derived from lung epithelial primary tumors but not for the neuroendocrine/small-cell and mesothelioma cell lines. siRNA knockouts to DDH-1 and DDH-2 were prepared with the cell line exhibiting the greatest resistance to cisplatin (A549) resulting in marked decreases in the DDH isoforms as assessed by real-time PCR, western blot and enzymatic activity. The DDH-1 knockout was far more sensitive to cisplatin than the DDH-2 knockout.

CONCLUSION

Thus, sensitivity to cisplatin appeared to be associated with DDH levels in epithelial lung cancer cell lines with the DDH-1 isoform producing the greatest effect. Results in keeping with transfection experiments with ovarian and other cell lines.

Serine phosphorylation-dependent coregulation of topoisomerase I by the p14ARF tumor suppressor

p14ARF (ARF) and topoisomerase I play central roles in cancer and have recently been shown to interact. The interaction activates topoisomerase I, an important target for camptothecin-like chemotherapeutic drugs, but the regulation of the interaction is poorly understood. We have used the H358 and H23 lung cancer cell lines and purified recombinant human topoisomerase I to demonstrate that the ARF/topoisomerase I interaction is regulated by topoisomerase I serine phosphorylation, a modification that regulates topoisomerase I activity. Both cell lines express wild-type ARF and topoisomerase I proteins at equivalent levels, but H23 topoisomerase I, unlike that of H358 cells, is largely devoid of serine phosphorylation, has low activity, and complexes poorly with ARF. The ability of H23 topoisomerase I to complex with ARF can be restored by treatment with the serine kinase, casein kinase II. Consistent with these observations, we show that the response of H23 cells to camptothecin treatment is unaffected by changes in intracellular levels of ARF. However, in H358 and PC-3 cells, which express a serine phosphorylated topoisomerase I that complexes with ARF, ectopic overexpression of ARF causes sensitization to camptothecin, and siRNA-mediated down-regulation of endogenous ARF causes desensitization to camptothecin. These biological responses correlate with increased and decreased levels, respectively, of ARF/topoisomerase I complex and DNA-bound topoisomerase I. Thus, ARF is a serine phosphorylation-dependent coregulator of topoisomerase I in vivo, and it regulates cellular sensitivity to camptothecin by interacting with topoisomerase I. Certain cancer associated defects affecting ARF/topoisomerase I complex formation could contribute to cellular resistance to camptothecin.

Dihydrodiol dehydrogenases regulate the generation of reactive oxygen species and the development of cisplatin resistance in human ovarian carcinoma cells

We have previously demonstrated that overexpression of dihydrodiol dehydrogenase isoform 1 (DDH1) or DDH2 leads to the induction of drug resistance to platinum based drugs in human ovarian, lung, cervical and germ cell tumor cell lines. DDH belongs to a family of aldoketo reductases that are involved in the detoxification of several endogenous and exogenous substrates. DDH1 and DDH2 in particular have been shown to be involved in the detoxification (activation?) of polycyclic aromatic hydrocarbons (PAH). Based on the involvement of DDH in the detoxification of electrophilic PAH intermediates, the effect of DDH on the production of reactive oxygen species (ROS) in a cisplatin-sensitive and -resistant human ovarian carcinoma cell line was investigated in the current study. In addition to the overexpression of DDH1 and DDH2, increased expression of DDH3 was demonstrated in the cisplatin-resistant 2008/C13* cells, compared to the parental 2008 cells. However, as assessed by RT-PCR, neither cell line expressed DDH4. The 2008/C13* cells were eightfold resistant to cisplatin, and transfection experiments utilizing cisplatin-sensitive 2008 cells suggest that this could be mediated by overexpression of either DDH1, DDH2, or DDH3. The 2008/C13* cells had lower basal intracellular ROS level as compared to the 2008 cells and ROS production was decreased in the recombinant 2008 cells with forced, constitutive overexpression of either, DDH1, DDH2, or DDH3. Transfection of siRNA against DDH1 or DDH2 in the cisplatin-resistant 2008/C13* cells not only significantly decreased their cisplatin-resistance index (as assayed by MTT and colony formation assay) but also led to an increase in the basal levels of ROS production (although transfection of siRNA against DDH3 resulted in cell death). The 2008/C13* cells were found to be cross-resistant to the cytotoxic effects of hydrogen peroxide and tert-butyl hydroperoxide and knockdown of either DDH1 or DDH2 expression (using siRNA) resulted in sensitization of the resistant cells to these agents. These results support the conclusion that the increased levels of DDH in the 2008/C13* cells are directly responsible for the reduced production of ROS and that this may play a role in the development of cisplatin resistance.

Recent insights into platinum drug resistance in cancer

Cisplatin and its analogs have become important components of chemotherapeutic regimens for the treatment of solid tumors, however, their overall effectiveness is limited by the emergence of drug-resistant tumor cells. Resistance to the platinum drugs is multifactorial consisting of mechanisms that prevent the formation of lethal platinum-DNA adducts and mechanisms that operate downstream of the drug/target interaction to promote cell survival. Continued progress in the study of the drug resistance phenotype as well as the development of new platinum analogs may eventually lead to improved therapies and increased survival rates.

Increased expression of dihydrodiol dehydrogenase induces resistance to cisplatin in human ovarian carcinoma cells

We employed cDNA microarrays to identify the differentially expressed genes in a cisplatin-sensitive parental (2008) human ovarian carcinoma cell line and its cisplatin-resistant variant (2008/C13*). Differential expression of five genes was found in the 2008/C13* cells, a result confirmed by semi-quantitative reverse transcription-PCR. The five genes were identified as fibroblast muscle-type tropomyosin and skeletal muscle-type tropomyosin, dihydrodiol dehydrogenase, apolipoprotein J and glucose-6-phosphate dehydrogenase variant-A. Treatment of the 2008 cells with cisplatin (at its IC(50) concentration of 2 microm) induced expression of these genes, as determined by semi-quantitative reverse transcription-PCR analysis using gene-specific primers. In contrast, treatment of the drug-resistant 2008/C13* cells with cisplatin (at its IC(50) concentration of 20 microm) did not lead to the induction of any of the aforementioned genes. Most importantly, constitutive overexpression of dihydrodiol dehydrogenase (but not the other genes) in the 2008 cells led to induction of cisplatin resistance, clearly indicating its role in the development of the resistance phenotype in the 2008/C13* cells. The development of cisplatin resistance in the transfected cells was associated with an increase in the dihydrodiol dehydrogenase enzyme activity. Although at present it is not clear how dihydrodiol dehydrogenase is involved in cisplatin resistance, the identification of this gene as a causal factor suggests the existence of a hitherto undefined pathway resulting in cisplatin resistance.

Antitumor activity of protein kinase C inhibitors and cisplatin in human head and neck squamous cell carcinoma lines

Protein kinase C (PKC) plays a pivotal role in signal transduction involved in the control of cell proliferation, differentiation and apoptosis. Interference with such signaling pathways may result in altered tumor cell response to antineoplastic drugs. We investigated the effects of two selective PKC inhibitors as single agents and in combination with cisplatin in cell lines derived from squamous cell carcinomas of the head and neck (SCCHN). Safingol (Saf) is directed against the regulatory domain, whereas chelerythrine (Che) interacts with the catalytic domain of PKC. In six SCCHN cell lines (UM-SCC 11B, 14A, 14C and 22B, 8029NA, and a 5-fold cisplatin-resistant subline 8029DDP). PKC activities ranged between 1 and 158 IU/1 x 10(7) cells, and they were inversely proportional to the amount of cellular epidermal growth factor receptor. Using the colorimetric MTT assay, PKC inhibitors Saf and Che showed comparable dose-dependent growth inhibition. The 50% inhibitory concentrations (IC50) were between 3.8-8.6 microM for Saf and 8.5-13.6 microM for Che with no relationship to PKC activity or cisplatin sensitivity of the respective cell lines. Combinations of cisplatin (IC50 = 0.4-5.8 microg/ml) and either PKC inhibitor (5 microM Saf, 10 microM Che) led to a significant decrease of cisplatin IC50 values in most cell lines. However, comparison with theoretical additive dose-response curves showed additive rather than synergistic effects for both PKC inhibitors.

The kiss of death: promises and failures of death receptors and ligands in cancer therapy

Death receptors and their ligands exert important regulatory functions in the maintenance of tissue homeostasis and the physiological regulation of programmed cell death. Currently, six different death receptors are known including tumor necrosis factor (TNF) receptor-1, CD95 (Fas/APO-1), TNF receptor-related apoptosis-mediating protein (TRAMP), TNF-related apoptosis-inducing ligand (TRAIL) receptor-1 and -2, and death receptor-6 (DR6). The signaling pathways by which these receptors induce apoptosis are similar and rely on oligomerization of the receptor by death ligand binding, recruitment of an adapter protein through homophilic interaction of cytoplasmic domains, and subsequent activation of an inducer caspase which initiates execution of the cell death programme. The ability of these receptors and their ligands to kill malignant cells was discovered early and helped to coin the term 'tumor necrosis factor' for the first identified death ligand. This review summarizes the current and rapidly expanding knowledge about the signaling pathways triggered by death receptor/ligand systems, their potency in experimental cancer therapy, and their therapeutic limitations, especially regarding their toxicity for non-malignant cells.

In vivo radiosensitizing effects of recombinant interleukin 6 on radiation resistant BCL-1 B-lineage leukemia cells in a murine syngeneic bone marrow transplant model system

The ability of total body irradiation (TBI) to eradicate clonogenic leukemia cells from B-lineage acute lymphoblastic leukemia patients prior to bone marrow transplantation (BMT) is greatly hampered by their inherent or acquired radiation resistance. The radiorefractory nature of these cells is believed to contribute to the high relapse rate subsequent to TBI and BMT in patients with B-lineage acute lymphoblastic leukemia (ALL). A method by which clonogenic leukemia cells could be radiosensitized in vivo could be clinically beneficial. In the present study, we used a highly radiation resistant subclone of the murine B-lineage leukemia cell line BCL-1 in a syngeneic BMT model to investigate if any of the B-cell stimulatory cytokines interleukin 2, interleukin 4, interleukin 5, or interleukin 6 could have radiosensitizing effects. All untreated BALB/c mice (N = 33) inoculated with 1 x 10(6) BCL-1 cells died of disseminated leukemia within 24 days with a median survival of 13.3 days. TBI (700 cGy = LD100/30 for BALB/c mice) followed by syngeneic BMT (N = 70) extended the median survival to 23.6 days (P < 0.001 by log-rank test). A single intraperitoneal bolus injection of 100 ng, 500 ng, or 2500 ng recombinant murine interleukin 6(rmIL-6) 2-4 hours before TBI extended the median survival to 32.5 days, 31.0 days, and 30.5 days, respectively (P < 0.01 by log-rank test for all dose groups). The improved survival was not due to any direct anti-leukemic activity of rmIL-6 and all control BALB/c mice (N = 15) that received the same doses of rmIL-6 but did not undergo TBI and BMT died of BCL-1 leukemia within 28 days with a median survival of 13.6 days. In contrast to rmIL-6, recombinant murine interleukin 5 (rmIL-5) had minimal radiosensitizing effects.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhancement of drug sensitivity of human malignancies by epidermal growth factor

We have previously shown that epidermal growth factor (EGF) enhances the in vitro and in vivo sensitivity of human ovarian carcinoma 2008 cells to cisplatin. EGF was found to enhance selectively the in vivo toxicity of cisplatin to 2008 cell xenografts without altering the toxicity of cisplatin to non-malignant target tissues such as the kidney or bone marrow. We now show that recombinant human EGF (rhEGF) enhances the cisplatin sensitivity of cell lines representative of many other types of malignancies in addition to ovarian carcinoma, including cancers of the head and neck, cervix, colon, pancreas and prostate, as well as non-small-cell carcinoma of the lung. In addition, rhEGF was found to sensitise cells to other platinum-containing drugs and several other classes of chemotherapeutic agents. rhEGF sensitised 2008 cells not only to cisplatin, but also to carboplatin and tetraplatin, as well as taxol, melphalan and 5-fluorouracil. We conclude that modulation of drug sensitivity by rhEGF is observed in cell lines representative of many human malignancies and for multiple classes of chemotherapeutic agents, indicating that it alters one or more components of the cellular damage response that are both common between cell lines and classes of drugs and fundamental to survival.

Comparison of effects of growth factors and protein kinase C activators on cellular sensitivity to cis-diamminedichloroplatinum(II)

The anti-proliferative activity of the DNA-interactive anti-cancer agent cis-diamminedichloroplatinum(II) (cDDP) can be modulated by intracellular signaling systems. We have investigated the effects of growth factors on the sensitivity of human cervical carcinoma (HeLa) cells to cDDP. A 24-hr pretreatment of HeLa cells with 10 ng/ml epidermal growth factor (EGF) or transforming growth factor-alpha increased the anti-proliferative activity of cDDP by 2- to 4-fold. A similar pretreatment of HeLa cells with EGF did not alter cellular sensitivity to doxorubicin or vincristine. A brief exposure (15 min) to growth factors was not sufficient for cDDP sensitization. EGF caused a modest and transient increase in cellular diacylglycerol, the endogenous activator of protein kinase C. Bryostatin I, a partial agonist of protein kinase C, antagonized phorbol ester-mediated cDDP sensitization but had no effect on EGF-mediated sensitization to cDDP. Both EGF and phorbol 12,13-dibutyrate (PDBu) enhanced the rate of [195mPt]cDDP uptake but had no effect on the rate of [195mPt]cDDP efflux in HeLa cells. Bryostatin I reversed the increase in [195mPt]cDDP content by PDBu but failed to block EGF-induced increase in [195mPt]cDDP accumulation. Therefore, although the mechanism of cDDP sensitization by both EGF and phorbol ester appears to involve enhanced drug uptake, they may utilize distinct signal transduction pathways.

Signaling and drug sensitivity

Even though alterations in receptor and nonreceptor kinases are involved in the development of human cancer, many cancer cell lines still retain their responsiveness to growth factors. We have investigated the hypothesis that cellular signaling events regulate the sensitivity of cancer cells to chemotherapeutic agents. In 2008 human ovarian carcinoma cells, activation of a number of different transduction pathways resulted in a 2 to 4-fold increase in the sensitivity to cisplatin. These signaling events include pathways activated by the epidermal growth factor (EGF) receptor, tumor necrosis factor alpha (TNF alpha) receptor, bombesin receptor, protein kinase A (PKA), and protein kinase C (PKC). Enhanced sensitivity to chemotherapeutic agents is presumed to be mediated by phosphorylation of critical target protein(s). beta-tubulin has been identified as one such target for the protein kinase signaling cascade. For other signal transduction pathways the key substrates that regulate drug sensitivity have not yet been identified. Recent work has shown that DNA damaging agents activate signaling cascades one of which involves the Src, Ras, and Raf proteins as intermediates and results in induction of a number of genes, including c-fos, c-jun, and the growth arrest and DNA damage-inducible (gadd) genes. This signaling cascade has been shown to involve activation of protein kinase C and to have a protective function. With the growing understanding of how signaling events relate to damage response and drug sensitivity, new and potentially useful strategies for modulating drug sensitivity are evolving.