Modulation of sensitivity of human ovarian cancer cells to cis-diamminedichloroplatinum(II) by 12-O-tetradecanoylphorbol-13-acetate and D,L-buthionine-S,R-sulphoximine

Preclinical Assessment of Low Doses of Cisplatin in the Management of Acute Promyelocytic Leukemia

Cis-diamminedichloroplatinum (II) (cisplatin) is the most widely used chemotherapeutic drug for various cancers, but its effectiveness is limited by tumor cell resistance and the severe side effects it causes. Since high level of cisplatin is cytotoxic to both cancer and normal cells, the goal of the present study was to explore the effectiveness of prolonged low doses of cisplatin in the management of leukemia. To achieve our goal, human leukemia (HL-60) cells were treated with different doses (1, 2, or 3 µM) of cisplatin for 24, 48, 72 and 96 hours. Cell viability was assessed by MTS assay. Both oxidative stress damage and genotoxicity were estimated by antioxidants, lipid peroxidation, and comet assays, respectively. Data obtained from the MTS assay demonstrated that cisplatin treatment decreased the number of viable tumor cells by direct cell killing or by simply decreasing the rate of cellular proliferation in a dose- and time-dependent fashion. The results of the lipid peroxidation showed a significant increase (p<0.05) of malondialdehyde levels with increasing cisplatin doses. Results obtained from super oxide dismutase and catalase assays showed a gradual increase in antioxidant enzyme activity in cisplatin-treated cells compared to control cells. Data generated from the Comet assay demonstrated a significant dose-dependent increase in genotoxicity with respect to DNA damage as a result of cisplatin treatment. Taken together, our research demonstrated that cisplatin-induced cytotoxicity in HL-60 cells is mediated at least in part via induction of oxidative stress and oxidative damage.

Cisplatin in cancer therapy: molecular mechanisms of action

Cisplatin, cisplatinum, or cis-diamminedichloroplatinum (II), is a well-known chemotherapeutic drug. It has been used for treatment of numerous human cancers including bladder, head and neck, lung, ovarian, and testicular cancers. It is effective against various types of cancers, including carcinomas, germ cell tumors, lymphomas, and sarcomas. Its mode of action has been linked to its ability to crosslink with the purine bases on the DNA; interfering with DNA repair mechanisms, causing DNA damage, and subsequently inducing apoptosis in cancer cells. However, because of drug resistance and numerous undesirable side effects such as severe kidney problems, allergic reactions, decrease immunity to infections, gastrointestinal disorders, hemorrhage, and hearing loss especially in younger patients, other platinum-containing anti-cancer drugs such as carboplatin, oxaliplatin and others, have also been used. Furthermore, combination therapies of cisplatin with other drugs have been highly considered to overcome drug-resistance and reduce toxicity. This comprehensive review highlights the physicochemical properties of cisplatin and related platinum-based drugs, and discusses its uses (either alone or in combination with other drugs) for the treatment of various human cancers. A special attention is paid to its molecular mechanisms of action, and its undesirable side effects.

Cellular responses to Cisplatin-induced DNA damage

Cisplatin is one of the most effective anticancer agents widely used in the treatment of solid tumors. It is generally considered as a cytotoxic drug which kills cancer cells by damaging DNA and inhibiting DNA synthesis. How cells respond to cisplatin-induced DNA damage plays a critical role in deciding cisplatin sensitivity. Cisplatin-induced DNA damage activates various signaling pathways to prevent or promote cell death. This paper summarizes our current understandings regarding the mechanisms by which cisplatin induces cell death and the bases of cisplatin resistance. We have discussed various steps, including the entry of cisplatin inside cells, DNA repair, drug detoxification, DNA damage response, and regulation of cisplatin-induced apoptosis by protein kinases. An understanding of how various signaling pathways regulate cisplatin-induced cell death should aid in the development of more effective therapeutic strategies for the treatment of cancer.

Promoter hypermethylation contributes to frequent inactivation of a putative conditional tumor suppressor gene connective tissue growth factor in ovarian cancer

Connective tissue growth factor (CTGF) is a secreted protein belonging to the CCN family, members of which are implicated in various biological processes. We identified a homozygous loss of CTGF (6q23.2) in the course of screening a panel of ovarian cancer cell lines for genomic copy number aberrations using in-house array-based comparative genomic hybridization. CTGF mRNA expression was observed in normal ovarian tissue and immortalized ovarian epithelial cells but was reduced in many ovarian cancer cell lines without its homozygous deletion (12 of 23 lines) and restored after treatment with 5-aza 2'-deoxycytidine. The methylation status around the CTGF CpG island correlated inversely with the expression, and a putative target region for methylation showed promoter activity. CTGF methylation was frequently observed in primary ovarian cancer tissues (39 of 66, 59%) and inversely correlated with CTGF mRNA expression. In an immunohistochemical analysis of primary ovarian cancers, CTGF protein expression was frequently reduced (84 of 103 cases, 82%). Ovarian cancer tended to lack CTGF expression more frequently in the earlier stages (stages I and II) than the advanced stages (stages III and IV). CTGF protein was also differentially expressed among histologic subtypes. Exogenous restoration of CTGF expression or treatment with recombinant CTGF inhibited the growth of ovarian cancer cells lacking its expression, whereas knockdown of endogenous CTGF accelerated growth of ovarian cancer cells with expression of this gene. These results suggest that epigenetic silencing by hypermethylation of the CTGF promoter leads to a loss of CTGF function, which may be a factor in the carcinogenesis of ovarian cancer in a stage-dependent and/or histologic subtype-dependent manner.

Model for paraaortic lymph node metastasis produced by orthotopic implantation of ovarian carcinoma cells in athymic nude mice

Lymph node metastasis through the lymphatic vessels is a critical step in determining the outcome of ovarian cancer patients, and prognosis should be improved by preventing lymph node metastasis. However, experimental models for lymph node metastasis of ovarian carcinoma are not available. We developed an orthotopic transplantation model to study this process in nude mice using the human ovarian carcinoma cell lines, KF and MH. Highly metastatic sublines (KF-LN3 and MH-LN3) were selected in vivo in nude mice by repeated orthotopic transplantation, lymph node metastasis formation and culturing the tumour cells in vitro. Because this model seems to correspond to the advanced clinical stage of ovarian carcinomas, it should be useful in understanding the molecular biology of ovarian carcinomas and in the development of therapeutic modalities against lymph node metastasis.

Follicle-stimulating hormone promotes the growth of human epithelial ovarian cancer cells through the protein kinase C-mediated system

We have previously described that follicle-stimulating hormone (FSH) stimulated the growth of human epithelial ovarian cancer tissues and cells. In order to determine the signaling pathway on FSH action in ovarian cancer, we used an epithelial ovarian cancer cell line (HRA line) which constitutively FSH receptors (FSHRs). FSH significantly increased cell proliferation (230.1 +/- 20.5%, P < 0.05) and (3)H-thymidine uptake (443.5 +/- 35.1%, P < 0.01). 1-(5-Isoquinolinesulfonyl)-2-methyipiperazine (H7, 1 5 nM), staurosponine (STR, 5 nM) and calphostin C (5 nM), specific protein kinase C (PKC) inhibitors, significantly suppressed the FSH-stimulated cell growth (120.2-140.2%, P < 0.05) and (3)H-thymidine uptake (140.5-173.9%, P < 0.05), whereas N-(2-guanidinoethyl)-5-isoquinoline-sulfon-amide (HA1004, l5 nM), which is a derivant of H7 and inhibits most of protein kinases except PKC, showed no effect on the FSH-stimulated cell growth and (3)H-thymidine uptake. A pretreatment with 12-0-tetradecanoylphorbol-13 acetate (TPA, 100 ng/ml) or STR (20 nM) significantly suppressed the subsequent FSH-stimulated cell growth (TPA; 152.3 +/-10.3%, STR; 160.4 +/- 15.9%, P < 0.05) and (3)H-thymidine uptake (TPA; 250.4 +/-18.3%, STR; 208.7 +/- 15.9%, P < 0.05). STR abolished the suppression of TPA preincubation on the subsequent FSH-stimulated cell growth and (3)H-thymidine uptake. HRA cells constitutively expressed PKCalpha but not PKCbeta nor PKCgamma. The levels of either expression of PKCalpha protein and mRNA were significantly amplified by FSH. These data suggest that stimulation of PKCalpha transcription is involved in the FSH-stimulated cell growth and DNA synthesis in epithelial ovarian cancer cells.

Modulation of protein kinase C in antitumor treatment

PKC isoenzymes were found to be involved in proliferation, antitumor drug resistance and apoptosis. Therefore, it has been tried to exploit PKC as a target for antitumor treatment. PKC alpha activity was found to be elevated, for example, in breast cancers and malignant gliomas, whereas it seems to be underexpressed in many colon cancers. So it can be expected that inhibition of PKC activity will not show similar antitumor activity in all tumors. In some tumors it seems to be essential to inhibit PKC to reduce growth. However, for inhibition of tumor proliferation it may be an advantage to induce apoptosis. In this case an activation of PKC delta should be achieved. The situation is complicated by the facts that bryostatin leads to the activation of PKC and later to a downmodulation and that the PKC inhibitors available to date are not specific for one PKC isoenzyme. For these reasons, PKC modulation led to many contradicting results. Despite these problems, PKC modulators such as miltefosine, bryostatin, safingol, CGP41251 and UCN-01 are used in the clinic or are in clinical evaluation. The question is whether PKC is the major or the only target of these compounds, because they also interfere with other targets. PKC may also be involved in apoptosis. Oncogenes and growth factors can induce cell proliferation and cell survival, however, they can also induce apoptosis, depending on the cell type or conditions in which the cells or grown. PKC participates in these signalling pathways and cross-talks. Induction of apoptosis is also dependent on many additional factors, such as p53, bcl-2, mdm2, etc. Therefore, there are also many contradicting results on PKC modulation of apoptosis. Similar controversial data have been reported about MDR1-mediated multidrug resistance. At present it seems that PKC inhibition alone without direct interaction with PGP will not lead to successful reversal of PGP-mediated drug efflux. One possibility to improve chemotherapy would be to combine established antitumor drugs with modulators of PKC. However, here also very contrasting results were obtained. Many indicate that inhibition, others, that activation of PKC enhances the antiproliferative activity of anticancer drugs. The problem is that the exact functions of the different PKC isoenzymes are not clear at present. So further investigations into the role of PKC isoenzymes in the complex and interacting signalling pathways are essential. It is a major challenge in the future to reveal whether modulation of PKC can be used for the improvement of cancer therapy.

Regulation of proliferation and apoptosis by epidermal growth factor and protein kinase C in human ovarian surface epithelial cells

Epidermal growth factor (EGF) is produced in the ovary and influences proliferation of the malignant ovarian surface epithelium (OSE); yet its role in malignancy or in regulating the normal surface epithelium is unclear. In human OSE cells derived from primary cultures of normal tissue transfected with SV40 large T antigen (IOSE cells), EGF promoted survival but not proliferation. This survival effect was reversed by acute treatment with the phorbol ester, 12-0-tetradecanoyl-13-phorbol acetate (TPA) which alone markedly inhibited IOSE proliferation. We tested whether the activities of the mitogen-activated protein kinases (ERK1/2 and JNK1) varied in response to EGF, TPA, or combinations of these agonists and if the same treatments altered patterns of immediate early gene expression. Alone, EGF activated ERK1/2, increased and sustained levels of c-jun mRNA, but had almost no effect on JNK1 activation. Conversely, PKC activation resulted in a rapid, but transient induction of c-fos RNA and of both kinases, JNK1 and ERK2. When combined, EGF and TPA further enhanced the phosphorylation of both enzymes despite inhibiting survival. Though JNKs and ERKs are thought to transduce opposing cellular responses, in IOSE cells, robust costimulation of the JNK and ERK pathways may redirect the survival message.

Growth-inhibitory effects of N,N-diethyl-2-[4-(phenylmethyl)phenoxy]-ethanamine-HCl combined with cisplatin on human ovarian cancer cells inoculated into nude mice

In 5-day incubation of an estrogen receptor-negative human ovarian cancer cell line (KF) with N,N-diethyl-2-[4-(phenylmethyl)phenoxy]ethanamine-HCl (DPPE), the concentration of DPPE required for 50% inhibition of KF cell proliferation (IC50) was 1.7 microM. The IC50 of DPPE for inhibition of protein kinase C (PKC) activity was 3.0 microM, a similar value to those of other antiestrogens such as tamoxifen and clomiphene. DPPE also inhibited phosphorylation of mitogen-activated protein kinase in KF cells. When treatment with DPPE was started 7 days after inoculation of KF cells into nude mice, 50 mg/kg DPPE alone resulted in a significant growth retardation in the early stage of tumor growth. Although 25 mg/kg DPPE showed a similar effect to 2 mg/kg cisplatin (CDDP), the combination had the most marked tumor growth-inhibitory effect. Nude mice treated with combinations of CDDP and DPPE survived significantly longer than not only untreated, but also CDDP-alone-treated mice, while 50 mg/kg but not 25 mg/kg DPPE alone had an effect comparable to that of 2 mg/kg CDDP alone. If treatment with DPPE was begun from the day after tumor inoculation, the inhibitory effect of DPPE was further enhanced, especially when combined with CDDP. If treatment with DPPE was started in nude mice with a lower tumor burden, 25 mg/kg as well as 50 mg/kg DPPE had a similar effect to 2 mg/kg CDDP, in terms of survival. When DPPE was combined with CDDP, the effect was significantly enhanced, compared to that of either alone. These treatments could be done without any adverse side effect. Thus, we conclude that DPPE has an antiestrogen action and its tumor growth-inhibiting activity is enhanced on administration in combination with CDDP.

Altered expression of gamma-glutamylcysteine synthetase, metallothionein and topoisomerase I or II during acquisition of drug resistance to cisplatin in human ovarian cancer cells

This study was designed to elucidate the mechanisms of cisplatin (CDDP) resistance using two human ovarian cancer cell lines, KF and TYK, and two CDDP-resistant lines, KFr and TYK/R, derived from the former lines. KFr and TYK/R showed about 3-fold higher resistance to the cytotoxic effects of CDDP than their parental lines. They also showed a significant increase in sensitivity to not only etoposide, but also (+)-(4S)-4, 11-diethyl-4-hydroxy-9-[(4-piperidino -piperidino)carbonyloxy]-1H -pyrano[3',4':6,7]inodolizino[1,2-b]quinoline-3,14(4H, 12H)-dione hydrochloride trihydrate (CPT-11). Cellular CDDP accumulation levels in KFr and TYK/R were decreased from those of the parental cells. By contrast, the cellular glutathione (GSH) content in KFr cells was 1.7-fold higher than that in KF, whereas TYK/R cells had a 40% lower content than TYK cells. Cellular mRNA levels of drug-resistance-related genes, such as DNA topoisomerase (topo) I and topo II, glutathione S-transferase-pi (GST-pi), gamma-glutamylcysteine synthetase (gamma-GCS), and metallothionein (hMT) genes, were compared between drug-sensitive KF or TYK and KFr or TYK/R. KFr cells had 8.5- and 24.7-fold higher mRNA levels of gamma-GCS and topo II genes than KF cells while KFr had only a slight increase in GST-pi mRNA level as compared with KF. By contrast, TYK/R cells had 2.9- and 1.7-fold higher hMT and topo I mRNA levels than TYK cells. Acquisition of CDDP resistance in human ovarian cancer cells thus appeared to be related mainly to expression of gamma-GCS, topo II and hMT genes, and partly to that of topo I and GST-pi genes, in addition to a decrease in CDDP accumulation.

Enhancement of antitumour activity of cisplatin by N,N-diethyl-2-[4-(phenylmethyl)phenoxy] ethanamine. HCl in human ovarian cancer cells with intrinsic or acquired resistance to cisplatin

This study was designed to the elucidate sensitising effects of the intracellular histamine antagonist, N,N-diethyl-2[4-(phenylmethyl)phenoxy] ethanamine HCl (DPPE) on the antitumour activity of cis-diamminedichloroplatinum (II) (CDDP) using human ovarian cancer cell lines with different sensitivities to CDDP (KF, sensitive) KFra (acquired CDDP resistant derived from KF), and KK and MH, intrinsically CDDP resistant. The KF cells were most sensitive to CDDP among cell lines used in this study and followed by MH, KK and KFra showing approximately 3.5, 4.0 and 9.1-fold IC50 values to KF, respectively. The acquired CDDP resistant KFra cells were approximately 6.1-fold more sensitive to DPPE than the parent KF cells, while MH and KK cells were more than 10-fold more resistant to DPPE than the KF cells. With regard to the inhibition of human ovarian cancer cell proliferation, phenyltoloxamine and L-histidinol were 5-2500-fold less cytotoxic than DPPE. Analysis of flow cytometry (FCM) revealed that with concentrations based on the IC50 to KF and KFra cells, DPPE resulted in G2-M accumulation in the KF (but not KFra) cells in a time-dependent manner during the course of 48 h incubation time. In addition, from a median effect analysis, DPPE seemed to have additive and somewhat synergistic effects on the antitumour activity of CDDP in KK and MH cells with intrinsic CDDP resistance, while minor antagonism in KFra cells with acquired CDDP resistance was observed. Although DPPE alone did not significantly inhibit the tumour growth of nude mice bearing KF cells, combinations of DPPE with CDDP resulted in improved survival compared with treatment with only CDDP. Adverse side-effects, as confirmed by monitoring haematocrit and the body weight were not observed during the experimental period. These results suggest that DPPE may be of clinical use for the treatment of intrinsically refractory ovarian carcinoma when combined with CDDP.

Multifactorial mechanism for the potentiation of cisplatin (CDDP) cytotoxicity by all-trans retinoic acid (ATRA) in human ovarian carcinoma cell lines

All-trans retinoic acid (ATRA) has been previously shown to inhibit the proliferation of some human ovarian carcinoma cell lines, and this inhibition was accompanied by cellular changes that were indicative of differentiation (Caliaro et al, 1994). In this work, a pretreatment of these adenocarcinoma cells with ATRA, for their respective doubling time, enhanced cisplatin (CDDP) cytotoxicity in the cell ines that were sensitive to its antiproliferative effect, but not in the ATRA-resistant ones. Results were assessed using median effect analysis in two ATRA-sensitive cell lines (OVCCR1 and NIHOVCAR3 cells) and in one ATRA-insensitive cell line (IGROV1 cells). Synergy between these two agents was observed only in cells sensitive to ATRA, regardless of their relative sensitivity to CDDP. Potential mechanisms for this synergy were investigated. ATRA did not increase the cellular platinum content, did not decrease the cellular glutathione and had no influence on the metallothionein IIA mRNA levels in NIHOVCAR3 cells. Moreover, the protein kinase C (PKC) activity was modulated by this differentiating agent in all cell lines tested, indicating that this activity was not directly involved in this potentiation. However, an ATRA inhibition of glutathione-S-transferase activity associated with an increase in the total DNA adducts formation could explain the potentiation of the CDDP cytotoxicity observed in NIHOVCAR3 cells. Finally, the ATRA modulation of the epidermal growth factor (EGF) receptor mRNA level could also be implicated in this synergy.

Cytotoxicity of antitumor platinum complexes with L-buthionine-(R,S)-sulfoximine and/or etanidazole in human carcinoma cell lines sensitive and resistant to cisplatin

Human 2008 ovarian carcinoma cells and the C13 CDDP-resistant subline and human MCF-7 breast carcinoma cells and the MCF-7/CDDP CDDP-resistant subline were exposed to L-buthionine-(S,R)-sulfoximine (50 microM) for 48 h prior to and during exposure for 1 h to the antitumor platinum complexes, cis-diamminedichloroplatinum(II), carboplatin or D,L-tetraplatin and/or to etanidazole (1 mM) for 2 h prior to and during exposure for 1 to the antitumor platinum complexes. These modulators alone did not significantly alter the cytotoxicity of CDDP toward either parental line. A twofold enhancement in cytotoxicity was observed with carboplatin in the 2008 cells and with D,L-tetraplatin in both parental lines with the single modulators. The modulator combination (buthionine sulfoximine/etanidazole) was very effective along with D,L-tetraplatin in both the MCF-7 parent and MCF-7/CDDP cell lines where at the higher platinum complex concentrations there was 1.5 to 3 logs increased killing of cells by the drug plus the modulators compared with the drug alone. Similarly, when C13 cells were exposed to CDDP (100 microM) or D,L-tetraplatin (100 microM) along with buthionine sulfoximine and etanidazole there was a 2-log increase in cell killing compared with exposure to the platinum complex alone. Treatment of each of the four cell lines with buthionine sulfoximine decreased both the non-protein and total sulfhydryl content of the cells. Treatment with the combination of modulators did not produce a further decrease in cellular sulfhydryl content compared with buthionine sulfoximine alone. The total sulfhydryl content in MCF-7 cells and 2008 cells exposed to buthionine sulfoximine and etanidazole was 58% and 31% of normal and the total sulfhydryl content of MCF-7/CDDP cells and C13 cells treated the same way was 54% and 23% of normal, respectively. DNA alkaline elution was used to assess the impact of exposure to the modulators, buthionine sulfoximine and etanidazole, alone and in combination on the cross linking of DNA by the antitumor platinum complexes in the MCF-7 and MCF-7/CDDP cell lines. Overall, the increases in DNA cross linking factors were greater in the MCF-7 cells than in the MCF-7/CDDP cells. These results indicate a possible clinical potential for this modulator combination.

Preclinical studies of antitumor prostaglandins by using human ovarian cancer cells

Pleiotropic actions of antitumor prostaglandins (PGs) on tumor cells are reviewed including our preclinical results focused on human ovarian cancer. Regarding inhibition of cell proliferation, antitumor PGs exerts its action as a G1 blocking agent. The cyclopentenone PGs inhibit myc oncogene expression while inhibiting the cell cycle progression and results in apoptotic cell death and growth inhibition. Cyclopentenone PGs inhibit growth of various tumors transplanted to mice or nude mice and show adjuvant effects to cis-diamminedichloroplatinum(II) (CDDP). In order to elucidate a role of antitumor PGs in immune systems, relevance of effects on tumor growth with those on the immune systems are also discussed with our results.