Cyclosporin A suppresses cisplatin-induced oncogene expression in human cancer cells

Synergistic Effects of Sanglifehrin-Based Cyclophilin Inhibitor NV651 with Cisplatin in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC), commonly diagnosed at an advanced stage, is the most common primary liver cancer. Owing to a lack of effective HCC treatments and the commonly acquired chemoresistance, novel therapies need to be investigated. Cyclophilins-intracellular proteins with peptidyl-prolyl isomerase activity-have been shown to play a key role in therapy resistance and cell proliferation. Here, we aimed to evaluate changes in the gene expression of HCC cells caused by cyclophilin inhibition in order to explore suitable combination treatment approaches, including the use of chemoagents, such as cisplatin. Our results show that the novel cyclophilin inhibitor NV651 decreases the expression of genes involved in several pathways related to the cancer cell cycle and DNA repair. We evaluated the potential synergistic effect of NV651 in combination with other treatments used against HCC in cisplatin-sensitive cells. NV651 showed a synergistic effect in inhibiting cell proliferation, with a significant increase in intrinsic apoptosis in combination with the DNA crosslinking agent cisplatin. This combination also affected cell cycle progression and reduced the capacity of the cell to repair DNA in comparison with a single treatment with cisplatin. Based on these results, we believe that the combination of cisplatin and NV651 may provide a novel approach to HCC treatment.

Novel Cyclophilin Inhibitor Decreases Cell Proliferation and Tumor Growth in Models of Hepatocellular Carcinoma

Simple Summary

Cyclophilins, a family of proteins with peptidyl prolyl isomerase activity, have been found to be overexpressed in several cancers, including hepatocellular carcinoma (HCC), and their expression is correlated to a poor prognosis. Cyclophilins play an important role in proliferation and cancer resistance in HCC. In this study, we evaluated the potential capacity of cyclophilin inhibitors as a treatment against HCC. We showed that our selected cyclophilin inhibitor, NV651, was able to decrease cell proliferation in vitro and induce an accumulation of cells in the G₂/M phase due to a mitotic block. We could also confirm its capacity to decrease tumor growths in mice and its safety in vitro as well as in vivo.

Abstract

Hepatocellular carcinoma (HCC), the most common primary liver cancer, is usually diagnosed in its late state. Tyrosine kinase inhibitors such as sorafenib and regorafenib are one of the few treatment options approved for advanced HCC and only prolong the patient’s life expectancy by a few months. Therefore, there is a need for novel effective treatments. Cyclophilins are intracellular proteins that catalyze the cis/trans isomerization of peptide bonds at proline residues. Cyclophilins are known to be overexpressed in HCC, affecting therapy resistance and cell proliferation. In the present study, we explored the potential of cyclophilin inhibitors as new therapeutic options for HCC in vitro and in vivo. Our results showed that the novel cyclophilin inhibitor, NV651, was able to significantly decrease proliferation in a diverse set of HCC cell lines. The exposure of HCC cells to NV651 caused an accumulation of cells during mitosis and consequent accumulation in the G₂/M phase of the cell cycle. NV651 reduced tumor growth in vivo using an HCC xenograft model without affecting the body weights of the animals. The safety aspects of NV651 were also confirmed in primary human hepatocytes without any cytotoxic effects. Based on the results obtained in this study, we propose NV651 as a potential treatment strategy for HCC.

PRKAR1B-AS2 Long Noncoding RNA Promotes Tumorigenesis, Survival, and Chemoresistance via the PI3K/AKT/mTOR Pathway

Many long noncoding RNAs have been implicated in tumorigenesis and chemoresistance; however, the underlying mechanisms are not well understood. We investigated the role of PRKAR1B-AS2 long noncoding RNA in ovarian cancer (OC) and chemoresistance and identified potential downstream molecular circuitry underlying its action. Analysis of The Cancer Genome Atlas OC dataset, in vitro experiments, proteomic analysis, and a xenograft OC mouse model were implemented. Our findings indicated that overexpression of PRKAR1B-AS2 is negatively correlated with overall survival in OC patients. Furthermore, PRKAR1B-AS2 knockdown-attenuated proliferation, migration, and invasion of OC cells and ameliorated cisplatin and alpelisib resistance in vitro. In proteomic analysis, silencing PRKAR1B-AS2 markedly inhibited protein expression of PI3K-110α and abrogated the phosphorylation of PDK1, AKT, and mTOR, with no significant effect on PTEN. The RNA immunoprecipitation detected a physical interaction between PRKAR1B-AS2 and PI3K-110α. Moreover, PRKAR1B-AS2 knockdown by systemic administration of 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine nanoparticles loaded with PRKAR1B-AS2–specific small interfering RNA enhanced cisplatin sensitivity in a xenograft OC mouse model. In conclusion, PRKAR1B-AS2 promotes tumor growth and confers chemoresistance by modulating the PI3K/AKT/mTOR pathway. Thus, targeting PRKAR1B-AS2 may represent a novel therapeutic approach for the treatment of OC patients.

Berberine, an epiphany against cancer

Alkaloids are used in traditional medicine for the treatment of many diseases. These compounds are synthesized in plants as secondary metabolites and have multiple effects on cellular metabolism. Among plant derivatives with biological properties, the isoquinoline quaternary alkaloid berberine possesses a broad range of therapeutic uses against several diseases. In recent years, berberine has been reported to inhibit cell proliferation and to be cytotoxic towards cancer cells. Based on this evidence, many derivatives have been synthesized to improve berberine efficiency and selectivity; the results so far obtained on human cancer cell lines support the idea that they could be promising agents for cancer treatment. The main properties of berberine and derivatives will be illustrated.

Use of ribozymes and antisense oligodeoxynucleotides to investigate mechanisms of drug resistance

Chemotherapy can cure a number of human cancers but resistance (either intrinsic or acquired) remains a significant problem in many patients and in many types of solid tumour. Combination chemotherapy (using drugs with different cellular targets/mechanisms) was introduced in order to kill cells which had developed resistance to a specific drug, and to allow delivery of a greater total dose of anti-cancer chemicals by combining drugs with different side-effects (Pratt et al., 1994). Nearly all anti-cancer drugs kill tumour cells by activating an endogenous bio-chemical pathway for cell suicide, known as programmed cell death or apoptosis.

Protein-protein interface-binding peptides inhibit the cancer therapy target human thymidylate synthase

Human thymidylate synthase is a homodimeric enzyme that plays a key role in DNA synthesis and is a target for several clinically important anticancer drugs that bind to its active site. We have designed peptides to specifically target its dimer interface. Here we show through X-ray diffraction, spectroscopic, kinetic, and calorimetric evidence that the peptides do indeed bind at the interface of the dimeric protein and stabilize its di-inactive form. The "LR" peptide binds at a previously unknown binding site and shows a previously undescribed mechanism for the allosteric inhibition of a homodimeric enzyme. It inhibits the intracellular enzyme in ovarian cancer cells and reduces cellular growth at low micromolar concentrations in both cisplatin-sensitive and -resistant cells without causing protein overexpression. This peptide demonstrates the potential of allosteric inhibition of hTS for overcoming platinum drug resistance in ovarian cancer.

Anti-apoptotic effects of protein kinase C-delta and c-fos in cisplatin-treated thyroid cells

BACKGROUND AND PURPOSE

We showed previously that cisplatin inititates a signalling pathway mediated by PKC-delta/extracellular signal-regulated kinase (ERK), important for maintaining viability in PC Cl3 thyroid cells. The studies described herein examined whether c-fos was associated with cisplatin resistance and the signalling link between c-fos and PKC-delta/ERK.

EXPERIMENTAL APPROACH

Cells were treated with various pharmacological inhibitors of PKCs and ERK, or were depleted of c-fos, PKC-delta, PKC-epsilon and caspase-3 by small interfering RNA (siRNA), then incubated with cisplatin and cytotoxicity assessed.

KEY RESULTS

Cisplatin provokes the induction of c-fos and the activation of conventional PKC-beta, and novel PKC-delta and -epsilon. The cisplatin-provoked c-fos induction was decreased by Gö6976, a PKC-beta inhibitor; by siRNA for PKC-delta- but not that for PKC-epsilon or by PD98059, a mitogen-activated protein kinase/ERK kinase inhibitor. Expression of c-fos was abolished by GF109203X, an inhibitor of all PKC isoforms, or by PD98059 plus Gö6976 or by PKC-delta-siRNA plus Gö6976. When c-fos expression was blocked by siRNA, cisplatin cytotoxicity was strongly enhanced with increased caspase-3 activation. In PKC-delta-depleted cells treated with cisplatin, caspase-3 activation was increased and cell viability decreased. In these PKC-delta-depleted cells, PD98059 did not affect caspase-3 activation.

CONCLUSIONS AND IMPLICATIONS

In PC Cl3 cells, in the cell signalling pathways that lead to cisplatin resistance, PKC-delta controls ERK activity and, together with PKC-beta, also the induction of c-fos. Hence, the protective role of c-fos in thyroid cells has the potential to provide new opportunities for therapeutic intervention.

Phase II trial of carboplatin and infusional cyclosporine with alpha-interferon in recurrent ovarian cancer: a California Cancer Consortium Trial

The purpose of this study was to estimate the response rate of 26-h continuous infusion cyclosporine A (CSA) combined with carboplatin (CBDCA) and subcutaneous alpha-interferon (IFN), in recurrent ovarian cancer (OC), and to measure their effects on CBDCA pharmacokinetics. OC patients relapsing following platinum-based chemotherapy received CBDCA area under the curve (AUC 3) with CSA and IFN, every 3 weeks. The pharmacokinetics of CSA and CBDCA were determined in a subset of patients. Thirty patients received 84 courses of therapy. Three partial responses were observed. Nine patients were stable for >4 months. Toxicity was similar to that observed in our previously reported phase I study and consisted of myelosuppression, nausea, vomiting, and headache. The mean end of infusion CSA level (high-performance liquid chromatographic assay [HPLC]) was 1109 +/- 291 microg/mL (mean +/- SD). CBDCA pharmacokinetics revealed a measured AUC of 3.61 versus a targeted AUC of 3, suggesting a possible effect of IFN on CBDCA levels versus errors in the estimation of CBDCA clearance using measured creatinine clearance. Steady-state levels of >1 microg/mL CSA (HPLC assay) are achievable in vivo. Insufficient clinical resistance reversal was observed in this study to warrant further investigation of this combination.

Phase II trial of carboplatin and infusional cyclosporine in platinum-resistant recurrent ovarian cancer

PURPOSE

To determine the response rate to 26-h continuous infusion cyclosporine A (CSA) combined with a fixed dose level of carboplatin (CBDCA) in patients with recurrent ovarian cancer, and to determine the effect of CSA on the pharmacokinetics of CBDCA.

EXPERIMENTAL DESIGN

To examine the effect of duration of CSA exposure on reversal of CBDCA resistance, clonogenic assays were performed in vitro in platinum-resistant A2780 cells. CBDCA (AUC 4) with CSA repeated every 3 weeks was then administered to patients on this phase II study. Pharmacokinetics of CSA and CBDCA were determined in a subset of patients.

RESULTS

Preincubation of platinum-resistant A2780 cells with CSA reversed CBDCA resistance in a concentration-dependent and time-dependent manner. A group of 23 patients received 58 courses of CBDCA/CSA therapy. One partial response was observed. Eight patients achieved disease stabilization. Toxicity was similar to that observed in our previous phase I study and consisted of myelosuppression, nausea, vomiting, and headache. The mean +/- SD end-of-infusion CSA level (HPLC assay) was 1253 +/- 400 microg/ml. The pharmacokinetic studies suggest that CSA does not increase CBDCA AUC.

CONCLUSIONS

Steady-state levels of >1 microg/ml CSA (HPLC assay) are achievable in vivo. Modest partial reversal of platinum resistance (in one patient with an objective response and in eight patients with stable disease noted) is achievable in vivo in patients pretreated with CSA. This phenomenon is not explained by alterations in CBDCA pharmacokinetics.

Methodologic guidelines for the design of high-dose chemotherapy regimens

PURPOSE

The objective of this report is to review the research methods that have been used in the design, analysis, and reporting of Phase I dose-escalation studies of high-dose chemotherapy (HDCT) with bone marrow or stem cell support and to propose new guidelines for such studies that incorporate emerging principles of pharmacology, toxicity assessment, statistical design, and long-term follow-up.

METHODS

We performed a search of original, English-language, peer-reviewed full-length reports of HDCT (with or without radiotherapy) and unmanipulated hematopoietic precursor support (autologous bone marrow or stem cells or allogeneic bone marrow) in which one or more drug doses were escalated to identify dose-limiting toxicities needed for the design of subsequent Phase II trials. We reviewed the design, execution, analysis, and reporting of these trials to develop a coherent set of guidelines for the initiation of new HDCT regimens. The primary elements included in our analysis were the technique of dose escalation, the choice and application of toxicity grading scale, and the pharmacologic correlates of dose escalation. We also evaluated the methods employed to define dose-limiting toxicities and to select the maximum tolerated dose and the dose recommended for further study. We then examined whether subsequent Phase II trials based on these definitions corroborated the findings from the prior Phase I studies and summarized the findings from pharmacologic analyses that were reported from a subset of these investigations.

RESULTS

Thirty-five reports met the criteria for our literature review. Two standard methods of dose escalation (fixed increments or modified Fibonacci increments) were described in detail and were employed in the majority (30/35) of the studies. In 5 studies, the details of dose escalation were either not provided or not adequately referenced. There was marked heterogeneity among toxicity grading methods; scales used included the National Cancer Institute Common Toxicity Criteria (or similar scales such as the United States cooperative group or World Health Organization scales) as well as substantially modified versions of those instruments. Wide variations in the methods used to identify dose-limiting toxicities were observed. Statistical considerations, applied to the identification of the maximum tolerated or Phase II recommended dose, were similarly heterogeneous. Phase II trial designs varied from a simple expansion of the Phase I trial to separate, formally conducted studies. Nine Phase I trials featured pharmacologic analyses, and these ranged from simple pharmacokinetic evaluations to more complex analyses of the relationship between drug dose and the molecular targets of drug action.

CONCLUSIONS

Phase I clinical trials in the HDCT setting have been designed, analyzed, and reported using heterogeneous methods that limited their application to Phase II and II investigations. Moreover, correlative pharmacologic analyses have not been routinely undertaken during this critical Phase I stage. We propose guidelines for the design of new Phase I studies of HDCT based on 4 essential elements: (1) rational preclinical and clinical pharmacologic foundation for the regimen and for the agent selected for dose escalation; (2) incorporation of analytical pharmacology in the design and analysis of the regimen under investigation; (3) clear, prospective definitions of the dose- or exposure-limiting toxicities that can be distinguished from modality-dependent toxicities; selection of an appropriate toxicity grading scale, including an assessment of cumulative, delayed, and long-term effects of HDCT, particularly when designing tandem or repetitive cycle regimens; and (4) statistical input into the design, execution, analysis, interpretation, and reporting of these studies.

Reversal of cisplatin and multidrug resistance by ribozyme-mediated glutathione suppression

gamma-Glutamylcysteine synthetase (gamma-GCS) is a key enzyme in glutathione (GSH) synthesis, and is thought to play a significant role in intracellular detoxification, especially of anticancer drugs. Increased levels of GSH are commonly found in the drug-resistant human cancer cells. We designed a hammerhead ribozyme against gamma-GCS mRNA (anti-gamma-GCS Rz), which specifically down-regulated gamma-GCS gene expression in the HCT-8 human colon cancer cell line. The aim of this study was to reverse the cisplatin and multidrug resistance for anticancer drugs. The cisplatin-resistant HCT-8 cells (HCT-8DDP cells) overexpressed MRP and MDR1 genes, and showed resistance to not only cisplatin (CDDP), but also doxorubicin (DOX) and etoposide (VP-16). We transfected a vector expressing anti-gamma-GCS Rz into the HCT-8DDP cells (HCT-8DDP/Rz). The anti-gamma-GCS Rz significantly suppressed MRP and MDR, and altered anticancer drug resistance. The HCT-8DDP/Rz cells were more sensitive to CDDP, DOX and VP-16 by 1.8-, 4.9-, and 1.5-fold, respectively, compared to HCT-8DDP cells. The anti-gamma-GCS Rz significantly down-regulated gamma-GCS gene expression as well as MRP/MDR1 expression, and reversed resistance to CDDP, DOX and VP-16. These results suggested that gamma-GCS plays an important role in both cisplatin and multidrug resistance in human cancer cells.

Cisplatin resistance and oncogenes--a review

Cisplatin is among the most widely used broadly active cytotoxic anticancer drugs; however, its clinical efficacy is often limited by primary or the development of secondary resistance. Several mechanisms have been implicated in cisplatin resistance, including reduced drug uptake, increased cellular thiol/folate levels and increased DNA repair. More recently, additional pathways have been characterized indicating that altered expression of oncogenes that subsequently limit the formation of cisplatin-DNA adducts and activate anti-apoptotic pathways may also contribute to the resistance phenotype. Several lines of evidence suggest that expression of ras oncogenes can confer resistance to cisplatin by reducing drug uptake and increasing DNA repair; however, this is not a uniform finding. Tumor cells, in contrast to normal cells, respond to cisplatin exposure with transient gene expression to protect or repair their chromosomes. The c-fos/AP-1 complex, a master switch for turning on other genes in response to DNA-damaging agents, has been shown to play a major role in cisplatin resistance. In addition, AP-2 transcription factors, modulated by protein kinase A, are also implicated in cisplatin resistance by regulating genes encoding for DNA polymerase beta and metallothionines. Furthermore, considerable evidence indicates that mutated p53 plays a significant role in the development of cisplatin resistance since several genes implicated in drug resistance and apoptosis (e.g. mismatch repair, bcl-2, high mobility group proteins, DNA polymerases alpha and beta, PCNA, and insulin-like growth factor) are known to be regulated by the p53 oncoprotein. Improved understanding of molecular factors for the development of cisplatin resistance may allow the prediction of clinical response to cisplatin-based treatment. Furthermore, the identification of oncogenes involved in cisplatin resistance has already led to in vitro approaches which successfully inactivated these genes using ribozymes or antisense oligodeoxynucleotides, thus restoring cisplatin sensitivity. It is conceivable that these strategies, once transferred to a clinical setting, may have the potential to enhance the efficacy of cisplatin against a great variety of malignancies and thus more fully exploit the antineoplastic and curative potential of this drug.

Influence of the proto-oncogene c-fos on cisplatin sensitivity

Cisplatin resistance has been associated with overexpression of the c-fos gene in a human ovarian carcinoma cell line. To determine whether the correlation between c-fos overexpression and cisplatin resistance was limited to this cell line or was a more generalized phenomenon, we investigated cisplatin sensitivity in rat fibroblast cells that overexpressed the c-fos gene. The cisplatin Ic50 values for two different c-fos transfectants, CMVc-fos and L1-3c-fos, were 7.6 +/- 0.8 and 5.6 +/- 1.0 microM, respectively, whereas the cisplatin Ic50 value for the parental line, 208F, was 2.4 +/- 0.1 microM. This represented a 3.2- and 2.3-fold resistance to cisplatin for CMVc-fos and L1-3c-fos cells, respectively. The correlation between c-fos expression and cisplatin resistance also was examined in a human ovarian carcinoma cell line, 2008, and its cisplatin-resistant variant, C13*. Expression of c-fos was elevated slightly at both the mRNA and protein levels in the C13* cells compared with 2008 cells, and c-Fos protein levels were induced in C13* cells following cisplatin treatment. In addition, it was observed that C13* cells were significantly more sensitive than 2008 cells to a c-fos antisense oligonucleotide. The Ic50 values for the c-fos antisense oligonucleotide were 19.9 +/- 5.0 pmol for C13* cells and 58.1 +/- 6.0 pmol for 2008 cells (P = 0.0012). Furthermore, combinations of c-fos antisense and cisplatin reduced the amount of cisplatin required to kill 50% of the C13* cells, although the interaction was not synergistic. These results suggest that expression of the c-fos gene can influence cisplatin sensitivity, and that c-fos antisense oligonucleotide based therapy may be effective at killing parental and cisplatin-resistant ovarian carcinoma cells, either alone or in combination with cisplatin.

Mitochondrial membrane potential regulation is independent of c-fosexpression

Tumour cells contain mitochondria with elevated membrane potentials compared with normal cells, and thus this feature provides a selective target for destroying tumour cells. To improve mitochondrial-based therapies, a better understanding of the factors involved in regulating mitochondria are required. Since v-fos overexpression has been shown to elevate mitochondrial membrane potentials in rat fibroblasts, we investigated whether the human homologue, c-fos, was also capable of regulating the mitochondrial membrane potential in cells. Rat fibroblasts transfected with the c-fos gene did not accumulate more rhodamine 123 (Rh123) nor did they retain this Rh123 for extended periods of time compared with their parental line. Moreover, there was no difference in survival following dequalinium chloride (Deca) treatment between transfectants and controls. Similarly, reduction of c-fos expression in rat fibroblasts did not significantly alter their mitochondrial membrane potential. In addition, human ovarian carcinoma cells, which overexpress the c-fos gene, did not accumulate more Rh123 nor were they hypersensitive to Deca compared with their parental line. In another human ovarian carcinoma cell line, selection of variants with lower mitochondrial membrane potential did not alter c-fos mRNA or protein levels. These data suggest that alterations in c-fos expression do not regulate the magnitude of the mitochondrial membrane potential.Key words: c-fos, mitochondria, membrane potential, rhodamine 123 (Rh123), lipophilic cations.

Modulation of excision repair cross complementation group 1 (ERCC-1) mRNA expression by pharmacological agents in human ovarian carcinoma cells

Excision repair cross complementation group 1 (ERCC-1) is a DNA repair gene that is essential for life, and it appears to be a marker gene for nucleotide excision repair activity. Overexpression of ERCC-1 during cisplatin-based chemotherapy is associated with clinical and cellular drug resistance. We therefore began to assess the influence of various pharmacological agents on the induction of ERCC-1 mRNA in A2780/CP70 human ovarian carcinoma cells. Cisplatin exposure in culture resulted in a 4- to 6-fold induction for the steady-state level of ERCC-1 mRNA in A2780/CP70 cells. ERCC-1 mRNA induction was concentration and time dependent. Cyclosporin A and herbimycin A, which suppress c-fos and c-jun gene expressions, respectively, blocked the cisplatin-induced increase in ERCC-1 mRNA. This effect of cyclosporin A or herbimycin A on the down-regulation of ERCC-1 correlates with enhanced cytotoxicity of cisplatin in this system. The products of c-fos and c-jun are components of the transcription factor AP-1 (activator protein 1). 12-O-Tetradecanoylphorbol 13-acetate (TPA), a known AP-1 agonist, induced ERCC-1 mRNA to the same extent as cisplatin, but did not synergize with cisplatin in this regard. The TPA effect was biphasic, with an initial increase during the first 1-6 hr, followed by decreasing mRNA levels at 24-72 hr. These data suggest that the effects of these pharmacological agents on ERCC-1 gene expression may be mediated through the modulation of AP-1 activities.

Malignant neoplasms in cyclosporin A-induced autoimmunity (CyA-AI)

Lethally X-irradiated LEW rats reconstituted with syngeneic bone marrow and given low-dose Cyclosporine A (CyA) for 5 weeks develop, after withdrawal of CyA, symptoms of disease resembling graft-vs.-host disease (GVHD) as seen after allogeneic bone-marrow transplantation. Symptoms of disease may include acute dermatitis and chronic disease resembling scleroderma. Since anti-class II MHC cytotoxic lymphocytes are generated in this model, it has been proposed as an anti-tumor regimen in humans. We now report that LEW rats treated according to this protocol may, after cessation of CyA administration, paradoxically develop malignant neoplasms. Of 48 experimental animals, 31 developed rapidly progressive subcutaneous and/or intracutaneous tumors commencing at 6 weeks, 13 weeks and 6 months after cessation of CyA. Tumors were of mesenchymal origin, usually high-grade sarcoma, adenocarcinoma or both mesenchymal and epithelial tumors. Such tumor incidence exceeded the incidence of tumor growth in X-irradiated controls, and in rats subjected to thymectomy prior to X-irradiation and CyA administration. CyA by itself induced no tumors. Our results show that total body X-irradiation is required for tumor development but that the presence of CyA-induced autoimmune disease increases the incidence significantly.

Expression of resistance-related proteins in tumoral and peritumoral tissues of patients with lung cancer

Twenty tumoral and peritumoral tissues from patients with lung cancer were analyzed immunohistochemically for the drug resistance-related proteins P-glycoprotein (P-170), topoisomerase II (Topo-II), glutathione S-transferase-pi (GST-pi), metallothionein (MT), heat shock protein-70 (HSP-70) and the putative regulators of resistance (ErbB1, Fos and Jun). Protein expression of Topo-II, GST-pi, MT, HSP-70, ErbB1, Fos and Jun was elevated in tumor tissue in comparison to normal tissue. The different expression of the proteins between tumoral and normal tissues was statistically significant for Topo-II (P = 0.05), MT (P = 0.03), and HSP-70 (P = 0.01), whereas ErbB1 showed a borderline significance. The expression of the proteins was frequently increased in smokers in comparison to non-smokers. In general, the increase of the proteins of smokers corresponded in tumoral and non-tumoral tissue. Different expression was only found with MT and HSP-70 which were higher in tissues of smokers.

Modulation of resistance to cisplatin by amphotericin B and aphidicolin in human larynx carcinoma cells

The aim of this study was to examine whether resistance to cisplatin [cis-diamminedichloroplatinum (II)] (CDDP) could be overcome by amphotericin B, cyclosporin A and aphidicolin in two sublines of human larynx carcinoma HEp2 cells. The sensitivity of parental and cisplatin-resistant CA3 and CK2 cells to amphotericin B, cyclosporin A and aphidicolin, and also the effects of these drugs (given in maximal nontoxic concentrations) on cisplatin sensitivity were determined by clonogenic survival assay. CA3 and CK2 cells were sensitive to amphotericin B, and resistant to cyclosporin A and aphidicolin, compared with their parental cells. Amphotericin B increased cisplatin toxicity 2-fold in CA3 cells and 2.7-fold in CK2 cells, while it had no effect in parental HEp2 cells. Cyclosporin A did not influence the sensitivity of examined cells to cisplatin. The sensitizing effect of aphidicolin was more obvious in cisplatin-resistant cells. Cisplatin toxicity was increased by aphidicolin: 1.5-fold in HEp2 cells, 2-fold in CA3 cells, and 1.9-fold in CK2 cells. Therefore, the resistance to cisplatin in human larynx carcinoma CA3 and CK2 cells can be partially reversed by amphotericin B and aphidicolin.

Drug resistance in brain tumors

Resistance to chemotherapy in brain tumors is complex and may involve multiple mechanisms. For commonly used drugs, such as nitrosoureas and platinum compounds, major mechanisms may involve increaded DNA repair or removal of the drug-DNA adducts. For water soluble nitrosoureas and also for platinum compounds, other mechanisms, such as alteration in drug transport, may be important. Another major mechanism may involve glutathione and glutathione-S-transferase pathways. For vinca alkaloids and epipodophyllotoxins p-glycoprotein mediated MDR appears to be the major feature in drug resistance. In addition, alteration of tubulin and topoisomerase II have been described in resistance to vinca alkaloids and epipodophyllotoxins respectively. Recently, increased multidrug resistance associated protein gene expression has been found in glioma cells and brain tumor samples; its clinical significance requires further investigation.

BCNU-resistant human glioma cells with over-representation of chromosomes 7 and 22 demonstrate increased copy number and expression of platelet-derived growth factor genes

We used standard karyotypic analyses of first-division cells to identify a subpopulation of cells in primary malignant gliomas with over-representation of chromosomes 7 and 22. These cells are a minor subpopulation in the primary tumor but become the dominant population after treatment in vitro of the cells with the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). The selection for a cell with this specific karyotypic abnormality suggests that these chromosomes contain genes important to the growth of BCNU-resistant cells. Southern blot hybridization analyses demonstrate an increased copy number of the genes encoding platelet-derived growth factor (PDGF) A-chain and B-chain, which have been mapped to chromosomes 7 and 22, respectively. Reverse transcription followed by polymerase chain reaction (RT-PCR) analysis demonstrates increased expression of these genes. In addition, these cells secrete a mitogenic factor that stimulates 3H-thymidine uptake in NIH 3T3 cells. This factor is sensitive to anti-PDGF antibodies and beta-mercaptoethanol, but not to anti-EGF antibodies. These data suggest that autocrine and/or paracrine mechanisms occur in human malignant gliomas, and that over-expression of PDGF may play a role in the growth of BCNU-resistant cells in these tumors.

Cisplatin resistance in human cancers

Cancer chemotherapeutic agents primarily act by damaging cellular DNA directly or indirectly. Tumor cells, in contrast to normal cells, respond to cisplatin with transient gene expression to protect and/or repair their chromosomes. Repeated cisplatin treatments results in a stable resistant cell line with enhanced gene expression but lacking gene amplification for the proteins that will limit cisplatin cytotoxicity. Recently, several new human cell lines have been characterized for cisplatin resistance. These cell lines have led to a better understanding of the molecular and biochemical basis of cisplatin resistance. The c-fos proto-oncogene, a master switch for turning on other genes in response to a wide range of stimuli, has been shown to play an important role in cisplatin resistance both in vitro and in patients. Based on these studies, new strategies have been developed to circumvent and/or exploit clinical cisplatin resistance.