Cell cycle changes associated with formation of Pt-DNA adducts in human ovarian carcinoma cells with different cisplatin sensitivity

Cellular Toxicity Mechanisms and the Role of Autophagy in Pt(IV) Prodrug-Loaded Ultrasmall Iron Oxide Nanoparticles Used for Enhanced Drug Delivery

Ultrasmall iron oxide nanoparticles (<10 nm) were loaded with cis-diamminetetrachloroplatinum (IV), a cisplatin (II) prodrug, and used as an efficient nanodelivery system in cell models. To gain further insight into their behavior in ovarian cancer cells, the level of cellular incorporation as well as the platination of mitochondrial and nuclear DNA were measured using inductively coupled plasma mass spectrometry (ICP-MS) strategies. Quantitative Pt results revealed that after 24 h exposure to 20 µM Pt in the form of the Pt(IV)-loaded nanoparticles, approximately 10% of the incorporated Pt was associated with nuclear DNA. This concentration increased up to 60% when cells were left to stand in drug-free media for 3 h. These results indicated that the intracellular reducing conditions permitted the slow release of cisplatin (II) from the cisplatin (IV)-loaded nanoparticles. Similar results were obtained for the platination of mitochondrial DNA, which reached levels up to 17,400 ± 75 ng Pt/ mg DNA when cells were left in drug-free media for 3 h, proving that this organelle was also a target for the action of the released cisplatin (II). The time-dependent formation of Pt-DNA adducts could be correlated with the time-dependent decrease in cell viability. Such a decrease in cell viability was correlated with the induction of apoptosis as the main route of cell death. The formation of autophagosomes, although observed upon exposure in treated cells, does not seem to have played an important role as a means for cells to overcome nanoparticles’ toxicity. Thus, the designed nanosystem demonstrated high cellular penetration and the “in situ” production of the intracellularly active cisplatin (II), which is able to induce cell death, in a sustained manner.

Cisplatin's potential for type 2 diabetes repositioning by inhibiting CDKN1A, FAS, and SESN1

Cisplatin is a DNA-damaging chemotherapeutic agent used for treating cancer. Based on cDNA dataset analysis, we investigated how cisplatin modified gene expression and observed cisplatin-induced dysregulation and system-level variations relating to insulin resistance and type 2 diabetes mellitus (T2DM). T2DM is a multifactorial disease affecting 462 million people in the world, and drug-induced T2DM is a serious issue. To understand this etiology, we designed an integrative, system-level study to identify associations between cisplatin-induced differentially expressed genes (DEGs) and T2DM. From a list of differential expressed genes, cisplatin downregulated the cyclin-dependent kinase inhibitor 1 (CDKN1A), tumor necrosis factor (FAS), and sestrin-1 (SESN1) genes responsible for modifying signaling pathways, including the p53, JAK-STAT, FOXO, MAPK, mTOR, P13-AKT, Toll-like receptor (TLR), adipocytokine, and insulin signaling pathways. These enriched pathways were expressively associated with the disease. We observed significant gene signatures, including SMAD3, IRS, PDK1, PRKAA1, AKT, SOS, RAS, GRB2, MEK1/2, and ERK, interacting with source genes. This study revealed the value of system genetics for identifying the cisplatin-induced genetic variants responsible for the progression of T2DM. Also, by cross-validating gene expression data for T2DM islets, we found that downregulating IRS and PRK families is critical in insulin and T2DM signaling pathways. Cisplatin, by inhibiting CDKN1A, FAS, and SESN1, promotes IRS and PRK activity in a similar way to rosiglitazone (a popular drug used for T2DM treatment). Our integrative, network-based approach can help in understanding the drug-induced pathophysiological mechanisms of diabetes.

Targeting Ovarian Cancer Cell Cytotoxic Drug Resistance Phenotype with Xanthium strumarium L. Extract

Emerging drugs aim at targeting the genomic integrity and replication machinery in ovarian cancer. While the antiproliferative activity of Xanthium strumarium L. extract (XFC), a traditional herbal medicine, is believed to alter the mitotic apparatus of Chinese hamster ovary epithelial cells, its capacity to target and overcome the chemoresistance phenotype in ovarian cancer is unknown. Among the cancer cell lines tested, we found that the best proliferation inhibitory effect for XFC was against ovarian cancer cells and ranged from 30 to 35 μg/mL. XFC efficiently targeted both the cytotoxic drug chemoresistance phenotype of SKOV-3 cells and of the chemosensitive ES-2 cells. Early apoptosis and late apoptosis were effectively induced by XFC extract in ES-2 cells, whereas late apoptosis and necrosis events were triggered in SKOV-3 cells. Cell cycling regulation was trapped by XFC extract in the G2/M phase in both the ES-2 and SKOV-3 cell models. This effect was, in part, attributable to increased dose-dependent tubulin polymerization, which was increased in SKOV-3 cells. Whereas XFC extract triggered poly (ADP-Ribose) polymerase (PARP) cleavage in both ES-2 and SKOV-3 cells, it only lowered Nrf2 in ES-2 cells and phosphorylated Akt levels in SKOV-3 cells. Interestingly, cell cycling regulators Cdk4, Cyclin D3, and p27 were all decreased in SKOV-3 cells. XFC extracts were effective in inhibiting in vitro migration in both ovarian cancer cell models. Our data support the potential anticancer targeting of chemoresistant human ovarian cancer cells phenotype by XFC extract.

Combinatorial Synthesis to Identify a Potent, Necrosis-Inducing Rhenium Anticancer Agent

Combinatorial synthesis can be applied for developing a library of compounds that can be rapidly screened for biological activity. Here, we report the application of microwave-assisted combinatorial chemistry for the synthesis of 80 rhenium(I) tricarbonyl complexes bearing diimine ligands. This library was evaluated for anticancer activity in three different cancer cell lines, enabling the identification of three lead compounds with cancer cell growth-inhibitory activities of less than 10 μM. These three lead structures, Re-9B, Re-9C, and Re-9D, were synthesized independently and fully characterized by NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray crystallography. The most potent of these three complexes, Re-9D, was further explored to understand its mechanism of action. Complex Re-9D is equally effective in both wild-type and cisplatin-resistant A2780 ovarian cancer cells, indicating that it circumvents cisplatin resistance. This compound was also shown to possess promising activity against ovarian cancer tumor spheroids. Additionally, flow cytometry showed that Re-9D does not induce cell cycle arrest or flipping of phosphatidylserine to the outer cell membrane. Analysis of the morphological changes of cancer cells treated with Re-9D revealed that this compound gives rise to rapid plasma membrane rupture. Collectively, these data suggest that Re-9D induces necrosis in cancer cells. To assess the in vivo biodistribution and stability of this compound, a radioactive ^99mTc analogue of Re-9D, ^99mTc-9D(H₂O), was synthesized and administered to naı̈ve BALB/c mice. Results of these studies indicate that ^99mTc-9D(H₂O) exhibits high metabolic stability and a distinct biodistribution profile. This research demonstrates that combinatorial synthesis is an effective approach for the development of new rhenium anticancer agents with advantageous biological properties.

Cisplatin resistance in cell models: evaluation of metallomic and biological predictive biomarkers to address early therapy failure

Cisplatin, one of the most extensively used metallodrugs in cancer treatment, presents the important drawback of patient resistance. This resistance is the consequence of different processes including those preventing the formation of DNA adducts and/or their quick removal. Thus, a tool for the accurate detection and quantitation of cisplatin-induced adducts might be valuable for predicting patient resistance. To prove the validity of such an assumption, highly sensitive plasma mass spectrometry (ICP-MS) strategies were applied to determine DNA adduct levels and intracellular Pt concentrations. These two metal-relative parameters were combined with an evaluation of biological responses in terms of genomic stability (with the Comet assay) and cell cycle progression (by flow cytometry) in four human cell lines of different origins and cisplatin sensitivities (A549, GM04312, A2780 and A2780cis), treated with low cisplatin doses (5, 10 and 20 μM for 3 hours). Cell viability and apoptosis were determined as resistance indicators. Univariate linear regression analyses indicated that quantitation of cisplatin-induced G-G intra-strand adducts, measured 1 h after treatment, was the best predictor for viability and apoptosis in all of the cell lines. Multivariate linear regression analyses revealed that the prediction improved when the intracellular Pt content or the Comet data were included in the analysis, for all sensitive cell lines and for the A2780 and A2780cis cell lines, respectively. Thus, a reliable cisplatin resistance predictive model, which combines the quantitation of adducts by HPLC-ICP-MS, and their repair, with the intracellular Pt content and induced genomic instability, might be essential to identify early therapy failure.

Potential synergistic effect of phosphodiesterase inhibitors with chemotherapy in lung cancer

Purpose: Lung cancer remains the leading cause of cancer-related deaths worldwide and novel therapeutic approaches targeting crucial pathways are urgently needed to improve its treatment. Differentiation-based therapeutics (Methylxanthines) and phosphodiesterase inhibitors (type 4 and 5), have been implicated in cancer treatment. Our objectives were to capture any potential anti-tumor effect of these drug combinations with chemotherapeutic agents in vitro. Methods: Theophylline as Methylxanthines, Roflumilast as phosphodiesterase type 4 (PDE4) inhibitor and Sildenafil as phosphodiesterase type 5 (PDE5) inhibitor are the drugs that we combined with the chemotherapeutic agents (Docetaxel, Cisplatin and Carboplatin) in vitro. Lung cancer cell lines (NCI-H1048-Small cell lung cancer-SCLC, A549- Non-small cell lung cancer-NSCLC) were purchased from ATCC LGC Standards. At indicated time-point, following 24h and 48h incubation, cell viability and apoptosis were measured with Annexin V staining by flow cytometry. Statistical analysis was performed by GraphPad Prism. Results: In SCLC, following 48h incubation, platinum combinations of carboplatin with roflumilast and sildenafil (p<0.001) and carboplatin with theophylline and sildenafil showed increased apoptosis when compared to carboplatin alone. Concerning the combinations of cisplatin, when combined with roflumilast, theophylline and sildenafil appeared with increased apoptosis of that alone (p<0.001, 24h and 48h incubation). In NSCLC, the 24h incubation was not enough to induce satisfactory apoptosis, except for the combination of cisplatin with roflumilast and theophylline (p<0.05) when compared to cisplatin alone. However, following 48h incubation, carboplatin plus sildenafil, carboplatin plus sildenafil, theophylline and roflumilast showed more cytotoxicity when compared to carboplatin alone (p<0.001). Docetaxel combinations showed no statistically significant results. Conclusion: The synergistic effect of PDE inhibitors with platinum-based agents has been demonstrated in lung cancer. Our suggestion is that these combinations could be used as additive and maintenance treatment in combination to antineoplastic agents in lung cancer patients.

Cisplatin-induced regulation of signal transduction pathways and transcription factors in p53-mutated subclone variants of hepatoma cells: Potential application for therapeutic targeting

Cisplatin is commonly recognized as a DNA-damaging drug; however, its versatile antitumor effects have been demonstrated to extend beyond this narrow functional attribute. The present study determined how cisplatin regulates alternative pathways and transcription factors to exert its additional antitumor actions. Cisplatin was observed to be able to trigger an endoplasmic reticulum stress response through aggravated nitrosative stress coupled to perturbed mitochondrial calcium (Ca²⁺) homeostasis, which substantially downregulated glucose-regulated protein (GRP) 78 expression by suppressing the cleavage of activating transcription factor (ATF) 6α (90 kDa) to its active 50 kDa subunit. Concomitantly, the ATF4-ATF3-C/emopamil binding protein homologous protein axis was activated by cisplatin, which triggered cellular glutathione (GSH) depletion by strongly inhibiting γ-glutamylcysteine synthetase heavy chain (γ-GCS_h), a key enzyme in GSH biosynthesis. The present study also demonstrated that cisplatin substantially inhibited β-catenin, causing a marked downregulation of survivin and B-cell lymphoma (Bcl)-2. Taken together, the present results uncovered a novel mechanism of cisplatin that could simultaneously trigger the inhibition of three prominent antiapoptotic effector molecules (Bcl-2, survivin and GRP78) and effectively promote GSH depletion by inhibiting γ-GCS_h. These newly discovered functional attributes of cisplatin can provide an avenue for novel combined therapeutic strategies to kill hepatocellular carcinoma cells effectively.

Effect of cisplatin on proteasome activity

Cisplatin is a widely used chemotherapy drug which exerts cytotoxic activity by affecting both nuclear and cytosolic pathways. Herewith, we report, for the first time, that cisplatin inhibits proteasome activity in vitro. Cisplatin induces a dose dependent inhibition of the three enzymatic activities of proteasome (i.e., the chymotrypsin-like activity, the trypsin-like activity and the caspase-like activity). Moreover, cisplatin administration to neuroblastoma cells brings about a fast loss of proteasome particle activity, which is followed by a de novo synthesis of proteasome. Lastly, we report that the simultaneous administration of lactacystin and cisplatin enhances the cytotoxicity of cisplatin alone. The overall bulk of data opens to an intriguing scenario, concerning the biological effects of cisplatin in the control of cellular life, which goes beyond the well established genotoxic effect.

Overcoming cisplatin resistance using gold(III) mimics: anticancer activity of novel gold(III) polypyridyl complexes

Gold(III) compounds have been recognized as anticancer agents due to their structural and electronic similarities with currently employed platinum(II) species. An added benefit to gold(III) agents is the ability to overcome cisplatin resistance. This work identified four gold(III) compounds, [Au(Phen)Cl(2)]PF(6), [Au(DPQ)Cl(2)]PF(6), [Au(DPPZ)Cl(2)]PF(6), and [Au(DPQC)Cl(2)]PF(6), (Phen = 1,10-phenanthroline, DPQ = dipyrido[3,2-d:2',3'-f]quinoxaline, DPPZ = dipyrido[3,2-a:2',3'-c] phenazine, DPQC = dipyrido[3,2-d:2',3'-f] cyclohexyl quinoxaline) that exhibited anticancer activity in both cisplatin sensitive and cisplatin resistant ovarian cancer cells. Two of these compounds, [Au(DPQ)Cl(2)]PF(6) (AQ) and [Au(DPPZ)Cl(2)]PF(6) (AZ), displayed exceptional anticancer activity and were the focus of more intensive mechanistic study. At the molecular level, AQ and AZ formed DNA adducts, generated free radicals, and upregulated pro-apoptotic signaling molecules (p53, caspases, PARP, death effectors). Taken together, these two novel gold(III) polypyridyl complexes exhibit potent antitumor activity in cisplatin resistant cancer cells. These activities may be mediated, in part, by the activation of apoptotic signaling.

Inhibition of DNA Synthesis by a Platinum-Acridine Hybrid Agent Leads to Potent Cell Kill in Non-Small Cell Lung Cancer

The platinum-acridine anti-cancer agent [PtCl(en)(LH)](NO(3))(2) (1) (en = ethane-1,2-diamine, LH = N-(2-(acridin-9-ylamino)ethyl)-N-methylpropionimidamide, acridinium cation) and the clinical drug cisplatin were studied in chemoresistant non-small cell lung cancer (NSCLC) cell lines for their cytotoxic potency and cell-kill mechanisms. In the three cell lines tested (NCI-H460, NCI-H522, and NCI-H1435) compound 1 shows a pronounced cytotoxic enhancement of 40-200-fold compared to cisplatin at inhibitory concentrations reaching the low-nanomolar range. Based on changes in cell adhesion and cell morphology, monitored in real time by impedance measurements, compound 1 kills NCI-H460 cells significantly more efficiently than cisplatin at equitoxic concentrations. Flow cytometry analysis of NCI-H460 cells reveals a robust S-phase arrest of cells treated with compound 1, whereas cells treated with cisplatin progress to G2/M of the cell cycle. A pronounced inhibition of DNA replication in 75% of viable cells is observed in NCI-H460 cells treated with compound 1 at an IC(90) molar concentration for 48 h, based on the reduced incorporation of the fluorophore-clickable nucleoside analogue 5-ethynyl-2´-deoxyuridine (EdU) into newly synthesized DNA. The distinct cell-cycle perturbations and cell-kill potential of compound 1 are discussed in the light of the DNA interactions of this agent and its potential to overcome cisplatin resistance in NSCLC.

Molecular biomarkers for predicting chemotherapy response in lung cancer

BACKGROUND

Chemotherapy in non-small-cell lung cancer (NSCLC) has reached a plateau, with no evidence of substantial improvement in survival. However, recent advances in the management of lung cancer have paved the way for the optimization of treatment. Several lines of evidence indicate that multiple genetic disturbances found in human cancer cell lines and in the tumors of NSCLC patients have a role as predictive markers for response and survival with chemotherapy regimens now in use.

OBJECTIVE

This review highlights relevant translational research findings on potential predictive markers in lung cancer with therapeutic impact in both the near and distant future.

CONCLUSION

The next step is to develop clinical trials that will prospectively validate the benefits of customizing chemotherapy, which should translate into an improvement in outcome in NSCLC patients.

PNAS-4, a novel pro-apoptotic gene, can potentiate antineoplastic effects of cisplatin

PURPOSE

PNAS-4, a novel pro-apoptotic gene activated during the early response to DNA damage, can inhibit proliferation via apoptosis when overexpressed in some tumor cells. The objectives of this study were to determine whether PNAS-4 could enhance apoptosis induced by cisplatin besides its induction of apoptosis, and to evaluate the usefulness of combined treatment with mouse PNAS-4 (mPNAS-4) gene therapy and low-dose cisplatin chemotherapy in the inhibition of tumor growth in colon carcinoma (CT26) and Lewis lung carcinoma (LL/2) murine models.

METHODS

In this study, the in vitro growth-inhibitory and pro-apoptotic effects of PNAS-4 and/or cisplatin on CT26, LL/2, and SKOV3 cancer cells were assessed by MTT assay, flow cytometric analysis, DNA fragmentation, and morphological analysis, respectively. The in vivo antitumor activity of combined treatment with mPNAS-4 gene therapy and low-dose cisplatin were evaluated in the inhibition of tumor growth in colon carcinoma (CT26) and Lewis lung carcinoma (LL/2) murine models. Tumor volume and survival time were observed. Induction of apoptosis was also assessed in tumor tissues.

RESULTS

In vitro, PNAS-4 inhibited proliferation of colon carcinoma (CT26), Lewis lung carcinoma (LL/2) and human ovarian cancer (SKOV3) cell lines via apoptosis, and significantly enhanced the apoptosis of CT26, LL/2, and SKOV3 cells induced by cisplatin. In vivo systemic administration of expression plasmid encoding mPNAS-4 (pcDNA3.1-mPS) and cisplatin, significantly decreased tumor growth through increased tumor cell apoptosis compared to treatment with mPNAS-4 or cisplatin alone.

CONCLUSIONS

Our data suggests that the combined treatment with mPNAS-4 plus cisplatin may augment the induction of apoptosis in tumor cells in vitro and in vivo, and that the augmented antitumor activity in vivo may result from the increased induction of apoptosis. The present study may provide a novel way to augment the antitumor efficacy of cytotoxic chemotherapy.

Non-DNA-binding platinum anticancer agents: Cytotoxic activities of platinum-phosphato complexes towards human ovarian cancer cells

DNA is believed to be the molecular target for the cytotoxic activities of platinum (Pt) anticancer drugs. We report here a class of platinum(II)- and platinum(IV)-pyrophosphato complexes that exhibit cytotoxicity comparable with and, in some cases, better than cisplatin in ovarian cell lines (A2780, A2780/C30, and CHO), yet they do not show any evidence of covalent binding to DNA. Moreover, some of these compounds are quite effective in cisplatin- and carboplatin-resistant cell line A2780/C30. The lack of DNA binding was demonstrated by the absence of a detectable Pt signal by atomic absorption spectroscopy using isolated DNA from human ovarian cells treated with a platinum(II)-pyrophosphato complex, (trans-1,2-cyclohexanediamine)(dihydrogen pyrophosphato) platinum(II), (pyrodach-2) and from NMR experiments using a variety of nucleotides including single- and double-stranded DNA. Furthermore, pyrodach-2 exhibited reduced cellular accumulations compared with cisplatin in cisplatin- and carboplatin-resistant human ovarian cells, yet the IC(50) value for the pyrophosphato complex was much less than that of cisplatin. Moreover, unlike cisplatin, pyrodach-2 treated cells overexpressed fas and fas-related transcription factors and some proapoptotic genes such as Bak and Bax. Data presented in this report collectively indicate that pyrodach-2 follows different cytotoxic mechanisms than does cisplatin. Unlike cisplatin, pyrodach-2 does not undergo aquation during 1 week and is quite soluble and stable in aqueous solutions. Results presented in this article represent a clear paradigm shift not only in expanding the molecular targets for Pt anticancer drugs but also in strategic development for more effective anticancer drugs.

Cisplatin-induced apoptosis involves membrane fluidification via inhibition of NHE1 in human colon cancer cells

We have previously shown that cisplatin triggers an early acid sphingomyelinase (aSMase)-dependent ceramide generation concomitantly with an increase in membrane fluidity and induces apoptosis in HT29 cells. The present study further explores the role and origin of membrane fluidification in cisplatin-induced apoptosis. The rapid increase in membrane fluidity following cisplatin treatment was inhibited by membrane-stabilizing agents such as cholesterol or monosialoganglioside-1. In HT29 cells, these compounds prevented the early aggregation of Fas death receptor and of membrane lipid rafts on cell surface and significantly inhibited cisplatin-induced apoptosis without altering drug intracellular uptake or cisplatin DNA adducts formation. Early after cisplatin treatment, Na+/H+ membrane exchanger-1 (NHE1) was inhibited leading to intracellular acidification, aSMase was activated, and ceramide was detected at the cell membrane. Treatment of HT29 cells with Staphylococcus aureus sphingomyelinase increased membrane fluidity. Moreover, pretreatment with cariporide, a specific inhibitor of NHE1, inhibited cisplatin-induced intracellular acidification, aSMase activation, ceramide membrane generation, membrane fluidification, and apoptosis. Finally, NHE1-expressing PS120 cells were more sensitive to cisplatin than NHE1-deficient PS120 cells. Altogether, these findings suggest that the apoptotic pathway triggered by cisplatin involves a very early NHE1-dependent intracellular acidification leading to aSMase activation and increase in membrane fluidity. These events are independent of cisplatin-induced DNA adducts formation. The membrane exchanger NHE1 may be another potential target of cisplatin, increasing cell sensitivity to this compound.

Characterization of the anti-Leishmania effect induced by cisplatin, an anticancer drug

The cis-diamminedichloroplatinum(II), known as cis-DDP or cisplatin is a widely used drug in cancer chemotherapy. Although a recent study has shown the anti-Leishmania activity of some cis-DDP derivatives, the cytotoxic properties were measured only on promastigotes, the insect vector form of the parasite. In this study the effect of cis-DDP on promastigotes and amastigotes, the vertebrate stage of the parasite is reported. The IC50, determined by flow cytometry, after 72 h of drug incubation was four times higher, 7.73+/-1.03 microM in the case of promastigotes compared to axenic amastigotes, 1.88+/-0.10 microM. In intracellular amastigotes the IC50, determined by counting the parasite index was 1.85+/-0.22 microM. By using flow cytometry, two patterns of cell cycle changes was observed: cis-DDP treated promastigotes and amastigotes accumulated in S phase and G2 phase, respectively. The cis-DDP response was also found to involve an "apoptosis-like" death of both promastigotes and amastigotes. However, DNA fragmentation was only detected in promastigote forms. In contrast mitochondrial transmembrane potential loss was observed for both stages of the parasite. Upon incubation of parasites with the drug an increase on GSH and GSSG levels and reactive oxygen species could be detected in the case of promastigote. Moreover, a slight increase of GSH level was detected on amastigote form. Taken together, these observations indicate that amastigotes are more sensitive to cis-DDP when compared to promastigotes. However, the signaling pathways leading to cell death could be different.

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.

Different cell cycle modulation following treatment of human ovarian carcinoma cells with a new platinum(IV) complex vs cisplatin

Platinum (IV) derivative with adamantylamine-LA-12-represents a new generation of highly efficient anti-cancer drug derived from cisplatin and is currently in the final stage of phase I clinical trials. Understanding the specific mechanisms of its effects on cell cycle is necessary for defining the mode of action of LA-12. In this study, we characterized the ability of LA-12 to induce cell cycle perturbations in ovarian cancer cell line A2780 as compared to equitoxic cisplatin treatment. LA-12 induced a permanent accumulation of A2780 cells in S phase while cisplatin caused G2/M arrest at 24-h time point, where we also detected an increased expression of Gadd45alpha protein. Although both derivatives induced a rapid increase of p53 expression, this was not associated with a down-regulation of Mdm2 protein. Increased expression of p21(Cip1/WAF1) protein and its association with cyclins A and B1 suggested that this cyclin-dependent kinase inhibitor might contribute significantly to the observed perturbations of cell cycle. The results of this study provide insight into the mechanism of action of platinum-based derivative with adamantylamine on cell cycle in ovarian cancer cells. The differences between effects of LA-12 and cisplatin suggest that more attention should be paid to elucidation of modes of action of novel platinum(IV) complexes at cellular level.

Overexpression of p73 enhances cisplatin-induced apoptosis in HeLa cells

To examine a possible synergistic role for p73 and cisplatin (cis-diamminedichloroplatinum II) in HeLa cells with a nonfunctional p53 protein, we established stable HeLa/p73 clones using a tetracycline inducible eukaryotic expression vector. The HeLa/p73 clones were not characterized by changes in growth or morphology. Cell death analysis, however, indicated a greater sensitivity to cisplatin in the p73-overexpressed HeLa cells than determined for the non-induced HeLa cells. This increased sensitivity seems to affect an induction of a sub-G1 population as assessed from flow cytometry analysis. The increased sub-G1 population may, in turn, result from a reduction of cyclin D1 and B1 expression by cisplatin in the presence of p73. Hoechest staining indicated an increased number of dead cells in the p73-induced cells compared to the non-induced cells. Poly ADP-ribose polymerase (PARP) cleavage was shown to be distinct in the p73-overexpressed cells compared to non-induced cells, which suggests that p73 modulates the cisplatin-induced apoptosis. Therefore, a synergistic effect of p73 and cisplatin to induce apoptosis could lead to new treatment for some types of human cancers.

Platinum(IV) complex with adamantylamine overcomes intrinsic resistance to cisplatin in ovarian cancer cells

OBJECTIVES

The resistance of tumor cells to cisplatin remains a major cause of treatment failure in cancer patients. In this study, the ability of Pt(IV) complex with adamantylamine-LA-12 and its reduced counterpart with lower oxidation state Pt(II)-LA-9 to overcome intrinsic cisplatin resistance was investigated.

METHODS

The ovarian adenocarcinoma SK-OV-3 cells were exposed to cisplatin, LA-9, or LA-12 for 72 h and the effects of drug concentrations that caused 10% or 50% inhibition of cell proliferation were determined. After 24-72 h of sustained exposure viability, apoptosis and inhibition of proliferation were analyzed. DNA synthesis and cell cycle analysis were performed simultaneously in order to determine the modulation of cell cycle after platinum complexes treatment.

RESULTS

Lung Resistance-related Protein (LRP/MVP) was detected in SK-OV-3 cells but not in the other two ovarian cancer lines with different sensitivity to cisplatin. LRP/MVP overexpression may be an important factor contributing to intrinsic cisplatin resistance. Interestingly, Pt(IV) complex-LA-12 had approximately 2.7-fold lower IC(50) concentration than LA-9 or cisplatin in SK-OV-3 cells. Moreover, LA-12 caused persistent accumulation of cells in S-phase of the cell cycle while LA-9 and cisplatin treatment-induced S-phase arrest was transient and shifted to G(2)/M-phase at later intervals. Apoptosis seemed to be not the dominant type of cell death caused by such the derivatives, but it was the most intensive after LA-12 treatment.

CONCLUSIONS

We found strong differences between effects of Pt(IV) complex-LA-12 and Pt(II) derivatives-LA-9 and cisplatin on cytokinetic parameters. Overall, LA-12 but not its reduced Pt(II) counterpart LA-9 is the compound effective in p53 null human ovarian cancer cells and it is able to overcome intrinsic cisplatin resistance in these cells.

High effectiveness of platinum(IV) complex with adamantylamine in overcoming resistance to cisplatin and suppressing proliferation of ovarian cancer cells in vitro

[(OC-6-43)-bis(acetato)(1-adamantylamine)amminedichloroplatinum(IV)], coded as LA-12, is an octahedral platinum(IV) complex containing a bulky hydrophobic ligand - adamantylamine. The use of bulky hydrophobic amines as non-leaving ligands, may increase uptake of the compound by the cancer cells. Therefore, the effects of LA-12 on sensitive (A2780) and cisplatin resistant (A2780cis) ovarian cancer cell lines were investigated and compared to those of cisplatin. IC(50) and IC(90) concentrations of LA-12 were 6- (A2780) or 18-fold (A2780cis) lower than those for cisplatin (MTT assay). Equitoxic concentrations (IC(50) or IC(90)) of both compounds caused a significant and similar time- and dose-dependent inhibition of cell proliferation and an increase in the number of floating cells which corresponded to the decrease of total cell viability. A different type and dynamics of cell cycle perturbation after cisplatin and LA-12 treatment were detected. Exposure to LA-12 resulted in transient accumulation of A2780 and A2780cis cells in S phase, while cisplatin caused G(2)/M arrest in sensitive and S phase arrest in resistant cells. A relatively low rate of apoptosis after exposure to IC(50) or IC(90) of both complexes was observed, markedly higher in resistant A2780cis cells. Western blot analysis indicated a concentration-dependent p53 level increase in both lines (higher after cisplatin treatment). PARP cleavage was observed only in A2780cis cells. In conclusion, LA-12 was found to be significantly more efficient than cisplatin, and it was able to overcome the acquired cisplatin resistance (showing resistance factor 2.84-fold lower than those for cisplatin). In spite of the low rate of apoptosis, LA-12 caused increase of p53 level and cell cycle perturbations in the ovarian cancer cell lines studied.

Inositol 1,4,5-trisphosphate (IP3) receptor type1 (IP3R1) modulates the acquisition of cisplatin resistance in bladder cancer cell lines

To investigate the molecules that regulate the acquisition of cis-diamminedichloroplatinum (II) (cisplatin) resistance, we performed cDNA microarrays using two pairs of parental and cisplatin-resistant bladder cancer cell lines. We found a markedly reduced expression of inositol 1,4,5-trisphosphate (IP3) receptor type1 (IP3R1), endoplasmic reticulum membrane protein, in cisplatin-resistant cells. The suppression of IP3R1 expression using small interfering RNA in parental cells prevented apoptosis and resulted in decreased sensitivity to cisplatin. Contrarily, overexpression of IP3R1 in resistant cells induced apoptosis and increased sensitivity to cisplatin. These results suggest that cisplatin-induced downregulation of IP3R1 expression was closely associated with the acquisition of cisplatin resistance in bladder cancer cells.

Phosphodiesterase inhibitors as anti-cancer drugs

It is well known that high intracellular levels of cAMP can effectively kill cancer cells in vitro. Unfortunately substances elevating cAMP such as forskolin, 8-bromo-cAMP, 8-chloro-cAMP, monobutiryl or dibutiryl cAMP are not recommended to be used as anti-cancer drugs because of their high cytotoxicity. In contrast blockers of phosphodieterases such as theophylline and aminophylline, which could elevate intracellular cAMP, are commonly used as anti-asthma drugs reaching concentrations in the blood of 10-20 microg/ml. We tested the effectiveness of theophylline and aminophylline to induce cell death alone or in combination with common anti-cancer drugs such as cisplatin and gemcitabine (gemzar). We examined such drug combinations in the induction of cell death in a variety of carcinoma cell lines derived from human ovarian, prostate and lung cancer and in granulosa cell line transformed by SV40 and Ras oncogene. While theophylline could induce moderate cell death alone, at 20-25 microg/ml concentrations, aminophylline was ineffective at this concentration. Theophylline (at 15-25 ng/ml) was found in all four representative cell lines to synergize with gemcitabine or cisplatin to induce programmed cell death, which permits a reduction in the effective doses of cisplatin and gemcitabine by 2-3-fold. The effect of theophylline in induction of apoptosis involved reduction of intracellular levels of Bcl2. Such a reduction was proportional to the extent of apoptosis induced by theophylline as well as by the combined drug treatments. Therefore, we propose that theophylline should be considered as a potential anti-cancer drug in combination with other chemotherapeutic drugs. Screening of other phosphodiesterase blockers, which are not severely toxic, could open a possibility to improved chemotherapeutic cancer treatments with reduced undesired side-effects. A clinical trial, using theophylline as an anti-cancer drug, is currently being conducted in lung cancer patients.

Cisplatin induces endoplasmic reticulum stress and nucleus-independent apoptotic signaling

DNA damage is believed to be the main cause of the antiproliferative effect of cisplatin, a cornerstone agent in anticancer therapy. However, cisplatin can be expected to react also with nucleophiles other than DNA. Using enucleated cells (cytoplasts) we demonstrate here that cisplatin-induced apoptotic signaling may occur independently of DNA damage. Cisplatin-induced caspase-3 activation in cytoplasts required calcium and the activity of the calcium-dependent protease calpain. It is known that calpain activation may be associated with endoplasmic reticulum (ER) stress, suggesting that the ER is a cytosolic target of cisplatin. Consistent with this hypothesis, cisplatin induced calpain-dependent activation of the ER-specific caspase-12 in cytoplasts as well as in intact cells. Cisplatin also induced increased expression of Grp78/BiP, another marker of ER stress. By contrast, the DNA-damaging topoisomerase II inhibitor etoposide did not induce apoptotic signaling in cytoplasts nor ER stress in intact cells. We have thus identified a novel mechanism of action of cisplatin. The results have implications for the understanding of resistance mechanisms as well as the unique efficiency of this drug.

Gold(III) complexes as a new family of cytotoxic and antitumor agents

In recent years, owing to the contributions of a few research groups, some new gold(III) compounds--either simple coordination complexes or organogold compounds--have been prepared that are sufficiently stable under physiological conditions and are promising candidates for pharmacological testing as cytotoxic and antitumor agents. In vitro pharmacological studies point out that some of these novel gold(III) complexes are highly cytotoxic toward cultured human tumor cell lines and are able to overcome resistance to platinum. Significant differences in the spectrum of action were observed compared with cisplatin. Studies are in progress to elucidate the mechanism of action of these compounds. The cellular effects of two representative gold(III) complexes are described. Preliminary results on binding to DNA in vitro are presented, pointing out that the interactions are generally weak. The implications of these results for the development of gold(III) complexes as a new family of cytotoxic and antitumor agents are discussed.

Prolonged wild-type p53 protein accumulation and cisplatin resistance

The major limitation for the chemotherapeutic use of DNA-damaging agent cisplatin is the development of resistance in initially responsive tumors. One of the main pathways regulating cell survival following DNA damage is the p53 pathway. In this study we compared the cisplatin-induced response of p53 protein and its downstream targets p21WAF-1 and Mdm2 in the cisplatin-sensitive ovarian carcinoma cell line A2780 and its cisplatin-resistant derivative CP70. A higher dose of cisplatin and a longer exposure time was required to achieve the same level of p53, p21WAF-1, and Mdm2 protein accumulation in the cisplatin-resistant CP70 cells versus cisplatin-sensitive A2780 cells. A significant difference between the two cell lines was observed in cisplatin-induced stabilization of p53 protein. The p53 half-life increased 31-fold in CP70 cells compared to only 6-fold in A2780 cells. In contrast, there was no difference in p21WAF-1 half-life between the two cell lines. These results demonstrate that in A2780 and CP70 cells resistance to cisplatin correlates with prolonged p53 protein stabilization and accumulation.

The novel trinuclear platinum complex BBR3464 induces a cellular response different from cisplatin

BBR3464 is a new platinum-based drug non cross-resistant with cisplatin. To characterise the cellular basis of BBR3464 cytotoxicity as opposed to cisplatin, we performed a comparative study of the two drugs in cisplatin-resistant neuroblastoma and astrocytoma cells. In both model systems, BBR3464 proved to be more potent than cisplatin and was able to overcome cisplatin resistance. The higher potency exhibited by BBR3464 correlated with an increased cellular platinum accumulation and DNA-adduct formation. At equitoxic doses, BBR3464 induced apoptosis to a lesser extent than cisplatin and failed to overcome the decreased susceptibility to cisplatin-induced apoptosis in cisplatin-resistant cells. Cell cycle analysis showed a dose-dependent G2/M arrest by BBR3464. In astrocytoma cells, cisplatin treatment resulted in the upregulation of p53, p21 and bax, while only p21 induction was observed after BBR3464 treatment. In cisplatin-resistant cells, the reduced sensitivity to cisplatin paralleled a resistance to the induction of p53/p21 pathway by cisplatin, while the same doses of BBR3464 induced p21 to a similar extent in the resistant cells as in the parental cells. In conclusion, BBR3464 induces a cellular response that is different from cisplatin, supporting the view that the two drugs act through different mechanisms. Our data indicate that BBR3464 may be a promising agent in the treatment of tumours unresponsive to cisplatin and with a non-functional p53.

Gene-specific repair of Pt/DNA lesions and induction of apoptosis by the oral platinum drug JM216 in three human ovarian carcinoma cell lines sensitive and resistant to cisplatin

JM216, an oral platinum drug entering into phase III clinical trial, exhibited comparable cytotoxicity to cisplatin in three human ovarian carcinoma cell lines: the sensitive (CH1), acquired resistant (CH1cisR) and intrinsically resistant (SKOV-3). Platinum accumulation and binding to DNA were similar in each of the three cell lines at equimolar doses, indicating that the resistant cell lines could tolerate higher intracellular platinum levels and platinum bound to DNA at IC50 concentrations of drug. Comparison with cisplatin demonstrated that intracellular platinum levels were marginally higher with JM216, but that platinum binding to DNA was similar for the two drugs in each of the cell lines. Each of the cell lines exhibited an ability to repair JM216 induced platinum/DNA lesions in the N-ras gene (gene-specific repair) at equitoxic concentrations of drug. However, this occurred to a greater extent in the two resistant cell lines such that by 24 h the CH1cisR and SKOV-3 had removed 72% and 67% respectively compared with approximately 32% for the CH1. Reduced gene-specific repair capacity in CH1 cells was also seen following incubation with 25 microM (or 5 microM - 2 x IC50) cisplatin, whereas the CH1cisR and SKOV-3 cell lines were repair proficient. JM216 induced apoptosis in the three cell lines following a 2h incubation with 2 x the IC50 of drug. Fluorescent microscopy of cells stained with propidium iodide showed that the detached cell population displayed typical apoptotic nuclei. Furthermore, field inversion gel electrophoresis demonstrated the presence of DNA fragments approximately 23-50 kb in size, indicative of apoptosis, in the detached cells. JM216 induced an S phase slow down in each of the three cell lines accompanied by a G2 block in the CH1 pair. Incubation with this concentration of JM216 also resulted in the induction of p53 in the CH1 and CH1cisR. These studies suggest that the relative sensitivity of the CH1 cell line to cisplatin and JM216 is at least partly attributable to a deficiency in gene-specific repair. The oral platinum drug, JM216, exerts its cytotoxic effects through the induction of apoptosis following a slow-down in S phase in both the sensitive and resistant lines.

Acquisition of chemoresistance in a human ovarian carcinoma cell is linked to a defect in cell cycle control

Chemoresistance is a major concern in cancer erradication; it involves various mechanisms, including defects in the apoptosis program induced by anticancer drugs. In order to further explore the mechanisms underlying the development of chemoresistance in ovarian carcinoma after cisplatin treatment, we established an in vitro model, mimicking a clinical protocol of administration of cisplatin. Therefore, IGROV1 ovarian carcinoma cells were exposed for 2 hr to the drug and allowed to recover for several weeks; this way of exposure was reiterated with escalating doses. We followed changes in cytotoxicity of the drug, cell cycle kinetics and long-term survival of cells after cisplatin treatment, and found that resistance to cisplatin was not associated with altered apoptosis pathway, since both cisplatin sensitive and resistant cells underwent apoptosis in a similar way. Acquisition of resistance to cisplatin was associated with the ability of the treated cells to progress through the cell cycle beyond the G1/S checkpoint; although most cells died by apoptosis, a few surviving cells proliferated and recolonized the cultures. Compared to sensitive cells, the chemoresistant variants were able to override the G1/S checkpoint whatever the dose, and the recurrent cells recolonized the cultures much faster. Analysis of alterations in gene expression suggests that the defect in cell cycle regulation could take place at the level of the cdk inhibitor p21(CIP1/WAF1).