cis-Diamminedichloroplatinum(II)-induced cell death through apoptosis in sensitive and resistant human ovarian carcinoma cell lines

Triphenyltin(IV) Carboxylates with Exceptionally High Cytotoxicity against Different Breast Cancer Cell Lines

Organotin(IV) carboxylates are a class of compounds explored as alternatives to platinum-containing chemotherapeutics due to propitious in vitro and in vivo results, and distinct mechanisms of action. In this study, triphenyltin(IV) derivatives of non-steroidal anti-inflammatory drugs (indomethacin (HIND) and flurbiprofen (HFBP)) are synthesized and characterized, namely [Ph3Sn(IND)] and [Ph3Sn(FBP)]. The crystal structure of [Ph3Sn(IND)] reveals penta-coordination of the central tin atom with almost perfect trigonal bipyramidal geometry with phenyl groups in the equatorial positions and two axially located oxygen atoms belonging to two distinct carboxylato (IND) ligands leading to formation of a coordination polymer with bridging carboxylato ligands. Employing MTT and CV probes, the antiproliferative effects of both organotin(IV) complexes, indomethacin, and flurbiprofen were evaluated on different breast carcinoma cells (BT-474, MDA-MB-468, MCF-7 and HCC1937). [Ph3Sn(IND)] and [Ph3Sn(FBP)], unlike the inactive ligand precursors, were found extremely active towards all examined cell lines, demonstrating IC50 concentrations in the range of 0.076–0.200 µM. Flow cytometry was employed to examine the mode of action showing that neither apoptotic nor autophagic mechanisms were triggered within the first 48 h of treatment. However, both tin(IV) complexes inhibited cell proliferation potentially related to the dramatic reduction in NO production, resulting from downregulation of nitric oxide synthase (iNOS) enzyme expression.

A Peptide-Based Fluorescent Sensor for Anionic Phospholipids

Anionic phospholipids are key cell signal mediators. The distribution of these lipids on the cell membrane and intracellular organelle membranes guides the recruitment of signaling proteins leading to the regulation of cellular processes. Hence, fluorescent sensors that can detect anionic phospholipids within living cells can provide a handle into revealing molecular mechanisms underlying lipid-mediated signal regulation. A major challenge in the detection of anionic phospholipids is related to the presence of these phospholipids mostly in the inner leaflet of the plasma membrane and in the membranes of intracellular organelles. Hence, cell-permeable sensors would provide an advantage by enabling the rapid detection and tracking of intracellular pools of anionic phospholipids. We have developed a peptide-based, cell-permeable, water-soluble, and ratiometric fluorescent sensor that entered cells within 15 min of incubation via the endosomal machinery and showed punctate labeling in the cytoplasm. The probe could also be introduced into living cells via lipofection, which allows bypassing of endosomal uptake, to image anionic phospholipids in the cell membrane. We validated the ability of the sensor toward detection of intracellular anionic phospholipids by colocalization studies with a fluorescently tagged lipid and a protein-based anionic phospholipid sensor. Further, the sensor could image the externalization of anionic phospholipids during programmed cell death, indicating the ability of the probe toward detection of both intra- and extracellular anionic phospholipids based on the biological context.

Cisplatin-cyclooxygenase inhibitor conjugates, free and immobilised in mesoporous silica SBA-15, prove highly potent against triple-negative MDA-MB-468 breast cancer cell line

For the development of anticancer drugs with higher activity and reduced toxicity, two approaches were combined: preparation of platinum(IV) complexes exhibiting higher stability compared to their platinum(II) counterparts and loading them into mesoporous silica SBA-15 with the aim to utilise the passive enhanced permeability and retention (EPR) effect of nanoparticles for accumulation in tumour tissues. Three conjugates based on a cisplatin scaffold bearing the anti-inflammatory drugs naproxen, ibuprofen or flurbiprofen in the axial positions (1, 2 and 3, respectively) were synthesised and loaded into SBA-15 to afford the mesoporous silica nanoparticles (MSNs) SBA-15|1, SBA-15|2 and SBA-15|3. Superior antiproliferative activity of both free and immobilised conjugates in a panel of four breast cancer cell lines (MDA-MB-468, HCC1937, MCF-7 and BT-474) with markedly increased cytotoxicity with respect to cisplatin was demonstrated. All compounds exhibit highest activity against the triple-negative cell line MDA-MB-468, with conjugate 1 being the most potent. However, against MCF-7 and BT-474 cell lines, the most notable improvement was found, with IC₅₀ values up to 240-fold lower than cisplatin. Flow cytometry assays clearly show that all compounds induce apoptotic cell death elevating the levels of both early and late apoptotic cells. Furthermore, autophagy as well as formation of reactive oxygen species (ROS) and nitric oxide (NO) were elevated to a similar or greater extent than with cisplatin.

Inhibition of the Nuclear Export Receptor XPO1 as a Therapeutic Target for Platinum-Resistant Ovarian Cancer

Purpose: The high fatality-to-case ratio of ovarian cancer is directly related to platinum resistance. Exportin-1 (XPO1) is a nuclear exporter that mediates nuclear export of multiple tumor suppressors. We investigated possible clinicopathologic correlations of XPO1 expression levels and evaluated the efficacy of XPO1 inhibition as a therapeutic strategy in platinum-sensitive and -resistant ovarian cancer.Experimental Design: XPO1 expression levels were analyzed to define clinicopathologic correlates using both TCGA/GEO datasets and tissue microarrays (TMA). The effect of XPO1 inhibition, using the small-molecule inhibitors KPT-185 and KPT-330 (selinexor) alone or in combination with a platinum agent on cell viability, apoptosis, and the transcriptome was tested in immortalized and patient-derived ovarian cancer cell lines (PDCL) and platinum-resistant mice (PDX). Seven patients with late-stage, recurrent, and heavily pretreated ovarian cancer were treated with an oral XPO1 inhibitor.Results: XPO1 RNA overexpression and protein nuclear localization were correlated with decreased survival and platinum resistance in ovarian cancer. Targeted XPO1 inhibition decreased cell viability and synergistically restored platinum sensitivity in both immortalized ovarian cancer cells and PDCL. The XPO1 inhibitor-mediated apoptosis occurred through both p53-dependent and p53-independent signaling pathways. Selinexor treatment, alone and in combination with platinum, markedly decreased tumor growth and prolonged survival in platinum-resistant PDX and mice. In selinexor-treated patients, tumor growth was halted in 3 of 5 patients, including one with a partial response, and was safely tolerated by all.Conclusions: Taken together, these results provide evidence that XPO1 inhibition represents a new therapeutic strategy for overcoming platinum resistance in women with ovarian cancer. Clin Cancer Res; 23(6); 1552-63. ©2016 AACR.

Platinum(II) Iodido Complexes of 7-Azaindoles with Significant Antiproliferative Effects: An Old Story Revisited with Unexpected Outcomes

A series of platinum(II) diiodido complexes containing 7-azaindole derivatives, having the general formula cis-[PtI₂(naza)₂] (1–8), has been prepared and thoroughly characterized, including X-ray structure analysis of cis-[PtI₂(2Me4Claza)₂]∙DMF (8∙DMF; 2Me4Claza = 2-methyl-4-chloro-7-azaindole). Complexes showed high in vitro cytotoxicity against nine human cancer cell lines (IC₅₀ ranging from 0.4 to 12.8 μM), including the cisplatin-resistant ovarian cancer cell line (A2780R; IC₅₀ = 1.0–3.5 μM). The results of in vivo testing, using the L1210 lymphocytic leukaemia model, at the equimolar doses of Pt with cisplatin (2 mg/kg) confirmed the activity of complex 8 comparable to cisplatin. From the mechanistic point of view, evaluated ex vivo by Western blot analyses on the samples of isolated tumour tissues, the treatment of the animals with complex 8, contrary to cisplatin, decreased the levels of tumour suppressor p53 and increased significantly the amount of intracellular anti-apoptotic protein MCL-1_L (37 kDa). Additionally, the active form of caspase 3 was significantly elevated in the sample of tumour tissues treated with complex 8, indicating that the activation of p53-independent cell-death pathway was initiated. The light and electron microscopy observations of the cancerous tissues revealed necrosis as a dominant mechanism of cell death, followed by scarce signs of apoptosis. The additional results (e.g. in vitro interaction experiments with selected biomolecules, cell cycle perturbations, gel electrophoretic studies on pUC19 plasmid DNA) supported the hypothesis that the complexes might be involved in the mechanism of action quite different from cisplatin.

Platinum(II) carboxylato complexes containing 7-azaindoles as N-donor carrier ligands showed cytotoxicity against cancer cell lines

The platinum(II) malonato (Mal) and decanoato (Dec) complexes of the general formulas [Pt(Mal)(naza)₂] (1-3) and cis-[Pt(Dec)₂(naza)₂] (4-7) were prepared, characterized and tested for their in vitro cytotoxicity against cisplatin-sensitive (A2780) and cisplatin-resistant (A2780R) human ovarian carcinoma cell lines and non-cancerous human lung fibroblasts (MRC-5); naza=halogeno-derivatives of 7-azaindole. Complexes 1-7 effectively overcome the acquired resistance of ovarian carcinoma cells to cisplatin. Complexes 2 (IC₅₀=26.6±8.9μM against A2780 and 28.9±6.7μM against A2780R), 4 (IC₅₀=14.5±0.6μM against A2780 and 14.5±3.8μM against A2780R) and 5 (IC₅₀=13.0±1.1μM against A2780 and 13.6±4.9μM against A2780R) indicated decreased toxicity against healthy MRC-5 cells (IC₅₀>50.0μM for 2 and >25.0μM for 4 and 5). The representative complexes 2 and 4 showed mutually different effect on the A2780 cell cycle at IC₅₀ concentrations after 24h exposure. Concretely, the complex 2 caused cell cycle arrest at G₀/G₁ phase, while 4 induced cell death by apoptosis with high population of cells in sub-G₁ cell cycle phase. The hydrolysis and interactions of the selected complexes with biomolecules (glutathione (GSH) and guanosine monophosphate (GMP)) were also studied by means of ¹H NMR and ESI+ mass spectra.

Neurotoxic Effects of Platinum Compounds: Studies in vivo on Intracellular Calcium Homeostasis in the Immature Central Nervous System

Platinum compounds cause significant clinical neurotoxicity. Several studies highlight neurological complications especially in paediatric oncology patients with Central Nervous System (CNS) and non-CNS malignancies. To understand the toxicity mechanisms of platinum drugs at cellular and molecular levels in the immature brain, which appears more vulnerable to injury than in the adult one, we compared the effects in vivo of the most used platinum compounds, i.e., cisdichlorodiammineplatinum (cisplatin, cisPt), and the new [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS). As models of developing brain areas, we have chosen the cerebellum and hippocampus dentate gyrus. Both areas show the neurogenesis events, from proliferation to differentiation and synaptogenesis, and therefore allow comparing the action of platinum compounds with DNA and non-DNA targets. Here, we focused on the changes in the intracellular calcium homeostasis within CNS architecture, using two immunohistochemical markers, the calcium buffer protein Calbindin and Plasma Membrane Calcium ATPase. From the comparison of the cisPt and PtAcacDMS effects, it emerges how essential the equilibrium and synergy between CB and PMCA1 is or how important the presence of at least one of them is to warrant the morphology and function of nervous tissue and limit neuroarchitecture damages, depending on the peculiar and intrinsic properties of the developing CNS areas.

Resistance to cisplatin and paclitaxel does not affect the sensitivity of human ovarian cancer cells to antiprogestin-induced cytotoxicity

Background

Antiprogestin compounds have been shown to be effective in blocking the growth of ovarian cancer cells of different genetic backgrounds. Herein we studied the anti-ovarian cancer effect of a series of antiprogestins sharing the chemical backbone of the most characterized antiprogestin, mifepristone, but with unique modifications in position C-17 of the steroid ring. We assessed the effect of mifepristone-like antiprogestins on the growth of ovarian cancer cells sensitive to the standard combination therapy cisplatin-paclitaxel or made double-resistant upon six cycles of pulse-selection with the drugs used at clinically relevant concentrations and exposure times.

Methods

IGROV-1 and SKOV-3 cells were pulsed with 20 μM cisplatin for 1 h followed by 100 nM paclitaxel for 3 h once a week for six weeks. The cells that did not die and repopulate the culture after the chemotherapies were termed Platinum-Taxane-EScape cells (PTES). Parental cells were compared against their PTES derivatives in their responses to further platinum-taxane treatments. Moreover, both ovarian cancer cells and their PTES siblings were exposed to escalating doses of the various antiprogestin derivatives. We assessed cell growth, viability and sub-G1 DNA content using microcapillary cytometry. Cyclin-dependent kinase inhibitors p21^cip1 and p27^kip1 and cleavage of downstream caspase-3 substrate PARP were used to assess whether cell fate, as a consequence of treatment, was limited to cytostasis or progressed to lethality.

Results

Cells subjected to six pulse-selection cycles of cisplatin-paclitaxel gave rise to sibling derivatives that displayed ~2-7 fold reduction in their sensitivities to further chemotherapy. However, regardless of the sensitivity the cells developed to the combination cisplatin-paclitaxel, they displayed similar sensitivity to the antiprogestins, which blocked their growth in a dose-related manner, with lower concentrations causing cytostasis, and higher concentrations causing lethality.

Conclusions

Antiprogestins carrying a backbone similar to mifepristone are cytotoxic to ovarian cancer cells in a manner that does not depend on the sensitivity the cells have to the standard ovarian cancer chemotherapeutics, cisplatin and paclitaxel. Thus, antiprogestin therapy could be used to treat ovarian cancer cells showing resistance to both platinum and taxanes.

A dual-targeting, apoptosis-inducing organometallic half-sandwich iridium anticancer complex

An iridium(iii) complex [(η⁵-C₅Me₄C₆H₄C₆H₅)Ir(phen)Cl]PF₆(phen = phenanthroline) exhibits dual effects in killing cancer cells causing nuclear DNA damage and mitochondrial dysfunction simultaneously.

Ethanolic extract of the Goldenseal, Hydrastis canadensis, has demonstrable chemopreventive effects on HeLa cells in vitro: Drug-DNA interaction with calf thymus DNA as target

This study tested chemotherapeutic potential of Hydrastis canadensis (HC) extract in HeLa cells in vitro, with emphasis on its drug-DNA interaction and apoptosis induction ability. Nuclear uptake of HC by DAPI, Ao/Eb staining and internucleosomal DNA damage by comet assay was studied through fluorescence microscopy. Possible changes in MMP and apoptotic signalling events were critically analyzed. Cell cycle progression studied through FACS and fragmented DNA through "TUNEL" assay were critically analyzed. RT-PCR studies were conducted for analyzing Cyt-C and Bax translocation in mitochondrial and cytosolic extracts, and Caspase 3 in whole cell lysate. Role of p53-mediated regulation of NF-κβ and TNF-α was elucidated by Western blot analysis. Data of CD and Tm profile of CT-DNA were analyzed. Overall results indicated anti-cancer potential of HC through its ability to induce apoptosis, and interaction with CT-DNA that changed structural conformation of DNA, proving HC to be a promising candidate for chemoprevention.

Self-assembled metalla-rectangles bearing azodipyridyl ligands: synthesis, characterization and antitumor activity

Sixteen arene-Ru based molecular-rectangles were self-assembled in high yields by the equimolar mixing of arene-Ru acceptors (Aa-Ad) with various azopyridyl ligands (1,2-di(pyridyl-4yl)diazene (L1), 1,2-bis(pyridin-4-ylmethylene)hydrazine (L2), 1,2-bis(1-(pyridin-4-yl)ethylidene)hydrazine (L3), 1,2-bis(pyridin-4-ylmethylene)hydrazine (L4)) in nitromethane-methanol solutions. These new molecular-rectangles were fully characterized by a host of analytical techniques including elemental analysis, (1)H and (13)C NMR and HR-ESI-MS. The solid-state structures of two molecular-rectangles (1b and 4d) were determined by single crystal X-ray diffraction data. UV-visible and fluorescence studies were also carried out for the entire suite of rectangles. As with recent studies of similar arene-Ru complexes, the anti-proliferative activities of these complexes were evaluated against SK-hep-1 (liver cancer) and A-549 (lung cancer) human cancer lines. Additionally, the cellular pharmacology and intracellular localizations in AGS (gastric cancer) human cancer cells were determined for selected complexes (1c, 1d and 4c) by apoptosis and fluorescence microscopy studies. These studies confirm that arene-Ru molecular-rectangles inhibit cell cycle progression to the G0 phase, in contrast to that of cisplatin which arrests cell growth in the G2 phase.

Mifepristone prevents repopulation of ovarian cancer cells escaping cisplatin-paclitaxel therapy

Background

Advanced ovarian cancer is treated with cytoreductive surgery and combination platinum- and taxane-based chemotherapy. Although most patients have acute clinical response to this strategy, the disease ultimately recurs. In this work we questioned whether the synthetic steroid mifepristone, which as monotherapy inhibits the growth of ovarian cancer cells, is capable of preventing repopulation of ovarian cancer cells if given after a round of lethal cisplatin-paclitaxel combination treatment.

Methods

We established an in vitro approach wherein ovarian cancer cells with various sensitivities to cisplatin or paclitaxel were exposed to a round of lethal doses of cisplatin for 1 h plus paclitaxel for 3 h. Thereafter, cells were maintained in media with or without mifepristone, and short- and long-term cytotoxicity was assessed.

Results

Four days after treatment the lethality of cisplatin-paclitaxel was evidenced by reduced number of cells, increased hypodiploid DNA content, morphological features of apoptosis, DNA fragmentation, and cleavage of caspase-3, and of its downstream substrate PARP. Short-term presence of mifepristone either enhanced or did not modify such acute lethality. Seven days after receiving cisplatin-paclitaxel, cultures showed signs of relapse with escaping colonies that repopulated the plate in a time-dependent manner. Conversely, cultures exposed to cisplatin-paclitaxel followed by mifepristone not only did not display signs of repopulation following initial chemotherapy, but they also had their clonogenic capacity drastically reduced when compared to cells repopulating after cisplatin-paclitaxel.

Conclusions

Cytostatic concentrations of mifepristone after exposure to lethal doses of cisplatin and paclitaxel in combination blocks repopulation of remnant cells surviving and escaping the cytotoxic drugs.

No correlation between the expression of FXR and genes involved in multidrug resistance phenotype of primary liver tumors

Farnesoid X receptor (FXR) has been recently reported to enhance chemoresistance through bile acid-independent mechanisms. Thus, FXR transfection plus activation with GW4064 resulted in reduced sensitivity to cisplatin-induced toxicity. This is interesting because primary tumors of the liver, an organ where FXR is expressed, exhibit marked refractoriness to pharmacological treatment. Here we have determined whether FXR is upregulated in hepatocellular carcinoma (HCC), cholangiocarcinoma (CGC) and hepatoblastoma (HPB) and whether this is related with the expression of genes involved in mechanisms of chemoresistance. Using RT-QPCR and Taqman low density arrays we have analyzed biopsies from healthy livers or surgically removed tumors from naive patients and cell lines derived from HCC (SK-HEP-1, Alexander and Huh7), CGC (TFK1) and HPB (HepG2), before and after exposure to cisplatin at IC50 for 72 h. In liver tumors FXR expression was not enhanced but significantly decreased (healthy liver > HCC > HPB ≈ CGC). Except for CGC, this was not accompanied by changes in the proportions of FXR isoforms. Changes in 36 genes involved in drug uptake/efflux and metabolism, expression/function of molecular targets, and survival/apoptosis balance were found. Changes affecting SLC22A1, CYP2A1 and BIRC5 were shared by HCC, CGC and HPB. Similarity in gene expression profiles between cell lines and parent tumors was found. Pharmacological challenge with cisplatin induced changes that increased this resemblance. This was not dependent upon FXR expression. Thus, although FXR may play a role in inducing chemoresistance under certain circumstances, its upregulation does not seem to be involved in the multidrug resistance phenotype characteristic of HCC, CGC and HPB.

Differences in the cellular response and signaling pathways between cisplatin and monodentate organometallic Ru(II) antitumor complexes containing a terphenyl ligand

The new monofunctional Ru(II)-arene complex [(η⁶-arene)Ru(II)(en)Cl]+, where en = 1,2-diaminoethane and the arene is para-terphenyl (complex 1) exhibits promising cytotoxic effects in human tumor cells including those resistant to conventional cisplatin (J. Med. Chem.2008, 51, 5310). The present study is focused on the cellular pharmacology of 1 to elucidate more deeply the mechanisms underlying its antitumor effects. We have identified several cellular mechanisms induced by 1 in human ovarian carcinoma cells, including inhibition of DNA synthesis, overexpression and activation of p53, expression of proapoptotic proteins p21(WAF1) and Bax, G₀/G₁ arrest, and nuclear fragmentation as a result of apoptotic, and, to a much lower extent, also necrotic processes. Thus, 1 inhibits growth of the cancer cells through induction of apoptotic cell death and G₀/G₁ cell cycle arrest. Further investigations have shown that 1 induces apoptosis by regulating the expression of Bcl-2 family proteins. There were significant differences in cellular responses to the treatment with 1 and with conventional cisplatin, particularly in the kinetics and the extent of these responses. In addition, the distinct p53 activation profile of 1 compared with cisplatin provides an explanation for the activity of this ruthenium drug against cisplatin-resistant cells. Hence complex 1 may provide an alternative therapy in patients with acquired cisplatin resistance, particularly with respect to its very low mutagenicity and different mode of action compared to platinum antitumor drugs in clinical use.

Developing central nervous system and vulnerability to platinum compounds

Comparative studies on the effects of the platinum complexes in use or in clinical trials are carried out in order to discover differences in the neurotoxic potential and the reversibility of neurotoxicity. In this paper, we summarized the current literature on neurotoxicity and chemoresistance of cisplatin (cisPt) and discussed our recent efforts on the interference of cisPt and a new platinum compound [Pt(O,O′-acac)(γ-acac)(DMS)] (PtAcacDMS), with high specific reactivity with sulphur ligands instead of nucleobases as cisPt, on some crucial events of rat postnatal cerebellum development. The acute effects of drug treatments on cell proliferation and death in the external granular layer and granule cell migration and the late effects on the dendrite growth of Purkinje cells were evaluated. Together with the demonstrated antineoplastic effectiveness in vitro, compared with cisPt, data suggest a lower neurotoxicity of PtAcacDMS, in spite of its presence in the brain that involves considerations on the blood brain barrier permeability.

The developmental neurotoxicity study of platinum compounds. Effects of cisplatin versus a novel Pt(II) complex on rat cerebellum

In the field of experimental oncology, many efforts are being carried out to search new platinum-based drugs overcoming the CNS toxicity and drug resistance. One of the adopted strategies is the synthesis of platinum compounds able to form Pt-DNA adducts different from the cisplatin ones or to react with other subcellular targets. In this context a novel Pt(II) complex, [Pt(O,O'-acac)(γ-acac)(DMS)](PtAcacDMS), was synthesized which reacts preferentially with protein thiols or thioethers. In this work we investigated the in vivo effects of cisplatin and PtAcacDMS on normal development. Moreover, to verify the dose-dependence of the effects, different groups of animals were treated with 5 μg/g or 10 μg/g body weight of cisPt and PtAcacDMS. We have focused our attention on the cerebellum because it provides a useful model system to evaluate the outcomes of perinatal treatment with chemotherapeutic agents on key CNS developmental processes such as neural cells proliferation, migration and differentiation. We have demonstrated the ability of both cisPt and PtAcacDMS to reach the brain tissue once injected. The brain platinum content after PtAcacDMS treatment was notably higher (approximately 4-fold as much) than after cisPt. The platinum accumulation in the brain was still considerable 7 days after PtAcacDMS administration. However, compared with cisplatin, PtAcacDMS induces less severe changes on fundamental events of neuroarchitecture development, such as no high apoptotic events, less altered granule cell migration and Purkinje cell dendrite growth, suggesting a low neurotoxicity of this new Pt complex for normal CNS. The mild damages could be attributable to the different subcellular target of this compound as well as to a greater efficiency of the cell repair system to recognize the drug-target adducts and to repair them. Together with the previously demonstrated antineoplastic effectiveness in vitro, the findings here reported suggest PtAcacDMS as a potential alternative to cisplatin indicating, at the same time, that the choice of platinum compounds with new subcellular targets could be a strategy to prevent neurotoxicity induced by cisplatin and overcome drug resistance induced by mutations in the intrinsic apoptotic pathway.

Overexpression of DDB2 enhances the sensitivity of human ovarian cancer cells to cisplatin by augmenting cellular apoptosis

Cisplatin is one of the most widely used anticancer agents, displaying activity against a wide variety of tumors. However, development of drug resistance presents a challenging barrier to successful cancer treatment by cisplatin. To understand the mechanism of cisplatin resistance, we investigated the role of damaged DNA binding protein complex subunit 2 (DDB2) in cisplatin-induced cytotoxicity and apoptosis. We show that DDB2 is not required for the repair of cisplatin-induced DNA damage, but can be induced by cisplatin treatment. DDB2-deficient noncancer cells exhibit enhanced resistance to cell growth inhibition and apoptosis induced by cisplatin than cells with fully restored DDB2 function. Moreover, DDB2 expression in cisplatin-resistant ovarian cancer cell line CP70 and MCP2 was lower than their cisplatin-sensitive parental A2780 cells. Overexpression of DDB2 sensitized CP70 cells to cisplatin-induced cytotoxicity and apoptosis via activation of the caspase pathway and downregulation of antiapoptotic Bcl-2 protein. Further analysis indicates that the overexpression of DDB2 in CP70 cells downregulates Bcl-2 expression through decreasing Bcl-2 mRNA level. These results suggest that ovarian cancer cells containing high level of DDB2 become susceptible to cisplatin by undergoing enhanced apoptosis.

Mifepristone abrogates repopulation of ovarian cancer cells in between courses of cisplatin treatment

Repopulation of cancer cells escaping lethal chemotherapy is a critical factor hindering treatment success. One strategy to inhibit tumor cell repopulation is the use of cytostatic compounds between courses of lethal chemotherapy. In this study, we tested the hypothesis that mifepristone (MF), a steroid compound with demonstrated growth inhibition activity in ovarian cancer, should be efficacious in inducing cytostasis and preventing repopulation of ovarian cancer cells if given among rounds of cisplatin (CDDP) treatment. We established an in vitro approach wherein ovarian cancer cells with high (OV2008) or low (SK-OV-3) sensitivity to CDDP were exposed to 3 (OV2008) or 2 (SK-OV-3) rounds of lethal doses of CDDP for 1 h, 12 (OV2008) or 24 (SK-OV-3) days apart. Every 4 or 8 days cell number, cell viability, cell cycle traverse, and colony-forming capacity of viable cells was analyzed. Although CDDP killed the vast majority of cells, there were remnant cells escaping CDDP lethality and repopulating the culture, as evidenced by increased cell number, improved clonogenic capacity of viable cells, and normalization of DNA synthesis. Conversely, when cells were exposed to CDDP for 1 h, and 5, 10 or 20 microM MF was present in the culture medium after CDDP removal, the number, clonogenic capacity, and DNA synthesis ability of the cells were reduced in a dose-dependent manner. The blockage by MF of post-CDDP repopulation was accompanied by a remarkable increase in the percentage of cells expressing the cell death marker cleaved poly(ADP-ribose) polymerase and the mitotic marker phospho-histone H3, suggesting that MF also potentiated CDDP lethality and that the cells likely die due to mitotic failure. In summary, this is the first study reporting that presence of cytostatic concentrations of MF after courses of lethal doses of CDDP prevents repopulation of remnant ovarian cancer cells surviving CDDP treatment.

Resistance to cisplatin does not affect sensitivity of human ovarian cancer cell lines to mifepristone cytotoxicity

BACKGROUND

The prototypical antiprogestin mifepristone exhibits potent growth inhibition activity towards ovarian cancer cells in vitro and in vivo. The aim of this research was to establish whether mifepristone is capable of inhibiting cell proliferation and inducing apoptotic cell death regardless of the degree of sensitivity ovarian cancer cells exhibit to cisplatin.

METHODS

OV2008, OV2008/C13, A2780, A2780/CP70, Caov-3, and SK-OV-3 cell lines exhibiting a range of sensitivities to cisplatin were used. Growth inhibition, cell viability, and sub-diploid DNA content in response to treatment with escalating doses of either mifepristone or cisplatin were assessed by microcapillary cytometry. Apoptotic cell death was evaluated by measuring genomic DNA fragmentation and cleavage of caspase-3 and poly (ADP ribose) polymerase (PARP).

RESULTS

The sensitivities to cisplatin manifested by the cell lines were OV2008 > A2780 > Caov-3 > SK-OV-3 > OV2008/C13 > A2780/CP70. Mifepristone inhibited the growth of all six cell lines in a dose-related manner with IC50s ranging from ~6-12 muM and without significant correlation with the relative sensitivities the cells displayed for cisplatin. Moreover, at the highest concentration studied, mifepristone triggered apoptotic death in all six cell lines as evidenced by the increase in sub-diploid fragmented DNA content and cleavage of caspase-3 and of its downstream substrate PARP.

CONCLUSION

Mifepristone is cytotoxic towards ovarian cancer cells independent of the sensitivity exhibited by the cells to cisplatin, displaying cytostatic effects at lower concentrations and lethal effects at higher concentrations. Mifepristone monotherapy emerges as a valuable therapeutic alternative for platinum-resistant ovarian cancers.

Role of p53, PUMA, and Bax in wogonin-induced apoptosis in human cancer cells

We observed that treatment of prostate cancer cells for 24 h with wogonin, a naturally occurring monoflavonoid, induced cell death in a dose- and time-dependent manner. Exposure of wogonin to LNCaP cells was associated with increased intracellular levels of p21(Cip-1), p27(Kip-1), p53, and PUMA, oligomerization of Bax, release of cytochrome c from the mitochondria, and activation of caspases. We also confirmed the role of p53 by noting that knock-in in p53 expression by transfecting p53 DNA increased wogonin-induced apoptosis in p53-null PC-3 cells. To study the mechanism of PUMA up-regulation, we determined the activities of PUMA promoter in the wogonin treated and untreated cells. Increase of the intracellular levels of PUMA protein was due to increase in transcriptional activity. Data from chromatin immunoprecipitation (ChIP) analyses revealed that wogonin activated the transcription factor p53 binding activity to the PUMA promoter region. We observed that the up-regulation of PUMA mediated wogonin cytotoxicity. Further characterization of the transcriptional response to wogonin in HCT116 human colon cancer cells demonstrated that PUMA induction was p53-dependent; deficiency in either p53 or PUMA significantly protected HCT116 cells against wogonin-induced apoptosis. Also, wogonin promoted mitochondrial translocation and multimerization of Bax. Interestingly, wogonin (100 microM) treatment did not affect the viability of normal human prostate epithelial cells (PrEC). Taken together, these results indicate that p53-dependent transcriptional induction of PUMA and oligomerization of Bax play important roles in the sensitivity of cancer cells to apoptosis induced by caspase activation through wogonin.

Trans-platinum(II) complexes with cyclohexylamine as expectator ligand induce necrosis in tumour cells by inhibiting DNA synthesis and RNA transcription

BACKGROUND

Enhanced removal of cisplatin-DNA adducts has been reported as one of main causes of cell resistance to cisplatin. This particular resistance mechanism may be circumvented by platinum complexes that bind differently to DNA. One line of work is focussed on trans platinum complexes, some of which exhibit antitumour activity similar to or even higher than that of their cis counterparts.

METHODS

We synthesised new trans platinum complexes, trans-[PtCl2(cyclohexylamine)(dimethylamine)] and trans-[PtCl2(OH)2(cyclohexylamine)(dimethylamine)], previously evaluated as cytotoxic agents towards different cancer and normal cell lines. These trans platinum compounds were highly effective against a panel of tumoral cell lines either sensitive to or with acquired resistance to cisplatin.

RESULTS

In the present work we examined the mechanisms induced by these compounds to cause tumour cells toxicity. We have found that these compounds induced a complete blockade at the S phase of the cell cycle inhibiting total mRNA transcription and precluding p53 activation.

CONCLUSION

In contrast to other DNA-damaging agents, these compounds do not induce senescence-associated permanent arrest. Furthermore, only a small percentage of these cells enter into apoptosis, with most of the population dying by a necrosis-like mechanism.

Mifepristone inhibits ovarian cancer cell growth in vitro and in vivo

PURPOSE

These studies were designed to determine whether the synthetic steroid mifepristone inhibits ovarian cancer growth in vitro and in vivo and the molecular mechanisms involved.

EXPERIMENTAL DESIGN

The effect of mifepristone on ovarian cancer cell growth in vitro was studied in ovarian cancer cell lines of different genetic backgrounds (SK-OV-3, Caov-3, OV2008, and IGROV-1). In addition, the growth inhibition capacity of mifepristone on ovarian carcinoma xenografts was tested in nude mice.

RESULTS

Mifepristone inhibited ovarian cancer cell proliferation in a dose- and time-dependent manner. The cytostatic effect of mifepristone was confirmed in a clonogenic survival assay and was not linked to loss of viability. Mifepristone blocked DNA synthesis, arrested the cell cycle at the G(1)-S transition, up-regulated cyclin-dependent kinase (cdk) inhibitors p21(cip1)and p27(kip1), down-regulated transcription factor E2F1, decreased expression of the E2F1-regulated genes cdk1 (cdc2) and cyclin A, and modestly decreased cdk2 and cyclin E levels. The abrupt arrest in cell growth induced by mifepristone correlated with reduced cdk2 activity, increased association of cdk2 with p21(cip1) and p27(kip1), increased nuclear localization of the cdk inhibitors, and reduced nuclear abundance of cdk2 and cyclin E. In vivo, mifepristone significantly delayed the growth of ovarian carcinoma xenografts in a dose-dependent manner and without apparent toxic effects for the animals.

CONCLUSIONS

These preclinical studies show that mifepristone is effective as a single agent in vitro and in vivo, inhibiting the growth of human epithelial ovarian cancer cells. Mifepristone markedly reduces cdk2 activity likely due to increased association of cdk2 with the cdk inhibitors p21(cip1) and p27(kip1) and reduced nuclear cdk2/cyclin E complex availability. Acting as a cytostatic agent, mifepristone promises to be of translational significance in ovarian cancer therapeutics.

RAD001 inhibits human ovarian cancer cell proliferation, enhances cisplatin-induced apoptosis, and prolongs survival in an ovarian cancer model

PURPOSE

mTOR (mammalian target of rapamycin) plays a central role in regulating cell growth and cell cycle progression and is regarded as a promising therapeutic target. We examined whether mTOR inhibition by RAD001 (everolimus) is therapeutically efficacious in the treatment of ovarian cancer as a single agent and in combination with cisplatin.

EXPERIMENTAL DESIGN

Using four human ovarian cancer cell lines, we determined the effect of RAD001 by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, Western blot, and apoptosis assays. We evaluated the association between phospho-AKT/mTOR activity and RAD001 sensitivity. We also determined the effect of RAD001 on tumor growth and malignancy using mice inoculated with human ovarian cancer cells.

RESULTS

RAD001 markedly inhibited cell proliferation of human ovarian carcinoma cells with high AKT activity (OVCAR10 and SKOV-3), but the effect was minimal in cells with low AKT activity (OVCAR4 and OVCAR5). Sensitivity to RAD001 was independent of p53 expression. RAD001 inhibited the phosphorylation of downstream 4E-BP1 and p70S6 kinase and attenuated the expression of Myc. RAD001 also attenuated the expression of HIF-1 alpha and vascular endothelial growth factor, important factors in angiogenesis and tumor invasiveness. RAD001 enhanced cisplatin-induced apoptosis in cells with high AKT/mTOR activity, with minimal effect in cells with low AKT-mTOR activity. Mouse xenografts of SKOV-3 cells revealed that RAD001 inhibits tumor growth, angiogenesis, and i.p. dissemination and ascites production and prolongs survival. Moreover, treatment with RAD001 significantly enhanced the therapeutic efficacy of cisplatin in vivo.

CONCLUSION

These results indicate that RAD001 could have therapeutic efficacy in human ovarian cancers with hyperactivated AKT/mTOR signaling.

Newtrans-Platinum Drugs with Phosphines and Amines as Carrier Ligands Induce Apoptosis in Tumor Cells Resistant to Cisplatin

Cisplatin resistance observed in some human tumors has prompted research in platinum derivatives that can circumvent this effect. Despite initial works reporting lack of activity of trans-platinum derivatives, complexes with the general formula PtCl2(L)(L') exhibit cytotoxic activity in cisplatin-sensitive and -resistant cell lines. Here we reported the chemical and biological properties of seven platinum complexes with PPh3 or PMe2Ph in trans to several amines. They show important antitumoral properties in tumor cell lines. Among the compounds, those with a replacement of an ammine ligand in the inactive trans-DDP by a phosphine ligand have an important enhancement of their cytotoxic activity. In SKOV3, no G1 nor G2/M accumulation was observed after treatments, and apoptosis was launched probably by a mechanism independent of classical checkpoints activation. Our data indicate that our compounds are not cross-resistant with cisplatin and might be promising agents in the treatment of tumors unresponsive to cisplatin.

Structure-activity relationship of new trans-platinum(II) and (IV) complexes with cyclohexylamine. Interference with cell cycle progression and induction of cell death

The new trans-Pt complexes, derived from trans-[PtCl2(amine)(dimethylamine)] and trans-[PtCl2(OH)2(amine)(dimethylamine)], were synthesized and characterized studying the structure-activity relationship and testing their antiproliferative activity. Their evaluation as cytotoxic agents towards different cancer and normal cell lines is presented. These compounds are active in a panel of tumor cell lines at low micromolar range. Compounds seems to be more active in tumoral than in normal primary human cell lines. Cytotoxic activity is closely related to the amine ligand. Cyclohexylamine ligand was the most active among the amine-ligands tested. Cytotoxic activity correlates with an increase in annexin V positive cells indicating an apoptotic effect of the compounds. Mechanistically, the antitumor activity correlates with a blockade of the cell cycle in S phase and a complete abolishment of G2/M checkpoint arrest suggesting physical interaction of compound with DNA inhibiting S phase transition.

Cytotoxic activity of 3-nitropyrazolo[5,1-c][1,2,4]benzotriazine derivatives: a new series of anti-proliferative agents

We report the synthesis and biological evaluation of a new series of 3-nitropyrazolo[5,1-c][1,2,4]benzotriazine derivatives (compounds 1-4) bearing appropriate substitutions in positions 7 and/or 8. The objective of this investigation was to study the effects of these substitutions on the cytotoxic activity of four new compounds against established human cancer cell lines (i.e. HT29 and HCT-8, colon carcinoma, MCF7, breast carcinoma, and A549, lung carcinoma cells). The inhibitory effects of compounds 1-4 on cell growth were assessed by the sulforhodamine B assay. Also, the effects of these compounds on cell cycle distribution of human colon carcinoma cells (HCT-8) were analyzed by flow cytometry. 3-Nitropyrazolo[5,1-c][1,2,4]benzotriazine derivatives displayed IC(50) values in the micromolar range on the growth of the four cell lines tested. Cell cycle perturbations induced on HCT-8 cells by study compounds at the IC(50) values consisted prevalently of a slight accumulation of cells in G(0)/G(1) phase and a slight decrease in G(2)/M phase. However, compound 3 induced a marked accumulation of cells into S phase with concomitant decrease in G(0)/G(1) and G(2)/M phases. Cytotoxicity data, compared to those obtained with 3-cyano-8-chloropyrazolo[5,1-c][1,2,4]benzotriazine 5-oxide (compound 5, NSC 683334) and other compounds previously synthesized in our laboratory, demonstrated a similar or even improved cytotoxic potency. Cell cycle perturbations caused by these compounds support the hypothesis that they may act by a direct or an indirect inhibition of DNA synthesis.

Tumour-cell apoptosis after cisplatin treatment is not telomere dependent

Cisplatin is a major chemotherapeutic agent, especially for the treatment of neuroblastoma. Telomeres with their sequence (TTAGGG)n are probable targets for cisplatin intrastrand cross-linking, but the role of telomeres in mediating cisplatin cytotoxicity is not clear. After exposure to cisplatin as single dose or continuous treatment, we found no loss of telomeres in either SHSY5Y neuroblastoma cells (telomere length, approximately 4 kbp), HeLa 229 cells (telomere length, 20 kbp) or in the acute lymphoblastic T cell line 1301 (telomere length, approximately 80 kbp). There was no induction of telomeric single strand breaks, telomeric overhangs were not degraded and telomerase activity was down-regulated only after massive onset of apoptosis. In contrast, cisplatin induced a delayed formation of DNA strand breaks and induced DNA damage foci containing gamma-H2A.X at nontelomeric sites. Interstitial DNA damage appears to be more important than telomere loss or telomeric damage as inducer of the signal pathway towards apoptosis and/or growth arrest in cisplatin-treated tumour cells.

The BH3-only protein, PUMA, is involved in oxaliplatin-induced apoptosis in colon cancer cells

Oxaliplatin, the first line chemotherapeutic of colon cancer, induces damage to tumors via induction of apoptosis. PUMA (p53 up-regulate modulator of apoptosis) is an important pro-apoptotic member of Bcl-2 family and regulated mainly by p53. Here we investigated the role of PUMA in oxalipaltin-induced apoptosis and the potential mechanism. We showed that oxaliplatin-induced PUMA expression in a time- and dose-dependent manner and suppression of PUMA expression by stable transfecting anti-sense PUMA plasmid decreased oxaliplatin-induced apoptosis in colon cancer cells. By abrogating the function of p53, we further demonstrated that the induction was p53-independent. We also found that oxaliplatin could inactivate ERK and suppression of ERK activity by its specific inhibitor (PD98059), and dominant negative plasmid (DN-MEK1) enhanced the oxaliplatin-induced PUMA expression and apoptosis in a p53-independent manner. Taken together, our data suggest that PUMA plays an important role in oxaliplatin-induced apoptosis and the induction could be both p53-dependent and p53-independent. Moreover, PUMA expression and apoptosis in oxaliplatin-treated colon cancer cells could be regulated partly by ERK inactivation. Identification of the molecular components involved in regulating the cellular sensitivity to oxaliplatin may provide potential targets for development of novel compounds that may be useful in enhancement of oxaliplatin cytotoxicity in p53 deficient colon cancer.

Proteins associated with Cisplatin resistance in ovarian cancer cells identified by quantitative proteomic technology and integrated with mRNA expression levels

Nearly all women diagnosed with ovarian cancer receive combination chemotherapy including cis- or carboplatin. Despite high initial response rates, resistance to cisplatin develops in roughly one-third of women during primary treatment and in all women treated for recurrent disease. ICAT coupled with tandem MS is a quantitative proteomic technique for high throughput protein expression profiling of complex protein mixtures. Using ICAT/MS/MS we profiled the nuclear, cytosolic, and microsomal fractions obtained from IGROV-1 [corrected] (cisplatin-sensitive) and IGROV-1/CP [corrected] (cisplatin-resistant) ovarian cancer cell lines. The proteomes of cisplatin-sensitive and -resistant ovarian cancer cells were compared, and protein expression was correlated with mRNA expression profiles. A total of 1117 proteins were identified and quantified. The relative expression of 121 of these varied between the two cell lines. Sixty-three proteins were overexpressed in cisplatin-sensitive, and 58 were over expressed in cisplatin-resistant cells. Examples of proteins at least 5-fold overexpressed in resistant cells and with biological relevance to cancer include cell recognition molecule CASPR3 (13.3-fold), S100 protein family members (8.7-fold), junction adhesion molecule Claudin 4 (7.2-fold), and CDC42-binding protein kinase beta (5.4-fold). Examples of cancer-related proteins at least 5-fold overexpressed in sensitive cells include hepatocyte growth factor inhibitor 1B (13.3-fold) and programmed cell death 6-interacting protein (12.7-fold). The direction of changes in expression levels between proteins and mRNAs were not always in the same direction, possibly reflecting posttranscriptional control of protein expression. We identified proteins whose expression profiles correlate with cisplatin resistance in ovarian cancer cells. Several proteins may be involved in modulating response to cisplatin and have potential as markers of treatment response or treatment targets.

Tumour resistance to cisplatin: a modelling approach

Although chemotherapy has revolutionized the treatment of haematological tumours, in many common solid tumours the success has been limited. Some of the reasons for the limitations are: the timing of drug delivery, resistance to the drug, repopulation between cycles of chemotherapy and the lack of complete understanding of the pharmacokinetics and pharmacodynamics of a specific agent. Cisplatin is among the most effective cytotoxic agents used in head and neck cancer treatments. When modelling cisplatin as a single agent, the properties of cisplatin only have to be taken into account, reducing the number of assumptions that are considered in the generalized chemotherapy models. The aim of the present paper is to model the biological effect of cisplatin and to simulate the consequence of cisplatin resistance on tumour control. The 'treated' tumour is a squamous cell carcinoma of the head and neck, previously grown by computer-based Monte Carlo techniques. The model maintained the biological constitution of a tumour through the generation of stem cells, proliferating cells and non-proliferating cells. Cell kinetic parameters (mean cell cycle time, cell loss factor, thymidine labelling index) were also consistent with the literature. A sensitivity study on the contribution of various mechanisms leading to drug resistance is undertaken. To quantify the extent of drug resistance, the cisplatin resistance factor (CRF) is defined as the ratio between the number of surviving cells of the resistant population and the number of surviving cells of the sensitive population, determined after the same treatment time. It is shown that there is a supra-linear dependence of CRF on the percentage of cisplatin-DNA adducts formed, and a sigmoid-like dependence between CRF and the percentage of cells killed in resistant tumours. Drug resistance is shown to be a cumulative process which eventually can overcome tumour regression leading to treatment failure.

Disruption of WT1 gene expression and exon 5 splicing following cytotoxic drug treatment: Antisense down-regulation of exon 5 alters target gene expression and inhibits cell survival

Deregulated expression of the Wilms' tumor gene (WT1) has been implicated in the maintenance of a malignant phenotype in leukemias and a wide range of solid tumors through interference with normal signaling in differentiation and apoptotic pathways. Expression of high levels of WT1 is associated with poor prognosis in leukemias and breast cancer. Using real-time (Taqman) reverse transcription-PCR and RNase protection assay, we have shown up-regulation of WT1 expression following cytotoxic treatment of cells exhibiting drug resistance, a phenomenon not seen in sensitive cells. WT1 is subject to alternative splicing involving exon 5 and three amino acids (KTS) at the end of exon 9, producing four major isoforms. Exon 5 splicing was disrupted in all cell lines studied following a cytotoxic insult probably due to increased exon 5 skipping. Disruption of exon 5 splicing may be a proapoptotic signal because specific targeting of WT1 exon 5–containing transcripts using a nuclease-resistant antisense oligonucleotide (ASO) killed HL60 leukemia cells, which were resistant to an ASO targeting all four alternatively spliced transcripts simultaneously. K562 cells were sensitive to both target-specific ASOs. Gene expression profiling following treatment with WT1 exon 5–targeted antisense showed up-regulation of the known WT1 target gene, thrombospondin 1, in HL60 cells, which correlated with cell death. In addition, novel potential WT1 target genes were identified in each cell line. These studies highlight a new layer of complexity in the regulation and function of the WT1 gene product and suggest that antisense directed to WT1 exon 5 might have therapeutic potential.

Induction of apoptosis and necrosis in A549 cells by the cis-Pt(II) complex of 3-aminoflavone in comparison with cis-DDP

Non-small cell lung cancer (NSCLC) includes a group of tumors that respond poorly to drugs. cis-Diamminedichloroplatinum(II) (cis-DDP) toxicity still remains problematic, and not completely solved by the improvement of supportive care. Therefore, the cis-Pt(II) complex of 3-aminoflavone was selected from cis-DDP analogues with a more favourable toxic profile towards normal cells and at least similar or better anti-tumor activity in comparison with cis-DDP. The aim of this research is to compare the ability of the cis-Pt(II) complex of 3-aminoflavone and cis-DDP to induce apoptosis and necrosis in the human non-small cancer cell line A549. Trypan blue dye exclusion, fluorochrome staining (acridine orange/ethidium bromide double staining), MTT and TUNEL (TdT-mediated dUTP Nick-End Labeling) assays were used. The results obtained show that the cis-Pt(II) complex of 3-aminoflavone is more active in inducing apoptosis and necrosis and in decreasing viability in A549 cells than cis-DDP, which suggests that it could be a potential chemotherapeutic drug.

Synthesis and biological evaluation of novel chloroethylaminoanthraquinones with potent cytotoxic activity against cisplatin-resistant tumor cells

Novel 1- and 1,4-substituted chloroethylaminoanthraquinones with DNA binding and alkylating properties along with their respective hydroxyethylaminoanthraquinone intermediates were synthesized. Selected chloroethylaminoanthraquinones were shown to cross-link DNA and alkylate guanines (at low nM concentration) with a preference for reaction sites containing 5'-PyG. A compound (Alchemix) with the bis-chloroethyl functionality confined to one side chain alkylated but did not cross-link DNA. All the 1,4-disubstituted chloroethylaminoanthraquinones were potently cytotoxic (nM IC(50)s) against cisplatin-resistant ovarian cancer cell lines.

Cisplatin: mode of cytotoxic action and molecular basis of resistance

Cisplatin is one of the most potent antitumor agents known, displaying clinical activity against a wide variety of solid tumors. Its cytotoxic mode of action is mediated by its interaction with DNA to form DNA adducts, primarily intrastrand crosslink adducts, which activate several signal transduction pathways, including those involving ATR, p53, p73, and MAPK, and culminate in the activation of apoptosis. DNA damage-mediated apoptotic signals, however, can be attenuated, and the resistance that ensues is a major limitation of cisplatin-based chemotherapy. The mechanisms responsible for cisplatin resistance are several, and contribute to the multifactorial nature of the problem. Resistance mechanisms that limit the extent of DNA damage include reduced drug uptake, increased drug inactivation, and increased DNA adduct repair. Origins of these pharmacologic-based mechanisms, however, are at the molecular level. Mechanisms that inhibit propagation of the DNA damage signal to the apoptotic machinery include loss of damage recognition, overexpression of HER-2/neu, activation of the PI3-K/Akt (also known as PI3-K/PKB) pathway, loss of p53 function, overexpression of antiapoptotic bcl-2, and interference in caspase activation. The molecular signature defining the resistant phenotype varies between tumors, and the number of resistance mechanisms activated in response to selection pressures dictates the overall extent of cisplatin resistance.

As(2)O(3) enhances retroviral reverse transcription and counteracts Ref1 antiviral activity

Potent drugs such as cyclosporine have provided effective probes of signal transduction pathways and, as well, of human immunodeficiency virus type 1 (HIV-1) replication mechanisms. Recently, it was reported that As(2)O(3), a drug used to treat acute promyelocytic leukemia (PML), stimulates HIV-1 replication. We found that As(2)O(3) accelerates the kinetics of a spreading HIV-1 infection in human T cells and increases the number of cells bearing HIV-1 provirus after a single round of infection. The stimulatory effect occurred after membrane fusion and resulted in increased steady-state levels of newly synthesized viral cDNA. Stimulation was independent of HIV-1 env and most viral accessory genes, and As(2)O(3) had no detectable effects on viral expression postintegration or virion assembly. Murine leukemia virus (MLV) transduction was enhanced by As(2)O(3) to the same extent as HIV-1 transduction, but As(2)O(3) had no additional effect on Fv1 restriction. In contrast, As(2)O(3) largely overcame the specific block to N-tropic MLV reverse transcription posed by human Ref1. As(2)O(3) disrupts PML bodies, nuclear structures named for a major component, the PML protein. We observed no changes in PML bodies in response to HIV-1 infection. Experiments with PML-null target cells indicated that PML has no effect on HIV-1 infectivity and is dispensable for the stimulatory effect of As(2)O(3). As(2)O(3) caused cell death in uninfected cells at the same concentrations which stimulate HIV-1 replication. Among four additional apoptosis-inducing agents, a boost in HIV-1 infectivity was observed only with carbonyl cyanide m-chlorophenylhydrazone, a compound which, like As(2)O(3), disrupts the mitochondrial transmembrane potential. In summary, As(2)O(3) stimulates retroviral reverse transcription, perhaps via effects on mitochondria, and provides a useful tool for characterizing Ref1.

Using flow cytometry to follow the apoptotic cascade

Flow cytometry has been extensively used to follow the apoptotic cascade and to enumerate apoptotic cells, both in cell cultures and, to a lesser extent, in tissue biopsies. An overview of the apoptotic cascade and how flow cytometric measurements can be used to observe the different elements of this process is presented.

Overexpression of BclXL in a human ovarian carcinoma cell line: paradoxic effects on chemosensitivity in vitro versus in vivo

The effect of overexpressing the antiapoptotic protein BclXL in a human ovarian carcinoma cell line has been investigated in terms of sensitivity to the 2 major drugs used to treat this disease, paclitaxel and cisplatin. Stable transfection of BclXL into CH1 cells, which are relatively sensitive to cisplatin, resulted in around 2.7-fold higher expression in comparison with empty vector controls. However, this level of overexpression did not result in significant resistance in vitro to paclitaxel or cisplatin at the 50% inhibition level, using either short-term (4-day) growth inhibition or longer term colony-forming assays. By contrast, parallel subcutaneous xenograft models of these isogenic ovarian carcinoma cells in vivo, differing only in BclXL status, showed that this low-level BclXL overexpression conferred significant resistance to both paclitaxel and cisplatin in comparison with parent, nontransfected tumours. Whereas parent non-BclXL transfected tumours were highly responsive, with the disappearance of tumours for at least 50 days post treatment, tumours overexpressing BclXL grew back after 30 and 20 days after treatment with paclitaxel and cisplatin, respectively. These differences in responsiveness to paclitaxel in vivo were not attributable to any significant changes in the delivery of drug to the tumour. These data suggest that the responsiveness of ovarian cancer to paclitaxel and cisplatin in vivo, and therefore perhaps clinically, is influenced by levels of the antiapoptotic protein BclXL. Such effects may be missed in vitro when using short-term growth inhibition or clonogenic assays.

Current status of the development of trans-platinum antitumor drugs

The discovery in the 1990s of several trans-Pt complexes with in vitro and in vivo activity against tumor cells sensitive and/or resistant to cisplatin has forced the re-evaluation of the structure-activity relationships for platinum antitumor drugs. Because the determinant factors of cytotoxic activity of trans-platinum complexes do not follow the same patterns as those found for cisplatin and its analogues, the differences in cellular and biochemical pharmacology between trans-platinum antitumor complexes and cisplatin might be systematically exploited to design novel trans-platinum complexes with a clinical profile complementary to that of cisplatin and related analogues. Therefore, there may exist a novel molecular rationale for new platinum antitumor drugs development in the twenty-first century.