Potent Killing of Paclitaxel- and Doxorubicin-resistant Breast Cancer Cells by Calphostin C Accompanied by Cytoplasmic Vacuolization

Cystathionine gamma-lyase/H2 S signaling facilitates myogenesis under aging and injury condition

Hydrogen sulfide (H₂ S) can be endogenously produced and belongs to the class of signaling molecules known as gasotransmitters. Cystathionine gamma-lyase (CSE)-derived H₂ S is implicated in the regulation of cell differentiation and the aging process, but the involvements of the CSE/H₂ S system in myogenesis upon aging and injury have not been explored. In this study, we demonstrated that CSE acts as a major H₂ S-generating enzyme in skeletal muscles and is significantly down-regulated in aged skeletal muscles in mice. CSE deficiency exacerbated the age-dependent sarcopenia and cardiotoxin-induced injury/regeneration in mouse skeletal muscle, possibly attributed to inefficient myogenesis. In contrast, supplement of NaHS (an H₂ S donor) induced the expressions of myogenic genes and promoted muscle regeneration in mice. In vitro, incubation of myoblast cells (C2C12) with H₂ S promoted myogenesis, as evidenced by the inhibition of cell cycle progression and migration, altered expressions of myogenic markers, elongation of myoblasts, and formation of multinucleated myotubes. Myogenesis was also found to upregulate CSE expression, while blockage of CSE/H₂ S signaling resulted in a suppression of myogenesis. Mechanically, H₂ S significantly induced the heterodimer formation between MEF2c and MRF4 and promoted the binding of MEF2c/MRF4 to myogenin promoter. MEF2c was S-sulfhydrated at both cysteine 361 and 420 in the C-terminal transactivation domain, and blockage of MEF2c S-sulfhydration abolished the stimulatory role of H₂ S on MEF2c/MRF4 heterodimer formation. These findings support an essential role for H₂ S in maintaining myogenesis, presenting it as a potential candidate for the prevention of age-related sarcopenia and treatment of muscle injury.

Calotropis procera (Aiton) Dryand (Apocynaceae) as an anti-cancer agent against canine mammary tumor and osteosarcoma cells

Our goal was to evaluate phytochemical characterization and the antitumor potential of Calotropis procera. The phytochemical constitution of the crude extract (CE) revealed the presence of flavonoids, glycosides and cardenolide. The MTT assay was used to evaluate the cytotoxicity of CE, methanolic (MF) and ethyl acetate fractions (EAF) of C. procera in canine osteosarcoma cells (OST), canine mammary tumor (CMT), and canine skin fibroblasts (non-tumor cell). Doxorubicin was also used as a positive control. Results showed that CE, MF and EAF promoted a decrease in the viability of OST and CMT cells and did not alter the fibroblasts viability. C. procera also decreased the number of cells, corroborating to the decrease in proliferation and the cell cycle arrest in the G0/G1 phase. It was also evaluated the cell morphology by light and fluorescence microscopy, being demonstrated a reduction in cytoplasmic and cell rounding characteristic of programmed cell death. Moreover, flow cytometry data demonstrated that CE treatment promoted increase of caspase-3 and p53, showing that the cell death was activated in OST cells. In addition, there was a decrease in CD31, VEGF, osteopontin and TGF-β after CE treatment, suggesting that CE exerts its antitumor effect by reducing angiogenesis and tumor progression in OST cells. Moreover, CMT cells showed a reduction in PCNA after treatment with MF and CE. Analyzing the data together, C. procera, especially CE, showed an antitumor potential in both OST and CMT cells, encouraging us to continue investigating its use in cancer therapy.

Role of autophagy and lysosomal drug sequestration in acquired resistance to doxorubicin in MCF-7 cells

Background

The roles and mechanisms involved in starvation-induced autophagy in mammalian cells have been extensively studied. However, less is known about the potential role for autophagy as a survival pathway in acquired drug resistance in cancer cells under nutrient-rich conditions.

Methods

We selected MCF-7 breast tumor cells for survival in increasing concentrations of doxorubicin and assessed whether the acquisition of doxorubicin resistance was accompanied by changes in doxorubicin and lysosome localization and the activation of autophagy, as assessed by laser scanning confocal microscopy with or without immunohistochemical approaches. The ultrastructure of cells was also viewed using transmission electron microscopy. Cellular levels of autophagy and apoptosis-related proteins were assessed by immunoblotting techniques, while protein turnover was quantified using a flux assay.

Results

As cells acquired resistance to doxorubicin, the subcellular location of the drug moved from the nucleus to the perinuclear region. The location of lysosomes and autophagosomes also changed from being equally distributed throughout the cytoplasm to co-localizing with doxorubicin in the perinuclear region. There was an apparent temporal correlation between the acquisition of doxorubicin resistance and autophagy induction, as measured by increases in monodansylcadaverine staining, LC3-II production, and co-localization of LAMP1 and LC3-II immunofluorescence. Electron microscopy revealed an increase in cytoplasmic vacuoles containing mitochondria and other cellular organelles, also suggestive of autophagy. Consistent with this view, a known autophagy inhibitor (chloroquine) was highly effective in restoring doxorubicin sensitivity in doxorubicin-resistant cells. Moreover, this induction of autophagy correlated temporally with increased expression of the selective cargo receptor p62, which facilitates the delivery of doxorubicin-damaged mitochondria and other organelles to autophagosomes. Finally, we suggest that autophagy associated with doxorubicin resistance may be distinct from classical starvation-induced autophagy, since Beclin 1 and Atg7 expression did not change upon acquisition of doxorubicin resistance, nor did recombinant Bcl2 overexpression or an Atg7 knockdown alter doxorubicin cytotoxicity.

Conclusion

Taken together, our findings suggest that doxorubicin resistance in MCF-7 breast cancer cells is mediated, at least in part, by the activation of autophagy, which may be distinct from starvation-induced autophagy.

RNA disruption is associated with response to multiple classes of chemotherapy drugs in tumor cell lines

BACKGROUND

Cellular stressors and apoptosis-inducing agents have been shown to induce ribosomal RNA (rRNA) degradation in eukaryotic cells. Recently, RNA degradation in vivo was observed in patients with locally advanced breast cancer, where mid-treatment tumor RNA degradation was associated with complete tumor destruction and enhanced patient survival. However, it is not clear how widespread chemotherapy induced "RNA disruption" is, the extent to which it is associated with drug response or what the underlying mechanisms are.

METHODS

Ovarian (A2780, CaOV3) and breast (MDA-MB-231, MCF-7, BT474, SKBR3) cancer cell lines were treated with several cytotoxic chemotherapy drugs and total RNA was isolated. RNA was also prepared from docetaxel resistant A2780DXL and carboplatin resistant A2780CBN cells following drug exposure. Disruption of RNA was analyzed by capillary electrophoresis. Northern blotting was performed using probes complementary to the 28S and 18S rRNA to determine the origins of degradation bands. Apoptosis activation was assessed by flow cytometric monitoring of annexin-V and propidium iodide (PI) binding to cells and by measuring caspase-3 activation. The link between apoptosis and RNA degradation (disruption) was investigated using a caspase-3 inhibitor.

RESULTS

All chemotherapy drugs tested were capable of inducing similar RNA disruption patterns. Docetaxel treatment of the resistant A2780DXL cells and carboplatin treatment of the A2780CBN cells did not result in RNA disruption. Northern blotting indicated that two RNA disruption bands were derived from the 3'-end of the 28S rRNA. Annexin-V and PI staining of docetaxel treated cells, along with assessment of caspase-3 activation, showed concurrent initiation of apoptosis and RNA disruption, while inhibition of caspase-3 activity significantly reduced RNA disruption.

CONCLUSIONS

Supporting the in vivo evidence, our results demonstrate that RNA disruption is induced by multiple chemotherapy agents in cell lines from different tissues and is associated with drug response. Although present, the link between apoptosis and RNA disruption is not completely understood. Evaluation of RNA disruption is thus proposed as a novel and effective biomarker to assess response to chemotherapy drugs in vitro and in vivo.

A novel approach to overcome multidrug resistance: utilization of P-gp mediated efflux of paclitaxel to attack neighboring vascular endothelial cells in tumors

We tried to overcome the paclitaxel (PTX) resistance of cancer cells due to P-glycoprotein (P-gp) overexpression in the in vivo anti-tumor chemotherapy by utilizing polyethylene glycol-modified liposomal paclitaxel (PL-PTX). First of all, established were PTX-resistant Colon-26 cancer cells (C26/PTX) overexpressing P-gp, which provided IC50 value of PTX solution about 30 times larger than that obtained for control C26 (C26/control) in the in vitro MTT assay. Western blot analysis confirmed P-gp expression in C26/PTX 10 times higher than that in C26/control, indicating that the resistance acquisition of C26/PTX to PTX would be ascribed to the enhanced efflux of PTX by P-gp overexpressed in C26/PTX. However, the in vivo anti-tumor effect of PL-PTX in C26/PTX-bearing mice was similar to that in C26/control-bearing mice. Double immunohistochemical staining of vascular endothelial cells and apoptotic cells within tumor tissues demonstrated that the apoptotic cell death was preferentially observed in vascular endothelial cells in C26/PTX tumors after intravenous administration of PL-PTX, while that was in tumor cells in C26/control tumors. These results suggest that the in vivo anti-tumor effect of PL-PTX in C26/PTX-bearing mice would be ascribed to the cytotoxic action of PTX pumped out of tumor cells by overexpressed P-gp to vascular endothelial cells in tumor tissues.

Distinct genetic alterations occur in ovarian tumor cells selected for combined resistance to carboplatin and docetaxel

BACKGROUND

Current protocols for the treatment of ovarian cancer include combination chemotherapy with a platinating agent and a taxane. However, many patients experience relapse of their cancer and the development of drug resistance is not uncommon, making successful second line therapy difficult to achieve. The objective of this study was to develop and characterize a cell line resistant to both carboplatin and docetaxel (dual drug resistant ovarian cell line) and to compare this cell line to cells resistant to either carboplatin or docetaxel.

METHODS

The A2780 epithelial endometrioid ovarian cancer cell line was used to select for isogenic carboplatin, docetaxel and dual drug resistant cell lines. A selection method of gradually increasing drug doses was implemented to avoid clonal selection. Resistance was confirmed using a clonogenic assay. Changes in gene expression associated with the development of drug resistance were determined by microarray analysis. Changes in the expression of selected genes were validated by Quantitative Real-Time Polymerase Chain Reaction (QPCR) and immunoblotting.

RESULTS

Three isogenic cell lines were developed and resistance to each drug or the combination of drugs was confirmed. Development of resistance was accompanied by a reduced growth rate. The microarray and QPCR analyses showed that unique changes in gene expression occurred in the dual drug resistant cell line and that genes known to be involved in resistance could be identified in all cell lines.

CONCLUSIONS

Ovarian tumor cells can acquire resistance to both carboplatin and docetaxel when selected in the presence of both agents. Distinct changes in gene expression occur in the dual resistant cell line indicating that dual resistance is not a simple combination of the changes observed in cell lines exhibiting single agent resistance.

Perylenequinones: Isolation, Synthesis, and Biological Activity

The perylenequinones are a novel class of natural products characterized by pentacyclic conjugated chromophore giving rise to photoactivity. Potentially useful light-activated biological activity, targeting protein kinase C (PKC), has been identified for several of the natural products. Recently discovered new members of this class of compound, as well as several related phenanthroperylenequinones, are reviewed. Natural product modifications that improve biological profiles, and avenues for the total synthesis of analogs, which are not available from the natural product series, are outlined. An overview of structure/function relationships is provided.

Synthesis and evaluation of indole-based chalcones as inducers of methuosis, a novel type of nonapoptotic cell death

Methuosis is a novel caspase-independent form of cell death in which massive accumulation of vacuoles derived from macropinosomes ultimately causes cells to detach from the substratum and rupture. We recently described a chalcone-like compound, 3-(2-methyl-1H-indol-3-yl)-1-(4-pyridinyl)-2-propen-1-one (i.e., MIPP), which can induce methuosis in glioblastoma and other types of cancer cells. Herein, we describe the synthesis and structure-activity relationships of a directed library of related compounds, providing insights into the contributions of the two aryl ring systems and highlighting a potent derivative, 3-(5-methoxy, 2-methyl-1H-indol-3-yl)-1-(4-pyridinyl)-2-propen-1-one (i.e., MOMIPP) that can induce methuosis at low micromolar concentrations. We have also generated biologically active azide derivatives that may be useful for future studies aimed at identifying the protein targets of MOMIPP by photoaffinity labeling techniques. The potential significance of these studies is underscored by the finding that MOMIPP effectively reduces the growth and viability of Temozolomide-resistant glioblastoma and doxorubicin-resistant breast cancer cells. Thus, it may serve as a prototype for drugs that could be used to trigger death by methuosis in cancers that are resistant to conventional forms of cell death (e.g., apoptosis).

Enhancing photodynamyc therapy efficacy by combination therapy: dated, current and oncoming strategies

Combination therapy is a common practice in many medical disciplines. It is defined as the use of more than one drug to treat the same disease. Sometimes this expression describes the simultaneous use of therapeutic approaches that target different cellular/molecular pathways, increasing the chances of killing the diseased cell. This short review is concerned with therapeutic combinations in which PDT (Photodynamyc Therapy) is the core therapeutic partner. Besides the description of the principal methods used to assess the efficacy attained by combinations in respect to monotherapy, this review describes experimental results in which PDT was combined with conventional drugs in different experimental conditions. This inventory is far from exhaustive, as the number of photosensitizers used in combination with different drugs is very large. Reports cited in this work have been selected because considered representative. The combinations we have reviewed include the association of PDT with anti-oxidants, chemotherapeutics, drugs targeting topoisomerases I and II, antimetabolites and others. Some paragraphs are dedicated to PDT and immuno-modulation, others to associations of PDT with angiogenesis inhibitors, receptor inhibitors, radiotherapy and more. Finally, a look is dedicated to combinations involving the use of natural compounds and, as new entries, drugs that act as proteasome inhibitors.

Mechanisms of resistance to photodynamic therapy

Photodynamic therapy (PDT) involves the administration of a photosensitizer (PS) followed by illumination with visible light, leading to generation of reactive oxygen species. The mechanisms of resistance to PDT ascribed to the PS may be shared with the general mechanisms of drug resistance, and are related to altered drug uptake and efflux rates or altered intracellular trafficking. As a second step, an increased inactivation of oxygen reactive species is also associated to PDT resistance via antioxidant detoxifying enzymes and activation of heat shock proteins. Induction of stress response genes also occurs after PDT, resulting in modulation of proliferation, cell detachment and inducing survival pathways among other multiple extracellular signalling events. In addition, an increased repair of induced damage to proteins, membranes and occasionally to DNA may happen. PDT-induced tissue hypoxia as a result of vascular damage and photochemical oxygen consumption may also contribute to the appearance of resistant cells. The structure of the PS is believed to be a key point in the development of resistance, being probably related to its particular subcellular localization. Although most of the features have already been described for chemoresistance, in many cases, no cross-resistance between PDT and chemotherapy has been reported. These findings are in line with the enhancement of PDT efficacy by combination with chemotherapy. The study of cross resistance in cells with developed resistance against a particular PS challenged against other PS is also highly complex and comprises different mechanisms. In this review we will classify the different features observed in PDT resistance, leading to a comparison with the mechanisms most commonly found in chemo resistant cells.

Tamoxifen inhibits TRPV6 activity via estrogen receptor-independent pathways in TRPV6-expressing MCF-7 breast cancer cells

The epithelial calcium channel TRPV6 is upregulated in breast carcinoma compared with normal mammary gland tissue. The selective estrogen receptor modulator tamoxifen is widely used in breast cancer therapy. Previously, we showed that tamoxifen inhibits calcium uptake in TRPV6-transfected Xenopus oocytes. In this study, we examined the effect of tamoxifen on TRPV6 function and intracellular calcium homeostasis in MCF-7 breast cancer cells transiently transfected with EYFP-C1-TRPV6. TRPV6 activity was measured with fluorescence microscopy using Fura-2. The basal calcium level was higher in transfected cells compared with nontransfected cells in calcium-containing solution but not in nominally calcium-free buffer. Basal influxes of calcium and barium were also increased. In transfected cells, 10 mumol/L tamoxifen reduced the basal intracellular calcium concentration to the basal calcium level of nontransfected cells. Tamoxifen decreased the transport rates of calcium and barium in transfected cells by 50%. This inhibitory effect was not blocked by the estrogen receptor antagonist, ICI 182,720. Similarly, a tamoxifen-induced inhibitory effect was also observed in MDA-MB-231 estrogen receptor-negative cells. The effect of tamoxifen was completely blocked by activation of protein kinase C. Inhibiting protein kinase C with calphostin C decreased TRPV6 activity but did not alter the effect of tamoxifen. These findings illustrate how tamoxifen might be effective in estrogen receptor-negative breast carcinomas and suggest that the therapeutic effect of tamoxifen and protein kinase C inhibitors used in breast cancer therapy might involve TRPV6-mediated calcium entry. This study highlights a possible role of TRPV6 as therapeutic target in breast cancer therapy.

Killing of cancer cells by the photoactivatable protein kinase C inhibitor, calphostin C, involves induction of endoplasmic reticulum stress

Calphostin C (cal-C) is a photoactivatable inhibitor that binds to the regulatory domain of protein kinase C (PKC) and to other proteins that contain diacylglycerol/phorbol ester binding sites. Cal-C is cytotoxic against many types of cancer cells, yet the basis for this activity remains poorly understood. Here, we show that one of the earliest effects of cal-C is an impairment of glycoprotein export from the endoplasmic reticulum (ER), accompanied by formation of ER-derived vacuoles. Vacuolization of the ER is correlated with induction of an ER stress response that includes activation of c-Jun N-terminal kinase and protein kinase R-like ER kinase, as well as increased expression of CCAAT/enhancer binding protein homologous transcription factor (CHOP; GADD153). These effects of cal-C are not mimicked by staurosporine, an inhibitor of PKC catalytic activity, indicating that ER stress is due to interaction of cal-C with targets other than PKC. In conjunction with the induction of ER stress, breast carcinoma cells undergo caspase-dependent cell death with early activation of caspases 9 and 7 and cleavage of poly(ADP-ribose)polymerase. Reduction of CHOP expression by short hairpin RNA decreases the sensitivity of the cells to cal-C, suggesting that induction of apoptosis by cal-C is related, at least in part, to ER stress triggered by disruption of ER morphology and transport function. Antineoplastic drugs that work by inducting ER stress have shown promise in preclinical and clinical trials. Thus, the present findings raise the possibility that cal-C may be useful for photodynamic therapy based on induction of ER stress in some forms of cancer.

Design, synthesis, and investigation of protein kinase C inhibitors: total syntheses of (+)-calphostin D, (+)-phleichrome, cercosporin, and new photoactive perylenequinones

The total syntheses of the PKC inhibitors (+)-calphostin D, (+)-phleichrome, cercosporin, and 10 novel perylenequinones are detailed. The highly convergent and flexible strategy developed employed an enantioselective oxidative biaryl coupling and a double cuprate epoxide opening, allowing the selective syntheses of all the possible stereoisomers in pure form. In addition, this strategy permitted rapid access to a broad range of analogues, including those not accessible from the natural products. These compounds provided a powerful means for evaluation of the perylenequinone structural features necessary to PKC activity. Simpler analogues were discovered with superior PKC inhibitory properties and superior photopotentiation in cancer cell lines relative to the more complex natural products.

Induction of 1C aldoketoreductases and other drug dose-dependent genes upon acquisition of anthracycline resistance

OBJECTIVES

Recent studies suggest that tumor cells overexpressing aldoketoreductases (AKRs) exhibit increased resistance to DNA damaging agents such as anthracyclines. AKRs may induce resistance to the anthracycline doxorubicin by catalyzing its conversion to the less toxic 13-hydroxy metabolite doxorubicinol. However, it has not been established whether during selection for anthracycline resistance, AKR overexpression in tumor cells can be correlated with the onset or magnitude of drug resistance and with appreciable conversion of anthracyclines to 13-hydroxy metabolites.

METHODS AND FINDINGS

Through microarray and quantitative polymerase chain reaction studies involving rigid selection criteria and both correlative discriminate statistics and time-course models, we have identified several genes whose expression can be correlated with the onset and/or magnitude of anthracycline resistance, including AKR1C2 and AKR1C3. Also associated with the onset or magnitude of anthracycline resistance were genes involved in drug transport (ABCB1, ABCC1), cell signaling and transcription (RDC1, CXCR4), cell proliferation or apoptosis (BMP7, CAV1), protection from reactive oxygen species (AKR1C2, AKR1C3, FTL, FTH, TXNRD1, MT2A), and structural or immune system proteins (IFI30, STMN1). As expected, doxorubicin-resistant and epirubicin-resistant cells exhibited higher levels of doxorubicinol than wild-type cells, although at insufficient levels to account for significant drug resistance. Nevertheless, an inhibitor of Akr1c2 (5beta-cholanic acid) almost completely restored sensitivity to doxorubicin in ABCB1-deficient doxorubicin-resistant cells, while having no effect on ABCB1-expressing epirubicin-resistant cells.

CONCLUSION

Taken together, we show for the first time that a variety of genes (particularly redox genes such as AKR1C2 and AKR1C3) can be temporally and causally correlated with the acquisition of anthracycline resistance in breast tumor cells.

Light scattering measurements of subcellular structure provide noninvasive early detection of chemotherapy-induced apoptosis

We present a light scattering study using angle-resolved low coherence interferometry (a/LCI) to assess nuclear morphology and subcellular structure within MCF-7 cells at several time points after treatment with chemotherapeutic agents. Although the nuclear diameter and eccentricity are not observed to change, the light scattering signal reveals a change in the organization of subcellular structures that we interpret using fractal dimension (FD). The FD of subcellular structures in cells treated with paclitaxel and doxorubicin is observed to increase significantly compared with that of control cells as early as 1.5 and 3 hours after application, respectively. The FD is then found to decrease slightly at 6 hours postapplication for both agents only to increase again from 12 to 24 hours posttreatment when the observations ceased. The changes in structure appear over two time scales, suggesting that multiple mechanisms are evident in these early apoptotic stages. Indeed, quantitative image analysis of fluorescence micrographs of cells undergoing apoptosis verifies that the FD of 4',6-diamidino-2-phenylindole-stained nuclear structures does not change significantly in cells until 12 hours after treatment, whereas that of MitoTracker stained mitochondria is seen to modulate as early as 3 hours after treatment. In contrast, cells receiving an increased dose of paclitaxel that induced G(2)-M arrest, but not apoptosis, only exhibited the early change in subcellular structure but did not show the later change associated with changes in nuclear substructure. These results suggest that a/LCI may have utility in detecting early apoptotic events for both clinical and basic science applications.

Role of drug transporters and drug accumulation in the temporal acquisition of drug resistance

Background

Anthracyclines and taxanes are commonly used in the treatment of breast cancer. However, tumor resistance to these drugs often develops, possibly due to overexpression of drug transporters. It remains unclear whether drug resistance in vitro occurs at clinically relevant doses of chemotherapy drugs and whether both the onset and magnitude of drug resistance can be temporally and causally correlated with the enhanced expression and activity of specific drug transporters. To address these issues, MCF-7 cells were selected for survival in increasing concentrations of doxorubicin (MCF-7_DOX-2), epirubicin (MCF-7_EPI), paclitaxel (MCF-7_TAX-2), or docetaxel (MCF-7_TXT). During selection cells were assessed for drug sensitivity, drug uptake, and the expression of various drug transporters.

Results

In all cases, resistance was only achieved when selection reached a specific threshold dose, which was well within the clinical range. A reduction in drug uptake was temporally correlated with the acquisition of drug resistance for all cell lines, but further increases in drug resistance at doses above threshold were unrelated to changes in cellular drug uptake. Elevated expression of one or more drug transporters was seen at or above the threshold dose, but the identity, number, and temporal pattern of drug transporter induction varied with the drug used as selection agent. The pan drug transporter inhibitor cyclosporin A was able to partially or completely restore drug accumulation in the drug-resistant cell lines, but had only partial to no effect on drug sensitivity. The inability of cyclosporin A to restore drug sensitivity suggests the presence of additional mechanisms of drug resistance.

Conclusion

This study indicates that drug resistance is achieved in breast tumour cells only upon exposure to concentrations of drug at or above a specific selection dose. While changes in drug accumulation and the expression of drug transporters does occur at the threshold dose, the magnitude of resistance cannot be attributed solely to changes in drug accumulation or the activity of drug transporters. The identities of these additional drug-transporter-independent mechanisms are discussed, including their likely clinical relevance.

Non-apoptotic programmed cell death induced by a copper(II) complex in human fibrosarcoma cells

A0, a Cu(II) thioxotriazole complex, produces severe cytotoxic effects on HT1080 human fibrosarcoma cells with a potency comparable to that exhibited by cisplatin. A0 induced a characteristic series of changes, hallmarked by the formation of eosin- and Sudan Black-B-negative vacuoles. No evidence of nuclear fragmentation or caspase-3 activation was detected in cells treated with A0 which, rather, inhibited cisplatin-stimulated caspase-3 activity. Membrane functional integrity, assessed with calcein and propidium iodide, was spared until the late stages of the death process induced by the copper complex. Vacuoles were negative to the autophagy marker monodansylcadaverine and their formation was not blocked by 3-methyladenine, an inhibitor of autophagic processes. Negativity to the extracellular marker pyranine excluded vacuole derivation from the extracellular fluid. Ultrastructural analysis indicated that A0 caused the appearance of many electronlight cytoplasmic vesicles, possibly related to the endoplasmic reticulum, which progressively enlarge and coalesce to form large vacuolar structures that eventually fill the cytoplasm. It is concluded that A0 triggers a non-apoptotic, type 3B programmed cell death (Clarke in Anat Embryol (Berl) 181:195-213, 1990), characterized by an extensive cytoplasmic vacuolization. This peculiar cytotoxicity pattern may render the employment of A0 to be of particular interest in apoptosis-resistant cell models.

Cardenolide-induced lysosomal membrane permeabilization demonstrates therapeutic benefits in experimental human non-small cell lung cancers

Non-small cell lung cancers (NSCLCs) are the leading cause of cancer deaths in most developed countries. Targeting heat shock protein 70 (Hsp70) expression and function, together with the induction of lysosomal membrane permeabilization (LMP), could overcome the multiple anti-cell death mechanisms evidenced in NSCLCs that are responsible for the failure of currently used chemotherapeutic drugs. Because cardenolides bind to the sodium pump, they affect multiple signaling pathways and thus have a number of marked effects on tumor cell behavior. The aim of the present study was to characterize in vitro and in vivo the antitumor effects of a new cardenolide (UNBS1450) on experimental human NSCLCs. UNBS1450 is a potent source of in vivo antitumor activity in the case of paclitaxel-and oxaliplatin-resistant subcutaneous human NCI-H727 and orthotopic A549 xenografts in nude mice. In vitro UNBS1450-mediated antitumor activity results from the induction of nonapoptotic cell death. UNBS1450 mediates the decrease of Hsp70 at both mRNA and protein levels, and this is at least partly due to UNBS1450-induced downregulation of NFAT5/TonEBP (a factor responsible for the transcriptional control of Hsp70). These effects were paralleled by the induction of LMP, as evidenced by acridine orange staining and immunofluorescence analysis for cathepsin B accumulation.

Autophagy, the Trojan horse to combat glioblastomas

✓ Malignant gliomas, among which glioblastomas constitute the largest group, are characterized by a dramatically diffuse infiltration into the brain parenchyma with, as a consequence, the fact that no patient with glioblastoma multiforme (GBM) has been cured to date. Migrating GBM cells are resistant to apoptosis (Type I programmed cell death), and thus to radiotherapy and conventional chemotherapy, because of the constitutive activation of several intracellular signaling pathways, of which the most important identified to date are the pathways controlled by phosphatidylinositol 3-kinase, Akt, and the mammalian target of rapamycin (mTOR). Migrating GBM cells seem to be less prone to resist autophagy (Type II programmed cell death), and disruption of the pathway controlled by mTOR induces marked autophagic processes in GBM cells. Temozolomide is the most efficacious cytotoxic drug employed today to combat glioblastoma, and this drug exerts its cytotoxic activity through proautophagic processes. Thus, autophagy represents a kind of Trojan horse that can be used to bypass, at least partly, the dramatic resistance of glioblastoma to radiotherapy and proapoptotic-related chemotherapy.

Possible future issues in the treatment of glioblastomas: special emphasis on cell migration and the resistance of migrating glioblastoma cells to apoptosis

PURPOSE

The present review aims to emphasize that malignant gliomas are characterized by the diffuse invasion of distant brain tissue by a myriad of single migrating cells that exhibit decreased levels of apoptosis (programmed cell death type I), thus a resistance to cytotoxic insult.

METHODS

The present review surveys the molecular mechanisms of migration in malignant gliomas and potential issues arising from treatments, in addition to relationships between glioma cell migration and resistance to apoptosis in terms of the molecular signaling pathways.

RESULTS

Clinical and experimental data demonstrate that glioma cell migration is a complex combination of multiple molecular processes, including the alteration of tumor cell adhesion to a modified extracellular matrix, the secretion of proteases by the cells, and modifications to the actin cytoskeleton. Intracellular signaling pathways involved in the acquisition of resistance to apoptosis by migrating glioma cells concern PI3K, Akt, mTOR, NF-kappaB, and autophagy (programmed cell death type II).

CONCLUSION

A number of signaling pathways can be constitutively activated in migrating glioma cells, thus rendering these cells resistant to cytotoxic insults. However, these pathways are not all constitutively activated at the same time in any one glioma. Particular inhibitors should therefore only be chosen if the target is present in the tumor tissue, but this is only possible if individual patients are submitted to the molecular profiling of their tumors before undergoing any treatment to combat their migratory glioma cells. Specific antimigratory compounds should be added to conventional radio- and/or chemotherapy.