Potentiation of lonidamine and diazepam, two agents acting on mitochondria, in human glioblastoma treatment

Targeting mitochondrial energetics reverses panobinostat- and marizomib-induced resistance in pediatric and adult high-grade gliomas

In previous studies, we demonstrated that panobinostat, a histone deacetylase inhibitor, and bortezomib, a proteasomal inhibitor, displayed synergistic therapeutic activity against pediatric and adult high-grade gliomas. Despite the remarkable initial response to this combination, resistance emerged. Here, in this study, we aimed to investigate the molecular mechanisms underlying the anticancer effects of panobinostat and marizomib, a brain-penetrant proteasomal inhibitor, and the potential for exploitable vulnerabilities associated with acquired resistance. RNA sequencing followed by gene set enrichment analysis (GSEA) was employed to compare the molecular signatures enriched in resistant compared with drug-naïve cells. The levels of adenosine 5'-triphosphate (ATP), nicotinamide adenine dinucleotide (NAD)+ content, hexokinase activity, and tricarboxylic acid (TCA) cycle metabolites required for oxidative phosphorylation to meet their bioenergetic needs were analyzed. Here, we report that panobinostat and marizomib significantly depleted ATP and NAD+ content, increased mitochondrial permeability and reactive oxygen species generation, and promoted apoptosis in pediatric and adult glioma cell lines at initial treatment. However, resistant cells exhibited increased levels of TCA cycle metabolites, which required for oxidative phosphorylation to meet their bioenergetic needs. Therefore, we targeted glycolysis and the electron transport chain (ETC) with small molecule inhibitors, which displayed substantial efficacy, suggesting that resistant cell survival is dependent on glycolytic and ETC complexes. To verify these observations in vivo, lonidamine, an inhibitor of glycolysis and mitochondrial function, was chosen. We produced two diffuse intrinsic pontine glioma (DIPG) models, and lonidamine treatment significantly increased median survival in both models, with particularly dramatic effects in panobinostat- and marizomib-resistant cells. These data provide new insights into mechanisms of treatment resistance in gliomas.

Diazepam diminishes temozolomide efficacy in the treatment of U87 glioblastoma cell line

AIMS

Many patients with glioblastoma (GBM) suffer from comorbid neurological/psychiatric disorders and, therefore, are treated with psychopharmacological agents. Diazepam (DIA) is widely adopted to treat status epilepticus, alleviate anxiety, and inhibit chemotherapy-associated delayed emesis in GBM patients. Even though temozolomide (TMZ) and DIA could be found as possible combination therapy in clinical practice, there are no reports of their combined effects in GBM. Hence, it may be of interest to investigate whether DIA enhances the antitumor efficacy of TMZ in GBM cells.

METHODS

U87 human GBM was used to examine the effects of combined TMZ and DIA on cell viability, and the oxygen consumption within the cells, in order to evaluate mitochondrial bioenergetic response upon the treatment.

RESULTS

The cooperative index showed the presence of antagonism between TMZ and DIA, which was confirmed on long-term observation. Moreover, the level of apoptosis after the TMZ treatment was significantly decreased when administered with DIA (p < 0.001). Concomitant use of TMZ and DIA increased the basal cell respiration rate, the oxidative phosphorylation rate, and maximal capacity of mitochondrial electron transport chain, as well as the activities of complexes I and II, vs. TMZ alone (p < 0.001).

CONCLUSION

Comparing our results with data reported that DIA elicits cell cycle arrest in the G0/G1 phase and favors senescence reveals that DIA diminishes TMZ efficacy in concomitant use in the treatment of GBM. However, due to its great potency to hinder GBM proliferation and metabolism, it could be considered using DIA as maintenance therapy after TMZ cycles.

Lonidamine-ethyl ester-mediated remodelling of the Sertoli cell cytoskeleton induces phosphorylation of plakoglobin and promotes its interaction with α-catenin at the blood–testis barrier

Several compounds affect male fertility by disrupting the adhesion of germ cells to Sertoli cells, which results in the release of undeveloped germ cells into the seminiferous tubule lumen that are incapable of fertilising the ovum. Indazole carboxylic acids are one class of compounds exhibiting such effects and they have been investigated as non-hormonal contraceptives for potential human use. The aims of this study were to investigate the effects of lonidamine-ethyl ester, an indazole carboxylic acid, on spermatogenesis and cell junctions, in particular, desmosomes. We found two doses of lonidamine-ethyl ester at 50 mg kg–1 to disrupt Sertoli–germ cell adhesion. By light and fluorescent microscopy, pronounced changes were observed in the distribution of actin microfilaments and intermediate filaments, as well as in the localisation of plakoglobin, a protein with structural and signalling roles at the desmosome and adherens junction at the blood–testis barrier. Furthermore, immunoblotting and immunoprecipitation experiments using testis lysates revealed a significant upregulation (P < 0.01) of plakoglobin and Tyr-phosphorylated plakoglobin. Co-immunoprecipitation experiments showed an increase in the interaction between plakoglobin and fyn proto-oncogene, an Src family non-receptor tyrosine kinase, after treatment, as well as an increase in the interaction between plakoglobin and α-catenin. Taken collectively, these data indicate that a disruption of Sertoli cell and spermatocyte–spermatid adhesion in the seminiferous epithelium by lonidamine-ethyl ester results in the phosphorylation of plakoglobin, thereby promoting its interaction with α-catenin at the blood–testis barrier.

New treatment strategies for malignant gliomas

Malignant gliomas are the most prevalent type of primary brain tumor in adults. Despite progress in brain tumor therapy, the prognosis of malignant glioma patients remains dismal. The median survival of patients with glioblastoma multiforme, the most common grade of malignant glioma, is 10-12 months. Conventional therapy of surgery, radiation and chemotherapy is largely palliative. Essentially, tumor recurrence is inevitable. Salvage treatments upon recurrence are palliative at best and rarely provide significant survival benefit. Therapies targeting the underlying molecular pathogenesis of brain tumors are urgently required. Common genetic abnormalities in malignant glioma specimens are associated with aberrant activation or suppression of cellular signal transduction pathways and resistance to radiation and chemotherapy. Several low molecular weight signal transduction inhibitors have been examined in preclinical and clinical malignant glioma trials. The efficacy of these agents as monotherapies has been modest, at best; however, small subsets of patients who harbor specific genetic changes in their tumors may display favorable clinical responses to defined small molecule inhibitors. Multitargeted kinase inhibitors or combinations of agents targeting different mitogenic pathways may overcome the resistance of tumors to single-agent targeted therapies. Well designed studies of small molecule kinase inhibitors will include assessment of safety, drug delivery, target inhibition and correlative biomarkers to define mechanisms of response or resistance to these agents. Predictive biomarkers will enrich for patients most likely to respond in future clinical trials. Additional clinical studies will combine novel targeted therapies with radiation, chemotherapies and immunotherapies.

Glycolytic enzyme inhibitors in cancer treatment

BACKGROUND

The radio- and chemotherapeutics currently used for the treatment of cancer are widely known to be characterized by a low therapeutic index. An interesting approach to overcoming some of the limits of these techniques is the exploitation of the so-called Warburg effect, which typically characterizes neoplastic cells. Interestingly, this feature has already been utilized with good results, but only for diagnostic purposes (PET and SPECT). From a pharmacological point of view, drugs able to perturb cancer cell metabolism, specifically at the level of glycolysis, may display interesting therapeutic activities in cancer.

OBJECTIVE

The pharmacological actions of these glycolytic enzyme inhibitors, based primarily on ATP depletion, could include: i) amelioration of drug selectivity by exploiting the particular glycolysis addiction of cancer cell; ii) inhibition of energetic and anabolic processes; iii) reduction of hypoxia-linked cancer-cell resistance; iv) reduction of ATP-dependent multi-drug resistance; and v) cytotoxic synergism with conventional cancer treatments.

CONCLUSION

Several glycolytic inhibitors are currently in preclinical and clinical development. Their clinical value as anticancer agents, above all in terms of therapeutic index, strictly depends on a careful reevaluation of the pathophyiological role of the unique metabolism of cancer cells in general and of Warburg effect in particular.

Caspase-independent apoptosis is activated by diazepam-induced mitotic failure in HeLa cells, but not in human primary fibroblasts

DZ, a benzodiazepine known to affect centrosome separation at prophase, leads to a higher degree of mitotic arrest in HeLa cells than in primary human fibroblasts. In fact, differently from fibroblasts, which undergo a transient block in prophase-to-prometaphase transition, a high proportion of tumor cells attempt to escape from the DZ-imposed mitotic block, fail to undergo complete mitosis and die by mitotic failure. DZ-treated samples showed certain biochemical hallmarks of apoptosis, such as induction of the proapototic Bax protein, mitochondrial alterations assessed by JC-1 staining and TEM analysis, PARP cleavage, and DNA fragmentation. However, in DZ-treated cells, we observed a very low or absent caspase activation as shown by immunofluorescence and immunoblot experiments with antibodies directed to activated caspases and by staining with the pancaspase inhibitor FITC-VAD-FMK. Experiments on mitochondrial depolymerization and apoptosis induction carried out in the presence of specific inhibitors of caspase-2 and caspase-3/7 indicated a caspase-independent apoptotic process induced by DZ. Accordingly, TEM analysis of treated cells revealed ultrastructural features resembling those reported for caspase-independent apoptosis. In conclusion, we hypothesize that HeLa cells override the prophase block imposed by DZ, producing a high rate of aberrant pro-metaphases, which, in turn, activates caspase-independent, apoptosis-like mitotic catastrophe.

[Antimitochondrial agents: a new class of anticancer agents]

Over the last 2 decades, the role of apoptosis in anticancer agent cytotoxicity has become clear. Defects in the regulation of apoptosis (programmed cell death) make important contributions to the pathogenesis and progression of most cancers and leukemias. Apoptosis defects also have a key role in cell resistance to chemotherapy. Mitochondria play a central part in cell death in response to anticancer agents. Most of these agents target mitochondria via caspases or other regulator elements of the apoptotic machinery. Nevertheless, some anticancer agents, already in clinical use (paclitaxel, vinblastine, lonidamine, etoposide, arsenic trioxide) or in pre-clinical development (betulinic acid, MT21), directly target and permeabilize mitochondria. The acknowledgement of mitochondria as a new target for anticancer agents provides a new way to bypass cancer cell chemoresistance.

Inhibition of tumor growth and prolonged survival of rats with intracranial gliomas following administration of clotrimazole

OBJECT

Clotrimazole, an imidazole derivative and inhibitor of cytochrome P-450, inhibits the proliferation of cancer cells by downregulating the movement of intracellular Ca++ and K+ and by interfering with the translation initiation process. Clotrimazole inhibits the proliferation of human glioblastoma multiforme cells; it induces morphological changes toward differentiation and blocks the cell cycle in the G1/G1 phase. In vitro, clotrimazole enhances the antitumor effect of cisplatin by inducing wild-type p53-mediated apoptosis. The authors examined the effect of clotrimazole on tumor growth, sensitivity to cisplatin, and survival of rats with intracranial gliomas.

METHODS

Cultured C6 and 9L glioma cells were exposed to clotrimazole, and cell growth was assessed using the 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide colorimetric assay. Clotrimazole produced a dose- and time-dependent inhibition of cell proliferation. The growth inhibitory effect of clotrimazole could not be overcome by exogenous stimulation with epidermal growth factor. Both C6 and 9L glioma cells were implanted into the rat brain and after 5 days, the animals were treated with a daily single dose of clotrimazole for 8 consecutive days. Clotrimazole treatment caused a significant inhibition of intracranial tumor growth. The survival of rats with 9L gliomas was analyzed after 10 days of treatment with clotrimazole, cisplatin, or a combination of clotrimazole and cisplatin. Rats treated with either drug displayed a significantly prolonged survival time; however, the combination treatment resulted only in an additional survival benefit.

CONCLUSIONS

Clotrimazole effectively inhibits cell proliferation and tumor growth, and prolongs survival of rats with intracranial gliomas. Clotrimazole may be considered a potential anticancer drug for treatment of intracranial gliomas.

PK11195 potently sensitizes to apoptosis induction independently from the peripheral benzodiazepin receptor

1-(2-Chlorophenyl-N-methylpropyl)-3-isoquinolinecarboxamide (PK11195) is a prototypic ligand of the peripheral benzodiazepine receptor (PBR), a mitochondrial outer membrane protein. PK11195 can be used to chemosensitize tumor cells to a variety of chemotherapeutic agents, both in vitro and in vivo. PK11195 has been suggested to exert this effect via inhibition of the multiple drug resistance (MDR) pump and by direct mitochondrial effects which could be mediated by the PBR. Here, we established a model system in which PK11195 and another PBR ligand, 7-chloro-5-(4-chlorophenyl)-1,3-dihydro-1-methyl-2H-1,4-benzodiazepin-2-one (Ro5-4864), sensitize to nutrient depletion-induced cell death. In this MDR-independent model, PK11195 and Ro5-4864 are fully active even when the PBR is knocked down by small interfering RNA. Cells that lack PBR possess low-affinity binding sites for PK11195 and Ro5-4864. The starvation-sensitizing effects of PK11195 are not due to a modulation of the adaptive response of starved cells, namely autophagy and NF-kappaB activation. Rather, it appears that the combination of PK11195 with autophagy or NF-kappaB inhibitors has a potent synergistic death-inducing effect. Starved cells treated with PK11195 exhibit characteristics of apoptosis, including loss of the mitochondrial transmembrane potential, mitochondrial cytochrome c release, caspase activation and chromatin condensation. Accordingly, stabilization of mitochondria by overexpression of Bcl-2 or expression of the viral mitochondrial inhibitor (vMIA) from cytomegalovirus inhibits cell death induced by PK11195 plus starvation. Thus, PK11195 potently sensitizes to apoptosis via a pathway that involves mitochondria, yet does not involve the PBR.

Anaesthesia and anti-cancer chemotherapeutic drugs

PURPOSE OF REVIEW

This is a review of anti-cancer chemotherapeutic drugs, describing their actions, interactions, and toxicity with a particular focus on the relevance for the anaesthetist.

RECENT FINDINGS

Anti-cancer chemotherapeutics have a vast array of adverse effects, some of which, i.e. cardiac and pulmonary toxicity, are of particular anaesthesiological relevance. Recently it has been shown that following chemotherapy with anthracyclines subtle abnormalities in cardiac function may exist even in those patients with a normal resting cardiac function, which become apparent only during anaesthesia or exercise. Children and adolescents with previous anthracycline treatment and normal cardiac function at rest had a significantly greater decrease in fractional shortening, a marker of left-ventricular systolic function, and stroke-volume index during a balanced anaesthesia with isoflurane [1 minimum alveolar concentration (MAC)] in N2O/O2. Notably, delayed cardiotoxicity (years after completed chemotherapy) has been seen only after anthracycline therapy. With respect to regional anaesthetics, one should be aware that in a considerable percentage of patients a sub-clinical, unrecognized neuropathy may be present in patients with previous chemotherapy, particularly after cisplatin treatment. Recently, a diffuse brachial plexopathy after interscalene blockade has been reported in a patient receiving cisplatin chemotherapy. Thus, if regional anaesthesia is contemplated, a detailed pre-operative neurological examination and careful assessment of the risks and benefits is warranted.

SUMMARY

Anti-cancer chemotherapeutic drugs may cause generalized and specific organ toxicities and may also give rise to various unpredictable or life-threatening peri-operative complications, rendering a detailed pre-operative assessment of patients with previous chemotherapy mandatory.

Lonidamine causes inhibition of angiogenesis-related endothelial cell functions

The aim of this study was to assess whether lonidamine (LND) interferes with some steps in angiogenesis progression. We report here, for the first time, that LND inhibited angiogenic-related endothelial cell functions in a dose-dependent manner (1-50 microg/ml). In particular, LND decreased proliferation, migration, invasion, and morphogenesis on matrigel of different endothelial cell lines. Zymographic and Western blot analysis assays showed that LND treatment produced a reduction in the secretion of matrix metalloproteinase-2 and metalloproteinase-9 by endothelial cells. Vessel formation in a matrigel plug was also reduced by LND. The viability, migration, invasion, and matrix metalloproteinase production of different tumor cell lines were not affected by low doses of LND (1-10 microg/ml), whereas 50 microg/ml LND, which corresponds to the dose used in clinical management of tumors, triggered apoptosis both in endothelial and tumor cells. Together, these data demonstrate that LND is a compound that interferes with endothelial cell functions, both at low and high doses. Thus, the effect of LND on endothelial cell functions, previously undescribed, may be a significant contributor to the antitumor effect of LND observed for clinical management of solid tumors.

Contribution of gap junctional communication between tumor cells and astroglia to the invasion of the brain parenchyma by human glioblastomas

Background

Gliomas are "intraparenchymally metastatic" tumors, invading the brain in a non-destructive way that suggests cooperation between glioma cells and their environment. Recent studies using an engineered rodent C6 tumor cell line have pointed to mechanisms of invasion that involved gap junctional communication (GJC), with connexin 43 as a substrate. We explored whether this concept may have clinical relevance by analyzing the participation of GJC in human glioblastoma invasion.

Results

Three complementary in vitro assays were used: (i) seeding on collagen IV, to analyze homocellular interactions between tumor cells (ii) co-cultures with astrocytes, to study glioblastoma/astrocytes relationships and (iii) implantation into organotypic brain slice cultures, that mimic the three-dimensional parenchymal environment. Carbenoxolone, a potent blocker of GJC, inhibited cell migration in the two latter models. It paradoxically increased it in the first one. These results showed that homocellular interaction between tumor cells supports intercellular adhesion, whereas heterocellular glioblastoma/astrocytes interactions through functional GJC conversely support tumor cell migration. As demonstrated for the rodent cell line, connexin 43 may be responsible for this heterocellular functional coupling. Its levels of expression, high in astrocytes, correlated positively with invasiveness in biopsied tumors.

Conclusions

our results underscore the potential clinical relevance of the concept put forward by other authors based on experiments with a rodent cell line, that glioblastoma cells use astrocytes as a substrate for their migration by subverting communication through connexin 43-dependent gap junctions.

Peripheral benzodiazepine receptor and its clinical targeting

Tumor cell targeted therapies, by induction or enhancement of apoptosis, constitute recent promising approaches achieving more specific anti-tumor efficacy. The peripheral benzodiazepine receptor (PBR), which belongs to the permeability transition pore (PTP), the central regulatory complex of apoptosis, is a potential target. A number of findings argue in favor of the development of PBR targeting approaches: (i) overexpression of PBR has been described in a large range of human cancers, (ii) PTP-mediated regulation of programmed cell death is an apoptotic-inducing factor-independent check-point that could be modulated by various conventional cancer therapies, and (iii) PBR ligation enhances apoptosis induction in many types of tumors and reverses Bcl-2 cytoprotective effects. Altogether, these observations support the use of PBR-directed drugs, particularly PBR ligands such as Ro5-4864, in the treatment of human cancers.

Anaesthetic implications of anticancer chemotherapy

In anaesthetic practice we deal with cancer patients who are scheduled for operations on tumours or other manifestations of malignant disease. Those patients are often debilitated and have significant weight loss accompanied with hypoproteinaemia, anaemia and coagulation disorders. Oncological patients usually present to the anaesthetist before tumour disease surgery, but they are also candidates for elective operations (e.g. hernia repair) and urgent/emergency surgery (e.g. trauma, fractures and ileus). Chemotherapeutic agents given to these patients are potentially noxious, can affect the conduct of anaesthesia and, furthermore, may aggravate the patient's condition. In this review the most commonly used cytostatic drug regimens and their common side-effects are listed. Some preclinical studies on anaesthetic and cytostatic drug metabolism and interactions are emphasized, as well as clinically relevant perioperative alterations that may affect anaesthetic management in cancer patients. An anaesthetist may have to modify a routine anaesthetic regimen in cancer patients especially if anticancer chemotherapeutics were given. Clinically silent toxic drug effects may become apparent during operation, trauma or in the early postoperative course in such patients. Altered reactions to commonly used anaesthetics in patients receiving chemotherapeutics and an impaired stress reaction may occur in such patients. Special attention must be drawn to protection against opportunistic infections.

Apoptosis in glioma cells: review and analysis of techniques used for study with focus on the laser scanning cytometer

Traditional approaches to the treatment of brain tumors are based on the hypothesis that tumors arise and grow because of the disordered regulation of cell proliferation. More recently, it has become apparent that tumor growth depends not only on the rate of cell proliferation but also on the rate of apoptosis (programmed cell death). Genomic alterations that occur in malignancy may limit the cell's ability to undergo apoptosis. Many new treatment strategies for gliomas stem from the use of techniques aimed at manipulating apoptosis. Being able to assess the efficacy of experimental treatments with refined techniques and being able to use instruments that can provide accurate measurements of the apoptotic markers will open the door for discovering novel strategies with the potential to induce effective and selective cytotoxicity. We discuss here in detail the major traditional techniques of assessing apoptosis. We provide an overview of cytometric techniques, including flow cytometry (FC), and will compare it with the laser scanning cytometer (LSC). This is a powerful new tool with potential for obtaining a fast and objective analysis of apoptosis through multiple mechanisms, as well as for assessing proliferation and DNA ploidy in solid malignant tumors.

Phase II study of lonidamine and diazepam in the treatment of recurrent glioblastoma multiforme

Recurrent glioblastoma multiforme (GBM) is resistant to most therapeutic endeavours, with low response rates and survival rarely exceeding 6 months. There are no standard chemotherapeutic regimens and new therapeutic approaches have to be found. We report an open-label, uncontrolled, multicentre phase II trial of lonidamine (LND) and diazepam in 16 patients with GBM at first relapse and a Karnofsky performance status > or = 70. The treatment regimen consisted of LND 450 mg/day and diazepam 15 mg/day orally of every 28-day cycle until progression or unacceptable toxicity. Patients received a median of three cycles (range, 1-12). No complete or partial response was observed. Therefore, according to the design of the study, no additional patients were enrolled and the trial was closed. Nevertheless, seven stabilizations (50%) were observed. Median time to progression was 8 weeks (range, 5-19 weeks). Median overall survival from recurrence was 15 weeks (range, 14-61 weeks). No grade 3-4 toxicity, except somnolence, was observed and there were no therapy-related deaths. Dose reduction for diazepam due to somnolence (grade III) was performed in 9 patients. The combination of LND and diazepam is well tolerated. LND and diazepam, acting on two distinct mitochondrial sites involved in cellular energy metabolism, may exert a cytostatic effect on tumour growth as shown by the high percentage of stable patients. The LND-diazepam at the used dosing schedule did not show a complete or partial response. LND plus diazepam may be interesting in the adjuvant setting or associated to chemotherapy to act on different targets and increase the therapeutic index.

Mitochondria as a target for inducing death of malignant hematopoietic cells

Mitochondria plays a central role in apoptotic cell death. The intermembrane space of mitochondria contains a number of soluble molecules whose release from the organelle to the cytosol or the nucleus induces cell death. Thus, molecules that directly trigger mitochondria membrane permeabilisation are efficient cytotoxic drugs. Mitochondria is one of the cellular targets for commonly used epipodophyllotoxins, adenine deoxynucleoside analogs and taxanes as well as recently developped agents such as the pentacyclic triterpene betulinic acid and the lymphotoxic agent FTY720. Most informations on anthracyclines point to the mitochondrial membrane as the main target of cardiotoxicity. Mitochondria is also a target for arsenite trioxide, an old cytotoxic agent recently used for treating acute promyelocytic leukemia, lonidamine, a dichlorinated derivative of indazole-3-carboxylic acid developped as a chemosensitizer, the retinoic acid receptor gamma activator CD437 and nitric oxide (NO). Recently, cytotoxic drugs have been specifically designed to directly affect the mitochondrial function. These include the positively charged alpha-helical peptides, which are attracted to and disrupt the negatively charged mitochondrial membrane, thus inducing mammalian cell apoptosis when targeted intracellularly. Various strategies have been proposed also to directly inhibit Bcl-2 and related anti-apoptotic proteins, including antisense oligonucleotides (e.g. Genasense, currently tested in phase III trials), small molecules that mimic the BH3 dimerization domain of these proteins and kinase inhibitors. Ligands of the mitochondrial benzodiazepine receptor such as the isoquinolone carboxamide derivative PK11195 also overcome the membrane-stabilizing effect of Bcl-2, whereas the adenosine nucleotide translocator (ANT) and the mitochondrial DNA are two other potential cellular targets for cytotoxic agents. Potentially, new compounds directly targeting the mitochondria may be useful in treating hematological malignancies. The challenge is now to selectively target these mitochondria permeabilizing agents to malignant cells. This review briefly summarizes the role of the mitochondria in cell death and describes these various strategies for targeting the mitochondria to induce apoptosis.

Chemotherapy: targeting the mitochondrial cell death pathway

One of the mechanisms by which chemotherapeutics destroy cancer cells is by inducing apoptosis. Apoptosis can be activated through several different signalling pathways, but these all appear to converge at a single event - mitochondrial membrane permeabilization (MMP). This 'point-of-no-return' in the cell death program is a complex process that is regulated by the composition of the mitochondrial membrane and pre-mitochondrial signal-transduction events. MMP is subject to a complex regulation, and local alterations in the composition of mitochondrial membranes, as well as alterations in pre-mitochondrial signal-transducing events, can determine chemotherapy resistance in cancer cells. Detecting MMP might thus be useful for detecting chemotherapy responses in vivo. Several cytotoxic drugs induce MMP by a direct action on mitochondria. This type of agents can enforce death in cells in which upstream signals normally leading to apoptosis have been disabled. Cytotoxic components acting on mitochondria can specifically target proteins from the Bcl-2 family, the peripheral benzodiazepin receptor, or the adenine nucleotide translocase, and/or act by virtue of their physicochemical properties as steroid analogues, cationic ampholytes, redox-active compounds or photosensitizers. Some compounds acting on mitochondria can overcome the cytoprotective effect of Bcl-2-like proteins. Several agents which are already used in anti-cancer chemotherapy can induce MMP, and new drugs specifically designed to target mitochondria are being developed.

Nucleoside analogues and nucleobases in cancer treatment

Cytotoxic nucleoside analogues and nucleobases were among the first chemotherapeutic agents to be introduced for the medical treatment of cancer. This family of compounds has grown to include a variety of purine and pyrimidine nucleoside derivatives with activity in both solid tumours and malignant disorders of the blood. These agents behave as antimetabolites, compete with physiological nucleosides, and interact with a large number of intracellular targets to induce cytotoxicity. Progress has recently been made in the identification and characterisation of nucleoside transporters and the enzymes of nucleoside metabolism. In addition, there is now greater understanding of the molecular mechanisms of anticancer nucleoside activity, which provides opportunities for potentiating their antitumour effects. Strategies to optimise intracellular analogue accumulation and to enhance cancer-cell selectivity are proving beneficial in clinical trials.

A matrix-assisted laser desorption ionization post-source decay (MALDI-PSD) analysis of proteins released from isolated liver mitochondria treated with recombinant truncated Bid

A crucial event in the process of apoptosis is caspase-dependent generation of truncated Bid (tBid), inducing release of cytochrome c. In an in vitro reconstitution system we combined purified recombinant tBid with isolated liver mitochondria and identified the released proteins using a proteomic matrix-assisted laser desorption ionization post-source decay (MALDI-PSD) approach. In order to meet physiological conditions, the concentration of tBid was chosen such that it was unable to induce cytochrome c release in mitochondria derived from liver-specific Bcl-2-transgenic mice. Several mitochondrial proteins were identified to be released in a tBid-dependent way, among which cytochrome c, DIABLO/Smac, adenylate kinase 2, acyl-CoA-binding protein, endonuclease G, polypyrimidine tract-binding protein, a type-I RNA helicase, a WD-40 repeat-containing protein and the serine protease Omi. Western blotting confirmed the absence of adenylate kinase 3, a matrix mitochondrial protein. These results demonstrate that a physiologically relevant concentration of tBid is sufficient to induce release of particular intermembrane mitochondrial proteins belonging to a broad molecular-mass range.

Diazepam enhances etoposide-induced cytotoxicity in U-87 MG human glioma cell line

Various approaches might be employed in an effort to increase efficacy of the chemotherapeutic treatment of cancer. Recently, various modulators of anticancer therapy effectiveness have been studied. Antiproliferative effects of peripheral benzodiazepine receptor (PBR) ligands might be exploited to enhance cytotoxic effect of a chemotherapeutic drug towards cancer cells. In this work, we sought to enhance cytotoxic effect of etoposide (VP-16) by a PBR ligand, diazepam (DZ) in U-87 MG human glioma cells. Cytotoxicity of VP-16, DZ and their combinations was assessed by using the microculture MTT assay. Cell survival, effective concentrations (EC) and the onset of cytotoxic effect were determined. After 72 h of cultivation, survival of U-87 MG cells was reduced to 57 +/- 7% in the presence of VP-16 at 12.5 microg/mL alone, whereas DZ at 10-4 mol/L alone caused 28 +/- 6% reduction in cell survival. Coincubation of VP-16 at 12.5 microg/mL with DZ at 10-4 mol/L led to a further decrease in cell survival to 45 +/- 6%. Furthermore, DZ at 10-4 mol/L significantly decreased effective concentrations, EC10, EC30 and EC50, of VP-16 and the dose-response curves were shifted to the left. Addition of DZ at 10-4 mol/L to VP-16 also facilitated the onset of its cytotoxic effect. The same decrease in survival was thus achieved approximately 30 h earlier in comparison with VP-16 alone. However, DZ at 10-9 mol/L failed both to exert any effect on glioma cells survival and enhance cytotoxic effect of VP-16. DZ at 10-4 mol/L was capable of both reducing U-87 MG glioma cells survival when applied alone and also enhancing the cytotoxic effect of VP-16. No such observation was made for the lower concentrations of DZ. Potential implementation of diazepam in the antiglioma/anticancer armamentarium awaits further experimentation but phase I and phase II clinical trials could be suggested.

Synergistic efficacy of 3n-butyrate and 5-fluorouracil in human colorectal cancer xenografts via modulation of DNA synthesis

BACKGROUND & AIMS

Butyrate, produced in the colon lumen, maintains mucosal cell homeostasis. Poorly diffusible, its access is compromised in growing colon cancers and absent in distant metastases. Butyrate regulates DNA synthesis. We postulated that systemic administration of butyrate should reduce colon cancer growth and enhance 5-fluorouracil (5-FU) efficacy.

METHODS

A stable derivative of butyrate (3n-But) was used. The antitumoral efficacy of 5-FU and 3n-But, alone or combined, was evaluated in human colorectal cancers (hCRCs) subcutaneously, orthotopically, or intrasplenically grafted into nude mice. Thymidylate synthase (TS) and thymidine kinase (TK) mRNA expression, proliferation, apoptosis, and cell cycle alterations were studied.

RESULTS

In vivo, 5-FU alone inhibited growth of only 3 of the 12 hCRCs tested and 3n-But alone had no effect; the 5-FU/3n-But combination inhibited growth of all 16 hCRCs tested. The hCRCs differed in their p53 and microsatellite instability status. 5-FU/3n-But decreased TK and TS mRNA expression by 20- and 40-fold, respectively, and TS activity by 75%, stopped cell proliferation without affecting cell differentiation, and significantly enhanced apoptosis. 3n-But potentiated the efficacy of Tomudex and methotrexate, 2 TS inhibitors, but not that of oxaliplatin. In vitro, 5-FU/3n-But inhibited [3H]thymidine but not bromodeoxyuridine incorporation and induced apoptosis in hCRC cell lines. Cells treated with 5-FU/3n-But did not accumulate in G1 nor in S phase of the cell cycle, while 5-FU and 3n-But arrested the cycle in S and in G1 phase, respectively. 3n-But prevented the cell rescue from 5-FU-induced cytotoxicity by uridine or thymidine.

CONCLUSIONS

3n-But and TS inhibitors acted synergistically against colorectal cancers, independently of the genetic alterations of the hCRCs. The mechanism of action of 5-FU/3n-But could be enhanced reduction of TS and prevention of thymidine salvage in DNA synthesis.

The peripheral benzodiazepine receptors: a review

Peripheral benzodiazepine receptors (PBRs) have been identified in various peripheral tissues as well as in glial cells in the brain. This review describes the tissue and subcellular distribution of the PBR in mammalian tissues and analyzes its many putative endogenous ligands. It deals with the pharmacological, structural and molecular characterization of the PBR, the proteins associated with the receptor (VDAC, ANC, PRAX-1) and their roles in cell growth and differentiation, cancer, steroid biosynthesis, and other physiological roles.

Mass spectrometric identification of proteins released from mitochondria undergoing permeability transition

Mitochondrial membrane permeabilization is a rate-limiting step of cell death. This process is, at least in part, mediated by opening of the permeability transition pore complex (PTPC) Several soluble proteins from the mitochondrial intermembrane space and matrix are involved in the activation of catabolic hydrolases including caspases and nucleases. We therefore investigated the composition of a mixture of proteins released from purified mitochondria upon PTPC opening. This mixture was subjected to a novel proteomics/mass spectrometric approach designed to identify a maximum of peptides. Peptides from a total of 79 known proteins or genes were identified. In addition, 21 matches with expressed sequence tags (EST) were obtained. Among the known proteins, several may have indirect or direct pro-apoptotic properties. Thus endozepine, a ligand of the peripheral benzodiazepin receptor (whose occupation may facilitate mitochondrial membrane permeabilization), was found among the released proteins. Several proteins involved in protein import were also released, namely the so-called X-linked deafness dystonia protein (DDP) and the glucose regulated protein 75 (grb75), meaning that protein import may become irreversibly disrupted in mitochondria of apoptotic cells. In addition, a number of catabolic enzymes are detected: arginase 1 (which degrades arginine), sulfite oxidase (which degrades sulfur amino acids), and epoxide hydrolase. Although the functional impact of each of these proteins on apoptosis remains elusive, the present data bank of mitochondrial proteins released upon PTPC opening should help further elucidation of the death process.

Effect of 1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide (PK11195), a specific ligand of the peripheral benzodiazepine receptor, on the lipid fluidity of mitochondria in human glioma cells

When human glioma cells were incubated for 24 hr in serum-free medium with nanomolar concentrations of 1-(2-chlorophenyl)-N-methyl-N(1-methylpropyl)-3-isoquinoline carboxamide (PK11195), a specific ligand of the peripheral benzodiazepine receptor (PBR), a significant increase in the membrane fluidity of mitochondria isolated from these cells was registered. These effects were not observed with a shorter incubation time (2 hr) of the cells with PK11195 nor in the presence of serum. Other significant associated changes were observed: a significant increase of 16+/-4% of [3H]thymidine incorporation into DNA was detected in cells in the presence of PK11195 in serum-free medium, and an increase of 33+/-5% as compared to controls in nonyl acridine orange uptake, as indicator of mitochondrial mass, was also registered in cells treated with 10 nM PK11195. [3H]PK11195 binding was decreased in cells incubated with PK11195; a 45% decrease compared to controls was obtained. In view of the effect of PBR ligands on DNA synthesis, changes in mitochondrial lipid metabolism through interaction with PBRs might lead to biogenesis of mitochondria to support the increased metabolic requirements for cell division, which is even higher in malignant cells.

Arsenite induces apoptosis via a direct effect on the mitochondrial permeability transition pore

The molecular mode of action of arsenic, a therapeutic agent employed in the treatment of acute promyelocytic leukemia, has been elusive. Here we provide evidence that arsenic compounds may act on mitochondria to induce apoptosis. Arsenite induces apoptosis accompanied by a loss of the mitochondrial transmembrane potential (Delta Psim). Inhibition of caspases prevents the arsenite-induced nuclear DNA loss, but has no effect on the Delta Psim dissipation and cytolysis induced by arsenite. In contrast, Bcl-2 expression induced by gene transfer prevents all hallmarks of arsenite-induced cell death, including the Delta Psim collapse. PK11195, a ligand of the mitochondrial benzodiazepine receptor, neutralizes this Bcl-2 effect. Mitochondria are required in a cell-free system to mediate arsenite-induced nuclear apoptosis. Arsenite causes the release of an apoptosis-inducing factor (AIF) from the mitochondrial intermembrane space. This effect is prevented by the permeability transition (PT) pore inhibitor cyclosporin A, as well as by Bcl-2, which is known to function as an endogenous PT pore antagonist. Arsenite also opens the purified, reconstituted PT pore in vitro in a cyclosporin A- and Bcl-2-inhibitible fashion. Altogether these data suggest that arsenite can induce apoptosis via a direct effect on the mitochondrial PT pore.

Lonidamine triggers apoptosis via a direct, Bcl-2-inhibited effect on the mitochondrial permeability transition pore

The molecular mode of action of lonidamine, a therapeutic agent employed in cancer chemotherapy, has been elusive. Here we provide evidence that lonidamine (LND) acts on mitochondria to induce apoptosis. LND provokes a disruption of the mitochondrial transmembrane potential which precedes signs of nuclear apoptosis and cytolysis. The mitochondrial and cytocidal effects of LND are not prevented by inhibitors of caspases or of mRNA or protein synthesis. However, they are prevented by transfection-enforced overexpression of Bcl-2, an oncoprotein which inhibits apoptosis by stabilizing the mitochondrial membrane barrier function. Accordingly, the cell death-inducing effect of LND is amplified by simultaneous addition of PK11195, an isoquinoline ligand of the peripheral benzodiazepine receptor which antagonizes the cytoprotective effect of Bcl-2. When added to isolated nuclei, LND fails to provoke DNA degradation unless mitochondria are added simultaneously. In isolated mitochondria, LND causes the dissipation of the mitochondrial inner transmembrane potential and the release of apoptogenic factors capable of inducing nuclear apoptosis in vitro. Thus the mitochondrion is the subcellular target of LND. All effects of LND on isolated mitochondria are counteracted by cyclosporin A, an inhibitor of the mitochondrial PT pore. We therefore tested the effect of LND on the purified PT pore reconstituted into liposomes. LND permeabilizes liposomal membranes containing the PT pore. This effect is prevented by addition of recombinant Bcl-2 protein but not by a mutant Bcl-2 protein that has lost its apoptosis-inhibitory function. Altogether these data indicate that LND represents a novel type of anti-cancer agent which induces apoptosis via a direct effect on the mitochondrial PT pore.