Monica Lupi

Mitochondrial dysfunction and death in motor neurons exposed to the glutathione-depleting agent ethacrynic acid

This study investigated the mechanisms of toxicity of glutathione (GSH) depletion in one cell type, the motor neuron. Ethacrynic acid (EA) (100 microM) was added to immortalized mouse motor neurons (NSC-34) to deplete both cytosolic and mitochondrial glutathione rapidly. This caused a drop in GSH to 25% of the initial level in 1 h and complete loss in 4 h. This effect was accompanied by enhanced generation of reactive oxygen species (ROS) with a peak after 2 h of exposure, and by signs of mitochondrial dysfunction such as a decrease in 3-(4,5-dimethyl-2-thiazoyl)-2,5-diphenyltetrazolium bromide (MTT) (30% less after 4 h). The increase in ROS and the MTT reduction were both EA concentration-dependent. Expression of heme oxygenase-1 (HO-1), a marker of oxidative stress, also increased. The mitochondrial damage was monitored by measuring the mitochondrial membrane potential (MMP) from the uptake of rhodamine 123 into mitochondria. MMP dropped (20%) after only 1 h exposure to EA, and slowly continued to decline until 3 h, with a steep drop at 5 h (50% decrease), i.e. after the complete GSH loss. Quantification of DNA fragmentation by the TUNEL technique showed that the proportion of cells with fragmented nuclei rose from 10% after 5 h EA exposure to about 65% at 18 h. These results indicate that EA-induced GSH depletion rapidly impairs the mitochondrial function of motor neurons, and this precedes cell death. This experimental model of oxidative toxicity could be useful to study mechanisms of diseases like spinal cord injury (SCI) and amyotrophic lateral sclerosis (ALS), where motor neurons are the vulnerable population and oxidative stress has a pathogenic role.

Combined inhibition of Chk1 and Wee1: In vitro synergistic effect translates to tumor growth inhibition in vivo

Targeting Chk1 protein kinase can enhance the antitumor effects of radio- and chemotherapy. Recent evidence disclosed a role of Chk1 in unperturbed cell proliferation and survival, implying that Chk1 inhibitors could also be effective as single agents in tumors with a specific genetic background. To identify genes in synthetic lethality with Chk1, we did a high-throughput screening using a siRNA library directed against 719 human protein kinases in the human ovarian cancer cell line OVCAR-5, resistant to Chk1 inhibitors. Wee1 tyrosine kinase was the most significant gene in synthetic lethality with Chk1. Treatment with non-toxic concentrations of a Chk1 inhibitor (PF-00477736) and a Wee1 inhibitor (MK-1775) confirmed the marked synergistic effect in various human cancer cell lines (breast, ovarian, colon, prostate), independently of the p53 status. Detailed molecular analysis showed that the combination caused cancer cells to undergo premature mitosis before the end of DNA replication, with damaged DNA leading to cell death partly by apoptosis. In vivo treatment of mice bearing OVCAR-5 xenografts with the combination of Chk1 and Wee1 inhibitors led to greater tumor growth inhibition than with the inhibitors used as single agents with no toxicity. These data provide a strong rationale for the clinical investigation of the combination of a Chk1 and a Wee1 inhibitor.

Induction of miR-21 by Retinoic Acid in Estrogen Receptor-positive Breast Carcinoma Cells BIOLOGICAL CORRELATES AND MOLECULAR TARGETS

Retinoids are promising agents for the treatment/prevention of breast carcinoma. We examined the role of microRNAs in mediating the effects of all-trans-retinoic acid (ATRA), which suppresses the proliferation of estrogen receptor-positive (ERα+) breast carcinoma cells, such as MCF-7, but not estrogen receptor-negative cells, such as MDA-MB-231. We found that pro-oncogenic miR-21 is selectively induced by ATRA in ERα+ cells. Induction of miR-21 counteracts the anti-proliferative action of ATRA but has the potentially beneficial effect of reducing cell motility. In ERα+ cells, retinoid-dependent induction of miR-21 is due to increased transcription of the MIR21 gene via ligand-dependent activation of the nuclear retinoid receptor, RARα. RARα is part of the transcription complex present in the 5′-flanking region of the MIR21 gene. The receptor binds to two functional retinoic acid-responsive elements mapping upstream of the transcription initiation site. Silencing of miR-21 enhances ATRA-dependent growth inhibition and senescence while reverting suppression of cell motility afforded by the retinoid. Up-regulation of miR-21 results in retinoid-dependent inhibition of the established target, maspin. Knockdown and overexpression of maspin in MCF-7 cells indicates that the protein is involved in ATRA-induced growth inhibition and contributes to the ATRA-dependent anti-motility responses. Integration between whole genome analysis of genes differentially regulated by ATRA in MCF-7 and MDA-MB-231 cells, prediction of miR-21 regulated genes, and functional studies led to the identification of three novel direct miR-21 targets: the pro-inflammatory cytokine IL1B, the adhesion molecule ICAM-1 and PLAT, the tissue-type plasminogen activator. Evidence for ICAM-1 involvement in retinoid-dependent inhibition of MCF-7 cell motility is provided.

The Molecular Assembly of Amyloid Aβ Controls Its Neurotoxicity and Binding to Cellular Proteins

Accumulation of β-sheet-rich peptide (Aβ) is strongly associated with Alzheimers disease, characterized by reduction in synapse density, structural alterations of dendritic spines, modification of synaptic protein expression, loss of long-term potentiation and neuronal cell death. Aβ species are potent neurotoxins, however the molecular mechanism responsible for Aβ toxicity is still unknown. Numerous mechanisms of toxicity were proposed, although there is no agreement about their relative importance in disease pathogenesis. Here, the toxicity of Aβ 1–40 and Aβ 1–42 monomers, oligomers or fibrils, was evaluated using the N2a cell line. A structure-function relationship between peptide aggregation state and toxic properties was established. Moreover, we demonstrated that Aβ toxic species cross the plasma membrane, accumulate in cells and bind to a variety of internal proteins, especially on the cytoskeleton and in the endoplasmatic reticulum (ER). Based on these data we suggest that numerous proteins act as Aβ receptors in N2a cells, triggering a multi factorial toxicity.

Cell cycle effects of gemcitabine.

Gemcitabine (2′,2′‐difluoro‐2′‐deoxycytidine, or dFdC) is a promising anticancer agent with demonstrated clinical activity in solid tumours currently undergoing clinical trials. Despite extensive studies on the biochemical mechanism of action, cell cycle perturbations induced by dFdC have not yet been thoroughly investigated, apart from the expected inhibition of DNA synthesis. The aim of our study was to clarify whether cell population kinetics is a vital factor in the cytotoxicity of dFdC in single or repeated treatments and in the dFdC‐cisplatin combination. Ovarian cancer cells growing in vitro were treated with dFdC for 1 hr in a range of concentrations from 10 nM to 10 μM. Cell kinetics was investigated by DNA‐bromodeoxyuridine flow cytometry, using different experimental protocols to measure either the time course of DNA‐synthesis inhibition or the fate of cells in G1, S or G2M at the time of dFdC treatment or 24 hr later. A modified sulforhodamine B test was used to assess the growth inhibition caused by dFdC given alone or with cisplatin. Although dFdC promptly inhibited DNA synthesis, cytotoxicity on proliferating cells was not specific for cells initially in the S phase. DNA synthesis was restored after a G1 block of variable, dose‐dependent length, but recycling cells were intercepted at the subsequent checkpoints, resulting in delays in the G2M and G1 phases. The activity of repeated treatment with dFdC+dFdC or dFdC+cisplatin was highly dependent on the interval length between them. These results suggest that the kinetics of cell recycling from a first dFdC treatment strongly affects the outcome of a second treatment with either dFdC itself or cisplatin.

Low levels of ALS-linked Cu/Zn superoxide dismutase increase the production of reactive oxygen species and cause mitochondrial damage and death in motor neuron-like cells

Mutations of Cu/Zn superoxide dismutase (SOD1) are found in patients with familial amyotrophic lateral sclerosis (FALS). A cellular model of FALS was developed by stably transfecting the motor neuron-like cell line NSC-34 with human wild type (wt) or mutant (G93A) SOD1. Expression levels of G93ASOD1 were close to those seen in the human disease. The presence of G93ASOD1 did not alter cell proliferation but toxicity was evident when the cells were in the growth plateau phase. Flow cytometry analysis indicated that, in this phase, G93ASOD1 significantly lowered viability and that the level of reactive oxygen species was significantly higher in living G93ASOD1 cells compared to wt SOD1 cells. Biparametric analysis of mitochondrial membrane potential and viability of transfected cells highlighted a peculiar population of damaged cells with strong mitochondrial depolarization in the G93ASOD1 cells. Mitochondrial function seemed related to the level of the mutant protein since MTT conversion decreased when expression of G93ASOD1 doubled after treating cells with sodium butyrate. The mutant protein rendered G93ASOD1 cells more sensitive to mitochondrial dysfunction induced by stimuli that alter cellular free radical homeostasis, like serum withdrawal, depletion of glutathione by ethacrynic acid or rotenone-mediated inhibition of complex I of the mitochondrial electron transport chain. In conclusion, even a small amount of mutant SOD1 put motor neurons in a condition of oxidative stress and mitochondrial damage that causes cell vulnerability and death.

Synthesis of surfactant free PCL-PEG brushed nanoparticles with tunable degradation kinetics

A delivery system based on polymer nanoparticles (NPs) is developed and tested in relevant biological conditions for breast cancer treatment. ɛ-Caprolactone (CL) and polyethylene glycol (PEG) copolymers have been used for the one pot synthesis of surfactant free PEGylated NPs which are monodispersed, stable in physiological conditions and have size in the range 90-250 nm. The degradation behavior of these NPs has been investigated in cell medium and a relation between degradation time and molecular weight of the starting CL-based material has been established. This allows producing NPs with controlled degradation kinetics. Finally, selected NPs have been tested in 4T1 breast cancer cells to check their toxicity and to investigate the uptake process, in order to validate their use as targeted vectors for breast cancer treatment.

Heterogeneous cell response to topotecan in a CFSE-based proliferation test

Carboxyfluorescein diacetate succinimidyl ester (CFSE) is currently used to investigate migration and proliferation of hemopoietic cells. In principle, CFSE is retained by the cells and is shared by the daughter cells at each division, resulting in multimodal flow cytometric CFSE histograms, with each cell generation clustering around half the fluorescence intensity of the previous one. However, intercell variability of CFSE loading results in overlapping peaks, thereby limiting its use with cancer cell lines.

Neurodegeneration induced by complex I inhibition in a cellular model of familial amyotrophic lateral sclerosis

G93A Cu/Zn superoxide dismutase (SOD1), a human mutant SOD1 associated with familial amyotrophic lateral sclerosis, increased the toxicity of the mitochondrial toxin rotenone in the NSC-34 motoneuronal cell line. G93ASOD1 cells died more than untransfected and wild-type SOD1 cells after 6 and 24h exposure to 12.5 microM rotenone. Biparametric flow cytometry showed that rotenone induced rapid hyperpolarization of mitochondrial membrane potential (deltapsi(m)) in all the cell lines, followed by depolarization, and then by cell death. However, G93ASOD1 mitochondria were significantly more likely to shift from a hyperpolarized to a depolarized condition, and within the still viable cell population there was a higher proportion with depolarized mitochondria, a condition that can be envisaged as a commitment to cell death. ATP, which is needed to prevent loss of deltapsi(m), decreased more rapidly and to a greater extent in rotenone-treated G93ASOD1 cells than in the untransfected and wtSOD1cells. In all the cell lines, 1h after rotenone exposure, mitochondrial hyperpolarization was accompanied by the formation of a comparable amount of reactive oxygen species. However, G93ASOD1 cells reached the highest reactive oxygen species level since their basal level was higher than in untransfected and wild-type SOD1 cells. Our findings indicate that the mutant protein G93ASOD1 enhances the vulnerability of motor neurons to rotenone by mechanism(s) involving oxidative stress and perturbed mitochondrial homeostasis. This suggests that motor neurons from individuals carrying the mutant G93ASOD1 are at greater risk of death after inhibition of the electron transport chain.

Investigation of size, surface charge, PEGylation degree and concentration on the cellular uptake of polymer nanoparticles

In this work a large number of polymer nanoparticles (NPs) with different features have been synthesized through emulsion polymerization-based methods. Poly(methyl methacrylate) (PMMA), poly-ɛ-caprolactone (PCL), and poly(lactic acid) (PLA) based NPs with different size, hydrophobicity, surface charge, PEGylation degree, type of emulsifier and ζ potential have been produced and characterized. All the different NPs have been adopted for cellular uptake studies, leading to a precise quantification of the number of internalized NPs into a selected tumor cell line. The experiments summarize, emphasize and improve the comprehension of the influence of NPs features on the uptake efficiency. In detail, a linear relationship between uptake and both size and NP concentration independently upon other NP characteristics was found. Moreover, it was confirmed that cells are able to internalize and retain for a long time preferentially positively charged NPs. Finally, by coupling results of uptake studies with cell viability measurements, an easy and fast check to control the effectiveness of a selected polymer as drug carrier has been proposed. In particular, we observed that biodegradable PLA-based NPs with high molecular weight, non-PEGylated and positively charged PCL NPs are the better choice to maximize the uptake and minimize side effect against cells.