Proefschrift-Amsterdam.

Thesis (M.S.)--Duquesne University, 2008. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 79-83) and index.

Approximately 20,000 tonnes of arsenic (As)-bearing emissions from roasting arsenopyrite ore were aerially released from 1949-1999 at Giant Mine, located outside Yellowknife, NT. As part of the process used to free refractory gold (Au) from arsenopyrite (FeAsS), roasting created As-bearing roaster off-gases that condensed into As2O3, one of the most toxic As compounds to humans. Roaster emissions also contained some As-bearing iron (Fe)- oxides. Arsenic emission controls were first implemented in 1951, and by the time the emission control process was completely refined in 1963, 86% of the total aerial As emissions at Giant had been released into the surrounding area. The continued presence of roaster-derived As2O3 in surface soils at Giant has been previously documented despite its theoretical instability in oxidizing surface environments. Wrye (2008) found As concentrations in roaster-affected soils occurring on rock outcrop (covering ~30% of the Giant property) greater than in many other surface soils; most outcrop soils were not considered when delineating areas of contaminated material for future removal in the Giant Mine Remediation Plan (currently undergoing environmental assessment). To investigate roaster-derived As persistence, outcrop soils and soil pore waters were analyzed. Comparing proportions of As, Sb, and Au concentrations in soil samples and historic As2O3-rich dust captured by emission controls show that most of the roaster-derived As in soils at Giant was likely deposited before 1964. Thin section examination has shown that while the vast majority of discrete As hosts in soils are As2O3, textural relationships and certain secondary As hosts in soils indicate that As2O3 is not static in surface soils and could be transforming over time, albeit very slowly. Bulk chemical relationships among As, antimony (Sb), and carbon support this. Topographic restriction by rock outcrops and dry, cold climate probably play a large role in elevated As concentrations and As2O3 persistence in outcrop soils. In light of possible future human exposure, As bioaccessibility from three adjacent samples was determined for synthetic human gastric (34%) and lung (18%) fluids. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2011-11-22 16:16:24.721

Thesis (M.Sc.(Biochemistry)) -- University of Limpopo, 2019. / Retinoblastoma binding protein 6 (RBBP6) is the protein encoded by the Retinoblastoma Binding Protein 6 (RBBP6) gene that is located in chromosome 16p12.2. There is a growing list of newly discovered RBBP6 hypothetical splice variants but there are only three RBBP6 splice variants that are well documented. RBBP6 has been previously implicated in the regulation of cell cycle and apoptosis but little is known about the expression and regulation of the human RBBP6 splice variants during cell cycle progression and breast cancer development. This study was aimed at determining the expression pattern of RBBP6 alternatively spliced variants during arsenic trioxide-induced cell cycle arrest and apoptosis in breast cancer MCF-7 cells. It was also aimed at determining RBBP6 specific microRNAs and how they are regulated in MCF-7 breast cancer cells. MCF-7 cells were maintained and subjected to arsenic trioxide-induced cell cycle arrest and apoptosis. The MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) and the Muse™ Count & Viability assays were used to evaluate the effect of arsenic trioxide on the viability of MCF-7 cells. Cell cycle arrest using 11 μM arsenic trioxide and apoptosis using 32 μM arsenic trioxide were analysed using the MUSE® Cell Analyzer, light and fluorescence microscopy. Arsenic triode-induced apoptosis was analysed using the Muse™ Annexin V & Dead Cell Kit, MultiCaspase and MitoPotential assays using the Muse™ MultiCaspase Kit and Muse™ MitoPotential Kit. Arsenic trioxide-induced cell cycle arrest was analysed using the Muse™ Cell Cycle Kit. Semi-quantitative analysis of RBBP6 variants was carried out using the conventional Polymerase Chain Reaction (PCR), while the quantitative analysis was done using the Real-Time Quantitative PCR. The localization of RBBP6 isoforms was done using Immunocytochemistry (ICC). Web based Bioinformatics tools were used to identify RBBP6-specific microRNAs. The MTT results showed that arsenic trioxide decreased the viability of the MCF-7 cells in a dose-dependent manner. The Muse™ Cell Cycle analysis showed that 11 μM of arsenic trioxide induced G2/M cell cycle arrest in MCF-7 cells, while the Muse™ Annexin V & Dead Cell assay showed that 32 μM of arsenic trioxide induced the extrinsic apoptotic pathway in MCF-7 breast cancer cells. Using the conventional PCR, the MCF-7 cells were found to express the RBBP6 variant 1 transcript but lacks the expression of variant 2 and 3 transcripts, contrary to the kidney embryonic Hek 293 cells that exhibited the expression of RBBP6 variant 1, 2 and 3. Additionally, arsenic trioxide downregulated RBBP6 variant 1 in breast cancer cells during cell cycle arrest and apoptosis. The Real-Time PCR confirmed that MCF-7 cells lowly express RBBP6 variant 3. On the other hand, the ICC analysis showed that RBBP6 isoform 1 is localized and highly expressed in MCF-7 breast cancer cells. The Web based Bioinformatics tools showed that RBBP6 variant 1 specific microRNAs are down regulated in MCF-7 breast cancer cells. These results together showed that As2O3 is effective against MCF-7 cells and also regulated the expression of RBBP6 variants, especially, variant 1. This study showed that there are RBBP6 variants that are involved in breast cancer progression and there are those that may be involved in breast cancer suppression. Targeting these RBBP6 variants for therapeutic development is a promising strategy. In conjunction with RBBP6 expression, arsenic trioxide should be further explored as a breast cancer drug.

Thesis (M.Sc. (Biochemistry)) -- University of Limpopo, 2019 / Survivin is the smallest and a well-studied member of the inhibitors of apoptosis proteins (IAPs) family, which is involved in the regulation of cell division, inhibition of both caspasedependent and -independent apoptosis in cancer cells and promotion of angiogenesis. Survivin is detectable during embryonic and foetal development but is undetectable in normal adult tissues. It is, however, expressed in transformed cell lines as well as in most common types of human cancers. Regulation of survivin remains poorly understood, and the discovery of the regulatory biomolecules, microRNAs (MiRs) present an interesting opportunity to investigate the regulation of this protein and its variants in cancers, especially breast cancer. Additionally, the expression of the survivin splice variants during cell cycle progression and apoptosis is not fully understood. The aims of this study were to investigate the role of arsenic trioxide on the expression of survivin splice variants and their specific microRNAs during cell cycle progression and apoptosis in human breast cancer MCF-7 cells. The study also aimed at ascertaining the toxicity and efficacy of using coal fly ash-derived β-cyclodextrin carbon nanospheres to deliver arsenic trioxide into the MCF-7 cells. Carbon nanospheres (CNSs) were synthesised using a chemical vapour deposition method while arsenic trioxide was deposited using wet impregnation method to form the arsenic trioxide-β-cyclodextrin carbon nanospheres (ATO-β-cyclodextrin-CNSs). The formation of the CNSs and the loading of arsenic trioxide to CNSs were confirmed using scanning electron microscopy/energy dispersive X-ray detection (SEM-EDX). The in vitro cytotoxicity effect of the β-cyclodextrin carbon nanospheres (CNSs), arsenic trioxide and arsenic trioxide-β-cyclodextrin CNSs against KMST-6 and MCF-7 cells was analysed using the 3-(4, 5-dimethylthiazol-2-yl)-2, 5 diphenyltetrazolium bromide (MTT) Assay, Muse® Count and Viability Assay and light/fluorescence microscopy. Cellular apoptosis, cell cycle analysis, Multi-Caspase activation, mitochondrial membrane potential, MAPK activation and PI3K activation were analysed using the Muse® Cell Analyser. Polymerase Chain Reaction (PCR) and Immunohistochemistry were used to analyse survivin mRNA variants and protein expression, respectively. The survivin specific MiRs were predicted using both bioinformatics platforms and literature surveys. In order to understand the applicability of delivering arsenic trioxide for the treatment of breast cancer, skin fibroblast (KMST-6) and MCF-7 cells were exposed to β-cyclodextrin CNSs. The novel β-cyclodextrin CNSs did not show any cytotoxic effect on the KMST-6 cells but demonstrated such activity against the MCF-7 cells. More so, arsenic trioxide-βcyclodextrin CNSs were found to significantly reduce the viability of the MCF-7 cells and were shown to inhibit their cell growth through the induction of apoptosis. The MTT Assay results revealed arsenic trioxide inhibited the growth of the MCF-7 cells in a concentration-dependent manner. The Muse® Cell Analyser showed that arsenic trioxide induced G2/M cell cycle arrest and promoted cellular apoptosis without any damage to the mitochondrial membrane of MCF-7 cells. Furthermore, arsenic trioxide also deactivated two survival pathways, Mitogen-Activated Protein Kinase (MAPK) and Phosphoinositide 3-Kinase (PI3K) signalling pathways in MCF-7 cells. The deactivation of the two pathways was shown to be accompanied by the upregulation of survivin 3α during arsenic trioxide-induced G2/M cell cycle arrest and apoptosis. Survivin 2B was found to be upregulated only during arsenic trioxide-induced G2/M cell cycle arrest, but downregulated during arsenic trioxide-induced apoptosis. However, wild-type survivin was highly expressed in untreated MCF-7 cells, but the expression was upregulated during arsenic trioxide-induced G2/M cell cycle arrest and was downregulated during arsenic trioxide-induced apoptosis. Survivin variant ΔEx3 was undetected in both untreated and treated MCF-7 cells. Survivin 2α was upregulated during arsenic trioxideinduced apoptosis whereas, survivin 3B was only detected in the untreated MCF-7 cells. Additionally, survivin proteins were localised in both the nuclei and cytoplasm in MCF-7 cells and highly upregulated during arsenic trioxide-induced G2/M cell cycle arrest, which can be attributed to the upregulation of survivin-2B. Using TargetScan, MIRD and mirTarbase, a few MiRs were identified and confirmed to target wild-type survivin, survivin 2B and survivin ΔEx3. These include the MiR-542-3p and MiR-335-5p, which are both upregulated during apoptosis and MiR-218-5p, which is upregulated during cell arrest. MiR-218-5p targets survivin 2B, which was upregulated during G2M cell cycle arrest. The fly ash-derived CNSs can be used to deliver arsenic trioxide for therapeutic purposes, especially against breast cancer. Most importantly, these nanoparticles induced typical apoptotic characteristics in breast cancer MCF-7 cells. Arsenic trioxide can be used as therapeutic target for breast cancer treatment and nanotechnology can be used for its delivery. This study provided the first evidence that novel survivin 2B splice variant may be involved in the regulation of arsenic trioxide-induced G2/M cell cycle arrest only. This splice variant can therefore, be targeted for therapeutic purposes against Luminal A breast cancer cells

Dissertation submitted in partial compliance with the requirements of the Master's Degree in Technology: Homoeopathy, Durban University of Technology, 2010. / The therapeutic effects of homoeopathic Arsenicum album potencies were investigated in-vitro, using human cell cultures which were previously antagonised by arsenic trioxide (As2O3). Primary cell culture (peripheral blood mononuclear cells) and a continuous cell line (MT4) were treated with succussed and unsuccussed homoeopathic potencies, 6CH, 30CH and 200CH. This study aimed to verify the homoeopathic law of similars and to determine whether potencies diluted beyond Avogadro’s constant had physiological effects on cells; whether various potencies would cause different effects as proposed by the Arndt-Schultz law; whether succussed and unsuccussed homoeopathic potencies had different effects on the cells; and to establish whether a biotechnological method could be used to evaluate the above. Initial experiments involved isolation and culturing of the peripheral blood mononuclear cells (PBMCs) and the MT4 cell line. Cell titres were determined using the trypan blue dye exclusion assay. The solubilization method of As2O3 was optimized through various dissolution experiments, so as to attain a homogenous arsenical solution. The MTT assay was used to measure the percentage cytotoxicity and the half maximal inhibitory concentration (IC50) caused by the antagonist As2O3 on the PBMCs and the MT4 cell line. The two cell cultures were compared with regard to their susceptibility to As2O3 and their reliability of response. The homoeopathic potencies of Arsenicum album (6CH, 30CH and 200CH) were prepared by initially triturating the As2O3, and then either hand succussing 10 times (succussed) or allowing to diffuse for 30 s (unsuccussed) in sterile distilled water, with the final potencies made up in cell culture media, RPMI. The MTT assay was used to determine the percentage cell viability when the As2O3-antagonised cells were treated with the Arsenicum album potencies. All assays were performed in triplicate. v The As2O3 was found to fully dissolve when 396 mg of dry As2O3 was added to 100 mL of sterile distilled Milli-Q water, which was left to stand for 10 days at 80°C. The cytotoxicity results showed that the PBMCs were not as reliable as the MT4 cells, which showed significant susceptibility to the As2O3. The IC50 of As2O3 on 1 mL of MT4 cells was found to be 5 μM As2O3 (133 μL) for 48 h. The trypan blue dye exclusion assay demonstrated that the viable MT4 cells decreased in number after exposure to the As2O3, with an increase in number of the non-viable cells. Microscopically, the cells were fewer in number and displayed signs of possible blebbing and cell shrinkage, showing potential cell death due to apoptosis. The cell viability results showed that the Arsenicum album 6CH resulted in the lowest absorbance readings and the Arsenicum album 200CH gave the highest readings; this verified the therapeutic effects of homoeopathic remedies when given according to the law of similars; that potencies diluted beyond Avogadro’s constant had stimulating effects; and that the more dilute potencies stimulated recovery in the cells more than the lower potencies, verifying the Arndt-Schultz law. The treatments and the times of exposure were found to be statistically significant determinants of cell viability, whereas succussion did not cause any significant variation in the results. The study thereby provided evidence that a biotechnological method could be used to scientifically evaluate the physiological effects of homoeopathic potencies on human cells; that the homoeopathic potencies did have therapeutic effects; and that succussion was not required in the potentization method in order to produce a curative remedy.

The aim of this study was to investigate the removal of cobalt from zinc sulfate solution by cementation with the help of conventional and new type of additives that were 4% Sn-zinc alloy powder and 10% Sn-zinc alloy powder, respectively. Synthetic leach solutions containing 150 g/l Zn and 75 mg/l Co were prepared and used in all of the experiments. The parameters researched with the conventional method were the amount of arsenic trioxide and the effect of copper sulfate on cementation of cobalt. While using the alloys, the parameters studied were the amounts of arsenic trioxide, copper sulfate and tin containing zinc alloy powder additions, cementation duration and temperature. The difference in the optimization of alloy additions was in the amount of addition of arsenic trioxide. The amount of 4%Sn-zinc alloy powder was tried to be optimized with the addition of arsenic trioxide whereas the optimization was tried to be done without any arsenic addition while using 10%Sn-zinc alloy. The XRD and SEM studies of the cementates were also performed. The obtained results indicated that tin containing alloys were much better than pure zinc. With the additions of 4 g/l 4%Sn-Zn alloy dust, 1.2 g/l CuSO4.5H2O, 0.12 g/l As2O3 and in 2 hours of cementation duration at 85-90oC, the maximum amount of cobalt cementation efficiency was achieved. The experiments indicated that cobalt in the solution could be reduced to about 2 mg/l by using 10%Sn-zinc alloy powder with an initial Sn/Co weight ratio of 13.25:1 without the addition of arsenic trioxide at 85oC in 2 hours of cementation duration.

M.Tech. (Homoeopathy) / The ability to consume oxygen during exercise relies on the functionality of the cardiorespiratory system to deliver oxygen to the working muscles and therefore generate ATP or energy (Astrand et al., 2003). Performance enhancement drugs are becoming increasingly popular as athletes are under extreme pressure to enhance their performance (Shermer, 2008). The purpose of this study was to look for a safe alternative to increase oxygen consumption during exercise. The aim included determining whether the homeopathic remedy Arsenicum album 200CH had an effect on oxygen consumption during submaximal cycling. The study consisted of 32 healthy participants who were randomly divided into a control (placebo) or experimental (treatment) group. Two baseline tests were performed where no medication (remedy or placebo) was given two days apart and the average of the two were taken as the baseline average. After a further two days, the first medication test was conducted after participants were given the treatment 5 minutes prior to testing to ascertain the immediate effect of the medication. The last test was performed after one week of administering where the medication was given twice daily to distinguish what the prolonged effect of the medication was on oxygen consumption. The test consisted of a warm-up at 25-Watts for women and 50-Watts for men, the test included cycling at 3 minute increments where the wattage was increased every 3 minutes by 25-Watts until the participants reached their age-predicted maximum. When this maximum was reached, the wattage was decreased to the warm-up wattage and a cool-down commenced. Heart rate was recorded every minute and documented. The participant was also asked to rate their perceived rate of exertion at the end of every 3minute stage, as a subjective measurement. Although the time periods of administration yielded different results, both were statistically insignificant. The immediate administration showed a negative trend whereas the prolonged administration showed a positive trend in the treatment group after one week. Despite not showing statistical significance, it warrants additional research over a longer period of time.

O meduloblastoma (MB) é o tumor maligno cerebral mais frequente em crianças e adolescentes. Trata-se de uma doença heterogênea sob o aspecto genético, sendo reconhecido ao menos 12 subgrupos genético-moleculares, com impacto na apresentação clínicopatológica. Pacientes do subgrupo SHH apresentam mutação somática em genes da via Hedgehog, incluindo PTCH1, SUFU, SMO e ativação dos genes GLI1 e GLI2. Mutações no gene TP53 também podem estar presentes, particularmente em crianças acima de 3 anos, e conferem um pior prognóstico. O trióxido de arsênio (ATO) possui ação inibitória sobre os genes da via SHH, mas pouco se sabe sobre sua ação no MB. O presente estudo objetivou avaliar os potenciais efeitos citotóxicos e radiossensibilizantes do ATO sobre as linhagens de MB pediátrico grupo SHH (ONS-76: TP53-selvagem; DAOY: TP53-mutado c.725G>T e UW402, TP53-mutado c.464C>A). Foram comparadas as taxas de proliferação celular, clonogenicidade e apoptose nas linhagem de MB antes e após o tratamento com ATO. Também foi avaliada a clonogenicidade da associação droga e irradiação. Foram investigadas proteínas responsáveis pelo reparo dos danos causados ao DNA (Rad51 e Ku86) através de Western Blot. Foi realizada análise da expressão gênica relativa por QPCR e estudados genes que integram a via SHH, assim como efetores finais desta via de sinalização. A viabilidade celular foi monitorada nos tempos de 24 à 120 horas pelo ensaio de resazurina. A taxa de apoptose foi mensurada por meio de marcação com anexina e iodeto de propídio e avaliada por citometria de fluxo. Os ensaios foram realizados em triplicata e analisados por One Way e Two Way ANOVA, utilizando o pós-teste Bonferroni, e sendo considerados resultados significativos valores de p<0,05. Foi possível observar uma diminuição na viabilidade celular após tratamento com ATO nas três linhagens estudadas. Além disso, houve uma diminuição significativa na capacidade clonogênica. Observou-se também um aumento nas taxas de apoptose nas linhagens, sendo acima de 70% de morte celular para a linhagem DAOY. Foi observado que o tratamento com ATO radiossensibilizou a linhagem UW402, TP53-mutado. Não foi encontrada associação com proteínas de reparo no tempo e dose estudados. O estudo de expressões relativas dos genes estudados demonstrou inibição, principalmente nas linhagens de interesse DAOY e UW402 -(SHH TP53) mutado. Estes achados in vitro apontam para um efeito citotóxico do ATO sobre as linhagens de MB pediátrico, podendo apresentar efeito radiossenssibilizante. O ATO deve ser melhor explorado como droga alvo para MB SHH+, em caráter experimental. / Medulloblastoma (MB) is the most common malignant brain tumor in children and adolescents. It is a heterogeneous disease under the genetic aspect, with at least 12 geneticmolecular subgroups being recognized, with impact on the clinical-pathological presentation. Patients of the SHH subgroup present somatic mutation in genes of the Hedgehog pathway, including PTCH1, SUFU, SMO and activation of the genes GLI1 and GLI2. Mutations in the TP53 gene may also be present, particularly in children over 3 years, and confer a worse prognosis. The arsenic trioxide (ATO) has an inhibitory action on SHH pathway genes, but little is known about its action. The present study aimed to evaluate the potential cytotoxic and radiosensitizing effects of ATO on the pediatric MB cells of SHH group (ONS-76: TP53- wild type; DAOY: TP53-mutated c.725GT and UW402 TP53-mutated c.464C>A). Cell proliferation, clonogenicity and apoptosis were compared in the MB strains following ATO treatment. The clonogenicity assay of ATO combined with irradiation was also evaluated. We investigated proteins responsible for repairing DNA damage and performed Western blotting of the Rad51 and Ku86 proteins. Gene expression analysis was performed using the real-time PCR. Selected genes integrating the SHH pathway as well as final effectors of signaling were also assesed. Cell viability was monitored at endpoints from 24 to 120h by the resazurin assay. The rate of apoptosis was measured by labeling with annexin and propidium iodide, as assessed by flow cytometry. The assays were performed in triplicate and analyzed by One Way and Two Way ANOVA, using the Bonferroni post-test, and being considered significant results a p value less than 0.05. It was possible to observe a decrease in cell viability in the three studied strains. In addition, there was a significant decrease in clonogenic capacity. There was also an increase in the apoptosis rates in the lineages, being above 70% of cell death for the DAOY lineage. It was found that the ATO treatment radiosensitized the UW402 strain - TP53-mutated. No association with time and dose of ATO and irradiation on the repair proteins was found. The study of the relative expressions of the studied genes demonstrated inhibition, mainly in the mutant line of interest DAOY and UW-402, a SHHTP53 mutated cell-line. These in vitro findings point to a cytotoxic effect of ATO on pediatric medulloblastoma lines, with a potential radiosensitizing effect. This study offers rationale for further assesment of ATO on SHH-MB, either alone or along with radiotherapy as a preclinical drug.

O meduloblastoma (MB) é o tumor maligno cerebral mais frequente em crianças e adolescentes. Trata-se de uma doença heterogênea sob o aspecto genético, sendo reconhecido ao menos 12 subgrupos genético-moleculares, com impacto na apresentação clínicopatológica. Pacientes do subgrupo SHH apresentam mutação somática em genes da via Hedgehog, incluindo PTCH1, SUFU, SMO e ativação dos genes GLI1 e GLI2. Mutações no gene TP53 também podem estar presentes, particularmente em crianças acima de 3 anos, e conferem um pior prognóstico. O trióxido de arsênio (ATO) possui ação inibitória sobre os genes da via SHH, mas pouco se sabe sobre sua ação no MB. O presente estudo objetivou avaliar os potenciais efeitos citotóxicos e radiossensibilizantes do ATO sobre as linhagens de MB pediátrico grupo SHH (ONS-76: TP53-selvagem; DAOY: TP53-mutado c.725G>T e UW402, TP53-mutado c.464C>A). Foram comparadas as taxas de proliferação celular, clonogenicidade e apoptose nas linhagem de MB antes e após o tratamento com ATO. Também foi avaliada a clonogenicidade da associação droga e irradiação. Foram investigadas proteínas responsáveis pelo reparo dos danos causados ao DNA (Rad51 e Ku86) através de Western Blot. Foi realizada análise da expressão gênica relativa por QPCR e estudados genes que integram a via SHH, assim como efetores finais desta via de sinalização. A viabilidade celular foi monitorada nos tempos de 24 à 120 horas pelo ensaio de resazurina. A taxa de apoptose foi mensurada por meio de marcação com anexina e iodeto de propídio e avaliada por citometria de fluxo. Os ensaios foram realizados em triplicata e analisados por One Way e Two Way ANOVA, utilizando o pós-teste Bonferroni, e sendo considerados resultados significativos valores de p<0,05. Foi possível observar uma diminuição na viabilidade celular após tratamento com ATO nas três linhagens estudadas. Além disso, houve uma diminuição significativa na capacidade clonogênica. Observou-se também um aumento nas taxas de apoptose nas linhagens, sendo acima de 70% de morte celular para a linhagem DAOY. Foi observado que o tratamento com ATO radiossensibilizou a linhagem UW402, TP53-mutado. Não foi encontrada associação com proteínas de reparo no tempo e dose estudados. O estudo de expressões relativas dos genes estudados demonstrou inibição, principalmente nas linhagens de interesse DAOY e UW402 -(SHH TP53) mutado. Estes achados in vitro apontam para um efeito citotóxico do ATO sobre as linhagens de MB pediátrico, podendo apresentar efeito radiossenssibilizante. O ATO deve ser melhor explorado como droga alvo para MB SHH+, em caráter experimental. / Medulloblastoma (MB) is the most common malignant brain tumor in children and adolescents. It is a heterogeneous disease under the genetic aspect, with at least 12 geneticmolecular subgroups being recognized, with impact on the clinical-pathological presentation. Patients of the SHH subgroup present somatic mutation in genes of the Hedgehog pathway, including PTCH1, SUFU, SMO and activation of the genes GLI1 and GLI2. Mutations in the TP53 gene may also be present, particularly in children over 3 years, and confer a worse prognosis. The arsenic trioxide (ATO) has an inhibitory action on SHH pathway genes, but little is known about its action. The present study aimed to evaluate the potential cytotoxic and radiosensitizing effects of ATO on the pediatric MB cells of SHH group (ONS-76: TP53- wild type; DAOY: TP53-mutated c.725GT and UW402 TP53-mutated c.464C>A). Cell proliferation, clonogenicity and apoptosis were compared in the MB strains following ATO treatment. The clonogenicity assay of ATO combined with irradiation was also evaluated. We investigated proteins responsible for repairing DNA damage and performed Western blotting of the Rad51 and Ku86 proteins. Gene expression analysis was performed using the real-time PCR. Selected genes integrating the SHH pathway as well as final effectors of signaling were also assesed. Cell viability was monitored at endpoints from 24 to 120h by the resazurin assay. The rate of apoptosis was measured by labeling with annexin and propidium iodide, as assessed by flow cytometry. The assays were performed in triplicate and analyzed by One Way and Two Way ANOVA, using the Bonferroni post-test, and being considered significant results a p value less than 0.05. It was possible to observe a decrease in cell viability in the three studied strains. In addition, there was a significant decrease in clonogenic capacity. There was also an increase in the apoptosis rates in the lineages, being above 70% of cell death for the DAOY lineage. It was found that the ATO treatment radiosensitized the UW402 strain - TP53-mutated. No association with time and dose of ATO and irradiation on the repair proteins was found. The study of the relative expressions of the studied genes demonstrated inhibition, mainly in the mutant line of interest DAOY and UW-402, a SHHTP53 mutated cell-line. These in vitro findings point to a cytotoxic effect of ATO on pediatric medulloblastoma lines, with a potential radiosensitizing effect. This study offers rationale for further assesment of ATO on SHH-MB, either alone or along with radiotherapy as a preclinical drug.