Involvement of Mitochondria in the Selective Response to Microsecond Pulsed Electric Fields on Healthy and Cancer Stem Cells in the Brain

In the last few years, pulsed electric fields have emerged as promising clinical tools for tumor treatments. This study highlights the distinct impact of a specific pulsed electric field protocol, PEF-5 (0.3 MV/m, 40 μs, 5 pulses), on astrocytes (NHA) and medulloblastoma (D283) and glioblastoma (U87 NS) cancer stem-like cells (CSCs). We pursued this goal by performing ultrastructural analyses corroborated by molecular/omics approaches to understand the vulnerability or resistance mechanisms triggered by PEF-5 exposure in the different cell types. Electron microscopic analyses showed that, independently of exposed cells, the main targets of PEF-5 were the cell membrane and the cytoskeleton, causing membrane filopodium-like protrusion disappearance on the cell surface, here observed for the first time, accompanied by rapid cell swelling. PEF-5 induced different modifications in cell mitochondria. A complete mitochondrial dysfunction was demonstrated in D283, while a mild or negligible perturbation was observed in mitochondria of U87 NS cells and NHAs, respectively, not sufficient to impair their cell functions. Altogether, these results suggest the possibility of using PEF-based technology as a novel strategy to target selectively mitochondria of brain CSCs, preserving healthy cells.

Characterization of Early and Late Damage in a Mouse Model of Pelvic Radiation Disease

Pelvic radiation disease (PRD), a frequent side effect in patients with abdominal/pelvic cancers treated with radiotherapy, remains an unmet medical need. Currently available preclinical models have limited applications for the investigation of PRD pathogenesis and possible therapeutic strategies. In order to select the most effective irradiation protocol for PRD induction in mice, we evaluated the efficacy of three different locally and fractionated X-ray exposures. Using the selected protocol (10 Gy/day × 4 days), we assessed PRD through tissue (number and length of colon crypts) and molecular (expression of genes involved in oxidative stress, cell damage, inflammation, and stem cell markers) analyses at short (3 h or 3 days after X-ray) and long (38 days after X-rays) post-irradiation times. The results show that a primary damage response in term of apoptosis, inflammation, and surrogate markers of oxidative stress was found, thus determining a consequent impairment of cell crypts differentiation and proliferation as well as a local inflammation and a bacterial translocation to mesenteric lymph nodes after several weeks post-irradiation. Changes were also found in microbiota composition, particularly in the relative abundance of dominant phyla, related families, and in alpha diversity indices, as an indication of dysbiotic conditions induced by irradiation. Fecal markers of intestinal inflammation, measured during the experimental timeline, identified lactoferrin, along with elastase, as useful non-invasive tools to monitor disease progression. Thus, our preclinical model may be useful to develop new therapeutic strategies for PRD treatment.

Safety in Rats of a Novel Nasal Spray Formulation for the Prevention of Airborne Viral Infections

Hexedra+^® is a nasal spray containing hydroxypropyl methylcellulose, beta-cyclodextrin, and usnic acid. It has been developed with the aim of reducing the risk of transmission of airborne viral infections, with particular reference to influenza and COVID-19. As part of the preclinical development of the product, we carried out a study on thirty male Wistar rats divided into three study groups and treated with Hexedra+, an alternative formulation containing a double concentration of usnic acid (0.015% instead of 0.0075%) or saline solution. Products were administered at the dose of 30 μL into each nostril, three times a day for seven consecutive days by means of a micropipette. By the end of the treatment period, no significant changes were observed in body weight. Histological examination of nasal mucosa and soft organs did not show any significant difference in the three study groups. Serum transaminase level remained in the normal limit in all the animals treated. The serum level of usnic acid was measured in order to assess the absorption of the molecule through the nasal mucosa. By the end of the study period, the usnic acid serum level was negligible in all the animals treated. In conclusion, the safety profile of Hexedra+ appears favorable in the animal model studied.

Aglianico Grape Seed Semi-Polar Extract Exerts Anticancer Effects by Modulating MDM2 Expression and Metabolic Pathways

Grapevine (Vitis vinifera L.) seeds are rich in polyphenols including proanthocyanidins, molecules with a variety of biological effects including anticancer action. We have previously reported that the grape seed semi-polar extract of Aglianico cultivar (AGS) was able to induce apoptosis and decrease cancer properties in different mesothelioma cell lines. Concomitantly, this extract resulted in enriched oligomeric proanthocyanidins which might be involved in determining the anticancer activity. Through transcriptomic and metabolomic analyses, we investigated in detail the anticancer pathway induced by AGS. Transcriptomics analysis and functional annotation allowed the identification of the relevant causative genes involved in the apoptotic induction following AGS treatment. Subsequent biological validation strengthened the hypothesis that MDM2 could be the molecular target of AGS and that it could act in both a p53-dependent and independent manner. Finally, AGS significantly inhibited tumor progression in a xenograft mouse model of mesothelioma, confirming also in vivo that MDM2 could act as molecular player responsible for the AGS antitumor effect. Our findings indicated that AGS, exerting a pro-apoptotic effect by hindering MDM2 pathway, could represent a novel source of anticancer molecules.

Liver Steatosis and Steatohepatitis Alter Bile Acid Receptors in Brain and Induce Neuroinflammation: A Contribution of Circulating Bile Acids and Blood-Brain Barrier

A tight relationship between gut-liver diseases and brain functions has recently emerged. Bile acid (BA) receptors, bacterial-derived molecules and the blood-brain barrier (BBB) play key roles in this association. This study was aimed to evaluate how non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) impact the BA receptors Farnesoid X receptor (FXR) and Takeda G-protein coupled receptor 5 (TGR5) expression in the brain and to correlate these effects with circulating BAs composition, BBB integrity and neuroinflammation. A mouse model of NAFLD was set up by a high-fat and sugar diet, and NASH was induced with the supplementation of dextran-sulfate-sodium (DSS) in drinking water. FXR, TGR5 and ionized calcium-binding adaptor molecule 1 (Iba-1) expression in the brain was detected by immunohistochemistry, while Zonula occludens (ZO)-1, Occludin and Plasmalemmal Vesicle Associated Protein-1 (PV-1) were analyzed by immunofluorescence. Biochemical analyses investigated serum BA composition, lipopolysaccharide-binding protein (LBP) and S100β protein (S100β) levels. Results showed a down-regulation of FXR in NASH and an up-regulation of TGR5 and Iba-1 in the cortex and hippocampus in both treated groups as compared to the control group. The BA composition was altered in the serum of both treated groups, and LBP and S100β were significantly augmented in NASH. ZO-1 and Occludin were attenuated in the brain capillary endothelial cells of both treated groups versus the control group. We demonstrated that NAFLD and NASH provoke different grades of brain dysfunction, which are characterized by the altered expression of BA receptors, FXR and TGR5, and activation of microglia. These effects are somewhat promoted by a modification of circulating BAs composition and by an increase in LBP that concur to damage BBB, thus favoring neuroinflammation.

Effects of Ultra-Short Pulsed Electric Field Exposure on Glioblastoma Cells

Glioblastoma multiforme (GBM) is the most common brain cancer in adults. GBM starts from a small fraction of poorly differentiated and aggressive cancer stem cells (CSCs) responsible for aberrant proliferation and invasion. Due to extreme tumor heterogeneity, actual therapies provide poor positive outcomes, and cancers usually recur. Therefore, alternative approaches, possibly targeting CSCs, are necessary against GBM. Among emerging therapies, high intensity ultra-short pulsed electric fields (PEFs) are considered extremely promising and our previous results demonstrated the ability of a specific electric pulse protocol to selectively affect medulloblastoma CSCs preserving normal cells. Here, we tested the same exposure protocol to investigate the response of U87 GBM cells and U87-derived neurospheres. By analyzing different in vitro biological endpoints and taking advantage of transcriptomic and bioinformatics analyses, we found that, independent of CSC content, PEF exposure affected cell proliferation and differentially regulated hypoxia, inflammation and P53/cell cycle checkpoints. PEF exposure also significantly reduced the ability to form new neurospheres and inhibited the invasion potential. Importantly, exclusively in U87 neurospheres, PEF exposure changed the expression of stem-ness/differentiation genes. Our results confirm this physical stimulus as a promising treatment to destabilize GBM, opening up the possibility of developing effective PEF-mediated therapies.

Contribution of Genetic Background to the Radiation Risk for Cancer and Non-Cancer Diseases in Ptch1+/- Mice

Experimental mouse studies are important to gain a comprehensive, quantitative and mechanistic understanding of the biological factors that modify individual risk of radiation-induced health effects, including age at exposure, dose, dose rate, organ/tissue specificity and genetic factors. In this study, neonatal Ptch1+/- mice bred on CD1 and C57Bl/6 background received whole-body irradiation at postnatal day 2. This time point represents a critical phase in the development of the eye lens, cerebellum and dentate gyrus (DG), when they are also particularly susceptible to radiation effects. Irradiation was performed with γ rays (60Co) at doses of 0.5, 1 and 2 Gy, delivered at 0.3 Gy/min or 0.063 Gy/min. Wild-type and mutant mice were monitored for survival, lens opacity, medulloblastoma (MB) and neurogenesis defects. We identified an inverse genetic background-driven relationship between the radiosensitivity to induction of lens opacity and MB and that to neurogenesis deficit in Ptch1+/- mutants. In fact, high incidence of radiation-induced cataract and MB were observed in Ptch1+/-/CD1 mutants that instead showed no consequence of radiation exposure on neurogenesis. On the contrary, no induction of radiogenic cataract and MB was reported in Ptch1+/-/C57Bl/6 mice that were instead susceptible to induction of neurogenesis defects. Compared to Ptch1+/-/CD1, the cerebellum of Ptch1+/-/C57Bl/6 mice showed increased radiosensitivity to apoptosis, suggesting that differences in processing radiation-induced DNA damage may underlie the opposite strain-related radiosensitivity to cancer and non-cancer pathologies. Altogether, our results showed lack of dose-rate-related effects and marked influence of genetic background on the radiosensitivity of Ptch1+/-mice, supporting a major contribution of individual sensitivity to radiation risk in the population.

miRNA-Signature of Irradiated Ptch1+/- Mouse Lens is Dependent on Genetic Background

One harmful long-term effect of ionizing radiation is cataract development. Recent studies have been focused on elucidating the mechanistic pathways involved in this pathogenesis. Since accumulating evidence has established a role of microRNAs in ocular diseases, including cataract, the goal of this work was to determine the microRNA signature of the mouse lens, at short time periods postirradiation, to understand the mechanisms related to radio-induced cataractogenesis. To evaluate the differences in the microRNA profiles, 10-week-old Patched1 heterozygous (Ptch1+/-) mice, bred onto two different genetic backgrounds (CD1 and C57Bl/6J), received whole-body 2 Gy γ-ray irradiation, and 24 h later lenses were collected. Next-generation sequencing and bioinformatics analysis revealed that genetic background markedly influenced the list of the deregulated microRNAs and the mainly predicted perturbed biological functions of 2 Gy irradiated Ptch1+/- mouse lenses. We identified a subset of microRNAs with a contra-regulated expression between strains, with a key role in regulating Toll-like receptor (TLR)-signaling pathways. Furthermore, a detailed analysis of miRNome data showed a completely different DNA damage response in mouse lenses 24 h postirradiation, mainly mediated by a marked upregulation of p53 signaling in Ptch1+/-/C57Bl/6J lenses that was not detected on a CD1 background. We propose a strict interplay between p53 and TLR signaling in Ptch1+/-/C57Bl/6J lenses shortly after irradiation that could explain both the resistance of this strain to developing lens opacities and the susceptibility of CD1 background to radiation-induced cataractogenesis through activation of epithelial-mesenchymal transition.

G-quadruplex ligand RHPS4 radiosensitizes glioblastoma xenograft in vivo through a differential targeting of bulky differentiated- and stem-cancer cells

BACKGROUND

Glioblastoma is the most aggressive and most lethal primary brain tumor in the adulthood. Current standard therapies are not curative and novel therapeutic options are urgently required. Present knowledge suggests that the continued glioblastoma growth and recurrence is determined by glioblastoma stem-like cells (GSCs), which display self-renewal, tumorigenic potential, and increased radio- and chemo-resistance. The G-quadruplex ligand RHPS4 displays in vitro radiosensitizing effect in GBM radioresistant cells through the targeting and dysfunctionalization of telomeres but RHPS4 and Ionizing Radiation (IR) combined treatment efficacy in vivo has not been explored so far.

METHODS

RHPS4 and IR combined effects were tested in vivo in a heterotopic mice xenograft model and in vitro in stem-like cells derived from U251MG and from four GBM patients. Cell growth assays, cytogenetic analysis, immunoblotting, gene expression and cytofluorimetric analysis were performed in order to characterize the response of differentiated and stem-like cells to RHPS4 and IR in single and combined treatments.

RESULTS

RHPS4 administration and IR exposure is very effective in blocking tumor growth in vivo up to 65 days. The tumor volume reduction and the long-term tumor control suggested the targeting of the stem cell compartment. Interestingly, RHPS4 treatment was able to strongly reduce cell proliferation in GSCs but, unexpectedly, did not synergize with IR. Lack of radiosensitization was supported by the GSCs telomeric-resistance observed as the total absence of telomere-involving chromosomal aberrations. Remarkably, RHPS4 treatment determined a strong reduction of CHK1 and RAD51 proteins and transcript levels suggesting that the inhibition of GSCs growth is determined by the impairment of the replication stress (RS) response and DNA repair.

CONCLUSIONS

We propose that the potent antiproliferative effect of RHPS4 in GSCs is not determined by telomeric dysfunction but is achieved by the induction of RS and by the concomitant depletion of CHK1 and RAD51, leading to DNA damage and cell death. These data open to novel therapeutic options for the targeting of GSCs, indicating that the combined inhibition of cell-cycle checkpoints and DNA repair proteins provides the most effective means to overcome resistance of GSC to genotoxic insults.

Alterations in Morphology and Adult Neurogenesis in the Dentate Gyrus of Patched1 Heterozygous Mice

Many genes controlling neuronal development also regulate adult neurogenesis. We investigated in vivo the effect of Sonic hedgehog (Shh) signaling activation on patterning and neurogenesis of the hippocampus and behavior of Patched1 (Ptch1) heterozygous mice (Ptch1^+/−). We demonstrated for the first time, that Ptch1^+/− mice exhibit morphological, cellular and molecular alterations in the dentate gyrus (DG), including elongation and reduced width of the DG as well as deregulations at multiple steps during lineage progression from neural stem cells to neurons. By using stage-specific cellular markers, we detected reduction of quiescent stem cells, newborn neurons and astrocytes and accumulation of proliferating intermediate progenitors, indicative of defects in the dynamic transition among neural stages. Phenotypic alterations in Ptch1^+/− mice were accompanied by expression changes in Notch pathway downstream components and TLX nuclear receptor, as well as perturbations in inflammatory and synaptic networks and mouse behavior, pointing to complex biological interactions and highlighting cooperation between Shh and Notch signaling in the regulation of neurogenesis.

Synthetic lethal genetic interactions between Rad54 and PARP-1 in mouse development and oncogenesis

Mutations in DNA repair pathways are frequent in human cancers. Hence, gaining insights into the interaction of DNA repair genes is key to development of novel tumor-specific treatment strategies. In this study, we tested the functional relationship in development and oncogenesis between the homologous recombination (HR) factor Rad54 and Parp-1, a nuclear enzyme that plays a multifunctional role in DNA damage signaling and repair. We introduced single or combined Rad54 and Parp-1 inactivating germline mutations in Ptc1 heterozygous mice, a well-characterized model of medulloblastoma, the most common malignant pediatric brain tumor. Our study reveals that combined inactivation of Rad54 and Parp-1 causes a marked growth delay culminating in perinatallethality, providing for the first time evidence of synthetic lethal interactions between Rad54 and Parp-1 in vivo. Although the double mutation hampered investigation of Rad54 and Parp-1 interactions in cerebellum tumorigenesis, insights were gained by showing accumulation of endogenous DNA damage and increased apoptotic rate in granule cell precursors (GCPs). A network-based approach to detect differential expression of DNA repair genes in the cerebellum revealed perturbation of p53 signaling in Rad54-/-/Parp-1-/-/Ptc1+/-, and MEFs from combined Rad54/Parp-1 mutants showed p53/p21-dependent typical senescent features. These findings help elucidate the genetic interplay between Rad54 and Parp-1 by suggesting that p53/p21-mediated apoptosis and/or senescence may be involved in synthetic lethal interactions occurring during development and inhibition of tumor growth.

A multidisciplinary approach unravels early and persistent effects of X-ray exposure at the onset of prenatal neurogenesis

Background

In humans, in utero exposure to ionising radiation results in an increased prevalence of neurological aberrations, such as small head size, mental retardation and decreased IQ levels. Yet, the association between early damaging events and long-term neuronal anomalies remains largely elusive.

Methods

Mice were exposed to different X-ray doses, ranging between 0.0 and 1.0 Gy, at embryonic days (E) 10, 11 or 12 and subjected to behavioural tests at 12 weeks of age. Underlying mechanisms of irradiation at E11 were further unravelled using magnetic resonance imaging (MRI) and spectroscopy, diffusion tensor imaging, gene expression profiling, histology and immunohistochemistry.

Results

Irradiation at the onset of neurogenesis elicited behavioural changes in young adult mice, dependent on the timing of exposure. As locomotor behaviour and hippocampal-dependent spatial learning and memory were most particularly affected after irradiation at E11 with 1.0 Gy, this condition was used for further mechanistic analyses, focusing on the cerebral cortex and hippocampus. A classical p53-mediated apoptotic response was found shortly after exposure. Strikingly, in the neocortex, the majority of apoptotic and microglial cells were residing in the outer layer at 24 h after irradiation, suggesting cell death occurrence in differentiating neurons rather than proliferating cells. Furthermore, total brain volume, cortical thickness and ventricle size were decreased in the irradiated embryos. At 40 weeks of age, MRI showed that the ventricles were enlarged whereas N-acetyl aspartate concentrations and functional anisotropy were reduced in the cortex of the irradiated animals, indicating a decrease in neuronal cell number and persistent neuroinflammation. Finally, in the hippocampus, we revealed a reduction in general neurogenic proliferation and in the amount of Sox2-positive precursors after radiation exposure, although only at a juvenile age.

Conclusions

Our findings provide evidence for a radiation-induced disruption of mouse brain development, resulting in behavioural differences. We propose that alterations in cortical morphology and juvenile hippocampal neurogenesis might both contribute to the observed aberrant behaviour. Furthermore, our results challenge the generally assumed view of a higher radiosensitivity in dividing cells. Overall, this study offers new insights into irradiation-dependent effects in the embryonic brain, of relevance for the neurodevelopmental and radiobiological field.

Electronic supplementary material

The online version of this article (doi:10.1186/1866-1955-7-3) contains supplementary material, which is available to authorized users.

The Patched 1 tumor-suppressor gene protects the mouse lens from spontaneous and radiation-induced cataract

Age-related cataract is the most common cause of visual impairment. Moreover, traumatic cataracts form after injury to the eye, including radiation damage. We report herein that sonic hedgehog (Shh) signaling plays a key role in cataract development and in normal lens response to radiation injury. Mice heterozygous for Patched 1 (Ptch1), the Shh receptor and negative regulator of the pathway, develop spontaneous cataract and are highly susceptible to cataract induction by exposure to ionizing radiation in early postnatal age, when lens epithelial cells undergo rapid expansion in the lens epithelium. Neonatally irradiated and control Ptch1(+/-) mice were compared for markers of progenitors, Shh pathway activation, and epithelial-to-mesenchymal transition (EMT). Molecular analyses showed increased expression of the EMT-related transforming growth factor β/Smad signaling pathway in the neonatally irradiated lens, and up-regulation of mesenchymal markers Zeb1 and Vim. We further show a link between proliferation and the stemness property of lens epithelial cells, controlled by Shh. Our results suggest that Shh and transforming growth factor β signaling cooperate to promote Ptch1-associated cataract development by activating EMT, and that the Nanog marker of pluripotent cells may act as the primary transcription factor on which both signaling pathways converge after damage. These findings highlight a novel function of Shh signaling unrelated to cancer and provide a new animal model to investigate the molecular pathogenesis of cataract formation.

Developmental and oncogenic radiation effects on neural stem cells and their differentiating progeny in mouse cerebellum

Neural stem cells are highly susceptible to radiogenic DNA damage, however, little is known about their mechanisms of DNA damage response (DDR) and the long-term consequences of genotoxic exposure. Patched1 heterozygous mice (Ptc1(+/-)) provide a powerful model of medulloblastoma (MB), a frequent pediatric tumor of the cerebellum. Irradiation of newborn Ptc1(+/-) mice dramatically increases the frequency and shortens the latency of MB. In this model, we investigated the mechanisms through which multipotent neural progenitors (NSCs) and fate-restricted progenitor cells (PCs) of the cerebellum respond to DNA damage induced by radiation, and the long-term developmental and oncogenic consequences. These responses were assessed in mice exposed to low (0.25 Gy) or high (3 Gy) radiation doses at embryonic day 13.5 (E13.5), when NSCs giving rise to the cerebellum are specified but the external granule layer (EGL) has not yet formed, or at E16.5, during the expansion of granule PCs to form the EGL. We found crucial differences in DDR and apoptosis between NSCs and fate-restricted PCs, including lack of p21 expression in NSCs. NSCs also appear to be resistant to oncogenesis from low-dose radiation exposure but more vulnerable at higher doses. In addition, the pathway to DNA repair and the pattern of oncogenic alterations were strongly dependent on age at exposure, highlighting a differentiation-stage specificity of DNA repair pathways in NSCs and PCs. These findings shed light on the mechanisms used by NSCs and PCs to maintain genome integrity during neurogenesis and may have important implications for radiation risk assessment and for development of targeted therapies against brain tumors.

Oncogenic radiation abscopal effects in vivo: interrogating mouse skin

PURPOSE

To investigate the tissue dependence in transmission of abscopal radiation signals and their oncogenic consequences in a radiosensitive mouse model and to explore the involvement of gap junction intercellular communication (GJIC) in mediating radiation tumorigenesis in off-target mouse skin.

METHODS AND MATERIALS

Patched1 heterozygous (Ptch1(+/-)) mice were irradiated at postnatal day 2 (P2) with 10 Gy of x-rays. Individual lead cylinders were used to protect the anterior two-thirds of the body, whereas the hindmost part was directly exposed to radiation. To test the role of GJICs and their major constituent connexin43 (Cx43), crosses between Ptch1(+/-) and Cx43(+/-) mice were similarly irradiated. These mouse groups were monitored for their lifetime, and skin basal cell carcinomas (BCCs) were counted and recorded. Early responses to DNA damage - Double Strand Breaks (DSBs) and apoptosis - were also evaluated in shielded and directly irradiated skin areas.

RESULTS

We report abscopal tumor induction in the shielded skin of Ptch1(+/-) mice after partial-body irradiation. Endpoints were induction of early nodular BCC-like tumors and macroscopic infiltrative BCCs. Abscopal tumorigenesis was significantly modulated by Cx43 status, namely, Cx43 reduction was associated with decreased levels of DNA damage and oncogenesis in out-of-field skin, suggesting a key role of GJIC in transmission of oncogenic radiation signals to unhit skin.

CONCLUSIONS

Our results further characterize the nature of abscopal responses and the implications they have on pathologic processes in different tissues, including their possible underlying mechanistic bases.

Protective role of 17 β-estradiol on medulloblastoma development in Patched 1 heterozygous mice

Medulloblastoma (MB) is the most common pediatric tumor of the CNS, representing ∼20% of all childhood CNS tumors. Although in recent years many molecular mechanisms that control MB development have been clarified, the effects of biological factors such as sex on this tumor remain to be explained. Epidemiological data, in fact, indicate a significant difference in the incidence of MB between the 2 sexes, with considerably higher susceptibility of males than females. Besides this different susceptibility, female sex is also a significant favorable prognostic factor in MB, with girls having a much better outcome. Despite these literature data, there has been little investigation into estrogen influence on MB development. In our study, we evaluated how hormone deficiency resulting from ovariectomy and hormone replacement influences the development of early and advanced MB stages in Patched1 heterozygous mice, a well-characterized mouse model of radiation-induced MB. Susceptibility to MB development was significantly increased in ovariectomized Ptch1(+/-) females and restored to levels observed in control mice after estrogen replacement. We next investigated the molecular mechanisms by which estrogen might influence tumor progression and show that ERβ, but not ERα, is involved in modulation of MB development by estrogens. Finally, our study shows that a functional interaction between estrogen- and IGF-I-mediated pathways may be responsible for the effects observed.

Developmental and oncogenic effects of insulin-like growth factor-I in Ptc1+/- mouse cerebellum

Background

Medulloblastoma is amongst the most common malignant brain tumors in childhood, arising from neoplastic transformation of granule neuron precursors (GNPs) of the cerebellum via deregulation of pathways involved in cerebellar development. Deregulation of the Sonic hedgehog/Patched1 (Shh/Ptc1) signaling pathway predisposes humans and mice to medulloblastoma. In the brain, insulin-like growth factor (IGF-I) plays a critical role during development as a neurotrophic and neuroprotective factor, and in tumorigenesis, as IGF-I receptor is often activated in medulloblastomas.

Results

To investigate the mechanisms of genetic interactions between Shh and IGF signaling in the cerebellum, we crossed nestin/IGF-I transgenic (IGF-I Tg) mice, in which transgene expression occurs in neuron precursors, with Ptc1^+/- knockout mice, a model of medulloblastoma in which cancer develops in a multistage process. The IGF-I transgene produced a marked brain overgrowth, and significantly accelerated tumor development, increasing the frequency of pre-neoplastic lesions as well as full medulloblastomas in Ptc1^+/-/IGF-I Tg mice. Mechanistically, tumor promotion by IGF-I mainly affected preneoplastic stages through de novo formation of lesions, while not influencing progression rate to full tumors. We also identified a marked increase in survival and proliferation, and a strong suppression of differentiation in neural precursors.

Conclusions

As a whole, our findings indicate that IGF-I overexpression in neural precursors leads to brain overgrowth and fosters external granular layer (EGL) proliferative lesions through a mechanism favoring proliferation over terminal differentiation, acting as a landscape for tumor growth. Understanding the molecular events responsible for cerebellum development and their alterations in tumorigenesis is critical for the identification of potential therapeutic targets.

Physical, heritable and age-related factors as modifiers of radiation cancer risk in patched heterozygous mice

PURPOSE

To address the tumorigenic potential of exposure to low/intermediate doses of ionizing radiation and to identify biological factors influencing tumor response in a mouse model highly susceptible to radiogenic cancer.

METHODS AND MATERIALS

Newborn Ptc1 heterozygous mice were exposed to X-ray doses of 100, 250, and 500 mGy, and tumor development was monitored for their lifetime. Additional groups were irradiated with the same doses and sacrificed at fixed times for determination of short-term endpoints, such as apoptosis and early preneoplastic lesions in cerebellum. Finally, groups of Ptc1 heterozygous mice were bred on the C57BL/6 background to study the influence of common variant genes on radiation response.

RESULTS

We have identified a significant effect of low-intermediate doses of radiation (250 and 500 mGy) in shortening mean survival and inducing early and more progressed stages of tumor development in the cerebellum of Ptc1(+/-) mice. In addition, we show that age at exposure and heritable factors are potent modifiers of radiation-related cancer risk.

CONCLUSIONS

The Ptc1 knockout mouse model offers a highly sensitive system that may potentially help to improve understanding and quantification of risk at low doses, such as doses experienced in occupational and medical exposures, and clarify the complex interactions between genetic and environmental factors underlying cancer susceptibility.

Modulation of basal and squamous cell carcinoma by endogenous estrogen in mouse models of skin cancer

Patched1 heterozygous mice (Ptch1(+/-)) are useful for basal cell carcinoma (BCC) studies, being remarkably susceptible to BCC induction by ultraviolet or ionizing radiation. Analogously, skin carcinogenesis-susceptible (Car-S) mice are elective for studies of papilloma and squamous cell carcinoma (SCC) induction. We previously reported a striking effect of gender on BCC induction in Ptch1(+/-) mice, with total resistance of females; likewise, Car-S females show increased skin tumor resistance relative to males. Here, we investigated the protective role of endogenous estrogen in skin keratinocyte tumorigenesis. Control (CN) and ovariectomized Ptch1(+/-) or Car-S females were irradiated for BCC induction or topically treated with chemical carcinogens for SCC induction. Susceptibility to BCC or SCC was dramatically increased in ovariectomized Ptch1(+/-) and Car-S females and restored to levels observed in males. Remarkably, progression of initially benign papillomas to malignant SCC occurred only in ovariectomized Car-S females. We explored the mechanisms underlying tumor progression and report overexpression of estrogen receptor (ER)-alpha, downregulation of ERbeta and upregulation of cyclin D1 in papillomas from ovariectomized Car-S relative to papillomas from CN females. Thus, an imbalanced ERalpha/ERbeta expression may be associated with estrogen-mediated modulation of non-melanoma skin carcinogenesis, with a key role played by cyclin D1. Our findings underscore a highly protective role of endogenous estrogen against skin tumorigenesis by diverse agents in two independent mouse models of skin cancer.

PARP-1 cooperates with Ptc1 to suppress medulloblastoma and basal cell carcinoma

The patched (Ptc1) protein is a negative regulator of sonic hedgehog signaling, a genetic pathway whose perturbation causes developmental defects and predisposition to specific malignant tumors. Humans and mice with mutated Ptc1 are prone to medulloblastoma and basal cell carcinoma (BCC), both tumors showing dependence on radiation damage for rapid onset and high penetrance. Poly(ADP-ribose) polymerase (PARP-1) is a nuclear enzyme that plays a multifunctional role in DNA damage signaling and repair. In healthy and fertile PARP-1-null mice, radiation exposure reveals an extreme sensitivity and a high genomic instability. To test for interactions between PARP-1 and sonic hedgehog signaling, PARP-1-null mice were crossed to Ptc1 heterozygous mice. PARP-1 deletion further accelerated medulloblastoma development in irradiated Ptc1(+/-) mice, showing that PARP-1 inactivation sensitizes cerebellar cells to radiation tumorigenic effects. In addition to increased formation and slowed down kinetics of disappearance of gamma-H2AX foci, we observed increased apoptosis in PARP-1-deficient granule cell progenitors after irradiation. Double-mutant mice were also strikingly more susceptible to BCC, with >50% of animals developing multiple, large, infiltrative tumors within 30 weeks of age. The results provide genetic evidence that PARP-1 function suppresses sonic hedgehog pathway-associated tumors arising in response to environmental stress.

Inhibition of medulloblastoma tumorigenesis by the antiproliferative and pro-differentiative gene PC3

Medulloblastoma, the most common brain tumor in childhood, appears to originate from cerebellar granule cell precursors (GCPs), located in the external granular layer (EGL) of the cerebellum. The antiproliferative gene PC3 (Tis21/BTG2) promotes cerebellar neurogenesis by inducing GCPs to shift from proliferation to differentiation. To assess whether PC3 can prevent the neoplastic transformation of GCPs and medulloblastoma development, we crossed transgenic mice conditionally expressing PC3 (TgPC3) in GCPs with Patched1 heterozygous mice (Ptc(+/-)), a model of medulloblastoma pathogenesis characterized by hyperactivation of the Sonic Hedgehog pathway. Perinatal up-regulation of PC3 in Ptc(+/-)/TgPC3 mice results in a decrease of medulloblastoma incidence of approximately 40% and in a marked reduction of preneoplastic abnormalities, such as hyperplastic EGL areas and lesions. Moreover, overexpression of cyclin D1, hyperproliferation, and defective differentiation--observed in Ptc(+/-) GCPs--are restored to normality in Ptc(+/-)/TgPC3 mice. The PC3-mediated inhibition of cyclin D1 expression correlates with recruitment of PC3 to the cyclin D1 promoter, which is accompanied by histone deacetylation. Remarkably, down-regulation of PC3 is observed in preneoplastic lesions, as well as in human and murine medulloblastomas. As a whole, this indicates that PC3 may prevent medulloblastoma development by controlling cell cycle and promoting differentiation of GCPs.

Hair cycle-dependent basal cell carcinoma tumorigenesis in Ptc1neo67/+ mice exposed to radiation

We examined the effects of hair cycle phase on basal cell carcinoma (BCC) tumorigenesis induced by radiation in mice lacking one Patched allele (Ptc1(neo67/+)). Our results show that Ptc1(neo67/+) mouse skin irradiated in early anagen is highly susceptible to tumor induction, as a 3.2-fold incidence of visible BCC-like tumors was observed in anagen-irradiated compared with telogen-irradiated mice. Microscopic nodular BCC-like tumors were also enhanced by irradiation during active hair-follicle growth phases. Interestingly, histologic examination of the tumors revealed a qualitative difference in BCC tumorigenesis depending on hair growth phase at the time of exposure. In fact, in addition to typical BCC-like tumors, we observed development of a distinct basal cell tumor subtype characterized by anti-cytokeratin 14 and anti-smooth muscle actin reactivity. These tumors showed relatively short latency and rapid growth and were strictly dependent on age at irradiation, as they occurred only in mice irradiated in early anagen phase. Examination of anatomic and immunohistochemical relationships revealed a close relation of these tumors with the follicular outer root sheath of anagen skin. In contrast, there are strong indications for the derivation of typical, smooth muscle actin-negative BCC-like tumors from cell progenitors of interfollicular epidermis. These results underscore the role of follicular bulge stem cells and their progeny with high self-renewal capacity in the formation of basal cell tumors and contribute to clarify the relationship between target cell and tumor phenotype in BCC tumorigenesis induced by radiation.

Two-hit model for progression of medulloblastoma preneoplasia in Patched heterozygous mice

Inactivation of one Ptc1 allele predisposes humans and mice to spontaneous medulloblastoma development, and irradiation of newborn Ptc1 heterozygous mice results in dramatic increase of medulloblastoma incidence. While a role for loss of wild-type (wt) Ptc1 (LOH) in radiation-induced medulloblastomas from Ptc1(neo67/+) mice is well established, the importance of this event in spontaneous medulloblastomas is still unclear. Here, we demonstrate that biallelic Ptc1 loss plays a crucial role in spontaneous medulloblastomas, as shown by high rate of wt Ptc1 loss in spontaneous tumors. In addition, remarkable differences in chromosomal events involving the Ptc1 locus in spontaneous and radiation-induced medulloblastomas suggest distinct mechanisms for Ptc1 loss. To assess when, during tumorigenesis, Ptc1 loss occurs, we characterized cerebellar abnormalities that precede tumor appearance in Ptc1(neo67/+) mice. We show that inactivation of only one copy of Ptc1 is sufficient to give rise to abnormal cerebellar proliferations with different degree of altered cell morphology, but lacking potential to progress to neoplasia. Furthermore, we identify biallelic Ptc1 loss as the event causally related to the transition from the preneoplastic stage to full blown medulloblastoma. These results underscore the utility of the Ptc1(neo67/+) mouse model for studies on the mechanisms of medulloblastoma and for development of new therapeutic strategies.

Linking DNA damage to medulloblastoma tumorigenesis in patched heterozygous knockout mice

Hemizygous Ptc1 mice have many features of Gorlin syndrome, including predisposition to medulloblastoma development. Ionizing radiation synergize with Ptc1 mutation to induce medulloblastoma only in neonatally exposed mice. To explore the mechanisms underlying age-dependent susceptibility, we irradiated Ptc(neo67/+) mice at postnatal day 1 (P1) or 10 (P10). We observed a dramatic difference in medulloblastoma incidence, which ranged from 81% in the cerebellum irradiated at P1 to 3% in the cerebellum irradiated at P10. A striking difference was also detected in the frequency of cerebellar preneoplastic lesions (100 versus 14%). Our data also show significantly lower induction of apoptosis in the cerebellum of medulloblastoma-susceptible (P1) compared to -resistant (P10) mice, strongly suggesting that medulloblastoma formation in Ptc1 mutants may be associated with resistance to radiation-induced cell killing. Furthermore, in marked contrast with P10 mice, cerebellum at P1 displays substantially increased activation of the cell survival-promoting Akt/Pkb protein, and markedly decreased p53 levels in response to radiation-induced genotoxic stress. Overall, these results show that developing cerebellar granule neuron precursors' (CGNPs) radiosensitivity to radiation-induced cell death increases with progressing development and inversely correlates with their ability to neoplastically transform.

Modulation of Patched-Associated Susceptibility to Radiation Induced Tumorigenesis by Genetic Background

We described previously a basal cell carcinoma (BCC) and medulloblastoma (MB) phenotype for CD1Ptch1(neo67/+) mice exposed to ionizing radiation. Ptch1 heterozygous mice mimic the predisposition to BCC and MB development of patients affected by nevoid BCC syndrome that inherit a mutant Patched (Ptch1) allele. To examine the impact of genetic background on development of BCCs and other tumors we used two outbred mouse lines characterized by extremely high, carcinogenesis-susceptible (Car-S), and low, carcinogenesis-resistant (Car-R), susceptibility to skin carcinogenesis. Crosses between Ptch1(neo67/+) mice and Car-S (F1S) or Car-R mice (F1R) were exposed to ionizing radiation. F1SPtch1(neo67/+) mice were highly susceptible to radiation-induced BCCs, whereas F1RPtch1(neo67/+) mice were completely resistant, indicating that tumor penetrance can be modulated by genetic background. Development of microscopic and macroscopic BCC lesions was influenced by Car-S and Car-R genotypes, suggesting a genetic-background effect on both initiation and progression of BCC. Susceptibility was additionally increased in N2 backcross mice (Car-S x F1SPtch1(neo67/+)), showing a contribution from recessive-acting Car-S modifiers. The modifying effects of Car-S-derived susceptibility alleles were tissue specific. In fact, despite higher susceptibility to BCC induction, Car-S-derived lines had lower MB incidence compared with CD1Ptch1(neo67/+) mice. BCC-associated somatic events were not influenced by genetic background, as shown by similar rate of wild-type Ptch1 loss in BCCs from F1SPtch1(neo67/+) (93%) and CD1Ptch1(neo67/+) mice (100%). Finally, microsatellite analysis of BCCs showed Ptch1 loss through interstitial deletion. These results are relevant to humans, in which BCC is the commonest malignancy, because this model system may be used to study genes modifying BCC development.

Only a subset of 12-O-tetradecanoylphorbol-13-acetate-promoted mouse skin papillomas are promotable by benzoyl peroxide

The two-stage skin carcinogenesis model of initiation and promotion in Carcinogenesis-susceptible (Car-S) mice has been used to investigate the pathways of promotional activity of 12-O-tetradecanoylphorbol-13-acetate (TPA), a phorbol ester tumor promoter, and benzoyl peroxide (BzPo), a free radical-generating compound. To test whether distinct populations of 9,10-dimethyl-1,2-benzanthracene (DMBA)-initiated epidermal keratinocytes are responsive to the two promoters, tandem experiments were performed. DMBA-initiated Car-S mice were promoted twice weekly with maximal promoting doses of TPA or BzPo. When the number of papillomas/mouse reached a plateau, promotion in the TPA and BzPo groups was switched to BzPo or TPA, respectively, until achievement of a new plateau. Mice promoted with BzPo developed 11.0 +/- 1.3 papillomas/mouse and subsequent TPA promotion induced 13.8 additional papillomas, for a total of 24.8 +/- 2.1 papillomas/mouse. TPA-promoted mice developed 23.3 +/- 1.1 papillomas/mouse, and subsequent BzPo promotion for 91 days did not promote additional papillomas. Our results show a less than additive tumor response after sequential promotion with BzPo and TPA, or vice versa, indicating that the pathways of promotional activity of TPA and BzPo are interacting. While the final papilloma yield was similar at the end of the two tandem promotion experiments independently of promoter sequence, the percentage of mice developing carcinomas was significantly higher in mice that were promoted with BzPo in the first stage. No significant differences in the frequency and type of c-Ha-ras mutations were observed in TPA- and BzPo-promoted tumors, suggesting that promotion of DMBA-initiated cells by BzPo requires introduction of additional molecular alterations compared to TPA.

Basal cell carcinoma and its development: insights from radiation-induced tumors in Ptch1-deficient mice

Loss-of-function mutations in Patched (Ptch1) are implicated in constitutive activation of the Sonic hedgehog pathway in human basal cell carcinomas (BCCs), and inherited Ptch1 mutations underlie basal cell nevus syndrome in which a typical feature is multiple BCC occurring with greater incidence in portals of radiotherapy. Mice in which one copy of Ptch1 is inactivated show increased susceptibility to spontaneous tumor development and hypersensitivity to radiation-induced tumorigenesis, providing an ideal in vivo model to study the typical pathologies associated with basal cell nevus syndrome. We therefore examined BCC development in control and irradiated Ptch1(neo67/+) mice. We show that unirradiated mice develop putative BCC precursor lesions, i.e., basaloid hyperproliferation areas arising from both follicular and interfollicular epithelium, and that these lesions progress to nodular and infiltrative BCCs only in irradiated mice. Data of BCC incidence, multiplicity, and latency support the notion of epidermal hyperproliferations, nodular and infiltrative BCC-like tumors representing different stages of tumor development. This is additionally supported by the pattern of p53 protein expression observed in BCC subtypes and by the finding of retention of the normal remaining Ptch1 allele in all nodular, circumscribed BCCs analyzed compared with its constant loss in infiltrative BCCs. Our data suggest chronological tumor progression from basaloid hyperproliferations to nodular and then infiltrative BCC occurring in a stepwise fashion through the accumulation of sequential genetic alterations.

High incidence of medulloblastoma following X-ray-irradiation of newborn Ptc1 heterozygous mice

Individuals affected with the Gorlin syndrome inherit a germ-line mutation of the patched (Ptc1) developmental gene and, analogously to Ptc1 heterozygous mice, show an increased susceptibility to spontaneous tumor development. Human and mouse Ptc1 heterozygotes (Ptc1(+/-)) are also hypersensitive to ionizing radiation (IR)-induced tumorigenesis in terms of basal cell carcinoma (BCC) induction. We have analysed the involvement of Ptc1 in the tumorigenic response to a single dose of 3 Gy X-rays in neonatal and adult Ptc1 heterozygous and wild type mice. We report that irradiation dramatically increased the incidence of medulloblastoma development (51%) over the spontaneous rate (7%) in neonatal but not adult Ptc1 heterozygotes, indicating that medulloblastoma induction by IR is subjected to temporal restriction. Analysis of Ptc1 allele status in the tumors revealed loss of the wild type allele in 17 of 18 medulloblastomas from irradiated mice and in two of three spontaneous medulloblastomas. To our knowledge, irradiated newborn Ptc1(+/-) heterozygous mice constitute the first mouse model of IR-induced medulloblastoma tumorigenesis, providing a useful tool to elucidate the molecular basis of medulloblastoma development.

The genetic control of chemically and radiation-induced skin tumorigenesis: a study with carcinogenesis-susceptible and carcinogenesis-resistant mice

Outbred carcinogenesis-resistant (Car-R) and carcinogenesis-susceptible (Car-S) mouse lines were generated by phenotypic selection for resistance or susceptibility to two-stage skin carcinogenesis. These two Car mouse lines differ by >100-fold in susceptibility. In the present study, we tested the hypothesis that a subset of genetic loci responsible for susceptibility or resistance to chemical skin tumorigenesis may also be involved in radiation-induced skin tumorigenesis. Skin tumorigenesis was tested in groups of Car-S/R mice after X-ray initiation and 12-O-tetradecanoylphorbol-13-acetate (TPA) promotion. We found that ionizing radiation can initiate skin tumors in Car-S mice but not in Car-R mice. In Car-S mice, the most effective radiation doses (6 and 10 Gy given in four fractions) gave a threefold increase in tumor multiplicity and a twofold increase in tumor incidence compared to a TPA-only control group. We performed a molecular analysis of Hras gene mutations in skin tumors of Car-S mice induced by X-ray initiation/TPA promotion or by TPA promotion alone. The most notable difference emerging from the comparison of these mutation patterns is the high incidence ( approximately 50%) of papillomas lacking Hras gene mutations in X-ray-initiated/TPA-promoted papillomas compared to 13% in papillomas induced by TPA alone, suggesting that lack of Hras gene mutations is a consistent feature of radiation-induced papillomas.

Nitric oxide production in Caco-2 cells exposed to different inducers, inhibitors and natural toxins

The involvement of the NO pathway in several intestinal inflammatory diseases is under investigation. In vitro models may provide a useful approach to better characterise this pathway at the cellular level. For this purpose, we have used Caco-2 cells, which are able to spontaneously differentiate in long-term culture to small intestine enterocytes. The effect of different NO pathway inducers [gamma-interferon (IFN-gamma) and phorbol myristate acetate (PMA)] has been studied. Our results demonstrate that Caco-2 cells constitutively express NOS at very low levels, while the induction with PMA+IFN-gamma triggers the expression of the inducible isoform with a stronger effect starting from day 14 of differentiation. The use of specific inhibitors of gene expression, at transcriptional and translational level, suggests that new synthesis of iNOS mRNA is required, through direct activation of the gene or new synthesis of transcription-required factors, as indicated by CHX inhibition. The morphological alteration induced by PMA+IFN-gamma is reversed by iNOS inhibitor, suggesting that the NO pathway may be involved in the cytoskeletal alterations. The DSP toxins, OA and DTX-1, induce NO production at levels corresponding to their different toxicity, previously detected in Caco-2 cells.