Oncolytic viruses as therapeutic tools for pediatric brain tumors

In recent years, we have seen an important progress in our comprehension of the molecular basis of pediatric brain tumors (PBTs). However, they still represent the main cause of death by disease in children. Due to the poor prognosis of some types of PBTs and the long-term adverse effects associated with the traditional treatments, oncolytic viruses (OVs) have emerged as an interesting therapeutic option since they displayed safety and high tolerability in pre-clinical and clinical levels. In this review, we summarize the OVs evaluated in different types of PBTs, mostly in pre-clinical studies, and we discuss the possible future direction of research in this field. In this sense, one important aspect of OVs antitumoral effect is the stimulation of an immune response against the tumor which is necessary for a complete response in preclinical immunocompetent models and in the clinic. The role of the immune system in the response of OVs needs to be evaluated in PBTs and represents an experimental challenge due to the limited immunocompetent models of these diseases available for pre-clinical research

The oncolytic virus Delta-24-RGD elicits an antitumor effect in pediatric glioma and DIPG mouse models

Pediatric high-grade glioma (pHGG) and diffuse intrinsic pontine gliomas (DIPGs) are aggressive pediatric brain tumors in desperate need of a curative treatment. Oncolytic virotherapy is emerging as a solid therapeutic approach. Delta-24-RGD is a replication competent adenovirus engineered to replicate in tumor cells with an aberrant RB pathway. This virus has proven to be safe and effective in adult gliomas. Here we report that the administration of Delta-24-RGD is safe in mice and results in a significant increase in survival in immunodeficient and immunocompetent models of pHGG and DIPGs. Our results show that the Delta-24-RGD antiglioma effect is mediated by the oncolytic effect and the immune response elicited against the tumor. Altogether, our data highlight the potential of this virus as treatment for patients with these tumors. Of clinical significance, these data have led to the start of a phase I/II clinical trial at our institution for newly diagnosed DIPG (NCT03178032)

Effect of hypoxia on caveolin-1 expression, caveolae structure and insulin signaling

Obesity courses with the hypertrophy and hyperplasia of adipose tissue, which has been related to the development of hypoxia and, as consequence, insulin resistance. In this sense, insulin receptor is enriched in a specialized invagination of the plasma membrane named caveolae. Caveolin-1 (Cav-1) is one of the main proteins of caveolae and promotes insulin receptor (IR) phosphorylation and the subsequent activation of insulin signaling. In this study we have demonstrated that hypoxia inhibits 3T3-L1 adipocyte differentiation process and insulin signaling. Furthermore, 48 hours of hypoxia reduced the glucose uptake induced by insulin whereas the basal uptake was increased. This result was consistent with the upregulation of GLUT1, a facilitative glucose transporter independent of insulin, and the downregulation of the insulin-dependent transporter GLUT4, which also showed defective translocation to plasma membrane when adipocytes are stimulated with this hormone. On the other hand, hypoxia, whether continuous (48 hours) or intermittent, produced alterations in caveolae structure in 3T3-L1 cells and in mouse adipose tissue respectively, suggesting that caveolae disruption is implicated in the obesity-related insulin resistance. Furthermore, we also showed that caveolae density in plasma membrane of endothelial cells was reduced and that Cav-1 is accumulated in the nucleus of these cells by hypoxia. The role of HIF-1 in all these effects was addressed using echinomycin, which inhibits HIF-1 binding to Hypoxia Response Elements (HRE), indicating that the expression of GLUT4, Cav-1, Cav-2 and SDPR/Cavin-2 genes is regulated by HIF-1 in hypoxic 3T3-L1 adipocytes. Moreover, a Chromatin immunoprecipitation (ChIP) assay demonstrated that HIF-1 directly binds to the hypoxia response element identified in mouse Cav-1 promoter (-442 TSS) by bioinformatics analysis. A microarray of gene expression was also performed to explore new genes implicated in hypoxia response of 3T3-L1 adipocytes. The results of this analysis confirmed that pathways related to caveolae structure and function, insulin response, glucose transport and lipid biosynthesis are affected by hypoxia and highlighted the involvement of other genes such as Sort1, Ghrh and Igf in the effects of hypoxia on adipocytes

Effect of hypoxia on caveolin-1 expression, caveolae structure and insulin signaling

Obesity courses with the hypertrophy and hyperplasia of adipose tissue, which has been related to the development of hypoxia and, as consequence, insulin resistance. In this sense, insulin receptor is enriched in a specialized invagination of the plasma membrane named caveolae. Caveolin-1 (Cav-1) is one of the main proteins of caveolae and promotes insulin receptor (IR) phosphorylation and the subsequent activation of insulin signaling. In this study we have demonstrated that hypoxia inhibits 3T3-L1 adipocyte differentiation process and insulin signaling. Furthermore, 48 hours of hypoxia reduced the glucose uptake induced by insulin whereas the basal uptake was increased. This result was consistent with the upregulation of GLUT1, a facilitative glucose transporter independent of insulin, and the downregulation of the insulin-dependent transporter GLUT4, which also showed defective translocation to plasma membrane when adipocytes are stimulated with this hormone. On the other hand, hypoxia, whether continuous (48 hours) or intermittent, produced alterations in caveolae structure in 3T3-L1 cells and in mouse adipose tissue respectively, suggesting that caveolae disruption is implicated in the obesity-related insulin resistance. Furthermore, we also showed that caveolae density in plasma membrane of endothelial cells was reduced and that Cav-1 is accumulated in the nucleus of these cells by hypoxia. The role of HIF-1 in all these effects was addressed using echinomycin, which inhibits HIF-1 binding to Hypoxia Response Elements (HRE), indicating that the expression of GLUT4, Cav-1, Cav-2 and SDPR/Cavin-2 genes is regulated by HIF-1 in hypoxic 3T3-L1 adipocytes. Moreover, a Chromatin immunoprecipitation (ChIP) assay demonstrated that HIF-1 directly binds to the hypoxia response element identified in mouse Cav-1 promoter (-442 TSS) by bioinformatics analysis. A microarray of gene expression was also performed to explore new genes implicated in hypoxia response of 3T3-L1 adipocytes. The results of this analysis confirmed that pathways related to caveolae structure and function, insulin response, glucose transport and lipid biosynthesis are affected by hypoxia and highlighted the involvement of other genes such as Sort1, Ghrh and Igf in the effects of hypoxia on adipocytes

Oncolytic Viruses as Therapeutic Tools for Pediatric Brain Tumors

In recent years, we have seen an important progress in our comprehension of the molecular basis of pediatric brain tumors (PBTs). However, they still represent the main cause of death by disease in children. Due to the poor prognosis of some types of PBTs and the long-term adverse effects associated with the traditional treatments, oncolytic viruses (OVs) have emerged as an interesting therapeutic option since they displayed safety and high tolerability in pre-clinical and clinical levels. In this review, we summarize the OVs evaluated in different types of PBTs, mostly in pre-clinical studies, and we discuss the possible future direction of research in this field. In this sense, one important aspect of OVs antitumoral effect is the stimulation of an immune response against the tumor which is necessary for a complete response in preclinical immunocompetent models and in the clinic. The role of the immune system in the response of OVs needs to be evaluated in PBTs and represents an experimental challenge due to the limited immunocompetent models of these diseases available for pre-clinical research

Expression of caveolin 1 is enhanced by DNA demethylation during adipocyte differentiation. status of Insulin signaling

Caveolin 1 (Cav-1) is an essential constituent of adipocyte caveolae which binds the beta subunit of the insulin receptor (IR) and is implicated in the regulation of insulin signaling. We have found that, during adipocyte differentiation of 3T3-L1 cells the promoter, exon 1 and first intron of the Cav-1 gene undergo a demethylation process that is accompanied by a strong induction of Cav-1 expression, indicating that epigenetic mechanisms must have a pivotal role in this differentiation process. Furthermore, IR, PKB-Akt and Glut-4 expression are also increased during the differentiation process suggesting a coordinated regulation with Cav-1. Activation of Cav-1 protein by phosphorylation arises during the differentiation process, yet in fully mature adipocytes insulin is no longer able to significantly increase Cav-1 phosphorylation. However, these long-term differentiated cells are still able to respond adequately to insulin, increasing IR and PKB-Akt phosphorylation and glucose uptake. The activation of Cav-1 during the adipocyte differentiation process could facilitate the maintenance of insulin sensitivity by these fully mature adipocytes isolated from additional external stimuli. However, under the influence of physiological conditions associated to obesity, such as chronic inflammation and hypoxia, insulin sensitivity would finally be compromised

Oncolytic viruses as therapeutic tools for pediatric brain tumors

In recent years, we have seen an important progress in our comprehension of the molecular basis of pediatric brain tumors (PBTs). However, they still represent the main cause of death by disease in children. Due to the poor prognosis of some types of PBTs and the long-term adverse effects associated with the traditional treatments, oncolytic viruses (OVs) have emerged as an interesting therapeutic option since they displayed safety and high tolerability in pre-clinical and clinical levels. In this review, we summarize the OVs evaluated in different types of PBTs, mostly in pre-clinical studies, and we discuss the possible future direction of research in this field. In this sense, one important aspect of OVs antitumoral effect is the stimulation of an immune response against the tumor which is necessary for a complete response in preclinical immunocompetent models and in the clinic. The role of the immune system in the response of OVs needs to be evaluated in PBTs and represents an experimental challenge due to the limited immunocompetent models of these diseases available for pre-clinical research

The oncolytic virus Delta-24-RGD elicits an antitumor effect in pediatric glioma and DIPG mouse models

Pediatric high-grade glioma (pHGG) and diffuse intrinsic pontine gliomas (DIPGs) are aggressive pediatric brain tumors in desperate need of a curative treatment. Oncolytic virotherapy is emerging as a solid therapeutic approach. Delta-24-RGD is a replication competent adenovirus engineered to replicate in tumor cells with an aberrant RB pathway. This virus has proven to be safe and effective in adult gliomas. Here we report that the administration of Delta-24-RGD is safe in mice and results in a significant increase in survival in immunodeficient and immunocompetent models of pHGG and DIPGs. Our results show that the Delta-24-RGD antiglioma effect is mediated by the oncolytic effect and the immune response elicited against the tumor. Altogether, our data highlight the potential of this virus as treatment for patients with these tumors. Of clinical significance, these data have led to the start of a phase I/II clinical trial at our institution for newly diagnosed DIPG (NCT03178032)