The Role of Autophagy in Tumor Immunology-Complex Mechanisms That May Be Explored Therapeutically.

The tumor microenvironment (TME) is complex, and its composition and dynamics determine tumor fate. From tumor cells themselves, with their capacity for unlimited replication, migration, and invasion, to fibroblasts, endothelial cells, and immune cells, which can have pro and/or anti-tumor potential, interaction among these elements determines tumor progression. The understanding of molecular pathways involved in immune escape has permitted the development of cancer immunotherapies. Targeting molecules or biological processes that inhibit antitumor immune responses has allowed a significant improvement in cancer patient's prognosis. Autophagy is a cellular process required to eliminate dysfunctional proteins and organelles, maintaining cellular homeostasis. Usually a process associated with protection against cancer, autophagy associated to cancer cells has been reported in response to hypoxia, nutrient deficiency, and oxidative stress, conditions frequently observed in the TME. Recent studies have shown a paradoxical association between autophagy and tumor immune responses. Tumor cell autophagy increases the expression of inhibitory molecules, such as PD-1 and CTLA-4, which block antitumor cytotoxic responses. Moreover, it can also directly affect antitumor immune responses by, for example, degrading NK cell-derived granzyme B and protecting tumor cells. Interestingly, the activation of autophagy on dendritic cells has the opposite effects, enhancing antigen presentation, triggering CD8+ T cells cytotoxic activity, and reducing tumor growth. Therefore, this review will focus on the most recent aspects of autophagy and tumor immune environment. We describe the dual role of autophagy in modulating tumor immune responses and discuss some aspects that must be considered to improve cancer treatment.

ANIMAL MODELS FOR COLORECTAL CANCER.

INTRODUCTION: Colorectal cancer is a very frequent sort of neoplasm among the population, with a high mortality rate. It develops from an association of genetic and environmental factors, and it is related to multiple cell signaling pathways. Cell cultures and animal models are used in research to reproduce the process of disease development in humans. Of the existing animal models, the most commonly used are animals with tumors induced by chemical agents and genetically modified animals. OBJECTIVE: To present and synthesize the main animal models of colorectal carcinogenesis used in the research, comparing its advantages and disadvantages. METHOD: This literature review was performed through the search for scientific articles over the last 18 years in PubMed and Science Direct databases, by using keywords such as "animal models", "colorectal carcinogenesis" and "tumor induction". RESULTS: 1,2-dimethylhydrazine and azoxymethane are carcinogenic agents with high specificity for the small and large intestine regions. Therefore, the two substances are widely used. Concerning the genetically modified animal models, there is a larger number of studies concerning mutations of the APC, p53 and K-ras genes. Animals with the APC gene mutation develop colorectal neoplasms, whereas animals with p53 and K-ras genes mutations are able to potentiate the effects of the APC gene mutation as well as the chemical inducers. CONCLUSION: Each animal model has advantages and disadvantages, and some are individually efficient as to the induction of carcinogenesis, and in other cases the association of two forms of induction is the best way to obtain representative results of carcinogenesis in humans.

Animal models for colorectal cancer / Modelos animais de carcinogênese colorretal

ABSTRACT Introduction: Colorectal cancer is a very frequent sort of neoplasm among the population, with a high mortality rate. It develops from an association of genetic and environmental factors, and it is related to multiple cell signaling pathways. Cell cultures and animal models are used in research to reproduce the process of disease development in humans. Of the existing animal models, the most commonly used are animals with tumors induced by chemical agents and genetically modified animals. Objective: To present and synthesize the main animal models of colorectal carcinogenesis used in the research, comparing its advantages and disadvantages. Method: This literature review was performed through the search for scientific articles over the last 18 years in PubMed and Science Direct databases, by using keywords such as "animal models", "colorectal carcinogenesis" and "tumor induction". Results: 1,2-dimethylhydrazine and azoxymethane are carcinogenic agents with high specificity for the small and large intestine regions. Therefore, the two substances are widely used. Concerning the genetically modified animal models, there is a larger number of studies concerning mutations of the APC, p53 and K-ras genes. Animals with the APC gene mutation develop colorectal neoplasms, whereas animals with p53 and K-ras genes mutations are able to potentiate the effects of the APC gene mutation as well as the chemical inducers. Conclusion: Each animal model has advantages and disadvantages, and some are individually efficient as to the induction of carcinogenesis, and in other cases the association of two forms of induction is the best way to obtain representative results of carcinogenesis in humans.

RESUMO Introdução: O câncer de cólon e reto é bastante frequente na população e com elevado índice de mortalidade. Ele se desenvolve a partir da associação de fatores genéticos e ambientais e está relacionado a múltiplas vias de sinalização celular. Para o estudo da doença são utilizados cultivos celulares e modelos animais, que sejam capazes de reproduzir o processo de desenvolvimento da doença em humanos. Dos modelos existentes, os mais comumente utilizados são os animais induzidos ao desenvolvimento tumoral por agentes químicos e os animais geneticamente modificados. Objetivo: Apresentar e sintetizar os principais modelos animais de carcinogênese colorretal utilizados na pesquisa, comparando suas vantagens e desvantagens. Método: Para o desenvolvimento dessa revisão foi realizada uma busca por artigos científicos dos últimos 18 anos nas bases de dados PubMed e Science Direct, utilizando como palavras-chave "modelos animais", "carcinogênese colorretal" e "indução tumoral". Resultado: O 1,2 dimetilhidrazina e o azoximetano são agentes carcinógenos com alta especificidade para o intestino delgado e grosso. Por isso, as duas substâncias são amplamente utilizadas. Dos modelos animais geneticamente modificados observa-se maior quantidade de estudos referentes às mutações dos genes APC, p53eK-ras. Os animais com mutação do gene APC desenvolvem neoplasias colorretais, enquanto que animais com mutações dos genes p53 e K-ras são capazes de potencializar os efeitos da mutação do gene APC, bem como dos indutores químicos. Conclusão: Cada modelo animal apresenta vantagens e desvantagens, sendo que alguns são individualmente eficientes na indução da carcinogênese, e em outros casos a associação de duas formas de indução é a melhor maneira de se obter resultados representativos da carcinogênese em humanos.