Prostate carcinogenesis chemically induced by N-methyl-N-nitrosourea (MNU) in Mongolian gerbils: association with steroids promoters and high-fat diet

Abstract

One of the recognized deficiencies in prostate cancer research is the lack of model systems that allow the investigation of pathological, biochemical and genetic factors of this disease. The gerbil Meriones unguiculatus has enabled the assessment of progression of prostatic lesions from benign to malignant invasive stage after relatively short period of treatment with the carcinogen N-methyl-N-nitrosourea (MNU), a potent DNA methylating agent. Therefore, the objectives of this study are: evaluation of epithelial and stromal biomarkers of proliferative lesions induced by MNU association with synthetic steroids and high-fat diet. In addition, the possible role of gene products of the family of proto-oncogenes ras (H-ras, K-ras, N-ras) in the molecular pathway of tumor induction by MNU will also be monitored. For this, we used 100 adult gerbils (90 days) that will be randomly divided into 7 groups (2 and 5 controls experimental) and submitted to procedures to increase the incidence of proliferative prostatic lesions and decrease tumor latency. All of them will be subjected to a single intraperitoneal dose of MNU (50mg/kg), except the control group, of intact animals, the control that will receive the vehicle and an experimental group (will receive 4 doses of MNU 30mg/kg). Additionally, the experimental groups will be subjected to chronic exposure to androgen, estrogen, or high-fat diet, to maximize sensitivity to carcinogen insult. One experimental group will be analyzed in order to verify possible effects of the combination between mineral oil and MNU, as already described for the corn oil. Additional treatments will begin 48h after MNU administration. Seven animals from each group will be killed after 3 or 6 months of treatment. The methodologies involve quantitative and statistics analysis of relative prostate weight, hormonal and morphological analyzes using techniques: 1) Cytochemical (HE, Feulgen reaction, AgNOR); through these staining will be conducted quantitative (stereological and cariometric) and statistical analysis of the epithelium and stromal components in prostatic lesions. 2) Immunohistochemical (androgen and estrogen receptors, tumor markers associated with MNU and markers of changes in cellular and extracellular matrix components). 3) Proliferative index of abnormal epithelium (anti-PCNA immunostaining). 4) Molecular analysis of Ras proteins possibly involved in induced-carcinogenesis. All procedures aim to improve the understanding of the pathways that control changes in epithelial and stromal components during the progression of prostatic carcinogenesis from benign to malignant lesions, highlighting the contribution of stromal components in the process of invasiveness. The possible participation of products of ras-mediated carcinogenesis in MNU in gerbils will bring new insights into the molecular pathways activated. In a future step this could be used as a rodent model for study strategies for prevention and treatment of prostate cancer. (AU)