Molecular characterization of N-methyl-N-nitrosourea-induced bladder urothelial tumor in rats
Human bladder cancer has recently been characterized based on RNA/protein expression and genomic alterations, indicating intrinsic subtypes of the disease associated with prognosis and response to systemic therapy. Meanwhile, N-methyl-N-nitrosourea (MNU)-induced bladder tumor in rodents are widely used for study of human bladder cancer. Although the model mimics papillary morphology and step-wise progression of human bladder cancer, little is known about molecular similarities to human bladder cancer. In this study, we characterized MNU-induce bladder tumor in rats using immunohistochemistry, qRT-PCR, and RNA sequencing.
Fisher 344 rats at age of 7 weeks intravesically received 4 doses of 1.5mg/kg MNU. Animals were sacrificed at week 16 and 30, and bladders were processed for pathological evaluation. RNA was also extracted from normal urothelium and cancerous area in paraffin embedded tissue, and subjected to qRT-PCR and RNA sequencing. Sequencing data was analyzed with publicly available dataset of human bladder cancer.
At week 16, all rats were found to have non-muscle invasive bladder tumor. Rats developed 5-10-mm, protruding tumors in their bladders at week 30. H&E staining showed MNU-induced tumors were histologically similar to human papillary bladder tumors. Three out of 6 bladders at week 30 showed muscle invasion. Immunohistochemistry and qRT-PCR revealed enrichment of basal markers in MNU tumors compared to normal urothelium, while maintaining luminal markers. Analysis of sequencing data showed that MNU tumors were clustered with human luminal tumors with upregulation of FGFR3 signature.
Combination of immunohistochemistry, qRT-PCR, and RNA sequencing demonstrated that MNU-induced tumor was closely related to the luminal/UroB tumor subtype of human bladder cancer. MNU-induced bladder tumor in rats offers a good experimental platform that mimics a subset of human bladder cancer in immunocompetent environment.
Funding: The Greenberg Bladder Cancer Institute Research Grant and the Urology Care Foundation.