Molecular characterization of non-muscle invasive tumor from N-methyl-N-nitrosourea (MNU)-induced urothelial carcinoma in a rat model reveals hallmarks of both luminal and basal subtypes

With the advances in molecular classification of bladder cancer subtypes, pre-clinical rodent models used to study urothelial tumorigenesis must be profiled to reflect clinical relevance and optimize translational research strategies. Murine models of bladder cancer such as the autochthonous N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN) model and genetically-engineered Upk3a-Cre^ERT2; Trp53^L/L; Pten^L/L; Rosa26^LSL-Luc (UPPL) model are muscle invasive models which have been found to correlate with basal and luminal subtypes, respectively. The rat MNU model has been used to represent non-muscle invasive bladder cancer, however the MNU non-muscle invasive tumors have not been fully molecularly characterized. Intravesical MNU instillations were administered to female rats to induce bladder tumors which were harvested for pathologic staging and immunohistochemistry. Bulk RNA sequencing was performed on non-muscle invasive (stage T1) tumors and compared to gene expression data from human and murine bladder cancer datasets. Rat MNU-treated bladders showed step-wise progression from non-muscle invasive tumor over 16 weeks which progressed to muscle invasive blader cancer over 30 weeks. Luminal and basal protein marker expression was positively expressed in all stages of MNU-induced tumors. Cluster analysis of gene expression data from non-muscle invasive MNU-induced T1 tumors more closely resemble luminal papillary and stroma-rich human bladder cancer subtypes as well as murine UPPL luminal-like tumors, while inference of immune cell markers reveals MNU-induced T1 tumors are more immune infiltrated, similar to human basal/squamous and murine BBN basal-like tumors. These data reveal the rat MNU model of non-muscle invasive bladder cancer (NMIBC) harbors characteristics of both basal and luminal bladder cancer subtypes and provide a framework for how this model may be used to guide clinically relevant investigations aimed at improving and developing novel therapies for more luminal like-immune infiltrated NMIBC.