The MMTV-Wnt1 murine model produces two phenotypically distinct subtypes of mammary tumors with unique therapeutic responses to an EGFR inhibitor (RNA-seq)

The Wnt gene family is an evolutionarily conserved group of proteins that regulate cell growth, differentiation, and stem cell self-renewal. Aberrant Wnt signaling in human breast tumors has been proposed to be an attractive drug target, especially in the basal-like subtype where canonical Wnt signaling is both enriched and predictive of poor clinical outcomes. The development of effective Wnt based therapeutics, however, has been slowed in part by a limited understanding of the context dependent nature with which these aberrations influence breast tumorigenesis. We recently reported that MMTV-Wnt1 mice, which are an established model for studying Wnt signaling in breast tumors, develop two subtypes of tumors by gene expression classification: Wnt1-EarlyEx and Wnt1-LateEx. Here, we extend this initial observation and show that Wnt1-EarlyEx tumors had high expression of canonical Wnt, non-canonical Wnt, and EGFR signaling pathway signatures. Therapeutically, Wnt1-EarlyEx tumors had a dynamic reduction in tumor volume when treated with an EGFR inhibitor. Wnt1-EarlyEx tumors also had primarily Cd49fpos/Epcamneg FACS profiles, but were unable to be serially transplanted into wild-type FVB female mice. Wnt1-LateEx tumors, conversely, had a bloody gross pathology, which was highlighted by the presence of 'blood lakes' by H&E staining. These tumors had primarily Cd49fpos/Epcampos FACS profiles, but also contained a secondary Cd49fpos/Epcamneg subpopulation. Wnt1-LateEx tumors were enriched for activating Hras1 mutations and were capable of reproducing tumors when serially transplanted into wild-type FVB female mice. This study definitely shows that the MMTV-Wnt1 mouse model produces two phenotypically distinct subtypes of mammary tumors. Importantly, these subtypes differ in their therapeutic response to an EGFR inhibitor, suggesting that a subset of human tumors with aberrant Wnt signaling may also respond to erlotinib. Overall design: Agilent gene expression microarrays were performed comparing RNA from FVB/n MMTV-Wnt1 mammary tumors to a common mouse reference sample. Agilent CGH microarrays were performed comparing DNA from FVB/n MMTV-Wnt1 mammary tumors to DNA from FVB wild-type mice. RNAseq libraries were prepared from FVB/n MMTV-Wnt1 mammary tumors using a TruSeq RNA kit before being submitted to the Lineberger Comprehensive Cancer Center Genomics Core to be run on the Illumina HiSeq 2000.

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Pfefferle AD, Darr DB, Calhoun BC, Mott KR, Rosen JM, Perou CM