Inhibition of IGF1R in Early MMTV-Wnt1 Mammary Tumors: A Transcriptomic Analysis

Background: The insulin-like growth factor 1 receptor (IGF1R) is a receptor tyrosine kinase whose both overexpression and underexpression have been implicated in the initiation and progression of breast tumorigenesis. The mechanism through which underexpression of the receptor contributes to a more aggressive phenotype is currently less understood. Methods: Through the expression of a dominant-negative IGF1R, we studied the phenotypic effects of receptor inhibition on early MMTV-Wnt1 mouse mammary tumors. Utilizing histopathological techniques and single-cell RNA-sequencing, we explored cellular heterogeneity and transcriptional alterations that occur as a result of IGF1R inhibition. Results: Examination of primary tumors failed to reveal obvious differences in tissue architecture or expression of differentiation markers with IGF1R inhibition. Both cohorts of tumors produced metastatic lesions in the lung. Single-cell RNA-sequencing identified previously unknown epithelial subpopulations that were present in both tumor types. In tumors with inhibited IGF1R, a previously undescribed epithelial population marked by expression of both Krt14 and Krt6a was identified, transcriptionally distinct from its MMTV-Wnt1 counterpart, and present in the smallest lung metastases. In human breast cancer patients, expression levels of KRT14 and KRT6A negatively correlated with expression of IGF1R. Conclusions: Inhibition of the IGF1R in a mouse model of basal-like breast cancer produces transcriptionally distinct Krt6a⁺/Krt14⁺ epithelial cells, which are present in the smallest metastatic lesions identified in the lung. Expression of genes associated with this population may potentially be effective biomarkers of metastatic capacity in basal-like breast tumors with low levels of IGF1R expression.