Abstract P6-06-08: Transcriptome analysis of patient derived xenograft mouse models of inflammatory breast cancer to gain insights into the contribution of tumor microenvironment
Authors: Rahal Omar , Yang Jie , Li Li , Larson Richard , Van Laere Steven , Ueno Naoto , Sulman Erik , Woodward Wendy 
Published: March 2020

Purpose: Inflammatory breast cancer (IBC) is an aggressive variant of breast cancer characterized by visible skin symptoms on the breast at the time of presentation. We demonstrated mesenchymal stem cells (MSC) promote skin symptoms in the SUM149 xenograft model. Here, we extend this finding to IBC patient-derived xenograft (PDX) lines and performed RNA-sequencing analysis of tumors from IBC patient-derived xenograft (PDX) lines by presence of skin symptoms. We hypothesize host MSC variation may explain sporadic skin symptoms in IBC PDX tumors across generations. Methods: MSC were co-injected at the time of tumor initiation in PDX tumors (IBC-3, 5, 6, and 7) and skin symptoms assessed visually and at the time of gross resection. A priori analysis plan was to group PDX by treatment group irrespective of PDX line. IBC PDX models spontaneously but inconsistently develop skin symptoms after multiple passages. RNA sequencing was performed on IBC-PDX tumors (n=33) and non-IBC PDX tumors (n=12) across generations from IBC PDX lines 5, 6, and 7 and non-IBC PDX lines 2, 3, and 4. Four samples were discarded due to poor quality. TSNE was applied using the top differential expressed genes. Xenome analysis was performed to examine host stromal expression by skin involvement. Samples from PDX lines 5 were compared with lines 6 and 7 and the top differentially expressed genes were compared with the Molecular Signatures Databases (MSigDB). CIBERSORT was performed to deconvolute cell type composition. Results: Co-injecting MSC with PDX transplant increased skin symptoms (57% of PDX animals (cohort from IBC5, IBC6, IBC7 and non-IBC4) with MSC vs. 0% without (cohort from IBC5, IBC6, IBC7, non-IBC2 and non-IBC4) (P = 0.0007). TSNE analysis of IBC PDX split samples into three subgroups distinguished by PDX lines and skin invasion. Xenome was used to split reads from human or mouse: samples show high percentage of reads coming from human (mean±SD, 97.44%± 8.98%). Seventy-four genes show FDR ≤ 0.2 between PDX line 5 and line 6 and comparing these top 74 genes with MSigDb for interaction revealed pathways such as GPCR, signal transduction, and sensory perception. CIBERSORT revealed no enrichment for MSC in IBC PDX with skin invasion, however significant differences in CD8 expression in these immunosuppressed PDX models casts doubt on the robustness of this finding. Conclusions: Exogenous MSC enhance skin symptoms in a cohort of IBC and non-IBC PDX. Skin symptoms segregate IBC PDX tumors by expression suggesting specific biology drives this presentation. However, we are unable to demonstrate evidence for spontaneous MSC signaling in these models. Future work is warranted to link top skin symptom related signaling to stromal signals and unravel the unexpected CD8 signaling identified in these models.

Citation Format: Omar Rahal, Jie Yang, Li Li, Richard Larson, Steven Van Laere, Naoto Ueno, Erik Sulman, Wendy Woodward. Transcriptome analysis of patient derived xenograft mouse models of inflammatory breast cancer to gain insights into the contribution of tumor microenvironment [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-06-08.