Circulating and disseminated tumor cells from breast cancer patient-derived xenograft-bearing mice as a novel model to study metastasis

Mario Giuliano, Sabrina Herrera, Pavel Christiny, Chad Shaw, Chad J Creighton, Tamika Mitchell, Raksha Bhat, Xiaomei Zhang, Sufeng Mao, Lacey E Dobrolecki, Ahmed Al-rawi, Fengju Chen, Bianca M Veneziani, Xiang H-F Zhang, Susan G Hilsenbeck, Alejandro Contreras, Carolina Gutierrez, Rinath M Jeselsohn, Mothaffar F Rimawi, C Kent Osborne, Michael T Lewis, Rachel Schiff, Meghana V Trivedi

IntroductionReal-time monitoring of biological changes in tumors may be possible by investigating the transitional cells such as circulating tumor cells (CTCs) and disseminated tumor cells in bone marrow (BM-DTCs). However, the small numbers of CTCs and the limited access to bone marrow aspirates in cancer patients pose major hurdles. The goal of this study was to determine if breast cancer (BC) patient-derived xenograft (PDX) mice could provide a constant and renewable source of CTCs and BM-DTCs, thereby representing a unique system for the study of metastatic processes.MethodsCTCs and BM-DTCs, isolated from BC PDX-bearing mice, were identified by immunostaining for human pan-cytokeratin and nuclear counter staining of red blood cell-lysed blood and bone marrow fractions, respectively. The lung metastasis (LM) rate was previously reported in these lines. Associations between the presence of CTCs, BM-DTCs, and LM were assessed by the Fisher¿s Exact and Cochran-Mantel-Haenszel tests. Two separate genetic signatures associated with the presence of CTC clusters and with lung metastatic potential were computed using the expression arrays of primary tumors from different PDX lines and subsequently overlapped to identify common genes.ResultsA total of 18 BC PDX lines were evaluated. CTCs and BM-DTCs, present as either single cells or clusters, were detected in 83% (15/18) and 62.5% (10/16) of the lines, respectively. There was a positive association between the presence of CTCs and BM-DTCs within the same mice. LM was previously found in 9 out of 18 (50%) lines, of which all 9 had detectable CTCs. The presence of LM was strongly associated with the detection of CTC clusters but not with individual cells or detection of BM-DTCs. Overlapping of the 2 genetic signatures of the primary PDX tumors associated with the presence of CTC clusters and with lung metastatic potential identified 4 genes (HLA-DP1A, GJA1, PEG3, and XIST). This 4-gene profile predicted distant metastases-free survival in publicly available datasets of early BC patients.ConclusionThis study suggests that CTCs and BM-DTCs detected in BC PDX-bearing mice may represent a valuable and unique preclinical model for investigating the role of these rare cells in tumor metastases.