Abstract 1589: Development of a mouse model for bone marrow disseminated tumor cells with human tumor xenografts

Objective: Disseminated tumor cells (DTCs) found in the bone marrow (BM) of breast cancer patients portends a poor prognosis. BM DTCs are thought to be intermediaries in the metastatic process. Study of these cells has been limited due to their scarcity. To overcome this limitation, we have developed an animal model for DTCs employing the Human and Mouse Linked Evaluation of Tumor (HAMLET) system. Experimental procedures: After informed consent, human breast adenocarcinomas were prospectively collected from 5 patients with estrogen receptor negative/Her2 negative tumors and implanted into a humanized NOD/SCID mouse mammary fat pad as previous described. BM was collected from the femur and tibia from mice at varying passages of the tumors and analyzed for human-specific GADPH (hGAPDH) expression by qRT-PCR. The presence of other human gene transcripts, previously detected in the BM of breast cancer patients and believed to be associated with the presence of DTCs, was also determined by qRT-PCR. Human gene expression array analysis (Affymetrix Human gene 1.0ST) was performed on the primary xenograft tumor, a spleen metastatic nodule and BM from all WHIM17 mice. Results: BM was screened from 16 tumor bearing mice for the presence of DTCs. 10 animals, with tumors derived from 2 patients, developed metastatic disease and 9 had detectable levels of hGAPDH. The CT ratio human to mouse GAPDH varied from 1.06 to 2.23. In particular, high levels of hGAPDH were found in one HAMLET mouse line, WHIM 17, in which all animals developed metastases (CT ratio human to mouse GAPDH=1.06 to 1.31). One mouse with detectable hGAPDH died of other causes and could not be assed for metastatic disease development. There was no detectable hGAPDH in five mice, derived from 3 patient tumors, which did not develop metastatic tumors and in control mice with humanized mammary fat pads. Human-specific transcripts for SNAIL1, GSC, FOXC2 and KRT19 were detectable in the BM of the WHIM 17 mice whereas control, non-tumor bearing humanized mice demonstrated no expression of any of these markers. Microarray analysis confirmed the presence of human cells in mouse BM, allowing the identification of genes specifically associated with BM DTC cell populations. Conclusion: We have utilized a mouse xenograft model for the study of DTCs using primary human breast adenocarcinomas transplanted into NOD/SCID mice. The presence of human cells in mice BM appears to correlate with metastatic tumor development. The gene expression patterns of these cells indicate that they maintain molecular profiles similar to DTCs isolated directly from the BM of breast cancer patients. We believe that this model will allow for a better understanding of the metastatic process in breast cancer patients and provide an in vivo model for monitoring and assessing the efficacy of new therapeutic agents in eradicating micrometastatic disease and ultimately, improving survival in breast cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1589. doi:10.1158/1538-7445.AM2011-1589