01.01 Development of a Novel Orthotopic Brain Metastasis Patient-Derived Xenograft Model for Breast Cancer

M. Oshi1, M. Okano1, A. L. Butash1, K. Takabe1  1Roswell Park Cancer institute,Department Of Surgical Oncology,Buffalo, NY, USA

Introduction: Despite the fact that the 5-year survival rate for breast cancer(BC) is outstanding compared to other cancers, there are 40,000 deaths annually due to the disease in the US. The vast majority of the mortality results from distant metastasis and therefore pre-clinical models are essential for development of proper and precise treatment for each patient. Patient-derived xenograft (PDX) maintains the features of the donor tumors such as intra-tumor heterogeneity. However, the establishment of an orthotopic metastatic model is still lacking due to procedural difficulty. We demonstrate our novel methods to develop an orthotopic brain metastasis patient-derived xenograft model (PDMOX) for BC brain metastasis.

Methods: PDMOX were created using metastatic brain tumors from BC patients and implanting them in the brain of NSG female mice aged 8-12m through a frontal bone burr hole into the right caudate putamen. Tumors of ~1mm3 were implanted in 2 different forms: single solid piece or mechanically minced tissue with medium.

Results:In the “manual push” method, a minced tumor mixed with 3µl medium is instilled at a depth of 4 mm by using a 23G needle, and a single solid piece of tumor is implanted by using forceps. In the “pipette tip” method, we utilized either a pipette for minced tissue, or a Hamilton syringe with a tip for solid tissue in order to inoculate tumor at the same depth. One hour post-surgical survival after implantation of minced tumor by “manual push” method was only 37.5% (3/8), whereas 100% (30/30) of the mice inoculated with the “pipette tip” method survived. The advantage of the “pipette tip” method was to minimize mechanical forces during inoculation into the brain by using a pipette or tip as a stopper. All tumors were well engrafted in surviving mice in both methods. With the “manual push” method, more tumors formed on the brain surface rather than within the brain parenchyma when compared to the “pipette tip” method. There was a large variation in tumor growth after “manual push”(Median 20±25.0, range: 12-24d. Tumor volume: median 5.6±21.0, range 2.8-48.7mm3). Although 2 out of 3 mice that underwent the “manual push” method had sudden death, all mice that underwent the “pipette tip” method lived until the tumor grew to 125-200mm3 without neurological symptoms. There was no difference in the time of engraftment and tumor growth rate between solid piece and minced tumor tissue using the “pipette tip” method. The success rate of passage for 2nd and 3rd generation was 100% (26/26).

Conclusion:Various surgical techniques used to generate PDMOX BC models showed major differences in the tumors and outcomes. These novel models are expected to become powerful tools for preclinical studies in metastatic BC.