Abstract P6-03-04: Successful development of patient-derived orthotopic xenograft models of brain and lung metastases of human breast cancer
Authors: Oshi M , Okano M , Takabe K 
Published: May 2019

Abstract
Background: Metastatic breast cancer is the reason that we continue to lose 40,000 women every year in the US. Without appropriate pre-clinical model, success rate of clinical trials continue to suffer. Because syngeneic mouse models utilize murine neoplasm that may not represent human cancer, patient-derived xenografts (PDX) have emerged as a pre-clinical model that maintains human cancer features such as intratumoral heterogeneity. However, there is no established orthotopic PDX model for metastatic breast cancer even though the main cause of death is brain and lung metastasis. Orthotopic brain or lung PDX is expected to reproduce the original tumor microenvironment. We describe our new patient-derived metastasis orthotopic xenograft (PDMOX) mouse models of human breast cancer.
Methods: All work was performed in female NSG mice of age 8-12 m. Breast cancer metastatic tumors from brain and lung that had been passaged 3x in mammary fat pads were used. Tumors of 1 mm3 were implanted orthotopically in two forms: solid piece, or minced tissue with 3 μl Matrigel. Tumor growth was monitored by MRI.
Results: Two methods for brain PDMOX were compared. “Manual push” method implanted minced tumor through a frontal bone burr hole into right caudate putamen at 4 mm depth using forceps. “Pipette tip” method utilized either a pipetter for minced tissue or Hamilton syringe for solid tissue to inoculate tumor. One hour post-surgical survival was 37.5% (3/8) after “manual push”, and 100% (30/30) after “Pipette tip” method. All tumors engrafted in surviving mice with either method. However, the tumors formed on brain surface and parenchyma invasion was rare after “manual push” method, whereas solid tumor invaded parenchyma by “pipette tip” method. Therefore, it was no surprise to find large variation in tumor growth after “Manual push” (detection time 17±5.0 d, range: 17-26; volume 5.6±21.0 mm3, range 2.8-48.7). One mouse developed ptosis, and 2 out of 3 mice that underwent “Manual push” had sudden death. On the other hand, all mice that underwent “Pipette tip” method lived until tumor grew to 125-200 mm3, without neurological symptoms. These brain tumors could be passaged with 100% success (9/9). For right lung PDMOX, “thoracotomy” and “non-thoracotomy” methods were compared. “Thoracotomy” method implanted a solid tissue using forceps or 8-0 nylon suture, or injected minced tissue 1 mm below pleura. “Non-thoracotomy” method injected minced tissue using 23G needle. One hour post-surgical survival was 30% (9/30, 8/30) after “thoracotomy” method using forceps or suture, resp. However, survival using suture method could be significantly improved to 97% (29/30) by reducing thoracotomy length (&lt;10 vs. ≥10 mm: t test P = 0.003). Post-operative survival was not affected by age, weight, or operation or anesthesia time. On the other hand, all mice after “non-thoracotomy” method survived, but chest wall implantation occurred in 67% (4/6) when the method was performed using a cell line.
Conclusion: By simple modifications of surgical techniques, we could establish orthotopic brain and lung xenografts of breast cancer tumors with almost zero mortality and 100% engraftment. Our novel PDMOX models can be powerful tools for preclinical studies.
Citation Format: Oshi M, Okano M, Takabe K. Successful development of patient-derived orthotopic xenograft models of brain and lung metastases of human breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-03-04.