Abstract 423: Novel patient-derived orthotopic xenograft model for preclinical studies of breast cancer brain metastasis
Authors: Oshi Masanori , Okano Maiko , Takabe Kazuaki 
Published: September 2020

Abstract
BACKGROUND: Currently available breast cancer brain metastasis patient-derived xenografts (PDX) are technically challenging to generate with unstable results. Such PDXs are critical for preclinical studies of drug development for treatment of brain metastasis. This is because the biology and microenvironment of metastasis in brain are very different from those of primary tumors or metastases at other organs. Brain metastasis occurs in as many as 30% of patients with advanced breast cancer and is a major cause of mortality. Here, we describe a new method of breast cancer brain metastasis PDXs. We also compare drug responsiveness of orthotopic brain PDXs made with the new method and ectopic PDXs grown in mouse mammary fat pad (MFP).
METHODS: One mm3 fragments of metastatic brain tumors of breast cancer patients were xenografted in brain caudate putamen or MFP of immunodeficient NSG mice using various methods. MRI was used to assess engraftment and tumor growth. Brain and MFP PDXs were examined for responsiveness to epothilone B.
RESULTS: We tested 3 methods for tumor implantation in brain: direct placement of tumor fragment using fine forceps (Forceps method), and injection of gently crushed tumor fragment using beveled 23 G needle with syringe (Needle method) or a pipettor with 10-ul pipette tip of 1 mm bore (Pipette method). PDXs in 8-10 mice were generated using each method. Post-operative mortality was zero with the Forceps and Pipette methods. However, 5 of 8 mice died within a day of implantation with the Needle method. At 6 weeks post-implantation, tumors were detectable in 80%, 67%, and 100% of surviving mice implanted using the Forceps, Needle, and Pipette methods, respectively. Tumor volumes were less variable with the Pipette compared to the Forceps method. Unlike the 100% engraftment for brain PDXs, the engraftment rate of patient brain metastasis implanted ectopically in MFP was only 75%. However, both orthotopic and ectopic PDXs grew about 2-fold faster after 3x serial passaging (all t test P &lt; 0.05). To assess the effect of tumor site on drug sensitivity, we compared response of the brain and MFP PDXs (n = 5 each) to one intravenous dose of Epothilone B, a taxane-like drug that can pass through the blood-brain barrier. While this drug is effective against primary breast tumors, it failed to demonstrate activity against breast cancer brain metastasis tumors in a recent phase II clinical trial. Tumor progression of MFP PDXs was retarded by approximately 3-fold compared to control mice (P &lt; 0.05). On the other hand, the drug had no effect on brain PDXs (P = 0.95). Our result implicate that the use of our model could have detected the ineffectiveness of this compound prior to clinical trial.
CONCLUSION: We established and characterized orthotopic breast cancer brain metastasis PDXs that were generated using a novel method that was facile, inexpensive, and efficient. PDXs created with our novel method may be powerful tools for preclinical studies of metastatic breast cancer.
Citation Format: Masanori Oshi, Maiko Okano, Kazuaki Takabe. Novel patient-derived orthotopic xenograft model for preclinical studies of breast cancer brain metastasis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 423.