Abstract PS17-47: Treatment naïve patient-derived xenograft model compared to the post-neoadjuvant model from the same patient diagnosed with triple negative breast cancer
Authors: Windsor Gabrielle Olivia , Matossian Margarite , Wright Maryl , Elliott Steven , Nguyen Khoa , Collins-Burow Bridgette , Burow Matthew 
Published: February 2021

Abstract
Triple negative breast cancer (TNBC) is an aggressive and difficult-to-treat subtype of breast cancer that typically exhibits rapid growth rates, high rates of metastasis, and resistance to commonly used oncological drugs. Historically, cell lines have been utilized in order to study TNBC; recently, however, patient derived xenografts (PDX) models have evolved as the new standard that offers a translational approach to the research and subsequent treatment of breast cancer. Here, we characterize two novel PDX models for TNBC: TU-BcX-4QA and TU-BcX-4QAN. The former derived from a biopsy specimen prior to any therapies, and the latter derived from a mastectomy of the same patient after three rounds of AC-T therapy (doxorubicin and cyclophosphamide followed by paclitaxel). In establishing a treatment naïve and post-neoadjuvant therapy PDX model pair, we created a prime model that examines the effects of chemotherapy on tumor heterogeneity, clonal selection, and the overall characteristics of a tumor. Furthermore, we examined the evolution of the characteristics of the post-neoadjuvant therapy PDX model after continual passaging within the SCID/Beige murine models. Through serial implantation in SCID/Beige murine models for tissue propagation, we observed that TU-BcX-4QAN consistently had a higher tumor growth rate and a smaller number of metastatic lesions that developed on the lungs and liver in comparison to the TU-BcX-4QA model. In treating the tumor derived cell lines with NCI-approved oncological drugs, we distinguished the variations in their responses to various, commonly used therapies, and determined that TU-BcX-4QAN had a more resistant profile. Using qRT-PCR, we further discovered the differences between the two models in their contrasting gene expression; preliminary data indicates an increase in certain mesenchymal genes (CDH2, VIM, and ZEB2), a decrease in cell cycle genes (p21, p53), and an increase in proliferation genes (MK167) in TU-BcX-4QAN compared to TU-BcX-4QA. Additionally, serial passages are correlated with a decrease trend in human gene expression within TU-BcX-4QAN. This suggest that treatment can select for certain cancer cells within the primary tumor that allows for the growth of a different tumor altogether and illustrates both the advantages and limitations of the TU-BcX-4QA andTU-BcX-4QAN model pair in translational research.
Citation Format: Gabrielle Olivia Windsor, Margarite Matossian, Maryl Wright, Steven Elliott, Khoa Nguyen, Bridgette Collins-Burow, Matthew Burow. Treatment naïve patient-derived xenograft model compared to the post-neoadjuvant model from the same patient diagnosed with triple negative breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-47.