Abstract 5600: Establishment and characterization of a unique circulating tumor cells-derived xenograft (CDX) in prostate cancer
Authors: Faugeroux Vincent , Pailler Emma , Deas Olivier , Marty Virginie , Alexandrova Kamélia , Andree Kiki , Scoazec Jean-Yves , Stoecklein Nikolas , Manaresi Nicolo , Tramalloni Dominique , Ngo-Camus Maud , Nicotra Claudio , Terstappen Leon , Lapierre Valérie , Fizazi Karim , Loriot Yohann , Judde Jean-Gabriel , Farace Françoise 
Published: August 2018

Abstract
Background: The rarity of in vivo and in vitro human prostate cancer (PCa) models has hampered progress in understanding disease pathogenesis, metastatic progression and drug resistance mechanisms. Using CTCs from a leukapheresis product of a patient with advanced PCa, we report the establishment of a CDX and an in vitro cell line derived from this CDX. The phenotypic and molecular characterization of patient tumor-biopsies, CTCs, CDX and CDX-derived cell-line are presented.
Methods: Leukapheresis was performed in seven patients with advanced castration-resistant prostate cancer (CRPC). CTCs from the seven leukapheresis products were enriched by RosetteSep and implanted in Nod/Scid-IL2Rγ-/-mice. The CDX tumor was propagated in successive generations of mice. All samples, including eight tumor-biopsies performed at diagnosis two years prior leukapheresis and CTCs isolated at the single cell level during leukapheresis were characterized by immunofluorescence, immunohistochemistry, and whole-exome sequencing (WES).
Results: Based on CellSearch® counts in leukapheresis products, the estimated median number of engrafted CTCs was 697 (range: 10-19988). A mouse engrafted with 19988 CTCs developed a tumor within 193 days. Immunohistochemistry performed on the CDX and two tumor-biopsies indicated that the CDX and biopsies were positive for EpCAM, CK5/6/8/18, negative for CK7 and vimentin, and weakly positive for synaptophysin. While biopsies expressed PSA and the androgen receptor, the CDX was negative for both indicating tumor evolution. In contrast to tumor biopsies, the CDX strongly expressed Ki67, NSE and chromogranin, evidencing emergence of a neuroendocrine phenotype. The in vitro cell line established by culturing dissociated CDX cells for five months, grew in microspheres and expressed epithelial and ALDH and CD133 cancer stem-cell markers. By WES, a high degree of intra-tumor heterogeneity was observed in the eight tumor biopsies and CTCs as already reported in this tumor type. Only 2.8% (58/2087) and 2.3% (49/2087) of the mutations present in the tumor biopsies were identified in CTCs and the CDX respectively, indicating that a very few number of mutations have the potential to support the dissemination and tumorigenic activity of CTC. Trunk mutations in TP53, NF1 and LRP1B genes were identified in all samples including the CDX while PTEN gene loss was acquired lately and detected only in CTCs and the CDX. Mutational similarity of the CDX and the in vitro cell line was 91%. The analysis of copy number variations is ongoing in all samples and will be presented.
Conclusion: We report the first PCa CDX model, demonstrating the tumorigenicity of CTCs from CRPC. This CDX model represents a unique tool to identify clonal mutations associated with the tumor-initiating capacity of CTCs and explore the genetic and phenotypic basis of metastasis and drug resistance in advanced CRPC.
Citation Format: Vincent Faugeroux, Emma Pailler, Olivier Deas, Virginie Marty, Kamélia Alexandrova, Kiki Andree, Jean-Yves Scoazec, Nikolas Stoecklein, Nicolo Manaresi, Dominique Tramalloni, Maud Ngo-Camus, Claudio Nicotra, Leon Terstappen, Valérie Lapierre, Karim Fizazi, Yohann Loriot, Jean-Gabriel Judde, Françoise Farace. Establishment and characterization of a unique circulating tumor cells-derived xenograft (CDX) in prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5600.