Abstract 2597: Development and characterization of novel non-small cell lung cancer (NSCLC) circulating tumor cells (CTCs)-derived xenograft (CDX) models

Background: CDX models are expected to provide crucial information on mechanisms involved in metastatic progression, tumor-initiating properties of CTCs and the development of drug resistance. However, excepted for small-cell lung cancer (SCLC), CDX models are very difficult to develop. Here, we report the establishment, phenotypic and molecular characterization of four NSCLC CDX models and three in vitro cell lines derived from these CDXs. Methods: CTCs were enriched by RosetteSep from 30 ml blood samples and implanted subcutaneously into Nod/Scid-IL2Rγ-/- (NSG) mice. CDXs were phenotypically and genetically characterized by immunofluorescence, immunohistochemistry and whole-exome sequencing (WES). CDX-derived cell lines were established after mouse fibroblast depletion using classical culture medium. Standard conditions were used for IC50 determination. Results: Between January 2014 and June 2017, CTCs from 58 NSCLC patients with advanced metastatic disease were implanted into NSG mice resulting in the establishment of four CDXs. All had an epithelial phenotype. Based on CellSearch® counts, median and mean numbers of engrafted CTCs were 9 and 693 respectively (range, 0-17,694). GR-CDXL1, GR-CDXL2, GR-CDXL3, GR-CDXL4 were established starting from 3500, 35, 330, and 1102 CTCs respectively. Measurable tumors were obtained between 100 and 200 days after CTC implantation and were maintained by successive transplantations in NSG mice. Three in-vitro cell lines were established from GR-CDXL1, GR-CDXL3 and GR-CDXL4 tumors, and expressed an epithelial phenotype and CSC-markers such as ALDH, CD133 and CD90. Immunohistochemistry with epithelial and neuroendocrine markers, TTF1 and Ki67 indicated that CDXs and CDX-derived cell lines were representative of the corresponding patient tumor specimens (available in three patients). WES indicated 86%, 93%, 82% mutational similarity between GR-CDXL2, GR-CDXL3 and GR-CDXL4 and the corresponding tumor biopsies. The mutational similarity of GR-CDXL1, GR-CDXL3 and GR-CDXL4 and their corresponding in vitro cell lines was 24%, 83% and 84% respectively. WES of individual CTCs isolated at the time of CTC implantation is ongoing. In in vitro cytotoxicity assays, CDX-derived cell lines mirrored the patient's responsiveness to cisplatin and paclitaxel chemotherapy. The results of ongoing in vivo drug efficacy assays and of mutational tree analyses reconstructing the phylogenic evolution of tumor biopsies, CTCs, CDX and cell lines wi