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Purpose: Patient-derived xenograft models are considered to represent the heterogeneity of human cancers and advanced preclinical models. Our consortium joins efforts to extensively develop and characterize a new collection of patient-derived colorectal cancer (CRC) models.Experimental Design: From the 85 unsupervised surgical colorectal samples collection, 54 tumors were successfully xenografted in immunodeficient mice and rats, representing 35 primary tumors, 5 peritoneal carcinoses and 14 metastases. Histologic and molecular characterization of patient tumors, first and late passages on mice includes the sequence of key genes involved in CRC (i.e., APC, KRAS, TP53), aCGH, and transcriptomic analysis.Results: This comprehensive characterization shows that our collection recapitulates the clinical situation about the histopathology and molecular diversity of CRC. Moreover, patient tumors and corresponding models are clustering together allowing comparison studies between clinical and preclinical data. Hence, we conducted pharmacologic monotherapy studies with standard of care for CRC (5-fluorouracil, oxaliplatin, irinotecan, and cetuximab). Through this extensive in vivo analysis, we have shown the loss of human stroma cells after engraftment, observed a metastatic phenotype in some models, and finally compared the molecular profile with the drug sensitivity of each tumor model. Through an experimental cetuximab phase II trial, we confirmed the key role of KRAS mutation in cetuximab resistance.Conclusions: This new collection could bring benefit to evaluate novel targeted therapeutic strategies and to better understand the basis for sensitivity or resistance of tumors from individual patients.

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2+dependent dissociation of epithelial integrity was found to correlate strictly with SRF-mediated transcription. In cells lacking E-cadherin expression, no SRF activation was observed. Direct evidence is provided that signalling occurs via monomeric actin and MAL. Dissociation of epithelial junctions is accompanied by induction of RhoA and Rac1. However, usingclostridial cytotoxins, we demonstrate that Rac, but not RhoA, is required for SRF and target gene induction in epithelial cells, in contrast to serum-stimulated fibroblasts. Actomyosin contractility is a prerequisite for signalling but failed to induce SRF activation, excluding a sufficient role of the Rho-ROCKactomyosin pathway. We conclude that E-cadherin-dependent cell-cell junctions facilitate transcriptional activation via Rac, G-actin, MAL and SRF upon epithelial disintegration. Supplementary material available online at

SummaryMonomeric actin regulates gene expression through serum response factor (SRF) by inhibiting its transcriptional coactivator myocardinrelated transcription factor (MAL/MRTF). Many affected genes encode cytoskeletal components. We have analysed the migratory effects of actin-MAL signalling and of new target genes in non-invasive highly adherent cells. Expression of active MAL impaired migration of both fibroblasts and epithelial cells, whereas dominant-negative constructs and partial knockdown of MAL/MRTF enhanced motility. Knockdown of three newly characterised G-actin-regulated MAL targets, integrin a5, plakophilin 2 (Pkp2) and FHL1, enhanced cell migration. All three were upregulated by external stimulation through actin-MAL-SRF signalling, and MAL and SRF were inducibly recruited to cis-regulatory elements of the integrin a5 and Pkp2 genes. Finally, the reduced migration of epithelial cells stably expressing MAL was partially reversed by knockdown of Pkp2 and FHL1. We conclude that the actin-MAL pathway promotes adhesive gene expression, including integrin a5, Pkp2 and FHL1, and that this is anti-motile for non-invasive cells harbouring high basal activity.

Background: Genomic analysis of circulating tumor cells (CTCs) could provide a unique and accessible representation of tumor diversity but remains hindered by technical challenges associated with CTC rarity and heterogeneity. Objective: To evaluate CTCs as surrogate samples for genomic analyses in metastatic castration-resistant prostate cancer (mCRPC). Design, setting, and participants: Three isolation strategies (filter laser-capture microdissection, self-seeding microwell chips, and fluorescence-activated cell sorting) were developed to capture CTCs with various epithelial and mesenchymal phenotypes and isolate them at the single-cell level. Whole-genome amplification (WGA) and WGA quality control were performed on 179 CTC samples, matched metastasis biopsies, and negative controls from 11 patients. All patients but one were pretreated with enzalutamide or abiraterone. Whole-exome sequencing (WES) of 34 CTC samples, metastasis biopsies, and negative controls were performed for seven patients. Outcome measurements and statistical analysis: WES of CTCs was rigorously qualified in terms of percentage coverage at 10Â depth, allelic dropout, and uncovered regions. Shared somatic mutations between CTCs and matched metastasis biopsies were identified. A customized approach based on determination of mutation rates for CTC samples was developed for identification of CTC-exclusive mutations. Results and limitations: Shared mutations were mostly detected in epithelial CTCs and were recurrent. For two patients for whom a deeper analysis was performed, a few CTCs were sufficient to represent half to one-third of the mutations in the

148 Background: Molecular characterization of metastatic castration resistant prostate cancer (mCRPC) is limited by tumor tissue availability. The analysis of circulating tumor cells (CTC) offers an attractive noninvasive surrogate option to analyze molecular alterations. We report whole exome sequencing (WES) of CTCs at the single cell level in mCRPC patients. Methods: Blood samples were drawn from 11 enzalutamide or abiraterone pre-treated mCRPC patients enrolled in the clinical program MOSCATO (NCT02613962). CTC enrichment, immunofluorescent detection and single cell isolation were performed using three methods (ISET filtration, CellSearch and the VyCap puncher system and RosetteSep enrichment) to obtain pools of 1-10 CTCs with distinct epithelial or mesenchymal phenotypes. After Whole Genome Amplification (WGA), WES was performed on the Illumina HiSeq 2000 platform. GATK Haplotype Caller enabled identification of germline polymorphisms from each patient in normal DNA, metastatic sample and CTCs in order to consider WGA induced bias. The detection of sSNV in tumor biopsies and CTCs was assessed with Mutect and IndelGenotyper respectively. Results: 189 WGA of CTC pools were performed. 34 pools of phenotypically different CTCs from 7 patients were selected and sequenced. Mean coverage of 51% was obtained at a sequencing depth of 10X. Allelic drop out was lower for CTC pools containing 5-10 cells. 17/34 (50%) CTC samples had shared sSNV with the paired tumor sample (range 0.35%-68%) Epithelial CTCs had more shared sSNV with metastatic biopsies than CTCs of other phenotypes but shared sSNV were also detected in large non epithelial CTC pointing out a high level of genetic heterogeneity between CTC. Overall, 89 deleterious protein-coding mutations were found only in pools of CTC, including mutations affecting oncogenic drivers such as MAPK1, HSP90AB1 or KDM5B. Conclusions: We present single cell WES of CTCs harboring distinct phenotypes. The detection of shared sSNV between CTC pools and corresponding biopsy could validate the use of CTCs as a liquid biopsy. The finding of sSNV specific to CTCs could offer additional data on tumor heterogeneity.

Well characterized models representing the heterogeneity of human colorectal cancers (CRC) are needed to develop effective therapeutic agents. Establishment of such tools will allow a better prediction of the clinical outcome, taking into account the diversity of each patient tumor phenotype and genotype. For this purpose and with the financial support of the French Ministry of Industry, we have associated efforts from hospitals, academic groups, biotech and pharmaceutical companies. From May 2007 to January 2009, 86 surgical specimens [59 primary (P) tumors, 19 metastasis (M), and 8 peritoneal carcinomatosis (C)] were collected from CRC patients (with informed consents and negative HBV, HCV, and HIVs serologies). Tumor samples were subcutaneously xenografted in nude mice. The take rate was 57% (P), 55% (C), and 82% (M) with a difference in the take rate between tumor stages (p= 0.0184). We further engrafted in nude mice, SCID mice and nude rats. No significant difference in the take rate and growth was observed between the 2 mouse strains. Most of the mouse-growing tumors (95%) were successfully engrafted in nude rats, however their growth was significantly slower showing a more pronounced stromal component when compared with mice. Characteristics of our models are in accordance with the CRC clinical heterogeneity. Sequence analysis of 54 models has been performed and mutations were observed for KRAS (46%), APC (44%), TP53 (59%), BRAF (11%), PI3KCA (11%), FBXW7 (6%), CTNNB1 (2%), EGFR (2%), and 5/21 present a MSI status. Besides molecular markers, we compared the gene copy number using CGH technology before and after engraftment. The results exhibit high similarity between early passages of xenografts and the original clinical tumor samples. The histological structure and molecular profile were preserved, indicating the relevance of these models. Nevertheless the quality control is required to follow potential molecular deviation after multiple in vivo passages. The established models are being evaluated for ex vivo and in vivo sensitivities to colon anticancer drugs (5-FU, oxaliplatin, irinotecan and cetuximab). In vivo studies performed in our panel show 14/19 models sensitive to 5-FU, 1/19 to oxaliplatin, 7/8 to irinotecan, and 6/19 to cetuximab. We will present the correlation between pharmacological studies, molecular profile and patient clinical history. Preclinical studies on patient-derived tumor models will bring benefits to evaluate novel targeted therapeutic strategies and potentially help the stratification strategy for cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4169.