Next-Generation Sequencing Analysis and Algorithms for PDX and CDX Models.

Patient-derived xenograft (PDX) and circulating tumor cell-derived explant (CDX) models are powerful methods for the study of human disease. In cancer research, these methods have been applied to multiple questions, including the study of metastatic progression, genetic evolution, and therapeutic drug responses. As PDX and CDX models can recapitulate the highly heterogeneous characteristics of a patient tumor, as well as their response to chemotherapy, there is considerable interest in combining them with next-generation sequencing to monitor the genomic, transcriptional, and epigenetic changes that accompany oncogenesis. When used for this purpose, their reliability is highly dependent on being able to accurately distinguish between sequencing reads that originate from the host, and those that arise from the xenograft itself. Here, we demonstrate that failure to correctly identify contaminating host reads when analyzing DNA- and RNA-sequencing (DNA-Seq and RNA-Seq) data from PDX and CDX models is a major confounding factor that can lead to incorrect mutation calls and a failure to identify canonical mutation signatures associated with tumorigenicity. In addition, a highly sensitive algorithm and open source software tool for identifying and removing contaminating host sequences is described. Importantly, when applied to PDX and CDX models of melanoma, these data demonstrate its utility as a sensitive and selective tool for the correction of PDX- and CDX-derived whole-exome and RNA-Seq data.Implications: This study describes a sensitive method to identify contaminating host reads in xenograft and explant DNA- and RNA-Seq data and is applicable to other forms of deep sequencing. Mol Cancer Res; 15(8); 1012-6. ©2017 AACR.

Molecular analysis of circulating tumor cells identifies distinct copy-number profiles in patients with chemosensitive and chemorefractory small-cell lung cancer.

In most patients with small-cell lung cancer (SCLC)-a metastatic, aggressive disease-the condition is initially chemosensitive but then relapses with acquired chemoresistance. In a minority of patients, however, relapse occurs within 3 months of initial treatment; in these cases, disease is defined as chemorefractory. The molecular mechanisms that differentiate chemosensitive from chemorefractory disease are currently unknown. To identify genetic features that distinguish chemosensitive from chemorefractory disease, we examined copy-number aberrations (CNAs) in circulating tumor cells (CTCs) from pretreatment SCLC blood samples. After analysis of 88 CTCs isolated from 13 patients (training set), we generated a CNA-based classifier that we validated in 18 additional patients (testing set, 112 CTC samples) and in six SCLC patient-derived CTC explant tumors. The classifier correctly assigned 83.3% of the cases as chemorefractory or chemosensitive. Furthermore, a significant difference was observed in progression-free survival (PFS) (Kaplan-Meier P value = 0.0166) between patients designated as chemorefractory or chemosensitive by using the baseline CNA classifier. Notably, CTC CNA profiles obtained at relapse from five patients with initially chemosensitive disease did not switch to a chemorefractory CNA profile, which suggests that the genetic basis for initial chemoresistance differs from that underlying acquired chemoresistance.

Hypoxia-driven splicing into noncoding isoforms regulates the DNA damage response.

Tumour hypoxia is associated with poor patient outcome and resistance to therapy. It is accompanied by widespread changes in gene expression mediated largely through the transcription factors HIF1/2/3α. Hypoxia impacts on multiple pathways throughout the cell and has widespread effects on phenotype. Here we use sample-specific annotation approaches to determine the changes in transcript architecture that arise as result of alternative splicing in hypoxic cells. Using in vivo data generated from a time course in reduced oxygenation we identified genome-wide switching between coding and noncoding isoforms, including a significant number of components of the DNA damage response pathway. Notably, HDAC6, a master regulator of the cytotoxic response, and TP53BP1, which sits at the nexus of the double-strand break repair pathway, both underwent a marked transition towards an intron-retention pattern with a concomitant decline in protein levels. These transitions from coding to noncoding isoforms were recapitulated in a large and independent cohort of 499 colorectal samples taken from The Cancer Genome Atlas (TCGA). The set of altered genes was enriched for multiple components of the Fanconi Anaemia, nucleotide excision and double-strand break repair pathways, and together correlating with tumour status at last contact. Altogether, these data demonstrate a new role for hypoxia-driven alternative splicing in regulating DNA damage response, and highlight the importance of considering alternative splicing as a critical factor in our understanding of human disease.