Characterization of genetic intratumor heterogeneity in colorectal cancer and matching patient-derived spheroid cultures.

Patient-derived in vitro cultures of colorectal cancer (CRC) may help guide treatment strategies prior to patient treatment. However, most previous studies have been performed on a single biopsy per tumor. The purpose of this study was to analyze multiple spatially distinct biopsies from CRCs and see how well intratumor heterogeneity (ITH) was recapitulated in matching patient-derived spheroids. Three to five biopsies were collected from six CRC tumors. Each biopsy was split in two; one half was used for spheroid culturing, the other half was used for direct DNA and RNA purification. For two of the patients, lymph node metastases were analyzed. Somatic mutations were called from whole exome sequencing data. Each tumor contained multiple mutations shared across all biopsies and spheroids, including major CRC drivers such as APC, KRAS, and TP53. At the same time, all tumors exhibited ITH on both mutation and copy number level. The concordance between biopsies and spheroids ranged between 40-70% for coding mutations. For three of the patients the biopsy and spheroid from matching areas clustered together, meaning that the spheroid resembled the area of origin more than the other areas. However, all biopsies and spheroids contained private mutations. Thereby, multiple cultures from spatially distinct sites of the tumor increase the insight into the genetic profile of the entire tumor. RNA sequencing based molecular subtyping was stable and seemed independent of genetic ITH. In conclusion, all examined CRC tumors contained genetic ITH on mutation and copy number level. Spheroid cultures partly reflected this ITH, meaning that multiple cultures from distinct sites of the tumor improved the representation of the different genetic subclones in the primary tumor. This should be taken in to account when establishing patient-derived models for drug screening.

Type: Other
Archiver: European Genome-Phenome Archive (EGA)

3 Datasets 1 Publication

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Dataset ID	Description	Technology	Samples
EGAD00001003820	Whole transcriptome, strand-specific RNA-seq libraries were prepared from total RNA purified using RNeasy mini kit (Qiagen) using Ribo-Zero technology (Epicentre, an Illumina company) for depletion of rRNA followed by library preparation using ScriptSeq ScriptSeq RNA-Seq Library preparation Kit from Illumina. The paired raw sequence reads were processed using TopHat2 and mapped to the humane reference genome HG19.	NextSeq 500	16
EGAD00001003821	WES was performed using the KAPA-Hyper prep kit from Illumina (Roche, Basel, Switzerland) for library construction, followed by exome capture using Niblegen SeqCap EZ Human Exome Library v3.0 (Roche). Reads were mapped using BWA MEM against the humane reference genome HG19.	NextSeq 500	42
EGAD00001003823	Somatic mutations were called using whole exome Sequencing (WES) data from colorectal cancer samples (dataset EGAD00001003821) using MuTect2, with matched constitutional WES-data obtained from leukocytes samples as reference.		37

Publications	Citations
Characterization of genetic intratumor heterogeneity in colorectal cancer and matching patient-derived spheroid cultures. Árnadóttir SS, Jeppesen M, Lamy P, Bramsen JB, Nordentoft I, Nordentoft I, Knudsen M, Vang S, Madsen MR, Thastrup O, Thastrup J, L Andersen C. Mol Oncol 12: 2018 132-147	29