Abstract 4378: Gastric cancer organoid culture shows preserved genomic stability in long-term passage

With recent advances in 3D organoid culture techniques, normal epithelial and tumor cells can be directly cultured from clinical specimens in vitro and expanded long-term with a very high success rate. Thus, this constitutes a good platform for various mechanistic functional studies and clinical applications. A previous karyotyping and gene expression profiling study has indicated that organoid culture of normal epithelial cells can be propagated for long periods of time without genomic alterations. However, data on the genomic stability of tumor organoids in long-term culture are not yet available. We have successfully established organoid cultures derived from either primary tumor or lymph node metastasis from 4 gastric cancer patients. For each sample, we performed long-term culture for at least 6 months. DNA was extracted from blood, as well as the early and late passages of these organoids, and submitted for whole-exome sequencing (WES), achieving a mean coverage approaching 50X. Somatic mutations detected in early versus late passage gastric cancer organoids were compared. Furthermore, we examined the organoids for copy number variations based on the coverage and loss of heterozygosity (LOH) information derived from exome sequencing. We detected between 80 to 228 somatic mutations in the 4 early passage organoids, in which over 84-99% of them were retained during long-term culture. We detected 16, 20, 31 and 98 new mutations in the 4 long-term cultures, respectively. The one case with a substantially large number of new mutations (n=98) appeared to have emerged from a subclone of TP53 wild-type cells in a TP53 mutant tumor. Notably, the C>T mutation was the most dominant mutation spectrum in this case, constituting 48%. Despite the presence of frequent long segment LOH and chromosomal aberrations in early passage organoids, indicating the presence of chromosomal instability, these patterns of aberrations were stably maintained in long-term passage. Overall, with the current organoid culture protocol, tumor genomes are mostly stably maintained with the accumulation of only a small number of new mutations. Our results indicate that this is a reliable and stable in vitro cell culture model for various cancer-related and clinical studies. Citation Format: Sarah Siu Kuen Yue, Helen Hoi Ning Yan, Hoi Cheong Siu, Siu Lun Ho, Wai Yin Tsui, Dessy Chan, Annie Shuk Yee Chan, Bernard Chi Hang Lee, Anthony Kin Wang Chan, Suet Yi Leung. Gastric cancer organoid cul