Abstract 1494: Etiologies of patient-derived colorectal cancer organoid growth heterogeneity across multiple patient samples and culture conditions
Authors: Sunil Aishwarya , Kratz Jeremy D. , Makkar Sarbjeet K. , Rehman Suhjah , Gillette Amani A. , Johnson Katherine A. , Pasch Cheri A. , Clipson Linda , Matkowskyj Kristina A. , Skala Melissa C. , Deming Dustin A. 
Published: September 2020

Abstract
Background: Patient-derived cancer organoids (PDCOs) are emerging as an in vitro model to recapitulate the molecular and phenotypic features of colorectal cancer (CRC). Heterogeneity in established CRC PDCOs has been observed in the underlying molecular profiles and growth characteristics at the individual organoid level. Here, we present a dedicated assessment of individual organoid growth as a function of experimental culture parameters.
Methods: CRC PDCO cultures were established from patient biopsy/resection specimens following patient consent to an IRB-approved protocol. Growth was assessed by relative change in diameter at 48h. Baseline size was compared to relative growth at 48h using coefficient of determination (R). Interquartile sets were compared by effect size of Glass's Delta (GΔ) to compare change difference in average growth normalized to standard deviation and defined with significance 1.0. Impact of density was assessed by manual count of spheroids and lines plated across varied densities and compared to 48h relative growth. Growth rates were compared as both absolute and relative passage number.
Results: 22 unique cultures were established from fresh tissue and representative of CRC including pathologic alterations in APC, KRAS, NRAS, BRAF, PIK3CA TP53, MTOR and PTEN. Pairwise spheres were assessed at baseline and 48h for analysis (n=1714) with mean relative growth rate of 27.1% (range -40.0, 156.2%). Baseline size did not predict relative growth at 48h (R=0.023) with insignificant interquartile effect size [0.10, 0.07, 0.32]. Replicates (n=63) across a range of passages [1, 36] including line-specific relative passage number [0-14] did not predict change in relative growth (R&lt;0.001) with insignificant interquartile effect size [-0.02, 0.15, 0.19]. Fields of view (n=135) were assessed for absolute sphere number [1, 72]. Increased sphere density across cultures also did not predict change in relative growth (R=0.002) with insignificant interquartile effect size [-0.29, -0.32, -0.29]. Two individual cultures were assessed for the impact of density on respective growth without significance at relative plating ratios of 1:5 (GΔ=-0.52, 0.42), 1:10 (GΔ=-0.63, 0.07), and 1:50 (GΔ=-0.40, 0.12).
Conclusions: Following culture maturation, CRC PDCOs have heterogeneous growth rates at the organoid level. These studies demonstrate that the growth rate is independent of baseline organoid size, passage number, or culture plating density. Understanding the effect of culture variation helps to define meaningful population effects in response and resistance to therapy and supports the translation of this technology as a future predictive biomarker.
Citation Format: Aishwarya Sunil, Jeremy D. Kratz, Sarbjeet K. Makkar, Suhjah Rehman, Amani A. Gillette, Katherine A. Johnson, Cheri A. Pasch, Linda Clipson, Kristina A. Matkowskyj, Melissa C. Skala, Dustin A. Deming. Etiologies of patient-derived colorectal cancer organoid growth heterogeneity across multiple patient samples and culture conditions [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1494.