Abstract 3048: Murine-derived colorectal cancer organoid culture high-throughput drug screening to identify novel combinations targeting PIK3CA mutant cancers
Authors: DeZeeuw Alyssa K. , DeStefanis Rebecca A. , Sha Gioia , Pasch Cheri A. , Clipson Linda , Deming Dustin A. 
Published: September 2020

Abstract
Introduction: Colorectal cancer (CRC) treatment is becoming increasingly individualized as clinical mutation profiling is a standard of care. Oncogenic mutations of the PIK3CA gene induce a constitutively active phosphatidylinositol 3-kinase with downstream effects that promote tumor initiation and progression. Effective clinical therapeutic strategies targeting this subtype of colorectal cancer have remained elusive. Here we develop a high-throughput organoid drug screening platform to examine combination strategies targeting PIK3CA mutant CRC.
Methods: Murine-derived CRC organoids (MDCOs) were derived from a transgenic mouse model of PIK3CA and APC mutated colorectal cancer (F1 (FVBxB6) Apcfl/+ Pik3caH1047R), matured for 48 hours and plated in 96 well plates. A total of 96 compounds chosen from clinically available anticancer drugs and select drugs in clinical development were analyzed for their efficacy in reducing organoid growth on their own, as well as in combination with copanlisib (PI3K/MTOR inhibitor) over 48 hours. Select treatments were confirmed using our standard 24 well plate assay. Additionally, irinotecan (SN38; topoisomerase-I inhibitor), panitumumab (EGFR inhibitor), and olaparib (PARP inhibitor) were investigated alone and in combination with copanlisib based on clinical use for this population or recent promising clinical trial data.
Results: SN38, olaparib, and panitumumab yielded insignificant changes in spheroid size in the combination regimen compared to copanlisib alone (median relative change in organoid diameter - copanlisib -8%, p&lt;0.001; SN38 combo -8%, p=0.5; olaparib combo -13%, p=0.6; and panitumumab combo 1%, p=0.9). The MDCOs were successfully utilized for the high-throughput drug screen. Differential sensitivity was identified using change in organoid diameter without the need for reagents or dyes which could complicate the screening method. Of the 96 compounds investigated in the high-throughput screen, 12 resulted in enhanced treatment effect when combined with copanlisib. Three of these 12 compounds inhibit microtubule formation, and others inhibit components of the RAS pathway. Two of these drug combinations were examined further and significant treatment responses were confirmed.
Conclusion: Advances in the understanding of the molecular basis of cancer allow for a more precise approach to cancer treatment. High-throughput techniques are needed to better identify novel treatment strategies for molecular subtypes. Here we describe a label free murine-derived cancer organoid method to screen drugs for combination treatment strategies.
Citation Format: Alyssa K. DeZeeuw, Rebecca A. DeStefanis, Gioia Sha, Cheri A. Pasch, Linda Clipson, Dustin A. Deming. Murine-derived colorectal cancer organoid culture high-throughput drug screening to identify novel combinations targeting PIK3CA mutant cancers [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 3048.