Stable Biotherapeutic Penetration Screening in Critically Small Colorectal Metastatic Cancer Biopsies Allows for Oncolytic Virus‐Delivered Chemotherapeutic Response Assessment through 3D Bioprinted Organoid Expansion

Abstract Oncolytic viral‐delivered chemotherapeutics have exciting potential for metastatic cancer therapies, including colorectal cancer, but require advanced screening systems for better patient prediction. We optimized primary metastatic colorectal tumor processing and 3D (3‐dimensional) bioprinted tumors to prove efficacy as long‐term screening systems. Normally, this time period would use animals, but we show it is possible to gain useful data in vitro before preclinical stages, to reduce animal modeling and give better clinical trial predictions. Liver tumors were collected from 12 colorectal cancer patients, evaluated for expansion, 3D bioprinted, and tested for ability to create long‐term organoid models with screening of oncolytic viral‐loaded FCU1 enzyme conversion of 5‐fluorocytosine (5‐FC) into the highly toxic 5‐fluorouracil (5‐FU). Donated tumor size was the limiting factor. 75% of patients could be used for screening of viral delivery. Response between patients was overall positive, with good secondary tumor development, outer active cellular content and inner necrotic core. Oncolytic challenge shows good screening potential and cellular targeting, demonstrating an added bystander effect, optimizing the low‐dose. Stable long‐term metastatic organoid models were made, lasting many months, with potential for retesting rather than one‐off analysis. Oncolytic virus‐delivered chemotherapy is promising and warrants further investigation for metastatic colorectal cancers.