A New Assay to Measure Intestinal Crypt Survival after Irradiation: Challenges and Opportunities

Colorectal cancer develops inherent radiosensitivity that can be predicted using patient-derived organoids

Identifying colorectal cancer patient populations responsive to chemotherapy or chemoradiation therapy before surgery remains a challenge. Recently validated mouse protocols for organoid irradiation employ the single hit multi-target (SHMT) algorithm, which yields a single value, the D0, as a measure of inherent tissue radiosensitivity. Here we translate these protocols to human tissue to evaluate radioresponsiveness of patient-derived organoids (PDOs) generated from normal human intestines and rectal tumors of patients undergoing neoadjuvant therapy. While PDOs from adenomas with a logarithmically-expanded Lgr5+-intestinal stem cell population retain the radioresistant phenotype of normal colorectal PDOs, malignant transformation yields PDOs from a large patient subpopulation displaying marked radiosensitivity due to reduced homologous recombination-mediated DNA repair. A proof-of-principle pilot clinical trial demonstrated that rectal cancer patient responses to neoadjuvant chemoradiation, including complete response, correlate closely with their PDO D0 values. Overall, upon transformation to colorectal adenocarcinoma, broad radiation sensitivity occurs in a large subset of patients that can be identified using SHMT analysis of PDO radiation responses.

Disruption of the crypt niche promotes outgrowth of mutated colorectal tumor stem cells

Recent data establish a logarithmic expansion of leucine rich repeat containing G protein coupled receptor 5–positive (Lgr5⁺) colonic epithelial stem cells (CESCs) in human colorectal cancer (CRC). Complementary studies using the murine 2-stage azoxymethane–dextran sulfate sodium (AOM-DSS) colitis-associated tumor model indicate early acquisition of Wnt pathway mutations drives CESC expansion during adenoma progression. Here, subdivision of the AOM-DSS model into in vivo and in vitro stages revealed DSS induced physical separation of CESCs from stem cell niche cells and basal lamina, a source of Wnt signals, within hours, disabling the stem cell program. While AOM delivery in vivo under non-adenoma-forming conditions yielded phenotypically normal mucosa and organoids derived thereof, niche injury ex vivo by progressive DSS dose escalation facilitated outgrowth of Wnt-independent dysplastic organoids. These organoids contained 10-fold increased Lgr5⁺ CESCs with gain-of-function Wnt mutations orthologous to human CRC driver mutations. We posit CRC originates by niche injury–induced outgrowth of normally suppressed mutated stem cells, consistent with models of adaptive oncogenesis.