Stromal Regulation of Colorectal Cancer Plasticity

Colorectal cancer (CRC) tumours with high stromal content have a worse outcome, but the mechanisms governing this are unclear. Through high-throughput single-cell perturbation analysis of CRC patient-derived organoids (PDOs) and cancer-associated fibroblasts (CAFs) we find that epithelial cells with high stromal-communication potential are marked by the transcriptional co-repressor DACH1. To determine the molecular regulators of stromal-epithelial signalling, we developed a novel single-cell intercellular CRISPR screening of the CAF secretome and discovered that stromal PTGS2 (COX2) is a dominant regulator of CRC plasticity. Stromal Prostaglandin E2 (PGE2) can switch DACH1+ CRC cells from a chemosensitive proliferative colonic stem cell (proCSC) state to a chemorefractory and pro-metastatic revival colonic stem cell (revCSC) state. PGE2-driven epithelial transdetermination is rapid and reversible, providing an acute mechanism for stromal-driven plasticity in CRC tumours. Genetic and pharmacological inhibition of stromal COX2 inhibits epithelial plasticity, trapping CRC epithelia in an anti-metastatic and chemosensitive proCSC state. PTGS2+ CAFs support a spatially resolved revCSC-to-proCSC plasticity gradient in human CRC tumours marked by increasing DACH1 expression. These results reveal that stromal prostaglandin is a dominant spatial regulator of epithelial plasticity and may explain the benefit of anti-COX2 therapies in both preventing and treating CRC.