Discovery of Gut-Restricted PRMT5 Inhibitors to Intercept Colorectal Cancer in Patients with Genetic Loss of Tumor Suppressor Adenomatous Polyposis Coli

Loss of the functional Adenomatous Polyposis Coli (APC-LOF) tumor suppressor gene represents the disease-initiating event in most colorectal cancer (CRC) cases. A newly identified dependency between PRMT5 and APC-LOF suggests that inhibiting PRMT5 may help intercept CRC. To circumvent hematological toxicities associated with orally bioavailable first-generation PRMT5 inhibitors, we aimed to limit systemic exposure after oral administration. We describe our efforts, challenges, and compound evaluation workflow resulting in gut-restricted PRMT5 inhibitors. A two-pronged approach was envisioned, consisting of (1) minimizing passive absorption, and (2) maximizing systemic clearance by incorporation of a metabolic "soft spot". This resulted in 9 and 18, displaying low absorption in preclinical species and high first-pass extraction mediated by aldehyde oxidase. 9 and 18 demonstrated in vivo colon pharmacodynamics without signs of systemic on-target toxicity, confirming gut-restriction. Administering 9 to dextran sodium sulfate (DSS)-treated polyp-bearing Apc^Min/+ mice significantly reduced polyp number, indicating local treatment efficacy.