Inhibitory Activity on Dog Bladder Cancer Organoids by Lanostane-type Triterpenes from Inonotus obliquus and Reinvestigation of Their NMR Assignments

Dog bladder cancer organoids (DBCO) serve as a model of human muscle-invasive bladder cancer (MIBC), for which suitable human organoid models remain limited. Inonotus obliquus (Chaga) extract reportedly reduces DBCO growth, but its active constituents were unidentified. We isolated four lanostane-type triterpenes from Chaga extract through fractionation guided by DBCO viability and revised their previous NMR assignments. All compounds reduced DBCO viability at 21.8 µM (10 µg/mL), with compound 3 showing the greatest potency, suggesting that C-21/C-24 stereochemistry may influence cytotoxicity.