Steroids from Ganoderma sinense as new natural inhibitors of cancer-associated mutant IDH1

Isocitrate dehydrogenase (IDH) is one of the key enzymes in the tricarboxylic acid cycle, and IDH mutations have been associated with many cancers, including glioblastoma, sarcoma, acute myeloid leukemia, etc. Three natural steroids 1-3 from Ganoderma sinense, a unique and rare edible-medicinal fungi in China, were found as potential IDH1 inhibitors by virtual ligand screening method. Among the three compounds, 3 showed the highest binding affinity to IDH1 with significant calculated binding free energy. Enzymatic kinetics demonstrated that 3 inhibited mutant enzyme in a noncompetitive manner. The half effective concentration of 3 for reducing the concentration of D-2HG in HT1080 cells was 35.97 μM. The levels of histone H3K9me3 methylation in HT1080 cells were reduced by treating with 3. Furthermore, knockdown of mutant IDH1 in HT1080 cells decreased the anti-proliferative sensitivity to 3. In short, our findings highlight that compound 3 may have clinical potential in tumor therapies as an effective inhibitor of mutant IDH1.