Cassane diterpenoid derivative induces apoptosis in IDH1 mutant glioma cells through the inhibition of glutaminase in vitro and in vivo

Background: Glioblastoma multiforme (GBM) is the most frequent, lethal and aggressive tumour of the central nervous system in adults. The discovery of novel anti-GBM agents based on the isocitrate dehydrogenase (IDH) mutant phenotypes and classifications have attracted comprehensive attention. Purpose: Diterpenoids are a class of naturally occurring 20-carbon isoprenoid compounds, and have previously been shown to possess high cytotoxicity for a variety of human tumours in many scientific reports. In the present study, 31 cassane diterpenoids of four types, namely, butanolide lactone cassane diterpenoids (I) (1-10), tricyclic cassane diterpenoids (II) (11-15), polyoxybutanolide lactone cassane diterpenoids (III) (16-23), and fused furan ring cassane diterpenoids (IV) (24-31), were tested for their anti-glioblastoma activity and mechanism underlying based on IDH1 mutant phenotypes of primary GBM cell cultures and human oligodendroglioma (HOG) cell lines. Results: We confirmed that tricyclic-type (II) and compound 13 (Caesalpin A, CSA) showed the best antineoplastic potencies in IDH1 mutant glioma cells compared with the other types and compounds. Furthermore, the structure-relationship analysis indicated that the carbonyl group at C-12 and an alpha, beta-unsaturated ketone unit fundamentally contributed to enhancing the anti-glioma activity. Studies investigating the mechanism demonstrated that CSA induced oxidative stress via causing glutathione reduction and NOS activation by negatively regulating glutaminase (GLS), which proved to be highly dependent on IDH mutant type glioblastoma. Finally, GLS overexpression reversed the CSA-induced anti-glioma effects in vitro and in vivo, which indicated that the reduction of GLS contributed to the CSA-induced proliferation inhibition and apoptosis in HOG-IDH1-mu cells. Conclusion: Therefore, the present results demonstrated that compared with other diterpenoids, tricyclic-type diterpenoids could be a targeted drug candidate for the treatment of secondary IDH1 mutant type glioblastoma through negatively regulating GLS.