Spirohydantoin derivatives exert dopamine D2-like receptor-independent cytotoxicity in glioblastoma cells with possible involvement of calpain inhibition

Glioblastoma multiforme (GBM) maintains one of the most aggressive brain tumor with increasing resistance. Herein in vitro study investigates spirohydantoin derivatives with diversified dopamine D₂R-like affinity as potential anti-glioblastoma agents. Cytotoxic studies with three human GBM cell lines (U87MG, A172 and U138MG) and human skin fibroblasts as non-tumor control, led to choose compounds 4, 6 and 7 with selective cell-damaging activity much greater than these observed for clinically used chemotherapeutic temozolomide (TMZ). The IC₅₀ values for A172 cells were 56, 5, 21 and 513 µM for 4, 6, 7 and TMZ, respectively. Moreover, we demonstrated the potency of 4, 6 and 7 as adjuvant therapeutics, even in GBM resistant phenotype. Interestingly, we observed a cell-damaging effect of calpain inhibitors in GBM cells and their higher cytotoxicity when combined with 4, 6 and 7, which together with molecular docking studies suggest that tested hydantoins might be also calpain inhibitors. Comparing the IC₅₀ values between used GBM cell lines, dopamine receptors' affinities and associating these data with expression level of D₂-like receptors, we rather exclude the involvement of these receptors in anticancer mechanism of investigated compounds. Collectively, these results justify further investigation of compounds from hydantoin family as anti-glioblastoma candidates.