Synthesis and biological investigation of phenothiazine-based derivatives as potential HDAC6 inhibitors for treatment of glioblastoma multiforme

Glioblastoma multiforme (GBM) remains a challenging brain tumor, necessitating innovative therapeutic approaches. Targeting histone deacetylase 6 (HDAC6), a cytosolic isoform implicated in oncogenic pathways, represents a promising strategy with a potentially improved safety profile. In this study, a novel series of derivatives were designed and synthesized as HDAC6 inhibitors based on the phenothiazine scaffold. Among them, compound 6d exhibited potent inhibitory activity, displaying nanomolar inhibition of HDAC6 (IC₅₀ = 0.074 μM) with a high selectivity index of 52.4 over HDAC1, which significantly exceeds the positive control SAHA. Moreover, 6d effectively inhibited the proliferation of U87-MG glioma cells (IC₅₀ = 2.65 μM) and triggered dose-dependent Apoptosis and G2/M phase cell cycle arrest, with superior efficacy compared to SAHA. Favorable in silico ADMET properties supported its drug-like potential. Molecular docking and molecular dynamics simulations preliminarily predicted the binding pattern of 6d toward HDAC6. The simulated trajectory parameters exhibited partial convergence throughout the simulation period, indicating tentative intermolecular interactions including hydrophobic contacts, hydrogen bonds, and π-π stacking, rather than fully stable binding. Collectively, these findings confirm that compound 6d is a potential HDAC6 Inhibitor and a promising lead for the development of novel anti-GBM therapeutics.