A novel harmine derivative, N-(4-(hydroxycarbamoyl)benzyl)-1-(4- methoxyphenyl)-9H-pyrido[3,4-b]indole-3-carboxamide (HBC), as histone deacetylase inhibitor: in vitro antiproliferation, apoptosis induction, cell cycle arrest, and antimetastatic effects

This study aims to design and synthesize a novel harmine derivative N-(4-(hydroxycarbamoyl) benzyl)-1-(4-methoxyphenyl)-9H-pyrido [3,4-b]indole-3-carboxamide (HBC) as histone deacetylase (HDAC) inhibitor, and evaluate its antitumor activities and anti-metastasis mechanism. HBC not only exerted significant ant-proliferation activity against five human cancer cell lines, especially for HepG2 cell with an IC₅₀ value of 2.21 μM, which is nearly three-fold lower than SAHA (IC₅₀ = 6.26 µM), but also showed selective HDAC1/6 inhibitory effects in vitro. However, HBC had little effect on normal hepatic cells LO2. Furthermore, HBC simultaneously increased the acetylation of histone H3, H4, and α-tubulin, induced hypochromism by electrostatical interaction with CT-DNA, triggered more significant cancer cell apoptosis and cell cycle arrest at G2/M than SAHA by inhibition of both CDK1 and cyclin B in a concentration dependent manner. In addition, scratch and invasion assay showed that HBC also dose-dependently suppressed migration and invasion capacities of highly metastatic HCC HepG2 cells through down-regulated the expression of tumor metastasis related proteins MMP-2 and MMP-9, significantly better than SAHA. Finally, HBC showed low acute toxicity to mice and significant growth inhibition of the hepatoma tumor in vivo. These results demonstrate that novel harmine-based HDAC inhibitor HBC not only exhibited selective HDAC1/6 inhibitory activity and significant in vitro and in vivo antitumor activity, but also possessed DNA binding effect, apoptosis induction, cell cycle arrest effects, and potent anti-metastasis mechanisms, which may hold great promise as therapeutic agent targeting HDAC1/6 for the intervention of human cancers.