Design, Synthesis, And Antitumor Activity Of Cyclic Tetrapeptide HDACi Based On Chlamydocin Framework

Reversible acetylation and deacetylation of lysine residus on histone tails by histone acetyl transferase(HAT) and histone deacetylase(HDAC) enzymes play a fundamental role in the regulation of gene expression by changing the chromatin structure and transcriptional activity. High HDAC activity due to abnormal recruitment of HDACs is associated with a number of malignant diseases. Inhibitors of HDACs have demonstrated efficacy against cancer cell lines.Naturally occurring cyclic tetrapeptide chlamydocin which is isolated from fungus Diheterosporia Chlamdosphoria containing Aib, L-Phe, D-Pro, and L-Aoe shows a highly HDACs inhibition with an IC50 of 1.3 nmol/L in vitro. L-Aoe provides an epoxyketone moiety in the side chain which irreversible inhibits HDACs.To expect reversible and high active HDAC inhibitors, we replaced epoxykeone moiety of Aoe with sulfhydryl group and hydroxamic acid. To improve the hydrophobic interaction of the cap groups with HDACs, we replaced L-Phe to L-Phe(4-Me) in chlamydocin framework. In this paper we designed and synthesized three novel cyclic tetrapeptide HDAC inhibitors:cyclo(-L-Am7(S2Py)-Aib-L-Phe-D-Pro-),cyclo(-L-Am7(S2Py)-Aib-L-Phe(4-Me)-D-Pro-) and cyclo(-L-Asu(NHOH)-Aib-L-Phe(4-Me)-D-Pro-).The conventional liquid phase method was used to synthesize the cyclic tetrapeptides. The amino acids were protected by Boc/Bzl and Z/tBu. The coupling regent was DCC/HOBt. Their final chemical structures were characterized by 1H and 13C NMR and ESI-MS.The cyclic peptides were tested for cytotoxic activity against three cancer cell lines, including MCF-7,Hela and 7721 cells. All the compounds demonstrated exciting antitumor abilities. The cellular shapes changed obviously with HDACi-treated for 24 h.Molecular docking method was used to analysis the interactions between the cyclic tetrapeptides HDAC inhibitors and histone-like protein (HDLP). The results showed that the thiol and hydroxamic acid could well chelating with Zn2+ at the active site of HDLP. Surface recognition cap groups of the cyclic tetrapeptides contact with the amino acid residues around the pocket of HDLP which stabilize the binding of enzyme and cyclic tetrapeptides.