The compound millepachine and its derivatives inhibit tubulin polymerization by irreversibly binding to the colchicine-binding site in β-tubulin

Abstract

Inhibitors that bind to the paclitaxel- or vinblastine-binding sites of tubulin have been part of the pharmacopoeia of anticancer therapy for decades. However, tubulin inhibitors that bind to the colchicine-binding site are not used in clinical cancer therapy, because of their low therapeutic index. To address multidrug resistance to many conventional tubulin-binding agents, numerous efforts have attempted to clinically develop inhibitors that bind the colchicine-binding site. Previously, we have found that millepachine (MIL), a natural chalcone-type small molecule extracted from the plant , and its two derivatives (MDs) SKLB028 and SKLB050 have potential antitumor activities both and However, their cellular targets and mechanisms are unclear. Here, biochemical and cellular experiments revealed that the MDs directly and irreversibly bind β-tubulin. X-ray crystallography of the tubulin-MD structures disclosed that the MDs bind at the tubulin intradimer interface and to the same site as colchicine and that their binding mode is similar to that of colchicine. Of note, MDs inhibited tubulin polymerization and caused G/M cell-cycle arrest. Comprehensive analysis further revealed that free MIL exhibits an s- conformation, whereas MIL in the colchicine-binding site in tubulin adopts an s- conformation. Moreover, introducing an α-methyl to MDs to increase the proportion of s- conformations augmented MDs' tubulin inhibition activity. Our study uncovers a new class of chalcone-type tubulin inhibitors that bind the colchicine-binding site in β-tubulin and suggests that the s- conformation of these compounds may make them more active anticancer agents.

Design, Synthesis and Evaluation of 2,4‐Diaminoquinazoline Derivatives as Potential Tubulin Polymerization Inhibitors

“…Except for C239, the residues comprising the binding site are highly conserved between the two human isoforms and the G. gallus . Furthermore, Sus barbatus α‐tubulin was replaced in the heterodimer with that of Sus scrofa (PDB ID: 5yl2) because the orientation of the loop comprising the T179 residue in this last structure is key for the internalization of molecules into COL binding site and to avoid structural clashes.…”

Colchicine-Binding Site Inhibitors from Chemistry to Clinic: A Review

“…Chalcone 63 induced cell cycle arrest at an average concentration of 5 nM versus 24.8 nM for 61 without the additional methyl group, across five cells lines. Similarly, 64 had a promising average IC 50 of 21 nM versus 131.5 nM for 62 [126]. These compounds have great potential as covalent inhibitors to target cancers which cannot be treated by standard, reversibly-binding MTAs.…”

“…Yang et al have recently carried out biochemical and cellular experimentation, revealing through X-ray co-crystal structures of tubulin-millepachine derivatives that millepachine and derivatives were CBSIs [126]. Ring B modifications increased antiproliferative properties for millepachine derivatives.…”

“…Emerging research suggests that another potential mechanism of overcoming drug resistance is the design of irreversible covalent inhibitors at β-tubulin. Yang et al found SKLB028 (62, Figure 9) bound irreversibly to tubulin [126]. Cells failed to recover from cell cycle arrest up to 72 h after treatment, indicating that covalent bonding had occured.Designing anti-cancer compounds which covalently bind to their target is a well-known approach to overcome drug resistance [127,128].…”

Tegumental Alterations on Raillietina galli, an Intestinal Parasite of Fowl, after Treatment with Millettia taiwaniania Extract

“…4-Hydroxylonchocarpin and deguelin from the seeds have high antiinflammatory activities by inhibiting synthesis of ni-tric oxide, activity of inducible NO synthase (iNOS) and expression of iNOS gene (Ye et al, 2014). Millepachine has been among the promising lead compounds showing broad-spectrum activities against different cancer cells (Wu et al, 2016;Yang et al, 2018).…”