Synthesis and antiproliferative evaluation of 3‐chloroazetidin‐2‐ones with antimitotic activity: Heterocyclic bridged analogues of combretastatin a‐4

Abstract

Antimitotic drugs that target tubulin are among the most widely used chemotherapeutic agents; however, the development of multidrug resistance has limited their clinical activity. We report the synthesis and biological properties of a series of novel 3‐chloro‐β‐lactams and 3,3‐di-chloro‐β‐lactams (2‐azetidinones) that are structurally related to the tubulin polymerisation inhibitor and vascular targeting agent, Combretastatin A‐4. These compounds were evaluated as potential tubulin polymerisation inhibitors and for their antiproliferative effects in breast cancer cells. A number of the compounds showed potent activity in MCF‐7 breast cancer cells, e.g., compound 10n (3‐chloro‐4‐(3‐hydroxy‐4‐methoxy‐phenyl)‐1‐(3,4,5‐trimethoxyphenyl)azetidin‐2‐one) and compound 11n (3,3‐dichloro‐4‐(3‐hydroxy‐4‐methoxyphenyl)‐1‐(3,4,5‐trimethoxyphenyl)‐azetidin‐2‐ one), with IC50 values of 17 and 31 nM, respectively, and displayed comparable cellular effects to those of Combretastatin A‐4. Compound 10n demonstrated minimal cytotoxicity against non‐tumorigenic HEK‐293T cells and inhibited the in vitro polymerisation of tubulin with significant G2/M phase cell cycle arrest. Immunofluorescence staining of MCF‐7 cells confirmed that β‐lactam 10n caused a mitotic catastrophe by targeting tubulin. In addition, compound 10n promoted apoptosis by regulating the expression of pro‐apoptotic protein BAX and anti‐apoptotic proteins Bcl‐2 and Mcl‐1. Molecular docking was used to explore the potential molecular interactions between novel 3‐chloro‐β‐lactams and the amino acid residues of the colchicine binding active site cavity of β‐ tubulin. Collectively, these results suggest that 3‐chloro‐2‐azetidinones, such as compound 10n, could be promising lead compounds for further clinical anti‐cancer drug development.