Downregulation of oncogenic RAS and c-Myc expression in MOLT-4 leukaemia cells by a salicylaldehyde semicarbazone copper(II) complex

Yan-Yih Goh,Peter P F Lee,Nguan Soon Tan,Su-Ann Goh,You-Chuan Teoh,Shang Li,Yaw-Kai Yan

doi:10.1038/srep36868

Abstract

Copper complexes with potent anti-tumor effect have been extensively developed. Most investigations of their modes of action focused on the biomolecular targets but not the signal transduction between target binding and cell death. We have previously shown that the cytotoxic complex pyridine(2,4-dihydroxybenzaldehyde dibenzyl semicarbazone)copper(II) (complex 1) shows selective binding to human telomeric G-quadruplex DNA over double-stranded DNA in vitro. Herein, we elucidate the mechanism of action by which complex 1 induces apoptosis in MOLT-4 cells. Complex 1 accumulates in the nuclei and differentially downregulates the expression of c-Myc, c-Kit and KRAS oncogenes. Chemical affinity capture assay results show that the complex is associated with c-Myc and KRAS quadruplex sequences in MOLT-4 cells. We further showed that the reduction in Ras protein expression resulted in attenuated MEK-ERK and PI3K-Akt signalling activities, leading to the activation of caspase-dependent apoptosis. Notably, complex 1 increased the sensitivity of MOLT-4 cells to cisplatin and vice versa. Overall, we demonstrated that complex 1 induces apoptosis, at least in part, by suppressing KRAS, c-Kit and c-Myc oncogene expression and the pro-survival MEK-ERK and PI3K-Akt signalling pathways.

Highlights

The initial success of cisplatin in the clinical treatment of a variety of cancers has placed coordination chemistry in the limelight in the fight against cancers
Cellular copper levels are expressed as ng of copper/mg of protein of cell and the results reported are a mean of four separate experiments for each data point (Fig. 1B)
Very little nuclear copper was located in the soluble nuclear fraction (e.g. 41.8 vs 2.4 ng copper/mg of protein found in intact vs soluble nuclear fraction at 12 h after treatment) suggesting that the copper complex was mostly bound to chromosomal DNA, rather than the soluble nucleoplasm fraction

Summary

Introduction

The initial success of cisplatin in the clinical treatment of a variety of cancers has placed coordination chemistry in the limelight in the fight against cancers. Even though cisplatin is highly effective in treating various cancers, its efficacy is limited by its side effects and intrinsic or acquired resistance[1,2] This stimulated extensive research to develop various families of small molecules, based on different metals, and different targets, with improved pharmacological properties[3,4]. Most investigations focused on the ability of copper complexes to interact with duplex DNA, either through covalent bonding or non-covalent interaction[5,9] In many cases, this interaction resulted in DNA oxidative cleavage through a Fenton-type reaction to generate high levels of reactive oxygen species (ROS)[10]. The synergistic effect of complex 1 and cisplatin on the inhibition of MOLT-4 cells was investigated

Methods

Results

Conclusion