Designing platinum(II) complexes with G-quadruplex DNA affinity

Abstract

Conventional platinum(II)-based anticancer drugs present a variety of clinical issues, including numerous severe side-effects due to their non-selective mechanism of action. The discovery of G-Quadruplex DNA (G4-DNA) has opened a new area of research for the design of selective anticancer agents with reduced side-effects. Various molecules, both organic and inorganic have been shown to selectively stabilise G4-DNA. In particular, platinum(II) complexes have shown to exhibit strong G4-DNA binding affinity, such as those consisting of 1,10-phenantrholine (Phen)-based ligands. Previous studies have shown [Pt(3,4,7,8-tetramethyl-1,10-phenanthroline)2]2+ to be a strong G4-DNA binder. Building upon this background, the aim of this project is to design platinum(II)-based G4-DNA stabilisers consisting of Phen and 2,2²-bipyridine (Bpy)-based ligands and with particular focus on the 3,4,7,8-tetramethyl-1,10-phenanthroline (Me4phen) ligand. Seven novel asymmetric platinum(II) complexes were synthesised using improved synthetic methods and complexes were subsequently purified using flash chromatography. These complexes were characterised using high pressure liquid chromatography (HPLC), nuclear magnetic resonance (NMR) spectroscopy, high resolution mass spectroscopy (HR-MS) and ultraviolet-visible (UV-Vis) spectroscopy. Six of the resulting complexes consisted of the Me4phen ligand. Five complexes consisted of two Phen-based ligands, while two consisted of one coordinated Phen-based ligand and one coordinated Bpy-based ligand. The binding interactions of the synthesised complexes were determined using docking simulations, circular dichroism (CD) and electron spray ionisation mass spectroscopy (ESI-MS) and their efficacy was determined using cytotoxicity assays. Docking simulations indicated that the complexes with larger aromatic surface areas exhibit the best binding affinity (i.e. [Pt(3,4,7,8-tetramethyl-1,10-phenanthroline)(pyrazino[2,3-f]1,10-phenanthroline)]Cl2, P4P6). However, docking simulations did not correlate with CD and ESI-MS binding experiments, with [Pt(3,4,7,8-tetramethyl-1,10-phenanthroline)(4,7-dimethyl-1,10-phenanthroline)]Cl2 (P4P2) being the most potent G4-DNA stabiliser in vitro. Cytotoxicity assays on a number of cancer cell lines were performed to identify any correlations that exist between G4-DNA binding affinity and cytotoxicity. No correlations were identified, suggesting that other mechanisms of actions may be contributing to cytotoxic effects. Complex [Pt(5,6-dimethyl-1,10-phenanthroline)(1,10-phenanthroline)]Cl2 (P3P1), even though found to be a poor G4-DNA binder, performed the best in cytotoxicity assays, showing up to a 5-fold better activity than cisplatin in pancreatic (MIA) and colon cell lines (HT29).

Date of Award	2019
Original language	English