PhD Scientific Days 2023

Pharmaceutical Sciences I.

A link to the future! Linkers to increase potency of Ru(II) piano-stool complexes

Text of the abstract

With cancer now affecting 1 in 2 of the population, new treatments eligible for all patients need to be developed. Ru(II) piano-stool complexes offer an alternative to Pt(II) complexes by exploiting different mechanisms of action (MOA), avoiding cross resistance. Ru(II) complexes are also often non-toxic in in vitro and in vivo models, in contrast to Pt(II) complexes which lack specificity. In Endothelial ovarian cancer (EOC), Pt(II) complexes are used but suffer from high recurrence and continually increasing death rates demonstrating treatment improvement is required.
We aimed to synthesise and characterise twelve Ru(II) complexes differing in their monodentate and bidentate ligand. Then determine the potential of a CH2 linker for increasing potency and altering MOA.
Synthesis was done by amine-aldehyde nucleophilic addition followed by chelation to the Ru(II) to form the complexes which were assessed by UV-Vis stability studies, NMR, DFT and other physicochemical characterisations. Growth inhibition was tested by MTT, followed by further MOA screening in A2780 by a variety of cellular and molecular techniques including microscopy, flow cytometry and DNA analysis.
All complexes were stable in PBS and a variety of biologically relevant matrices for 24h. Antiproliferative activity screening revealed that complexes with a ‘linker’ (Im-CH2-Py) were significantly more potent (up to 5.4×) than their ‘non-linked’ (Im-Py) counterparts. The most potent complexes, [Ru(Ƞ6-p-Cym)(Im-Py)I]PF6 (RAB23) and [Ru(Ƞ6-p-Cym)(Im-CH2-Py)I]PF6 (RAB38) were investigated further. RAB23 exhibited sub-G1 cell cycle arrest while RAB38 caused G1 arrest. RAB23 induced an increased population of late apoptotic cells compared to RAB38. Neither complex appeared to induce ROS generation or mitochondrial membrane depolarization. Nuclear morphology was significantly distorted by both complexes yet RAB23 and RAB38 do not appear to interact with ctDNA. Comet assays revealed ssDNA damage caused by RAB38 but not RAB23. While δ-H2A.X fluorescence (dsDNA damage) was increased by RAB23.
The structural modification appears to facilitate steric changes in the bidentate ligand, changing MOA from dsDNA to ssDNA breaks, increasing number of breaks, and resulting in greater potency. This highlights the potential improvement of similar highly potent complexes with the addition of a flexible linker.