Mechanisms of anti-cancer action of gold porphyrin, oxaliplatin and berberine : identification of direct molecular targets and proteomics analysis

Abstract

Since the landmark discovery of the anti-cancer properties of cisplatin, there has been an upsurge of interest in developing metal complexes as anti-cancer therapeutic agents. Over the past decades, several novel platinum(II)complexes other than cisplatin have been developed and used in cancer treatment. Gold complexes have also been attracting considerable interest as potential new anti-cancer agents. Although a number of anti-cancer platinum and gold complexes have entered into clinical trial studies, the drugs’ mechanisms of anti-cancer action, including their direct molecular targets, remain to be understood.

Identification of the molecular targets of anti-cancer metal complexes is a formidable challenge as most of them are unstable against ligand exchange reactions or biological reduction under physiological conditions. Gold(III) meso-tetraphenylporphyrin ([Au(TPP)]Cl, gold-1a) has been reported to possess high stability under physiological conditions and resistance to reduction by glutathione, and displays potent anti-cancer activities in vivo. In chapter 3, a trifunctional clickable photo-affinity probe of gold-1a (probe-3.1) was used to identify heat shock protein 60 (Hsp60) as a direct molecular target of gold(III) porphyrin complexes in cellular conditions. This finding was supported by additional chemical biology studies including cellular thermal shift, saturation-transfer difference NMR, protein fluorescence quenching and protein chaperone assays. Hsp60 is a mitochondrial chaperone and a potential molecular target for anti-cancer therapy. Structure-activity relationship study using non-porphyrin gold(III) complexes and other metalloporphyrins demonstrated that the presence of gold(III) ion and porphyrin ligand are essential for the inhibition of Hsp60 activity. There is mounting interest in developing “theranostic” agents that possess both anti-cancer and luminescent properties. In Chapter 4, a fluorescent 1-(3-hydroxybenzo[b]thiophen-2-yl)ethanone (HO^O) ligand was used to develop a panel of luminescent platinum(II) complexes(complexes 4.1-4.3). These platinum(II) complexes showed in vitro cytotoxicity against various cancer cell lines, in vivo tumor growth inhibition and potent photo-toxicity. Among these complexes, 4.1displayeda higher potency of anti-cancer action than commonly used platinum(II) drugs. The luminescent properties of platinum(II) complexes and HO^O ligand allowed real time tracking and visualization of these new anti-cancer platinum(II) complexes inside live cells, including monitoring their intracellular distribution and release of the coordinated HO^O ligand. Profiling of protein expression changes mediated by anti-cancer compounds through mass spectrometry-based proteomics analysis, followed by bioinformatics analysis, provides a means to delineate the potential molecular targets and cellular pathways involved in the chemotherapeutic mechanism of action. In Chapters 5 and 6, the findings of quantitative proteomic pathway analysis provided insights into the dominant signaling pathways which are responsible for the anti-cancer action of oxaliplatin and berberine, respectively. Oxaliplatin was found to first activate DNA damage-mediated cell cycle arrest, and then induce cellular apoptosis involvingp53, caspase and Fas pathways. The anti-cancer effect of berberine was attributable to a complex process involving a number of stress response pathways, cell cycle arrest, reactive oxygen species production, inhibition of protein synthesis and cell death.