Synthesis and biological evaluation of metal chelators of the hydroxypyridinone family as potential treatment of Parkinson’s disease and cancer

Kyriakou, Sotiris (2019) Synthesis and biological evaluation of metal chelators of the hydroxypyridinone family as potential treatment of Parkinson’s disease and cancer. Doctoral thesis, Northumbria University.

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Abstract

A series of 9 hydroxypyridinones (HOPO) metal-based iron chelators (from which 6 of them are novel) have been prepared, characterised and derivatized in a manner to exploit an active transport mechanism; Large neutral Amino Acid Transporter-1 (LAT-1), which is found to be
overexpressed in various types of cancer as well as to be presented in the blood-brain barrier (BBB) (Figure i).

Figure (i): Structure of HOPO based compounds synthesised. Novel compounds are in the dotted frames.

Additionally, it appears that the involvement of iron into metabolic pathways and/or the
formation of low levels of reactive oxygen species (ROS) enhances the survival and
proliferation of various types of cancer including malignant melanoma. The anticancer
capacity of the series of HOPO based metal chelators, have been evaluated in an in vitro model
ii
consisting of human (eg. A375, VVM1, HS-294T) and rodent (eg. B16F-10) melanoma cells as well as non-melanoma epidermoid carcinoma (eg. A431) and immortalized, non-malignant keratinocyte (eg. HaCaT) cells. The results of this study demonstrated that a single compound a methylated analogue of L-mimosine, can exert anticancer capacity as at the administered concentration it acts as a pro-oxidant triggering the production of high (toxic) levels of ROS, selectively in melanoma cell lines. The accumulation of ROS, drives the cells to apoptosis via activation of a well characterised downstream cascade that includes that activation of the terminal caspase 3/7 via the action of intrinsic (activation of caspase-9 pathway) and extrinsic (activation of caspase-8 pathway).

Additionally, the excessive production of oxidative cellular stress and iron misregulation may be substantially involved in the dopaminergic neuron degeneration seen in the brains of Parkinson's disease (PD) patients. Here we evaluated the effectiveness of the synthesised iron chelators, based on the hydroxypyridinone core with the ability to cross the BBB and penetrate the brain. Immortalised human dopaminergic neuronal precursor cells (LUHMES) were treated with the PD-related toxins 6-hydroxydopamine (6-OHDA), which generates superoxide radicals, 1-methyl-4-phenylpyridinium (MPP+), a mitochondrial complex I inhibitor, and the ferroptosis activator, erastin. Extensive cytotoxicological profiling revealed that three (rac-SK-2, rac-SK-3 and L-SK-4) out of the five tested compounds (rac-SK-1, rac-SK-2, rac-SK-3, L-SK-4 and rac-SK-5) rescue dopaminergic neuronal cells without inducing any toxic effects to cells, revealed through multiple cytotoxicological assays.

In order to validate which structural features were essential for the transportation and the action of the compound, a series of control compounds (which they were lacking either the amino acid moiety or the coordination unit) have also been designed and screened against both melanoma cancer as well as PD cell lines. These control compounds of the associated molecules supported the rational design behind them according to which, the HOPO core is essential for the metal binding and the amino acid side vector for the transportation across the biological membranes via LAT-1.

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