The formation of DNA adducts caused by cisplatin and other closely related platinum-based drugs

Abstract

Cisplatin is a platinum-based drug that has been used world-wide to treat cancer, particularly in the clinical treatment of testicular cancer, following its discovery by Barnett Rosenberg in 1965. The drug's anti-tumour activity is a result of its capacity to form covalent bonds with DNA, known as DNA adducts, which prevent processes such as DNA replication and transcription from occurring within the cell. This ultimately leads to cell death and subsequent tumour regression. Cisplatin forms DNA adducts, primarily at the guanine and adenine purine bases, through which it elicits its cytotoxic effects. Although these DNA adducts can effectively cause cancer cell death, there are a range of associated cytotoxic side effects (such as nephrotoxicity and neurotoxicity) and drug resistance issues (such as through the repair of DNA adducts by DNA repair proteins) that still need to be resolved. Therefore, a range of novel drug analogues are currently in development with the aim to circumvent these issues. The work described in this thesis applies molecular biology-based techniques in order to characterise the biological properties of a range of novel mononuclear and dinuclear platinum-based compounds, to ultimately assess their potential as anti-cancer drug candidates. The novel mononuclear compounds that were analysed included DACH, RR-and SS-DACP, 3478MEEN, 56MEEN, 56MESS and 4FH. The novel dinuclear compounds that were synthesised and analysed included 1,8 platinum, 1,10 platinum and 1,12 platinum. Cisplatin is a well characterised compound and was therefore utilised as a control compound for all experiments. There are three main approaches that have been carried out in this doctoral study to characterise the biological properties of these novel compounds. The first approach focuses on assessing their DNA binding sequence specificity in a DNA template consisting of seven human telomeric repeat sequences of TTAGGG, through the application of a fluorescence-based linear amplification reaction. The second approach focuses on assessing their cytotoxic activity within HeLa cells, through the application of a colorimetric cell viability assay. The third approach focuses on assessing their ability to induce structural distortions to DNA, such as interstrand cross-linking of double-stranded DNA and DNA unwinding, through the application of agarose gel electrophoresis techniques. In summary, this doctoral study has successfully characterised the sequence specificity, cytotoxic activity, DNA unwinding and DNA interstrand cross-linking properties of a range of mononuclear and dinuclear platinum-based compounds. In the long term, it is anticipated that a knowledge of these properties, along with an understanding of how they are mediated by DNA repair pathways in the cell, will facilitate the rational design and synthesis of a range of platinum-based drugs with desirable chemotherapeutic properties that surpass the clinical efficacy of cisplatin.

Date of Award	2015
Original language	English