Characterisation and quantification of O6-alkylguanine adducts in DNA for clinical assessment of cancer risk

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Exposure of DNA to alkylating agents can produce alkylated DNA base adducts that induce mutations (base changes) following DNA replication. Damage to the base guanine to produce an O6-alkylguanine is considered to be one of the more detrimental of these processes and results in mutational patterns that are particularly common in patients diagnosed with colorectal cancer, the third most common cancer in the UK. Although chemical workers may be exposed directly to alkylating agents, there are many other sources of exposure that include environmental e.g. inhalation of tobacco smoke or vehicle exhaust fumes, dietary e.g. N-nitrosamines found in many foods or following cancer chemotherapy involving the use of methylating agents such as temozolomide. Although adducts such as O6-methylguanine are fairly well characterised, there are many other types of adducts that have been detected in DNA, for example O6-(carboxymethyl)guanine whose formation has been linked to diets high in red meat. Characterising the nature of O6-alkylguanines and the relative amounts of such adducts in human DNA (e.g. from a biopsy) would allow considerable improvements to be made in defining cancer risk and additionally would be hugely beneficial in monitoring patients undergoing chemotherapy.This project builds on our expertise in nucleic acid chemistry and biology and aims to further characterise the O6-alkylguanines that can arise in human DNA and to develop methods for their quantification. Techniques will involve synthetic organic and nucleic acid chemistry for the synthesis of O6-alkylguanosine and labelled standards, O6-alkylguanine-containing oligodeoxyribonucleotides and the development of analytical techniques such as mass spectrometry to characterise and to accurately quantify O6-alkylguanine adducts in DNA.