Cisplatin is widely used as a cancer chemotherapeutic agent and this review covers the mechanism of action of cisplatin, cellular resistance to cisplatin, the genomic location of cisplatin adducts and the properties of DNA-targeted Pt complexes. A particular focus of this review is the interaction of Pt compounds with DNA. The technology involved in determining Pt-drug/DNA interactions has advanced and permits clearer views of this process. In particular, molecular biological techniques permit a more accurate and precise determination of the sequence specific preference of Pt adduct formation. Prospects for the sequence specific genome-wide determination of Pt adduct formation using next-generation sequencing are also discussed. Cisplatin analogues that are targeted to DNA via an attached DNA-affinic moiety are potentially beneficial anti-tumour agents. In particular the 9-aminoacridine Pt complexes possess a number of important characteristics, including activity against cisplatin-resistant cells. Their ability to circumvent resistance due to increased DNA repair may allow these DNA-targeted analogues to avoid many of the drawbacks associated with current clinical oncology treatment. This ability is thought to be due to their altered DNA sequence specificity, compared with cisplatin, where Pt adduct formation for the 9- aminoacridine Pt complexes was shifted away from consecutive guanines towards 5'-CG and 5'-GA dinucleotide sequences. Evidence for this evasion of repair processes and avoidance of cellular cisplatin resistance was found for 9-aminoacridine Pt complexes in studies with cisplatin resistant cells. The prospects for clinical use of these DNA-targeted anti-tumour agents were evaluated.

In this study, the DNA sequence specificity of four DNA-targeted 9-aminoacridine carboxamide Pt complexes was compared with cisplatin, using two specially constructed plasmid templates. One plasmid contained 5'-CG and 5'-GA insert sequences while the other plasmid contained a G-rich transferrin receptor gene promoter insert sequence. The damage profiles of each compound on the different DNA templates were quantified via a polymerase stop assay with fluorescently labelled primers and capillary electrophoresis. With the plasmid that contained 5'-CG and 5'-GA dinucleotides, the four 9-aminoacridine carboxamide Pt complexes produced distinctly different damage profiles as compared with cisplatin. These 9-aminoacridine complexes had greatly increased levels of DNA damage at CG and GA dinucleotides as compared with cisplatin. It was shown that the presence of a CG or GA dinucleotide was sufficient to reveal the altered DNA sequence selectivity of the 9-aminoacridine carboxamide Pt analogues. The DNA sequence specificity of the Pt complexes was also found to be similarly altered utilising the transferrin receptor DNA sequence.

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