Mechanistic insights into toxic effects of a benzotriazolate-bridged dinuclear platinum(II) compound in tumor cells

The interactions of novel mononuclear platinum-based complexes with DNA

Background

Cisplatin has been widely used for the treatment of cancer and its antitumour activity is attributed to its capacity to form DNA adducts, predominantly at guanine residues, which impede cellular processes such as DNA replication and transcription. However, there are associated toxicity and drug resistance issues which plague its use. This has prompted the development and screening of a range of chemotherapeutic drug analogues towards improved efficacy. The biological properties of three novel platinum-based compounds consisting of varying cis-configured ligand groups, as well as a commercially supplied compound, were characterised in this study to determine their potential as anticancer agents.

Methods

The linear amplification reaction was employed, in conjunction with capillary electrophoresis, to quantify the sequence specificity of DNA adducts induced by these compounds using a DNA template containing telomeric repeat sequences. Additionally, the DNA interstrand cross-linking and unwinding efficiency of these compounds were assessed through the application of denaturing and native agarose gel electrophoresis techniques, respectively. Their cytotoxicity was determined in HeLa cells using a colorimetric cell viability assay.

Results

All three novel platinum-based compounds were found to induce DNA adduct formation at the tandem telomeric repeat sequences. The sequence specificity profile at these sites was characterised and these were distinct from that of cisplatin. Two of these compounds with the enantiomeric 1,2-diaminocyclopentane ligand (SS and RR-DACP) were found to induce a greater degree of DNA unwinding than cisplatin, but exhibited marginally lower DNA cross-linking efficiencies. Furthermore, the RR-isomer was more cytotoxic in HeLa cells than cisplatin.

Conclusions

The biological characteristics of these compounds were assessed relative to cisplatin, and a variation in the sequence specificity and a greater capacity to induce DNA unwinding was observed. These compounds warrant further investigations towards developing more efficient chemotherapeutic drugs.

Characterisation of the DNA sequence specificity, cellular toxicity and cross-linking properties of novel bispyridine-based dinuclear platinum complexes

Background

The anti-tumour activity of cisplatin is thought to be a result of its capacity to form DNA adducts which prevent cellular processes such as DNA replication and transcription. These DNA adducts can effectively induce cancer cell death, however, there are a range of clinical side effects and drug resistance issues associated with its use. In this study, the biological properties of three novel dinuclear platinum-based compounds (that contain alkane bridging linkers of eight, ten and twelve carbon atoms in length) were characterised to assess their potential as anticancer agents.

Methods

The properties of these compounds were determined using a DNA template containing seven tandem telomeric repeat sequences. A linear amplification reaction was used in combination with capillary electrophoresis to quantify the sequence specificity of DNA adducts formed by these compounds at base pair resolution. The DNA cross-linking ability of these compounds was assessed using denaturing agarose gel electrophoresis and cytotoxicity was determined in HeLa cells using a colorimetric cell viability assay.

Results

The dinuclear compounds were found to preferentially form DNA adducts at guanine bases and they exhibited different damage intensity profiles at the telomeric repeat sequences compared to that of cisplatin. The dinuclear compounds were found to exhibit a low level of cytotoxicity relative to cisplatin and their cytotoxicity increased as the linker length increased. Conversely, the interstrand cross-linking efficiency of the dinuclear compounds increased as the linker length decreased and the compound with the shortest alkane linker was six-fold more effective than cisplatin.

Conclusions

Since the bifunctional compounds exhibit variation in sequence specificity of adduct formation and a greater ability to cross-link DNA relative to cisplatin they warrant further investigation towards the goal of developing new cancer chemotherapeutic agents.

Metal complex interactions with DNA

Increasing numbers of DNA structures are being revealed using a diverse range of transition metal complexes and biophysical spectroscopic techniques. Here we present a review of metal complex-DNA interactions in which several binding modes and DNA structural forms are explored.