Quadruplex DNA-Stabilising Dinuclear Platinum(II) Terpyridine Complexes with Flexible Linkers.

Four dinuclear terpyridineplatinum(II) (Pt-terpy) complexes were investigated for interactions with G-quadruplex DNA (QDNA) and duplex DNA (dsDNA) by synchrotron radiation circular dichroism (SRCD), fluorescent intercalator displacement (FID) assays and fluorescence resonance energy transfer (FRET) melting studies. Additionally, computational docking studies were undertaken to provide insight into potential binding modes for these complexes. The complexes demonstrated the ability to increase the melting temperature of various QDNA motifs by up to 17 °C and maintain this in up to a 600-fold excess of dsDNA. This study demonstrates that dinuclear Pt-terpy complexes stabilise QDNA and have a high degree of selectivity for QDNA over dsDNA.

Probing the Interactions of Cytotoxic [Pt(1S,2S-DACH)(5,6-dimethyl-1,10-phenanthroline)] and Its PtIV Derivatives with Human Serum.

The discrepancy between the in vitro cytotoxic results and the in vivo performance of Pt56MeSS prompted us to look into its interactions and those of its PtIV derivatives with human serum (HS), human serum albumin (HSA), lipoproteins, and serum-supplemented cell culture media. The PtII complex, Pt56MeSS, binds noncovalently and reversibly to slow-tumbling proteins in HS and in cell culture media and interacts through the phenanthroline group with HSA, with a Kd value of ∼1.5×10-6 m. All PtIV complexes were found to be stable toward reduction in HS, but those with axial carboxylate ligands, cct-[Pt(1S,2S-DACH)(5,6-dimethyl-1,10-phenantroline)(acetato)2 ](TFA)2 (Pt56MeSS(OAc)2 ) and cct-[Pt(1S,2S-DACH)(5,6-dimehtyl-1,10-phenantroline)(phenylbutyrato)2 ](TFA)2 (Pt56MeSS(PhB)2 ), were spontaneously reduced at pH 7 or higher in phosphate buffer, but not in Tris buffer (pH 8). HS also decreased the rate of reduction by ascorbate of the PtIV complexes relative to the reduction rates in phosphate buffer, suggesting that for this compound class, phosphate buffer is not a good model for HS.

Synthesis, characterization and in vitro and in vivo anticancer activity of Pt(iv) derivatives of [Pt(1S,2S-DACH)(5,6-dimethyl-1,10-phenanthroline)].

This report describes the synthesis, characterization and biological activity of a series of platinum(iv) derivatives of [Pt(1S,2S-DACH)(5,6-dimethyl-1,10-phenanthroline)] (Pt56MeSS) with non-bioactive, lipophilic and bioactive axial ligands. In an attempt to explore the anticancer activity potential of the Pt(iv) derivatives, 2D and 3D cytotoxic screening and a preliminary in vivo study were performed. The average IC50 values of the platinum(iv) derivatives ranged from 1.26 to 5.39 µM, compared with 1.24 µM for Pt56MeSS, suggesting that the axial ligands have a relatively minor effect on the potency of the compounds. Preliminary in vivo studies indicate that the platinum(iv) derivatives of Pt56MeSS are active in vivo and can reduce the tumor to a similar extent to cisplatin.

Probing the interaction of bisintercalating (2,2':6',2″-terpyridine)platinum(II) complexes with glutathione and rabbit plasma.

Platinum(II) complexes have demonstrated considerable success in the treatment of cancer, but severe toxic side effects drive the search for new complexes with increased tumour selectivity and better efficacy. A critical concept that has to be considered in the context of designing novel Pt complexes is their interactions with biomolecules other than DNA. To this end, here the interactions of 16 previously reported bisintercalating (2,2':6',2″-terpyridine)platinum(II) complexes, [{Pt(terpy)}2µ-(X)]n+ (where X is a linker) with glutathione (GSH) by means of 1H and 195Pt NMR spectroscopy were investigated. The GSH half-life (GSH t1/2) was determined following the incubation of each [{Pt(terpy)}2µ-(X)]n+ complex with GSH (8mM). It was observed that complexes 1-7, 11, 12 and 14-16 reacted more rapidly than cisplatin, whereas complexes 8-10, 13 and 17 reacted more slowly (≥200min). There was no apparent correlation between linker length and the GSH t1/2. In order to understand these interactions, two complexes: 1 (t1/2<1min) and a previously studied 17 [Pt(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)] (56MESS) (GSH t1/2=4080min) were incubated with rabbit plasma. A "metallomics" approach was used to analyse plasma for all platinum species at the 5 and the 60min time point and provided results that were congruent with the reaction of the selected Pt complexes with GSH. Our studies demonstrate that the combined application of NMR spectroscopy, cytotoxicity studies and a metallomics approach can contribute to better understand the interaction of [{Pt(terpy)}2µ-(X)]n+ complexes with biomolecules to better assess which compounds may be advanced to in vivo studies.

The synthesis, characterisation and cytotoxicity of bisintercalating (2,2':6',2''-terpyridine)platinum(II) complexes.

Dinuclear (2,2':6',2''-terpyridine)platinum(II) (PtTerpy) complexes were synthesised by tethering either thiol or pyridine based linkers. All intermediates and resulting complexes were characterised using a combination of (1)H and (195)Pt NMR, two-dimensional (1)H correlation spectroscopy (NOSY/COSY), two-dimensional (1)H/(195)Pt heteronuclear multiple bond correlation spectroscopy (HMQC), elemental analysis and electrospray ionisation mass spectrometry (ESI-MS). The cytotoxicity of the complexes was determined against human A2780 ovarian carcinoma cells and its cisplatin-resistant sub-line A2780cis, as well as L1210 murine leukemia cells.

Combination studies of platinum(II)-based metallointercalators with buthionine-S,R-sulfoximine, 3-bromopyruvate, cisplatin or carboplatin.

With current chemotherapeutic treatment regimes often limited by adverse side effects, the synergistic combination of complexes with anticancer activity appears to offer a promising strategy for effective cancer treatment. This work investigates the anti-proliferative activity using a combination therapy approach where metallointercalators of the type [Pt(IL)(AL)](2+) (where IL is the intercalating ligand and AL is the ancillary ligand) are used in combination with currently approved anticancer drugs cisplatin and carboplatin and organic molecules buthionine-S,R-sulfoximine and 3-bromopyruvate. Synergistic relationships were observed, indicating a potential to decrease dose-dependent toxicity and improve therapeutic efficacy.

The effects of 56MESS on mitochondrial and cytoskeletal proteins and the cell cycle in MDCK cells.

BACKGROUND: 56MESS has been shown to be cytotoxic but the mode of this action is unclear. In order to probe the mechanism of action for 56MESS, MDCK cells were utilised to investigate the effect on treated cells. RESULTS: IC50 values for 56MESS and cisplatin in the MDCK cell line, determined by a SRB assay, were 0.25 ± 0.03 and 18 ± 1.2 µM respectively. In a preliminary study, cells treated with 56MESS displayed no caspase-3/7 activity, suggesting that the mechanism of action is caspase independent. Protein expression studies revealed an increase the expression in the MTC02 protein associated with mitochondria in cells treated with 56MESS and cisplatin. Non-synchronised 56MESS-treated cells caused an arrest in the G2/M phase of the cell cycle, in comparison to the S phase arrest of cisplatin. In G0/G1 synchronised cells, both 56MESS and cisplatin both appeared to arrest within the S phase. CONCLUSIONS: these results suggest that 56MESS is capable of causing cell-cycle arrest, and that mitochondrial and cell cycle proteins may be involved in the mode of action of cytotoxicity of 56MESS.