Cationic FeII Triplex-Forming Metallohelices as DNA Bulge Binders.

Bulges are essential structural elements in nucleic acids. The detection and targeting of bulged DNA sequences are highly important. Small molecules capable of targeting DNA bulges have attracted considerable attention because they cannot only be used as reagents for bulge recognition, but also as potential therapeutic drugs. Herein, the interactions of DNA duplexes, containing bulges of various sizes and base compositions, with a series of FeII triplex-forming metallohelices are reported. The results obtained, with the aid of molecular biophysics methods, show that the investigated metallohelices prefer to bind to bulged DNA, rather than double-stranded DNA, and that their binding affinities towards bulges differ among individual metallohelices. Moreover, their binding affinities towards bulges strongly depend on the bulge size and the base composition of the bulge loop. The investigated metallohelices can enter eukaryotic cells and accumulate in the cell nucleus, allowing them to interact with nucleic acids. Hence, it is reasonable to suggest that the interaction of metallohelices with nucleic acid bulges might contribute to the mechanism of their biological activity.

cis-Pt I2(NH3)2: a reappraisal.

The investigation of cis-PtI2(NH3)2, the diiodido analogue of cisplatin (cisPtI2 hereafter), has been unjustly overlooked so far mainly because of old claims of pharmacological inactivity. Some recent - but still fragmentary - findings prompted us to reconsider more systematically the chemical and biological profile of cisPtI2 in comparison with cisplatin. Its solution behaviour, interactions with DNA and cytotoxic properties versus selected cancer cell lines were thus extensively analysed through a variety of biophysical and computational methods. Notably, we found that cisPtI2 is highly cytotoxic in vitro toward a few solid tumour cell lines and that its DNA platination pattern closely reproduces that of cisplatin; cisPtI2 is also shown to completely overcome resistance to cisplatin in a platinum resistant cancer cell line. The differences in the biological actions of these two Pt complexes are most likely related to slight but meaningful differences in their solution behaviour and reactivity. Overall, a very encouraging and unexpected pharmacological profile emerges for cisPtI2 with relevant implications both in terms of mechanistic knowledge and of prospective clinical application. An ab initio DFT study is also included to support the interpretation of the solution behaviour of cisPtI2 under physiological and slightly acidic pH conditions.