Influence of pyridine versus piperidine ligands on the chemical, DNA binding and cytotoxic properties of light activated trans,trans,trans-[Pt(N3)2(OH)2(NH3)(L)]

The photocytotoxicity and photobiochemical properties of the new complex trans, trans, trans-[Pt(N3)2(OH)2(NH3)(piperidine)] (5) are compared with its analogue containing the less basic and less lipophilic ligand pyridine (4). The log P (n-octanol/water) values were of -1.16 and -1.84 for the piperidine and pyridine complexes, respectively, confirmed that piperidine increases the hydrophobicity of the complex. DFT and TDDFT calculations indicate that 5 has accessible singlet and triplet states which can promote ligand dissociation when populated by both UVA and visible white light. When activated by UVA or white light, both compounds showed similar cytotoxic potencies in various human cancer cell lines although their selectivity was different. The time needed to reach similar antiproliferative activity was noticeably decreased by introducing the piperidine ligand. Neither compound showed cross-resistance in three oxoplatin-resistant cell lines. Furthermore, both compounds showed similar anticlonogenic activity when activated by UVA radiation. Interactions of the light-activated complexes with DNA showed similar kinetics and levels of DNA platination and similar levels of DNA interstrand cross-linking (ca. 5 %). Also the ability to unwind double stranded DNA where comparable for the piperidine analogue (24°, respectively), while the piperidine complex showed higher potency in changing the conformation of DNA, as measured in an ethidium bromide binding assay. These results indicate that the nature of the heterocyclic nitrogen ligand can have subtle influences on both the phototoxicity and photobiochemistry of this class of photochemotherapeutic agents

Structure-activity relationships of novel heteroaryl-acrylonitriles as cytotoxic and antibacterial agents.

Eighteen new 2,6-disubstituted acrylonitriles and two new (benzimidazol-1-yl)-acetamide derivatives were prepared and screened for antibacterial and cytotoxic activities on 12 human cancer cell lines. Based on the lead structure 2-(benzimidazol-2-yl)-3-(5-nitrothiophen-2-yl) acrylonitrile it was found that placement of methyl groups at the 5,6 positions of the benzimidazole ring lead to a 3-fold increase in overall cytotoxic activity. Replacing the nitrothiophene for pyridine reduced cytotoxic activity as did replacing the nitro group for a methoxy group. Cytotoxic activity was only slightly reduced when the benzimidazole ring was replaced by a imidazo[4,5-b]pyridine or a benzthiazole ring but replacement by benzoxazole led to a substantial decrease in activity. Moving the acrylonitrile group from position 2 to position 1 of the benzimidazole ring also resulted in moderately active compounds. (Benzimidazol-1-yl)acetamides showed only modest activity. The structure-activity relationships found in the cytotoxicity studies are mirrored in the results of the antibacterial experiments