Interactions of DNA with a new Platinum(IV) Azide Dipyridine complex activated by UVA and visible light : relationship to toxicity in tumor cells

The Pt IV diazido complex trans,trans,trans-[Pt(N 3) 2(OH) 2(pyridine) 2] (1) is unreactive in the dark but is cytotoxic when photoactivated by UVA and visible light. We have shown that 1 when photoactivated accumulates in tumor cells and binds strongly to nuclear DNA under conditions in which it is toxic to tumor cells. The nature of the DNA adducts, including conformational alterations, induced by photoactivated 1 are distinctly different from those produced in DNA by conventional cisplatin or transplatin. In addition, the observation that major DNA adducts of photoactivated 1 are able to efficiently stall RNA polymerase II more efficiently than cisplatin suggests that transcription inhibition may contribute to the cytotoxicity levels observed for photoactivated 1. Hence, DNA adducts of 1 could trigger a number of downstream cellular effects different from those triggered in cancer cells by DNA adducts of cisplatin. This might lead to the therapeutic effects that could radically improve chemotherapy by platinum complexes. The findings of the present work help to explain the different cytotoxic effects of photoactivated 1 and conventional cisplatin and thereby provide new insights into mechanisms associated with the antitumor effects of platinum complexes photoactivated by UVA and visible light. © 2012 American Chemical Society

Study of Copper and Purine-Copper Complexes on Modified Carbon Electrodes by Cyclic and Elimination Voltammetry

Using a paraffin impregnated graphite electrode (PIGE) and mercury-modifiedpyrolytic graphite electrode with basal orientation (Hg-PGEb) copper(II) and Cu(II)-DNApurine base solutions have been studied by cyclic (CV) and linear sweep voltammetry(LSV) in connection with elimination voltammetry with linear scan (EVLS). In chlorideand bromide solutions (pH 6), the redox process of Cu(II) proceeded on PIGE with twocathodic and two anodic potentially separated signals. According to the eliminationfunction E4, the first cathodic peak corresponds to the reduction Cu(II) e- → Cu(I) withthe possibility of fast disproportionation 2Cu(I) → Cu(II) Cu(0). The E4 of the secondcathodic peak signalized an electrode process controlled by a surface reaction. Theelectrode system of Cu(II) on Hg-PGEb in borate buffer (pH 9.2) was characterized by onecathodic and one anodic peak. Anodic stripping voltammetry (ASV) on PIGE and cathodicstripping voltammetry (CSV) on Hg-PGEb were carried out at potentials where thereduction of copper ions took place and Cu(I)-purine complexes were formed. By usingASV and CSV in combination with EVLS, the sensitivity of Cu(I)-purine complexdetection was enhanced relative to either ASV or CSV alone, resulting in higher peakcurrents of more than one order of magnitude. The statistical treatment of CE data wasused to determine the reproducibility of measurements. Our results show that EVLS inconnection with the stripping procedure is useful for both qualitative and quantitativemicroanalysis of purine derivatives and can also reveal details of studied electrodeprocesses

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

Valuable Insight into the Anticancer Activity of the Platinum-Histone Deacetylase Inhibitor Conjugate, <i>cis</i>-[Pt(NH₃)₂malSAHA_–2H)]

<i>cis</i>-[Pt^II(NH₃)₂(malSAHA_–2H)], a cisplatin adduct conjugated to a potent histone deacetylase inhibitor (HDACi), suberoylanilide hydroxamic acid (SAHA), was previously developed as a potential anticancer agent. This Pt–HDACi conjugate was demonstrated to have comparable cytotoxicity to cisplatin against A2780 ovarian cancer cells but significantly reduced cytotoxicity against a representative normal cell line, NHDF. Thus, with a view to (i) understanding more deeply the effects that may play an important role in the biological (pharmacological) properties of this new conjugate against cancer cells and (ii) developing the next generation of Pt–HDACi conjugates, the cytotoxicity, DNA binding, cellular accumulation and HDAC inhibitory activity of <i>cis</i>-[Pt^II(NH₃)₂(malSAHA_–2H)] were investigated and are reported herein. <i>cis</i>-[Pt^II(NH₃)₂(malSAHA_–2H)] was found to have marginally lower cytotoxicity against a panel of cancer cell lines as compared to cisplatin and SAHA. <i>cis</i>-[Pt^II(NH₃)₂(malSAHA_–2H)] was also found to accumulate better in cancer cells but bind DNA less readily as compared to cisplatin. DNA binding experiments indicated that c<i>is</i>-[Pt^II(NH₃)₂(malSAHA_–2H)] bound DNA more effectively in cellulo as compared to in cell-free media. Activation of the Pt–HDACi conjugate was therefore investigated. The binding of c<i>is</i>-[Pt^II(NH₃)₂(malSAHA_–2H)] to DNA was found to be enhanced by the presence of thiol-containing molecules such as glutathione and thiourea, and activation occurred in cytosolic but not nuclear extract of human cancer cells. The activity of <i>cis</i>-[Pt­(NH₃)₂(malSAHA_–2H)] as a HDAC inhibitor was also examined; the conjugate exhibited no inhibition of HDAC activity in CH1 cells. In light of these results, novel Pt–HDACi conjugates are currently being developed, with particular emphasis, through subtle structural modifications, on enhancing the rate of DNA binding and enhancing HDAC inhibitory activity

Differences in the cellular response and signaling pathways between cisplatin and monodentate organometallic Ru(II) antitumor complexes containing a terphenyl ligand

The new monofunctional Ru(II)-arene complex [(η6-arene)Ru(II)(en)Cl]+, where en = 1,2-diaminoethane and the arene is para-terphenyl (complex 1) exhibits promising cytotoxic effects in human tumor cells including those resistant to conventional cisplatin (J. Med. Chem.2008, 51, 5310). The present study is focused on the cellular pharmacology of 1 to elucidate more deeply the mechanisms underlying its antitumor effects. We have identified several cellular mechanisms induced by 1 in human ovarian carcinoma cells, including inhibition of DNA synthesis, overexpression and activation of p53, expression of proapoptotic proteins p21WAF1 and Bax, G0/G1 arrest, and nuclear fragmentation as a result of apoptotic, and, to a much lower extent, also necrotic processes. Thus, 1 inhibits growth of the cancer cells through induction of apoptotic cell death and G0/G1 cell cycle arrest. Further investigations have shown that 1 induces apoptosis by regulating the expression of Bcl-2 family proteins. There were significant differences in cellular responses to the treatment with 1 and with conventional cisplatin, particularly in the kinetics and the extent of these responses. In addition, the distinct p53 activation profile of 1 compared with cisplatin provides an explanation for the activity of this ruthenium drug against cisplatin-resistant cells. Hence complex 1 may provide an alternative therapy in patients with acquired cisplatin resistance, particularly with respect to its very low mutagenicity and different mode of action compared to platinum antitumor drugs in clinical use