Correction: Simultaneous delivery of olaparib and carboplatin in PEGylated liposomes imparts this drug combination hypersensitivity and selectivity for breast tumor cells.

[This corrects the article DOI: 10.18632/oncotarget.25466.].

Simultaneous delivery of olaparib and carboplatin in PEGylated liposomes imparts this drug combination hypersensitivity and selectivity for breast tumor cells.

Combination regiments involving platinum anticancer drugs and agents with unrelated mechanisms of action are a subject of widespread interest. Here, we show that synergistic toxic action in cancer cells of combinations of antitumor platinum drug carboplatin and effective PARP inhibitor olaparib is considerably improved if these combined drugs are encapsulated into liposomes. Notably, the formation of such nano-formulations, called OLICARB, leads to a marked enhancement of activity in human cancer cell lines (including those resistant to conventional platinum antitumor drugs) and selectivity towards tumor cells. We used immunofluorescence analysis of γH2AX expression and examined DNA damage in cancerous cells treated with the investigated compounds. We find that the synergistic toxic effects in cancer cells of both drugs used in combination, nonencapsulated or embedded in the OLICARB nanoparticles, positively correlates with DNA damage. These results also suggest that the enhancement of the toxic effects of carboplatin by olaparib in cancer cells is a consequence of an accumulation of cytotoxic lesions in DNA due to the inhibition of repair of platinated DNA augmented by the synergistic action of olaparib as an effective PARP inhibitor. Our findings also reveal that the combination of olaparib with carboplatin encapsulated in the OLICARB nanoparticles is particularly effective to inhibit the growth of 3D mammospheres. Collectively, the data provide convincing evidence that the encapsulation of carboplatin and olaparib into liposomal constructs to form the OLICARB nanoparticles may represent the viable approach for the treatment of tumors with the aim to eliminate the possible effects of acquired resistance.

Enhancing Tumor Cell Response to Chemotherapy through the Targeted Delivery of Platinum Drugs Mediated by Highly Stable, Multifunctional Carboxymethylcellulose-Coated Magnetic Nanoparticles.

The fabrication of nanoparticles using different formulations, and which can be used for the delivery of chemotherapeutics, has recently attracted considerable attention. We describe herein an innovative approach that may ultimately allow for the selective delivery of anticancer drugs to tumor cells by using an external magnet. A conventional antitumor drug, cisplatin, has been incorporated into new carboxymethylcellulose-stabilized magnetite nanoparticles conjugated with the fluorescent marker Alexa Fluor 488 or folic acid as targeting agent. The magnetic nanocarriers possess exceptionally high biocompatibility and colloidal stability. These cisplatin-loaded nanoparticles overcome the resistance mechanisms typical of free cisplatin. Moreover, experiments aimed at the localization of the nanoparticles driven by an external magnet in a medium that mimics physiological conditions confirmed that this localization can inhibit tumor cell growth site-specifically.

Potentiation of mitochondrial dysfunction in tumor cells by conjugates of metabolic modulator dichloroacetate with a Pt(IV) derivative of oxaliplatin.

The molecular and cellular mechanisms of enhanced toxic effects in tumor cells of the Pt(IV) derivatives of antitumor oxaliplatin containing axial dichloroacetate (DCA) ligands were investigated. DCA ligands were chosen because DCA has shown great potential as an apoptosis sensitizer and anticancer agent reverting the Wartburg effect. In addition, DCA reverses mitochondrial changes in a wide range of cancers, promoting tumor cell apoptosis in a mitochondrial-dependent pathway. We demonstrate that (i) the transformation of oxaliplatin to its Pt(IV) derivatives containing axial DCA ligands markedly enhances toxicity in cancer cells and helps overcome inherent and acquired resistance to cisplatin and oxaliplatin; (ii) a significant fraction of the intact molecules of DCA conjugates with Pt(IV) derivative of oxaliplatin accumulates in cancer cells where it releases free DCA; (iii) mechanism of biological action of the Pt(IV) derivatives of oxaliplatin containing DCA ligands is connected with the effects of DCA released in cancer cells from the Pt(IV) prodrugs on mitochondria and metabolism of glucose; (iv) treatments with the Pt(IV) derivatives of oxaliplatin containing DCA ligands activate an autophagic response in human colorectal cancer cells; (v) the toxic effects in cancer cells of the Pt(IV) derivatives of oxaliplatin containing DCA ligands can be potentiated if cells are treated with these prodrugs in combination with 5-fluorouracil. These properties of the Pt(IV) derivatives of oxaliplatin containing DCA ligands provide opportunities for further development of new platinum-based agents with the capability of killing cancer cells resistant to conventional antitumor platinum drugs used in the clinic.

Internalization of Ineffective Platinum Complex in Nanocapsules Renders It Cytotoxic.

Anticancer therapy by platinum complexes, based on nanocarrier-based delivery, may offer a new approach to improve the efficacy and tolerability of the platinum family of anticancer drugs. The original rules for the design of new anticancer platinum drugs were affected by the fact that, although cisplatin (cis-[PtCl2 (NH3)2) was an anticancer drug, its isomer transplatin was not cytotoxic. For the first time, it is demonstrated that simple encapsulation of an inactive platinum compound in phospholipid bilayers transforms it into an efficient cytotoxic agent. Notably, the encapsulation of transplatin makes it possible to overcome the resistance mechanisms operating in cancer cells treated with cisplatin and prevents inactivation of transplatin in the extracellular environment. It is also shown that transplatin delivered to the cells in nanocapsules, in contrast to free (nonencapsulated) complex, forms cytotoxic cross-links on DNA.

New insights into the molecular and epigenetic effects of antitumor Pt(IV)-valproic acid conjugates in human ovarian cancer cells.

Substitutionally inert Pt(IV) prodrugs, combining bioactive axial ligands with Pt(IV) derivatives of antitumor Pt(II) compounds, represent a new generation of anticancer drugs. The rationale behind these prodrugs is to release, by reductive elimination inside the cancer cell, an active Pt(II) drug which binds nuclear DNA as well as bioactive ligands that may potentiate toxic effects of the Pt(II) drugs by an independent pathway. Platinum prodrugs, such as Pt(IV) derivatives of cisplatin containing axial valproic acid (VPA) ligands, destroy cancer cells with greater efficacy than conventional cisplatin. These axial ligands were chosen because VPA inhibits histone deacetylase (HDAC) activity, thereby decondensing chromatin and subsequently increasing the accessibility of DNA within chromatin to DNA-binding agents. We examined the mechanism of cytotoxic activity of Pt(IV) derivatives of cisplatin with VPA axial ligands. Particular attention was paid to the role of the VPA ligand in these Pt(IV) prodrugs in the mechanism underlying their toxic effects in human ovarian tumor cells. We demonstrate that (i) treatment of the cells with these prodrugs resulted in enhanced histone H3 acetylation and decondensation of heterochromatin markedly more effectively than free VPA; (ii) of the total Pt inside the cells, a considerably higher fraction of Pt from the Pt(IV)-VPA conjugates is bound to DNA than from the conjugates with biologically inactive ligands. The results indicate that the enhanced cytotoxicity of the Pt(IV)-VPA conjugates is a consequence of several processes involving enhanced cellular accumulation, downregulation of HDACs and yet other biochemical processes (not involving HDACs) which may potentiate antitumor effects.

The study of naphthoquinones and their complexes with DNA by using Raman spectroscopy and surface enhanced Raman spectroscopy: new insight into interactions of DNA with plant secondary metabolites.

Naphthoquinones represent the group of plant secondary metabolites with cytotoxic properties based on their ability to generate reactive oxygen species and interfere with the processes of cell respiration. Due to this fact, the possible cytotoxic mechanisms on cellular and subcellular levels are investigated intensively. There are many targets of cytotoxic action on the cellular level; however, DNA is a critical target of many cytotoxic compounds. Due to the cytotoxic properties of naphthoquinones, it is necessary to study the processes of naphthoquinones, DNA interactions (1,4-naphthoquinone, binapthoquinone, juglone, lawsone, plumbagin), especially by using modern analytical techniques. In our work, the Raman spectroscopy was used to determine the possible binding sites of the naphthoquinones on the DNA and to characterize the bond of naphthoquinone to DNA. Experimental data reveals the relationships between the perturbations of structure-sensitive Raman bands and the types of the naphthoquinones involved. The modification of DNA by the studied naphthoquinones leads to the nonspecific interaction, which causes the transition of B-DNA into A-DNA conformation. The change of the B-conformation of DNA for all measured DNA modified by naphthoquinones except plumbagin is obvious.

Antitumor platinum(IV) derivatives of oxaliplatin with axial valproato ligands.

We report new anticancer prodrugs, platinum(IV) derivatives of oxaliplatin conjugated with valproic acid (VPA), a well-known drug having histone deacetylase inhibitory activity. Like most platinum(IV) derivatives, the cytotoxicity of the conjugates was lower in cell culture than that of oxaliplatin, but greater than those of its Pt(IV) derivative containing biologically inactive axial ligands in several cancer cell lines. Notably, these conjugates display activity in both cisplatin sensitive- and resistant tumor cells capable of both markedly enhanced accumulation in tumor cells and acting in a dual threat manner, concurrently targeting histone deacetylase and genomic DNA. These results demonstrate the dual targeting strategy to be a valuable route to pursue in the design of platinum agents which may be more effective in cancer types that are typically resistant to therapy by conventional cisplatin. Moreover, platinum(IV) derivatives containing VPA axial ligands seem to be promising dual-targeting candidates for additional preclinical studies.

Conformation and recognition of DNA damaged by antitumor cis-dichlorido platinum(II) complex of CDK inhibitor bohemine.

A substitution of the ammine ligands of cisplatin, cis-[Pt(NH3)2Cl2], for cyclin dependent kinase (CDK) inhibitor bohemine (boh), [2-(3-hydroxypropylamino)-6-benzylamino-9-isopropylpurine], results in a compound, cis-[Pt(boh)2Cl2] (C1), with the unique anticancer profile which may be associated with some features of the damaged DNA and/or its cellular processing (Travnicek Z et al. (2003) J Inorg Biochem94, 307-316; Liskova B (2012) Chem Res Toxicol25, 500-509). A combination of biochemical and molecular biology techniques was used to establish mechanistic differences between cisplatin and C1 with respect to the DNA damage they produce and their interactions with critical DNA-binding proteins, DNA-processing enzymes and glutathione. The results show that replacement of the NH3 groups in cisplatin by bohemine modulates some aspects of the mechanism of action of C1. More specifically, the results of the present work are consistent with the thesis that, in comparison with cisplatin, effects of other factors, such as: (i) slower rate of initial binding of C1 to DNA; (ii) the lower efficiency of C1 to form bifunctional adducts; (iii) the reduced bend of longitudinal DNA axis induced by the major 1,2-GG intrastrand cross-link of C1; (iv) the reduced affinity of HMG domain proteins to the major adduct of C1; (v) the enhanced efficiency of the DNA adducts of C1 to block DNA polymerization and to inhibit transcription activity of human RNA pol II and RNA transcription; (vi) slower rate of the reaction of C1 with glutathione, may partially contribute to the unique activity of C1.

Insight into the toxic effects of cis-dichloridoplatinum(II) complexes containing 7-azaindole halogeno derivatives in tumor cells.

The cisplatin analogues cis-[PtCl2(3ClHaza)2] (1) and cis-[PtCl2(3IHaza)2] (2) (3ClHaza and 3IHaza are 3-chloro-7-azaindole and 3-iodo-7-azaindole, respectively) are quite toxic to ovarian tumor cells, with moderately better IC50 values than for cisplatin in the cisplatin-sensitive cell line A2780. We investigated potential factors which might be involved in the mechanism underlying the cytotoxic effects of 1 and 2 and compared these factors with those involved in the mechanism underlying the effects of conventional cisplatin. Our data indicate that the higher cytotoxicity of 1 and 2 originates mainly from their efficient cellular accumulation, different effects at the level of cell cycle regulation, and reduced propensity for DNA adduct repair. Studies of their reactivity toward cellular components reveal efficient binding to DNA, which is typically required for an active platinum drug. Further results suggest that 1 and 2 are capable of circumventing resistance to cisplatin induced by alterations in cellular accumulation and DNA repair. Hence, the latter two factors appear to be responsible for differences in the toxicity of 1 or 2, and cisplatin in tumor cells. The results of this work reinforce the idea that direct analogues of conventional cisplatin-containing halogeno-substituted 7-azaindoles offer much promise for the design of novel therapeutic agents.

Unique DNA binding mode of antitumor trinuclear tridentate platinum(II) compound.

The new trinuclear tridentate Pt(II) complex [Pt(3)Cl(3)(hptab)](3+) (1; hptab = N,N,N',N',N'',N''-hexakis(2-pyridylmethyl)-1,3,5-tris(aminomethyl)benzene) exhibits promising cytotoxic effects in human and mouse tumor cells including those resistant to conventional cisplatin (Dalton Trans. 2006, 2617; Chem. Eur. J. 2009, 15, 5245). The present study is focused on the molecular pharmacology of 1, in particular on its interactions with DNA (which is the major pharmacological target of platinum antitumor drugs), to elucidate more deeply the mechanism underlying its antitumor effects. Results obtained with the aid of methods of molecular biophysics and pharmacology reveal new details of DNA modifications by 1. Complex 1 binds to DNA forming in the absence of proteins and molecular crowding agents mainly trifunctional intrastrand cross-links. In these DNA adducts all three Pt(II) centers of 1 are coordinated to DNA base residues, which leads to extensive conformational alterations in DNA. An intriguing aspect of the DNA-binding mode of this trinuclear Pt(II) complex 1 is that it can cross-link proteins to DNA. Even more interestingly, 1 can cross-link in the presence of molecular crowding agent, which mimics environmental conditions in cell nucleus, two DNA duplexes in a high yield--a feature observed for the first time for antitumor trinuclear platinum complexes. Thus, the concept for the design of agents capable of forming intramolecular tridentate DNA adducts, DNA-protein and interduplex DNA-DNA cross-links based on trinuclear tridentate Pt(II) complexes with semirigid aromatic linkers may result in new compounds which exhibit a variety of biological effects and can be also useful in nucleic acids research.

Organometallic half-sandwich iridium anticancer complexes.

The low-spin 5d(6) Ir(III) organometallic half-sandwich complexes [(η(5)-Cp(x))Ir(XY)Cl](0/+), Cp(x) = Cp*, tetramethyl(phenyl)cyclopentadienyl (Cp(xph)), or tetramethyl(biphenyl)cyclopentadienyl (Cp(xbiph)), XY = 1,10-phenanthroline (4-6), 2,2'-bipyridine (7-9), ethylenediamine (10 and 11), or picolinate (12-14), hydrolyze rapidly. Complexes with N,N-chelating ligands readily form adducts with 9-ethylguanine but not 9-ethyladenine; picolinate complexes bind to both purines. Cytotoxic potency toward A2780 human ovarian cancer cells increases with phenyl substitution on Cp*: Cp(xbiph) > Cp(xph) > Cp*; Cp(xbiph) complexes 6 and 9 have submicromolar activity. Guanine residues are preferential binding sites for 4-6 on plasmid DNA. Hydrophobicity (log P), cell and nucleus accumulation of Ir correlate with cytotoxicity, 6 > 5 > 4; they distribute similarly within cells. The ability to displace DNA intercalator ethidium bromide from DNA correlates with cytotoxicity and viscosity of Ir-DNA adducts. The hydrophobicity and intercalative ability of Cp(xph) and Cp(xbiph) make a major contribution to the anticancer potency of their Ir(III) complexes.

Different features of the DNA binding mode of antitumor cis-amminedichlorido(cyclohexylamine)platinum(II) (JM118) and cisplatin in vitro.

cis-Amminedichlorido(cyclohexylamine)platinum(II) (JM118) is an antitumor Pt(II) analogue of cisplatin exhibiting considerably higher activity than cisplatin in human tumor cells. JM118 is also the major metabolite of the first orally administered Pt(IV) drug satraplatin. In an effort to design improved platinum antitumor agents, it is important to elucidate the biochemical factors that affect the cytotoxic properties of existing platinum drugs. Since DNA is considered the major pharmacological target of platinum drugs, the objective in the present work was to understand more fully the DNA binding mode of antitumor JM118. We examined the rate of aquation of the first chloride of bifunctional JM118 and found that it was considerably lower than that of cisplatin; consequently, the rate of the reaction of JM118 with DNA was lower compared to cisplatin. The influence of global modification by JM118 and its major site-specific adducts on DNA conformation by biochemical methods was investigated as well. While examination of the global modification revealed in several cases no substantial differences in the lesions induced by JM118 and cisplatin, DNA bending due to the 1,2-GG intrastrand adduct of JM118 was lower than that of cisplatin. The bending angles afforded by the adducts of JM118 were only slightly affected by the orientation of the cyclohexylamine ligand toward the 3' or 5' direction of the duplex. We also used in vitro assays that make it possible to monitor DNA repair synthesis by cell-free extracts and DNA-protein cross-linking to probe properties of DNA adducts of JM118. These results showed a higher DNA-protein cross-linking efficiency of JM118 and a less efficient removal from DNA of the adducts of JM118 in comparison with cisplatin. Thus, the results of the present work provide additional evidence that DNA binding of JM118 is in several aspects different from that of conventional cisplatin.

Conformation and recognition of DNA modified by a new antitumor dinuclear PtII complex resistant to decomposition by sulfur nucleophiles.

Reported herein is a detailed biochemical and molecular biophysics study of the molecular mechanism of action of antitumor dinuclear Pt(II) complex [{PtCl(DACH)}(2)-mu-Y](4+) [DACH=1,2-diaminocyclohexane, Y=H(2)N(CH(2))(6)NH(2)(CH(2))(2)NH(2)(CH(2))(6)NH(2)] (complex 1). This new, long-chain bifunctional dinuclear Pt(II) complex is resistant to metabolic decomposition by sulfur-containing nucleophiles. The results show that DNA adducts of 1 can largely escape repair and yet inhibit very effectively transcription so that they should persist longer than those of conventional cisplatin. Hence, they 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. In addition, the findings of the present work make new insights into mechanisms associated with antitumor effects of dinuclear/trinuclear Pt(II) complexes possible.

Cytotoxicity, cellular uptake, glutathione and DNA interactions of an antitumor large-ring Pt II chelate complex incorporating the cis-1,4-diaminocyclohexane carrier ligand.

Earlier studies have described promising antitumor activity of a large-ring chelate complex [PtCl(2)(cis-1,4-DACH)] (DACH=diaminocyclohexane). Encouraging antitumor activity of this analogue of cisplatin prompted us to perform studies focused on the mechanistic basis of pharmacological effects of this complex. Four early steps in the mechanism of biological activity of cisplatin have been delineated: cell entry, reactions with sulfur-containing compounds, platinum-DNA binding along with processing platinated DNA by proteins (enzymes) and DNA repair. Here, we describe comparative experiments (involving also cisplatin) revealing: (i) improved cytotoxicity (3.4-5.4-fold) of [PtCl(2)(cis-1,4-DACH)] in human tumor ovarian cell lines; (ii) enhanced cellular uptake (approximately 1.5-fold) of [PtCl(2)(cis-1,4-DACH)]; (iii) somewhat enhanced rate of reactions of [PtCl(2)(cis-1,4-DACH)] with glutathione (approximately 1.5-fold), but a similar rate of reactions with metallothionenin-2; (iv) enhanced rate of DNA binding of [PtCl(2)(cis-1,4-DACH)] in cell-free media (approximately 2-fold); (v) similar sequence preference of DNA binding of [PtCl(2)(cis-1,4-DACH)] in cell-free media; (vi) identical DNA interstrand cross-linking efficiency (6%); (vii) similar bending (32 degrees) and enhanced local unwinding (approximately 1.5-fold) induced in DNA by the major 1,2-GG-intrastrand cross-link; (viii) markedly enhanced inhibiting effects of DNA adducts of [PtCl(2)(cis-1,4-DACH)] on processivity of DNA polymerase; and (ix) a slightly lower efficiency of DNA repair systems to remove the adducts of [PtCl(2)(cis-1,4-DACH)] from DNA.

Mechanistic studies of the modulation of cleavage activity of topoisomerase I by DNA adducts of mono- and bi-functional PtII complexes.

Using electrophoresis and replication mapping, we show that the presence of DNA adducts of bifunctional antitumor cisplatin or monodentate [PtCl(dien)]Cl (dien = diethylenetriamine) in the substrate DNA inhibits eukaryotic topoisomerase 1 (top1) action, the adducts of cisplatin being more effective. The presence of camptothecin in the samples of platinated DNA markedly enhances effects of Pt-DNA adducts on top1 activity. Interestingly, the effects of Pt-DNA adducts on the catalytic activity of top1 in the presence of camptothecin differ depending on the sequence context. A multiple metallation of the short nucleotide sequences on the scissile strand, immediately downstream of the cleavage site impedes the cleavage by top1. On the other hand, DNA cleavage by top1 at some cleavage sites which were not platinated in their close proximity is notably enhanced as a consequence of global platination of DNA. We suggest that this enhancement of DNA cleavage by top1 may consist in its inability to bind to other cleavage sites platinated in their close neighborhood; thus, more molecules of top1 may become available for cleavage at the sites where top1 normally cleaves and where platination does not interfere.

Investigation of the in vitro metabolism of the analgesic flupirtine.

The in vitro metabolism of flupirtine, ethyl-N-[2-amino-6-(4-fluorophenylmethyl-amino)pyridine-3-yl]carbamate, a centrally acting analgesic with muscle tone-reducing activity, was studied. Two flupirtine metabolites were already known: the N-acetylated analog D13223 and 4-fluorohippuric acid. The structure of flupirtine suggested that redox chemistry may play a role in metabolism, and cyclic voltammetry studies showed that the drug undergoes facile and irreversible redox reactions. Thus, oxidative metabolism was investigated first. With CYP3A1-induced rat liver microsomes an 18% turnover of flupirtine and a 20 to 25% turnover of D13223 took place over 30 min, but less than 5% turnover of flupirtine was observed with all human liver microsomal preparations tested, evidence that cytochrome P450 does not contribute appreciably to the metabolism in humans. Likewise, no involvement of human monoamine oxidase (isoforms A and B) was found for either flupirtine or D13223. In contrast, flupirtine was an excellent substrate for both human myeloperoxidase and horse radish peroxidase (HRP). These enzymes produced detectable amounts of oxidation products. Incubations of flupirtine with HRP produced an oxidation product that could be trapped with glutathione, the resulting glutathione conjugate was characterized by mass spectrometry and NMR. Metabolism of D13223 by both peroxidases was also observed but to a much lesser extent. Porcine liver esterases cleave the carbamate group of flupirtine, and both human N-acetyltransferases 1 and 2 acetylated the hydrolysis product, presumably descarboethoxyflupirtine, with nearly equal efficiencies to yield D13223. Incubations of human liver microsomes with flupirtine or the metabolite D13223 together with UDP-glucuronic acid gave two isomeric N-glucuronides in both cases.

Cytotoxicity, cellular uptake, and DNA interactions of new monodentate ruthenium(II) complexes containing terphenyl arenes.

We have compared the cancer cell cytotoxicity, cell uptake, and DNA binding properties of the isomeric terphenyl complexes [(eta(6)-arene)Ru(en)Cl](+), where the arene is ortho- (2), meta- (3), or para-terphenyl (1) (o-, m-, or p-terp). Complex 1, the X-ray crystal structure of which confirms that it has the classical "piano-stool" geometry, has a similar potency to cisplatin but is not cross-resistant and has a much higher activity than 2 or 3. The extent of Ru uptake into A2780 or A2780cis cells does not correlate with potency. Complex 1 binds to DNA rapidly and quantitatively, preferentially to guanine residues, and causes significant DNA unwinding. Circular and linear dichroism, competitive binding experiments with ethidium bromide, DNA melting, and surface-enhanced Raman spectroscopic data are consistent with combined intercalative and monofunctional (coordination) binding mode of complex 1. This unusual DNA binding mode may therefore make a major contribution to the high potency of complex 1.

Amide-based prodrugs of spermidine-bridged dinuclear platinum. Synthesis, DNA binding, and biological activity.

The chemistry and biology of acetyl-protected spermidine-bridged dinuclear platinum complexes [{ trans-PtCl(NH 3) 2] 2-mu-NH 2(CH 2) 3N(COR)(CH 2) 4NH 2]X 2 (R = H, X = Cl (1,1/t,t-spermidine, BBR3571); R = CH 3 , X = Cl ( 2); R = CH 2 Cl, X = ClO 4 ( 3); R = CF 3 , X = Cl ( 4)) are compared with their carbamate analogues. The compounds are potential prodrugs for the parent compound 1, a highly potent antitumor agent. At pH 6-8 hydrolysis of the blocking group with the release of the "parent" protonated species follows the order 4 > 3 >> 2. For 4, rate constants for the deprotection increase in this pH range. The DNA binding profile of 4 is similar to the Boc derivative, confirming the central influence of charge on DNA binding properties. The differences in cytotoxicity for the protected compounds in ovarian carcinoma cell lines sensitive and resistant to cisplatin cannot completely be explained by spontaneous release of 1,1/t,t-spermidine at physiological pH. Inherent cytotoxicity and cell line specificity may contribute to the observed behavior. The properties of the compounds present them also as possible "second-generation" analogues of the clinically relevant trinuclear complex [{ trans-PtCl(NH 3) 2} 2-mu- trans-Pt(NH 3) 2(NH 2(CH 2) 6NH 2) 2](NO 3) 4, ( 8, BBR3464).

Synthesis, biophysical studies, and antiproliferative activity of platinum(II) complexes having 1,2-bis(aminomethyl)carbobicyclic ligands.

A selected chemical library of six platinum(II) complexes having 1,2-bis(aminomethyl)carbobicyclic ligands were synthesized after a rational design in order to evaluate their antiproliferative activity and the structure-activity relationships. The cytotoxicity studies were performed using cancer cell lines sensitive (A2780) and resistant (A2780R) to cisplatin. Excellent cytotoxicity was observed for most of complexes, which presented better resistance factors than cisplatin against the A2780R cell line. The interaction of these complexes with DNA, as the target biomolecule, was evaluated by several methods: DNA-platinum binding kinetics, changes in the DNA melting temperature, evaluation of the unwinding angle of supercoiled DNA, evaluation of the interstrand cross-links, and replication mapping. The kinetics of the interaction with glutathione was also investigated to better understand the resistant factors observed for the new complexes.