Cisplatin and zoledronic acid: two drugs combined in a Pt(II) complex with potential antitumor activity towards bone tumors and metastases.

Treatment of primary bone malignancies comprises surgery, radiotherapy, chemotherapy, and analgesics. Platinum-based chemotherapeutics, such as cisplatin, are commonly used for the treatment of bone cancer but, despite their success, outcomes are limited by toxicity and resistance. Recently, dinuclear Pt complexes with a bridging geminal bisphosphonate ligand proved to be endowed with selective accumulation in bone tumors or metastases leading to improved efficacy and reduced systemic toxicity. Further improvement could be expected by the use of a bisphosphonate ligand with intrinsic pharmacological activity such as zoledronic acid (ZL). In the present work is reported the synthesis and full characterization of the dinuclear Pt(II) complex [{cis-Pt(NH3)2}2(ZL)]HSO4 which combines two drugs with antitumor activity, cisplatin and zoledronic acid. Both drugs, individually, are already approved by the U.S. Food and Drug Administration and the European Medicinal Agency for clinical use. The in vitro cytotoxicity of the new Pt(II)-ZL complex has been tested against a panel of human tumor cell lines.

Improvement of Kiteplatin Efficacy by a Benzoato Pt(IV) Prodrug Suitable for Oral Administration.

Kiteplatin, [PtCl2(cis-1,4-DACH)] (DACH = diaminocyclohexane), contains an isomeric form of the oxaliplatin diamine ligand trans-1R,2R-DACH and has been proposed as a valuable drug candidate against cisplatin- and oxaliplatin-resistant tumors, in particular, colorectal cancer. To further improve the activity of kiteplatin, it has been transformed into a Pt(IV) prodrug by the addition of two benzoato groups in the axial positions. The new compound, cis,trans,cis-[PtCl2(OBz)2(cis-1,4-DACH)] (1; OBz = benzoate), showed cytotoxic activity at nanomolar concentration against a wide panel of human cancer cell lines. Based on these very promising results, the investigation has been extended to the in vivo activity of compound 1 in a Lewis Lung Carcinoma (LLC) model and its suitability for oral administration. Compound 1 resulted to be remarkably stable in acidic conditions (pH 1.5 to mimic the stomach environment) undergoing a drop of the initial concentration to ~60% of the initial one only after 72 h incubation at 37 °C; thus resulting amenable for oral administration. Interestingly, in a murine model (2·106 LLC cells implanted i.m. into the right hind leg of 8-week old male and female C57BL mice), a comparable reduction of tumor mass (~75%) was observed by administering compound 1 by oral gavage and the standard drug cisplatin by intraperitoneal injection, thus indicating that, indeed, there is the possibility of oral administration for this dibenzoato prodrug of kiteplatin. Moreover, since the mechanism of action of Pt(IV) prodrugs involves an initial activation by chemical reduction to cytotoxic Pt(II) species, the reduction of 1 by two bioreductants (ascorbic acid/sodium ascorbate and glutathione) was investigated resulting to be rather slow (not complete after 120 h incubation at 37 °C). Finally, the neurotoxicity of 1 was evaluated using an in vitro assay.

MRSA in swine, farmers and abattoir workers in Southern Italy.

Methicillin-resistant Staphylococcus aureus (MRSA) is an important medical issue, since it causes serious and sometimes fatal infections in humans. Intensively reared swine may serve as reservoirs for MRSA that can infect swine workers, and also consumers (via contaminated meat). In this study, MRSA strains were isolated from 55 of the 85 (64.7%) intensive pig farms surveyed, and prevalence was greater on pig fattening farms than on breeding farms. In addition, we included in the study 63 foreign pigs imported for slaughter. Overall, the prevalence of MRSA in the 418 sampled swine was 59.1%; 12 genotypes were identified among the isolates; ST398 (96.4%) was most prevalent, followed by ST97 (2%), ST9 (0.8%) and ST1 (0.8%). MRSA isolates were also detected in 26 (17.3%) of the 150 operators included in the study; the genotypes detected were ST398 (85%), ST9 (7.6%), ST5 (3.8%) and ST1 (3.8%). All the strains were pvl negative and pia positive. Both swine and human strains displayed a multi-resistance pattern, and almost all were resistant to tetracycline. The results obtained in this study confirm the high prevalence of MRSA in swine reared and slaughtered in Italy, and underline the public health risk linked to the spread of antimicrobial-resistant Staphylococcus aureus among intensively reared pigs.

High Occurrence of Methicillin-Resistant Staphylococcus aureus in Horses at Slaughterhouses Compared with Those for Recreational Activities: A Professional and Food Safety Concern?

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in horses and its zoonotic potential is poorly understood. The objective of this study is to provide data on the prevalence and genetic characteristics of MRSA isolated from horses on farms, at racecourses, and at slaughterhouses in Italy, using standard and molecular methods. In addition, we report the prevalence of MRSA in horse handlers. Among 388 horses tested by nasal swabs, 27 (7%) were positive for MRSA ST398 (t011, t899, t1255) and ST1 (t127). The prevalence of MRSA in horses tested at slaughterhouses was significantly higher (p < 0.001) compared with those tested on farms and racecourses. Five (7%) out of 67 staff members working in close contact with horses (2 from slaughterhouse, 2 from riding stable, and 1 from racecourse) were carriers of MRSA ST398 (t011, t034) and ST1 (t127). The isolates from horses and humans carried SCCmec IVa or V and were pvl negative and pia positive. All the isolates from both horses and humans were resistant to at least two antimicrobial classes. The circulation of MRSA in horses and in humans working in close contact with them should be considered an emerging public health issue. In fact, it represents a potential risk for people who work in close contact with horses, and for horse meat consumers.

Novel Antitumor Platinum(II) Conjugates Containing the Nonsteroidal Anti-inflammatory Agent Diclofenac: Synthesis and Dual Mechanisms of Antiproliferative Effects.

One concept how to improve anticancer effects of conventional metallodrugs consists in conjugation of these compounds with other biologically (antitumor) active agents, acting by a different mechanism. Here, we present synthesis, biological effects, and mechanisms of action of new Pt(II) derivatives containing one or two nonsteroidal anti-inflammatory diclofenac (DCF) ligands also known for their antitumor effects. The antiproliferative properties of these metallic conjugates show that these compounds are potent and cancer cell selective cytotoxic agents exhibiting activity in cisplatin resistant and the COX-2 positive tumor cell lines. One of these compounds, compound 3, in which DCF molecules are coordinated to Pt(II) through their carboxylic group, is more potent than parental conventional Pt(II) drug cisplatin, free DCF and the congeners of 3 in which DCF ligands are conjugated to Pt(II) via a diamine. The potency of 3 is due to several factors including enhanced internalization that correlates with enhanced DNA binding and cytotoxicity. Mechanistic studies show that 3 combines multiple effects. After its accumulation in cells, it releases Pt(II) drug capable of binding/damaging DNA and DCF ligands, which affect distribution of cells in individual phases of the cell cycle, inhibit glycolysis and lactate transport, collapse mitochondrial membrane potential, and suppress the cellular properties characteristic of metastatic progression.

Anticancer potential of a photoactivated transplatin derivative containing the methylazaindole ligand mediated by ROS generation and DNA cleavage.

The limitations associated with the clinical utility of conventional platinum anticancer drugs have stimulated research leading to the design of new metallodrugs with improved pharmacological properties, particularly with increased selectivity for cancer cells. Very recent research has demonstrated that photoactivation or photopotentiation of platinum drugs can be one of the promising approaches to tackle this challenge. This is so because the application of irradiation can be targeted exclusively to the tumor tissue so that the resulting effects could be much more selective and targeted to the tumor. We show in this work that the presence of 1-methyl-7-azaindole in trans-[PtCl2(NH3)(L)] (L = 1-methyl-7-azaindole, compound 1) markedly potentiated the DNA binding ability of 1 when irradiated by UVA light in a cell-free medium. Concomitantly, the formation of cytotoxic bifunctional cross-links was markedly enhanced. In addition, 1, when irradiated with UVA, was able to effectively cleave the DNA backbone also in living cells. The incorporation of 1-methyl-7-azaindole moiety had also a profound effect on the photophysical properties of 1, which can generate singlet oxygen responsible for the DNA cleavage reaction. Finally, we found that 1, upon irradiation with UVA light, exhibited a pronounced dose-dependent decrease in viability of A2780 cells whereas it was markedly less cytotoxic if the cells were treated in the absence of light. Hence, it is possible to conclude that 1 is amenable to photodynamic therapy.

Folate-Cyclodextrin Conjugates as Carriers of the Platinum(IV) Complex LA-12.

Folic acid has emerged as an interesting cell-targeting moiety and a number of drugs have been conjugated to folate. In this context, new conjugates of ß-cyclodextrins with folate have been synthesised as drug carriers to improve their selectivity for cells overexpressing the folic acid receptor. In particular, both 3- and 6-functionalised ß-cyclodextrins, linked to the α- or γ-carboxylic group of folic acid, have been synthesised and fully characterised. As a proof of concept, the antitumour platinum(IV) complex cis-trans-cis-[PtCl2 (CH3 CO2 )2 (adamantylamine)(NH3 )] (LA-12) has been used as a guest drug. The LA-12-cyclodextrin inclusion complexes have been tested on tumour cells. In the presence of cyclodextrin-folate conjugates, LA-12 exhibited IC50 values four times smaller than those of LA-12 alone in MDA-MB-231 cells, which overexpress folic acid receptors on their membrane. No improvement of LA-12 cytotoxicity was found in control tumour cells that do not overexpress the folate receptor. Thus, the non-covalent approach, based on inclusion complexes with functionalised cyclodextrins, looks very promising for drug targeting.

Novel antitumor cisplatin and transplatin derivatives containing 1-methyl-7-azaindole: synthesis, characterization, and cellular responses.

The current work investigates the effect of new bifunctional and mononuclear Pt(II) compounds, the cis- and trans-isomers of [PtCl2(NH3)(L)] (L = 1-methyl-7-azaindole, compounds 1 and 2, respectively), on growth and viability of human carcinoma cells as well as their putative mechanism(s) of cytotoxicity. The results show that substitution of 1-methyl-7-azaindole for ammine in cisplatin or transplatin results in an increase of the toxic efficiency, selectivity for tumor cells in cisplatin-resistant cancer cells, and activation of the trans geometry. The differences in the cytotoxic activities of 1 and 2 were suggested to be due to their different DNA binding mode, different capability to induce cell cycle perturbations, and fundamentally different role of transcription factor p53 in their mechanism of action. Interestingly, both isomers make it possible to detect their cellular uptake and distribution in living cells by confocal microscopy without their modification with an optically active tag.

Synthesis, characterization, and biological activity of platinum II, III, and IV pivaloamidine complexes.

Imino ligands have proven to be able to activate the trans geometry of platinum(II) complexes towards antitumor activity. These ligands, like aromatic N-donor heterocycles, have a planar shape but, different from the latter, have still an H atom on the coordinating nitrogen which can be involved in H-bond formation. Three classes of imino ligands have been extensively investigated: iminoethers (HN=C(R)OR'), ketimines (HN=CRR'), and amidines (HN=C(R)NR'R″). The promising efficacy of the platinum compounds with amidines (activity comparable to that of cisplatin for cis complexes and much greater than that of transplatin for trans complexes) prompted us to extend the investigation to amidine complexes with a bulkier organic residue (R = t-Bu). The tert-butyl group can confer greater affinity for lipophilic environments, thus potentiating the cellular uptake of the compound. In the present study we describe the synthesis and characterization of pivaloamidine complexes of platinum(II), (cis and trans-[PtCl2(NH3){Z-HN=C(t-Bu)NH2}] and cis and trans-[PtCl2{Z-HN=C(t-Bu)NH2}2]), platinum(III) ([Pt2Cl4{HN=C(t-Bu)NH}2(NH3)2]), and platinum(IV) (trans-[PtCl4(NH3){Z-HN=C(t-Bu)NH2}] and trans-[PtCl4{Z-HN=C(t-Bu)NH2}2]). The cytotoxicity of all new Pt complexes was tested toward a panel of cultured cancer cell lines, including cisplatin and multidrug resistant variants. In addition, cellular uptake and DNA binding, perturbations of cell cycle progression, induction of apoptosis, and p53 activation were investigated for the most promising compound trans-[PtCl2(NH3){Z-HN=C(t-Bu)NH2}]. Remarkably, the latter complex was able to overcome both acquired and intrinsic cisplatin resistance.

Isomerization of platinum-coordinated iminoethers induced by spectator ligands: stabilization of the Z anti configuration.

Iminoether derivatives of the formula trans-[PtCl2{HN═C(R)OR'}2] proved to be endowed with remarkable antitumor activity in vivo. Moreover, these trans compounds were more cytotoxic than their cis congeners, a trend opposite to that generally observed for corresponding platinum complexes with ammines. The imino ligands can have either E or Z configuration about the C═N double bond, and in the case of R = R' = Me, the E configuration is by far thermodynamically preferred. However, substitution of chloride anions with neutral ligands (L) alters the relative stability of the E and Z isomers. Upon investigation of the derivatives with L = PPh3, AsPh3, Me2S═O, and (H2N)2C═S, it has been concluded that an electrostatic interaction between the oxygen lone pair of the iminoether and the platinum center, fostered by the net positive charge of the complex and the low dielectric constant around the metal core provided by the hydrophobic L ligands, stabilizes the Z configuration. The same factors can favor iminoether isomerization. These conclusions are fully supported by X-ray crystal data. In the case of a reaction with thiourea, an aminic group of thiourea can substitute the methoxy group of a cis-iminoether, leading to the formation of a cyclic compound in a process reminiscent of the McLafferty rearrangement. Such a rearrangement could play a role in the interaction of the platinum-iminoether compounds with target DNA and proteins.

trans-Chloridobis[(Z)-1-imino-1-methoxyethane-κN](triphenylphosphane-κP)platinum(II) chloride monohydrate.

The title compound, [PtCl(C(3)H(7)NO)(2)(C(18)H(15)P)]Cl·H(2)O or trans-[PtCl{Z-HN=C(Me)OMe}(2)(PPh(3))]Cl·H(2)O, crystallizes from an acetone solution of isomeric trans-[PtCl{E-HN=C(Me)OMe}(2)(PPh(3))]Cl. The two HN=C(Me)OMe ligands show typical π-bond delocalization over the N-C-O group [Cini, Caputo, Intini & Natile (1995). Inorg. Chem. 34, 1130-1137] and have the unprecedented Z-anti configuration. The relative orientation of the imino ether ligands is head-to-tail.

Dependence of the reduction products of platinum(IV) prodrugs upon the configuration of the substrate, bulk of the carrier ligands, and nature of the reducing agent.

Most evidence indicates that platinum(IV) prodrugs are rapidly reduced under physiological conditions by biologically relevant reducing agents, such as ascorbic acid and glutathione; however, the precise mechanisms of reduction are not fully understood, thus preventing rational design of compounds with better pharmacological properties. In the present study, reduction of three all-trans platinum(IV) compounds of formula [PtCl(2)(CH(3)COO)(2)LL'] (LL' = {E-HN═C(CH(3))OCH(3)}(2), 1c, (H(3)N)(cyclohexylamine), 2c, and (H(3)N)(1-adamantylamine), 3c) by two biologically relevant reductants (ascorbic acid and glutathione) and by a classical coordination chemistry reductant (triphenylphosphine) has been investigated. Reduction by triphenylphosphine and glutathione leads, in all cases examined, to loss of the two chlorides and formation of the diacetato species trans-[Pt(CH(3)COO)(2)LL']. This is in accord with an "inner-sphere" redox process in which a chlorido ligand bridges the reductant with the platinum(IV) center. In contrast, reduction by ascorbic acid/sodium ascorbate 1:1 leads, in addition to the diacetato complex, also to formation of a significant amount of dichlorido species, particularly in the case of 1c (31%) and to a lesser extent of 3c (16%). The latter results indicate that ascorbic acid is less efficient to promote an inner-sphere redox process (attack on a chlorido ligand), therefore allowing participation of an "outer-sphere" mechanism, ultimately leading to formation of the more stable dichlorido species. The dependence of the yield of diacetato species upon the steric hindrance of the carrier ligand (69%, 84%, and 95% for 1c, 3c, and 2c, respectively) points to the possible participation of a second type of inner-sphere mechanism in which the interaction between the ascorbate and a chlorido ligand of the platinum(IV) substrate is mediated by a platinum(II) catalyst, the transition state resembling that of a platinum(II)-catalyzed ligand substitution at a platinum(IV) center. This investigation demonstrates that different species can be obtained by reduction of a platinum(IV) prodrug (depending upon the configuration of the substrate and the nature of the intervening reducing agent) and can explain some lack of correlation between prodrug and putative active species as well as contrasting literature results.

Cationic intermediates in oxidative addition reactions of Cl2 to [PtCl2(cis-1,4-DACH)].

Oxidative addition and reductive elimination are fundamental processes in transition-metal chemistry. New interest in this field has been generated by the exploitation of platinum(IV) complexes as antitumor drugs. The two extra ligands can be used to render these species more resistant to attack by biological nucleophiles compared to their platinum(II) counterparts, to anchor additional pharmacologically active moieties, or, finally, to target the drug to specific sites by conferring responsiveness to some type of chemotaxis. On the other hand, platinum(IV) species are considered to be prodrugs and to require reduction to Pt(II) to become active. Thus, reductive elimination promoted by biological reducing agents becomes an important issue and it too could be exploited for targeting purposes. In this paper, we investigated the oxidation step in more detail and shown that, independent of the solvent used, a solvent molecule assists the reaction by entering in a trans position with respect to the attacking oxidant. In the case of bifunctional solvent molecules, such as dimethylsulfoxide, both S- and O-coordinated species are formed, the latter being thermodynamically favored. The substitution of the axially coordinated solvent molecule by a free chloride ion is found to be quite slow in organic solvents, as well as in water. It is also shown that the intermediate solvato-species can be exploited for binding just one molecule of another substrate in the axial position.

Single-stranded oligonucleotide adducts formed by Pt complexes favoring left-handed base canting: steric effect of flanking residues and relevance to DNA adducts formed by Pt anticancer drugs.

Platinum anticancer drug binding to DNA creates large distortions in the cross-link (G*G*) and the adjacent XG* base pair (bp) steps (G* = N7-platinated G). These distortions, which are responsible for anticancer activity, depend on features of the duplex (e.g., base pairing) and of the cross-link moiety (e.g., the position and canting of the G* bases). The duplex structure stabilizes the head-to-head (HH) over the head-to-tail (HT) orientation and right-handed (R) over left-handed (L) canting of the G* bases. To provide fundamental chemical information relevant to the assessment of such duplex effects, we examine (S,R,R,S)-BipPt(oligo) adducts (Bip = 2,2'-bipiperidine with S,R,R,S chiral centers at the N, C, C, and N chelate ring atoms, respectively; oligo = d(G*pG*) with 3'- and/or 5'-substituents). The moderately bulky (S,R,R,S)-Bip ligand favors L canting and slows rotation about the Pt-G* bonds, and the (S,R,R,S)-BipPt(oligo) models provide more useful data than do dynamic models derived from active Pt drugs. All 5'-substituents in (S,R,R,S)-BipPt(oligo) adducts favor the normal HH conformer (∼97%) by destabilizing the HT conformer through clashes with the 3'-G* residue rather than through favorable H-bonding interactions with the carrier ligand in the HH conformer. For all (S,R,R,S)-BipPt(oligo) adducts, the S pucker of the 5'-X residue is retained. For these adducts, a 5'-substituent had only modest effects on the degree of L canting for the (S,R,R,S)-BipPt(oligo) HH conformer. This small flanking 5'-substituent effect on an L-canted HH conformer contrasts with the significant decrease in the degree of R canting previously observed for flanking 5'-substituents in the R-canted (R,S,S,R)-BipPt(oligo) analogues. The present data support our earlier hypothesis that the distortion distinctive to the XG* bp step (S to N pucker change and movement of the X residue) is required for normal stacking and X·X' WC H bonding and to prevent XG* residue clashes.

X-ray structural characterization of the bis-guanine derivative of a cisplatin analogue having just one proton on each coordinated nitrogen and a head-to-head conformation: [Pt{(+/-)-N,N'-dimethyl-2,3-diaminobutane}(9-ethyl-guanine)2]dinitrate.

The X-ray structural and NMR characterization of a bis-guanine derivative of a cisplatin analogue designed to reduce the rate of the Pt-N7 rotation of the coordinated guanine nucleobases by more than 1-million-fold is reported. The [Pt{(+/-)-Me(2)dab}(9-EtG)(2)](NO(3))(2) (Me(2)dab = N,N'-dimethyl-2,3-diaminobutane, 9-EtG = 9-ethyl-guanine) complex crystallizes in the P2(1)/n space group, and the crystal contains a racemic mixture of complex molecules. The data were collected at 120 +/- 2 K, and the crystal and molecular structure (comprising one disordered nitrate) were resolved and refined to conventional agreement factors of R1 = 0.0270 and wR2 = 0.0565. The guanine ligands assume the less common head-to-head (HH) orientation, disclosing full details of the intramolecular relationships between cis guanines and between guanine and cis amine. Moreover, an understanding has been gained of the steric factors determining induction of asymmetry (from carbons to adjacent nitrogen atoms) and puckering of the chelate ring (delta or lambda for R,S,S,R or S,R,R,S configurations at the N,C,C,N chelate-ring atoms, respectively) within the Me(2)dab ligand. The chemical shift separation between H8 signals of the two HT atropisomers and between the two H8 signals of the single HH atropisomer can be explained in terms of canting of the nucleobases relative to the coordination plane and in terms of the different relationships between the H8 proton of one guanine and the shielding zone of the cis guanine. Furthermore, for each configuration of the Me(2)dab ligand (R,S,S,R or S,R,R,S), the NMR data indicate that the handedness of canting is similar for the two guanines in all three (two HT and one HH) conformers (R canting for R,S,S,R and L canting for S,R,R,S configuration).

"Lantern-Shaped" Platinum(III) Complexes with Axially Bound 9-Ethylguanine or 1-Methylcytosine (L) of General Formula [Pt(2){HN=C(Bu)O}(4)L(2)](NO(3))(2).

The synthesis, NMR characterization, and X-ray crystallography of "lantern-shaped" platinum(III) complexes with four pivaloamidate bridging ligands and two 9-ethylguanines (9-EtG) or 1-methylcytosines (1-MeC) in axial positions are reported: cis-N(2)O(2)-[Pt(2){HN=C(Bu(t))O}(4)(9-EtG)(2)](NO(3))(2) and cis-N(2)O(2)-[Pt(2){HN=C(Bu(t))O}(4)(1-MeC)(2)](NO(3))(2). The last complex is, to the best of our knowledge, the first dinuclear compound of platinum(III) with axially bound 1-MeC.

Solution behavior of amidine complexes: an unexpected cis/trans isomerization and formation of di- and trinuclear platinum(III) and platinum(II) species.

Platinum bis-amidine complexes (both the cis and trans isomers) are stable in acetone and chlorinated solvents but are unstable in protic solvents such as methanol or water. In the latter solvents an initial cis/trans isomerization leads to formation of an equilibrium mixture with a cis/trans ratio of about 1:4; subsequently a dinuclear platinum(III) complex (1) is formed under aerobic conditions while, under anaerobic conditions, a trinuclear platinum(II) compound (2) is obtained. We hypothesize that the process of isomerization and formation of polynuclear compounds (1 and 2) have a common precursor: a dinuclear platinum(II) species supported by two bridging amidinato ligands (3), formed in small yield, which can either dissociate back to monomers of cis/trans configuration or evolve in two different polynuclear species depending upon the aerobic/anaerobic conditions. In aerobic conditions, oxidation of platinum(II) to platinum(III) together with formation of two additional amidinato bridges across the two platinum centers takes place leading to compound 1. In contrast, in anaerobic conditions, oxidation of platinum is prevented and the dinuclear platinum(II) precursor remains in solution until it reacts with an extra molecule of the starting mononuclear complex which loses its two amidine ligands and cross-links the two bridging amidinato ligands of 3 to yield compound 2. This latter features two triply bridging amidinato ligands linking the three platinum units to form a pocket. Complexes 1 and 2 have been characterized by means of IR and NMR spectroscopy, mass spectrometry, elemental analysis, and X-ray crystallography.

Energetics, conformation, and recognition of DNA duplexes modified by methylated analogues of [PtCl(dien)]+.

In early studies of empirical structure-activity relationships, monodentate Pt(II) complexes were considered to be biologically inactive. Examples of such inactive monodentate Pt(II) compounds are [PtCl(dien)]+ (dien=diethylenetriamine) and [PtCl(NH3)3]+. DNA is considered the major biological target of platinum compounds. Thus, monodentate DNA binding of Pt(II) compounds was previously expected to display insignificant biological effects because it was assumed to affect DNA conformation and downstream cellular processes markedly less than the cross-links of bifunctional Pt(II) complexes. More recently it was shown that some monodentate Pt(II) complexes do exhibit biological effects; the active monodentate Pt(II) complexes commonly feature bulkier amine ligands than the hitherto used dien or NH(3) groups. We were therefore interested in determining whether a simple but marked enhancement of the bulkiness of the dien ligand in monodentate [Pt(NO3)(dien)]+ by multiple methylation of this ligand affects the early phases in which platinum compounds exert their biological activity. More specifically, the goals of this study, performed in cell-free media, were to determine how the modification of DNA duplexes by methylated analogues of [Pt(NO3)(dien)]+ affects their energetics and how the alterations of this biophysical parameter are reflected by the recognition of these duplexes by DNA polymerases and the DNA repair system. We have found that the impact of the methylation of [Pt(NO3)(dien)]+ on the biophysical properties of DNA (thermodynamic, thermal, and conformational properties) and its biochemical processes (DNA polymerization and the repair of DNA adducts) is remarkable. Hence, we conclude that monodentate DNA binding of Pt(II) compounds may considerably affect the biophysical properties of DNA and consequently downstream cellular processes as a result of a large increase in the bulkiness of the nonleaving ligands in this class of metal complex.

NMR and X-ray structural characterization of a cisplatin analogue able to slow down the Pt-N7 rotation of a coordinated guanine base by a billion-fold times: 2,2'-bipiperidine(dimethylmalonato)platinum(II) complex.

The synthesis and the NMR and X-ray structural characterization of a cisplatin analogue designed to reduce the Pt-N7 rotation of a coordinated guanine base by a billion times are reported. The [Pt(dmm){(+/-)-bip}] (dmm=dimethylmalonato; bip=2,2'-bipiperidine) complex crystallizes in the C2/m space group, which contemplates a mirror plane bisecting the bip and dmm ligands. Because the bip moiety (R, R or S, S configuration at the 2,2'-carbon atoms) does not have planes of symmetry, the requirements of the crystal symmetry are satisfied by a statistical disorder made of bip molecules of R, R or S, S configurations alternating at the same crystallographic site. Such an unexpected arrangement has been permitted by a "quasi planarity" of the bip ligand [maximum deviation from the mean plane through the C and N atoms of 0.2927(9) A], which allows bip molecules of different chiralities to fit in the same space. The bip array of heavy atoms is overlaid, from both sides, by a layer of "quasi axial" (C)H and (N)H atoms (six per side). Those on one side are hydrogen-bonded to the dmm oxygen atoms of another complex molecule joined in a pair. The distance between the average platinum coordination planes is as short as 3.498(1) A, comparable to those found in crystals of the [PtCl 2(bipy)] complex (bipy=2,2'-bipyridine) and of graphite, in which, however, all atoms of each unit are rigorously coplanar and there are no out-of-plane hydrogen atoms. The NMR data show a net chemical shift separation between geminal methylene protons, with the "quasi axial" protons being always at higher field with respect to the "quasi equatorial" ones. This is in accordance with a rigid bip ligand frame and the inability of the bip methylene protons adjacent to the coordinated nitrogen to rotate away from a cis-G base (G=guanine) during G rotation around the Pt-N7 bond.

Cytotoxicity, mutagenicity, cellular uptake, DNA and glutathione interactions of lipophilic trans-platinum complexes tethered to 1-adamantylamine.

Cytotoxicity and mutagenicity of trans,trans,trans-[PtCl2(CH3COO)2(NH3)(1-adamantylamine)] [trans-adamplatin(IV)] and its reduced analog trans-[PtCl2(NH3)(1-adamantylamine)] [trans-adamplatin(II)] were examined. In addition, the several factors underlying biological effects of these trans-platinum compounds using various biochemical methods were investigated. A notable feature of the growth inhibition studies was the remarkable circumvention of both acquired and intrinsic cisplatin resistance by the two lipophilic trans-compounds. Interestingly, trans-adamplatin(IV) was considerably less mutagenic than cisplatin. Consistent with the lipophilic character of trans-adamplatin complexes, their total accumulation in A2780 cells was considerably greater than that of cisplatin. The results also demonstrate that trans-adamplatin(II) exhibits DNA binding mode markedly different from that of ineffective transplatin. In addition, the reduced deactivation of trans-adamplatin(II) by glutathione seems to be an important determinant of the cytotoxic effects of the complexes tested in the present work. The factors associated with cytotoxic and mutagenic effects of trans-adamplatin complexes in tumor cell lines examined in the present work are likely to play a significant role in the overall antitumor activity of these complexes.