Bifunctional Platinum Research Articles

A novel anti-cancer bifunctional platinum drug candidate with dual DNA binding and histone deacetylase inhibitory activity

The successful design and synthesis of a novel multifunctional platinum drug candidate with DNA binding, histone deacetylase inhibitory activity and enhanced selectivity for cancer cells are described.

A bifunctional platinum(II) antitumor agent that forms DNA adducts with affinity for the estrogen receptor

A strategy is described for the re-design of DNA damaging platinum(II) complexes to afford elevated toxicity towards cancer cells expressing the estrogen receptor (ER). Two platinum-based toxicants are described in which a DNA damaging warhead, [Pt(en)Cl(2)] (en, ethylenediamine), is tethered to either of two functional groups. The first agent, [6-(2-amino-ethylamino)-hexyl]-carbamic acid 2-[6-(7alpha-estra-1,3,5,(10)-triene)-hexylamino]-ethyl ester platinum(II) dichloride ((Est-en)PtCl(2)), terminates in a ligand for the ER. The second agent is a control compound lacking the steroid; this compound, N-[6-(2-amino-ethylamino)-hexyl]-benzamide platinum(II) dichloride ((Bz-en)PtCl(2))), terminates in a benzamide moiety, which lacks affinity for the ER. Using a competitive binding assay, Est-en had 28% relative binding affinity (RBA) for the ER as compared to 17beta-estradiol. After covalent binding to a synthetic DNA duplex 16-mer, the compound retained its affinity for the ER; specificity of the binding event was demonstrated by the ability of free 17beta-estradiol as a competitor to disrupt the DNA adduct-ER complex. The (Est-en)PtCl(2) compound showed higher toxicity against the ER positive ovarian cancer cell line CAOV3 than did the control compound. (Est-en)PtCl(2) was also more toxic to the ER positive breast cancer line, MCF-7, than to an ER negative line, MDA-MB231.

Synthesis and activity measurement of the some bifunctional platinum loaded Beta zeolite catalysts for n-heptane hydroisomerization

In this study, two types of Beta zeolites having different Si/Al ratios (11.7 and 24.5) were synthesized hydrothermally using tetraethyl ammonium hydroxide (TEAOH) as a template. Different amounts of platinum (0.2%, 0.5% and 1.2%) were loaded on the protonated form of zeolite by incipient wet impregnation method applying hexachloroplatinic acid in 0.2N Cl − progressive ion solutions. Catalytic hydroisomerization reactions were carried out at atmospheric pressure in a fixed bed reactor with vertical placing and downward flow at three different temperatures, various WHSV (weight hourly space velocity) and n-H 2/ n-HC (molar hydrogen/hydrocarbon) ratio. Increase in Si/Al ratio in zeolites structures from 11.7 to 24.5 promoted selectivity and yield. It was found that optimum platinum content depends on the Si/Al ratio (zeolite acidity) in catalysts. Monobranched to dibranched isomers ratio were correlated with a linear function of n-heptane conversion. Such a correlation was found to be valid for various Si/Al ratios, metal content, processing temperature and pressure, WHSV and hydrogen to hydrocarbon ratio. This observation may indicate that in isomerization reactions, the monobranched isomers are first produced but subsequently transformed into multi-branched isomers.

Cis -Diammine(pyridine)chloroplatinum(II), a monofunctional platinum(II) antitumor agent: Uptake, structure, function, and prospects

We have identified unique chemical and biological properties of a cationic monofunctional platinum(II) complex, cis-diammine(pyridine)chloroplatinum(II), cis-[Pt(NH(3))(2)(py)Cl](+) or cDPCP, a coordination compound previously identified to have significant anticancer activity in a mouse tumor model. This compound is an excellent substrate for organic cation transporters 1 and 2, also designated SLC22A1 and SLC22A2, respectively. These transporters are abundantly expressed in human colorectal cancers, where they mediate uptake of oxaliplatin, cis-[Pt(DACH)(oxalate)] (DACH = trans-R,R-1,2-diaminocyclohexane), an FDA-approved first-line therapy for colorectal cancer. Unlike oxaliplatin, however, cDPCP binds DNA monofunctionally, as revealed by an x-ray crystal structure of cis-{Pt(NH(3))(2)(py)}(2+) bound to the N7 atom of a single guanosine residue in a DNA dodecamer duplex. Although the quaternary structure resembles that of B-form DNA, there is a base-pair step to the 5' side of the Pt adduct with abnormally large shift and slide values, features characteristic of cisplatin intrastrand cross-links. cDPCP effectively blocks transcription from DNA templates carrying adducts of the complex, unlike DNA lesions of other monofunctional platinum(II) compounds like {Pt(dien)}(2+). cDPCP-DNA adducts are removed by the nucleotide excision repair apparatus, albeit much less efficiently than bifunctional platinum-DNA intrastrand cross-links. These exceptional characteristics indicate that cDPCP and related complexes merit consideration as therapeutic options for treating colorectal and other cancers bearing appropriate cation transporters.

1,2-GG intrastrand cross-link of antitumor dinuclear bifunctional platinum compound with spermidine linker inhibits DNA polymerization more effectively than the cross-link of conventional cisplatin

In order to learn more about the molecular basis for the inhibition of DNA replication produced by antitumor platinum drugs, we investigated DNA polymerization using DNA templates site-specifically modified with the 1,2-GG intrastrand cross-link of dinuclear bifunctional [ { trans -PtCl ( NH 3 ) 2 } 2 { l-spermidine-N 1 ,N 8 } ] 3 + ( BBR3571 ) or conventional mononuclear cisplatin. These cross-links which have the same nature, but differ in the size and character of the conformational alteration induced in double-helical DNA, were analyzed for bypass ability with reverse transcriptase of human immunodeficiency virus type 1 and Klenow fragment of DNA polymerase I deficient in exonuclease activity. We found that the 1,2-GG intrastrand CL of BBR3571 inhibited DNA translesion synthesis markedly more than the same adduct of cisplatin. This result was explained by a larger size of the cross-link of BBR3571 and by a flexibility induced in DNA by this cross-link which can make the productive binding of this adduct at the polymerase site more difficult.

Deoxyribonuclease I footprinting reveals different DNA binding modes of bifunctional platinum complexes

Deoxyribonuclease I (DNase I) footprinting methodology was used to analyze oligodeoxyribonucleotide duplexes containing unique and single, site-specific adducts of trinuclear bifunctional platinum compound, [{trans-PtCl(NH3)2}2 mu-trans-Pt(NH3)2{H2N(CH2)6NH2}2]4+ (BBR3464) and the results were compared with DNase I footprints of some adducts of conventional mononuclear cis-diamminedichloroplatinum(II) (cisplatin). These examinations took into account the fact that the local conformation of the DNA at the sites of the contacts of DNase I with DNA phosphates, such as the minor groove width and depth, sequence-dependent flexibility and bendability of the double helix, are important determinants of sequence-dependent binding to and cutting of DNA by DNase I. It was shown that various conformational perturbations induced by platinum binding in the major groove translated into the minor groove, allowing their detection by DNase I probing. The results also demonstrate the very high sensitivity of DNase I to DNA conformational alterations induced by platinum complexes so that the platinum adducts which induce specific local conformational alterations in DNA are differently recognized by DNase I.

Recognition of DNA modified by trans‐[PtCl2NH3(4‐hydroxymethylpyridine)] by tumor suppressor protein p53 and character of DNA adducts of this cytotoxic complex

trans-[PtCl(2)NH(3)(4-Hydroxymethylpyridine)] (trans-PtHMP) is an analogue of clinically ineffective transplatin, which is cytotoxic in the human leukemia cancer cell line. As DNA is a major pharmacological target of antitumor platinum compounds, modifications of DNA by trans-PtHMP and recognition of these modifications by active tumor suppressor protein p53 were studied in cell-free media using the methods of molecular biology and biophysics. Our results demonstrate that the replacement of the NH(3) group in transplatin by the 4-hydroxymethylpyridine ligand affects the character of DNA adducts of parent transplatin. The binding of trans-PtHMP is slower, although equally sequence-specific. This platinum complex also forms on double-stranded DNA stable intrastrand and interstrand cross-links, which distort DNA conformation in a unique way. The most pronounced conformational alterations are associated with a local DNA unwinding, which was considerably higher than those produced by other bifunctional platinum compounds. DNA adducts of trans-PtHMP also reduce the affinity of the p53 protein to its consensus DNA sequence. Thus, downstream effects modulated by recognition and binding of p53 protein to DNA distorted by trans-PtHMP and transplatin are not likely to be the same. It has been suggested that these different effects may contribute to different antitumor effects of these two transplatinum compounds.

Ethylbenzene isomerization over bifunctional platinum alumina–EUO catalysts: Location of the active sites

The transformation of ethylbenzene (EB) was carried out on intimate mixtures of Pt/Al 2O 3 (PtA) and HEUO (Si/Al = 15) catalysts with different composition under the following conditions: fixed bed reactor, temperature 683 K, pressure of hydrogen and ethylbenzene equal to 8 and 2 bar respectively, weight hourly space velocity between 5 and 60. Products result from the following transformations of ethylbenzene or/and of the reaction products: the bifunctional desired isomerization of EB into xylenes (X), the acidic reactions of disproportionation, dealkylation of EB (followed by ethylene hydrogenation) and EB–X transalkylation, the hydrogenation of EB followed by ethylcyclohexane isomerization and cracking. The selectivity to isomers, which is very low on the fresh catalysts, increases significantly during an initial period of fast deactivation, essentially at the expense of disproportionation and dealkylation by products. This deactivation as well as the increase in the selectivities to isomers were shown to result from the blockage by carbonaceous deposits of the access to the inner sites of the EUO micropores. The selectivity to isomers of EB transformation over these inner sites is very low, which could be due to the trapping of ethylcyclohexene intermediates within the monodimensional channels of EUO zeolite. In contrast, over the stabilized catalysts for which only the protonic sites of large side pockets located on the outer surface can be active, the selectivity to isomers is very high, which could be related to the environment of these sites as well as to their easy access by cycloalkene intermediates.

553 Activation of trans geometry in bifunctional mononuclear platinum complexes by combining aliphatic and aromatic amines. Mechanistic studies on antitumor action

553 Activation of trans geometry in bifunctional mononuclear platinum complexes by combining aliphatic and aromatic amines. Mechanistic studies on antitumor action

Platinum over tungsten oxide or sulfate promoted zirconia: a study of the metallic and acid functions and their poisoning

Bifunctional platinum over tungsten oxide promoted zirconia (Pt/WZ) and platinum over sulfate promoted zirconia (Pt/SZ) were characterized by XRD, Sg, ICP-OES, DRIFTS and test reactions: cyclohexane dehydrogenation (metallic function) and n-pentane isomerization (acid function). Both reactions were carried out at 300 °C, atmospheric pressure and in the presence of hydrogen. Benzene and methylcyclopentane were obtained in the cyclohexane reaction and iso-pentane was the main product during n-pentane reaction. The poisoning with carbon disulfide (CS 2) and n-butylamine (BA) of the two reactions, were measured. Pt/WZ and Pt/SZ were sensitive to both poisons used. CS 2 affects directly the activity of the metal function and indirectly the one of the acid function because decreases the hydrogen dissociation capacity of Pt. BA only affects the acid function.

DNA interactions of new antitumor platinum complexes with trans geometry activated by a 2-metylbutylamine or sec-butylamine ligand

The global modification of mammalian and plasmid DNAs by novel platinum compounds, trans-[PtCl 2(NH 3)(Am)], where Am=2-methylbutylamine or sec-butylamine was investigated in cell-free media using various biochemical and biophysical methods. These modifications were analyzed in the context of the activity of these new compounds in several tumor cell lines including those resistant to antitumor cis-diamminedichloroplatinum(II) (cisplatin). The results showed that the replacement of one amine group by 2-methylbutylamine or sec-butylamine ligand in clinically ineffective trans-diamminedichloroplatinum(II) (transplatin) resulted in a radical enhancement of its activity in tumor cell lines so that they are more cytotoxic than cisplatin and exhibited significant antitumor activity including activity in cisplatin-resistant tumor cells. Importantly, this replacement also markedly altered DNA binding mode of transplatin and reduced the efficiency of repair systems to remove the adducts of the new analogues from DNA. The results support the view that one strategy to activate trans geometry in bifunctional platinum(II) compounds including circumvention of resistance to cisplatin may consist in a chemical modification of the ineffective transplatin which results in an increased efficiency to form DNA interstrand cross-links.

Activation of Trans Geometry in Bifunctional Mononuclear Platinum Complexes by a Piperidine Ligand: MECHANISTIC STUDIES ON ANTITUMOR ACTION

A paradigm for the structure-pharmacological activity relationship of bifunctional platinum antitumor drugs is that the trans isomer of antitumor cisplatin (transplatin) is clinically ineffective. To this end, however, several new complexes of the trans structure have been identified that exhibit cytotoxicity in tumor cells that is even better than that of the analogous cis isomers. We reported recently (Kasparkova, J., Marini, V., Najajreh, Y., Gibson, D., and Brabec, V. (2003) Biochemistry 42, 6321-6332) that the replacement of one ammine ligand by the heterocyclic ligand, such as piperidine, piperazine, or 4-picoline in the molecule of transplatin resulted in a radical enhancement of its cytotoxicity. We examined oligodeoxyribonucleotide duplexes bearing a site-specific cross-link of the transplatin analogue containing the piperidine ligand by biochemical methods. The results indicate that in contrast to transplatin, trans-(PtCl2(NH3)(piperidine)) forms stable 1,3-intrastrand cross-links in double-helical DNA that distort DNA and are not readily removed from DNA by nucleotide excision repair system. Hence, the intrastrand cross-links of trans-(PtCl2(NH3)(piperidine)) could persist for a sufficiently long time, potentiating its toxicity toward tumor cells. trans-(PtCl2(NH3)(piperidine)) also forms in DNA minor interstrand cross-links that are similar to those of transplatin so that these adducts appear less likely candidates for genotoxic lesion responsible for antitumor effects of trans-(PtCl2(NH3)(piperidine)). Hence, the role of structurally unique intrastrand cross-links in the anti-tumor effects of transplatin analogues in which one ammine group is replaced by a heterocyclic ligand may predominate.

P-523 Phase II trial of BBR3464, a novel, bifunctional platinum analog, as second line treatment of non-small cell lung cancer patients

P-523 Phase II trial of BBR3464, a novel, bifunctional platinum analog, as second line treatment of non-small cell lung cancer patients

DNA binding mode of the cis and trans geometries of new antitumor nonclassical platinum complexes containing piperidine, piperazine, or 4-picoline ligand in cell-free media. Relations to their activity in cancer cell lines.

The global modification of mammalian and plasmid DNAs by novel platinum compounds, cis- or trans-[PtCl(2)(NH(3))(Am)], where Am = NH(3), nonplanar heterocycle piperidine, piperazine, or aromatic planar heterocycle 4-picoline, was investigated in cell-free media using various biochemical and biophysical methods. These modifications have been compared with the activity of these new compounds in several tumor cell lines including those resistant to antitumor cis-diamminedichloroplatinum(II) (cisplatin). The results show that the replacement of the NH(3) group in cisplatin by the heterocyclic ligands does not considerably affect the DNA binding mode of this drug. Cytotoxicity studies have revealed that the replacement lowers the activity of the platinum compound in both sensitive and resistant cell lines. It has been suggested that the reduced activity of these analogues of cisplatin is associated with some features of the damaged DNA and/or its cellular processing. Alternatively, the reduced activity of the analogues of cisplatin might also be due to the factors that do not operate directly at the level of the target DNA, such as intracellular platinum uptake. In contrast to the analogues of cisplatin, the replacement of one ammine group by the heterocyclic ligand in its clinically ineffective trans isomer (transplatin) results in a radical enhancement of its activity in tumor cell lines. Importantly, this replacement also markedly alters the DNA binding mode of transplatin. The results support the view that one strategy of how to activate the trans geometry in bifunctional platinum(II) compounds including circumvention of resistance to cisplatin may consist of a chemical modification of the ineffective transplatin that results in an increased stability of its intrastrand cross-links in double-helical DNA and/or in an increased efficiency to form interstrand cross-links.

Ethylbenzene Isomerization on Bifunctional Platinum Alumina−Mordenite Catalysts. 2. Influence of the Pt Content and of the Relative Amounts of Platinum Alumina and Mordenite Components

Ethylbenzene transformation was carried out over intimate mixtures of Pt/Al2O3 (PtA) and HMOR zeolites under the following conditions: fixed-bed reactor, temperature 683 K, pressures of hydrogen and of ethylbenzene equal to 8 and 2 bar, respectively, weight hourly space velocity between 5 and 200. A significant number of these bifunctional PtA/HMOR catalysts were used, differing by the platinum content of PtA (0.5, 1.1 and 2.3 wt %), the framework Si/Al ratio of the mordenite (from 6.6 to 180), and especially by the relative proportions of the PtA and HMOR components. With all of the bifunctional catalysts, ethylbenzene undergoes isomerization into xylenes, disproportionation, dealkylation, secondary ethylbenzene−xylene transalkylation, hydrogenation followed by ethylcyclohexane isomerization, and secondary cracking of C8 naphthenes. The rate of isomerization which occurs through bifunctional catalysis was shown to depend mainly on the balance between hydrogenating and acid functions, taken here as the ratio between the concentration of accessible platinum atoms and of protonic acid sites (nPt/nH+). The rate of disproportionation per acid site does not depend on the relative proportion of zeolite and of Pt/Al2O3 in the bifunctional catalysts but increases with the density of protonic sites in the mordenite component. This suggests that this bimolecular reaction requires more than one acid site for its catalysis. Ethylbenzene dealkylation does not depend on the density of protonic sites but seems very sensitive to their strength. For these three reactions, the apparent activity of the protonic sites is significantly greater when the HMOR components of the bifunctional catalysts are dealuminated, hence present mesopores; most of the protonic sites of these dealuminated mordenites would be active, whereas for mordenites without mesopores, it would be the case only for the protonic sites of the shell of the crystallites. High selectivities to xylenes (≈75% at 35% conversion) were shown to be obtained on bifunctional catalysts with values of nPt/nH+ sufficiently high to have the acid isomerization of olefinic intermediates as the limiting step of ethylbenzene isomerization.

Ethylbenzene Isomerization on Bifunctional Platinum Alumina–Mordenite Catalysts: 1. Influence of the Mordenite Si/Al Ratio

The transformation of ethylbenzene was carried out on intimate mixtures of 0.5 wt% Pt/Al2O3 (75 wt%) with a platinum dispersion of 100% and of HMOR zeolites (25 wt%) with Si/Al ratios between 6.6 and 180. Products result from six main transformations of ethylbenzene or/and of the reaction products: the desired isomerization of ethylbenzene into xylenes (reaction 1), disproportionation of ethylbenzene (2), dealkylation followed by hydrogenation of ethylene (3), secondary ethylbenzene–xylene transalkylation (4), hydrogenation of ethylbenzene followed by ethylcyclohexane isomerization (5), and secondary cracking of C8 naphthenes (6). From the comparison of the product distributions over Pt/Al2O3, over HMOR and over the bifunctional catalysts, reactions 2–4 were confirmed to occur through acid catalysis and hydrogenation through metal catalysis, and reactions 1 and 6 through bifunctional catalysis. Whatever the catalyst, the selectivity to isomers increases with ethylbenzene conversion, which is due to thermodynamic limitations in reactions 2 and 5. A significant increase in selectivity to isomers is also observed when the Si/Al ratio of the mordenite component increases from 20 to 180. With these bifunctional catalysts, the initial rate of disproportionation is proportional to the square of the concentration of protonic sites, which suggests that this bimolecular reaction requires two protonic sites for its catalysis; furthermore, the rate of dealkylation (per protonic site) depends only on the strength of the protonic sites and the change of the isomerization rate with the balance between the metallic and acidic functions is the one expected from a classical bifunctional mechanism. For the bifunctional catalysts with HMOR6.6 and −10 as acidic components, the rates of disproportionation, dealkylation, and isomerization are lower than expected and the selectivity to isomers is higher. This can be explained by strong diffusion limitations in these zeolites which, in contrast to the other samples, do not present mesopores in addition to micropores.

Phase II trial of BBR3464, a novel, bifunctional platinum analog, in advanced but favorable out-come, Non Small Cell Lung Cancer patients

Phase II trial of BBR3464, a novel, bifunctional platinum analog, in advanced but favorable out-come, Non Small Cell Lung Cancer patients

Phase II clinical study of BBR 3464, a novel, bifunctional platinum analogue, in patients with advanced ovarian cancer

Phase II clinical study of BBR 3464, a novel, bifunctional platinum analogue, in patients with advanced ovarian cancer

Comparison of Pt/zeolite catalysts for n-hexadecane hydroisomerization

Bifunctional platinum (0.5 wt.%) catalysts containing ZSM-5, ZSM-22, SAPO-11, Al-MCM-41, H-Y and H-β were tested for the hydroisomerization of n-hexadecane and their catalytic activities were compared. The Pt/ZSM-5, Pt/ZSM-22 and Pt/H-β catalysts showed higher hydrocracking activity due to their strong acid sites, while the Pt/SAPO-11, Pt/Al-MCM-41 and Pt/H-Y catalysts with moderate acid strength showed better isomerization selectivity. Especially the Pt/Al-MCM-41 catalyst, where Al-MCM-41 was prepared by post-synthetic metal implantation method from siliceous MCM-41, showed the highest isomerization selectivity as well as the highest yield of multibranched isohexadecanes, presumably not only due to its moderately weak acidity and mesoscale pores but also due to higher metal dispersion. This result indicates that the Pt/Al-MCM-41 catalyst can be a promising candidate for good dewaxing catalysts.

DNA interactions of antitumor trans-[PtCl2(NH3)(quinoline)

Recent observations that several trans-platinum complexes exhibit antitumor activity including activity in cisplatin-resistant tumor cells, violates the classical structure/activity relationships of platinum(II) complexes. According to these relationships, only bifunctional platinum(II) complexes with cis-oriented leaving ligands should be therapeutically active. In order to contribute to the understanding of mechanisms underlying the antitumor activity of these new trans-platinum analogs, various biochemical and biophysical methods as well as molecular modeling techniques were employed to study the modifications of DNA by antitumor trans-[PtCl2(NH3)(quinoline)]. The results indicated that trans-[PtCl2(NH3)(quinoline)] coordinated monofunctionally to DNA with a similar rate as transplatin. The overall rate of the rearrangement to bifunctional adducts was also similar to that observed in the case of DNA modification by transplatin, i.e. it was relatively slow (after 48 h approximately 34% adducts remained monofunctional). In contrast to transplatin, however, trans-[PtCl2(NH3)(quinoline)] formed considerably more interstrand cross-links after 48 h (approximately 30%) with a much shorter half-time (approximately 5 h) (approximately 12% for transplatin, t1/2 > 11 h). The results also suggested that the quinoline ligand in all or in a significant fraction of DNA adducts of trans-[PtCl2(NH3)(quinoline)], in which platinum is coordinated to base residues, was well positioned to interact with the duplex. The adducts of trans-[PtCl2(NH3)(quinoline)] terminated in vitro RNA synthesis preferentially at guanine residues. Surprisingly, the type and extent of conformational alterations induced in DNA indicates that trans-[PtCl2(NH3)(quinoline)] behaves in some respects like cisplatin, as indicated by the fact that trans-[PtCl2(NH3)(quinoline)]-modified DNA is recognized by cisplatin-specific antibodies. Models for both monofunctional adducts and bifunctional interstrand cross-links are proposed. Computer-generated AMBER models show that the combination of monofunctional covalent binding and a stacking interaction between quinoline and the DNA bases can produce a kink in the duplex which is strongly suggestive of the directed bend produced by the major cisplatin-DNA adduct (1,2 intrastrand cross-link). Unique DNA adducts of this type formed by trans-[PtCl2(NH3)(quinoline)] may contribute to the antitumor efficacy of this agent.