Carboxylation of Dihydroxoplatinum(IV) Complexes via a New Synthetic Pathway

Platinum(IV)-azido monocarboxylato complexes are photocytotoxic under irradiation with visible light

Complexes trans,trans,trans-[Pt(N3)2(OH)(OCOR)(py)2] where py = pyridine and where OCOR = succinate (1); 4-oxo-4-propoxybutanoate (2) and N-methylisatoate (3) have been synthesized by derivation of trans,trans,trans-[Pt(OH)2(N3)2(py)2] (4) and characterised by NMR and EPR spectroscopy, ESI-MS and X-ray crystallography. Irradiation of 1-3 with green (517 nm) light initiated photoreduction to Pt(ii) and release of the axial ligands at a 3-fold faster rate than for 4. TD-DFT calculations showed dissociative transitions at longer wavelengths for 1 compared to 4. Complexes 1 and 2 showed greater photocytotoxicity than 4 when irradiated with 420 nm light (A2780 cell line IC50 values: 2.7 and 3.7 μM) and complex 2 was particularly active towards the cisplatin-resistant cell line A2780cis (IC50 3.7 μM). Unlike 4, complexes 1-3 were phototoxic under green light irradiation (517 nm), with minimal toxicity in the dark. A pKa(H2O) of 5.13 for the free carboxylate group was determined for 1, corresponding to an overall negative charge during biological experiments, which crucially, did not appear to impede cellular accumulation and photocytotoxicity.

A Pt(IV) Prodrug Combining Chlorambucil and Cisplatin: a Dual-Acting Weapon for Targeting DNA in Cancer Cells

In this study, two DNA-targeting agents, cisplatin and chlorambucil, were combined in a Pt(IV) prodrug, 1, which was thoroughly characterized by means of spectroscopic and spectrometric techniques. Tested towards a panel of various human tumor cell lines, this compound showed superior in vitro antitumor potential than the reference drug cisplatin. In addition, an antitumor potential of 1 was found, which is comparable to that of oxaliplatin in 3D spheroid models of colon cancer cells. Mechanistic studies performed in colon cancer cells confirmed that the conjugation of chlorambucil to Pt(IV) cisplatin-based scaffold tunes the lipophilicity of the prodrug, consequently improving the ability of the compound to accumulate into cancer cells and to target DNA, ultimately leading to apoptotic cancer cell death.

An unsymmetric cisplatin-based Pt(iv) derivative containing 2-(2-propynyl)octanoate: a very efficient multi-action antitumor prodrug candidate

The design, synthesis, characterization and biological properties of a Pt(iv) complex containing the very active inhibitor of histone deacetylase (2-propynyl)octanoic acid, POA, as an axial ligand are reported here. The title complex, namely (OC-6-44)-acetatodiamminedichlorido(2-(2-propynyl)octanoato)platinum(iv), 1, containing POA in racemic or in enantiomeric forms, was one/two orders of magnitude more active than cisplatin, depending on the chemo-sensitivity of the cancer cell lines. Moreover, 1 exhibited similar or even better antiproliferative activity than (OC-6-33)-diamminedichloridobis(2-propylpentanoato)platinum(iv), 2, containing two molecules of the well-known histone deacetylase inhibitor 2-propylpentanoic (valproic) acid. The high potency of 1 is likely due to its high cellular accumulation and to the synergism between the DNA-damaging cisplatin and the histone deacetylase inhibitor POA, both released upon the intracellular reduction of 1. Prodrug 1, after oral administration, caused an impressive reduction of the tumor mass (94%) in a model of solid tumor (murine Lewis lung carcinoma), compared to that of the control, whereas (intraperitoneal) cisplatin induced a tumor regression of 75% only. A good accumulation of 1 was observed in the tumor mass. The time course of the body weight attested that cisplatin induced elevated anorexia, whereas treatment with 1 did not induce significant body weight loss throughout the therapeutic experiment.

Increased immune cell infiltration in patient-derived tumor explants treated with Traniplatin: an original Pt(iv) pro-drug based on Cisplatin and Tranilast

Elevated intra-tumoral immune infiltrate is associated with an improved prognosis in cancer of distinct origins. Traniplatin (TPT) is a novel platinum(iv) pro-drug based on Cisplatin (CDDP) and the marketed drug Tranilast. When compared in vitro to Cisplatin, TPT showed increased cytotoxic activity against colon and lung cancer cells but decreased activity against immune cells. In addition, TPT efficiency was evaluated in tumor explants derived from colorectal cancer samples from patients subjected to intended curative surgery. TPT induced strong intra-tumoral cytotoxic activity yet was associated with an elevated presence of immune cell infiltrate, suggesting a reduced cytotoxic activity against immune cells in colorectal cancer.

Finely Tuned Asymmetric Platinum(IV) Anticancer Complexes: Structure-Activity Relationship and Application as Orally Available Prodrugs

Platinum(IV) bis-carboxylates are highly versatile prodrug scaffolds with different axial ligands that can be functionalized while keeping the platinum(II) pharmacophore intact. Using a sequential acylation strategy, we developed a class of Pt^IV prodrugs of cisplatin with contrasting lipophilic and hydrophilic ligands. We investigated their stability, reduction rates, lipophilicity, aqueous solubility, and antiproliferative efficacies, and assessed for correlations among the parameters that could be useful in drug design. We showed that compounds with high lipophilicity result in better antiproliferative effects in vitro and in vivo, with one of the three compounds tested showing better efficacy than satraplatin against an animal model of colorectal cancer, owing to its higher solubility and lower reduction rates. Our asymmetric Pt^IV prodrugs may pave the way for a highly predictable, fine-tuned class of orally available Pt^IV prodrugs for the treatment of colorectal cancer.

The effect of incorporating carboxylic acid functionalities into 2,2′-bipyridine on the biological activity of the complexes formed: synthesis, structure, DNA/protein interaction, antioxidant activity and cytotoxicity

Incorporation of carboxylic acid group in the bipyridine moiety has resulted in showing differences in DNA/protein binding affinity, efficiency in antioxidant activity and cytotoxicity.

A Lipophilic Pt(IV) Oxaliplatin Derivative Enhances Antitumor Activity

Side effects and acquired resistance by cancer cells limit the use of platinum anticancer drugs. Modification of oxaliplatin (OXA) into a lipophilic Pt(IV) complex [Pt(DACH)(OAc)(OPal)(ox)] (1), containing both lipophilic and hydrophilic axial ligands, was applied to improve performance and facilitate incorporation into polymeric nanoparticles. Complex 1 exhibited unique potency against a panel of cancer cells, including cisplatin-resistant tumor cells. [Pt(DACH)(OAc)(OPal)(ox)] incorporated nanoparticles (2) presented a mean diameter of 146 nm with encapsulation yields above 95% as determined by HPLC. Complexes 1 and 2 showed enhanced in vitro cellular Pt accumulation, DNA platination, and antiproliferative effect compared to OXA. Results of an orthotopic intraperitoneal model of metastatic ovarian cancer (SKOV-3) and a xenograft subcutaneous model of colon (HCT-116) tumor in SCID-bg mice showed that the activity of 1 and 2 significantly decreased tumor growth rates compared to control and OXA treatment groups. Consequently, these findings warrant further development toward clinical translation.

Bis- and Tetrakis(carboxylato)platinum(IV) complexes with mixed axial ligands - synthesis, characterization, and cytotoxicity

A series of twelve novel diamminetetrakis(carboxylato)platinum(IV) and 18 novel bis(carboxylato)dichlorido(ethane-1,2-diamine)platinum(IV) complexes with mixed axial carboxylato ligands was synthesized and characterized by multinuclear (1) H-, (13) C-, (15) N-, and (195) Pt-NMR spectroscopy. Their cytotoxic potential was evaluated (by MTT assay) against three human cancer cell lines derived from ovarian teratocarcinoma (CH1/PA-1), lung (A549), and colon carcinoma (SW480). In the cisplatin-sensitive CH1/PA-1 cancer cell line, diamminetetrakis(carboxylato)platinum(IV) complexes showed IC50 values in the low micromolar range, whereas, for the most lipophilic compounds of the bis(carboxylato)dichlorido(ethane-1,2-diamine)platinum(IV) series, IC50 values in the nanomolar range were found.

Anticancer Activities of Mononuclear Ruthenium(II) Coordination Complexes

Ruthenium compounds are highly regarded as potential drug candidates. The compounds offer the potential of reduced toxicity and can be tolerated in vivo. The various oxidation states, different mechanism of action, and the ligand substitution kinetics of ruthenium compounds give them advantages over platinum-based complexes, thereby making them suitable for use in biological applications. Several studies have focused attention on the interaction between active ruthenium complexes and their possible biological targets. In this paper, we review several ruthenium compounds which reportedly possess promising cytotoxic profiles: from the discovery of highly active compounds imidazolium [trans-tetrachloro(dmso)(imidazole)ruthenate(III)] (NAMI-A), indazolium [trans-tetrachlorobis(1H-indazole)ruthenate(III)](KP1019), and sodium trans-[tetrachloridobis(1H-indazole)ruthenate(III)] (NKP-1339) to the recent work based on both inorganic and organometallic ruthenium(II) compounds. Half-sandwich organometallic ruthenium complexes offer the opportunity of derivatization at the arene moiety, while the three remaining coordination sites on the metal centre can be functionalised with various coordination groups of various monoligands. It is clear from the review that these mononuclear ruthenium(II) compounds represent a strongly emerging field of research that will soon culminate into several ruthenium based antitumor agents.

Conjugation of cisplatin analogues and cyclooxygenase inhibitors to overcome cisplatin resistance

Cyclooxygenase (COX) is an enzyme involved in tumorigenesis and is associated with tumor cell resistance against platinum-based antitumor drugs. Cisplatin analogues were conjugated with COX inhibitors (indomethacin, ibuprofen) to study the synergistic effects that were previously observed in combination treatments. The conjugates ensure concerted transport of both drugs into cells, and subsequent intracellular cleavage enables a dual-action mode. Whereas the platinum(II) complexes showed cytotoxicities similar to those of cisplatin, the platinum(IV) conjugates revealed highly increased cytotoxic activities and were able to completely overcome cisplatin-related resistance. Although some of the complexes are potent COX inhibitors, the conjugates appear to execute their cytotoxic action via COX-independent mechanisms. Instead, the increased lipophilicity and kinetic inertness of the conjugates seem to facilitate cellular accumulation of the platinum drugs and thus improve the efficacy of the antitumor agents. These conjugates are important tools for the elucidation of the direct influence of COX inhibitors on platinum-based anticancer drugs in tumor cells.

Overcoming tumor resistance to cisplatin through micelle-mediated combination chemotherapy

The main obstacles to cancer therapy are the inability to target cancer cells and the acquired drug resistance after a period of chemotherapy. Reduced drug uptake and DNA repair are the two main mechanisms involved in cisplatin resistance. In the present investigation, canthaplatin, a Pt(iv) pro-drug of cisplatin and a protein phosphatase 2A (PP2A) inhibitor (4-(3-carboxy-7-oxa-bicyclo[2.2.1]heptane-2-carbonyl)piperazine-1-carboxylic acid tert-butyl ester), was designed and delivered using PEG-b-PLGA micelles for combination chemotherapy. Polymer/canthaplatin micelles facilitated the delivery of the drug into cancer cells through endocytosis and diminished DNA repair by PP2A inhibition, resulting in enhanced anti-tumor efficiency and excellent reversal ability of tumor resistance to cisplatin both in vitro and in vivo. Additionally, the polymer/canthaplatin micelles could prolong drug residence in the blood and decrease the side effects when compared to cisplatin.

A new entry to asymmetric platinum(IV) complexes via oxidative chlorination

Pt(IV) complexes are usually prepared by oxidation of the corresponding Pt(II) counterparts, typically using hydrogen peroxide or chlorine. A different way to synthesize asymmetrical Pt(IV) compounds is the oxidative chlorination of Pt(II) counterparts with N-chlorosuccinimide. The reaction between cisplatin cis-[PtCl2(NH3)2], carboplatin, cis-[PtCl2(dach)] and cis-[Pt(cbdc)(dach)] (cbdc = cyclobutane-1,1'-dicarboxylato; dach = cyclohexane-1R,2R-diamine) with N-chlorosuccinimide in ethane-1,2-diol was optimized to produce the asymmetric Pt(IV) octahedral complexes [PtA2Cl(glyc)X2] (A2 = 2 NH3 or dach; glyc = 2-hydroxyethanolato; X2 = 2 Cl or cbdc) in high yield and purity. The X-ray crystal structure of the [Pt(cbdc)Cl(dach)(glyc)] complex is also reported. Moreover, the oxidation method proved to be versatile enough to produce other mixed Pt(IV) derivatives varying the reaction medium. The two trichlorido complexes easily undergo a pH-dependent hydrolysis reaction, whereas the dicarboxylato compounds are stable enough to allow further coupling reactions for drug targeting and delivery via the glyc reactive pendant. Therefore, the coupling reaction between the [Pt(cbdc)Cl(dach)(glyc)] and a model carboxylic acid, a model amine, and selectively protected amino acids is reported.

Conjugates of cisplatin and cyclooxygenase inhibitors as potent antitumor agents overcoming cisplatin resistance

Cyclooxygenase-2 (COX-2) is an enzyme involved in tumorigenesis, and inhibitors of the enzyme are increasingly used as adjuvant modulators in anticancer therapies due to their synergistic effects with traditional chemotherapeutics. COX-2 is also reported to cause resistance towards antitumor agents, such as cisplatin. Here, the first covalently linked conjugates of cisplatin and COX inhibitors are reported. These conjugates exhibit concerted transport of both drugs into tumor cells and simultaneous action upon intracellular cleavage. These platinum(IV) complexes show highly increased cytotoxicity compared with cisplatin and are even able to overcome cisplatin-related resistance of tumor cells. While the results reported show that COX-2 inhibition is not directly responsible for the potent activities of these conjugates, they do represent useful tool compounds for the elucidation of the influence of COX inhibitors on the efficacy of antitumor agents.

Monofunctional and higher-valent platinum anticancer agents

Platinum compounds represent one of the great success stories of metals in medicine. Following the serendipitous discovery of the anticancer activity of cisplatin by Rosenberg, a large number of cisplatin variants have been prepared and tested for their ability to kill cancer cells and inhibit tumor growth. These efforts continue today with increased realization that new strategies are needed to overcome issues of toxicity and resistance inherent to treatment by the approved platinum anticancer agents. One approach has been the use of so-called "non-traditional" platinum(II) and platinum(IV) compounds that violate the structure-activity relationships that governed platinum drug-development research for many years. Another is the use of specialized drug-delivery strategies. Here we describe recent developments from our laboratory involving monofunctional platinum(II) complexes together with a historical account of the manner by which we came to investigate these compounds and their relationship to previously studied molecules. We also discuss work carried out using platinum(IV) prodrugs and the development of nanoconstructs designed to deliver them in vivo.

Diamminetetrakis(carboxylato)platinum(IV) complexes--synthesis, characterization, and cytotoxicity

A series of eight novel diamminetetrakis(carboxylato)platinum(IV) complexes was synthesized and characterized by multinuclear ¹H-, ¹³C-, ¹⁵N-, and ¹⁹⁵Pt-NMR spectroscopy. Their antiproliferative potency was evaluated in three human cancer cell lines representing ovarian (CH1), lung (A549), and colon carcinoma (SW480). In cisplatin-sensitive CH1 cancer cells, cytotoxicity was found in the low micromolar range, whereas, in inherently cisplatin-resistant A549 and SW480 cells, the activity was very low or negligible. Astonishingly, raise in lipophilicity of the complexes, as found in the case of cisplatin analogs, did not result in a significant enhancement of the cytotoxic effect.

Mono-carboxylated diaminedichloridoplatinum(IV) complexes--selective synthesis, characterization, and cytotoxicity

(OC-6-43)-Dichlorido(N,N-dimethyl-ethane-1,2-diamine)dihydroxidoplatinum(IV) could selectively be mono-carboxylated with succinic anhydride based on the steric hindrance caused by the two methyl groups of the equatorial ligand. Subsequent esterification of the uncoordinated carboxylic acid with alcohols of different lengths (methanol, butanol, hexanol and octanol) afforded the corresponding esters. The synthesized complexes were characterized in detail by elemental analysis, ESI-MS, multinuclear ((1)H, (13)C, (15)N and (195)Pt) NMR spectroscopy and in two cases by X-ray crystallography. Cytotoxicity of novel platinum(IV) compounds was investigated in four human cancer cell lines (CH1, A549, SW480 and SK-OV-3). Remarkably, the most lipophilic complexes showed IC(50) values down to the low micromolar or even nanomolar range.

Synthesis, characterization, and cytotoxicity of platinum(IV) carbamate complexes

The synthesis, characterization, and cytotoxicity of eight new platinum(IV) complexes having the general formula cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CNHR)(2)] are reported, where R = tert-butyl (4), cyclopentyl (5), cyclohexyl (6), phenyl (7), p-tolyl (8), p-anisole (9), 4-fluorophenyl (10), or 1-naphthyl (11). These compounds were synthesized by reacting organic isocyanates with the platinum(IV) complex cis,cis,trans-[Pt(NH(3))(2)Cl(2)(OH)(2)]. The electrochemistry of the compounds was investigated by cyclic voltammetry. The aryl carbamate complexes 7-11 exhibit reduction peak potentials near -720 mV vs Ag/AgCl, whereas the alkyl carbamate complexes display reduction peak potentials between -820 and -850 mV vs Ag/AgCl. The cyclic voltammograms of cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CCH(3))(2)] (1), cis,cis,trans-[Pt(NH(3))(2)Cl(2)(O(2)CCF(3))(2)] (2), and cis-[Pt(NH(3))(2)Cl(4)] (3) were measured for comparison. Density functional theory studies were undertaken to investigate the electronic structures of 1-11 and to determine their adiabatic electron affinities. A linear correlation (R(2) = 0.887) between computed adiabatic electron affinities and measured reduction peak potentials was discovered. The biological activity of 4-11 and, for comparison, cisplatin was evaluated in human lung cancer A549 and normal MRC-5 cells by the MTT assay. The compounds exhibit comparable or slightly better activity than cisplatin against the A549 cells. In MRC-5 cells, all are equally or slightly less cytotoxic than cisplatin, except for 4 and 5, which are more toxic.

Novel endothall-containing platinum(IV) complexes: synthesis, characterization, and cytotoxic activity

Two platinum(IV) complexes (OC-6-33)-dichlorido(ethane-1,2-diamine)dihydroxidoplatinum(IV) and (OC-6-33)-diammine(dichlorido)dihydroxidoplatinum(IV) were carboxylated using demethylcantharidin as carboxylation agent. The complexes were characterized by elemental analysis, mass spectrometry, multinuclear (1H, 13C, 15N, and 195Pt) NMR spectroscopy, and, in case of (OC-6-33)-diamminebis(3-carboxy-7exo-oxabicyclo[2.2.1]heptane-2-carboxylato)dichloridoplatinum(IV) via X-ray diffraction. Cytotoxicity of the complexes was studied in seven human cancer cell lines representing five tumor entities, i.e., ovarian carcinoma (CH1, SK-OV-3), cervical carcinoma (HeLa), colon carcinoma (SW480, HCT-116), osteosarcoma (U-2 OS), and hepatocellular carcinoma (Hep G2) by means of the MTT (=3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium hydrobromide) assay.

Novel bis(carboxylato)dichlorido(ethane-1,2-diamine)platinum(IV) complexes with exceptionally high cytotoxicity

(OC-6-33)-Dichlorido(ethane-1,2-diamine)dihydroxidoplatinum(IV) (1) was carboxylated using succinic- or 3-methylglutaric anhydride. The resulting bis(carboxylato)platinum(IV) complexes display free, uncoordinated carboxylic acid groups which were further derivatized with primary aliphatic alcohols. The complexes were characterized in detail by elemental analysis, ESI-MS, FT-IR, as well as multinuclear (1H, 13C, 15N, 195Pt) NMR spectroscopy. Cytotoxic properties were evaluated in four human tumor cell lines originating from ovarian carcinoma (CH1, SK-OV-3), cervical carcinoma (HeLa) and colon carcinoma (SW480) by means of the MTT assay (MTT = 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide). Structure-activity relationships showed that the cytotoxicity increased with increasing lipophilicity of the alcoholate moiety yielding IC50 values in the low micromolar or even low nanomolar range.

Synthesis and characterization of platinum(IV) anticancer drugs with functionalized aromatic carboxylate ligands: influence of the ligands on drug efficacies and uptake

A series of trans-platinum(IV) complexes with functionalized aromatic carboxylate ligands, cis,cis,trans-Pt(NH3)2Cl2(CO2C6H4R)2 (R = H (3), p-vinyl (4), p-methoxy (5), p-iodo (6), p-cyano (7), or o-carboxyl (8)) was synthesized and characterized by spectroscopic methods. Crystal structures of 3, 4, 7, and 8 were obtained, which revealed that their structural conformations were influenced by intramolecular H-bonding interactions. The complexes were evaluated for cellular uptake and inhibition of cell proliferation against a panel of lung, colon, and breast carcinoma cell lines. The functionalization of the aromatic carboxylate ligand was found to have a profound influence on the uptake, and hence, efficacy, of this class of complex.

Rational design of platinum(IV) compounds to overcome glutathione-S-transferase mediated drug resistance

A rationally designed Pt(IV) anticancer compound is described, employing the novel concept of tethering an inhibitor of glutathione-S-transferase, an enzyme associated with Pt-based drug-resistance, to cisplatin. Its enzyme inhibition activity, investigated using spectrophotometric and mass spectrometry-based techniques, and cytotoxic profile in resistant cancer cells are described.

Preparation and characterization of platinum(II) and (IV) complexes of 1,3-diaminepropane and 1,4-diaminebutane: circumvention of cisplatin resistance and DNA interstrand cross-link formation in CH1cisR ovarian tumor cells

The reaction of Pt(dimethyl sulfoxide)(2)CBDCA (CBDCA = 1,1-cyclobutanedicarboxylate) with 1,4-diaminebutane and 1,3-diaminepropane ligands yields, under certain conditions, new [Pt(diamine)(2)]CBDCA complexes (1a,b), where the CBDCA ligand has been removed from the coordination sphere of the platinum atom by the diamine ligand, instead of forming the expected [Pt(diamine)CBDCA] complexes (1'a,b). The structure of complexes 1a and 1'b was solved by X-ray diffraction. Complex 1a crystallizes in the orthorhombic system, in the noncentrosymmetric C222 space group, with unit cell parameters: a = 20.053(2) A; b = 8.655(2) A, c = 5.711(3) A; V = 991.2(6) A(3); delta (calcd) = 1.627 mg/m(3); and R = 0.050. The Pt atom displays an unexpected distorted tetrahedral coordination with a N-Pt-N inner bond angle equal to 81(2) degrees for N atoms of the same 1,3-propanediamine ligand and a N-Pt-N bond angle for different ligands equal to 135.4(9) degrees. Complex 1'b crystallizes in the monoclinic system, in the centrosymmetric P2(1)/c space group, with unit cell parameters: a = 6.007(2) A; b = 15.336(4) A, c = 13.232(5) A; beta = 101.90(3) degrees; V = 1192.8(7) A(3); delta (calcd) = 2.369 mg/m(3); and R = 0.067. Cytotoxicity data show that of all the synthesized compounds, only complexes 1'a and 1'b exhibit remarkable cytotoxic properties. Thus, in contrast with carboplatin (cis-diammine-1,1-cyclobutane dicarboxilatoplatinum(II)), compounds 1'a and 1'b, which also contain the CBDCA ligand, are able to circumvent cisplatin (cis-diamminedichloroplatinum(II)) resistance in several tumor cells. Moreover, after 24 h of incubation of CH1cisR ovarian tumor cells with 10 microM of compounds 1'a and 1'b, the level of DNA interstrand cross-links (ICLs) induced by compounds 1'a and 1'b is 3.3 and 3.8 times higher, respectively, than that of carboplatin and 3.5 and 4.0 times higher, respectively, than that of cisplatin. Interestingly, under the same conditions, the intracellular accumulation of compounds 1'a and 1'b is similar to that of carboplatin and cisplatin. However, the extent of binding to DNA of compounds 1'a and 1'b is similar to that of cisplatin but slightly higher than that of carboplatin. We propose that circumvention of cisplatin resistance in CH1cisR cells by compounds 1'a and 1'b might be related to its higher ability to form DNA ICLs relative to carboplatin and cisplatin.

Reduction of (imine)Pt(IV) to (imine)Pt(II) complexes with carbonyl-stabilized phosphorus ylides

A novel method is reported for generation of the difficult-to-obtain (imine)Pt(II) compounds that involves reduction of the corresponding readily available Pt(IV)-based imines by carbonyl-stabilized phosphorus ylides, Ph3P=CHCO2R, in nonaqueous media. The reaction between neutral (imino)Pt(IV) compounds [PtCl4[NH=C(Me)ON=CR1R2]2] [R1R2 = Me2, (CH2)4, (CH2)5, (Me)C(Me)=NOH], [PtCl4[NH=C(Me)ONR2]2] (R = Me, Et, CH2Ph), (R1 = H; R2 = Ph or C6H4Me; R3 = Me) as well as anionic-type platinum(IV) complexes (Ph3PCH2Ph)[PtCl5[NH=C(Me)ON=CR2]] [R2 = Me2, (CH2)4, (CH2)5] and 1 equiv of Ph3P=CHCO2R (R = Me, Et) proceeds under mild conditions (ca. 4 h, room temperature) to give selectively the platinum(II) products (in good to excellent isolated yields) without further reduction of the platinum center. All thus prepared compounds (excluding previously described Delta4-1,2,4-oxadiazoline complexes) were characterized by elemental analyses, FAB mass spectrometry, IR and 1H, 13C[1H], 31P[1H] and 195Pt NMR spectroscopies, and X-ray single-crystal diffractometry, the latter for [PtCl2[NH=C(Me)ON=CMe2]2] [crystal system tetragonal, space group P4(2)/n (No. 86), a = b = 10.5050(10) A, c = 15.916(3) A] and (Ph3PCH2CO2Me)[PtCl3(NCMe)] [crystal system orthorhombic, space group Pna2(1) (No. 33), a = 19.661(7) A, b = 12.486(4) A, c = 10.149(3) A]. The reaction is also extended to a variety of other Pt(II)/Pt(IV) couples, and the ylides Ph3P=CHCO2R are introduced as mild and selective reducing agents of wide applicability for the conversion of Pt(IV) to Pt(II) species in nonaqueous media, a route that is especially useful in the case of compounds that cannot be prepared directly from Pt(II) precursors, and for the generation of systematic series of Pt(II)/Pt(IV) complexes for biological studies.

Cisplatin stops tubulin assembly into microtubules. A new insight into the mechanism of antitumor activity of platinum complexes

Despite numerous studies considering DNA as a primary target of cisplatin attack, this work is the first to show the pure effect of cisplatin on the process of tubulin assembly/disassembly in vitro. When platinated, tubulin does not assemble into microtubules (direct electron microscopic studies). In place of them, highly stable and inert circled rings arise. Such tubulin aggregates are unable to participate in the process of chromosome separation during the mitosis, thus blocking cell division in living cells, which is a direct evidence of cisplatin antitumor activity. Cisplatin attack on tubulin causing blockage of tubulin assembly occurs via a two-step binding to GTP in the GTP center of tubulin ((195)Pt, (31)P NMR studies). The calculated binding rates are close to those reported in cisplatin-DNA interactions. The mechanism of cisplatin attack on tubulin is proposed.