V. D. Sen

Synthesis and antitumor activity of platinum(II) complexes with trans-3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl

Platinum complexes PtII(DAPO)X2 with diaminonitroxyl radical-trans-3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl (DAPO)-were synthesized by the direct reaction of DAPO with K2PtX4 (X = Cl, I) or by the replacement of chloro ligands in PtII(DAPO)Cl2 by bromo, nitrato, oxalato, malonato, and 1,1-cyclobutanedicarboxylato ligands. The complexes thus obtained were characterized by elemental analysis, infrared,electronic, electron paramagnetic resonance spectroscopic techniques, and high-performance liquid chromatography. The toxicity of compounds in terms of LD50 strongly depends on the nature of X-ligands, and varies between 11 mg/kg (X = NO3) and 400 mg/kg (X2 = 1,1-cyclobutanedicarboxylate). Up to 66% of mice bearing leukemia L1210 survive after the administration of these complexes. This effect is comparable to the effect of cisplatin (50% survive). An increase in the life span of the rest of the animals ranges from 158 to 383%. Complex PtII(DAPO)Cl2 appears to be more efficient than cisplatin against adenocarcinoma 755. Cisplatin, cis-diamminedichloroplatinum(II); CBDCA, 1,1-cyclobutanedicarboxylic acid; DAPO, trans-3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl; Mal, malonic acid; Ox, oxalic acid; IR, infrared; EPR, electron paramagnetic resonance; HPLC, high-performance liquid chromatography; Ca755, adenocarcinoma 755; LD50 and LD100, dose of compounds (mg/kg), causing a death of 50 or 100% or treated animals; ILS, increase in life span of mice.

Heparin-polynitroxides: Synthesis and preliminary evaluation as cardiovascular EPR/MR imaging probes and extracellular space-targeted antioxidants

We report here the synthesis of heparin-polynitroxide derivatives (HPNs) in which nitroxide moieties are linked either to uronic acid or glycosamine residues of the heparin macromolecule. HPNs have low anticoagulant activity, possess superoxide scavenging properties, bind to the vascular endothelium/extra-cellular matrix and can be detected by EPR and MRI techniques. As the vascular wall-targeted redox-active paramagnetic compounds, HPNs may have both diagnostic (molecular MRI) and therapeutic (ecSOD mimics) applications.

Spin-Labeled Heparins as Polarizing Agents for Dynamic Nuclear Polarization

A potentially biocompatible class of spin-labeled macromolecules, spin-labeled (SL) heparins, and their use as nuclear magnetic resonance (NMR) signal enhancers are introduced. The signal enhancement is achieved through Overhauser-type dynamic nuclear polarization (DNP). All presented SL-heparins show high (1)H DNP enhancement factors up to E=-110, which validates that effectively more than one hyperfine line can be saturated even for spin-labeled polarizing agents. The parameters for the Overhauser-type DNP are determined and discussed. A striking result is that for spin-labeled heparins, the off-resonant electron paramagnetic resonance (EPR) hyperfine lines contribute a non-negligible part to the total saturation, even in the absence of Heisenberg spin exchange (HSE) and electron spin-nuclear spin relaxation (T(1ne)). As a result, we conclude that one can optimize the use of, for example, biomacromolecules for DNP, for which only small sample amounts are available, by using heterogeneously distributed radicals attached to the molecule.

Platinum(IV)-nitroxyl complexes as possible candidates to circumvent cisplatin resistance in RT112 bladder cancer cells

The therapeutic efficacy of the anticancer drug cisplatin is limited by the development of resistance. We therefore investigated newly synthesized platinum-nitroxyl complexes (PNCs) for their potential to circumvent cisplatin resistance. The complexes used were PNCs with bivalent cis-PtII(R·NH2)(NH3)Cl2 and cis-PtII(DAPO)Ox and four-valent platinum cis,trans,cis-PtIV(R·NH2)(NH3)(OR)2Cl2 and cis,trans,cis-PtIV(DAPO)(OR)2Ox, where R· are TEMPO or proxyl nitroxyl radicals, DAPO is trans-3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl, and OR and Ox are carboxylato and oxalato ligands, respectively. The complexes were characterized by spectroscopic methods, HPLC, log Pow data and elemental analysis. We studied intracellular platinum accumulation, DNA platination and cytotoxicity upon treatment with the PNCs in a model system of the bladder cancer cell line RT112 and its cisplatin-resistant subline RT112-CP. Platinum accumulation and DNA platination were similar in RT112 and RT112-CP cells for both bivalent and four-valent PNCs, in contrast to cisplatin for which a reduction in intracellular accumulation and DNA platination was observed in the resistant subline. The PNCs were found to platinate DNA in relation to the length of their axial RO-ligands. Furthermore, the PNCs were increasingly toxic in relation to the elongation of their axial RO-ligands, with similar toxicities in RT112 and its cisplatin-resistant subline. Using a cell-free assay, we observed induction of oxidative DNA damage by cisplatin but not PNCs suggesting that cisplatin exerts its toxic action by platination and oxidative DNA damage, while cells treated with PNCs are protected against oxidatively induced lesions. Altogether, our study suggests that PNCs may provide a more effective treatment for tumors which have developed resistance toward cisplatin.

Heparin-polynitroxide derivatives: a platform for new diagnostic and therapeutic agents in cardiovascular disease?

Vascular wall extracellular oxidative stress Cardiovascular disease (CVD; mainly atherosclerosis, hypertension and diabetes mellitus) remains a major cause of death in western society [1]. Despite substantial progress achieved, the diagnosis of CVD often comes too late, when the disease has already advanced to therapeutically incurable stages. The development of efficient diagnostic probes allowing early non-invasive diagnostics, as well as drugs which can prevent or reverse CVD and/or its complications (e.g., myocardium infarctus and stroke) are highly desired tasks of the modern cardiovascular medicinal chemistry.

Binding of platinum-diaminonitroxyl complexes to animal DNA

Reaction of PtII(DAPO)X2 complexes (where DAPO is trans-3,4-diamino-2,2,6,6-tetramethylpiperidine-1-oxyl, X2 = (NO3)2, oxalato (Ox) or 1,1-cyclobutanedicarboxylato (Cbdca)) with a bovine spleen DNA in 0.01 M NaHCO3 at 37 degrees C for 24 h gives rise to formation of platinated DNA. The [bound PtII(DAPO)]/[nucleotide] ratio (r) depends on the initial ratio of the reagents and on the nature of leaving ligands X. Nitroxyl-nitroxyl distances in platinated DNA determined by the ESR suggest that at r > or = 0.1 PtII(DAPO) fragments are uniformly attached to DNA. But at lower r, the thermal characteristics of modified DNA (melting temperature Tm, melting range width delta T) and the guanine-to-adenine platination degree ratios GPt/APt imply that the nature of leaving ligands X affect the selectivity of DNA platination. At r > or = 0.1, nitroxyl groups can approach each other so close that, in an acidic medium, the electron transfer from one nitroxyl group to another becomes possible, and the nitroxyls readily disproportionate to diamagnetic products. Correlation time of nitroxyl rotation in PtII(DAPO)-DNA adducts is approximately 10(-8) s, which is related to predominantly bifunctional bonding of PtII(DAPO) with DNA. Platination-induced distortion of DNA was evidenced by changes in Tm, delta T and degree of hyperchromicity H. The major part of adducts form the intrastrand cross-links which destabilize the structure of DNA duplex. The interstrand PtII(DAPO) cross-linking (approximately 1% of the adducts) facilitates renaturation of despiralized DNA molecules upon cooling. Two types of PtII(DAPO)-DNA adducts are revealed, which differ substantially in their rates of deplatination with NaCN. ESR, electron spin resonance; r, degree of modification; cisplatin, cis-diamminedichloroplatinum(II); Tm, melting temperature; delta T, melting range width; H, degree of hyperchromicity; R, degree of renaturation; AAS, atomic absorption spectroscopy; HPLC, high performance liquid chromatography.

Synthesis, structure, and antitumor properties of platinum(iv) complexes with aminonitroxyl radicals

The platinum(iv) complexes cis,trans,cis-PtIV(RNH2)(NH3)(OH)2Cl2, where R is 2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl (1) or 2,2,5,5-tetramethyl-1-oxyl-3-pyrrolidinyl (2), were prepared by oxidation of the corresponding cis-PtII(RNH2)(NH3)Cl2 complexes with hydrogen peroxide. The reactions are catalyzed by tungstate salts, which makes it possible to carry out oxidation under mild conditions. The resulting complexes were characterized by elemental analysis, HPLC, and IR, UV, and ESR spectroscopy. The structure of complex 1 was established by X-ray diffraction analysis. Complex 1 exhibits the highest antitumor activity in an experimental tumor, viz., in P388 leukemia. The resistance of the tumor to this complex developed much slower than that to Cisplatin.

Stable nitroxyl radicals and hydroxylamines as inhibitors of methyl linoleate oxidation in micelles

The kinetics of methyl linoleate oxidation in micelles inhibited by nitroxyl radicals and hydroxylamines was studied. The regeneration of nitroxyl radicals in this process was found. The activity of the studied inhibitors increases with increasing their lipophilicity. This effect was explained by increasing the distribution coefficient of the antioxidants in a micelles–water system. The reaction of nitroxyl radicals with the hydroperoxide radical formed upon the oxidation of methyl linoleate in micelles is proposed to be the key reaction in nitroxyl radical regeneration.

Synthesis, structure, and biological activity of mixed-ligand platinum(II) complexes with aminonitroxides

Mixed-ligand platinum complexescis-PtII(R6NH2)(NH3)X2 andcis-PtII(R5NH2)(NH3)X2 (R6 is 2,2,6,6-tetramethyl-4-piperidyl-1-oxyl and R5 is 2,2,5,5-tetramethyl-3-pyrrolidinyl-1-oxyl) were synthesized by either the reaction of aminonitroxides RNH2 with Na[PtII(NH3)Cl2I] generatedin situ (for X2=ClI) or by replacement of the iodo-chloro ligands incis-Pt11(RNH2)(NH3)ClI by dichloro and oxalato ligands. The complexes obtained were characterized by elemental analysis and by IR, UV, and ESR spectra. Forcis-Pt11(R5NH2)(NH3)Cl2, crystal and molecular structures were determined by X-ray diffraction analysis. Cisplatin accelerates autooxidation of methyl linoleate and the platinum nitroxide complexes synthesized exhibit antioxidant properties. The rate of isolated DNA binding with the new complexes is almost as high as that for cisplatin.cis-Pt11(R6NH2)(NH3)Cl2 exhibits the highest antitumor activity. The high antitumor activity of platinum nitroxide complexes shows that the possible “radical component” is not a crucial factor in the cytotoxic action of cisplatin.

Synthesis of dinitroxylcis-diaminoplatinum(ii) complexes and their interaction with DNA

Dinitroxyl complexes of platinum,cis-PtII(APO)2X2, where APO is 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl, were obtained by either a direct reaction of APO with K2PtX4 (X=Cl or I) or a replacement of iodide ligands incis-PtII(APO)2I2 by nitrate and oxalate ligands. The interation of water-solublecis-PtII(APO)2(NO3)2 with, ox spleen DNA resulted in platinated DNA with a degree of modification (r)-7 times lower than that obtained withcis-PtII(NH3)2Cl2 (cisplatin). Melting pointTm, melting range ΔT, and the degree of hyperchromicity ΔH for platinated DNA showed that for equalr values, thecis-PtII(APO)2—DNA adducts increase heterogeneity in the DNA structure much more effectively than thecis-PtII(NH3)2—DNA adducts. Poor platinating activity, substantial disturbance of the DNA structure, as well as low toxicity and moderate antitumor activity ofcis-PtII(APO)2X2 complexes are probably explained by steric hindrances caused by two bulky APO ligands.