The Increase of Antileukemic Efficiency of Doxorubicin and Other Cytostatics Combined with Platinum(IV)-Nitroxyl Complex ВС118.

Combined treatment of murine leukemia P388 with doxorubicin and platinum(IV)-nitroxyl complex ВС118 administered in low doses improved efficiency of treatment (cure of 83% of animals) without increasing toxicity.

Influence of Tumor Suppressor p53 Functioning on the Expression of Antioxidant System Genes under the Action of Cytotoxic Compounds.

The effect of inhibition of the tumor suppressor p53 on the antioxidant system genes expression under the influence of cytotoxic compounds of the platinum group was studied. It was found that the action of platinum(II) and platinum(IV) complexes induced accumulation of p53 protein with a maximum in 12 h, which was confirmed by an increase in the expression of the P21 gene, the target gene of the p53 protein. It was shown that the action of platinum complexes activated the expression of catalase and superoxide dismutase 2 genes. Suppression of p53 protein functions with specific inhibitor α-piphitrin under the action of platinum complexes reduced the expression of catalase and superoxide dismutase 2 genes and the target gene P21, which attested to the p53-dependent regulation of these genes.

Comparison of the Effect of Platinum (IV) Complexes on Spheroids and Monolayer Culture of HeLa Cells.

We performed a comparative study of the cytotoxicity of cisplatin, JM216 complex, and aminonitroxyl platinum(IV) complexes for HeLa cells grown in monolayer and 3D culture. The growth dynamics of spheroids was studied and optimal conditions for evaluation of cytotoxicity were determined. Spheroids were less sensitive to the test compounds than cells in a monolayer. The resistance index (RI) of spheroids was determined as the ratio of IC50 for spheroids to IC50 for monolayer culture. Resistance index was 5.0±1.5 for cisplatin and ranged from 1.8 to 2.3 for platinum(IV) complexes. The observed differences are related to different physicochemical properties of the complexes and different mechanisms of their penetration into cells.

Effect of Chitosan-(Poly)Nitroxides on Normal and Tumor Cells under Conditions of Induced Oxidative Stress.

The cytotoxicity and antioxidant effects of chitosan-(poly)nitoxides of different molecular weights containing a nitroxide radical of the piperidine structure were studied on tumor (HeLa, A172, and HepG2) and normal (Vero) cell lines. The chitosan-(poly)nitroxides exhibited low cytotoxicity. Under conditions of oxidative stress induced with tert-butyl hydroperoxide, the most pronounced decrease in ROS levels in the presence of chitosan-(poly)nitroxides was observed in normal cells. In cell homogenates, the decrease in malondialdehyde levels was observed only in the presence of low-molecular-weight chitosan-(poly)nitroxide irrespective of the cell line. Our data demonstrate that the cell-specific antioxidant properties of chitosan-(poly)nitroxides are related to their penetration into cells and interaction with intracellular membranes.

Effect of Cytotoxic Compounds on Activity of Antioxidant Enzyme System in MCF-7 and H1299 Cells.

We studied the function of the antioxidant system in tumor cell lines MCF-7 and H1299 that differ by the state of tumor suppressor gene p53. Exposure to different classes of cytotoxic compounds induced several types of antioxidant system responses that depend on the type of cell line. The effects of platinum(II) and platinum(IV) complexes on activity of antioxidant enzymes vary, which can be explained by differences in their accumulation and biotransformation in tumor cells. Triazole and oxazolidinone derivatives had little effect on activity of superoxide dismutase and catalase in H1299 cells, but increased superoxide dismutase activity in MCF-7 cells.

[Antileukemic activity and development of resistance to cisplatin (CPT) and platinum (IV)-nitroxyl complex VS118].

Treatment with low doses (1/10 of LD50) of cisplatin and platinum (IV)-nitroxyl complex VS118 [e-ammin-d-(4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl)-a,f-bi s(acetate)-b,c-dichlorplatinum (IV)] was followed by a synergistic therapeutic effect (a 100% cure of animals) as compared with monotherapy with either drug. There was no synergistic increase in toxicity. The rates of resistance development decreased in the following order: P388/cPt+VS118, P388/cPt, P388/VS118. Resistant strains P388/cPt+VS18 and P388/VS118 were highly sensitive to doxorubicin, etoposide and cyclophoshamide. Further research in cPt+VS 118 combinations should be continued.

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 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.