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Aim: This investigation was designed to synthesize half-sandwich Rh(III) and Ru(II) complexes and study their antiproliferative activity in human cancer cell lines. Materials & methods: Nine compounds were prepared and tested by various assays for their anticancer activity and mechanism of action. Results: Hit Rh(III) complex 6 showed low-micromolar potency in cisplatin-sensitive (A2780) and -resistant (A2780cis) ovarian carcinoma cell lines, promising selectivity toward these cancer cells over normal lung fibroblasts and an unprecedented mechanism of action in the treated cells. DNA synthesis was decreased and CDKN1A expression was upregulated, but p21 expression was not induced. Conclusion: Rh complex 6 showed high antiproliferative activity, which is induced through a p21-independent mechanism of action.

Nine rhodium(III)and ruthenium(II) complexes were developed and screened for their anticancer activity on a panel of human cancer cell lines. The best-performing rhodium(III) complex (6) showed high activity in ovarian cancer cells, including the variant resistant to the conventional anticancer drug cisplatin, while it was less effective towards non-cancerous lung fibroblasts. In cancer cells, compound 6 induced a modification of the cell cycle connected with a significant decrease in DNA synthesis, which was not observed for cisplatin. The effect of 6 on the expression of proteins related to the cell cycle modification was analysed by quantitative PCR and western blot in cancer cells and the results indicated a p21-independent mode of anticancer action, which is different from cisplatin.

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Half-sandwich complexes [Ru(η6-pcym)(L1)X]PF6 (1, 3) and [Ir(η5-Cp*)(L1)X]PF6 (2, 4) featuring a thiadiazole-based ligand L1 (2-(furan-2-yl)-5-(pyridin-2-yl)-1,3,4-thiadiazole) were synthesized and characterized by varied analytical methods, including single-crystal X-ray diffraction (X = Cl or I, pcym = p-cymene, Cp* = pentamethylcyclopentadienyl). The structures of the molecules were analysed and interpreted using computational methods such as Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QT-AIM). A 1H NMR spectroscopy study showed that complexes 1-3 exhibited hydrolytic stability while 4 underwent partial iodido/chlorido ligand exchange in phosphate-buffered saline. Moreover, 1-4 demonstrated the ability to oxidize NADH (reduced nicotinamide adenine dinucleotide) to NAD+ with Ir(III) complexes 2 and 4 displaying higher catalytic activity compared to their Ru(II) analogues. None of the complexes interacted with reduced glutathione (GSH). Additionally, 1-4 exhibited greater lipophilicity than cisplatin. In vitro biological analyses were performed in healthy cell lines (CCD-18Co colon and CCD-1072Sk foreskin fibroblasts) as well as in cisplatin-sensitive (A2780) and -resistant (A2780cis) ovarian cancer cell lines. The results indicated that Ir(III) complexes 2 and 4 had no effect on human fibroblasts, demonstrating their selectivity. In contrast, complexes 1 and 4 exhibited moderate inhibitory effects on the metabolic and proliferation activities of the cancer cells tested (selectivity index SI > 3.4 for 4 and 2.6 for cisplatin; SI = IC50(A2780)/IC50(CCD-18Co)), including the cisplatin-resistant cancer cell line. Based on these findings, it is possible to emphasize that mainly complex 4 could represent a further step in the development of selective and highly effective anticancer agents, particularly against resistant tumour types.

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The platinum(II) iodido complexes 1-5 of the general formula cis-[PtI2(Ln)2], where Ln stands for O-substituted 9-deazahypoxanthine derivatives, were prepared and thoroughly characterized by various techniques, including multinuclear 1D and 2D NMR spectroscopy. The complexes were screened for their anticancer potential in vitro on ten human cancer cell lines, concretely breast adenocarcinoma (MCF7), osteosarcoma (HOS), lung carcinoma (A549), cervix epithelioid carcinoma (HeLa), malignant melanoma (G-361), prostate carcinoma (22Rv1, PC-3), hepatocellular carcinoma (HepG2), ovarian carcinoma (A2780) and cisplatin-resistant ovarian carcinoma (A2780R). The complexes exhibited significant wide-spectrum anticancer activity in vitro against all the employed cell lines, with IC50≈0.5-24.0µM. Very good correlation between the lipophilicity parameter log P and IC50 values of anticancer activity in vitro were obtained by simple QSAR analysis. The most lipophilic complexes 2, 4 and 5 showed the best results, as they reached the sub-micromolar IC50 values against the A2780 and A2780R sub-lines, with the best result equal 0.5±0.1µM on A2780 for complex 5. The in vivo testing of the representative complexes 1, 4 and 5 (applied at the same dose of Pt as 2mg/kg dose of cisplatin) on a L1210 leukaemia model revealed their positive effect on the prolongation of the mean survival time, even if it was lower than that of cisplatin. The 1H NMR interaction study revealed the ability of complexes to interact with glutathione (GSH) and 5'-guanosine monophosphate (GMP) and overall higher stability of the complexes 1-5 as compared to cisplatin. The electrospray-ionization mass spectrometry experiments with complex 1 identified the formation of a rich collection of hydrolytic species in water-containing media after 24h and the interaction intermediates with sulfur-containing biomolecule l-cysteine, but not with the reduced glutathione at physiologically relevant concentration levels.

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Halogenido and carboxylato Ru(II) half-sandwich complexes of the general composition [Ru(η6-p-cym)(dpa)X]PF6 (1-5) were prepared and thoroughly characterized with various techniques (e.g., mass spectrometry, NMR spectroscopy and X-ray analysis); dpa = 2,2'-dipyridylamine; p-cym = p-cymene; X = Cl- (for 1), Br- (for 2), I- (for 3), valproate(1-) (for 4) or 4-phenylbutyrate(1-) (for 5). A single-crystal X-ray analysis showed a pseudo-octahedral piano-stool geometry of [Ru(η6-p-cym)(dpa)I]PF6 (3), with a η6-coordinated p-cymene, bidentate N-donor dpa ligand and iodido ligand coordinated to the Ru(II) atom. The results of the ¹H-NMR solution behaviour studies proved that the complexes 1-5 hydrolyse were in the mixture of solvents used (10% MeOD-d4/90% D2O). Complexes 1-5 were in vitro inactive against the A2780 human ovarian carcinoma cell line, up to the highest tested concentration (IC50 > 100 µM).

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A series of innovative copper(II) complexes of the general composition [Cu(Ln)(phen)]NO3 (1-8; phen=1,10-phenanthroline), involving 2'-hydroxychalcone {(E)-1-(2'-hydroxyphenyl)-3-phenylprop-2-en-1-one} derivatives (HLn) was synthesized, thoroughly characterized and screened for in vitro cytotoxicity against a panel of ten human cancer cell lines. The most promising results were achieved for complex 2 with the best IC50 value of 1.1±0.7µM (against A2780 cell line). The toxicity testing on a primary culture of human hepatocytes (HH) revealed that complex 2 is the least toxic from the whole series with the IC50 value of 63.7µM. The complexes were shown to be able to efficaciously cleave pUC19 plasmid DNA as well as intercalate into calf thymus DNA with the same affinity and efficacy as ethidium bromide and interact by the ligand exchange mechanism with l-cysteine at physiological concentration levels.

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We report toxic effects of a photoactivatable platinum(IV) complex conjugated with suberoyl-bis-hydroxamic acid in tumor cells. The conjugate exerts, after photoactivation, two functions: activity as both a platinum(II) anticancer drug and histone deacetylase (HDAC) inhibitor in cancer cells. This approach relies on the use of a Pt(IV) pro-drug, acting by two independent mechanisms of biological action in a cooperative manner, which can be selectively photoactivated to a cytotoxic species in and around a tumor, thereby increasing selectivity towards cancer cells. These results suggest that this strategy is a valuable route to design new platinum agents with higher efficacy for photodynamic anticancer chemotherapy.

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A series of gold(I) complexes involving triphenylphosphine (PPh3) and one N-donor ligand derived from deprotonated mono- or disubstituted hypoxanthine (HLn) of the general composition [Au(Ln)(PPh3)] (1-9) is reported. The complexes were thoroughly characterized, including multinuclear high resolution NMR spectroscopy as well as single crystal X-ray analysis (for complexes 1 and 3). The complexes were screened for their in vitro cytotoxicity against human cancer cell lines MCF7 (breast carcinoma), HOS (osteosarcoma) and THP-1 (monocytic leukaemia), which identified the complexes 4-6 as the most promising representatives, who antiproliferative activity was further tested against A549 (lung adenocarcinoma), G-361 (melanoma), HeLa (cervical cancer), A2780 (ovarian carcinoma), A2780R (ovarian carcinoma resistant to cisplatin), 22Rv1 (prostate cancer) cell lines. Complexes 4-6 showed a significantly higher in vitro anticancer effect against the employed cancer cells, except for G-361, as compared with the commercially used anticancer drug cisplatin, with IC50 ≈ 1-30 µM. Anti-inflammatory activity was evaluated in vitro by the assessment of the ability of the complexes to modulate secretion of the pro-inflammatory cytokines, i.e. tumour necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß), in the lipopolysaccharide-activated macrophage-like THP-1 cell model. The results of this study identified the complexes as auspicious anti-inflammatory agents with similar or better activity as compared with the clinically applied gold-based antiarthritic drug Auranofin. In an effort to explore the possible mechanisms responsible for the biological effect, the products of interactions of selected complexes with sulfur-containing biomolecules (L-cysteine and reduced glutathione) were studied by means of the mass-spectrometry study.

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A series of gold(III) complexes involving differently substituted derivatives of a plant hormone N6-benzyladenine (HL1-5) is reported. The complexes have the general formula [Au(HL1-5)Cl3]∙nH2O (n=0 for 1, 3-5; and n=1 for 2), where N6-(2-fluorobenzyl)adenine (HL1), N6-(2-chlorobenzyl)adenine (HL2), N6-(3-chlorobenzyl)adenine (HL3), N6-(4-chlorobenzyl)adenine (HL4) and N6-(4-methylbenzyl)adenine (HL5) represent the N9-coordinated ligands. The results of thorough characterization (elemental and thermal analyses, FT-IR, Raman and NMR spectroscopies, ESI+ mass spectrometry, conductivity measurements, DFT calculations) showed that the presented complexes 1-5 involve a central gold(III) atom coordinated in a square-planar geometry by the N9 atom of the purine moiety of HL1-5 and by three chlorido ligands. The complexes (1-5) were studied in vitro for cytotoxicity and anti-inflammatory activity on LPS-activated macrophages (THP-1 cell line), and in vivo for anti-inflammatory effects (1, 2, 5) using the carrageenan-induced hind paw oedema model on rats. Surprisingly, the results on the in vitro level revealed that the complexes show negligible cytotoxicity and anti-inflammatory activity, however, the activity on the in vivo level was found to be significant, fully comparable with the utilized drug Indomethacin, or even better as compared to a gold-containing metallodrug Auranofin.

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