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Carbon monoxide, the "silent killer" gas, is increasingly recognised as an important signalling molecule in human physiology, which has beneficial biological properties. A particular way of achieving controlled CO administration is based on the use of biocompatible molecules that only release CO when triggered by internal or external factors. These approaches include the development of pharmacologically effective prodrugs known as CO releasing molecules (CORMs), which can supply biological systems with CO in well-regulated doses. An overview of transition metal-based CORMs with cytotoxic properties is here reported. The mechanisms at the basis of the biological activities of these molecules and their potential therapeutical applications with respect to their stability and CO releasing properties have been discussed. The activation of metal-based CORMs is determined by the type of metal and by the nature and features of the auxiliary ligands, which affect the metal core electronic density and therefore the prodrug resistance towards oxidation and CO release ability. A major role in regulating the cytotoxic properties of these CORMs is played by CO and/or CO-depleted species. However, several mysteries concerning the cytotoxicity of CORMs remain as intriguing questions for scientists. [ABSTRACT FROM AUTHOR]

A series of Pd(II) complexes of the general formula [PdX(NNS)] (X = Cl, Br, I, NCS and phenyl-tetrazole-thiolato; NNS = 2-quinolinecarboxyaldehyde-N4-phenylthiosemicarbazone) was tested against four malignant cell lines for their antiproliferative properties and the outcomes were compared to those seen in normal mouse splenocytes. Various auxiliary ligands were substituted in order to investigate the impact of the character of the ligand on the cytotoxicity of this class of Pd(II) complexes. The iodo complex was the most cytotoxic compound towards the Caco-2 cell line in this study. The improved apoptosis and necrosis cell modes were in accordance with the fragmentation results of DNA, which revealed increased fragmentation terminals, especially in isothiocyanate and tetrazole-thiolato complexes. After 24 hours, at half the IC50 of each complex, the complex-treated cells exhibited considerable genotoxicity when compared to the corresponding non-treated control especially in the case of isothiocyanate and tetrazole-thiolato complexes. [ABSTRACT FROM AUTHOR]

Human acute monocytic leukaemia cells were tested under both dark and light conditions for their susceptibility to Mn(I) and Ru(II) carbonyl complexes with a diphenyl pyridyl phosphine coligand. The Ru(II) complex (IC50 = 7.13 ± 0.8 μM) displayed higher outstanding potency against leukaemia than the Mn(I) analogue (54.58 ± 4.1 μM) in the dark and both complexes were completely harmless to healthy mouse bone marrow cells. [ABSTRACT FROM AUTHOR]

The cytotoxicity of two tricarbonyl Mn(I) complexes of the general formula fac-[MnBr(CO)3L] (L = quinoline-2-carboxaldehyde (A) and 8-amino quinoline (B)) towards triple negative breast cancer (MDA-MB-231) was reported. Complexes A and B released CO when exposed to 468 nm light. Compound B has a dose-dependent cytotoxicity, with half maximal inhibitory concentration values of 19.62 μM and 11.43 μM before and after illumination, respectively. Co-treatment of MDA-MB-231 with paclitaxel (30 nM) and complex B (10 μM) resulted in a 50% reduction in cell viability. [ABSTRACT FROM AUTHOR]

Reaction between [RuCl2(CO)2]n and 1H-benzimidazol-2-ylmethyl-(N-phenyl)amine ligands (LR) functionalized with various electron-donating and electron-withdrawing substituents on the phenyl ring (R = H, 4-CH3, 4-Cl, 4-COOCH3, and 3-COOCH3) afforded the dark-stable photoactivatable carbon monoxide prodrugs of the general formula [RuCl2(CO)2LR]. Release of the CO molecules from the Ru(II) compounds was examined by monitoring the electronic and IR spectra upon illumination at 365 nm. A noticeable decrease in the intensities of the two characteristic ν(C≡O) modes for Ru(CO) II2 species, and the growth of two new bands for the mono-carbonyl species and free CO, were the main features of the photolysis profiles. The cytotoxicity of the complexes towards breast cancer (MCF-7) cells was assessed with and without illumination at 365 nm. All the complexes except that with a 4-COOCH3 group (IC50 = 45.08 ± 3.5 μM) are nontoxic under dark conditions. Upon illumination, all the compounds acquired cytotoxicity in the following order: H > 4-COOCH3 > 4-CH3 > 4-Cl > 3-COOCH3. Investigation of the cytotoxicity of the CO-depleted fragments showed that the light-induced cytotoxicity can be attributed to the liberated CO and CO-depleted metal fragments, including the liberated benzimidazole ligands. [ABSTRACT FROM AUTHOR]

The titled carbon monoxide releasing molecule is capable of release CO upon illumination at 468 nm and demonstrates selective cytotoxicity towards human acute monocytic leukaemia in the dark without causing any harmful effect to the normal mice bone marrow stromal cells. [Display omitted] The reaction between bromo pentacarbonyl manganese(I) and two equivalents of 1-(chloromethyl)-1H-benzotriazole (BTZ-CH 2 Cl) afforded visible-light induced carbon monoxide releasing molecule of the general formula, fac -[MnBr(CO) 3 (BTZ-CH 2 Cl) 2 ]. The solvatochromism, dark-stability and photolysis profile of the titled complex was examined in organic solvents with various hydrogen-bonding propensities, coordinating capabilities, and solvent polarities as well as in the presence of proteins. The number of CO equivalents released from the titled complex upon the exposure to a 468 nm LED light was determined using myoglobin assay. The titled complex displayed selective cytotoxicity towards human acute monocytic leukaemia in the dark without causing any harmful effect to the normal mice bone marrow stromal cells. [ABSTRACT FROM AUTHOR]

Two series of photoinduced tricarbonyl manganese(I) compounds were prepared from the reaction of [MnBr(CO)3(2-C(H)＝O)] (2-C(H)＝O: quinoline-2-carboxaldehyde and pyridine-2-carboxaldehyde) and para-substituted aniline derivatives (X = OH, OCH3, Cl and NO2). Different electron-donating and electron-withdrawing substituents were introduced in the para-position of the phenyl ring to investigate their influence on the stability of the compounds in the dark and the photophysical properties upon illumination at 525 nm. When kept in the dark, the aerated solutions of the complexes in dimethyl sulfoxide (DMSO) and CH2Cl2 were stable. In the solution, the complexes bearing electron-withdrawing substituents, exchange their bromo ligands with DMSO solvent molecules, as evidenced from infrared and UV/Vis studies as well as time-dependent density functional theory (TDDFT) calculations. The complexes were assessed for their cytotoxicity, both in the dark and upon exposure to a 525 nm LED, against the human hepatocarcinoma cell line (HepG2). A marked reduction in the viability of HepG2 cells treated with the complex functionalized with quinoline and methoxy substituent was observed after illumination in a dose-dependent manner, with an IC50 value of 7.1 μM, making it the most phototoxic compound in our study. [ABSTRACT FROM AUTHOR]

We synthesized two biocompatible photoactivatable fac -[MnBr(CO) 3 (N∧O)] complexes with desirable properties such as water solubility and stability in anaerobic aqueous media, a low-power visible light requirement for CO release (468 nm), and a long half-life time of the CO release kinetics. [Display omitted] Two water-soluble fac -Mn(CO) 3 based complexes of the general formula fac -[MnBr(CO) 3 (N∧O)] (N∧O = pyridine-2-carboxaldehyde (A), and 2-acetylpyridine (B)) were described for their potential CO releasing properties upon illumination at 468 nm, solvatochromism features and cytotoxicity against different malignant cell lines in both the dark and upon the exposure to light source. Negative solvatochromism may be responsible for the red shift of the metal-to-ligand charge transfer band in increasingly less polar solvents. Compound B , which had been functionalized with 2-acetylpyridine, released CO in water faster than complex A , suggesting the role of the methyl group in regulating the CO release kinetics. According to myoglobin assay, the CO release pathway in water is slower than in DMSO revealing to the role of the solvent in controlling the CO release kinetics of Mn(I) carbon monoxide releasing molecules. [ABSTRACT FROM AUTHOR]

[Display omitted] Carbon monoxide has recently emerged to promote tissue regeneration, enhance the innate immune system, and have anti-inflammatory and antibacterial properties. While the first generation Ru(II) carbonyl prodrugs (CORM-2 and CORM-3) displayed several beneficial biological effects, a search in the literature shows that little work has been done to address the drawbacks of CORM-2/-3, exploring other CO triggered methods for the next generation Ru(CO) 2 II based compounds and examining their valuable biological impact. We present a summary of most work related to Ru(II) carbon monoxide-releasing molecules, protein bioconjugation, and antibacterial and anti-inflammatory properties. [ABSTRACT FROM AUTHOR]

Reaction between bromo tricarbonyl manganese(I) and N,N′-bis(phenyl)-1,4-diaza-1,3-butadiene ligands, bearing different electron-donating and electron-withdrawing groups R = OCH3, Cl, and NO2 in the ortho- and para-positions on the phenyl substituent, afforded [MnBr(CO)3(N–N)] complexes. The influence of the character and position of the substituent on the dark stability and carbon monoxide releasing kinetics was systematically investigated and correlated with the data of the time-dependent density functional theory calculations. The combined UV/Vis and IR data clearly revealed that the aerated solutions of [MnBr(CO)3(N–N)] in either coordinating or noncoordinating solvents are dark stable and the fluctuations observed during the incubation period especially in the case of the nitro derivatives may be attributed to the exchange of the axial bromo ligand with the coordinating solvent molecules. The free ligands and nitro complexes were non-cytotoxic to HepG2 cells under both the dark and illumination conditions. In the dark, Mn(I) compounds, incorporating o-OCH3 and o-Cl, exhibited excellent cytotoxicity with IC50 values of 18.1 and 11.8 μM, while their para-substituted analogues were inactive in the dark and active upon the irradiation at 365 nm with IC50 values of 5.7 and 6.7 μM, respectively. [ABSTRACT FROM AUTHOR]