Potentiation of radiation-induced bacterial cell killing by binuclear rhodium(II) complexes and their amines

Rhodium(II) binuclear complexes were surveyed for potentiation of radiation-induced cell killing of hypoxic and fully oxic Salmonella typhimurium cells. The Rh2 tetracarbonate ion substantially potentiated hypoxic cell radiation sensitivity. Phosphate interfered with this potentiation. In the latter two respects, radiation potentiation by Rh2 tetracarbonate is similar to that found for Rh2 tetracarboxylates. Amines such as ammonia, methylamine, ethylamine, n-propylamine, and n-butylamine were examined with both Rh2 tetracarbonate and tetraacetate complexes. With Rh2 tetraacetate in phosphate-buffered saline, these amines variably increased radiation potentiation to a maximum of nearly that seen by Rh2 tetraacetate alone in the absence of phosphate. With Rh2 tetracarbonate, particular amines were found to either enhance or restrict radiation potentiation. Results as a whole support the hypothesis that a radiolytic Rh species initiated in a one-electron reduction process external to the cell is responsible for the potentiation by Rh2 complexes in bacteria. Phosphate interference of potentiation by Rh2 tetracetate appears to be limited competitively by amines, suggesting that axial associations of phosphate with the Rh2 center may be involved in the inhibition of radiation potentiation. Of interest in this regard is the finding that 5'-adenosinemonophosphate eliminates the potentiation seen with Rh2 tetraacetate.     

An interrelatedness of the potentiation of radiation-induced bacterial cell killing by cisplatin and binuclear rhodium carboxylates

Cisplatin and binuclear rhodium (Rh2) carboxylates appear to potentiate radiation-induced killing of Salmonella typhimurium cells largely as a consequence of one-electron reduction that leads to an active radiolytic product. This conclusion is supported by results from experiments wherein the hydrated electron and the hydroxyl radical are competed for in the presence of cisplatin and Rh2 carboxylates, and by the similarly shaped radiation survival curves for cisplatin and Rh2 carboxylates wherein potentiation is expressed beyond variable thresholds of radiation dose. Increasing concentrations of phosphate and chloride also inhibit radiation potentiation by both cisplatin and Rh2 carboxylates, further supporting the contention for similar mechanisms. Radiation potentiation by cisplatin is relatively much more sensitive to the inhibition by chloride.     

Potentiation of bacterial killing activity of zinc chloride by pyrrolidine dithiocarbamate

Zinc has antimicrobial activity and zinc salts including zinc chloride (ZnCl₂) have been used for the control of oral malodor. In this study, we hypothesized that pyrrolidine dithiocarbamate (PDTC), a zinc ionophore, may enhance antimicrobial efficacy of ZnCl₂. The bactericidal effectiveness of ZnCl₂ alone (0.5–8 mM) or in combination with PDTC (1 or 10 μM) was evaluated by in vitro short (1 h) time-killing assays against Fusobacterium nucleatum and Porphyromonas gingivalis. Only a slight viability decrease was observed with ZnCl₂ or PDTC alone after 1-h incubation. By contrast, combination of ZnCl₂ and PDTC could achieve a more than 100-fold viability reduction compared with ZnCl₂ or PDTC alone in F. nucleatum and P. gingivalis. Therefore, PDTC greatly enhanced the bactericidal activity of ZnCl₂ against the oral malodor-producing bacteria. These results suggest that use of PDTC may be useful for enhancing bactericidal activity of antimalodor regimens of zinc salts.     

Studies of antibacterial activity of binuclear rhodium (II) complexes with heterocyclic nitrogen ligands

Binuclear rhodium (II) complexes, [Rh2(OOCPh)2(phen)2(H2O)2] (OOCPh)2 (1), [Rh2(OOCPh)2(bpy)2(H2O)2] (OOCPh)2 (2), [Rh2(OOCBu(n))2 (bpy)2(H2O)2] (OOCBu(n)2 (3), and [Rh2(OOCPr(n)2 (phen)2(H2O)2] (OOCPr(n)2 (4) (Phen = 1,10-phenanthroline and bpy = 2,2'-bipyridine), have been synthesized and characterized using NMR, IR and electronic spectra. Activity of these compounds against Gram-positive bacteria decreases in the order: 1?2?3 > 4. Complex 1 is active against many Staphylococcus strains resistant to commonly used antibiotics. The complexes 1-4 are much less active agents against Gram-negative bacteria.     

Synthesis and redox properties of dinuclear rhodium(II) carboxylates with 2,6-di-tert-butylphenol moieties

By exploiting the peculiar reactivity of [Rh₂(μ-O₂CBu^t)₄(H₂O)₂] (1) the examples of dinuclear rhodium(II) carboxylates containing N-donor axial ligands (2, 3) [Rh₂(μ-O₂CBu^t)₄L₂] [where L = benzonitrile (2), 3,5-di-tert-butyl-4-hydroxybenzonitrile (3)] were synthesized and characterized by elemental analysis, IR, multinuclear NMR spectroscopy, MALDI-TOF mass spectrometry. It was found by X-ray diffraction that pairs of 3 in crystals are associated through H atoms of phenol groups to produce a dimer of dimers. The chemical oxidation of dirhodium complexes with 2,6-di-tert-butyl-4-cyanоphenol pendants studied by means of ESR method in solutions leads to the formation of phenoxyl radicals 3′ in dirhodium system. The ESR data show the interaction of the unpaired electron with ligand nuclei (¹H, ¹⁴N) and ¹⁰³Rh. The stability of radical complexes with phenoxyl fragments in axial position is influenced by the temperature. The enthalpy of the 3′ decomposition followed by the formation of cyanophenoxyl radical as 20 ± 1 kJ/mol was estimated. Redox transformations in dirhodium system including both metal and axial ligands were investigated by electrochemistry. CV experiments confirm the assumption of the metal oxidation (Rh^II→Rh^III) as the first step following by the oxidation of the ligand.     

Potentiation of cell killing by inhibitors of poly(ADP-ribose) polymerase in four rodent cell lines exposed to N-methyl-N-nitrosourea or UV light

The sensitivities (Do-values) of the cytotoxic effect of MNU on four rodent cell lines were: mouse L1210, 0.07 mM; rat Yoshida sarcoma, 0.52 mM; Chinese hamster V79A, 0.70 mM and the UV sensitive, X-ray sensitive V79/79, 0.35 mM. The abilities of maximum non-toxic doses of the poly-(ADP-ribose) polymerase inhibitors, 5-methyl nicotinamide (5MeN), 3-methoxybenzamide (3MBA) and caffeine to potentiate this cytotoxicity and that of UV light in V79A and V79/79 was measured. The degree of potentiation (ratio Do without inhibitor/Do with inhibitor) was both agent and cell line dependent. In general the lymphoid cell lines L1210 and YS showed greater potentiation, up to 4-fold, than did the fibroblast lines V79A and V79/79. The use of inhibitors in pairs suggested that 5MeN and 3MBA affect one process whereas caffeine affects additional processes. The data provide further support for a role for poly(ADP-ribose) in DNA repair, but indicate that metabolic factors may modify the effectiveness of individual inhibitors of poly(ADP-ribose) polymerase in different cell lines.     

Redox modulation of human prostate carcinoma cells by selenite increases radiation-induced cell killing

Although selenium compounds have been extensively studied as chemopreventative agents for prostate cancer, little is known about the potential use of selenium compounds for chemotherapy. We have shown that selenite inhibits cell growth and induces apoptosis in androgen-dependent LAPC-4 prostate cancer cells. LAPC-4 cells were more sensitive to selenite-induced apoptosis than primary cultures of normal prostate cells. Selenite-induced apoptosis in LAPC-4 cells correlated with a decrease in the Bcl-2:Bax expression ratio. Selenite-induced oxidative stress and apoptosis are dependent upon its reaction with reduced GSH. LAPC-4 cells treated with selenite showed decreased levels of total GSH and increased concentrations of GSSG. Thus, selenite altered the intracellular redox status toward an oxidative state by decreasing the ratio of GSH:GSSG. Because increased levels of Bcl-2 and GSH are associated with radioresistance, we examined the ability of selenite to sensitize prostate cancer cells to gamma-irradiation. Both LAPC-4 and androgen-independent DU 145 cells pretreated with selenite showed increased sensitivity to gamma-irradiation as measured by clonogenic survival assays. Importantly, selenite-induced radiosensitization was observed in combination with a clinically relevant dose of 2 Gy. These data suggest that altering the redox environment of prostate cancer cells with selenite increases the apoptotic potential and sensitizes them to radiation-induced cell killing.     

Determinants of eukaryal cell killing by the bacterial ribotoxin PrrC

tRNA damage inflicted by the Escherichia coli anticodon nuclease PrrC (EcoPrrC) underlies an antiviral response to phage T4 infection. PrrC homologs are present in many bacterial proteomes, though their biological activities are uncharted. PrrCs consist of two domains: an N-terminal NTPase module related to the ABC family and a distinctive C-terminal ribonuclease module. In this article, we report that the expression of EcoPrrC in budding yeast is fungicidal, signifying that PrrC is toxic in a eukaryon in the absence of other bacterial or viral proteins. Whereas Streptococcus PrrC is also toxic in yeast, Neisseria and Xanthomonas PrrCs are not. Via analysis of the effects of 118 mutations on EcoPrrC toxicity in yeast, we identified 22 essential residues in the NTPase domain and 11 in the nuclease domain. Overexpressing PrrCs with mutations in the NTPase active site ameliorated the toxicity of wild-type EcoPrrC. Our findings support a model in which EcoPrrC toxicity is contingent on head-to-tail dimerization of the NTPase domains to form two composite NTP phosphohydrolase sites. Comparisons of EcoPrrC activity in a variety of yeast genetic backgrounds, and the rescuing effects of tRNA overexpression, implicate tRNA^Lys(UUU) as a target of EcoPrrC toxicity in yeast.     

Reduction of radiation-induced cell cycle blocks by caffeine does not necessarily lead to increased cell killing

The effect of caffeine upon the radiosensitivities of three human tumor lines was examined and correlated with its action upon the radiation-induced S-phase and G2-phase blocks. Caffeine was found to reduce at least partially the S-phase and G2-phase blocks in all the cell lines examined but potentiated cytotoxicity in only one of the three tumor lines. That reductions have been demonstrated to occur in the absence of increased cell killing provides supporting evidence for the hypothesis that reductions may not be causal in those cases when potentiation of radiation-induced cytotoxicity is observed in the presence of caffeine.     

Chiroptical properties of binuclear rhodium complexes of lanostane alcohols

The circular dichroism (CD) of the in situ-formed Rh2(OCOCF3)4 complexes of sterically hindered, secondary lanostane alcohols was investigated. The main object of the present studies are derivatives of 3beta-, 7alpha-, 7beta-, and 11beta-hydroxylanostanes with or without an additional functional group, e.g., double bond, oxo-, hydroxy-, or acetoxy groups. Up to five Cotton effects (CEs) can be found in the CD spectra of Rh-complexes of these alcohols in the spectral range between 650-300 nm. Correlation of the CEs signs with the absolute stereochemistry at the carbon atom bearing the hydroxy group was investigated. The Rh-complex with the 3beta-acetoxylanostan-11beta-ol ligand was isolated in the crystalline form. Its polymeric structure, determined by the X-ray method, shows the di-Rh-units linked by the axially ligating oxygen atoms of the hydroxy and acetoxy groups. In the latter case, the coordination takes place through the carbonyl oxygen.     

Antitumor activity of phenylene bridged binuclear bis(imino-quinolyl)palladium(II) and platinum(II) complexes

Antitumor effects of a known bis(imino-quinolyl)palladium(II) complex 1 and its newly synthesized platinum(II) analogue 2 were evaluated against human breast (MCF-7) and human colon (HT-29) cancer cell lines. The complexes gave cytotoxicity profiles that were better than the reference drug cisplatin. The highest cytotoxic activities were pronounced in complex 2 across the two examined cancer cell lines. Both compounds represent potential active drugs based on bimetallic complexes.     

Structure of binuclear Rh(II) carboxylato complexes with 2,2-bipyridine and an unprecedented rhodium wire with Rh4 core

Structures of rhodium(II) binuclear complexes [Rh₂(OOCCH₃)₂(bpy)₂(H₂O){(CH₃)₂CHOH}][B(C₆H₅)₄]₂ · H₂O (1), [Rh₂Cl₂(OOCCH₃)₂(bpy)₂] · 2H₂O (2), [Rh₂Br₂(OOCCH₃)₂(bpy)₂] · 3H₂O (3), and [Rh₂I₂(OOCCH₃)₂(bpy)₂] (4), as well as an unprecedented wire with infinite Rh-Rh chain, {[Rh₄(μ-OOCH)₄(bpy)₄](BF₄)}_n · 0.5nC₄H₈O₂ (5), have been determined and discussed. Mass spectra of complexes [Rh₂(OOCMe)₂(bpy)₂(H₂O)₂](MeCOO)₂ and [Rh₂(OOCMe)₂(phen)₂(H₂O)₂](MeCOO)₂ have showed stability of polynuclear cations with rhodium in oxidation states in the range +1.25 to +1.75.     

Potentiation of a tumor cell susceptibility to autologous CTL killing by restoration of wild-type p53 function

Inactivation of p53 has been implicated in many types of tumors particularly in non-small cell lung carcinoma, one of the most common cancers in which p53 mutation has been frequently identified. The aim of this study was to investigate the influence of p53 status on the regulation of tumor susceptibility to specific CTL-mediated cell death. For this purpose, we used a cytotoxic T lymphocyte clone, Heu127, able to lyse the human autologous lung carcinoma cell line, IGR-Heu, in a HLA-A2-restricted manner. Direct genomic DNA sequencing revealed that IGR-Heu expresses a mutated p53 at codon 132 of the exon 5 which results in the loss of p53 capacity to induce the expression of the p53-regulated gene product p21(waf/CIP1). Initial experiments demonstrated that IGR-Heu was resistant to Fas, TNF, and TRAIL apoptotic pathways. This correlated with the lack of p55 TNFRI, Fas, DR4, and DR5 expression. The effect of wild-type (wt) p53 restoration on the sensitization of IGR-Heu to autologous CTL clone lysis was investigated following infection of the tumor cell line with a recombinant adenovirus encoding the wt p53 (Adwtp53). We demonstrate that the restoration of wt p53 expression and function resulted in a significant potentiation of target cell susceptibility to CTL-mediated lysis. The wt p53-induced optimization of tumor cell killing by specific CTL involves at least in part Fas-mediated pathway via induction of CD95 expression by tumor cells but does not appear to interfere with granzyme B cytotoxic pathway.     

Synthesis and reactivity of binuclear halo-bridge palladium(II) isocyanide complexes

An equimolecular mixture of [Pd(RNC)₂Cl₂] (R = Ph, p-Me C₆H₄) and [Pd(MeCN)₂Cl₂] reacts in boiling, 1,2-dichloroethane to give the binuclear complexes [Pd(RNC)Cl₂]₂.These compounds undergo a variety of bridge-splitting reactions with neutral or anionic ligands yielding complexes of the type cis and trans [Pd(RNC)LX₂] or [Pd(RNC)X₃]⁻ (L = PPh₃, pyridine, C₆H₁₁NC; X = CL, Br).By reaction of [Pd(PhNC)Cl₃]⁻ with MeOH the anionic carbene complex [Pd{C(NHPh)OMe}Cl₃]⁻ is obtained.[Pd(PhNC)Cl₂]₂ reacts with p-toluidine (excess) or o-aminopyridine to give the corresponding mononuclear carbene derivatives.In the case of the mixed derivative [Pd(p-MeC₆H₄NC)(C₆H₁₁NC)Cl₂], only the more activated p-tolylisocyanide was found to react with p-toluidine.The complexes have been characterized by elemental analysis, conductivity measurements, i.r. and ¹H n.m.r. spectra where possible.