Nitric oxide delivery platforms derived from a photoactivatable Mn(II) nitrosyl complex: Entry to photopharmacology.

The manganese nitrosyl complex derived from a designed pentadentate ligand with one carboxamido group N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy3H; H is the dissociable carboxamide H), namely, [Mn(PaPy3)(NO)]ClO4 (1), serves as an excellent biocompatible source of nitric oxide (NO) when exposed to low power (10-100 mW/cm2) visible light. This complex has afforded a series of NO delivery platforms that could find applications in combating chronic infections by drug-resistant bacteria under the control of light.

Carbon Monoxide Inhibits Cytochrome P450 Enzymes CYP3A4/2C8 in Human Breast Cancer Cells, Increasing Sensitivity to Paclitaxel.

Paclitaxel (PTX) is a first-line treatment in breast cancer, though resistance develops quickly and frequently. Cytochrome P450 enzymes CYP3A4 and CYP2C8, which metabolically inactivate PTX in hepatic tissue, are overexpressed in malignant breast tissues. CYP3A4 expression correlates with PTX therapy failure and poor outcomes, though no direct evidence of CYP3A4 contributing to PTX sensitivity exists. Because CYP3A4/2C8 is susceptible to carbon monoxide (CO)-mediated inhibition and CO (a gaseous signaling molecule) has previously exhibited drug-sensitizing effects in cancer cells, we hypothesized that CO-mediated inhibition of CYP3A4/2C8 could lead to enhanced drug sensitivity. Using a photo-activated CO-releasing molecule, we have assessed the ability of CO to alter the pharmacokinetics of PTX in breast cancer cells via inhibition of CYP3A4/2C8 and determined that CO does enhance sensitivity of breast cancer cells to PTX. Inhibition of CYP3A4/2C8 by CO could therefore be a promising therapeutic strategy to enhance PTX response in breast cancer.

Gold Drugs with {Au(PPh3 )}+ Moiety: Advantages and Medicinal Applications.

Following the success of Auranofin as an anti-arthritic drug, search for novel gold drugs has afforded a large number of [L-Au(PPh3 )] complexes that exhibit notable salutary effects. Unlike Au(III)-containing species, these gold complexes with {Au(PPh3 )}+ moiety are stable in biological media and readily exchange L with S- and Se-containing enzymes or proteins. Such exchange leads to rapid reduction of microbial loads or induction of apoptotic cell death at malignant sites. In many cases the lipophilic {Au(PPh3 )}+ moiety delivers a desirable toxic L to the specific cellular target in addition to exhibiting its own beneficial activity. Further research and utilization of this synthon in drug design could lead to novel chemotherapeutics for treatment of drug-resistant pathogens and cancers.

Enhanced Bactericidal Effects of Pyrazinamide Toward Mycobacterium smegmatis and Mycobacterium tuberculosis upon Conjugation to a {Au(I)-triphenylphosphine}+ Moiety.

As part of the quest for new gold drugs, we have explored the efficacy of three gold complexes derived from the tuberculosis drug pyrazinamide (PZA), namely, the gold(I) complex [Au(PPh3)(PZA)]OTf (1, OTf = trifluoromethanesulfonate) and two gold(III) complexes [Au(PZA)Cl2] (2) and [Au(PZO)Cl2] (3, PZO = pyrazinoic acid, the metabolic product of PZA) against two mycobacteria, Mycobacterium tuberculosis and Mycobacterium smegmatis. Only complex 1 with the {Au(PPh3)}+ moiety exhibits significant bactericidal activity against both strains. In the presence of thiols, 1 gives rise to free PZA and {Au(PPh3)}-thiol polymeric species. A combination of PZA and the {Au(PPh3)}-thiol polymeric species appears to lead to enhanced efficacy of 1 against M. tuberculosis.

Diminished viability of human ovarian cancer cells by antigen-specific delivery of carbon monoxide with a family of photoactivatable antibody-photoCORM conjugates.

Carbon monoxide (CO)-releasing antibody conjugates were synthesized utilizing a photoactivatable CO-releasing molecule (photoCORM) and mouse monoclonal antibodies linked by a biotin-streptavidin system. Different monoclonal antibodies raised against different surface-expressed antigens that are implicated in ovarian cancer afforded a family of antibody-photoCORM conjugates (Ab-photoCORMs). In an immunosorbent/cell viability assay, Ab-photoCORMs accumulated onto ovarian cancer cells expressing the target antigens, delivering cytotoxic doses of CO in vitro. The results described here provide the first example of an "immunoCORM", a proof-of-the-concept antibody-drug conjugate that delivers a gaseous molecule as a warhead to ovarian cancer.

Reaction of carbon monoxide with cystathionine ß-synthase: implications on drug efficacies in cancer chemotherapy.

Photo-activatable carbon monoxide (CO)-releasing molecules (photoCORMs), have recently provided help to identify the salutary effects of CO in human pathophysiology. Among them notable is the ability of CO to sensitize chemotherapeutic-resistant cancer cells. Findings from our group have shown CO to mitigate drug resistance in certain cancer cells by the inhibition of cystathionine ß-synthase (CBS), a key regulator of redox homeostasis in the cell. Diminution of the antioxidant capacity of cancer cells leads to sensitization to reactive oxygen species-producing drugs like doxorubicin and paclitaxel upon cotreatment with CO as well as in mitigating the drug effects of cisplatin. We hypothesize that the development of CO delivery techniques for coadministration with existing cancer treatment regimens may ultimately improve clinical outcomes in cancer therapy.

Therapeutic Potential of Two Visible Light Responsive Luminescent photoCORMs: Enhanced Cellular Internalization Driven by Lipophilicity.

Herein we report the synthesis, characterization, and cellular internalization properties of two visible-light active luminescent Mn-based photoCORMs. The enhanced membrane permeability of the photoactive Mn carbonyl complex (photoCORM) derived from a designed lipophilic ligand namely, [Mn(CO)3(Imdansyl)(L1)](CF3SO3) (1) (where L1 = a diazabutadiene-based ligand containing two highly lipophilic adamantyl motifs, Imdansyl = dansylimidazole) promoted rapid internalization within human colorectal adenocarcinoma (HT-29) cells compared to [Mn(CO)3(Imdansyl)(L2)](CF3SO3) (2) (where L2 = a diazabutadiene ligand bearing two hydrophilic 1,3,5-triazaadamantyl group). Colocalization experiments using membrane stain indicate different extents of localization of the two CO complexes within the cellular matrix. Visible-light triggered CO release from the lipophilic photoCORM induced caspase-3/7 activation on HT-29 cells, which was detected using confocal microscopy. The rapid accumulation of the lipophilic photoCORM 1 in the cellular membrane resulted in more efficient CO-induced cell death compared to the hydrophilic analogue 2.

Peroxynitrite-Mediated Dimerization of 3-Nitrotyrosine: Unique Chemistry along the Spectrum of Peroxynitrite-Mediated Nitration of Tyrosine.

Peroxynitrite (ONOO-, PN) has long been considered a potent nitrating agent implicated in numerous inflammation-mediated diseases. The current work highlights an unexplored oxidation chemistry initiated under conditions of sustained PN exposure. Impetus for this investigation developed from mass spectral results that suggested dimerization of a model peptide with a single tyrosine residue that was first nitrated following extended exposure to PN generated in situ. In attempts to substantiate this dimerization event and divulge the possible mode of linkage between the tyrosine derivatives of the peptide monomers, 3-nitrotyrosine (3-NT) was exposed to sustained fluxes of PN in a two-component PN-generating platform developed in this laboratory. Such exposure afforded products with tandem mass spectrometry and fluorescence spectroscopy profiles indicative of C-O coupling between 3-NT moieties. Synthesis and comparative analysis of the C-C coupled 3-NT isomer corroborated these findings. Most notably, the mass spectral data of the C-C coupled 3-NT dimer displayed a 226.80 m/z peak following exposure to high collision energy, corresponding to symmetric cleavage of the parent dimer peak (m/z = 453) along with a fragmentation product at m/z = 180.04 (-NO2 species). This fragmentation profile was distinct from the C-O coupled 3-NT dimer that exhibited a predominant 209.14 m/z peak with a small secondary 226.15 m/z peak indicative of asymmetric cleavage of the parent dimer. Results of this study indicate that formation of C-O coupled 3-NT dimer is promoted by elevated levels of 3-NT formed under high and sustained flux of PN.

Carbon monoxide sensitizes cisplatin-resistant ovarian cancer cell lines toward cisplatin via attenuation of levels of glutathione and nuclear metallothionein.

Cisplatin resistance remains a major impediment to effective treatment of ovarian cancer. Despite initial platinum responsiveness, thiol-containing peptides and proteins, glutathione (GSH) and metallothionein (MT), bind and inactivate cisplatin in cancer cells. Indeed, high levels of GSH and MT in ovarian cancers impart cisplatin resistance and are predictive of poor prognosis. Cystathionine ß-synthase (CBS), an enzyme involved in sulfur metabolism, is overexpressed in ovarian cancer tissues and is itself associated with cisplatin resistance. Treatment with exogenous carbon monoxide (CO), a known inhibitor of CBS, may mitigate cisplatin resistance in ovarian cancer cells by attenuation of GSH and MT levels. Using a photo-activated CO-releasing molecule (photoCORM), [Mn(CO)3(phen)(PTA)]CF3SO3 (phen = 1,10-phenanthroline, PTA = 1,3,5-triza-7-phosphaadamantane) we assessed the ability of CO to sensitize established cisplatin-resistant ovarian cancer cell lines to cisplatin. Cisplatin-resistant cells, treated with both cisplatin and CO, exhibited significantly lower cell viability and increased poly (ADP-ribose) polymerase (PARP) cleavage versus those treated with cisplatin alone. These cisplatin-resistant cell lines overexpressed CBS and had increased steady state levels of GSH and expression of nuclear MT. Both CO treatment and lentiviral-mediated silencing of CBS attenuated GSH and nuclear MT expression in cisplatin resistant cells. We have demonstrated that CO, delivered from a photoCORM, sensitizes established cisplatin-resistant cell lines to cisplatin. Furthermore, we have presented strong evidence that the effects of CO in circumventing chemotherapeutic drug resistance is at least in part mediated by the inactivation of endogenous CBS.

A mononuclear nonheme {FeNO}6 complex: synthesis and structural and spectroscopic characterization.

While the synthesis and characterization of {FeNO}7,8,9 complexes have been well documented in heme and nonheme iron models, {FeNO}6 complexes have been less clearly understood. Herein, we report the synthesis and structural and spectroscopic characterization of mononuclear nonheme {FeNO}6 and iron(iii)-nitrito complexes bearing a tetraamido macrocyclic ligand (TAML), such as [(TAML)FeIII(NO)]- and [(TAML)FeIII(NO2)]2-, respectively. First, direct addition of NO(g) to [FeIII(TAML)]- results in the formation of [(TAML)FeIII(NO)]-, which is sensitive to moisture and air. The spectroscopic data of [(TAML)FeIII(NO)]-, such as 1H nuclear magnetic resonance and X-ray absorption spectroscopies, combined with computational study suggest the neutral nature of nitric oxide with a diamagnetic Fe center (S = 0). We also provide alternative pathways for the generation of [(TAML)FeIII(NO)]-, such as the iron-nitrite reduction triggered by protonation in the presence of ferrocene, which acts as an electron donor, and the photochemical iron-nitrite reduction. To the best of our knowledge, the present study reports the first photochemical nitrite reduction in nonheme iron models.

Incorporation of a Theranostic "Two-Tone" Luminescent Silver Complex into Biocompatible Agar Hydrogel Composite for the Eradication of ESKAPE Pathogens in a Skin and Soft Tissue Infection Model.

Microbial invasion and colonization of the skin and underlying soft tissues are among the most common types of infections, becoming increasingly prevalent in hospital settings. Systemic antibiotic chemotherapies are now extremely limited due to emergence of drug-resistant Gram-positive and multidrug-resistant Gram-negative bacterial strains. Topical administration of antimicrobials provides an effective route for the treatment of skin and soft tissue infections (SSTIs). Therefore, the development of new and effective materials for the delivery of these agents is of paramount importance. Silver is a broad-spectrum antibiotic used for the treatment and prevention of infections since ancient times. However, the high reactivity of silver cation (Ag+) makes its incorporation into delivery materials quite challenging. Herein we report a novel soft agar hydrogel composite for the delivery of Ag+ into infected wound sites. This material incorporates a Ag(I) complex [Ag2(DSX)2(NO3)2] (1; DSX = 5-(dimethylamino)- N, N-bis(pyridin-2-ylmethyl) naphthalene-1-sulfonamide) that exhibits a change in fluorescence upon Ag+ release and qualitatively indicates the end point of silver delivery. The antibacterial efficacy of the material was tested against several bacterial strains in an SSTI model. The complex 1-agar composite proved effective at eradicating the pathogens responsible for the majority of SSTIs. The theranostic (therapeutic/diagnostic) properties coupled with its stability, softness, ease of application, and removal make this material an attractive silver-delivery vehicle for the treatment and prevention of SSTIs.

Cationic Au(I) complexes with aryl-benzothiazoles and their antibacterial activity.

Two cationic Au(I) complexes derived from aryl-benzothiazoles, namely [(PPh3)Au(pbt)](OTf) (1) and [(PPh3)Au(qbt)](OTf) (2) (where pbt = 2­(pyridyl)benzothiazole and qbt = (quinolyl)benzothiazole, and OTf- = trifluoromethanesulfonate anion), have been synthesized and structurally characterized by X-ray crystallography. Both complexes exhibit strong antibacterial effects against Gram-negative bacteria such as Acinetobacter baumannii and Pseudomonas Aeruginosa. Results of examination of the reactions of 1 and 2 indicate that these cationic Au(I) complexes rapidly cross the bacterial membrane and exert drug action by disrupting cellular function(s) through binding of cytosolic thiol-containing peptides (such as glutathione) and proteins to the highly reactive (PPh3)Au+ intermediate formed upon in situ dissociation of pbt or qbt.

A Luminescent Manganese PhotoCORM for CO Delivery to Cellular Targets under the Control of Visible Light.

A photoactive manganese carbonyl complex derived from dansylimidazole (Imdansyl), namely, [Mn(Imdansyl)(CO)3(phen)](CF3SO3) (1), has been synthesized and structurally characterized. This is the first luminescent manganese carbonyl-based photoCORM reported in the literature. This complex exhibits CO release under the exclusive control of low-power broadband visible light. The corresponding rhenium carbonyl complex, namely, [Re(Imdansyl)(CO)3(phen)](CF3SO3) (2), has also been reported, which is luminescent but sensitive only to UV-B (λ<315 nm) light. The entry of the manganese photoCORM into the human colorectal adenocarcinoma cells (HT-29) has been demonstrated with the aid of fluorescence microscopy. Irradiation of the photoCORM-loaded cancer cells to visible light leads to a dose-dependent apoptotic cell death.

Eradication of HT-29 colorectal adenocarcinoma cells by controlled photorelease of CO from a CO-releasing polymer (photoCORP-1) triggered by visible light through an optical fiber-based device.

The gaseous signaling molecule carbon monoxide (CO) has recently been recognized for its wide range of physiological activity as well as its antineoplastic properties. However, site-specific delivery of this noxious gas presents a major challenge in hospital settings. In this work, a visible light-sensitive CO-releasing molecule (photoCORM) derived from manganese(I) and 2-(quinolyl)benzothiazole (qbt) namely, [Mn(CO)3(qbt)(4-vpy)](CF3SO3) (1), has been co-polymerized within a gas-permeable HEMA/EGDMA hydrogel. The resulting photoactive CO-releasing polymer (photoCORP-1) incorporates 1 such that neither the carbonyl complex nor its photoproduct(s) exits the polymer at any time. The material can be triggered to photorelease CO remotely by low-power broadband visible light (<1mWcm-2) with the aid of fiber optics technology. The CO photorelease rates of photoCORP-1 (determined by spectrophotometry) can be modulated by both the concentration of 1 in the hydrogel and the intensity of the light. A CO-delivery device has been assembled to deliver CO to a suspension of human colorectal adenocarcinoma cells (HT-29) under the control of visible light and the extent of CO-induced apoptotic death of the cancer cells has been determined via Annexin V/Propidium iodide stain and flow cytometry. This photoactive CO-releasing polymer could find use in delivering controlled doses of CO to cellular targets such as malignant tissues in remote parts of the body.

Attenuation of Antioxidant Capacity in Human Breast Cancer Cells by Carbon Monoxide through Inhibition of Cystathionine ß-Synthase Activity: Implications in Chemotherapeutic Drug Sensitivity.

Drug resistance is a major impediment to effective treatment of breast cancer. Compared to normal cells, cancer cells have an increased antioxidant potential due to an increased ratio of reduced to oxidized glutathione (GSH/GSSG). This is known to confer therapeutic resistance. Here, we have identified a mechanism, unique to breast cancer cells, whereby cystathionine ß-synthase (CBS) promotes elevated GSH/GSSG. Lentiviral silencing of CBS in human breast cancer cells attenuated GSH/GSSG, total GSH, nuclear factor erythroid 2-related factor 2 (Nrf2), and processes downstream of Nrf2 that promote GSH synthesis and regeneration of GSH from GSSG. Carbon monoxide (CO) reduced GSH/GSSG in three breast cancer cell lines by inhibiting CBS. Furthermore, CO sensitized breast cancer cells to doxorubicin. These results provide insight into mechanism(s) by which CBS increases the antioxidant potential and the ability for CO to inhibit CBS activity to alter redox homeostasis in breast cancer, increasing sensitivity to a chemotherapeutic.

Five- and Six-Coordinated Silver(I) Complexes Derived from 2,6-(Pyridyl)iminodiadamantanes: Sustained Release of Bioactive Silver toward Bacterial Eradication.

Silver(I) complexes of two designed tridentate ligands, namely, 2,6-(pyridyl)iminoditriazaadamantane (pydTAm) and 2,6-(pyridyl)iminodiadamantane (pydAm), have been synthesized and structurally characterized. [Ag(pydTAm)2](CF3SO3) (1), the hitherto unknown mer isomer of a silver(I) octahedral complex, crystallizes in a highly symmetric body-centered cubic I4̅3m space group. Quite in contrast, the AgI center in the analogous [Ag(pydAm)2](CF3SO3) (2) complex resides in a trigonal-bipyramidal geometry and crystallizes in a triclinic P1̅ space group with two crystallographically independent molecules in the asymmetric unit. Complex 1 exhibits exceptional solubility in aqueous media and leads to the efficient eradication of several bacterial strains upon sustained release of bioactive silver.

Luminescent Re(I) Carbonyl Complexes as Trackable PhotoCORMs for CO delivery to Cellular Targets.

A family of Re(I) carbonyl complexes of general formula [ReX(CO)3(phen)]0/1+ (where X = Cl-, CF3SO3-, MeCN, PPh3, and methylimidazole) derived from 1,10-phenanthroline (phen) exhibits variable emission characteristics depending on the presence of the sixth ancillary ligand/group (X). All complexes but with X = MeCN exhibit moderate CO release upon irradiation with low-power UV light and are indefinitely stable in anaerobic/aerobic environment in solution as well as in solid state when kept under dark condition. These CO donors liberate three, one, or no CO depending on the nature of sixth ligand upon illumination as studied with the aid of time-dependent IR spectroscopy. Results of excited-state density functional theory (DFT) and time-dependent DFT calculations provided insight into the origin of the emission characteristics of these complexes. The luminescent rheinum(I) photoCORMs uniformly displayed efficient cellular internalization by the human breast adenocarcinoma cells, MDA-MB-231, while the complex with PPh3 as ancillary ligand showed moderate nuclear localization in addition to the cytosolic distribution. These species hold significant promise as theranostic photoCORMs (photoinduced CO releasing molecules), where the entry of the pro-drug can be tracked within the cellular matrices.

Synthesis, Structures, and CO Release Capacity of a Family of Water-Soluble PhotoCORMs: Assessment of the Biocompatibility and Their Phototoxicity toward Human Breast Cancer Cells.

Two manganese(I) carbonyl complexes derived from 2-(pyridyl)benzothiazole (pbt) and 1,10-phenanthroline (phen) release carbon monoxide (CO) under low-power broad-band visible-light illumination. CO photorelease from [Mn(CO)3(pbt)(PTA)]CF3SO3 (1, where PTA = 1,3,5-triaza-7-phosphaadamantane) is accompanied by an emergence of a strong fluorescence around 400 nm from almost nonfluorescent preirradiated 1. However, [Mn(CO)3(phen)(PTA)]CF3SO3 (2) showed no such phenomenon upon prolonged illumination under similar experimental conditions. The two analogous rhenium(I) complexes, namely, [Re(CO)3(pbt)(PTA)]CF3SO3 (3) and [Re(CO)3(phen)(PTA)]CF3SO3 (4), have also been synthesized and characterized to compare their photo properties with the manganese congeners. Complexes 3 and 4 exhibit moderate CO release upon irradiation with low-power UV light. All four complexes are highly soluble in anaerobic/aerobic aqueous media and are also considerably more stable when kept under dark conditions. The inherently luminescent rhenium complex 3 was utilized to demonstrate cellular internalization of these types of compounds by MDA-MB-231 (human breast cancer) cells, while the two biocompatible manganese(I) complexes (1 and 2) have been applied to assess the cell viability of these malignant cells upon CO delivery.

Silver complexes of ligands derived from adamantylamines: Water-soluble silver-donating compounds with antibacterial properties.

Two new silver(I) complexes, namely [Ag(qyAm)2](CF3SO3) (1) and [Ag(qyTAm)2](CF3SO3) (2), (qyAm=2-(quinonyl)iminoadamantane, qyTAm=2-(quinonyl)iminotriazaadamantane) have been synthesized and characterized by elemental analyses, 1H NMR, IR, electronic absorption spectroscopy, and X-ray diffraction. The coordination geometry of the silver center in both complexes is distorted tetrahedral where their respective qyAm and qyTAm ligand bind in a bidentate fashion using the imine and quinoline nitrogen atoms. Complex 2 is soluble in water and exhibits strong antimicrobial actions on both Gram-negative (E. coli, and P. aeruginosa) and Gram-positive (S. aureus) bacteria. The minimal inhibitory concentration (MIC) values for complex 2 (4, 4, and 8 µg for E. coli, P. aeruginosa, and S. aureus, respectively) are comparable to MIC values of silver nitrate and silver sulfadiazine.

L-Edge X-ray Absorption Spectroscopic Investigation of {FeNO}6: Delocalization vs Antiferromagnetic Coupling.

NO is a classic non-innocent ligand, and iron nitrosyls can have different electronic structure descriptions depending on their spin state and coordination environment. These highly covalent ligands are found in metalloproteins and are also used as models for Fe-O2 systems. This study utilizes iron L-edge X-ray absorption spectroscopy (XAS), interpreted using a valence bond configuration interaction multiplet model, to directly experimentally probe the electronic structure of the S = 0 {FeNO}6 compound [Fe(PaPy3)NO]2+ (PaPy3 = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) and the S = 0 [Fe(PaPy3)CO]+ reference compound. This method allows separation of the σ-donation and π-acceptor interactions of the ligand through ligand-to-metal and metal-to-ligand charge-transfer mixing pathways. The analysis shows that the {FeNO}6 electronic structure is best described as FeIII-NO(neutral), with no localized electron in an NO π* orbital or electron hole in an Fe dπ orbital. This delocalization comes from the large energy gap between the Fe-NO π-bonding and antibonding molecular orbitals relative to the exchange interactions between electrons in these orbitals. This study demonstrates the utility of L-edge XAS in experimentally defining highly delocalized electronic structures.