Gheorghe Roman

A novel experimental heme oxygenase-1-targeted therapy for hormone-refractory prostate cancer.

Heme oxygenase-1 (HO-1), a member of the heat shock protein family, plays a key role as a sensor and regulator of oxidative stress. Herein, we identify HO-1 as a biomarker and potential therapeutic target for advanced prostate cancer (PCA). Immunohistochemical analysis of prostate tissue using a progression tissue microarray from patients with localized PCA and across several stages of disease progression revealed a significant elevation of HO-1 expression in cancer epithelial cells, but not in surrounding stromal cells, from hormone-refractory PCA (HRPCA) compared with hormone-responsive PCA and benign tissue. Silencing the ho-1 gene in HRPCA cells decreased the HO-1 activity, oxidative stress, and activation of the mitogen-activated protein kinase-extracellular signal-regulated kinase/p38 kinase. This coincided with reduced cell proliferation, cell survival, and cell invasion in vitro, as well as inhibition of prostate tumor growth and lymph node and lung metastases in vivo. The effect of ho-1 silencing on these oncogenic features was mimicked by exposure of cells to a novel selective small-molecule HO-1 inhibitor referred to as OB-24. OB-24 selectively inhibited HO-1 activity in PCA cells, which correlated with a reduction of protein carbonylation and reactive oxygen species formation. Moreover, OB-24 significantly inhibited cell proliferation in vitro and tumor growth and lymph node/lung metastases in vivo. A potent synergistic activity was observed when OB-24 was combined with Taxol. Together, these results establish HO-1 as a potential therapeutic target for advanced PCA.

The anti-malarial activity of bivalent imidazolium salts.

A series of compounds containing bivalent imidazolium rings and one triazolium analog were synthesized and evaluated for their ability to inhibit the replication of Plasmodium falciparum cultures. The activity and selectivity of the compounds for P. falciparum cultures were found to depend on the presence of electron-deficient rings that were spaced an appropriate distance apart. The activity of the compounds was not critically dependent on the nature of the linker between the electron-deficient rings, an observation that suggests that the rings were responsible for the primary interaction with the molecular target of the compounds in the parasite. The bivalent imidazolium and triazolium compounds disrupted the process whereby merozoites gain entry into erythrocytes, however, they did not appear to prevent merozoites from forming. The compounds were also found to be active in a murine Plasmodium berghei infection, a result consistent with the compounds specifically interacting with a parasite component that is required for replication and is conserved between two Plasmodium species.

Heme Oxygenase Inhibition by 2‐Oxy‐substituted 1‐Azolyl‐4‐phenylbutanes: Effect of Variation of the Azole Moiety. X‐Ray Crystal Structure of Human Heme Oxygenase‐1 in Complex with 4‐Phenyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone†

A series of 1‐azolyl‐4‐phenyl‐2‐butanones was designed and synthesized for the inhibition of heme oxygenases (heme oxygenase‐1 and heme oxygenase‐2). The replacement of imidazole by other azoles led to the discovery of novel 1H‐1,2,4‐triazole‐ and 1H‐tetrazole‐based inhibitors equipotent to a lead imidazole‐based inhibitor. The inhibitors featuring 2H‐tetrazole or 1H‐1,2,3‐triazole as the pharmacophore were less potent. Monosubstitution at position 2 or 4(5), or identical disubstitution at positions 4 and 5 of imidazole by a variety of electron‐withdrawing or electron‐donating, small or bulky groups, as well as the replacement of the traditional imidazole pharmacophore by an array of 3‐ or 5‐substituted triazoles, identically 3,5‐disubstituted triazoles, 5‐substituted‐1H‐ and 5‐substituted‐2H‐tetrazoles proved to be detrimental to the inhibition of HO, with a few exceptions. The azole‐dioxolanes and the azole‐alcohols derived from the active azole‐ketones were synthesized also, but these inhibitors were less active than the corresponding imidazole‐based analogs. The first reported X‐ray crystal structure of human heme oxygenase‐1 in complex with a 1,2,4‐triazole‐based inhibitor, namely 4‐phenyl‐1‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone, was also determined. The inhibitor binds to the human heme oxygenase‐1 distal pocket through the coordination of heme iron by the N 4 in the triazole moiety, whereas the phenyl group is stabilized by hydrophobic interactions from residues within the binding pocket.

Heme Oxygenase Inhibition by 1‐Aryl‐2‐(1H‐imidazol‐1‐yl/1H‐1,2,4‐triazol‐1‐yl)ethanones and Their Derivatives

Previous studies by our research group have been concerned with the design of selective inhibitors of heme oxygenases (HO‐1 and HO‐2). The majority of these were based on a four‐carbon linkage of an azole, usually an imidazole, and an aromatic moiety. In the present study, we designed and synthesized a series of inhibition candidates containing a shorter linkage between these groups, specifically, a series of 1‐aryl‐2‐(1H‐imidazol‐1‐yl/1H‐1,2,4‐triazol‐1‐yl)ethanones and their derivatives. As regards HO‐1 inhibition, the aromatic moieties yielding best results were found to be halogen‐substituted residues such as 3‐bromophenyl, 4‐bromophenyl, and 3,4‐dichlorophenyl, or hydrocarbon residues such as 2‐naphthyl, 4‐biphenyl, 4‐benzylphenyl, and 4‐(2‐phenethyl)phenyl. Among the imidazole‐ketones, five (36–39, and 44) were found to be very potent (IC50<5 μM) toward both isozymes. Relative to the imidazole‐ketones, the series of corresponding triazole‐ketones showed four compounds (54, 55, 61, and 62) having a selectivity index >50 in favor of HO‐1. In the case of the azole‐dioxolanes, two of them (80 and 85), each possessing a 2‐naphthyl moiety, were found to be particularly potent and selective HO‐1 inhibitors. Three non‐carbonyl analogues (87, 89, and 91) of 1‐(4‐chlorophenyl)‐2‐(1H‐imidazol‐1‐yl)ethanone were found to be good inhibitors of HO‐1. For the first time in our studies, two azole‐based inhibitors (37 and 39) were found to exhibit a modest selectivity index in favor of HO‐2. The present study has revealed additional candidates based on inhibition of heme oxygenases for potentially useful pharmacological and therapeutic applications.

Heme oxygenase inhibition by α-(1H-imidazol-1-yl)-ω-phenylalkanes: effect of introduction of heteroatoms in the alkyl linker.

Several α‐(1H‐imidazol‐1‐yl)‐ω‐phenylalkanes were synthesized and evaluated as novel inhibitors of heme oxygenase (HO). These compounds were found to be potent and selective for the stress‐induced isozyme HO‐1, showing mostly weak activity toward the constitutive isozyme HO‐2. The introduction of an oxygen atom in the alkyl linker produced analogues with decreased potency toward HO‐1, whereas the presence of a sulfur atom in the linker gave rise to analogues with greater potency toward HO‐1 than the carbon‐containing analogues. The most potent compounds studied contained a five‐atom linker between the imidazolyl and phenyl moieties, whereas the most HO‐1‐selective compounds contained a four‐atom linker between these groups. The compounds with a five‐atom linker containing a heteroatom (O or S) were found to be the most potent inhibitors of HO‐2; 1‐(N‐benzylamino)‐3‐(1H‐imidazol‐1‐yl)propane dihydrochloride, with a nitrogen atom in the linker, was found to be inactive.

The Effects of Azole-Based Heme Oxygenase Inhibitors on Rat Cytochromes P450 2E1 and 3A1/2 and Human Cytochromes P450 3A4 and 2D6

Heme oxygenases (HOs) catalyze the degradation of heme to biliverdin, carbon monoxide (CO), and free iron. The two major isoforms, HO-1 (inducible) and HO-2 (constitutive), are involved in a variety of physiological functions, including inflammation, apoptosis, neuromodulation, and vascular regulation. Major tools used in exploring these actions have been metalloporphyrin analogs of heme that inhibit the HOs. However, these tools are limited by their lack of selectivity; they affect other heme-dependent enzymes, such as cytochromes P450 (P450s), soluble guanylyl cyclase (sGC), and nitric-oxide synthase (NOS). Our laboratory has successfully synthesized a number of nonporphyrin azole-based HO inhibitors (QC-xx) that had little or no effect on sGC and NOS activity. However, their effects on various P450 isoforms have yet to be fully elucidated. To determine the effects of the QC-xx inhibitors on P450 enzyme activity, microsomal preparations of two rat P450 isoforms (2E1 and 3A1/3A2) and two human P450 supersome isoforms (3A4 and 2D6) were incubated with varying concentrations of HO inhibitor, and the activity was determined by spectrophotometric or fluorometric analysis. Results indicated that some QC compounds demonstrated little to no inhibition of the P450s, whereas others did inhibit these P450 isoforms. Four structural regions of QC-xx were analyzed, leading to the identification of structures that confer a decreased effect on both rat and human P450 isoforms studied while maintaining an inhibitory effect on the HOs.

Synthesis and Anti-Plasmodium Activity of Benzimidazole Analogues Structurally Related to Astemizole

A series of compounds structurally related to astemizole were designed and synthesized with the goal of determining their anti‐Plasmodium activity. Several modifications of the astemizole structure, namely the removal of the 4‐fluorobenzyl and/or 4‐methoxyphenethyl moieties, substitution of the benzene ring of the benzimidazole scaffold, replacement of the fluorine atom in the 4‐fluorobenzyl group, and variation of the 4‐aminopiperidine moiety, were explored. In vitro evaluation of the anti‐Plasmodium activity of these compounds using the ItG strain showed that astemizole and some of its structurally similar derivatives have IC50 values in the nanomolar range and exhibit toxicity towards the parasite over Chinese ovarian hamster (CHO) cells with a selectivity as high as 200. The presence of a secondary cyclic amine at position 2 and substitution with chlorine at positions 4 and 5 in the benzimidazole moiety are two modifications that resulted in potent and selective antimalarials based on astemizole.

Rapid, convenient method for screening imidazole-containing compounds for heme oxygenase inhibition.

INTRODUCTION Sensitive assays for measuring heme oxygenase activity have been based on the gas-chromatographic detection of carbon monoxide using elaborate, expensive equipment. The present study describes a rapid and convenient method for screening imidazole-containing candidates for inhibitory activity against heme oxygenase using a plate reader, based on the spectroscopic evaluation of heme degradation. METHODS A PowerWave XS plate reader was used to monitor the absorbance (as a function of time) of heme bound to purified truncated human heme oxygenase-1 (hHO-1) in the individual wells of a standard 96-well plate (with or without the addition of a test compound). The degradation of heme by heme oxygenase-1 was initiated using l-ascorbic acid, and the collected relevant absorbance data were analyzed by three different methods to calculate the percent control activity occurring in wells containing test compounds relative to that occurring in control wells with no test compound present. RESULTS In the cases of wells containing inhibitory compounds, significant shifts in λ(max) from 404 to near 412 nm were observed as well as a decrease in the rate of heme degradation relative to that of the control. Each of the three methods of data processing (overall percent drop in absorbance over 1.5h, initial rate of reaction determined over the first 5 min, and estimated pseudo first-order reaction rate constant determined over 1.5h) gave similar and reproducible results for percent control activity. The fastest and easiest method of data analysis was determined to be that using initial rates, involving data acquisition for only 5 min once reactions have been initiated using l-ascorbic acid. DISCUSSION The results of the study demonstrate that this simple assay based on the spectroscopic detection of heme represents a rapid, convenient method to determine the relative inhibitory activity of candidate compounds, and is useful in quickly screening a series or library of compounds for heme oxygenase inhibition.