George E. Magoulas

Syntheses and evaluation of the antioxidant activity of acitretin analogs with amide bond(s) in the polyene spacer.

Ester analogs of the antipsoriatic drug acitretin were synthesized by coupling either anilines with N-protected indole-3-carboxylic acid, followed by deprotection and coupling with O-monoprotected dicarboxylic acids or Wittig reaction of indole-3-carboxaldehyde, 3-acetyl-1-tosylpyrrole and 4-amino-9-fluorenone with Ph3P=CHCO2tBu, followed by N-deprotection, where necessary, and finally coupling with cinnamoyl fluorides. Corresponding free acids were obtained through TFA-mediated carboxyl group deprotection. Although these analogs and acitretin showed very low reducing abilities, analogs 5, 6, 8 and 12 strongly inhibited LOX with IC50 values ranging from 35-65 microM. Acitretin and its analogs 5-7, 10, 11 and 15 inhibited lipid peroxidation more strongly than trolox whereas acitretin and analog 4 were in vivo more potent anti-inflammatory agents on rat paw oedema induced by Carrageenan than indomethacin.

Conjugation with polyamines enhances the antibacterial and anticancer activity of chloramphenicol

Chloramphenicol (CAM) is a broad-spectrum antibiotic, limited to occasional only use in developed countries because of its potential toxicity. To explore the influence of polyamines on the uptake and activity of CAM into cells, a series of polyamine–CAM conjugates were synthesized. Both polyamine architecture and the position of CAM-scaffold substitution were crucial in augmenting the antibacterial and anticancer potency of the synthesized conjugates. Compounds 4 and 5, prepared by replacement of dichloro-acetyl group of CAM with succinic acid attached to N4 and N1 positions of N8,N8-dibenzylspermidine, respectively, exhibited higher activity than CAM in inhibiting the puromycin reaction in a bacterial cell-free system. Kinetic and footprinting analysis revealed that whereas the CAM-scaffold preserved its role in competing with the binding of aminoacyl-tRNA 3′-terminus to ribosomal A-site, the polyamine-tail could interfere with the rotatory motion of aminoacyl-tRNA 3′-terminus toward the P-site. Compared to CAM, compounds 4 and 5 exhibited comparable or improved antibacterial activity, particularly against CAM-resistant strains. Compound 4 also possessed enhanced toxicity against human cancer cells, and lower toxicity against healthy human cells. Thus, the designed conjugates proved to be suitable tools in investigating the ribosomal catalytic center plasticity and some of them exhibited greater efficacy than CAM itself.

Effect of an all-trans-retinoic acid conjugate with spermine on viability of human prostate cancer and endothelial cells in vitro and angiogenesis in vivo

Retinoids constitute a family of organic compounds that are being used for the treatment of various diseases, ranging from acne vulgaris to acute promyelocytic leukemia. Their use however is limited due to serious adverse effects and there is a great need for analogues with better safety profile. In the present work, the effect of N(1),N(12)-bis(all-trans-retinoyl)spermine (RASP), a conjugate of all-trans-retinoic acid (atRA) with spermine, on angiogenesis in vivo and viability of human endothelial and prostate cancer cells in vitro were studied. Both atRA and RASP dose-dependently inhibited angiogenesis in the chicken embryo chorioallantoic membrane model. RASP was more effective and could be used in a wider dose range due to lower toxicity compared with atRA. Both retinoids decreased the number of human umbilical vein endothelial and prostate cancer LNCaP and PC3 cells in a concentration-dependent manner. RASP was more effective and potent compared with atRA, spermine, their combination, or conjugates of spermine with other acidic retinoids and/or psoralens in prostate cancer cells. The inhibitory effect of both atRA and RASP seems to be related to an increase of the tumour repressing gene retinoic acid receptor beta mRNA, was mediated by retinoic acid receptor alpha, and was proportional to endogenous retinoic acid receptor beta expression. These data suggest that RASP is more effective than atRA in decreasing angiogenesis and prostate cancer cell growth and identify retinoic acid receptor alpha as the receptor through which it causes retinoic acid receptor beta up-regulation and decrease of prostate cancer cell growth.

Bioinspired Syntheses of Dimeric Hydroxycinnamic Acids (Lignans) and Hybrids, Using Phenol Oxidative Coupling as Key Reaction, and Medicinal Significance Thereof

Lignans are mainly dimers of 4-hydroxycinnamic acids (HCAs) and reduced analogs thereof which are produced in Nature through phenol oxidative coupling (POC) as the primary C-C or C-O bond-forming reaction under the action of the enzymes peroxidases and laccases. They present a large structural variety and particularly interesting biological activities, therefore, significant efforts has been devoted to the development of efficient methodologies for the synthesis of lignans isolated from natural sources, analogs and hybrids with other biologically interesting small molecules. We summarize in the present review those methods which mimic Nature for the assembly of the most common lignan skeleta by using either enzymes or one-electron inorganic oxidants to effect POC of HCAs and derivatives, such as esters and amides, or cross-POC of pairs of HCAs or HCAs with 4-hydrocycinnamyl alcohols. We, furthermore, provide outlines of mechanistic schemes accounting for the formation of the coupled products and, where applicable, indicate their potential application in medicine.

Synthesis and antimicrobial activity of chloramphenicol–polyamine conjugates

A series of chloramphenicol (CAM) amides with polyamines (PAs), suitable for structure-activity relationship studies, were synthesized either by direct attachment of the PA chain on the 2-aminopropane-1,3-diol backbone of CAM, previously oxidized selectively at its primary hydroxyl group, or from chloramphenicol base (CLB) through acylation with succinic or phthalic anhydride and finally coupling with a PA. Conjugates 4 and 5, in which the CLB moiety was attached on N4 and N1 positions, respectively, of the N(8),N(8)-dibenzylated spermidine through the succinate linker, were the most potent antibacterial agents. Both conjugates were internalized into Escherichia coli cells by using the spermidine-preferential uptake system and caused decrease in protein and polyamine content of the cells. Noteworthy, conjugate 4 displayed comparable activity to CAM in MRSA or wild-type strains of Staphylococcus aureus and Escherichia coli, but superior activity in E. coli strains possessing ribosomal mutations or expressing the CAM acetyltransferase (cat) gene. Lead compounds, and in particular conjugate 4, have been therefore discovered during the course of the present work with clinical potential.

Synthesis of nοvel artemisinin dimers with polyamine linkers and evaluation of their potential as anticancer agents

The natural product artemisinin and derivatives thereof are currently considered as the drugs of choice for the treatment of malaria. At the same time, a significant number of such drugs have also shown interesting anticancer activity. In the context of the present research work, artemisinin was structurally modified and anchored to naturally occurring polyamines to afford new artemisinin dimeric conjugates whose potential anticancer activity was evaluated. All artemisinin conjugates tested were more effective than artemisinin itself in decreasing the number of MCF7 breast cancer cells. The effect required conjugation and was not due to the artemisinin analogue or the polyamine, alone or in combination. To elucidate potential mechanism of action, we used the most effective conjugates 6, 7, 9 and 12 and found that they decreased expression and secretion of the angiogenic growth factor pleiotrophin by the cancer cells themselves, and inhibited angiogenesis in vivo and endothelial cell growth in vitro. These data suggest that the new artemisinin dimers are good candidates for the development of effective anticancer agents.

Synthesis and antiproliferative activity of two diastereomeric lignan amides serving as dimeric caffeic acid-l-DOPA hybrids

Two new diastereomeric lignan amides (4 and 5) serving as dimeric caffeic acid-l-DOPA hybrids were synthesized. The synthesis involved the FeCl3-mediated phenol oxidative coupling of methyl caffeate to afford trans-diester 1a as a mixture of enantiomers, protection of the catechol units, regioselective saponification, coupling with a suitably protected l-DOPA derivative, separation of the two diastereomers thus obtained by flash column chromatography and finally global chemoselective deprotection of the catechol units. The effect of hybrids 4 and 5 and related compounds on the proliferation of two breast cancer cell lines with different metastatic potential and estrogen receptor status (MDA-MB-231 and MCF-7) and of one epithelial lung cancer cell line, namely A-549, was evaluated for concentrations ranging from 1 to 256μM and periods of treatment of 24, 48 and 72h. Both hybrids showed interesting and almost equipotent antiproliferative activities (IC50 64-70μM) for the MDA-MB-231 cell line after 24-48h of treatment, but they were more selective and much more potent (IC50 4-16μM) for the MCF-7 cells after 48h of treatment. The highest activity for both hybrids and both breast cancer lines was observed after 72h of treatment (IC50 1-2μM), probably as the result of slow hydrolysis of their methyl ester functions.

(2E,4E,6E)-3-Methyl-7-(pyren-1-yl)octa-2,4,6-trienoic acid.

The title compound, C25H20O2, was synthesized by a Wittig reaction between triphenyl[1-(pyren-1-yl)ethyl]phosphonium bromide and ethyl (2E,4E)-3-methyl-6-oxohexa-2,4-dienoate, in the presence of n-butyl lithium, followed by saponification. It was obtained pure in the all-trans configuration following crystallization from ethyl acetate. The asymmetric unit contains two independent molecules (A and B), which are arranged almost parallel to each other within the crystal structure. The triene chain is not coplanar with the pyrene ring system, forming dihedral angles of 52.8 (1) and 42.2 (1)° for molecules A and B, respectively. Intermolecular hydrogen bonds between the carboxyl groups of the molecules link them into centrosymmetric pairs, AA and BB, each with the R 2 2(8) graph-set motif.

Synthesis and Evaluation of Chloramphenicol Homodimers: Molecular Target, Antimicrobial Activity, and Toxicity against Human Cells

As fight against antibiotic resistance must be strengthened, improving old drugs that have fallen in reduced clinical use because of toxic side effects and/or frequently reported resistance, like chloramphenicol (CAM), is of special interest. Chloramphenicol (CAM), a prototypical wide-spectrum antibiotic has been shown to obstruct protein synthesis via binding to the bacterial ribosome. In this study we sought to identify features intensifying the bacteriostatic action of CAM. Accordingly, we synthesized a series of CAM-dimers with various linker lengths and functionalities and compared their efficiency in inhibiting peptide-bond formation in an Escherichia coli cell-free system. Several CAM-dimers exhibited higher activity, when compared to CAM. The most potent of them, compound 5, containing two CAM bases conjugated via a dicarboxyl aromatic linker of six successive carbon-bonds, was found to simultaneously bind both the ribosomal catalytic center and the exit-tunnel, thus revealing a second, kinetically cryptic binding site for CAM. Compared to CAM, compound 5 exhibited comparable antibacterial activity against MRSA or wild-type strains of Staphylococcus aureus, Enterococcus faecium and E. coli, but intriguingly superior activity against some CAM-resistant E. coli and Pseudomonas aeruginosa strains. Furthermore, it was almost twice as active in inhibiting the growth of T-leukemic cells, without affecting the viability of normal human lymphocytes. The observed effects were rationalized by footprinting tests, crosslinking analysis, and MD-simulations.

Investigation on Toxicity and Teratogenicity in Rats of a Retinoid-Polyamine Conjugate with Potent Anti-Inflammatory Properties

Previous studies have shown that N(1),N(12)-bis(all-trans-retinoyl)spermine (RASP), a retinoid analog, inhibits RNase P activity and angiogenesis in the chicken embryo chorioallantoic membrane, demonstrates anti-tumor activity on prostate cancer cells, and acts as anti-inflammatory agent, being more effective and less toxic than all-trans retinoic acid. In an attempt to further characterize the biological profile of RASP, we tested its effects on organ toxicity and teratogenicity by daily oral gavage of RASP at a level of 50 mg/Kg of body weight in two generations of rats. We found that this compound does not induce changes to the body growth, the appearance of physical features, and the animals reflexes. Additionally, no substantial histopathological lesions were found in brain, heart, lung, thymus, liver, thyroid gland, adrenal gland, pituitary gland, kidneys, spleen, skin, femora, prostate, testis, epididymis, vagina, uterus, and ovaries of RASP-treated animals. These results suggest RASP, as a promising lead compound for the treatment of several dermatological disorders and certain cancer types, has apparently minimal toxic side-effects as revealed in this two-generation reproduction study in rats.