Multicomponent chemistry in the synthesis of carbonic anhydrase inhibitors

Abstract

Carbonic anhydrase inhibitors (CAIs) are of growing interest since various isoforms of the enzyme are identified as promising drug targets for treatment of disease. The principal drawback of the clinically used CAIs is the lack of isoform selectivity, which may lead to observable side effects. Studies aiming at the design of isoform-selective CAIs entail generation and biological testing of arrays of compounds, which is a resource- and time-consuming process. Employment of multicomponent reactions is an efficient synthetic strategy in terms of gaining convenient and speedy access to a range of scaffolds with a high degree of molecular diversity. However, this powerful tool appears to be underutilized for the discovery of novel CAIs. A number of studies employing multicomponent reactions in CAI synthesis have been reported in literature. Some of these reports provide inspiring examples of successful use of multicomponent chemistry to construct novel potent and often isoform-selective inhibitors. On critical reading of several publications, however, it becomes apparent that for some chemical series designed as CAIs, the desired inhibitory properties are only assumed and never tested for. In these cases, the biological profile is reported based on the results of phenotypical cellular assays, with no correlation with the intended on-target activity. Present review aims at critically assessing the current literature on the multicomponent chemistry in the CAI design.     

Isolation and characterization of high affinity aptamers against DNA polymerase iota

Human DNA-polymerase iota (Pol ι) is an extremely error-prone enzyme and the fidelity depends on the sequence context of the template. Using the in vitro systematic evolution of ligands by exponential enrichment (SELEX) procedure, we obtained an oligoribonucleotide with a high affinity to human Pol ι, named aptamer IKL5. We determined its dissociation constant with homogenous preparation of Pol ι and predicted its putative secondary structure. The aptamer IKL5 specifically inhibits DNA-polymerase activity of the purified enzyme Pol ι, but did not inhibit the DNA-polymerase activities of human DNA polymerases beta and kappa. IKL5 suppressed the error-prone DNA-polymerase activity of Pol ι also in cellular extracts of the tumor cell line SKOV-3. The aptamer IKL5 is useful for studies of the biological role of Pol ι and as a potential drug to suppress the increase of the activity of this enzyme in malignant cells.     

Chronic Exposure of NG108-15 Cells to Amyloid β Peptide (Aβ1–42) Abolishes Calcium Influx via N-Type Calcium Channels

We investigated whether amyloid--peptide (A_1–42) has an effect on the elevations of the intracellular concentration of Ca²⁺ ions ([Ca²⁺]_i) induced by depolarizations of NG108-15 cells and on related Ca²⁺ channels. A_1–42 (10-1000 nM) had no immediate effect on depolarization-induced [Ca²⁺]_i elevations. [Ca²⁺]_i increases were slightly diminished in cells grown in the presence of 100 or 1000 nM A_1–42. Nifedipine (1 M) reduced these elevations equally in cells grown in the absence or presence of A_1–42. In contrast, the ability of -conotoxin GVIA to diminish the depolarization-induced [Ca²⁺]_i responses became lost in cells grown in the presence of 100 nM A_1–42. This indicates that the influx of calcium through the N-type Ca²⁺ channels was compromised by the chronic exposure of cells to a submicromolar concentration of A_1–42, presumably because of impairement of their function or diminished expression. This may be important in the pathogeny of Alzheimer's dementia in view of the pivotal role of N-type Ca²⁺ channels in neurotransmitter release.     

The effect of different solvents on the ATP/ADP content and growth properties of HeLa cells

Testing of the effects of xenobiotics in cultured cells often requires the use of organic solvents to effect suspension of the test agents in cell culture media. However, the toxic effects of the solvents themselves may introduce artifacts, which obscure interpretation of the experimental results. In this article, the toxicity of different solvents commonly used for solvation of a variety of xenobiotic agents was studied. We show that ethanol, acetone, isooctane, methanol, and hexane were considerably less toxic than the more commonly used solvent, DMSO, when ATP content and growth rates of HeLa cells exposed to these solvents was measured. © 1998 John Wiley & Sons, Inc. J Biochem Toxicol 13: 11–15, 1999     

A parasitoid wasp induces overwintering behaviour in its spider host

Parasites and parasitoids control behaviors of their hosts. However, the origin of the behavior evoked by the parasitic organism has been rarely identified. It is also not known whether the manipulation is universal or host-specific. Polysphinctine wasps, koinobiont ectoparasitoids of several spider species that manipulate host web-spinning activity for their own protection during pupation, provide an ideal system to reveal the origin of the evoked behavior. Larva of Zatypota percontatoria performed species-specific manipulation of theridiid spiders, Neottiura bimaculata and Theridion varians, shortly before pupation. Parasitized N. bimaculata produced a dense web, whereas parasitized T. varians built a cupola-like structure. The larva pupated inside of either the dense web or the cupola-like structure. We discovered that unparasitized N. bimaculata produce an analogous dense web around their eggsacs and for themselves during winter, while T. varians construct an analogous 'cupola' only for overwintering. We induced analogous manipulation in unparasitized hosts by altering ambient conditions. We discovered that the behavior evoked by larvae in two hosts was functionally similar. The larva evoked protective behaviors that occur in unparasitized hosts only during specific life-history periods.     

Synthesis and biological evaluation of novel mono- and bivalent ASGP-R-targeted drug-conjugates

Asialoglycoprotein receptor (ASGP-R) is a promising biological target for drug delivery into hepatoma cells. Nevertheless, there are only few examples of small-molecule conjugates of ASGP-R selective ligand equipped by a therapeutic agent for the treatment of hepatocellular carcinoma (HCC). In the present work, we describe a convenient and versatile synthetic approach to novel mono- and multivalent drug-conjugates containing N-acetyl-2-deoxy-2-aminogalactopyranose and anticancer drug – paclitaxel (PTX). Several molecules have demonstrated high affinity towards ASGP-R and good stability under physiological conditions, significant in vitro anticancer activity comparable to PTX, as well as good internalization via ASGP-R-mediated endocytosis. Therefore, the conjugates with the highest potency can be regarded as a promising therapeutic option against HCC.     

Expression of human aldo-keto reductase 1C2 in cell lines of peritoneal endometriosis: potential implications in metabolism of progesterone and dydrogesterone and inhibition by progestins

The human aldo-keto reductase AKR1C2 converts 5α-dihydrotestosterone to the less active 3α-androstanediol and has a minor 20-ketosteroid reductase activity that metabolises progesterone to 20α-hydroxyprogesterone. AKR1C2 is expressed in different peripheral tissues, but its role in uterine diseases like endometriosis has not been studied in detail. Some progestins used for treatment of endometriosis inhibit AKR1C1 and AKR1C3, with unknown effects on AKR1C2. In this study we investigated expression of AKR1C2 in the model cell lines of peritoneal endometriosis, and examined the ability of recombinant AKR1C2 to metabolise progesterone and progestin dydrogesterone, as well as its potential inhibition by progestins. AKR1C2 is expressed in epithelial and stromal endometriotic cell lines at the mRNA level. The recombinant enzyme catalyses reduction of progesterone to 20α-hydroxyprogesterone with a 10-fold lower catalytic efficiency than the major 20-ketosteroid reductase, AKR1C1. AKR1C2 also metabolises progestin dydrogesterone to its 20α-dihydrodydrogesterone, with 8.6-fold higher catalytic efficiency than 5α-dihydrotestosterone. Among the progestins that are currently used for treatment of endometriosis, dydrogesterone, medroxyprogesterone acetate and 20α-dihydrodydrogesterone act as AKR1C2 inhibitors with low μM K(i) values in vitro. Their potential in vivo effects should be further studied.     

Isolation of ginkgolides A, B, C, J and bilobalide from G. biloba extracts

Ginkgolides A, B, C and J, together with bilobalide, are unique terpenoid components of the Ginkgo biloba tree. Due to similar chemical properties, their separation is quite tedious. We have developed an efficient and rapid protocol for separation of individual ginkgolides and bilobalide from G. biloba extracts. The procedure takes advantage of enhanced susceptibility of ginkgolides B and C to benzylation and the ease of separation of these products from ginkgolides A and J which do not react. The protocol is applicable to the previously reported enriched extracts prepared from G. biloba leaves. A single chromatographic step prior to benzylation provides bilobalide and mixture of ginkgolides A, B, C, and J. After benzylation, the individual ginkgolides are separated by chromatography.     

Adhesion forces measured at the level of a terminal plate of the fly's seta

The attachment pads of fly legs are covered with setae, each ending in small terminal plates coated with secretory fluid. A cluster of these terminal plates contacting a substrate surface generates strong attractive forces that hold the insect on smooth surfaces. Previous research assumed that cohesive forces and molecular adhesion were involved in the fly attachment mechanism. The main elements that contribute to the overall attachment force, however, remained unknown. Multiple local force-volume measurements were performed on individual terminal plates by using atomic force microscopy. It was shown that the geometry of a single terminal plate had a higher border and considerably lower centre. Local adhesion was approximately twice as strong in the centre of the plate as on its border. Adhesion of fly footprints on a glass surface, recorded within 20 min after preparation, was similar to adhesion in the centre of a single attachment pad. Adhesion strongly decreased with decreasing volume of footprint fluid, indicating that the layer of pad secretion covering the terminal plates is crucial for the generation of a strong attractive force. Our data provide the first direct evidence that, in addition to Van der Waals and Coulomb forces, attractive capillary forces, mediated by pad secretion, are a critical factor in the fly's attachment mechanism.