Inhibition Constants In Range Research Articles

The Coumarin-Binding Site in Carbonic Anhydrase Accommodates Structurally Diverse Inhibitors: The Antiepileptic Lacosamide As an Example and Lead Molecule for Novel Classes of Carbonic Anhydrase Inhibitors

Coumarins constitute a general and totally new class of inhibitors of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1), binding at the entrance of the active site cavity. We report here that the coumarin-binding site in CAs may interact with diverse compounds, such as the antiepileptic drug lacosamide, which inhibits mammalian CAs I-XV, with inhibition constants in range of 331 nM to 4.56 microM. Its X-ray crystal structure in adduct with CA II reveals the molecular basis for this inhibition. Lacosamide was found in the coumarin-binding site, making favorable van der Waals interactions with Thr200, Asn67, Gln92, and Phe131. No interactions with the Zn(II) ion were evidenced in the CA II-lacosamide adduct. The coumarin-binding site may thus accommodate structurally diverse compounds which possess an inhibition mechanism distinct of that of sulfonamides. This finding opens new possibilities for designing CA inhibitors/activators with various biomedical applications.

Carbonic anhydrase inhibitors: inhibition of transmembrane, tumor-associated isozyme IX, and cytosolic isozymes I and II with aliphatic sulfamates.

A series of aliphatic sulfamates and related derivatives incorporating cyclic/polycyclic (steroidal) moieties in their molecules has been synthesized and assayed as inhibitors of the zinc enzyme carbonic anhydrase (CA) and, more precisely, of the cytosolic isozymes CA I and II and the transmembrane, tumor-associated isozyme CA IX. The most potent CA I inhibitor was n-tetradecyl sulfamate and some (substituted)benzyl/phenethyl sulfamates (inhibition constants in the low micromolar range). Against CA II, low nanomolar inhibitors (0.7-3.4 nM) were n-decyl sulfamate and the (substituted)benzyl/phenethyl derivatives mentioned above. Effective CA II inhibition was also observed for the hydroxy/keto derivatives of dehydroepiandrosterone sulfamate. Efficient CA IX inhibitory properties, with inhibition constants in the range of 9-23 nM, were observed for the aliphatic sulfamates C(10)-C(16) (with the most potent inhibitor being the n-dodecyl derivative) and the (substituted)benzyl/phenethyl sulfamates. The inhibition profile of the three investigated isozymes with this type of compound was rather different, allowing us to hope that the preparation of CA IX-selective inhibitors is possible (selectivity ratios toward hCA IX versus hCA II in the range of 5-63 has been observed for some of these compounds, whereas for the clinically used sulfonamides this parameter is in the range of 0.23-0.51). These data are critical for the design of novel antitumor therapies, mainly for hypoxic tumors that overexpress CA IX, which are nonresponsive to radiation or chemotherapy.

7-Deazapurine 2'-deoxyribofuranosides are noncleavable competitive inhibitors of Escherichia coli purine nucleoside phosphorylase (PNP).

A series of 7-deazapurine 2'-deoxyribofuranosides were synthesized according to already known procedures and their substrate and inhibitor properties with purified E. coli purine nucleoside phosphorylase were examined. In agreement with previous findings, substrate activity was not detected for any of the compounds tested. Most of the nucleosides showed weak inhibition in the preliminary screening, i.e. at a concentration of about 100 microM. However some combinations of 6-chloro, 6-amino or 6-methoxy substituents with bulky hydrophobic groups at position 7 of the base and/or chloro, amino, methoxy or methylthio group at position 2 markedly enhanced affinity of such modified nucleosides for the E. coli enzyme. The most potent inhibition was observed for two nucleosides: 6-chloro- and 2-amino-6-chloro-7-deazapurine 2'-deoxyribofuranosides that show inhibition constants Ki = 2.4 and 2.3 microM, respectively. Several other compounds were also found to be good inhibitors, with inhibition constants in the range 5-50 microM. In all instances the inhibition was competitive vs. the nucleoside substrate 7-methylguanosine. Inhibition constants for 7-deazapurine nucleosides are in general several-fold lower than those observed for their purine counterparts. Therefore 7-deaza modification together with substitutions at positions 2, 6 and 7 of the base is a very promising approach to obtain competitive noncleavable inhibitors of E. coli PNP that may bind to the enzyme with inhibition constants in the microM range.