Sulfonamide inhibition studies of the ß-carbonic anhydrase from the newly discovered bacterium Enterobacter sp. B13.

The genome of the newly identified bacterium Enterobacter sp. B13 encodes for a ß-class carbonic anhydrases (CAs, EC 4.2.1.1), EspCA. This enzyme was recently cloned, and characterized kinetically by this group (J. Enzyme Inhib. Med. Chem. 2016, 31). Here we report an inhibition study with sulfonamides and sulfamates of this enzyme. The best EspCA inhibitors were some sulfanylated sulfonamides with elongated molecules, metanilamide, 4-aminoalkyl-benzenesulfonamides, acetazolamide, and deacetylated methazolamide (KIs in the range of 58.7-96.5nM). Clinically used agents such as methazolamide, ethoxzolamide, dorzolamide, brinzolamide, benzolamide, zonisamide, sulthiame, sulpiride, topiramate and valdecoxib were slightly less effective inhibitors (KIs in the range of 103-138nM). Saccharin, celecoxib, dichlorophenamide and many simple benzenesulfonamides were even less effective as EspCA inhibitors, with KIs in the range of 384-938nM. Identification of effective inhibitors of this bacterial enzyme may lead to pharmacological tools useful for understanding the physiological role(s) of the ß-class CAs in bacterial pathogenicity/virulence.

Carbonic anhydrase inhibitors: X-ray crystallographic structure of the adduct of human isozyme II with the perfluorobenzoyl analogue of methazolamide. Implications for the drug design of fluorinated inhibitors.

The X-ray crystal structure for the adduct of human carbonic anhydrase (hCA) II with 4-methyl-5-perfluorophenylcarboximido-delta2-1,3,4-thiadiazoline-2-sulfonamide (PFMZ), a topically acting antiglaucoma sulfonamide, has been resolved at a resolution of 1.8 A. This compound is almost 10 times more effective as a hCA II inhibitor (KI of 1.5 nM) compared to the lead molecule, methazolamide, a clinically used drug (KI of 14 nM). Its binding to the enzyme active site is similar to that of other sulfonamide inhibitors, considering the interactions of the sulfonamide zinc anchoring group and thiadiazoline ring contacts, but differs considerably when the perfluorobenzoylimino fragment of the molecule is analyzed. Indeed, several unprecedented strong hydrogen bonds involving the imino nitrogen, carbonyl oxygen, a fluorine atom in the ortho position of the inhibitor, and two water molecules, as well as Gln 92 of the enzyme active site were seen. A stacking interaction of the perfluorophenyl ring of the inhibitor and the aromatic ring of Phe 131 was also observed for the first time in a CA-sulfonamide adduct. All these findings prove that more potent CA inhibitors incorporating perfluoroaryl/alkyl tails may be designed, with potentially improved antiglaucoma properties, in view of the new types of interactions seen here between the enzyme and the perfluorobenzoylated analogue of methazolamide.

Penetration into the anterior chamber via the conjunctival/scleral pathway.

The importance of the conjunctival/scleral pathway as a route of entry into the ciliary body, and in particular uptake and deposition by vessels, was investigated. A constant concentration of methazolamide analogs as well as 6-carboxyfluorescein (6-CB) and rhodamine B (RB) was maintained on either the cornea or the conjunctiva/sclera tissue, the latter excluding the cornea. The solutions were applied with the use of a cylindrical well affixed to the cornea of an anesthetized white rabbit. After two hours, concentrations of drug or dye were measured in cornea, aqueous humor or iris/ciliary body for both routes of entry. Confocal microscopy methods were used to determine reflected fluorescence images for 6-CB and RB. Carbonic anhydrase inhibition, partitioning, solubility and intraocular pressure (IOP) measurements were also determined. Permeability calculations were estimated for drug diffusing against aqueous flow within the posterior chamber. The conjunctival/scleral route of entry produced higher iris/ciliary body concentrations for all compounds except for the lipophilic RB. Confocal microscopy results suggested that drug is gaining entry into the ciliary body through vessel uptake in the sclera. Following entry of drug into the conjunctival/scleral tissue, a significant portion enters scleral vessels and deposits within the ciliary body. Calculations are given that indicate that once drug penetrates the cornea it is highly unlikely drug diffuses through the pupil against aqueous flow to enter the posterior chamber and reach the ciliary body.

Acetazolamide-like carbonic anhydrase inhibitors with topical ocular hypotensive activity.

New carbonic anhydrase (EC 4.2.1.1) inhibitors were synthesized as potential drugs for the topical treatment of glaucoma. They were obtained by substituting the acetyl group of acetazolamide and methazolamide with bicarboxylic acids of different chain length (C4-C6). The terminal carboxyl was either kept free or esterified with alcohols of different size (C1-C12). A gamma-aminovaleric derivative was also prepared. All compounds proved active as carbonic anhydrase inhibitors in vitro, with an average IC50 of about 0.5 microM. Some proved also to be topically active in vivo in lowering the artificially elevated intraocular pressure in rabbits. The most active compound, carrying a succinic acid side chain, is the most soluble in aqueous buffers. Its duration of action is about 8 h and it is under evaluation as a topical antiglaucoma drug. It is hypothesized that the duration of action could be longer in compounds having both the same high water solubility and partition coefficient.

Ocular pharmacology of methazolamide analogs: distribution in the eye and effects on pressure after topical application.

The authors studied the relation between physicochemical properties and lowering of intraocular pressure (IOP) after topical application to rabbit in a series of 5-acylimino- and related imino-substituted analogs of methazolamide (Compound 4). All had Ki vs. carbonic anhydrase C of about 10(-8) M. The parent, methazolamide (5-acetyl) does not lower IOP, in contrast to the 5-CF3 acetyl compound (Compound 28). The 5-propionyl compound (6) unexpectedly was 3 times more water soluble than methazolamide and had 10 times greater CHCl3-buffer partition. The in vivo transcorneal permeability constant was 6 times greater than methazolamide. One hour after 1 drop of a 2% suspension of Compound 6, anterior aqueous concentration (in micromolar) was 69 (for methazolamide, 8), posterior aqueous was 19 and ciliary process was 17. IOP dropped 2.2 mm Hg and returned to normal in 4 hr. Other compounds in the series showed varying degrees of activity, ranging from Compound 28, which elicited an IOP fall of 3.5 mm Hg, to Compound 7, (n-pentyryl), for which the fall was 1.3 mm Hg. Also studied are substitutions for CH3 on the ring N at position 4. There are multiple criteria for in vivo activity; a major factor is the balance between water and lipid solubility. The methazolamide analogs are compared with benzothiazole-2-sulfonamides, another class under investigation as topical carbonic anhydrase inhibitors designed to treat glaucoma.

The effects of separate and combined topical treatment with timolol maleate and trifluormethazolamide on the intraocular pressure in normal rabbits.

The effects of separate and combined topical treatment with timolol maleate and trifluormethazolamide (TFM) on the intraocular pressure (IOP) were studied in normotensive rabbits. Timolol had a distinct, albeit small, dose related hypotensive effect. Unilateral application of timolol resulted in dose related decrease in IOP in the untreated fellow eye. These effects could be observed only by using a protocol that reduces the contribution of individual and diurnal variations to the overall variability in IOP in the rabbit. Topical treatment with TFM caused a reduction in the calculated outflow pressure of 32%, similar to that observed after systemic administration of acetazolamide and methazolamide. At the concentration and dosage employed here there was no significant difference between the hypotensive effects of timolol and TFM. The maximal decrease in the calculated outflow pressure for the different doses of timolol varied between 24% to 37%. The hypotensive effect of the combined timolol and TFM treatment (delta IOP = -2.4 +/- 0.4 mmHg, n = 12) was greater than that observed in rabbits treated with TFM alone (delta IOP = -1.6 +/- 0.5 mmHg, n = 12). The increment was smaller than the initial effect of either drug alone.

The effects of carbonic anhydrase inhibitors on aqueous humor chemistry and dynamics.

The effects of topical application of the carbonic anhydrase inhibitor trifluormethazolamide (TFM) on intraocular pressure (IOP), ascorbate and CO2 concentrations in aqueous humor, and aqueous humor flow were studied in rabbits. These effects were compared with those produced by systemic treatment with methazolamide. The decrease in IOP observed after TFM was accompanied by changes in the composition of the aqueous humor. Posterior aqueous ascorbate concentration showed a marked increase (up to 1.7-fold), whereas the anterior aqueous ascorbate did not change significantly. Similar changes were found in rabbits after systemic treatment with methazolamide. A small but statistically significant decrease in the CO2 content of both posterior and anterior aqueous was observed after topical TFM application. Methazolamide yielded a more profound lowering in the CO2 content of the aqueous humor, a reflection of the significant decrease in plasma CO2 content. For topical TFM or systemic methazolamide doses yielding complete inhibition of carbonic anhydrase in the eye, a 55-59% reduction of aqueous flow was calculated from the ascorbate data using the Kinsey and Palm equation. However, a 31-42% reduction in aqueous flow was obtained from the same data using an equation based only on posterior chamber data. The reasons for using only posterior aqueous ascorbate data for calculating the changes in aqueous humor flow are discussed.

The effect of topically administered carbonic anhydrase inhibitors on aqueous humor dynamics in rabbits.

Repeated topical administration of 2.5% trifluormethazolamide, a halogenated derivative of methazolamide, resulted in a unilateral decrease in intraocular pressure in rabbits. Mean (+/- S.E.M.) baseline intraocular pressure (19.8 +/- 2.1 mm Hg) was significantly (P less than .05) decreased 30 minutes (16.1 +/- 2.2 mm Hg) and 60 minutes (15.8 +/- 2.7 mm Hg) after drug administration. Trifluormethazolamide did not alter outflow facility. Aqueous humor flow calculated from the tonographic data was reduced 44% and flow measured by fluorophotometry was reduced 29%. Topical delivery of trifluormethazolamide decreased the level of carbon dioxide in the aqueous humor in the treated eye in a manner similar to that observed after systemic administration of carbonic anhydrase inhibitors. Topical administration of 10% acetazolamide did not decrease intraocular pressure. However, topical administration of either trifluormethazolamide or acetazolamide before oral administration of water resulted in a blunting of the water-induced ocular hypertensive response.