Characterization of cell death induced by ethacrynic acid in a human colon cancer cell line DLD-1 and suppression by N-acetyl-L-cysteine

Since ethacrynic acid (EA), an SH modifier as well as glutathione S-transferase (GST) inhibitor, has been suggested to induce apoptosis in some cell lines, its effects on a human colon cancer cell line DLD-1 were examined. EA enhanced cell proliferation at 20-40 microM, while it caused cell death at 60-100 microM. Caspase inhibitors did not block cell death and DNA ladder formation was not detected. Poly(ADP-ribose) polymerase, however, was cleaved into an 82-kDa fragment, different from an 85-kDa fragment that is specific for apoptosisis. The 82-kDa fragment was not recognized by antibody against PARP fragment cleaved by caspase 3. N-Acetyl-L-cysteine (NAC) completely inhibited EA-induced cell death, but 3(2)-t-butyl-4-hydroxyanisole or pyrrolidinedithiocarbamate ammonium salt did not. Glutathione (GSH) levels were dose-dependently increased in cells treated with EA and this increase was hardly affected by NAC addition. Mitogen-activated protein kinase (MAPK) kinase (MEK) 1, extracellular signal-regulated kinase (ERK) 1 and GST P1-1 were increased in cells treated with 25-75 microM EA, while c-Jun N-terminal kinase (JNK) 1 and p38 MAPK were markedly decreased by 100 microM EA. NAC repressed EA-induced alterations in these MAPKs and GST P1-1. p38 MAPK inhibitors, SB203580 and FR167653, dose-dependently enhanced EA-induced cell death. An MEK inhibitor, U0126, did not affect EA-induced cell death. These studies revealed that EA induced cell death concomitantly with a novel PARP fragmentation, but without DNA fragmentation. p38 MAPK was suggested to play an inhibitory role in EA-induced cell death.

Intra-cochlear administration of dexamethasone attenuates aminoglycoside ototoxicity in the guinea pig

This study demonstrates the attenuation of aminoglycoside ototoxicity by cochlear infusion of dexamethasone (Dex) using a microcannulation-osmotic pump delivery system. The results indicate that treating the cochlea with Dex both before and after kanamycin administration was more effective in preventing ototoxicity than Dex treatment only after kanamycin administration. A concentration of 1 ng/ml Dex showed the greatest protective effect on both kanamycin-induced threshold shift of the auditory brainstem response and outer hair cell survival. These results show that the Dex treatment attenuates both functional and structural damage of the inner ear from aminoglycoside toxicity.

Preclinical and clinical development of dexketoprofen

Dexketoprofen trometamol is a water-soluble salt of the dextrorotatory enantiomer of the nonsteroidal anti-inflammatory drug (NSAID) ketoprofen. Racemic ketoprofen is used as an analgesic and an anti-inflammatory agent, and is one of the most potent in vitro inhibitors of prostaglandin synthesis. This effect is due to the S(+)-enantiomer (dexketoprofen), while the R(-)-enantiomer is devoid of such activity. The pharmacokinetic profile of ketoprofen and its enantiomers was assessed in several animals species and in human volunteers. In humans, the relative bioavailability of oral dexketoprofen trometamol (12.5 and 25 mg, respectively) is similar to that of oral racemic ketoprofen (25 and 50 mg, respectively), as measured in all cases by the area under the concentration-time curve values for S(+)-ketoprofen. Dexketoprofen trometamol, given as a tablet, is rapidly absorbed, with a time to maximum plasma concentration (tmax) of between 0.25 and 0.75 hours, whereas the tmax for the S-enantiomer after the racemic drug, administered as tablets or capsules prepared with the free acid, is between 0.5 and 3 hours. Peak plasma concentrations of 1.4 and 3.1 mg/L are reached after administration of dexketoprofen trometamol 12.5 and 25 mg, respectively. From 70 to 80% of the administered dose is recovered in the urine during the first 12 hours, mainly as the acyl-glucuronoconjugated parent drug. No R(-)-ketoprofen is found in the urine after administration of dexketoprofen [S(+)-ketoprofen], confirming the absence of bioinversion of the S(+)-enantiomer in humans. in animal studies, the anti-inflammatory potency of dexketoprofen was always equivalent to that demonstrated by twice the dose of ketoprofen. Similarly, animal studies showed a high analgesic potency for dexketoprofen trometamol. The R(-)-enantiomer demonstrated a much lower potency, its analgesic action being apparent only in conditions where the metabolic bioinversion to the S(+)-enantiomer was significant. The gastric ulcerogenic effect of dexketoprofen at various oral doses (1.5 to 6 mg/kg) in the rat do not differ from those of the corresponding double doses (3 to 12 mg/kg) of racemic ketoprofen. Repeated (5-day) oral administration of dexketoprofen as the trometamol salt causes less gastric ulceration than was observed after the acid form of both dexketoprofen and the racemate. In addition, single dose dexketoprofen as the free acid at 10 to 20 mg/kg does not show a significant intestinal ulcerogenic effect in rats, while racemic ketoprofen 20 or 40 mg/kg is clearly ulcerogenic to the small intestine. The analgesic efficacy of oral dexketoprofen trometamol 10 to 20 mg is superior to that of placebo and similar to that of ibuprofen 400 mg in patients with moderate to serve pain after third molar extraction. The time to onset of pain relief appeared to be shorter in patients treated with dexketoprofen trometamol than in those treated with ibuprofen 400 mg. Dexketoprofen trometamol was well tolerated, with a reported incidence of adverse events similar to that of placebo.

Inactivation of mouse liver glutathione S-transferase YfYf (Pi class) by ethacrynic acid and 5,5'-dithiobis-(2-nitrobenzoic acid)

Mouse liver glutathione S-transferase YfYf (Pi class) reacts with [14C]ethacrynic acid to form a covalent adduct with a stoichiometry of 1 mol per mol of subunit. Proteolytic digestion of the enzyme-[14C]ethacrynic acid adduct with V8 protease produced an 11 kDa fragment containing radioactivity. Sequencing revealed this to be an N-terminal peptide (minus the first 15 residues, terminating at Glu-112) which contains only one cysteine residue (Cys-47). This is tentatively identified as the site of ethacrynic attachment. Kinetic studies reveal that glutathione S-conjugates protect against inactivation by ethacrynic acid, but the level of protection is not consistent with their potency as product inhibitors. A model is proposed in which glutathione S-conjugates and ethacrynic acid compete for the free enzyme, and a second molecule of ethacrynic acid reacts covalently with the enzyme-ethacrynic acid complex. The native protein contains one thiol reactive with 5,5'-dithiobis-(2-nitrobenzoic acid) at neutral pH. The resultant mixed disulphide, like the ethacrynic acid adduct, is inactive, but treatment with cyanide (which incorporates on a mol for mol basis) restores activity to 35% of that of the native enzyme.

Isoenzyme selective irreversible inhibition of rat and human glutathione S-transferases by ethacrynic acid and two brominated derivatives

In the present study it has been shown that ethacrynic acid can inhibit glutathione S-transferase (GST) of the pi-class irreversibly. [14C]Ethacrynic acid, 0.8 nmol/nmol human P1-1 and 0.8 nmol/nmol rat GST 7-7 could be incorporated, resulting in 65-93% inhibition of the activity towards 1-chloro-2,4-dinitrobenzene (CDNB). Isoenzymes of the alpha- and mu-class also bound [14C]ethacrynic acid, however without loss of catalytic activity. Incorporation ranged from 0.3 to 0.6 and 0.2 nmol/nmol enzyme for the mu- and alpha-class GST isoenzymes, respectively. For all isoenzymes, incorporation of [14C]ethacrynic acid could be prevented by preincubation with tetrachloro-1,4-benzoquinone, suggesting, that a cysteine residue is the target site. Protection of GST P1-1 against inhibition by ethacrynic acid by the substrate analog S-hexylglutathione, indicates an active site-directed modification. The monobromo and dibromo dihydro derivatives of ethacrynic acid were synthesized in an effort to produce more reactive compounds. The monobromo derivative did not exhibit enhanced irreversible inhibitory capacity. However, the dibromo dihydro derivative inhibited both human and rat GST isoenzymes of the pi-class very efficiently, resulting in 90-96% inhibition of the activity towards CDNB. Interestingly, this compound is also a powerful irreversible inhibitor of the mu-class GST isoenzymes, resulting in 52-70% inhibition. The two bromine atoms only marginally affect the strong (reversible) competitive inhibitory capacity of ethacrynic acid, with IC50 (microM) of 0.4-0.6 and 4.6-10 for the mu- and pi-class GST isoenzymes, respectively.

Effects of topical ethacrynic acid adducts on intraocular pressure in rabbits and monkeys

We evaluated the effect of topical ethacrynic acid on rabbit and monkey intraocular pressure. In a preliminary experiment, 100-mmol/L ethacrynic acid applied topically to Dutch-Belted rabbit eyes was associated with an 8-mm Hg lowering of intraocular pressure. However, corneal edema was severe, and the corneal epithelium sloughed off. To try to maintain the pressure-lowering effect but reduce the corneal side effects, we attempted to create an adduct of ethacrynic acid by utilizing ethacrynic acid's sulfhydryl reactivity. Ethacrynic acid was mixed with equimolar cysteine to bind the sulfhydryl-reactive sites on ethacrynic acid. The goal was to expose the cornea to adducted ethacrynic acid, which might then dissociate in the anterior chamber via a retro-Michael reaction. Intraocular pressure decreased 8.9 mm Hg (n = 40) with this treatment, and corneal edema was lessened (32 of 40 eyes had mild to no edema). However, we observed that when the eye was treated before ethacrynic acid-cysteine administration with topical acetylcysteine, the corneal side effects were reduced further and the intraocular pressure effect remained. In living cynomolgus monkeys receiving a single pretreatment drop of 75-mmol/L acetylcysteine followed by two drops of 130-mmol/L ethacrynic acid and 130-mmol/L cysteine, an intraocular pressure lowering of 9.9 mm Hg was observed (n = 7). However, in three of seven eyes corneal edema developed. Pretreatment with two drops of acetylcysteine eliminated the pressure-lowering effect but did not confer any added corneal protection. Our results indicate that topical ethacrynic acid-cysteine is effective in lowering the intraocular pressure of rabbits and cynomolgus monkeys and, when combined with acetylcysteine pretreatment, may offer the potential for a new topical therapeutic regimen for use in glaucoma.

Phase I study of thiotepa in combination with the glutathione transferase inhibitor ethacrynic acid

The glutathione transferases comprise a family of isoenzymes, one or more of which are involved in the conjugation of alkylating agents to glutathione (GSH). Increased GSH transferase activity has been shown to underlie acquired resistance to several alkylating agents. Ethacrynic acid inhibits the isoenzymes of GSH transferase with 50% inhibitory concentration values ranging from 0.3 to 6.0 microM and has been shown to restore sensitivity to alkylating agents in drug-resistant animal tumor models. We entered 27 previously treated patients with advanced cancer on a study of ethacrynic acid (25 to 75 mg/m2 p.o. every 6 h for 3 doses) and thiotepa (30 to 55 mg/m2 i.v. 1 h after the second dose of ethacrynic acid). The major toxicity of ethacrynic acid was diuresis, which was observed at every dose level; in addition, severe metabolic abnormalities occurred at 75 mg/m2. At 50 mg/m2, the diuretic effects were manageable. Myelosuppression was the most important effect of the combination. Two of seven courses of ethacrynic acid, 50 mg/m2, and thiotepa, 55 mg/m2, were associated with grade 3 or 4 neutropenia and/or thrombocytopenia. Nausea/vomiting greater than or equal to grade 2 was observed in 16% of courses. GSH transferase activity was assayed spectrophotometrically in the peripheral mononuclear cells of all patients. At each dose level, activity decreased following ethacrynic acid administration, with recovery by 6 h. Administration of ethacrynic acid, 50 mg/m2, resulted in a mean nadir of transferase activity of 37% of control. The pharmacokinetics of thiotepa and its principal metabolite TEPA were studied in 23 patients. The plasma disappearance of thiotepa fit a two-compartment open model with a terminal half-life of approximately 2 h. Plasma TEPA levels peaked at a mean of 2.16 h following thiotepa administration. The harmonic mean terminal half-life of TEPA was 10.4 h, and the TEPA area under the curve (AUC) did not increase with increasing thiotepa dose. The AUC of thiotepa was approximately twice, and the clearance about one-half, of the values obtained in a previous study of single agent thiotepa. The AUC of TEPA was lower than that previously observed. The data suggest that ethacrynic acid inhibits enzymes involved in the metabolic disposition of thiotepa, including its oxidative desulfuration to TEPA. The severity of the platelet toxicity was correlated with the AUC of thiotepa, but not with that of TEPA. This combination of thiotepa and ethacrynic acid will be tested further in Phase II trials.

Intracerebroventricular injection of ethacrynic acid induces status epilepticus

The intracerebroventricular (i.c.v.) injection of ethacrynic acid to mice at a dose of more than 25 micrograms induced repeated tonic-clonic convulsions with subsequent death. Ethacrynic acid was more potent than other loop diuretics such as furosemide and bumetanide. Diazepam and 2-amino-5-phosphonovaleric acid notably reduced both the incidence of convulsion and the lethality seen after ethacrynic acid administration. Both phenobarbital and ketamine suppressed the incidence of convulsions but not the lethality. Without effects on the incidence of convulsions or lethality, dextromethorphan prolonged, while phenytoin or atropine shortened, the time to the onset of convulsion. Neither ethosuximide, carbamazepine, nor muscimol had a significant effect on the responses to ethacrynic acid. The present findings indicate that i.c.v. injected ethacrynic acid shows strong convulsive activity, probably due to impairment of Cl- transport processes, concomitant with enhancement of excitatory amino acid activity in the brain.

Selective inhibition of leukotriene C4 synthesis and natural killer activity by ethacrynic acid

We have investigated the role of arachidonic acid (AA) metabolism in natural killer (NK) cell activity. Human nonadherent (NA) peripheral blood lymphocytes were used as effector cells against 51Cr-labeled K562 target cells. Synthesis of leukotriene C4 (LTC4) is dependent on glutathione S-transferase (GST). We have chosen to study three putative GST inhibitors, namely, ethacrynic acid (ET), caffeic acid (CA), and ferulic acid (FA), with regard to NK activity and with regard to their effect on AA metabolism. The GST inhibitors inhibited NK lysis when added directly to the NK assay. The GST inhibitors inhibited LTC4 synthesis as induced by calcium ionophore A23187 in a dose-dependent manner similar to their inhibition of NK activity. However, only ET was selective, for it had little effect on LTB4, 5-hydroxyeicosatetraenoic acid, and prostaglandin E2 synthesis. LTC4 synthesis was associated with the NK-enriched fractions obtained from discontinuous Percoll gradients. NK-specific anti-Leu-11b antibody and C treatment could abrogate NK activity and LTC4 synthesis. ET was also inhibitory when NA cells were cultured at 37 degrees C for 18 hr. In this case, LTC4 could reverse the inhibitory effect of ET. Our data suggest that LTC4 plays an important role in NK activity.

Inhibition of some polymorphonuclear leukocyte functions by ethacrynic acid

Ethacrynic acid (10(-4) M) inhibits exocytosis, phagocytosis and superoxide release in rabbit polymorphonuclear leukocytes (PMN's). Dihydroethacrynic acid is a much weaker inhibitor of these PMN functions. Though ethacrynic acid inhibits ATPase activity in the PMN, this occur at much higher concentrations than required for inhibition of exocytosis and superoxide release, thus a causal relationship seems unlikely. The same applies to inhibition of ATP generation by ethacrynic acid: the concentration required to decrease ATP level in PMN's is much higher than required for the inhibitory effect on exocytosis. Inhibition of exocytosis by ethacrynic acid can be prevented by dithiothreitol. It is concluded that vulnerable sulfhydryl groups are involved in the inhibition by ethacrynic acid.

[Experimental cholestasis by dibucaine and harmaline: effects on bile flow and hepatic transport of bile acids, ethacrynic acid and ouabain (author's transl)]

For further confirmation of the hypothesis that bile-salts independent bile flow depends on transepithelial Na+ fluxes, the effect of dibucaine (0.5 to 1.6 mM) and of harmaline (1.7 to 4.0 mM) on bile formation was studied in the isolated rat liver. Both compounds, which are known to inhibit passive Na+ entry into tissues other than liver, inhibit bile secretion in a dose-dependent fashion. Measurements of oxygen consumption and examination of liver tissue by electronmicroscopy exclude unspecific damage to liver cells as the cause for secretory failure. Cholestasis induced by dibucaine and harmaline is reversible upon wash-out of the drugs from the perfusion system. Simultaneously added choleretics, such as taurocholate, cholate, ethacrynic acid or ouabain, fail to elicit a secretory response. Since harmaline is an inhibitor of Na+-dependent transport processes, its effect and that of dibucaine on Na+-linked uptake of these choleretics by the isolated liver was determined. Harmaline and dibucaine reduce taurocholate transfer to the extent of the Na+-independent fraction only, but completely inhibit active entry of cholate, ethacrynic acid and ouabain. It is concluded that drug-membrane interactions primarily on the sinusoidal surface but possibly also at the canalicular pole of the hepatocytes are responsible for the impairment of basal and stimulated bile secretion.