Enhancement of iron excretion via monoanionic 3-hydroxypyrid-4-ones.

The ability of 3-hydroxypyrid-4-ones bearing either a carboxylic acid or sulfonic acid group to mobilize iron into the bile and urine of normal rats has been examined and compared with that produced by 1,2-dimethyl-3-hydroxypyrid-4-one (L1). The compounds tested were 3-hydroxy-1-methyl-4-oxopyridine-6-carboxylic acid and 1-[3-hydroxy-6-(hydroxymethyl)-4-oxopyridyl]-2-ethanesulfonic acid, whose synthesis, biological activity, and X-ray crystallographic properties are described. Although estimates of activity, based on polarity and membrane permeability, predict such compounds to be ineffective, they were found to have an iron-mobilizing ability similar to that of the compounds which do not bear any charge at physiological pH when given parenterally. When given orally, the 3-hydroxypyrid-4-one containing a carboxylate group enhanced the urinary excretion of iron, while the sulfonate analog did not substantially increase the excretion of iron in the urine relative to the controls. The results obtained here suggest that the previous emphasis on the preparation of 3-hydroxypyrid-4-ones that are electrically neutral at physiological pH is unnecessarily restrictive and that the presence of an appropriate group bearing a single negative charge is consistent with a high level of activity. It is proposed that such negatively charged molecules may gain access to the interior of cells in both the kidney and the liver via monoanionic transport systems. Such compounds may prove to be less toxic than the neutral 3-hydroxypyrid-4-ones.

Inhibition of cis-diamminedichloroplatinum (II)--induced renal toxicity in the rat.

The hydroxyl-containing dithiocarbamates, sodium (di(hydroxyethl)-dithiocarbamate (NaY) and sodium N-methyl, N-dithiocarboxy-D-glucamine (NaG), appear to possess definite advantages over sodium diethyldithiocarbamate (DDTC) in reducing the cis-dichlorodiammineplatinum (Cis-Pt)-induced renal damage in rats given Cis-Pt as an IV bolus of 7.5 mg/kg 1 h before the IP administration of the dithiocarbamate. Renal damage, as estimated by blood urea nitrogen (BUN) values and serum creatinine levels, was less at all times up until sacrifice in animals given NaY or NaG than in those given DDTC. An even more effective method for suppression of Cis-Pt renal toxicity is to use a combination of procedures. The most efficacious combination involves a 24-h pretreatment with DDTC or NaG plus acetazolamide and normal saline hydration 30 min before administration of Cis-Pt, followed by post-treatment with NaG. With this combination therapy renal function can be almost completely spared. Although DDTC or NaG pretreatment is highly effective when used in conjunction with NaG post-treatment, DDTC or NaG pretreatment alone has no renal sparing effect on renal function or renal platinum accumulation. In experiments in which antidotes were given 1 h after Cis-Pt and the animals were followed up for 75 days, a chronic interstitial nephritis at 75 days, suggesting a persistent cell-mediated immune response to Cis-Pt-induced renal damage, may be the basis for chronically abnormal renal function resulting from Cis-Pt. Treatment with all three dithiocarbamates, NaY, NaG, and DDTC, reduced the intensity of this cellular reaction and also reduced platinum levels in the kidneys. Although NaY and NaG are effective heavy metal chelators and renal function is spared and kidney platinum levels are substantially reduced by the dithiocarbamates, no parallel loss of antineoplastic activity by Cis-Pt on the rat Walker carcinoma was observed. Since the dithiocarbamates have no known human toxicity that would disqualify their clinical use, phase 1 clinical trials are indicated.

The relative nephrotoxicity of cisplatin, cis-[Pt(NH3)2(guanosine)2]2+, and the hydrolysis product of cisplatin in the rat.

An examination of the comparative nephrotoxicity in the rat of cisplatin, its hydrolysis product (mostly cis-[Pt(NH3)2Cl(H2O)]+ under the conditions applied), and cis-[Pt(NH3)2(guanosine)2]2+ revealed that these compounds differed significantly in the extent of renal damage they produced following their i.v. injection in Sprague-Dawley rats. The hydrolysis product was found to be the most toxic of the three complexes studied and produced nephrotoxicity at doses lower than those at which cisplatin was nephrotoxic. Under the conditions used, the i.v. administration of cis-[Pt(NH3)2(guanosine)2]2+ resulted in no observable signs of nephrotoxicity at levels at which an equimolar dose of cisplatin produces clear evidence of renal function impairment and morphological alterations. The nephrotoxicity of these complexes appears to be generally related to the ease with which they undergo nucleophilic substitution reactions. The lack of substantial nephrotoxicity found for cis-[Pt(NH3)2(guanosine)2]2+ suggests that the products resulting from the action of the DNA repair processes on platinated DNA do not contribute significantly to the nephrotoxicity of cisplatin. Renal platinum levels found following the administration of these compounds correlated with the degree of nephrotoxicity produced by each compound, but no general correlation of nephrotoxicity and renal platinum levels was found. The nephrotoxicity of cis-[Pt(NH3)2Cl(H2O)+ on a molar basis was estimated to be approximately 3 times as great as that of cisplatin itself.

Relative effectiveness of some compounds for the control of cisplatin-induced nephrotoxicity.

Several procedures which have been reported as effective for the control of cisplatin induced nephrotoxicity were compared in the Sprague-Dawley rat using the same dose of cisplatin. The treatments examined were based on the use of sodium thiosulfate, sodium diethyldithiocarbamate (DDTC), glutathione (GSH), sodium N-methyl-D-glucamine dithiocarbamate (NaG) and S-2-(3-aminopropylamino)ethylphosphorothioic acid (WR-2721). The differences in the effectiveness of the procedures were assessed using BUN and serum creatinine values, histopathological examination, body weight changes, and renal platinum levels as indices. The effect of such treatments on the antineoplastic activity of cisplatin were examined with both the Walker 256 carcinosarcoma in the rat and the L1210 murine leukemia in mice. Under the conditions used, GSH was found to be more effective than the other nucleophiles in protecting against the nephrotoxicity of cisplatin while providing the least amount of interference with the antitumor activity as measured against the Walker 256 carcinosarcoma and the L1210 murine leukemia. Simultaneous i.v. administration of cisplatin and any of the sulfur-containing nucleophiles leads to a significant protection against the nephrotoxicity but reduced the anti-neoplastic activity of cisplatin when measured against the Walker 256 carcinosarcoma.

Dependence on chelating agent properties of nephrotoxicity and testicular damage in male mice during cadmium decorporation.

An examination of the histopathological appearance of the kidneys of mice treated with cadmium chloride (s.c.) and simultaneously given 1 of 3 chelating agents (i.p.) reveals that the extent of nephrotoxicity is greatest when L-cysteine is the chelating agent. When either of 2 dithiocarbamates capable of mobilizing cadmium from its intracellular deposits, i.e. sodium N-methyl-D-glucamine dithiocarbamate (NaG) or sodium N-benzyl-D-glucamine dithiocarbamate (NaB) is used as the chelating agent, no morphological renal damage was evident. Under these same conditions the testes of the mice were protected to the extent of 95% by both of the dithiocarbamates, whereas the protection afforded by the L-cysteine was only about 50%. One factor governing the extent of nephrotoxicity appears to be the stability of the cadmium complexes which are formed and the manner in which this affects their behavior in vivo. Complexes which are preferentially excreted in the bile, cause little or no renal damage.

Prevention of cisplatin nephrotoxicity by exogenous atrial natriuretic peptide.

The ability of atrial natriuretic peptide (ANP) to prevent cisplatin-induced nephrotoxicity was compared to the protective effect of 3% NaCl. ANP (1 microgram/kg/min), 3% NaCl or peptide buffer vehicle (50 microliters/min) were infused for 45 min to conscious unrestrained rats immediately after cisplatin administration (5 mg/kg i.v.). Measurements taken 72 h after drug treatment indicated that compared to animals receiving cisplatin only, ANP co-treated rats had lower post-treatment plasma creatinine concentrations (0.70 +/- 0.07 vs 1.3 +/- 0.17 mg/dl; P < 0.05), blood urea nitrogen (BUN) concentrations (44.2 +/- 5.8 vs. 65.5 +/- 2.1 mg/dl; P < 0.05) and higher post-treatment glomerular filtration rates (GFR) (0.71 +/- 0.18 vs. 0.14 +/- 0.03 ml/min; P < 0.05). ANP was as effective as 3% NaCl in preventing cisplatin nephrotoxicity in this model. The effect of ANP co-treatment on the anti-tumor activity of cisplatin was also examined using the Walker 256 carcinosarcoma model. ANP treatment did not result in any observable loss in anti-tumor activity. When ANP was administered 72 h after cisplatin treatment, improvement in GFR was observed for the duration of the infusion, confirming the beneficial effect of ANP on cisplatin-damaged kidneys. ANP may have a role in the treatment and prevention of cisplatin nephrotoxicity especially in clinical situations where treatment with a large fluid volume is contraindicated.

Effect of chelate treatments on kidney, bone and brain lead levels of lead-intoxicated mice.

The effects of chelating agent treatment with meso-2,3-dimercaptosuccinic acid (DMSA), Na2CaEDTA, Na2ZnEDTA, and Na3ZnDTPA on the organ lead levels of lead-loaded mice have been determined. At 1 mmol/kg/day i.p., all caused reductions in the lead levels of the kidney after four injections, but only Na2CaEDTA produced a significant reduction in brain lead. All chelating agents caused significant reductions in kidney and brain lead levels when administered at a daily dose of 1 mmol/kg/day for eight days, but only DMSA reduced the bone lead level. In animals given 50 mg Pb/kg or 100 mg Pb/kg, the administration of Na2CaEDTA or DMSA at 1 mmol/kg/day x 8 produced significant reductions in kidney, bone and brain lead levels, but DMSA produced greater reductions of bone lead in both groups and of kidney lead in the group given 100 mg Pb/kg. An examination of published data describing the effect of chelating agent treatment on brain lead levels indicates that DMSA produces a reduction in brain lead levels under all conditions examined to date.

Mobilization of lead in mice by administration of monoalkyl esters of meso-2,3-dimercaptosuccinic acid.

The following six monoalkyl esters of meso-2,3-dimercaptosuccinic acid (DMSA) were synthesized and evaluated for relative activities in mobilizing lead from kidneys and brains of lead-bearing mice: n-propyl (Mn-PDMS), i-propyl (Mi-PDMS), n-butyl (Mn-BDMS), i-butyl (Mi-BDMS), n-amyl (Mn-ADMS) and i-amyl meso-2,3-dimercaptosuccinate (Mi-ADMS). DMSA was used as a positive control. When each was administered intraperitoneally (i.p.) as a single dose of 2.0 mmol/kg, DMSA lowered the kidney lead concentration 52%, while the monoesters effected reductions of 54-75%. Mn-ADMS was toxic at this dose. DMSA lowered the brain lead level 20% when given as a single dose, while the monoesters conferred reductions of 64-87%. When given as 5 daily i.p. injections at 0.5 mmol/kg, DMSA reduced the kidney lead concentration 45%, while the monoesters caused reductions of 56-73%. DMSA lowered the brain lead concentration 35% on the 5-day treatment regimen, while the monoesters evoked reductions of 59-75%. Mi-ADMS was equally effective when given orally or i.p. The i.p. LD50 value of this analog in mice is 3.0 mmol/kg, a value which lies between the reported LD50 doses of DMSA (16.0 mmol/kg) and dimercaprol (1.1 mmol/kg). It is suggested that the ability of these monoesters to cross cell membranes may account for their superiority to DMSA in mobilizing brain lead in this animal model.

Thiol and thioether suppression of cis-platinum-induced nephrotoxicity in rats bearing the Walker 256 carcinosarcoma.

An examination of eighteen thiols and thio ethers revealed that the simultaneous administration of several of these with cis-platinum (CDDP) at 7.5 mg/kg (25 mumols/kg) iv, as a single injection to rats bearing the Walker 256 carcinosarcoma led to significant reduction in the nephrotoxicity typically found with cis-platinum, and no apparent interference in its anti-neoplastic action towards this tumor. The thiols and thiol ethers were administered at a twenty-fold molar excess to the CDDP and were combined with the CDDP immediately prior to administration. The most effective compounds in suppression nephrotoxicity were D-, and L-methionine, methyl and ethyl L-methioninate, and N-acetyl-D, L-methionine.

Coadministration of dimethyl sulfoxide reduces cisplatin nephrotoxicity.

The administration of dimethyl sulfoxide with cisplatin at a mole ratio of 200:1 results in a considerable reduction in the nephrotoxicity produced when cisplatin alone is administered to Sprague-Dawley rats at 7.5 mg/kg. Observed measures of nephrotoxicity which were significantly improved by the coadministration of cisplatin and DMSO over the values found for cisplatin alone include BUN, serum creatinine, creatinine clearance and histopathological evidence of renal damage. The weight loss associated with cisplatin administration was also significantly reduced by DMSO coadministration. The use of DMSO did not result in any observable loss in antitumor activity of cisplatin against the Walker 256 carcinosarcoma.

Thioether suppression of cisplatin nephrotoxicity in the rat.

Six compounds containing a thioether group were examined as agents for the reduction of the nephrotoxicity caused by cisplatin (CDDP) in the rat. Of these, five were able to reduce the CDDP- induced nephrotoxicity when administered simultaneously with CDDP (8.0 mg/kg, iv). The compounds capable of reducing CDDP toxicity were L-methioninamide, cystathionine, methionyl-L-alanine, (methythio) acetic acid and 4-(methylthio) benzoic acid. Indices used to evaluate toxicity included body weight changes, BUN and serum creatinine levels and the histopathological examination of renal tissue. The platinum levels of renal tissue were determined but were found not to correlate well with other measures of renal function. Oral administration of the more effective of these compounds was found to provide a reduced level of protection against the nephrotoxicity caused by iv CDDP. The most effective of these compounds caused a very modest reduction in the anti-tumor activity of CDDP as measured against the L1210 murine leukemia.

Synthesis and iron(III) binding properties of 3-hydroxypyrid-4-ones derived from kojic acid.

In an attempt to reduce the toxicity of the 3-hydroxypyrid-4-ones, the more hydrophilic derivatives of kojic acid were explored and compared to the standard, 1,2-dimethyl-3-hydroxypyrid-4-one, L1. The synthesis and iron(III) binding properties of these chelators are described. Neither these compounds nor the clinically effective 1,2-dimethyl-3-hydroxypyrid-4 one is able to completely remove all of the iron(III) from the Fe(III)EDTA complex in sodium acetate buffered solutions, when the 3-hydroxypyrid-4-one: Fe(III) ratio is 6:1. The ability of these compounds to enhance the urinary excretion of iron in rats indicates that the behavior of the 3-hydroxypyrid-4-ones derived from kojic acid is comparable to the analogous derivatives of maltol and ethyl maltol. The structure of the iron(III) complex of 3-hydroxy-6-hydroxymethyl-1-methylpyrid-4-one was determined by x-ray diffraction and found to be similar to the previously reported structure of the iron(III) complex of L1.

Ethylenediaminetetra(methylenephosphonic) acid (EDTPO) as a therapeutic chelating agent.

Ethylenediaminetetra(methylenephosphonic) acid (EDTPO), when administered as its calcium salt, is an effective antidote for acute intoxication by a number of metal ions. Significant antidotal action was found for the following cations: Cd2+, Ni2+, Zn2+, Pb2+, Be2+ and UO2+(2). Because EDTPO is capable of chelating more than one calcium ion, better results were obtained when the Ca2EDTPO complex was administered.

A hypothesis for the selection of chelate antidotes for toxic metals.

The problem of finding antidotes for toxic metal species for which antidotes have not been previously reported can be approached via a consideration of the metal-ion preferences of chelating agents already in clinical use. The metal ion preferences of six types of chelating agents together with information on antidotes used for other elements in the same family in the periodic table can be used to obtain a preliminary notion of which of these six structural types might furnish efficacious antidotes. The results of animal tests on a few of these chelate types can then serve as a guide in the selection of further compounds for testing. The data from the literature on antidotes for 20 toxic metal ions is summarized to assist the selection process.

Control of nephrotoxicity in the rat during repeated cis-platinum treatments.

The nephrotoxicity of cis-platinum (CDDP) in the rat can be controlled throughout a series of weekly administrations of CDDP (each of 5 mg kg-1, i.v.) for at least three weeks by a combination of protective measures involving pretreatment with dithiocarbamates and diuretics and the administration of appropriate dithiocarbamates given 1 h after the CDDP. The use of dithiocarbamates with polar substitutents is effective in removing both renal and hepatic deposits of platinum from rats subsequent to its administration and in this respect these compounds are significantly superior to meso-2,3-dimercaptosuccinic acid (DMSA) in the rate at which platinum is removed and in the amounts removed. The most effective of the dithiocarbamates remove ca. 70% of the platinum from the kidneys and the liver; the least effective remove ca. 50% of the platinum from these organs when given at a level of 1.57 mmol kg-1 i.p. for 6 days subsequent to the administration of CDDP. Acetazolamide was shown to be much less effective in preventing renal damage than the dithiocarbamates and was not effective in reducing renal or hepatic levels of platinum. Pretreatment with sodium diethyldithiocarbamate 12 h prior to the administration of the CDDP was more effective in preventing renal damage than the administration of this compound 30 min before the cis-platinum. Several dithiocarbamates are found to be superior to sodium diethyldithiocarbamate in reducing renal platinum burdens of rats given CDDP at the level of 6 mg kg-1, and dose-response curves for the removal of renal and hepatic platinum were determined for sodium N-methyl-D-glucamine dithiocarbamate (NaG).(ABSTRACT TRUNCATED AT 250 WORDS)

Chelate antidotes for sodium vanadate and vanadyl sulfate intoxication in mice.

Eighteen different chelating agents, including all of those previously shown to have a protective action in vanadium intoxication, have been compared as antidotes for acute vanadium intoxication using mice. Of these compounds, those found to be effective antidotes for both vanadate (VO3(-3)) and vanadyl (VO2+) include ascorbic acid, deferoxamine, D-penicillamine, sodium calcium diethylenetriaminepentaacetic acid (Na3CaDTPA), Na2CaEDTA, glutathione, Tiron, and ethylenediaminetetra(methylene phosphonate). Of the compounds examined, ascorbic acid appeared to be the most promising for human use. When administered at the levels used in this study, it is an effective antidote for intoxication due to either the vanadate or the vanadyl ion. Certain compounds are able to act as antidotes for vanadate solely by virtue of their action as a reducing agent; when these compounds are unable to form complexes with the reduction product (vanadyl ion), they are effective antidotes for the higher oxidation state only when the concentration of vanadyl produced is less than the level that results in toxic effects.

Tiron (sodium 4,5-dihydroxybenzene-1,3-disulfonate) as an antidote for acute uranium intoxication in mice.

Tiron (sodium 4,5-dihydroxybenzene-1,3-disulfonate) administered intraperitoneally was found to antagonize the lethal action of intraperitoneally induced uranium(VI) toxicity. In a comparative study Tiron was evaluated against Na3CaDTPA (sodium calcium diethylenetriaminepentaacetate). The ability of these compounds to detoxify the uranyl ion in simple and complexed form and their efficacy in delayed treatment regimens and determined. Toxicities of the complexes were assessed by the administration of uranyl acetate at levels of 40 mg/kg or 80 mg/kg complexed at a mole ratio of 3:1 or 2:1 of chelating agent to uranium, prior to injection, followed by two additional doses of chelating agent given one and three hours later at a 10:1 mole ratio of chelating agent to uranium. Therapy in delayed treatment regimens consisted of three injections of antidote given 20 minutes, one hour, and three hours, at a 10:1 mole ratio of chelating agent to uranium, subsequent to an injection of 40 mg/kg uranyl acetate. Survival rates for animals receiving multiple injections of Tiron were enhanced over those receiving Na3CaDTPA. The low inherent toxicity of Tiron may make it appropriate for possible clinical application.

Restrictions on the applicability of mixed ligand chelate therapy (MLC) in acute cadmium intoxication.

An experimental study of the comparative effectiveness of single and mixed ligand chelates as antidotes for acute cadmium poisoning reveals few appreciable differences when the cadmium (as cadmium chloride or acetate) is administered ip. In each case the mixed ligand chelate system showed little or no improvement over the results obtained with the most effective of the individual components. This procedure, using mixed ligand chelate systems, may well be one which is limited to conditions more narrowly similar to those reported by Schubert and Derr (1978). It does not appear to possess the broad range of applicability which might be expected from the equilibrium principles on which it is based. By comparing our data with previous studies it can be seen that Na2CaEDTA is capable of offsetting the lethality of ip cadmium chloride when the latter is administered at rather higher levels that have previously been counteracted by any of the sulfur containing chelating agents tested to date.

Structural requirements for chelate antidotal efficacy in acute antimony(III) intoxication.

The LD50 for i.p. potassium antimonyl tartrate was determined to be 54.6 mg/kg in mice, with a 95% confidence range of 48.4 to 61.7 mg/kg. An examination of the antidotal efficacy of a number of different structural types of chelating agents showed that very few types were able to act as antidotes when potassium antimonyl tartrate was administered i.p. to mice at a level of 120 mg/kg. The most effective antidotes, by a substantial margin, were the water soluble vicinal dithiols: 2,3-dimercaptosuccinic acid and sodium 2.3-dimercaptopropane-1-sulfonate, with the first of these being significantly better than the second. Appreciably less effective, but still useful, was D-penicillamine. At this level of administration of antimony(III), BAL is not an effective antidote. Among other chelating agents which were also not effective at this level of antimony(III) are tartaric acid, EDTA, cysteine, sodium diethyldithiocarbamate and potassium dithiooxalate.

L-methionine suppresses pathological sequelae of cis-platinum in the rat.

The pathological changes characteristically observed in the kidney, bone marrow, thymus, spleen, and duodenum of the rat given 12.2 mg/kg of cis-platinum (CDDP) ip are reduced or eliminated when a CDDP solution containing a 20-fold excess of L-methionine to cis-platinum is administered. L-Methionine was also effective in reducing the renal toxicity induced by CDDP when given orally 20 min before the iv administration of 7.5 mg CDDP/kg. L-Methionine did not compromise the efficacy of CDDP when the antitumor activity of the combination of L-methionine and CDDP was measured against the Walker 256 carcinosarcoma in the rat. No significant reduction in the antitumor activity of the CDDP resulted from the parenteral administration of L-Methionine when evaluated against the L1210 murine leukemia. The oral administration of L-methionine (500 mg/kg) 30 min after the administration of CDDP has no significant effect on the antitumor activity of CDDP in mice bearing the L1210 murine leukemia. The results suggest that L-methionine may have some practical utility in the control of certain aspects of CDDP toxicity.