Mark A. Basinger

Structural requirements for Hg(II) antidotes

Abstract A study involving (a) the structural chemistry of Hg(II) complexes with thiol containing ligands, (b) the stability constants for such systems and (c) the relative efficacy of 29 compounds as antidotes for mercury poisoning has been carried out to determine the structural requirements for Hg(II) antidotes. This leads to the suggestion that instances in which two thiol groups on the same chelate molecule are simultaneously bonded to the same Hg(II) species in a complex, water soluble or otherwise, are not found and Hg(II) species bearing two sulfur donors generally have a bond angle of 180° or so between these two bonds. It was hypothesized, from this, that chelating agents bearing a single sulfhydryl group might be almost as effective as mercury antidotes as those bearing two groups. Data on the stability constants and antidotal effectiveness are presented for such structures, but in general molecules which do not have the potential ability to chelate are also inferior as antidotes. From the data assembled it would appear that the presence of a second donor group is required. Because of the lability of the mercury-thiol bond, this second site seems necessary to provide the required kinetic stability for the complex. In the case of dithiols, the mercury may move back and forth from one sulfur donor site to another but may not (and possibily cannot) bind firmly and simultaneously to both donor sites.

L-methionine antagonism of cis-platinum nephrotoxicity.

L-Methionine administered simultaneously with cis-platinum (CDDP) iv results in a significant reduction of the nephrotoxicity normally associated with CDDP without any apparent effect on the antineoplastic activity for rats bearing the Walker 256 carcinosarcoma. CDDP given with L-methionine at a 1:20 mole ratio can be administered to rats at doses up to 35 mg/kg iv with the survival of all treated animals (3/3) and up to 56 mg/kg iv (bolus injection) with the survival of 3/6 animals, while CDDP administered alone at these levels is lethal. A reduced level of protection against the nephrotoxicity was also achieved at lower mole ratios of L-methionine to CDDP. Renal function was monitored using BUN and serum creatinine levels, and gastrointestinal toxicity by weight changes during the course of the experiments. A histopathological examination of the kidneys was also performed to evaluate the protection provided by L-methionine. Under the conditions used, the reaction between L-methionine and CDDP does not appear to proceed so rapidly as to interfere with the antitumor activity of the CDDP. The examination of structural analogs as agents for the control of CDDP-induced nephrotoxicity revealed that the C-S-C-group is the essential group for the protective action in these structures. Although L-methionine can provide renal protection in rats given high doses of CDDP, it does not prevent the accumulation of platinum in the kidney.

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.

Control of the Nephrotoxicity of Cisplatin by Clinically Used Sulfur-Containing Compounds

Several clinically used sulfur-containing compounds were examined as potential antagonists for the nephrotoxicity of cis-platin in Sprague-Dawley rats. The compounds studied were biotin, captopril, cefoxitin, cephalexin, the sodium salt of penicillin G, sulfathiazole, and thiamine hydrochloride. Biotin, captopril, cephalexin, and sulfathiazole were found to have a significant effect in reducing the nephrotoxicity of cisplatin when administered simultaneously with cisplatin via an intravenous route in the rat. Biotin was the most effective in providing renal protection and sulfathiazole the least effective, based upon BUN, serum creatinine values, and weight changes, though all four of these compounds provided a considerable measure of protection against the typical cisplatin-induced nephrotoxicity. The effect of the simultaneous administration of cisplatin with biotin, cephalexin, and sulfathiazole was examined on the antitumor activity of cisplatin toward the L1210 murine leukemia in the DBA/2 mouse and the Walker 256 carcinosarcoma in the rat. With the L1210 murine leukemia no loss of antitumor activity was found for any of the compounds. With the Walker 256 carcinosarcoma some loss of antitumor activity was found with biotin. Both biotin and sulfathiazole are shown to be promising candidates for use in the suppression of the adverse effects of cisplatin, and other sulfur-containing compounds currently in clinical use may have equivalent or superior properties in this respect.

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

SummaryAn examination of the comparative nephrotoxicity in the tat of cisplatin, its hydrolysis product (mostlycis-[Pt(NH3)2Cl(H2O)]+ under the conditions applied), andcis-[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 ofcis-[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 forcis-[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 ofcis-[Pt(NH3)2Cl(H2O)]2+ 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.

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.

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

SummaryThe 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.

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.

Dithiocarbamate-induced biliary platinum excretion and the control of cis-platinum nephrotoxicity.

Treatment with any one of six different dithiocarbamates subsequent to the administration of cis-platinum (CDDP) is shown to promote the biliary excretion of platinum. The administration of the most effective of these compounds, sodium diethyldithiocarbamate (DDTC) at 1.57 mmol/kg, led to a 30-fold increase in the biliary excretion of platinum. For the other dithiocarbamates investigated, a similar dosage led to increases ranging from approximately 5-fold for sodium iminodiacetic acid dithiocarbamate, to 26-fold for sodium sarcosine dithiocarbamate. The presence of alkyl groups on the nitrogen of the dithiocarbamate increased the effectiveness of the compounds. There is no increase in the platinum levels of the brain when DDTC is used in this manner. A histopathological evaluation of the kidneys of rats given 15 mg CDDP/kg in 6.3% saline with and without the use of dithiocarbamates for renal protection shows significant additional protection due to the use of the dithiocarbamates. Dithiocarbamates given at an appropriate dosing schedule can lead to a significant reduction in the renal damage which is revealed by microphotographs. It is suggested that part of the renal protection obtained by the use of dithiocarbamates may be due to this shift of platinum excretion to the bile which obviates additional renal exposure to platinum. It was also found that the simultaneous injection of a dithiocarbamate with the cis-platinum has no obvious effect on the anti-cancer action of cis-platinum against the Walker 256 carcinosarcoma in rats.