Glen R. Gale

CIS-dichlorodiammineplatinum (II): Persistent and selective inhibition of deoxyribonucleic acid synthesis in vivo

Abstract Cis -dichlorodiammineplatinum(II) ( cis -[Pt(NH 3 ) 2 Cl 2 ] 0 ) at 10 −4 M inhibits the incorporation in vitro of thymidine-methyl- 3 H, uridine-5- 3 H, and l -leucine 14 C into the acid-insoluble fraction of Ehrlich ascites tumor cells from untreated mice only after a period ofpreincubation. Similarly, when mice bearing well developed tumors are given this compound intraperitoneally, subsequent assessment in vitro of incorporation of these isotopic precursors into tumor cells from injected mice shows marked impairment of incorporation of all three; the greatest inhibition occurs 6–12 hr after injection. After this depression, the rates of incorporation of uridine and l -leucine return to control values or somewhat greater, while a striking suppression of the rate of incorporation of thymidine persists for at least 96 hr. These data were interpreted as indicative of a possible metabolic transformation by the cells of the inorganic moiety from an inactive to an active form, although alternate tentative explanations were also proposed. It was suggested that if the persistent inhibitory action on DNA synthesis is directly related to the chemotherapeutic efficacy of this agent or a metabolic product thereof, a less frequent treatment regimen may be as effective as daily injections while evoking fewer toxic reactions.

Mode of action of alanosine

Abstract Alanosine inhibits the synthesis of RNA adenine from formate- 14 C and from glycine- 14 C in Ehrlich ascites tumor cells in vivo . There is no appreciable depression of the rate of RNA guanine synthesis. The incorporation of preformed adenine- 14 C into RNA purines is unaffected. Inhibition of RNA adenine synthesis is not antagonized by glutamine or aspartate. The incorporation of thymidine- 3 H, uridine- 3 H, and l -leucine- 14 C into the acid-insoluble fraction of the cells in vitro is unaffected by the drug. Evidence indicates that alanosine may interfere with the conversion of inosine monophosphate to adenosine monophosphate.

A proposed mode of action of antitumor platinum compounds based upon studies with cis-dichloro-([G-3H]dipyridine)platinum(II)

Abstract The neutral, square-planar platinum complex cis -dichloro(dipyridine)platinum (II) ( cis -PPC), which is a structural analog of cis -dichlorodiammineplatinum(II) ( cis -PtII) and possesses similar antitumor and antimitotic properties, was synthesized using [G- 3 H]pyridine and used to determine certain characteristics of its interactions with selected living and non-living systems. Cis -dichloro([G- 3 H]dipyridine)platinum(II) ( cis -PPC- 3 H) associates with intact Ehrlich ascites tumor cells in vitro at 2° and 37° and resists dissociation by washing with saline or trichloroacetic acid (TCA) as well as solubilization in alkali followed by reprecipitation with TCA. Dialysis experiments showed that cis -PPC- 3 H associates avidly with calf thymus DNA, high molecular weight yeast RNA, and bacterial and yeast transfer RNA, but not with bovine serum albumin, dextran, or purified erythrocyte membranes. Dialysis of the platinum-nucleic acid complexes in distilled water or NaCl results in loss of a portion of the original radioactivity. The platinum-DNA bond is also resistant to dissociation by solubilization in alkali followed by TCA precipitation. The homopolymers, polyadenylate and polycytidylate, bind cis -PPC- 3 H to the same extent as RNA on a weight basis; polyguanylate and polyuridylate bind the platinum complex to a greater extent than does RNA. Similar to nitrogen mustard (HN 2 ), bonding of cis -PPC- 3 H to DNA in vitro is inhibited by NaCl; however, prior alkylation of the DNA with HN 2 does not influence its subsequent bonding with cis -PPC- 3 H. It was proposed that the antitumor and antimitotic action of the square-planar platinum complex depends upon the dissociation of one or both chlorine atoms from the platinum atom. The resulting cationic, aquated species subsequently forms a bond with nucleic acid, and does so with a possibly greater affinity for guanylate and uridylate. The site of establishment of this bond(s) is probably dissimilar to that of the HN 2 -nucleic acid bond.

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.

Meso-2,3-Dimercaptosuccinic acid monoalkyl esters: effects on mercury levels in mice

Seven monoesters of meso-2,3-dimercaptosuccinic acid (DMSA) were evaluated for relative activities in mobilizing and promoting excretion of mercury in mercury-laden mice. Compounds assessed were the ethyl (M-EDMS), n-propyl (Mn-PDMS), isopropyl (Mi-PDMS), n-butyl (Mn-BDMS), isobutyl (Mi-BDMS), n-amyl (Mn-ADMS), and isoamyl (Mi-ADMS) esters. 2,3-Dimercaptopropane-1-sulfonate (DMPS) and DMSA were used as positive controls. After the first oral dose of each compound at 0.5 mmol/kg, DMSA and DMPS reduced the corporal mercury burden 16% and 24%, respectively, compared to controls, while the monoesters effected reductions of 35% (M-EDMS) to 49% (Mi-ADMS). After the second treatment at the same dose, the respective reductions produced by DMSA and DMPS were 24% and 38%, and those conferred by the monoesters ranged from 52% (M-EDMS) to 61% (Mn-BDMS). Determination of the comparative dose-response relationships of DMSA and Mi-ADMS on corporal and renal mercury concentrations revealed the monoester to be more active than DMSA on both parameters at each dose used. The cumulative amount of mercury excreted in urine by control mice over a 3-day period was 7.08 micrograms; this was increased 22%, 85%, and 94% by daily i.p. injections of DMSA, DMPS, and Mi-ADMS, respectively, at a daily dose of 0.1 mmol/kg. The respective cumulative 3-day totals recovered in feces from control mice and from mice treated with DMSA, DMPS, and Mi-ADMS were 9.76, 8.21, 10.44, and 11.73 micrograms. Parallel daily measurements of retained whole body radioactivity from 203Hg in mice were in good agreement with the values calculated from the excretion data.

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.

Cis-Dichlorodiammineplatinum [II]: Inhibition of Nucleic Acid Synthesis in Lymphocytes Stimulated with Phytohemagglutinin

Summary cis-Dichlorodiammineplatinum (II) (cis-[Pt(NH3)2Cl2]0) is a potent and probably irreversible inhibitor of deoxyribonucleic acid synthesis in cultures of human lymphocytes stimulated with phytohemagglutinin mitogen. At low concentration (3 × 10-6 M), selectivity for this process is quite evident; rates of synthesis of ribonucleic acid and protein are only slightly diminished. No resolvable cytologic lesion coincident with the action of the inhibitor was observed by electron microscopy. It was proposed that cis-[Pt(NH3)2Cl2]0 may undergo two sequential transformations, with the loss of one Cl- ion at each step, and that the resultant platinum species may act bifunctionally to cross-link adjacent nucleophilic centers through covalent binding.

Effects of alanosine on purine and pyrimidine synthesis.

Abstract Further studies were made of the mode of action of alanosine [L (−) 2-amino-3-nitroso hydroxylamino propionic acid] in a Candida albicans test system. The inhibition by the drug of the growth of the organism was antagonized by aspartate. The incorporation of aspartate- 14 C into RNA pyrimidines was inhibited, while the incorporation of uridine- 3 H was enhanced. Alanosine also depressed the rate of incorporation of formate- 14 C into RNA adenine, but increased the rate of its incorporation into RNA guanine. Formate- 14 C incorporation into acid-soluble adenine nucleotides was inhibited. It was tentatively concluded that the drug depresses the activity of aspartate transcarbamylase and adenylosuccinate synthetase.

Interactions of an antitumor platinum compound with deoxyribonucleic acid, histones, l-amino acids, poly-l-amino acids, nucleosides and nucleotides☆

Abstract Interaction of cis -dichloro(dipyridine)platinum(II) ( cis -PPC) with calf thymus DNA, calf thymus histone, l -amino acids, poly- l -amino acids, nucleosides, and nucleotides has been evaluated by equilibrium dialysis technics. At least a 28 % decrease in the association of cis -PPC with DNA occurs when the platinum compound is pre-incubated with l -amino acids. The greatest decrease in association is seen upon pre-incubation of the platinum compound with the free amino acids. Glut, Asp, Lys, Arg, and CySH, before the addition of a sack containing a solution of DNA. The low level of association between DNA and the amino acids tends to rule out competition between cis -PPC and amino acids for DNA association sites. cis -PPC was repelled from sacks containing positively charged poly- l -Lys, poly- l -Arg, and calf thymus histone; however, in the presence of poly- l -Glut and poly- l -Asp, cis -PPC associated with these negatively charged polymers to a considerable degree. Enhanced chloride dissociation from cis -PPC was observed in the presence of all of the amino acids and the nucleotides GMP, CMP, UMP, and TMP, but not in the presence of AMP or the nucleosides rG and dG. In the presence of calf thymus histone, the association of cis -PPC with calf thymus DNA was reduced by more than 50% at histone/DNA ratios of 0.8–1.0. These data suggest that cis -PPC or cis -Pt(II) may associate with electron-rich areas of not only nucleic acids and proteins but also with body pools of free nucleotides and amino acids. The presence of positively charged histones shielding DNA strands in vivo suggests that the most probable point of platinum-DNA association would be at de-repressed areas of DNA which are undergoing RNA synthesis. The aquated form of the platinum complex may also associate with acidic proteins which appear to be involved in the positive control of RNA synthesis and, as a result, this interaction may be of pharmacological significance.

N,N-Disubstituted dithiocarbamates as cadmium antagonists: N-(4-methoxybenzyl)-N-dithiocarboxy-d-glucamine

The newly synthesized dithiocarbamate analog, N-(4-methoxybenzyl)-N-dithiocarboxy-D-glucamine (MeOBDCG) reduced whole-body cadmium levels 66% in cadmium-laden mice when given as 3 injections at 1.0 mmol/kg. Renal and hepatic Cd concentrations were reduced 78 and 85%, respectively. After 6 injections, the whole-body cadmium burden was reduced 71%, while renal and hepatic levels were lowered 84% and 91%, respectively. Mobilized cadmium was excreted almost exclusively by the fecal route. There was no evident toxicity consequent to treatment as judged by mouse body weights and by gross appearance of organs upon dissection. On a molar dose basis, MeOBDCG was more effective than N-benzyl-N-dithiocarboxy-D-glucamine (BDCG) in removing cadmium from both renal and hepatic deposits. An in-vitro assessment of the interaction of MeOBDCG, BDCG and N-methyl-N-dithiocarboxy-D-glucamine with murine cadmium-metallothionein (Cd-MT) revealed a direct relationship between the extent of cadmium depletion from Cd-MT and the relative in-vivo efficacies of the 3 analogs.