Molecular pharmacology of hepsulfam, NSC 3296801: identification of alkylated nucleosides, alkylation site, and site of DNA cross-linking.

We have determined that hepsulfam, in common with its structural homologue busulfan, alkylates both free guanosine and GMP in DNA at the 7 nitrogen. Mass spectral analysis of the products of the reaction of hepsulfam with guanosine has identified the mono- and bis-alkylated guanosine adducts. UV spectrophotometry and mass spectrometry were used to confirm that alkylation occurred at the 7 nitrogen by following the formation of the formamidopyrimidyl form of the hepsulfam-guanosine adduct at high pH. We have also isolated and identified 1-guanyl,7-hydroxyheptane, 1-guanyl,7-sulfamylheptane, and 1,7-bis(guanyl)heptane from in vitro reaction mixtures of hepsulfam and calf thymus DNA. We have isolated bis-(7-formamidopyrimidyldeoxyguanosinyl)-heptane from an enzymatic digest of DNA treated with hepsulfam. Finally, we have found that hepsulfam forms interstrand cross-links at 5'-GXC-3' sites in model oligonucleotides.

Hepsulfam sensitivity in human breast cancer cell lines: the role of glutathione and glutathione S-transferase in resistance.

Hepsulfam (NSC 329680, 1,7-heptanediol disulfamate) is an alkylating agent that showed excellent activity against mouse and human mammary carcinoma in preclinical studies. We therefore studied the cytotoxicity of this drug in six human breast cancer cell lines (AdrRMCF7, WTMCF7, Hs578T, MDA-MB-231, T47D, and MDA-MB-468). Clonogenic assays of these cell lines showed a range of sensitivity with the 90% inhibitory concentration ranging from 3.1 microM hepsulfam (MDA-MB-468) to 32.3 microM hepsulfam (AdrRMCF7) after 24-h exposure to the drug. To evaluate possible mechanisms responsible for this observed variation in sensitivity to hepsulfam, we have studied glutathione S-transferase (GST) activity and glutathione (GSH) in these cell lines. Total cytoplasmic GST activity correlated with sensitivity; the most sensitive cell lines had the lowest GST activity, while the two most resistant cell lines, AdrRMCF7 and Hs578T, had the highest GST levels of the six cell lines. Western blot analysis showed that the only detectable isoenzyme was GST-pi. The amount of GST-pi isoform correlated with hepsulfam sensitivity in the three most resistant cell lines and was undetectable in the three most sensitive cell lines. Cellular concentrations of GSH did not correlate with hepsulfam sensitivity. However, GSH depletion with buthionine sulfoximine increased sensitivity to hepsulfam in a dose-dependent fashion in all six cell lines. Evaluation by mass spectrometry revealed that glutathione can form conjugates with hepsulfam. We conclude that the GST/GSH detoxication system plays a role in the sensitivity of these breast cancer cell lines to hepsulfam.

Kinetic analysis of the reaction of melphalan with water, phosphate, and glutathione.

The reaction kinetics of the hydrolysis, phosphatolysis, glutathionyl conjugation, and alpha-glutathione-S-transferase (GST)-catalyzed glutathione conjugation of [3H-ring]melphalan were investigated at pH 6.5 and 7.4. The distribution of products relative to the initial parent compound radioactivity over time was measured by HPLC and analyzed by nonlinear regression techniques using a system of rate and distribution equations that describe the complete precursor-product pathways applicable to each reaction condition. The kinetic parameters calculated in the analysis were the first- and second-order rate constants of formation and the product ratios of the aziridinium intermediates. The second-order rate constants were normalized to those obtained for the hydroxylation reactions to yield relative rate constants. The first-order rate constants of aziridinium ion formation from melphalan and from all the monosubstituted melphalan species, except chloro, hydroxyl melphalan, were similar under all reaction conditions. The relative second-order rate constant for nonenzymatic glutathionylation of the aziridinium intermediate was 7 times larger at pH 7.4 than at pH 6.5. GST was found to react only with the aziridinium intermediate formed from melphalan and to dissociate slowly from the resultant GST-product complex (dissociation half-life, 1 hr at pH 7.4 and 3.5 hr at pH 6.5). The kinetic parameter estimates found in this study can be used to make preliminary calculations of the impact that cellular phosphate, glutathione, and GST concentrations will have on the intracellular detoxication of melphalan.

Antiinflammatory C-glucosyl chromone from Aloe barbadensis.

A new antiinflammatory agent identified as 8-[C-beta-D-[2-O-(E)-cinnamoyl]glucopyranosyl]-2- [(R)-2-hydroxypropyl]-7-methoxy-5-methylchromone (1) has been isolated from Aloe barbadensis Miller. At a dose of 200 microg/mouse ear, 1 exhibited topical antiinflammatory activity equivalent to 200 microg/ear of hydrocortisone. There was no reduction in thymus weight caused by treatment with 1 for any of the doses tested, while 200 microg/ear of hydrocortisone resulted in a 50% decrease in thymus weight.

In vitro metabolic transformations of 2,4-dipyrrolidinylpyrimidine: a chemical probe for P450-mediated oxidation of tirilazad mesylate.

1. We have determined that 2,4-dipyrrolidinylpyrimidine (2,4-DPP), used as a model for studies of the metabolism of therapeutic agents containing this moiety, undergoes three characteristic hydroxylations when incubated with male rat liver microsomes. Analysis of microsomal incubates of stable isotope labelled analogues of 2,4-DPP by particle beam-liquid chromatography-mass spectrometry (LC-PB-MS) has shown that the three metabolites are 4-(3-hydroxypyrrolidinyl)-2-(pyrrolidinyl)-pyrimidine (M1), 4-(2-hydroxypyrrolidinyl)-2-(pyrrolidinyl)-pyrimidine (M2) and 2-(2-hydroxypyrrolidinyl)-4-(pyrrolidinyl)-pyrimidine (M3). 2. We determined that enzymes of the cytochrome P450 family are responsible for the in vitro hydroxylations of 2,4-DPP. 3. We observed that in microsomal incubations carried out in the presence of cyanide, a single cyanide adduct is formed implicating an iminium ion intermediate in the oxidation of the 2-pyrrolidine ring. 4. We also determined the intermolecular deuterium isotope effects for the formation of each of the three products. For M1, kH/kD = 14.55 +/- 0.54; for M2, kH/kD = 6.01 +/- 0.65; and for M3, kH/kD = 5.35 +/- 1.18. 5. We interpret these data as suggesting that M2 and M3 are formed by the same mechanism, probably including the formation of an iminium ion, and that M1 is formed by direct hydrogen abstraction.