Biochemical pharmacology
-
Biochemical pharmacology · Apr 2000
Triapine (3-aminopyridine-2-carboxaldehyde- thiosemicarbazone): A potent inhibitor of ribonucleotide reductase activity with broad spectrum antitumor activity.
Previous studies from our laboratories have shown that (a) Triapine() is a potent inhibitor of ribonucleotide reductase activity and (b) hydroxyurea-resistant L1210 leukemia cells are fully sensitive to Triapine. In an analogous manner, Triapine was similarly active against the wild-type and a hydroxyurea-resistant subline of the human KB nasopharyngeal carcinoma. Triapine was active in vivo against the L1210 leukemia over a broad range of dosages and was curative for some mice. ⋯ In addition, the duration of the inhibition of DNA synthesis in leukemia cells from mice treated with Triapine was considerably longer than in those from animals treated with hydroxyurea. Combination of Triapine with various classes of agents that damage DNA (e.g. etoposide, cisplatin, doxorubicin, and 1-acetyl-1,2-bis(methylsulfonyl)-2-(2-chloroethyl)hydrazine) resulted in synergistic inhibition of the L1210 leukemia, producing long-term survivors of tumor-bearing mice treated with several dosage levels of the combinations, whereas no enhancement of survival was found when Triapine was combined with gemcitabine or cytosine arabinoside. The findings demonstrate the superiority of Triapine over hydroxyurea as an anticancer agent and further suggest that prevention by Triapine of repair of DNA lesions created by agents that damage DNA may result in efficacious drug combinations for the treatment of cancer.
-
Biochemical pharmacology · Aug 1999
Effect of nitric oxide donors and nitric oxide synthase inhibitors in neonatal rat endotoxic shock.
Previous studies have shown an increased mortality in response to endotoxin in 24-hr-old neonatal rats compared with older neonates and adults. This increased susceptibility may be related to increased nitric oxide (NO) and thromboxane (TxB2) production. Twenty-four-hour-old neonatal rat pups were given either N(G)-nitro-L-arginine methyl ester (L-NAME; a nonspecific NO synthase inhibitor), S-methylthioisourea (SMT; a specific NO synthase inhibitor), or molsidomine (a NO donor) subcutaneously prior to or after an LD50 of intracardiac endotoxin. ⋯ There was no difference in TxB2 production with either the NO synthase inhibitor or the NO donor. In conclusion, at the several doses employed, neither nonselective or selective NO synthase inhibitors nor NO donors prevented endotoxin-induced mortality in rat neonatal shock. Although these findings do not preclude possible involvement of NO in neonatal pathophysiology, increased NO production thus does not appear to be the primary determinant of the increased susceptibility of the neonatal rat to endotoxic shock.
-
Biochemical pharmacology · Jul 1999
Drug uptake and cellular targets of hydroxymethylacylfulvene (HMAF).
Hydroxymethylacylfulvene (HMAF, MGI 114) is a novel antitumor drug and a potent pro-apoptotic agent that has the potential to alkylate cellular nucleophiles. The objective of these studies was to characterize drug uptake and cellular targets for drug binding in human leukemia CEM cells. The uptake of [14C]HMAF had two components: a rapid phase (0-10 min) and a slow phase. ⋯ Combinations of DNase, RNase, and proteinase K with perchloric acid precipitation showed that approximately 60, 30, and 10% of the covalently bound drug was associated with the protein, DNA, and RNA fractions, respectively. Incubation of 100 microM [14C]HMAF (24 hr) with purified DNA, serum albumin, thioredoxin, and thioredoxin reductase resulted in 6, 22, 14, and 11 pmol [14C]HMAF/microg DNA or protein, respectively. Results indicate that multiple targets for HMAF binding may contribute to the pro-apoptotic and antiproliferative action of the drug.
-
The specificity of tumor therapy may be improved by preferentially activating antineoplastic prodrugs at tumor cells pretargeted with antibody-enzyme conjugates. In this study, the conditions required for the efficient activation of p-hydroxyaniline mustard glucuronide (BHAMG) to p-hydroxyaniline mustard (pHAM) were investigated. pHAM induced cross-links in linearized double-stranded DNA at about 180-fold lower concentrations than BHAMG, indicating that the nucleophilicity of pHAM was decreased by the presence of a glucuronide group. The partition coefficient of BHAMG was about 1890 times lower than pHAM in an octanol-water two-phase system, suggesting that the reduced toxicity of BHAMG was due to both hindered diffusion across the lipid bilayer of cells and decreased reaction with nuclear DNA. ⋯ The extended retention of mAb RH1 on the surface of AS-30D cells was also consistent with extracellular activation of BHAMG. Taken together, our results indicate that the low toxicity of BHAMG was due to hindered cellular uptake and low alkylating activity. BHAMG must be enzymatically activated outside of tumor cells for maximum cytotoxicity, and non-internalizing antibodies are preferred for human tumor therapy by targeted antibody-enzyme activation of BHAMG.
-
Biochemical pharmacology · May 1999
ReviewRegulation of ryanodine receptors by reactive nitrogen species.
The ryanodine receptors (RyRs) are large intracellular calcium release channels that play an important role in the control of the calcium levels in excitable and non-excitable cells. Many endogenous modulators such as Mg2+, ATP, or calmodulin can affect the channel activities of the three known mammalian RyR isoforms. RyRs also are known to be redox-responsive. ⋯ Both an oxidative and a nitrosative modification of RyRs have been described, leading to either a reversible or irreversible alteration of RyR ion channel activity. Additional mechanisms of regulation may include cyclic GMP-dependent signaling pathways and NO modification of RyR regulatory proteins such as the surface membrane L-type Ca2+ channel. Modification of RyRs by NO may influence a variety of physiological functions such as insulin release, vasomotor control, and muscle contraction.