Attenuation of endogenous oxidative stress-induced cell death by cytochrome P450 inhibitors in primary cultures of rat hepatocytes.

This study reports an examination of the effects of endogenous oxidative stress on primary cultures of rat hepatocytes. To produce endogenous oxidative stress, 3-amino-1,2,4-triazole (ATZ) and mercaptosuccinic acid (MS), which are known to inhibit catalase and glutathione peroxidase activities, respectively, were used. When ATZ or MS was used alone, the extent of cell injuries was negligible, but a combination of the two agents resulted in cell death as assessed by trypan blue exclusion after 24 h of incubation. Cell death was accompanied by an approximately 5.8-fold the increase in the levels of thiobarbituric acid reactive substances, and showed chromatin condensation and DNA fragmentation. These deleterious effects were time dependent in that no significant change was detected up to 6 h. Treatment with SKF or 1-aminobenzotriazole, which are inhibitors of cytochrome P450, greatly attenuated this cell death as well as prevented chromatin condensation and DNA fragmentation. N(G)-monomethyl-L-arginine at 1 mM had no inhibitory effects on these changes. These findings suggest that endogenous oxidative stress under these conditions induced cell death that resembles apoptosis and that endogenous oxidative stress was directly related to the cytochrome P450 enzyme system in this system.

Evaluation of genetic stability of recombinant human factor VIII by peptide mapping and on-line mass spectrometric analysis.

PURPOSE: The genetic stability of a recombinant human factor VIII (rhFVIII) product expressed in Chinese hamster ovary cells (Recombinate) has been evaluated through comparisons of the protein produced at the beginning, middle and end of a typical production campaign. METHODS: Recombinant human factor VIII was incubated with thrombin, the resulting four polypeptides were isolated by RP-HPLC, subjected to proteolysis with trypsin, and the peptide mixtures were resolved by RP-HPLC. Tryptic peptide mixtures were subjected to online mass spectrometric analysis using an electrospray ionization source interfaced to a quadrupole mass analyzer scanning from 1950-200 amu, and the peptide ion data were compared for three lots produced from the beginning, middle and end of a production campaign. RESULTS: The UV elution profiles for each of the rhFVIIIa polypeptides were highly similar for factor VIII isolated from the beginning, middle and end of production. Total ion data from the peptide maps derived from three lots of rhFVIII were compared by MH1+ values as a function of scan range. A total of 918 ions were analyzed for the four polypeptides of rhFVIII produced at the beginning, middle and end of a production campaign. The ions were detected at the same relative retention times, as indicated by the similar scan numbers for the three lots. CONCLUSIONS: These observations support that rhFVIII preparations produced from the beginning, middle and end of a production campaign were highly similar, and demonstrate genetic stability in the manufacturing process of Recombinate.

(o- and p-Nitrobenzyloxycarbonyl)-5-fluorouracil derivatives as potential conjugated bioreductive alkylating agents.

A series of (o- and p-nitrobenzyloxycarbonyl)-5-fluorouracil derivatives were synthesized by reacting o- or p-nitrobenzyl chloroformate with 5-fluorouracil in the presence of triethylamine in DMF or Me2SO. The reductive activation of these agents was hypothesized to generate a reactive methide and 5-fluorouracil, two components that are capable of synergistic interaction through complementary inhibition. Measurement of the surviving fractions of EMT6 tumor cells treated with these agents in culture under conditions of hypoxia and aerobiosis resulted in equal cell kill regardless of the state of oxygenation. One of the synthesized agents, 3-(p-nitrobenzyloxycarbonyl)-5-fluorouracil (4), appeared to be superior to 5-fluorouracil in prolonging the survival time of mice bearing intraperitoneal implants of the P388 leukemia and Sarcoma 180.

Mechanism of action of arenesulfonylhydrazones of 2-pyridinecarboxaldehyde 1-oxide in L1210 cells.

The arenesulfonylhydrazones of 2-pyridinecarboxaldehyde 1-oxide represent a relatively new class of anticancer agents. The biochemical alterations responsible for antineoplastic activity were investigated using the most potent member of this class synthesized to date, the 3,4-dimethoxybenzenesulfonylhydrazone of 2-pyridinecarboxaldehyde 1-oxide (3,4-DSP), as the prototype compound. The primary biochemical lesion observed was the production of DNA single-strand breaks, which were analyzed using alkaline elution methodology. This production of DNA damage required the spontaneous chemical formation of a reactive species; thus, "aging" of a solution of 3,4-DSP prior to exposure of L1210 leukemia cells in culture markedly decreased the production of DNA single-strand breaks. The chemical production of an alkylating species from 3,4-DSP has been proposed to occur by the intramolecular abstraction of the nitrogen proton by the 1-oxide group, followed by release of arenesulfinic acid to form the potent alkylating species, 1-oxidopyridin-2-yldiazomethane. Replacement of the proton by a methyl group, lack of the 1-oxide group, or replacement of the aldehyde proton by a methyl group increases the chemical stability of the arenesulfonylhydrazones. These modifications have been shown in a previous publication (D .A. Shiba, J. A. May, Jr., and A. C. Sartorelli, Cancer Res., 43: 2023-2029, 1983) to lead to (a) an elimination of alkylating activity and (b) a decrease in in vitro cytotoxicity and in vivo anticancer activity. These effects are also accompanied by an inability to produce detectable DNA single-strand breaks. 3,4-DSP caused little or no inhibition of the biosyntheses of DNA, RNA, or protein, as measured by the incorporation of radiolabeled thymidine, uridine, or leucine, respectively, into acid-insoluble material; however, consistent with the production of DNA damage, 3,4-DSP inhibited the normal progression of L1210 cells through the cell cycle after a single treatment in vivo with drug (100 mg/kg). Cells were blocked in the G2-M phase of the cell cycle for 6 to 24 hr after exposure to 3,4-DSP; the cell population recovered by 48 hr after exposure and appeared to be progressing normally through the cell cycle.

Relationship of spontaneous chemical transformation of arylsulfonylhydrazones of 2-pyridinecarboxaldehyde 1-oxide to anticancer activity.

The arylsulfonyl-hydrazones of 2-pyridinecarboxaldehyde 1-oxide represent a relatively new class of antineoplastic agents with the potential for clinical usefulness. The requirement for spontaneous chemical transformation of these agents to exert anticancer activity was evaluated using as the prototype the most potent member of this class synthesized to date, the 3,4-dimethoxybenzene sulfonylhydrazone of 2-pyridinecarboxaldehyde 1-oxide (3,4-DSP. 3,4-DSP was chemically unstable, decomposing with a half-life of 19 min in 0.01 M potassium phosphate buffer (pH 7.4) at 37 degrees. The major chemical decomposition product was identified as 2-pyridylcarbinol 1-oxide by comparison with the authentic compound. This carbinol is hypothesized to be formed via the intramolecular abstraction of hydrogen from the arylsulfonyl-hydrazone, a process that leads to the release of 3,4-dimethoxybenzenesulfinic acid and the formation of 1-oxidopyridin-2-yldiazomethane, which subsequently reacts with water. The diazomethane intermediate is a potent alkylating agent which, if generated in cells, would have the potential to alkylate nucleophilic groups of biologically important macromolecules. The proposed reactive species was trapped using both 4-(4-nitrobenzyl)pyridine (NBP) and morpholine, and the latter product was characterized by mass spectroscopy. The importance of the chemical formation of an alkylating species to cytotoxicity was demonstrated by studies in which solutions of 3,4-DSP were "aged" prior to addition to L1210 leukemia cells in culture and prior to incubation with NBP. The "aging" of 3,4-DSP for 20 min resulted in a 4-fold decrease in cytotoxicity, and aging for 1 to 3 hr led to complete loss of cytotoxicity. Correspondingly, a 20-min aging period decreased alkylation of NBP by 51%, and 3-hr aging resulted in essentially no alkylation of the nucleophile. Further support for the above proposed chemical activation pathway was provided by correlations between in vitro cytotoxicity, in vivo antineoplastic activity, chemical stability, and the degree of alkylation of NBP by a wide variety of arylsulfonyl-hydrazones. The lack of the 1-oxide, envisioned to be required for intramolecular hydrogen abstraction, the steric prevention of the abstraction, or the replacement of the proton of the nitrogrn of the side-chain by a methyl group resulted in a marked increase in chemical stability and a corresponding loss of the ability to alkylate NBP and to inhibit the replication of L1210 leukemia cells in culture.

The in vivo cytotoxic activity of procarbazine and procarbazine metabolites against L1210 ascites leukemia cells in CDF1 mice and the effects of pretreatment with procarbazine, phenobarbital, diphenylhydantoin, and methylprednisolone upon in vivo procarbazine activity.

An in vivo assay of the activity of procarbazine, N-isopropyl-alpha-(2-methylhydrazino)-p-toluamide hydrochloride, and several metabolic intermediates against IP-implanted L1210 leukemia cells in CDF1 male mice is described. Treatment of tumor-bearing mice with procarbazine at doses of 300-500 mg/kg IP increased the mean lifespan of treated mice by 29%-32% relative to that of untreated animals. Procarbazine treatment with doses of 200-400 mg/kg/day given IP for 3 consecutive days increased mean lifespan by 39%-46%. The major circulating metabolite, azoprocarbazine (N-isopropyl-alpha-(2-methylazo)-p-toluamide), was as active as procarbazine when administered at equivalent doses for 3 consecutive days. A 2:1 mixture of azoxyprocarbazines (N-isopropyl-alpha-(2-methyl-ONN-azoxy)-: and N-isopropyl-alpha-(2-methyl-NNO-azoxy)-p-toluamide) was more active than procarbazine, increasing mean lifespan by 76% using the 3-consecutive-day dose schedule. The effects of pretreatment with procarbazine and drugs that are often co-administered with procarbazine, i.e., phenobarbital, diphenylhydantoin, and methylprednisolone, upon procarbazine anticancer activity against L1210 ascites leukemia cells was also determined. Pretreatment of CDF1 male mice with phenobarbital and diphenylhydantoin for 7 days was found to increase the antineoplastic activity of procarbazine by 13%-24%. Pretreatment with methylprednisolone did not significantly alter procarbazine activity. The effects of pretreatment with procarbazine, which is often administered daily for a period of 2-4 weeks, on procarbazine antineoplastic activity were varied. The results of these preliminary pretreatment studies combined with the finding that procarbazine metabolites have antitumor activity that is equal to or greater than that of the parent drug suggest that current clinical protocols that use procarbazine along with agents capable of altering procarbazine metabolism may involve drug interactions that alter the efficacy of procarbazine as an anticancer agent.

Quantitative analysis of procarbazine, procarbazine metabolites and chemical degradation products with application to pharmacokinetic studies.

Quantitative analytical methods are described for the analysis of the anticancer drug procarbazine and eight known metabolites including those known to have cytotoxic activity. A direct sample insertion mass spectrometric assay for procarbazine and the urinary excretion product, N-isopropyl-terephthalamic acid, has been developed. This method employs stable isotope labeled variants in a procedure that minimizes analytical errors that may be encountered in the quantitation of the chemically unstable parent drug. a liquid chromatographic method is described for the analysis of seven known procarbazine metabolites. Use of these methods is demonstrated by the analysis of procarbazine metabolism during incubation in a 9000-g rat liver homogenate preparation. Procarbazine disappearance and metabolite appearance are also monitored in rat plasma following intraperitoneal administration of a 150 mg/kg bolus dose. Applications to patient pharmacokinetics is demonstrated using the liquid chromatographic assay to follow the appearance of active procarbazine metabolites on the first and fourteenth day of an oral 250 mg/kg/day course of therapy of a patient being treated for cancer.