Plasma pharmacokinetics and tissue distribution in CD2F1 mice of Pc4 (NSC 676418), a silicone phthalocyanine photodynamic sensitizing agent

PURPOSE

Pc4 is a silicone phthalocyanine photosensitizing agent that is entering clinical trials. Studies were undertaken in mice to develop a suitable formulation and analytical methodology for use in pharmacokinetic studies and to define the plasma pharmacokinetics, tissue distribution, and urinary excretion of Pc4 after i.v. delivery.

METHODS

An HPLC method suitable for separation and quantification of Pc4 was developed and validated for use in mouse plasma, tissues, and urine. The stability of Pc4 was characterized in a variety of formulations as well as in mouse plasma. Before pursuing pharmacokinetic studies, preliminary toxicity studies were undertaken. These studies utilized Pc4 formulated in diluent 12:0. 154 M NaCl (1:3, v:v). Pharmacokinetic studies involved Pc4 doses of 40 mg/kg, 10 mg/kg and 2 mg/kg administered as i.v. boluses to female, CD2F1 mice. Doses of 40 mg/kg, 10 mg/kg, and 2 mg/kg were studied with drug formulated in diluent 12:0.154 M NaCl (1:3, v:v). Doses of 10 mg/kg and 2 mg/kg were also studied with drug formulated in a vehicle consisting of polyethylene glycol:Tween 80:0. 01 M sodium phosphate buffer, pH 7.0 (40:0.2:59.8, v:v:v). Compartmental and non-compartmental analyses were applied to the plasma concentration-versus-time data. Concentrations of Pc4 were also determined in a variety of tissues, including brain, lung, liver, kidney, skeletal muscle, skin, heart, spleen, and abdominal fat. Urine was collected from animals treated with each of the doses of Pc4 mentioned above, and daily, as well as cumulative drug excretion was calculated until 168 h after treatment.

RESULTS

At a dose of 80 mg/kg, two of five male and two of five female mice were dead by 24 h after injection. Pathologic examination revealed gross findings of blue discoloration affecting many tissues, with lungs that were grossly hemorrhagic and very blue-black. Microscopic examination of the lungs revealed mild acute interstitial pneumonia, with perivascular edema and inflammation, and a detectable margination of neutrophils around larger pulmonary blood vessels. Animals sacrificed 14 days after treatment showed mild granulomatous pneumonia, characterized by clusters of multi-nucleated giant cells, with fewer macrophages and neutrophils. The giant cells frequently contained phagocytized particles, which were clear and relatively fusiform. All mice treated with 40 mg/kg or 20 mg/kg survived and returned to pretreatment weight during the 14 days after treatment. Intravenous bolus delivery of Pc4, at a dose of 40 mg/kg, produced "peak" plasma Pc4 concentrations between 7.81 and 8.92 microg/ml in mice killed at 5 min after injection (the earliest time studied after drug delivery). Sequential reduction of the Pc4 dose to 10 mg/kg in diluent 12:0.154 M NaCl (1:3, v:v), 10 mg/kg in polyethylene glycol:Tween 80:sodium phosphate buffer (40:0.2:59.8, v:v:v), 2 mg/kg in diluent 12:0.154 M NaCl (1:3, v:v), and, finally, 2 mg/kg in polyethylene glycol:Tween 80:sodium phosphate buffer (40:0.2:59.8, v:v:v) resulted in "peak" plasma Pc4 concentrations between 2.07 and 3.24, 0.68 and 0.98 microg/ml, and 0.29 and 0.41 microg/ml, respectively. Pc4 persisted in plasma for prolonged periods of time (72-168 h). Non-compartmental analysis of plasma Pc4 concentration-versus-time data showed an increase in area under the plasma Pc4 concentration-versus-time curve (AUC) when the dose of Pc4 increased from 2 mg/kg to 40 mg/kg. Across the 20-fold range of doses studied, total body clearance (CL(tb)) varied from 376 to 1106 ml h(-1) kg(-1). Compartmental modeling of plasma Pc4 concentration versus time data showed the data to be fit best by a two-compartment, open, linear model. Minimal amounts of Pc4 were detected in the urine of mice. After i.v. bolus delivery to mice, Pc4 distributed rapidly to all tissues and persisted in most tissues for the duration of each pharmacokinetic study. Tissue exposure, as measured by AUC, increased in a dose-dependent fash

Tumor-targeted apoptosis by a novel spermine analogue, 1,12-diaziridinyl-4,9-diazadodecane, results in therapeutic efficacy and enhanced radiosensitivity of human prostate cancer

Interference with polyamine transport and biosynthesis has emerged as an important anticancer strategy involving polyamine analogues and specific inhibitors of key biosynthetic enzymes. Because the prostate gland has a high polyamine content, by using the polyamine transporter for selective uptake into cancer cells, alkylating polyamines are likely to be highly effective against prostatic tumors. We have recently synthesized a novel class of spermine analogues, the lead compound of which has efficacy against human cancer cells (P. S. Callery et al., U. S. patent, 5,612,239, Issued March 17, 1997.). In this study, to investigate the potential therapeutic efficacy of the lead spermine analogue 1,12-diaziridinyl-4, 9-diazadodecane (BIS), against advanced prostate cancer, we examined the in vitro effect and in vivo efficacy of the compound in two androgen-independent human prostate cancer cell lines, PC-3 and DU-145. BIS exhibited a dose-dependent cytotoxic effect against prostate cancer cells via induction of apoptosis. Treatment of cells with BIS (1 microM) for 24 h resulted in a significant induction of apoptosis (24%). Exposure of BIS-treated PC-3 prostate cancer cells to gamma-irradiation resulted in a significant increase in the number of cells undergoing apoptosis and a subsequent decrease in the IC50. Furthermore, BIS treatment led to a significant enhancement of loss of clonogenic survival in irradiated prostate cancer cells (both PC-3 and DU-145). In vivo efficacy trials demonstrated a significant antitumor effect of BIS against both PC-3 and DU-145 tumor xenografts in severe combined immunodeficient mice in a dose-dependent pattern at maximally tolerated doses. Terminal transferase end-labeling analysis indicated that BIS-mediated tumor regression in vivo occurs via induction of apoptosis among prostatic tumor cells. These results suggest that the novel spermine analogue BIS: (a) has a potent antitumor effect against prostatic tumors via induction of apoptosis; and (b) increases the radiosensitivity of human prostate cancer cells by decreasing the apoptotic threshold to radiation. This study may have important clinical implications for the manipulation of this antitumor activity of the polyamine analogue for the optimization of the therapeutic efficacy of radiation in patients with advanced prostate cancer.

Chromatographic methods of analysis of antibiotics in milk

The widespread use of antibiotics in dairy cattle management may result in the presence of antibiotic residues in milk. While rapid screening tests are commonly used to detect the presence of antibiotics in milk, more accurate chromatographic methods are required by government regulatory agencies to identify and confirm the identity and quantity of antibiotic present. This paper review recent developments in the chromatographic determination of antibiotic residues in milk.

Metabolism of 17-(allylamino)-17-demethoxygeldanamycin (NSC 330507) by murine and human hepatic preparations

17-(Allylamino)-17-demethoxygeldanamycin (17AAG), a compound that is proposed for clinical development, shares the ability of geldanamycin to bind to heat shock protein 90 and GRP94, thereby depleting cells of p185erbB2, mutant p53, and Raf-1. Urine and plasma from mice treated i.v. with 17AAG contained six materials with absorption spectra similar to that of 17AAG. Therefore, in vitro metabolism of 17AAG by mouse and human hepatic preparations was studied to characterize: (a) the enzymes responsible for 17AAG metabolism; and (b) the structures of the metabolites produced. These materials had retention times on high-performance liquid chromatography of approximately 2, 4, 5, 6, 7, and 9 min. When incubated in an aerobic environment with 17AAG, murine hepatic supernatant (9000 x g) produced each of these compounds; the 4-min metabolite was the major product. This metabolism required an electron donor, and NADPH was favored over NADH. Metabolic activity resided predominantly in the microsomal fraction. Metabolism was decreased by approximately 80% in anaerobic conditions and was essentially ablated by CO. Microsomes prepared from human livers produced essentially the same metabolites as produced by murine hepatic microsomes, but the 2-min metabolite was the major product, and the 4-min metabolite was next largest. There was no metabolism of 17AAG by human liver cytosol. Metabolism of 17AAG by human liver microsomes also required an electron donor, with NADPH being preferred over NADH, was inhibited by approximately 80% under anaerobic conditions, and was essentially ablated by CO. Liquid chromatography/mass spectrometry analysis of human and mouse in vitro reaction mixtures indicated the presence of materials with molecular weights of 545, 601, and 619, compatible with 17-(amino)-17-demethoxygeldanamycin (17AG), an epoxide, and a diol, respectively. The metabolite with retention time of 4 min was identified as 17AG by cochromatography and mass spectral concordance with authentic standard. Human microsomal metabolism of 17AAG was inhibited by ketoconazole, implying 3A4 as the responsible cytochrome P450 isoform. Incubation of 17AAG with cloned CYP3A4 produced metabolites 4 and 6. Incubation of 17AAG with cloned CYP3A4 and cloned microsomal epoxide hydrolase produced metabolites 2 and 4, with greatly decreased amounts of metabolite 6. Incubation of 17AAG with human hepatic microsomes and cyclohexene oxide, a known inhibitor of microsomal epoxide hydrolase, did not affect the production of metabolite 4 but decreased the production of metabolite 2 while increasing the production of metabolite 6. These data imply that metabolite 2 is a diol and metabolite 6 is an epoxide. Mass spectral fragmentation patterns and the fact that 17AG is not metabolized argue for the epoxide and diol being formed on the 17-allylamino portion of 17AAG and not on its ansamycin ring. These data have implications with regard to preclinical toxicology and activity testing of 17AAG as well as its proposed clinical development because: (a) production of 17AG requires concomitant production of acrolein from the cleaved allyl moiety; and (b) 17AG, which was not metabolized by microsomes, has been described as being as active as 17AAG in decreasing cellular p185erbB2.

Aminoalkylaziridines as substrates and inhibitors of lysyl oxidase: specific inactivation of the enzyme by N-(5-aminopentyl)aziridine

The reaction of lysyl oxidase was assessed with members of a series of aminoalkylaziridines in which the primary amino group and the aziridinyl nitrogen were separated by 3-7 methylene carbons. Among these, N-(5-aminopentyl)aziridine proved to be the poorest substrate by far and to inhibit the enzyme activity. Aminoalkylaziridines with chain lengths shorter or longer than five carbons did not inhibit the enzyme. The resulting inhibition was competitive with productive substrates and became irreversible with time, following pseudo first order kinetics with a KI of 0.22 mM. N-(5-aminopentyl)aziridine appears to act as a bifunctional affinity label covalently interacting with the active site of this enzyme.

In vitro metabolism by mouse and human liver preparations of halomon, an antitumor halogenated monoterpene

OBJECTIVES

To characterize the enzymes responsible for and metabolites produced from the metabolism of halomon, a halogenated monoterpene that is isolated from the red algae Portieria hornemanii and has in vitro activity in the NCI screen against brain, renal, and colon cancer cell lines.

MATERIALS AND METHODS

Mouse and human liver fractions, prepared by homogenization and differential centrifugation, were incubated with halomon, extracted with toluene, and analyzed by gas chromatography.

RESULTS

In the presence of NADPH, mouse-liver 9,000-g supernatant (S9) fractions metabolized halomon, but boiled S9 fractions did not. NADH could not substitute for NADPH. Further separation of murine hepatic S9 fractions produced a microsomal fraction that contained all of the halomon-metabolizing activity; cytosol had none. Carbon monoxide reduced murine hepatic microsomal metabolism of halomon, whereas an anaerobic, N2 environment greatly accelerated the disappearance of halomon. Human hepatic microsomes metabolized halomon and required NADPH to do so. Carbon monoxide completely inhibited human hepatic microsomal metabolism of halomon. Unlike murine hepatic microsomal metabolism of halomon, anaerobic conditions did not enhance the metabolism of halomon by human hepatic microsomes. Neither 100 microM diethyldithiocarbamate, 1 microM quinidine, 100 microM ciprofloxacin, 3 microM ketoconazole, nor 100 microM sulfinpyrazone inhibited the metabolism of halomon by human hepatic microsomes. Both murine and human hepatic microsomes produced a metabolite of halomon. The mass spectrum of this metabolite indicated the loss of one chlorine atom and one bromine atom.

CONCLUSIONS

Halomon is metabolized by mouse and human hepatic cytochrome P-450 enzymes, the identities of which remain unknown. Hepatic metabolism of halomon is very consistent with the concentrations of halomon measured in mouse tissues and urine after i.v. administration of the drug.

Comparative molecular field analysis-based predictive model of structure-function relationships of polyamine transport inhibitors in L1210 cells

Maintenance of intracellular polyamine concentrations necessary for cell growth and proliferation is regulated in part by an energy-dependent polyamine uptake system. To obtain information on the characteristics of the polyamine uptake system in L1210 leukemia cells, we have applied computational chemistry techniques to the study of relationships between structure and function of 57 polyamine analogues. Ki values of polyamine analogues, derived from competitive inhibition of [3H]spermidine transport into L1210 cells, were chosen as the measure of biological activity. Using comparative molecular field analysis (CoMFA), a model was constructed to relate molecular structure with biological activity. The model was based on 4 monocationic, 8 dicationic, 14 tricationic, and 20 tetracationic polyamine analogues with a range of Ki values for the inhibition of [3H]spermidine uptake of 0.97-521 microM. The CoMFA model successfully predicted the inhibitory potency of 11 polyamines that had not previously been tested for polyamine uptake inhibitory activity. The 11 values predicted were within 33 +/- 62% of the actual Ki values. The test group included aziridinyl diamines, acetylated spermidines, two new oxazolidinonyl spermidines, monoaziridinyl spermidines, and a diaziridinyl spermine. Several of the compounds from this test group have been shown to have anticancer activity in mice. Consistent with the CoMFA model, certain basic functional groups, such as aziridines that have pKa values in the range of 6-7, seem to interact with the polyamine transporter in a cationic form. The results suggest that the CoMFA model is useful in drug design strategies as a predictive tool for the discovery of new anticancer agents that utilize a polyamine transporter for cellular uptake.

Plasma pharmacokinetics, bioavailability, and tissue distribution in CD2F1 mice of halomon, an antitumor halogenated monoterpene isolated from the red algae Portieria hornemannii

The purpose of the present study was to define the plasma pharmacokinetics, bioavailability, and tissue distribution in mice of halomon, a halogenated monoterpene from Portieria hornemanii that is active in vitro against brain-, renal-, and colon-cancer cell lines. Halomon formulated in cremophor:ethanol:0.154 M NaCl (1:1:6, by vol.) was injected i.v. at 20, 60, 90, or 135 mg/kg into female CD2F1 mice. Doses of 135 mg/kg were also given i.p., s.c., and by enteral gavage to female CD2F1 mice and i.v. to male CD2F1 mice. Plasma halomon concentrations were measured with a gas-chromatography system using electron-capture detection. Halomon concentrations were also determined in the brains, hearts, lungs, livers, kidneys, spleens, skeletal muscles, fat, red blood cells, and, if present, testes of mice given 135 mg/kg i.v. Halomon plasma pharmacokinetics were well fit by a two-compartment, open linear model and were linear between 20 and 135 mg/kg. Population estimates of parameters describing halomon plasma pharmacokinetics in female CD2F1 mice were developed with a standard two-stage technique and also by simultaneous modeling of data from 20-, 60-, 90-, and 135-mg/kg i.v. studies in female mice. Halomon bioavailability was 45%, 47%, and 4% after i.p., s.c., and enteral dosing, respectively. Urinary excretion of the parent compound was minimal. Halomon was distributed widely to all tissues studied but was concentrated and persisted in fat. Halomon concentrations measured in the brain were comparable with concomitant concentrations detected in plasma and most other tissues. These data and models are helpful in the simulation and evaluation of conditions produced by preclinical screening and toxicology studies.

Plasma pharmacokinetics and urinary excretion of the polyamine analogue 1, 19-bis(ethylamino)-5, 10, 15-triazanonadecane in CD2F1 mice

The pharmacokinetics of 1, 19-bis(ethylamino)-5, 10, 15-triazanonadecane (BE-4-4-4-4) were determined in CD2F1 female mice after administration of i.v. bolus doses of 20 mg/kg (approximately the dose lethal to 10% of the study animals, approximately LD10) as well as 15, 10, and 5 mg/kg and after s.c., i.p., or p.o. doses of 20 mg/kg. BE-4-4-4-4 in plasma and urine was derivatized with dansyl chloride and measured by gradient high-performance liquid chromatography (HPLC) with fluorescence detection. Data were modeled by noncompartmental and compartmental methods. The declines observed in plasma BE-4-4-4-4 concentrations after i.v. delivery of 20, 15, 10, and 5 mg/kg were modeled simultaneously using an interval of 2000 min between doses and were best approximated by a two-compartment, open, linear model. The time courses of plasma BE-4-4-4-4 concentrations after i.p. and s.c. delivery were fit best by a two-compartment, open, linear model with first-order absorption. Peak plasma concentrations of BE-4-4-4-4 measured following an i.v. dose of 20 mg/kg ranged between 30 and 33 microgram/ml, the terminal elimination half-life was 94 min, and the volume of distribution (Vdss) was 850 ml/kg. The plasma pharmacokinetics of BE-4-4-4-4 were linear with dose. BE-4-4-4-4 (0.5 and 2.0 microM) in mouse plasma was approximately 67% protein-bound. Bio-availabilities after i.p., s.c., and p.o. delivery were 40%, 50%, and approximately 3%, respectively. Urinary excretion of parent BE-4-4-4-4 in the first 24 h after dosing accounted for less than 30% of the delivered dose. As BE-4-4-4-4 proceeds toward and undergoes clinical evaluation, the data and analytical method presented herein should prove useful in formulating a dose-escalation strategy and, possibly, evaluating toxicities encountered.

Synthesis and antitumor evaluation of a highly potent cytotoxic DNA cross-linking polyamine analogue, 1,12-diaziridinyl-4,9-diazadodecane

A diaziridinylspermine analogue, 1,12-diaziridinyl-4,9-diazadodecane (NSC-667005), was synthesized as a bisalkylating agent with a polyamine backbone. DNA cross-linking was detected in the reaction of linearized pBR322 DNA with 1,12-diaziridinyl-4,9-diazadodecane at concentrations comparable with that required for cross-linking by two nitrogen mustard drugs, mechlorethamine and melphalan. A significant increase in life span of female CD2F1 mice bearing L1210 murine leukemia was observed after intravenous administration of 1,12-diaziridinyl-4,9-diazadodecane in doses of less than 2.7 mg/kg, given on days 1, 5, and 9 of treatment.

Cytotoxic activity of N1- and N8-aziridinyl analogs of spermidine

Two isomeric aziridine-containing analogs of spermidine, a polyamine, were synthesized and evaluated for cytotoxic activity against cancer cell lines. Replacement of one of the primary amino groups of spermidine with an aziridinyl functionality yielded either N1-aziridinylspermidine [N-(3-aziridinylpropyl)-1,4-diaminobutane] or N8-aziridinylspermidine [N-(4-aziridinylbutyl)-1,3-diaminopropane]. N1-Aziridinylspermidine was cytotoxic in vitro against L1210 murine leukemia cells (IC50 0.15 microM) and HL60 human leukemia cells (IC50 0.11 microM). N8-Aziridinylspermidine was slightly less potent against L1210 (IC50 0.31 microM) and HL60 (IC50 0.30 microM) cells. When screened by the Developmental Therapeutics Program of the National Cancer Institute, these compounds proved cytotoxic against a wide variety of tumor types. Both compounds inhibited incorporation of radiolabeled thymidine, uridine, and valine into tricholoracetic acid-precipitable material by L1210 cells. Aminoguanidine did not affect the potency of the aziridinylspermidines.

Cellular pharmacology of N1- and N8-aziridinyl analogues of spermidine

We have previously described the synthesis and cytotoxic properties of 2 polyamine analogues in which either the N1- or N8-amino group of spermidine was replaced by the alkylating moiety, aziridine. However, the mechanisms by which these aziridinyl analogues of spermidine inhibit cell growth remain unknown. As a result, we have studied: (a) the effect of pretreatment with difluoromethyl ornithine (DFMO) and coincubation with exogenous spermidine on cytotoxicity induced by the aziridinyl spermidines; (b) the reversibility of the cytotoxicity induced by the aziridinyl spermidines; (c) the accumulation of N1- and N8-aziridinyl spermidine by cells and the effects of DFMO on this process; and (d) the impact of N1- and N8-aziridinyl spermidine on cellular polyamine pools and on cellular accumulation of spermidine. The cytotoxicity induced by these 2 aziridinyl derivatives of spermidine [concentration required to inhibit cell growth or incorporation of radiolabeled precursor into trichloroacetic acid-precipitable material by 50% (IC50) N1 = 0.2 microM, IC50 N8 = 0.4 microM)] was potentiated by pretreatment of L1210 cells for 24 h with 100 microM DFMO (IC50 N1 = 0.05 microM, IC50 N8 = 0.15 microM) and was prevented by coincubation with 3.7 microM spermidine (IC50 N1 = 1.1 microM, IC50 N8 = 2.4 microM). In contrast, similar pretreatment with DFMO or coincubation with spermidine had no effect on the cytotoxicity induced by the aziridine-containing alkylating agent, N,N',N"-triethylenethiophosphoramide (thiotepa) (IC50 = 2.4 microM). The cytotoxicity induced by 24-h incubation with either N1- or N8-aziridinyl spermidine was not altered by removal of those compounds and incubating treated cells in medium augmented with 3.7 microM spermidine. However, and as expected, similar maneuvers did not reverse the cell growth-inhibitory effect induced by 24-h incubation with 100 microM DFMO. Cellular accumulation of both N1- and N8-aziridinyl spermidine increased with increasing extracellular concentrations. N1-Aziridinyl spermidine was accumulated to a greater degree than was the N8-analogue, achieving up to 6-fold higher intracellular concentrations at the same extracellular concentration. Cellular accumulation of both aziridinyl compounds was greatly enhanced by 24-h pretreatment with DFMO. Both N1- and N8-aziridinyl spermidine inhibited the uptake of spermidine in a dose-dependent manner. The perturbation of polyamine biochemistry by the test compounds was characterized by their ability to deplete cellular putrescine, as well as spermidine and spermine. These results imply that the cytotoxic mechanism of the aziridinyl spermidine analogues is, to a great extent, dependent on their polyamine nature and may imply selectivity for rapidly growing and neoplastic cells.

Alkylamides as inducers of human leukemia cell differentiation: a quantitative structure-activity relationship study using comparative molecular field analysis

Computer assisted quantitative structure-activity studies using comparative molecular field analysis (CoMFA) were performed on a series of alkylamides that induce cell differentiation. The series included alkylformamides, alkylacetamides, alkylureas, and substituted hexyl analogues of acetamide. The biological activity studied for correlation with structure was the ability of each compound to induce differentiation of the human promyelocytic leukemia cell line, HL-60, to granulocyte-like cells. In the CoMFA study, both steric and electrostatic fields were used along with molecular weight to determine a correlation between biological activity of the compounds and their structural features. The CoMFA results indicated a linear structure-activity correlation with a high predictive value. There was almost an even contribution towards activity from steric interactions, electrostatic potential, and molecular weight. These findings confirm a previous report by Langdon and Hickman (S. P. Langdon and J. A. Hickman, Cancer Res., 47: 140-144, 1987) that the ability to induce cell differentiation is highly dependent on molecular weight. Additionally, CoMFA contour maps provided information about regions of the molecule that are favorable to increased steric bulk and electrostatic charge. CoMFA was used to predict the activities of six hexamethylene acetamide analogues: ethyl 6-acetamidohexanoate; 6-acetamidohexanol; 1,5-bis(acetamido)hexane; 6-acetamidohexanonitrile; 6-acetamidohexanoic acid; and caprolactam. Although the model incorrectly predicted high activity for 6-acetamidohexanoic acid, the predicted activities for the remaining compounds were 0.3 to 1.5 times that of the corresponding experimental activities, which is comparable to the results obtained from other published CoMFA studies.

Isotopically sensitive regioselectivity in the oxidative deamination of a homologous series of diamines catalyzed by diamine oxidase

The equivalence of aminomethylene groups in selected diamine substrates of diamine oxidase was exploited for the determination of intramolecular isotope effects. In the series of substrates, [1,1-2H2]-1,3-diaminopropane, [1,1-2H2]-1,5-diaminopentane, [1,1-2H2]-1,6-diaminohexane, [1,1-2H2]-1,7-diaminoheptane and [alpha,alpha-2H2]-4-(aminomethyl)benzylamine, the preference of the enzyme for reaction at the unlabeled methylene was found to vary from 1.45 to 10.5-fold. The observed partitioning ratios go through a minimum value with 1,5-diaminopentane, the best substrate of diamine oxidase of the compounds tested. The results suggest that fast substrates have less opportunity to reorient into alternate binding conformations while bound to the active site of the enzyme. On the other hand, diamine substrates tested that cannot exist in energetically favorable conformations with internitrogen distances of about 7-8 A showed larger intramolecular isotope effects.

Active-site directed irreversible inhibition of diamine oxidase by a homologous series of aziridinylalkylamines

Three electrophilic homologous aminoalkylaziridine analogues of putrescine, cadaverine, and 1,3-diaminopropane were synthesized and found to represent a mechanistically distinct class of irreversible inhibitors of diamine oxidase. The putrescine analogue, N-(4-aminobutyl)aziridine gave the lowest calculated IC50 value, whereas N-(3-aminopropyl)aziridine, an analogue of the poorest substrate of the series, showed the highest IC50. The findings suggest that the aziridinylalkylamines tested are site-directed agents that form irreversible complexes at the active site of diamine oxidase. Affinity of the inhibitors for the active site appeared to be dependent on alkyl chain length, suggesting that binding promotes the reactivity of the aziridinyl group.

Alkylation of DNA with aziridine produced during the hydrolysis of N,N',N''-triethylenethiophosphoramide

A reaction pathway by which thiotepa (N,N',N''-triethylenethiophosphoramide) and tepa (N,N',N''-triethylenethiophosphoramide), its major metabolite in humans, alkylate and depurinate DNA involves hydrolysis to aziridine (ethylene imine), a highly reactive monofunctional alkylating agent. Hydrolytic cleavage of an N-P bond of thiotepa releases aziridine which reacts with DNA, resulting in depurination and formation of the stable N-7 adduct 7-(2-aminoethyl)guanine and an aminoethyl adduct of adenine. Chromatographically identical alkylated products were observed in the reaction of thiotepa and tepa with individual nucleosides. Adducts with deoxycytidine or thymidine were not detected. Aziridine was measured by HPLC after derivatization with 1,2-naphthoquinone 4-sulfate. On the basis of the identity of the DNA adducts and the rate of formation of aziridine by hydrolysis in vitro, thiotepa is concluded to be a lipophilic, stabilized form of aziridine which serves as a cell-penetrating carrier of aziridine.

Induction of human leukemia cell differentiation by regiospecifically acetylated spermidines

The activity of two naturally occurring monoacetylated polyamines, N8-acetylspermidine and N1-acetylspermidine, as inducers of differentiation of HL60 human leukemia cells was assessed. Differentiation was quantified by morphological changes and the ability to reduce nitroblue tetrazolium. N8-Acetylspermidine produced 25-35 percent differentiation at 3 microM and 80-90 percent differentiation at 15 microM. Higher concentrations caused cell death. Cell growth was inhibited by N8-acetylspermidine at 3.8 microM. No differentiation activity or inhibition of cell growth was found with N1-acetylspermidine at concentrations up to 1.2 mM. The observed dependence of activity on the position of the acetyl group on monoacetylspermidine is in contrast to the broad structural specificity of known inducers of HL60 cell differentiation.

Supercritical fluid chromatography/chemical ionization/mass spectrometry of some anticancer drugs in a thermospray ion source

A packed-column supercritical-fluid chromatograph was interfaced with a mass spectrometer via a modification of a thermospray probe. This modification allowed a capillary restrictor for the supercritical fluid (CO2) and reagent gas for chemical ionization to be introduced directly into a thermospray source. Chemical ionization conditions were observed when either the filament or discharge electrode was used and the source pressure was above 0.5 torr. The discharge electrode produced more efficient ionization, resulting in approximately a tenfold larger signal than that observed in the filament mode. The usefulness of this instrumentation was demonstrated on several anticancer drugs. Methanol positive ion chemical ionization (PICI) spectra were recorded for cyclophosphamide, diaziquone, mitomycin C and thiotepa. Methane PICI spectra of thiotepa were obtained in the absence of methanol as a mobile-phase modifier. A 50 ng on-column injection of diaziquone produced approximately a 6:1 signal to noise ratio in the scanning mode.

Effects of the monoamine oxidase inhibitor, tranylcypromine, on induction of HL60 cell differentiation by hexamethylene bisacetamide and N-acetyl-1,6-diaminohexane

Hexamethylene bisacetamide (HMBA) is converted by successive deacetylation and oxidation reactions to four major metabolites; in vitro, the initial deacetylated metabolite, N-acetyl-1,6-diaminohexane (NAD-AH), is more potent than HMBA (Synder, S.W.; Egorin, M.J.; Geelhaar, L.A.; Hamburger, A.W.; Callery, P.S. Cancer Res. 48:3613-3616; 1988). We propose that monoamine oxidase (MAO) catalyzed metabolism of NADAH to 6-acetamidohexanoic acid (AcHA) is an inactivation pathway and, therefore, investigated whether blocking such metabolism with the MAO inhibitor, tranylcypromine, would potentiate induction of cell differentiation by HMBA and NADAH. Tranylcypromine, at concentrations up to 30 micrograms/mL, did not inhibit HL60 cell growth and did not induce differentiation of HL60 cells. Tranylcypromine did, however, produce concentration-dependent enhancement of HMBA- and NADAH-induced differentiation. In contrast, 30 micrograms/mL of tranylcypromine did not effect the ability of dimethylsulfoxide, at concentrations between 0.25% and 1.25%, to induce differentiation of HL60 cells. Tranylcypromine, at 30 micrograms/mL, did not change cellular concentrations of HMBA or NADAH but did reduce intracellular concentrations of AcHA, consistent with inhibition of MAO catalyzed conversion of NADAH to AcHA. These results support the hypothesis that MAO catalyzed metabolism of NADH to AcHA is an inactivation pathway and may provide the basis for a clinical trail in which HMBA metabolism is modulated with concurrent tranylcypromine therapy.

Metabolic conversion of 2-propylpentanal acetals to valproic acid in vitro. Model prodrugs of carboxylic acid agents

As part of an investigation to test the feasibility of using acetals as precursors of acidic drugs, the dimethyl, diethyl, [2H10]diethyl, and diisopropyl acetals of 2-propylpentanal were synthesized and their metabolic conversion to the anticonvulsant, valproic acid (2-propylpentanoic acid), was investigated. The acetals were incubated with either 10,000g supernatant or microsomes isolated from rat liver. Data from the measurement of the metabolite, valproic acid, with selected ion monitoring gas chromatography/mass spectrometry indicated that the dimethyl, diethyl, [2H10]diethyl, and diisopropyl acetals were substrates. The amount of valproic acid produced from the incubation of 2-propylpentanal diethyl acetal with 10,000g supernatant was reduced by the cytochrome P-450 inhibitor, SKF-525A. The production of acid was also decreased by lack of NADPH or oxygen. These data are consistent with a cytochrome P-450 mediated reaction. 2-Propyl-1-pentanol was the major metabolite identified from microsomal preparations free of soluble fraction enzymes. A deuterium isotope effect calculated as the ratio of the amount of valproic acid produced from unlabeled and [2H5]ethyl-labeled substrate was 1.2. Failure to detect an ester as a metabolite of 3-phenylpropanal diethyl acetal along with the results of the isotope effect studies suggest that the mechanistic pathway of acyclic acetal metabolism involves oxidation of an ether methylene and not oxidation at the acetal carbon.

A nuclear magnetic resonance (NMR) method for the determination of the cis/trans isomeric content of chlorprothixene

Proton NMR spectroscopy was applied to the assignment of the isomeric identity of commercially available chlorprothixene. Nuclear Overhauser effect studies confirmed that the clinically useful isomer is the cis (Z) configuration. An NMR method for determining the isomeric content of chlorprothixene was developed based on integration of the ratio of areas of signal strength of the cis-N-methyl in comparison to the trans-N-methyl resonances.

Liquid chromatography-thermospray mass spectrometry of DNA adducts formed with mitomycin C, porfiromycin and thiotepa

High-performance liquid chromatography (HPLC) and thermospray mass spectrometry were combined for the analysis of DNA adducts formed from the interaction of the anticancer drugs mitomycin C, porfiromycin and thiotepa with calf thymus DNA. The adducts formed from reaction of mitomycin C and porfiromycin with DNA were separated from unmodified nucleosides by HPLC on a C18 column and identified by thermospray mass spectrometry. Thiotepa DNA adducts readily depurinated from DNA and were chromatographed and identified by thermospray liquid chromatography-mass spectrometry as the modified bases without the ribose moiety attached. The utility of thermospray mass spectrometry for the identification of microgram quantities of nucleoside adducts and depurinated base adducts of these anticancer drugs was demonstrated.

An active, aldehydic metabolite of the cell-differentiating agent hexamethylene bisacetamide

6-Acetamidohexanal has been identified in human plasma and urine as a metabolite of the cell-differentiating agent, hexamethylene bisacetamide (HMBA). Synthesis of 6-acetamidohexanal was accomplished by oxidation of 6-acetamido-1-hexanol with pyridinium dichromate. A screen of 6-acetamidohexanal for cell-differentiating activity in HL60 human leukemia cells revealed a higher level of activity than HMBA or N-acetyl-1,6-diaminohexane, another active metabolite of HMBA. The results are consistent with a pathway which involves deacetylation of HMBA, oxidative deamination of the resulting N-acetyl-1,6-diaminohexane to yield 6-acetamidohexanal, and further oxidation to give 6-acetamidohexanoic acid.

Derivatization of N-methyl and cyclic amino acids with dimethylformamide dimethyl acetal

Six amino acids containing either an N-methyl or a cyclic secondary amine were converted to volatile derivatives by reaction with dimethylformamide dimethyl acetal. The amine functionalities were formylated by way of an amide acetal intermediate while the carboxylic acid groups were esterified directly. The resulting N-formyl esters were stable to solvent extraction and exhibited gas chromatography-mass spectrometry properties suitable for assay development.

A cyclic imine intermediate in the in vitro metabolic conversion of 1,6-diaminohexane to 6-aminohexanoic acid and caprolactam

1. 3,4,5,6-Tetrahydro-2H-azepine is an intermediate in the enzyme-catalyzed conversion of 1,6-diaminohexane to 6-aminohexanoic acid and its corresponding lactam, caprolactam, by mammalian liver aldehyde oxidase. 2. Identification of metabolites was based on analysis by gas chromatography-mass spectrometry and confirmed by comparison with the properties of authentic standards. 3. The results indicate that the cell differentiating agent hexamethylene bisacetamide is converted into 1,6-diaminohexane, and its metabolism therefore involves diamine oxidase. 4. The metabolic fate of 1,6-diaminohexane is similar to that of putrescine and cadaverine in that a cyclic imine is an intermediate in the formation of metabolites with ring (lactam) and chain (amino acid) structures.

Induction of differentiation of human promyelocytic leukemia cells (HL60) by metabolites of hexamethylene bisacetamide

We studied the ability of five metabolites of hexamethylene bisacetamide (HMBA), which we had previously identified in patient urine, to induce differentiation or to influence differentiation induced by HMBA of a human promyelocytic cell line. Differentiation of HL60 cells was quantified by morphological changes and by the ability to reduce nitroblue tetrazolium. N-Acetyl-1,6-diaminohexane (NADAH), the deacetylated, first metabolite of HMBA, was a more potent inducer of HL60 differentiation than was HMBA. NADAH produced 20-30% differentiation at 0.25 mM and 30-40% differentiation at 0.5 mM. NADAH (1 mM) induced 2-3-fold more differentiation than did 1 mM HMBA. HL60 differentiation, induced by various combinations of HMBA and NADAH, reflected a combined effect of the two compounds. In contrast, 1,6-diaminohexane, at 0.5-5 mM, failed to induce HL60 differentiation. Similarly, 0.5-5 mM 6-acetamidohexanoic acid, the major metabolite of HMBA, and 6-aminohexanoic acid failed to induce differentiation of HL60 cells. However, 6-acetamidohexanoic acid, when combined with HMBA or NADAH at various concentrations and ratios, enhanced the differentiation of HL60 cells induced by these two compounds. This enhancement was most apparent with addition of 0.50-3.0 mM 6-acetamidohexanoic acid to HL60 cells incubated with 1.0-3.0 mM HMBA or 0.25-1.0 mM NADAH. 6-Aminohexanoic acid similarly enhanced HMBA-induced differentiation of HL60 cells. These in vitro results have implications in terms of the clinical application of HMBA and interpretation of the results of clinical trials performed to date and may provide some insight into the mechanism of HMBA-induced cellular differentiation.

Metabolism of hexamethylene bisacetamide and its metabolites in leukemic cells

We investigated whether leukemic cell lines could convert hexamethylene bisacetamide (HMBA) to any of the metabolites previously identified and quantified in the urine and plasma of patients treated with HMBA. After 5-7 days of incubation with 1-2 mM HMBA, HL60 human promyelocytic leukemic cells, L1210 and P388 murine lymphoblastic leukemic cells, and Friend murine erythroleukemia cells contained 4 of the previously identified metabolites of HMBA. Gas chromatography/mass spectrometry confirmed the presence of N-acetyl-1,6-diaminohexane (NADAH), 1,6-diaminohexane (DAH), 6-acetamidohexanoic acid (AcHA), and 6-aminohexanoic acid (AmHA). Gas chromatography with nitrogen-phosphorus selective detection was used to quantify cellular concentrations of each metabolite. Cellular concentrations of AmHA and DAH were greater than those of NADAH and AcHA but no concentration of a metabolite exceeded that of HMBA. Metabolites were not detected in media from cells incubated with HMBA. Friend murine erythroleukemia cells that were resistant to HMBA contained only HMBA and NADAH. Moreover, the concentrations of NADAH in Friend murine erythroleukemia cells that were resistant to HMBA were less than those in the other cell lines studied. HL60 cells accumulated HMBA rapidly. NADAH, DAH, AcHA, and AmHA appeared sequentially in HL60 cells that were incubated with HMBA. NADAH appeared very rapidly, but concentrations of DAH were greater than or equal to those of NADAH by 8 h. AcHA and AmHA were not detected in cells before 24-48 h of incubation with HMBA. HL60 cells incubated with individual HMBA metabolites were able to accumulate each compound and to interconvert some: cells incubated with NADAH also contained DAH, AcHA, and AmHA; cells incubated with AcHA also contained low concentrations of AmHA; cells incubated with DAH also contained AmHA; and cells incubated with AmHA contained no other HMBA metabolites. HMBA was not present in cells incubated with any of its known metabolites. These results document the ability of various leukemic cells to metabolize HMBA, indicate the unidirectional catabolism of that compound, and may have implications as to its mechanism of action.

Involvement of monoamine oxidase and diamine oxidase in the metabolism of the cell differentiating agent hexamethylene bisacetamide (HMBA)

We have previously demonstrated a number of metabolites of hexamethylene bisacetamide (HMBA) in the urine of patients treated with HMBA. These include N-acetyl-1,6-diaminohexane (NADAH), 6-acetamidohexanoic acid (6AcHA), 1,6-diaminohexane (DAH) and 6-aminohexanoic acid (6AmHA). Because these compounds have potential roles in the dose-limiting metabolic acidosis and neurotoxicity associated with HMBA therapy, and are similar in structure to known substrates of monoamine oxidase (MAO) and diamine oxidase (DAO), we investigated the activities of these enzymes in the metabolic interconversion of HMBA metabolites. NADAH (5 mM) was incubated with MAO and aldehyde dehydrogenase. 6AcHA production was verified by gas chromatography-mass spectrometry and quantified by gas chromatography. 6AcHA production was linear for up to 4 hr. Complete inhibition of MAO activity was observed with 2 mM tranyl-cypromine or pargyline. Mouse liver microsomes, which do not contain MAO, did not convert NADAH to 6AcHA and, in control experiments, did not degrade 6AcHA. The HMBA metabolite, DAH, was a substrate for DAO, producing 3,4,5,6-tetrahydro-2H-azepine. Participation of DAO in the metabolism of HMBA implies potential interaction of HMBA and metabolites with polyamine metabolism and may represent a mechanism for HMBA's effects on cellular growth and differentiation. Metabolism of NADAH, also a differentiator, by MAO implies that concurrent use of HMBA and an MAO inhibitor may be clinically useful.

Plasma pharmacokinetics and urinary excretion of hexamethylene bisacetamide metabolites

In order to further understand the clinical toxicities of hexamethylene bisacetamide (HMBA) and to allow appropriate in vitro studies, we developed a suitable gas chromatographic assay and quantified plasma concentrations and urinary excretion of four metabolites which we had previously identified in urine of patients receiving 5-day HMBA infusions at 4.8-43.2 g/m2/day. 6-Acetamidohexanoic acid (AcHA) was the major plasma metabolite and reached steady state concentration (Css) by 24 h. AcHA Css increased from 0.12 +/- 0.02 (SD) mM at 4.8 g/m2/day to 0.72 mM at 43.2 g/m2/day. The Css AcHA:Css HMBA ratio decreased with increasing HMBA dosage. At dosages below 24 g/m2/day plasma Css of N-acetyl-1,6-diaminohexane (NADAH), the initial metabolite of HMBA, were below the limit of detection of our assay. With HMBA infusions of 24, 33.6, and 43.2 g/m2/day, Css of NADAH were 0.16 +/- 0.05, 0.14 +/- 0.06, and 0.19 +/- 0.04 mM, respectively. Css NADAH:Css HMBA ratios at 24, 33.6, and 43.2 g/m2/day were 0.18 +/- 0.06, 0.08 +/- 0.02, and 0.31 +/- 0.05, respectively. Plasma Css of 1,6-diaminohexane and 6-aminohexanoic acid were below the limit of detection of our assay. Each patient's urinary excretion of NADAH, AcHA, and 1,6-diaminohexane was consistent from day to day. The fraction of dose excreted in urine as AcHA was not affected by HMBA dosage and accounted for 12.7 +/- 3.9% of the daily dose. The percentage of daily HMBA dose accounted for by excretion of NADAH decreased with increasing HMBA dosage (10.8 +/- 6.0% at 4.8 g/m2/day to 4.2 +/- 1.2% at 33.6 g/m2/day). Urinary excretion of 1,6-diaminohexane always accounted for less than 3% of the daily dose. Our results indicate that: (a) plasma concentrations of AcHA alone cannot explain the degree of acidosis observed with toxic doses of HMBA; (b) NADAH is present in plasma at concentrations that we have found to cause differentiation in vitro; and (c) the probable rate-limiting step in HMBA metabolism is the initial deacetylation.

The chemical reduction of diaziquone: products and free radical intermediates

Sodium borohydride reduced diaziquone (AZQ) can cause cross-links between DNA molecules, between DNA and proteins and cause single- and double-strand DNA breaks. In order to understand these effects better, we investigated the reduction of diaziquone by borohydride, and looked at reaction products. We found that a major product was formed during the oxidation of the colorless 2-electron reduced AZQ, and that this product was a monoaziridinyl quinone. We interpret this result to mean that both the leaving aziridine as well as the remaining one can alkylate. This mode of alkylation does not explain cross-links which may occur by a different mechanism requiring simultaneous opening of the aziridine rings. Most of the antitumor activity of borohydride reduced AZQ is probably exerted during the oxidation of the 2-electron reduced AZQ (AZQH2).

Identification of metabolites of the cell-differentiating agent hexamethylene bisacetamide in humans

Hexamethylene bisacetamide, a compound which in vitro induces differentiation in a wide variety of human and animal cancer cell lines, is being investigated in phase I clinical trials. After i.v. administration of hexamethylene bisacetamide to humans, urine contained the parent compound and at least five metabolites formed by deacetylation and oxidation pathways. Identification of urinary metabolites was accomplished by gas chromatography-mass spectrometric analysis after isolation by ion exchange chromatography or extraction with ethyl acetate. Metabolites with amino or alcohol groups were trifluoroacetylated and acidic functional groups were esterified with 2,2,2-trifluoroethanol or methanol. The structure of each metabolite was confirmed by comparison with authentic standards. Metabolites identified included the major metabolite, 6-acetamidohexanoic acid; the monodeacetylated product, N-acetyl-1,6-diaminohexane; the bis-deacetylated diamine, 1,6-diaminohexane; and the amino acid, 6-aminohexanoic acid and its lactam, caprolactam.

1-Piperideine as an in vivo precursor of the gamma-aminobutyric acid homologue 5-aminopentanoic acid

Intraperitoneal injection of the cyclic imine 1-piperideine in mice resulted in measurable quantities of 5-aminopentanoic acid in brain. 5-Aminopentanoic acid is a methylene homologue of gamma-aminobutyric acid (GABA) that is a weak GABA agonist. 5-Aminopentanoic acid formed in the periphery was ruled out as the source of brain 5-aminopentanoic acid based on the absence of detection in brain following injection of 100 mg/kg of 5-aminopentanoic acid. Deuterium-labeled 1-piperideine was prepared by exchange in deuterated phosphate buffer. Injection of [3.3-2H2]1-piperideine yielded [2.2-2H2]5-aminopentanoic acid in brain. The results are consistent with uptake of 1-piperideine into brain and oxidation of the precursor to 5-aminopentanoic acid. Inhibition of GABA catabolism by pretreatment with aminooxyacetic acid increased brain concentrations of 5-aminopentanoic acid formed from 1-piperideine, suggesting that 5-aminopentanoic acid is an in vivo substrate of 4-aminobutyrate:2-oxoglutarate aminotransferase.

Superoxide radical reactions with anthracycline antibiotics

The reaction of superoxide with daunorubicin or its aglycones in the aprotic solvents dimethyl sulfoxide and dimethylformamide was studied. This interaction generated the blue anthracycline phenolate anion as monitored by u.v.-visible spectrometry and molecular oxygen as determined by a modified Clark-type oxygen electrode. The visible spectrum of the phenolate anion (gamma max 604, 652 nm) was subject to considerable shifts dependent on the size of the cation present. The phenolate anion could be further oxidized by molecular oxygen to generate the C-6, C-11 (B-ring) semiquinone as detected by a weak electron paramagnetic resonance spectrometry signal. These results raise the possibility that similar reactions of superoxide with anthracyclines in vivo may play a role in the antitumor activity and/or the etiology of the toxic side effects of this class of drugs.

Biosynthesis of 5-aminopentanoic acid and 2-piperidone from cadaverine and 1-piperideine in mouse

1-Piperideine, 5-aminopentanoic acid, and its lactam, 2-piperidone, were identified as metabolites of cadaverine in 10,000 g mouse liver supernatants to which diamine oxidase had been added. Both metabolites were also found when the cadaverine metabolite 1-piperideine was incubated with the preparation which suggested that 1-piperideine is an intermediate in the formation of 5-aminopentanoic acid and 2-piperidone. Identification of the metabolites was based on gas chromatography-mass spectrometric analysis in comparison to authentic standards. Mouse brain homogenates converted 1-piperideine to 5-aminopentanoic acid. The results suggest that the metabolic fate of cadaverine may provide precursors of pharmacologically active analogues of GABA.

Putrescine metabolism: enzymatic formation and non-enzymatic isotope exchange of delta1-pyrroline

The deamination of putrescine catalysed by diamine oxidase was carried out in deuterium oxide and deuterated buffers. Enamine and alpha, beta-unsaturated intermediates were excluded, based on the observation that deuterium was not incorporated into delta 1-pyrroline during its enzymatic formation in deuterium oxide. When the reaction mixture was buffered with phosphate, isolated delta 1-pyrroline contained two deuterium atoms at C-3, indicating that a phosphate-promoted, non-enzymatic isotope exchange had occurred. Using 5,5-dimethyl-delta 1-pyrroline as a model compound, the nature of the non-enzymatic deuterium exchange was studied and a bifunctional catalysis mechanism proposed. The results suggest that the choice of buffer could alter the conclusions drawn from enzyme mechanism studies involving imine-enamine tautomerism .

Intermolecular and intramolecular isotope effects in the deamination of putrescine catalyzed by diamine oxidase

The enzymatic deamination of 1,4-diaminobutane (putrescine) catalyzed by hog kidney diamine oxidase was studied with the aid of deuterium labeled substrates and mass spectrometry. An intermolecular deuterium isotope effect for the deamination of putrescine labeled with deuterium in all 4 alpha positions was observed to be 1.26. 1,4-Diaminobutane-1,1-d2 was synthesized and intramolecular isotope effects determined. The preference of diamine oxidase for the unlabeled alpha position was about 4 times greater than for the deuterated methylene. This work shows that intramolecular deuterium isotope effects are observable in enzyme systems other than cytochrome P-450.

Pyrrolines as prodrugs of gamma-aminobutyric acid analogues

delta 1-Pyrroline, 5-methyl-delta 1-pyrroline, and 5,5-dimethyl-delta 1-pyrroline have been identified as substances metabolized to gamma-aminobutyric acid (GABA), 4-aminopentanoic acid (methylGABA), and 4-amino-4-methylpentanoic acid (dimethylGABA), respectively. An enzyme system residing in the soluble fraction of rabbit liver catalyzes the conversion of delta 1-pyrroline to GABA and its lactam, 2-pyrrolidinone. Acetaldehyde, allopurinol, and cyanide inhibited the reaction. Incubation of deuterium-labeled delta 1-pyrroline with mouse brain homogenates produced deuterated GABA. Mouse liver 10,000 g supernatant and mouse brain homogenates converted 5-methyl-delta 1-pyrroline to methylGABA, and 5,5-dimethyl-delta 1-pyrroline to dimethylGABA. Four hours after intraperitoneal injection of 5-methyl-delta 1-pyrroline (200 mg/kg), methylGABA was detected in mouse brain (0.27 mumol/g). DimethylGABA (1.21 mumol/g) was determined in mouse brain 30 min after intraperitoneal administration of 5,5-dimethyl-delta 1-pyrroline (200 mg/kg). Neither methylGABA nor dimethylGABA penetrated into the central nervous system when administered in the periphery. The present studies suggest that pyrrolines may represent a chemical class of brain-penetrating precursors of pharmacologically active analogues of GABA.

Applications of deuterium labeling in the study of the in vitro conversion of delta 1-pyrroline to 4-aminobutanoic acid and 2-pyrrolidinone

delta 1-Pyrroline is a putrescine metabolite that is biotransformed by rabbit liver preparations to 4-aminobutanoic acid and its lactam, 2-pyrrolidinone. Analysis of dilute aqueous solutions of delta 1-pyrroline by proton nuclear magnetic resonance indicated the the predominating species in the liver incubation preparations was delta 1-pyrroline monomer, although other species, such as 4-aminobutyraldehyde an delta 1-pyrroline timer, may exist in equilibrium with the monomer. [2H12]-delta 1-Pyrroline trimer was synthesized from [2H5]pyrrolidine by conversion to the N-chloro derivative followed by dehydrohalogenation. 4-Aminobutanoic acid was measured by a gas chromatographic mass spectrometric assay after derivatization with dimethylformamide dimethyl acetal. The 4-aminobutanoic acid homologue, 5-aminovaleric acid, served as internal standard. 2-Pyrrolidinone was hydrolyzed and measured as 4-aminobutanoic acid. A comparison of the amounts of product formed following incubation of labeled and unlabeled delta 1-pyrroline indicated a significant isotope effect in the formation of 2-pyrrolidinone. The influence of the label was much less on 4-aminobutanoic acid production. The results suggest that there are two separate pathways involved in the reaction.

Membrane transport of Tc-99m-labeled radiopharmaceuticals, I. Brain uptake by passive transport

The membrane transport properties of twelve Tc-99m complexes were studied by determining each complex's brain uptake index (BUI), extent of protein binding, and octanol-to-saline partition coefficient. The chelating agents used were classified as either N-substituted carbamoylmethyliminodiacetates, substituted oxines, N,N'-diesters of EDTA, or N-substituted derivatives of DTPA. The Tc-99m complexes were found to cross the blood--brain barrier in proportion to their lipophilicity. Of the four types of chelating agents tested, substituted oxines appear to be most suitable for the development of diffusible Tc-99m-labeled compounds for imaging nonexcretory organs.

Synthesis and preliminary biological studies of 4- and 5-[2-hydroxy-3-(isopropylamino)propoxy]benzimidazoles: selective beta2 adrenergic blocking agents

Benzimidazoles carrying the 2-hydroxy-3-(isopropylamino)propoxy side chain at either the C-4 or C-5 ring positions were synthesized and investigated for beta-adrenergic blocking activity. Both compounds demonstrated beta2 selectivity when evaluated in guinea pig atrial and tracheal preparations. The C-4 isomer was 17 times more selective toward tracheal tissue, and its overall potency was roughly comparable to that of propranolol. beta2 selectivity of the C-5 isomer was minimal, with a potency about one-hundredth that of propranolol.

Detection of the in vivo conversion of 2-pyrrolidinone to gamma-aminobutyric acid in mouse brain

Labeled gamma-aminobutyric acid was detected in mouse brain following intravenous injections of deuterium labeled 2-pyrrolidinone. [2H6]Pyrrolidinone was prepared by the reduction of [2H4]succinimide with lithium aluminum deuteride. Quantification was accomplished by a gas chromatography mass spectrometry assay method. gamma-Aminobutyric acid and internal standard, 5-aminovaleric acid, were converted to volatile derivatives by treatment with N,N-dimethylformamide dimethyl acetal. Quantitative estimates were derived from peak area measurements obtained from monitoring the parent ions of the gamma-aminobutyric acid and internal standard derivatives by repetitive scanning during the GC run. The conversion of pyrrolidinone to gamma-aminobutyric acid may provide a method for labeling central gamma-aminobutyric acid pools.

Thermal decomposition of 1,3-dimethyl derivative of phenobarbital in trimethylanilinium hydroxide

Extensive degradation of the 1,3-dimethyl derivative of phenobarbital occurs when it is injected with trimethylanilinium hydroxide in methanol into a gas chromatograph. The application of mass spectrometry demonstrated that the major products are N-methyl-2-phenylbutyramide, N,N-dimethyl-2-phenylbutyramide, methyl 2-phenylbutyrate, N,N,N'-trimethylethylphenylmalondiamide, and N,N,N',N'-tetramethylethylphenylmalondiamide. The methyl group of the ester arises from the methanol solvent, whereas the methyl groups of the substituted amides arise from the parent compound or the methylating reagent. Tetramethylammonium hydroxide causes much more degradation than trimethylanilinium hydroxide under comparable conditions.