31P NMR studies of the kinetics of bisalkylation by isophosphoramide mustard: comparisons with phosphoramide mustard.

31P nuclear magnetic resonance spectroscopy was used to measure the pKa (4.28 +/- 0.2) of isophosphoramide mustard (IPM) at 20 degrees C and to study the kinetics and products of the decomposition of IPM at a solution pH value of ca. 7.4 and at temperatures between 20 and 47 degrees C in the presence of nucleophilic trapping agents. At 37 degrees C, the half-life for the first alkylation was ca. 77 min and ca. 171 min for the second alkylation; these data may be compared with those for phosphoramide mustard (Engle, T.W.; Zon, G.; Egan, W.J. Med. Chem. 1982, 25, 1347), wherein the half-lives for the first and second alkylations are approximately the same (18 min). The rate of fragmentation of aldoifosfamide to IPM and acrolein was also studied by NMR spectroscopy (pH 7.0; 37 degrees C; 0.07 M phosphate); under the noted conditions, the half-life of aldoifosfamide was found to be ca. 60 min.

Effect of stereochemistry on the oxidative metabolism of the cyclophosphamide metabolite aldophosphamide.

31P NMR and cell perfusion techniques were used to investigate the conversion of the individual enantiomers of aldophosphamide (AP) to carboxyphosphamide (CBP) as catalyzed by aldehyde dehydrogenase in human erythroleukemia K562 cells. R- and S-cyclophosphamides (CPs) were treated with ozone and hydrogen peroxide to yield Rp- and Sp-cis-4-hydroperoxycyclophosphamides (Rp- and Sp-cis-4-HO2-CP); reduction of each hydroperoxide gave the corresponding enantiomer of AP [along with its tautomer 4-hydroxycyclophosphamide (4-HO-CP)]. In separate experiments, K562 cells embedded in agarose gel threads were perfused at pH 7.4, 21 +/- 1 degrees, with solutions of 1.4 mM Rp- and Sp-4-HO-CP/AP, both with and without added mesna (an acrolein scavenger). A comparison of the 31P NMR spectral data derived from the experiments revealed little statistical difference (+/- 10-20% error limits) in the normalized intensities of the CBP peaks arising from the individual AP enantiomers [with added mesna, the ratio Rp-CBP:Sp-CBP was 1.00:1.24 +/- 0.13 (average deviation); without mesna, the same ratio was 1.00:1.35]. Using conventional methods for evaluating the in vitro drug toxicities, CP-resistant L1210 cells were treated in separate experiments with Rp- and Sp-cis-4-HO2-CP; there were no significant differences between the toxicities exhibited by the stereoisomers.

Arginine utilization by Mycoplasma fermentans is not regulated by glucose metabolism: a 13C-NMR study.

13C-NMR studies on the effect of glucose metabolism on arginine hydrolysis in Mycoplasma fermentans cells have been performed using a continuous perfusion technique. With this procedure we were able to show, in the presence of glucose, the rapid accumulation of lactic acid and, in the presence of arginine, the formation of citrulline that is apparently further metabolized. As the accumulation of lactate and the breakdown of arginine were observed in the simultaneous presence of both substrates, it is suggested that the glucose utilization has little or no effect on the deimination of arginine to citrulline.

Evidence for a role of chloroethylaziridine in the cytotoxicity of cyclophosphamide.

UNLABELLED: A number of investigators have observed that the use of 4-hydroperoxycyclophosphamide (4-HC) in multiwell plate cytotoxicity assays can be associated with toxicity to cells in wells that contain no drug. Previous reports have implicated diffusion of 4-HC decomposition products, and acrolein in particular, as the active species. PURPOSE: The purpose of this study was to elucidate the species responsible for the airborne cytotoxicity of 4-HC, and to devise ways to minimize such effects in chemosensitivity assays. METHODS: To this end, analogues of 4-HC were synthesized to identify the contributions of individual cyclophosphamide metabolites to cytotoxicity. The analogues were then tested for activity against three human breast tumor cell lines (including a line resistant to 4-HC), and one non-small-cell lung carcinoma line. Cytotoxicity was evaluated by assays that quantitate cellular metabolism and nucleic acid content. RESULTS: Didechloro-4-hydroperoxycyclophosphamide, a compound that generates acrolein and a nontoxic analogue of phosphoramide mustard, gave no cross-well toxicity. In contrast, a significant neighboring well effect was observed with phenylketophosphamide, a compound that generates phosphoramide mustard but not acrolein. Addition of authentic chloroethylaziridine reproduced the airborne toxicity patterns generated by 4-HC and phenylketophosphamide. Increasing the buffering capacity of the growth medium and sealing the microtiter plates prevented airborne cytotoxicity. CONCLUSION: Since it is unlikely that phosphoramide mustard is volatile, these findings implicate chloroethylaziridine rather than acrolein as the volatile metabolite of 4-HC that is responsible for airborne cytotoxicity. The fact that chloroethylaziridine is generated in amounts sufficient to volatilize, diffuse across wells and cause cytotoxicity indicates that it is an important component in the overall cytotoxicity of 4-HC in vitro. Furthermore, these findings suggest that chloroethylaziridine may also contribute to the toxicity of cyclophosphamide in vivo.

Home care training in internal medicine residencies: a national survey.

PURPOSE: To determine the amount and type of training U.S. internal medicine residents receive in providing home care to patients. METHOD: A four-item questionnaire was developed and sent to the program directors of all accredited internal medicine residencies in the United States (n = 397) to assess the amounts and types of training (didactic sessions or lectures, house calls, or both) internal medicine residents receive in providing home care. Demographic information about the residency programs was also collected and analyzed. RESULTS: A total of 312 (78.6%) of the program directors responded. Sixty-eight percent of their programs included instruction in home care consisting of house calls, lectures, or both. Fewer than half of the responding programs offered any lecture in home care in their curricula, and only 25% of them included a mandatory house-call experience for trainees. Residency programs that had primary care tracks were more likely than were other programs to include either of these experiences in their curricula. CONCLUSIONS: Most internal medicine residents receive limited training in home care. As a consequence, future internists may be inadequately prepared to meet the needs of their patients, particularly as the population ages.

Synthesis, hydrolytic behavior, and anti-HIV activity of selected acyloxyalkyl esters of trisodium phosphonoformate (foscarnet sodium).

The synthesis and anti-HIV activity of selected (acyloxy)alkyl esters of trisodium phosphonoformate (foscarnet sodium) are described. The conversion of bis(trimethylsilyl) (alkoxycarbonyl)phosphonates 11a-d to the corresponding disilver salts 12a-d and their subsequent reaction with iodoalkyl acrylates 4a-c gave the desired bis(acyloxyalkyl) phosphonates 6-9(a-c). Of the analogs tested, only the dichlorophenyl analog 9a showed a dose-dependent inhibition of HIV activity in H9 cells. Using 31P-NMR, bioreversibility has been investigated in an attempt to rationalize these results.

Human placenta does not Reduce AZT (zidovudine) to 3'-amino-3'-deoxythymidine.

Human placental tissue and human trophoblast cells (JAr) were examined after exposure to the anti-HIV nucleoside analog AZT (Zidovudine) for the presence of 3'-amino-3'-deoxythymidine (AMT), a toxic catabolite. Placental cells were exposed to 7.6 mM AZT for 48 hr, and placental lobular tissue was perfused with 3.8 mM AZT for 14 hr. Cell homogenates were prepared, and supernatants were subjected to HPLC analysis. Despite large cellular concentrations of AZT, AMT was not detected in any of the samples analyzed. Exposure of JAr cells to this concentration of AZT produces a 72% inhibition of cell proliferation when compared with unexposed controls. Based upon the results of the current study, AMT was not formed by placental cells exposed to AZT and, thus, not a mechanism for toxicity after in vitro exposure to AZT.

Direct detection of the intracellular formation of carboxyphosphamides using nuclear magnetic resonance spectroscopy.

31P nuclear magnetic resonance (NMR) spectroscopy was used in conjunction with cell perfusion techniques to monitor the intracellular chemistry of the cyclophosphamide (CP, CAS 6055-19-2) metabolites 4-hydroxy-cyclophosphamide (4-HO-CP) and aldophosphamide (AP) in U937 human histiocytic (CP-sensitive) and K562 human erythroleukemia (CP-resistant) cells. Similar experiments were carried out using the ifosfamide (IF, CAS3778-73-2) metabolites 4-hydroxyifosfamide (4-HO-IF) and aldoifosfamide (AIF). The hydroxy and aldehydic metabolites were generated by the triphenylphosphine reduction of 4-hydroperoxycyclophosphamide (4-HO2-CP) or 4-hydroperoxyifosfamide (4-HO2-IF) or by a spontaneous elimination/addition reaction involving water and 4-thiocyclophosphamide analogs 4-(2-hydroxyethyl) thiocyclophosphamide (4-ESCP) or mafosfamide. Cell death resulting from 4-HO-CP/AP perfusions was mimicked by perfusion with acrolein or an acrolein producing but non-alkylating, dechloro-CP analog. Acrolein toxicity was minimized by the presence of 2-mercaptoethanol or mesna (sodium 2-mercaptoethanesulfonate) in perfusion solutions as well as by fractional dose drug perfusions (sequential 2.5-3.0 h perfusions separated by cell washes with drug-free medium). The intracellular half-life for phosphoramide mustard (PM) at an intracellular pH value of 7.1 +/- 0.1 and an ambient probe temperature of 23 +/- 1 degree C in U937 cells was 2.1 h [k = (5.4 +/- 0.3) x 10(-3) min-1] and in K562 cells was 3.1 h [k = (3.7 +/- 0.4) x 10(-3) min-1]. Similar half-lives (2-4 h) were determined for intracellular isophosphoramide mustard (IPM). Fractional dose perfusion of U937 or K562 cells with 1.5 mmol/l 4-HO-CP/AP (generated from 4-HO2-CP) and 0.3 mmol/l mesna allowed for the observation of intracellular carboxyphosphamide (CBP); CBP was formed in higher concentrations in the CP-resistant K562 cells. Similar results were obtained using 4-ESCP and mafosfamide as sources of 4-HO-CP/AP. Identification of CBP was based on chemical shift, chemical stability, and membrane permeability studies of synthetic CBP. Concentrations of carboxyifosfamide (CBIF) formed in K562 cells were also greater than that in U937 cells.

Pharmacokinetic and toxicity studies of AZT (zidovudine) following perfusion of human term placenta for 14 hours.

Multiple exposures to AZT (Zidovudine) for 14 hr were examined in the dually perfused human term placental lobule in order to determine the pharmacokinetics of transfer, as well as several viability parameters of toxicity. In each experiment, three separate additions of AZT at a concentration of 3.8 mM was added to the maternal reservoir, and perfusate samples were obtained from both the maternal and the fetal compartments for determinations of AZT, glucose, lactate, oxygen, and human chorionic gonadotropin (hCG) concentrations. During 14 hr of continuous exposure to this high concentration of AZT, the production of hCG was significantly reduced by 75% when compared to the 2-hr control period before the administration of AZT. In addition, lactate production was reduced by 45% after AZT administration. Such changes in hCG and lactate production were not observed in separate experiments conducted over the same time interval, but with no AZT added. Based upon a lack of total perfusion fluid loss, changes in fetal arterial pressure, and histopathology, placental lobule integrity was maintained throughout the perfusion period. Further, AZT readily crossed the placenta into the fetal compartment reaching equilibrium with maternal levels within 60-90 min after addition of each administration of AZT. Based upon AZT levels in the fetal perfusate, AZT does not accumulate against a concentration gradient and therefore appears to be diffusion limited. Placental tissues obtained from perfused, partially perfused, and nonperfused regions at the conclusion of the experiment were analyzed for AZT levels. Substantial AZT levels in the nonperfused tissues indicated that AZT is a freely diffusible compound. The results of the current study demonstrate that high concentrations of AZT alter placental function resulting in reduced production of hCG and lactate.

Cleavage of oligodeoxyribonucleotides from controlled-pore glass supports and their rapid deprotection by gaseous amines.

A novel method for the deprotection of oligodeoxyribonucleotides has been developed. Gaseous amines such as ammonia or methylamine were employed under pressure to achieve mild and rapid deprotection conditions. For example, oligodeoxyribonucleotides having a (tert-butyl)phenoxyacetyl group for the protection of the exocyclic amino function of cytosine, adenine and guanine were released from controlled-pore glass supports and fully deprotected by ammonia or methylamine under gas phase conditions, at room temperature, within 35 or 2 min respectively.

High-frequency 1H NMR studies of the effects of growth factors and phorbol esters on normal Syrian hamster diploid fibroblast cells.

The nuclear magnetic resonance (NMR) parameters, spin-lattice (T1), and spin-spin (T2) relaxation time, are usually longer for neoplastic cells than for normal cells of the same cell type. This has generally been true at low NMR frequencies (less than or equal to 100 MHz) when comparisons have been made between normal and neoplastic cells that have both spent a short time in culture. We have previously demonstrated that although the T1 values of paired normal and neoplastic Syrian hamster (SH) fibroblastic cells in culture are not significantly different when measured at 300 MHz, the 300 MHz T2 values for the neoplastic cells are smaller than those of the normal cells. (Xin et al. (1986), Cell Biophysics 8, 213.) Since treatment of normal diploid cells with polypeptide growth factors or tumor promoters frequently results in reversible expression of neoplasia-associated phenotypes, T1 and T2 were obtained at 300 MHz for treated and untreated SH cells to see if these compounds could also produce smaller 300 MHz T2 values. Secondary culture SH fetal fibroblast cells were treated with epidermal growth factor (EGF), fibroblast growth factor (FGF), phorbol-12,13-didecanoate (PDD) and 4-alpha-phorbol-12,13-didecanoate (4 alpha PDD). Treatment with either growth factor resulted in smaller T2 values, but a statistically significant decrease was not observed for PDD or 4 alpha PDD. The observed reductions in T2 values were correlated with the morphological and growth-stimulatory effects of these compounds on the cells.