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H Ford

Publications and source records attributed to H Ford.

At least 55 records · Page 3Linked to original sources
PubMed1995

Site of action of two novel pyrimidine biosynthesis inhibitors accurately predicted by the compare program.

The computer algorithm COMPARE provides information regarding the biological mechanism of action of a compound. In this study, excellent correlations were obtained for 2,2'-[3,3'-dimethoxy[1,1'-biphenyl]-4,4'-diyl)diimino]bis- benzoic acid (redoxal) and 1-(p-bromophenyl)-2-methyl-1H- naphth[2,3-d]imidazole-4,9-dione (BNID) and two well-studied dihydroorotate dehydrogenase (DHOD) inhibitors, dichloroallyl lawsone and brequinar, in terms of antiproliferative activity against tumor cell lines in vitro. When redoxal and BNID were incubated with MOLT-4 cells for 72 hr, 50% growth inhibition was achieved at 0.7 and 3.5 microM, respectively. After 24 hr of incubation, pyrimidine triphosphate pools were shown to be decreased by 50% by redoxal (1 microM) and BNID (0.25 microM). Addition of either uridine (50 microM) or cytidine (100 microM) antagonized the cellular cytotoxicity caused by either drug; uridine corrected the UTP and CTP deficit, whereas cytidine corrected only the CTP deficit. Exposure of MOLT-4 cells to a 1 microM concentration of either drug for 18 hr followed by a 1-hr exposure to [14C]bicarbonate showed a 97% decrease of incorporation of [14C] into pyrimidine triphosphates accompanied by a 91- and 82-fold increase in radioactive incorporation into L-dihydroorotate and N-carbamyl-L-aspartate, respectively. By direct exposure of DHOD prepared from MOLT-4 cell mitochondria to a range of concentrations of the two drugs, apparent Ki values of 0.33 microM (redoxal) and 0.53 microM (BNID) were determined. These data provide direct evidence for inhibition of DHOD by redoxal and BNID in MOLT-4 lymphoblasts.

Aminobiphenyl Compounds↗
PubMed1995

Reversal by cytidine of cyclopentenyl cytosine-induced toxicity in mice without compromise of antitumor activity.

Among nine compounds surveyed, cytidine was found to be the most effective in reversing the antiproliferative effects of cyclopentenyl cytosine (CPEC) on human T-lymphoblasts (MOLT-4) in culture. Cytidine, at concentrations of 1-25 microM, enabled cells to maintain normal logarithmic growth when added up to 12 hr after exposure to a 200 nM concentration of the oncolytic nucleoside, CPEC. The most abundant CPEC metabolite, CPEC-5'-triphosphate, is a potent [K1 approximately 6 microM] inhibitor of CTP synthetase (EC 6.3.4.2). Accumulation of this inhibitor resulted in a depletion of CTP levels to 17% of their original cellular concentration. Exogenous cytidine reversed CPEC-induced cellular cytotoxicity by suppressing the formation of CPEC-5'-triphosphate by 70%, and by partially replenishing intracellular CTP to at least 60-70% of its original concentration. In vivo, cytidine (500 mg/kg) administered intraperitoneally 4 hr after each daily dose of CPEC (LD10-LD100) for 9 days reduced the toxicity and abolished the lethality of CPEC to non-tumored mice. Of greater practical importance is the finding that, under these experimental conditions, cytidine did not curtail the antineoplastic properties of CPEC in L1210 tumor-bearing mice. Moreover, the concentration range over which CPEC exhibited antineoplastic activity was extended with cytidine administration.

Animals↗
PubMed1995

Phase I clinical trial of continuous infusion cyclopentenyl cytosine.

Cyclopentenyl cytosine (CPE-C) is an investigational drug that is active against human solid tumor xenografts. The 5'-triphosphate of CPE-C inhibits CTP synthase, and depletes CTP and dCTP pools. We conducted a phase I clinical trial of CPE-C given as a 24-h continuous i.v. infusion every 3 weeks in 26 adults with solid tumors. The starting dose rate, 1 mg/m2 per h, was selected on the basis of both preclinical studies and pharmacokinetic data from two patients obtained after a test dose of 24 mg/m2 CPE-C as an i.v. bolus. Dose escalation was guided by clinical toxicity. A total of 87 cycles were given, and ten patients received four or more cycles. The mean CPE-C steady-state plasma levels (Cpss) increased linearly from 0.4 microM to 3.1 microM at dose levels ranging from 1 to 5.9 mg/m2 per h (actual body weight); the mean total body clearance was 146 +/- 38 ml/min per m2. CPE-C was eliminated by both renal excretion of intact drug and deamination to cyclopentenyl uracil in an apparent 2:1 ratio. CTP synthase activity in intact bone marrow mononuclear cells was inhibited by 58% to 100% at 22 h compared to matched pretreatment samples at all CPE-C dose levels. When all data were combined, flux through CTP synthase was decreased by 89.6% +/- 3.1% at 22 h (mean +/- SE, n = 16), and remained inhibited by 67.6% +/- 7.7% (n = 10) for at least 24 h post-CPE-C infusion. Granulocyte and platelet toxicities were dose-dependent, and dose-limiting myelosuppression occurred during the initial cycle in two of three patients treated with 5.9 mg/m2 per h. Four of 11 patients (4 of 20 cycles) who received 4.7 mg/m2 per h CPE-C experienced hypotension 24-48 h after completion of the CPE-C infusion during their first (n = 2), third (n = 1) and sixth cycles (n = 1), respectively. Two of these patients died with refractory hypotension despite aggressive hydration and cardiopulmonary resuscitation. One of 12 patients (28 total cycles) treated with 3.5 mg/m2 per h CPE-C experienced orthostatic hypotension during cycle 1, and this patient had a second episode of orthostatic hypotension at a lower dose (3.0 mg/m2 per h). Hypotension was not seen in patients receiving < or = 2.5 mg/m2 per h CPE-C.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1995

Induction at high incidence of ductal prostate adenocarcinomas in NBL/Cr and Sprague-Dawley Hsd:SD rats treated with a combination of testosterone and estradiol-17 beta or diethylstilbestrol.

This study determined the incidence of prostate adenocarcinoma following long-term treatment of NBL and Sprague-Dawley rats with estradiol-17 beta or diethylstilbestrol (DES) plus testosterone and it defined the origin of these tumors. NBL and Sprague-Dawley rats were treated with two Silastic tubing implants (i.d. 1.6 mm, o.d. 3.2 mm) containing a 2 cm long filling of testosterone and one implant containing a 1 cm long filling of estradiol-17 beta or DES. Control animals received empty implants. Treated animals were killed when moribund and controls were killed at 91 (NBL) or 75 (Sprague-Dawley) weeks after initiation of treatment and accessory sex glands were sampled for histopathological examination of multiple step sections. Prostatic adenocarcinoma occurred in 100% of NBL rats after treatment with estradiol-17 beta or DES plus testosterone for 44 and 59 weeks (group means) respectively. Adenocarcinoma incidences were lower in Sprague-Dawley rats. The adenocarcinomas were small, microscopic, invasive tumors and they were spatially closely associated with the periurethral ducts of the dorsal, lateral and/or anterior (= coagulating gland) prostate, but never with the ducts of the ventral lobe and seminal vesicles. One adenocarcinoma was of uncertain origin. Duct-acinar dysplastic lesions occurred in the periphery of the dorsal and lateral prostate of all hormone-treated NBL and many Sprague-Dawley rats, but did not appear to give rise to carcinoma. Although some adenocarcinomas were contiguous with dysplastic ducts of the peripheral dorsolateral prostate, the main mass of these neoplasms was located in the periurethral area. Also, most adenocarcinomas were only connected with the periurethral ducts, in which atypical hyperplasia occurred following hormone treatment for 36 weeks or longer. Thus atypical hyperplasia of the periurethral prostate ducts, but not peripheral duct-acinar dysplasia, appeared to be the likely precursor of the induced carcinomas. Testosterone plus DES, but not estradiol-17 beta, induced marked dysplasia-like lesions in the acini of the ventral prostate of all NBL and many Sprague-Dawley rats. These lesions had progressed to carcinoma in situ (or adenoma) in 46% of NBL rats.

Adenoma↗
PubMed1995

Improved synthesis of zebularine [1-(beta-D-ribofuranosyl)-dihydropyrimidin-2-one] nucleotides as inhibitors of human deoxycytidylate deaminase.

The 2'-deoxy (2a) and 2'-ara-fluoro (3a) derivatives of zebularine [1-(beta-D-ribofuranosyl)-dihydropyrimidin-2-one, 1a] were phosphorylated in high yield to the 5'-nucleotides 2b and 3b, respectively, and characterized by HPLC, enzyme degradation, 1H, 13C and 31P NMR, and high resolution mass spectral analysis. Their inhibitory activity against partially purified MOLT-4 deoxycytidylate deaminase (dCMPD) in the presence of the allosteric effector deoxycytidine triphosphate (dCTP) and Mg+2 ion was examined. Compounds 2b and 3b inhibited dCMPD with Ki values of 2.1 x 10(-8) M and 1.2 x 10(-8) M, respectively. The parent nucleotide, zebularine monophosphate 1b was ineffective at concentrations > 100 mumol. The effect of the nucleosides, 1a-3a, as well as tetrahydrouridine (THU) and 2'-deoxy THU (dTHU), on the cellular production of DNA precursors was examined in human MOLT-4 peripheral lymphoblasts. It was shown that 1a, 2a and 3a all elevated intracellular dCTP and TTP levels in whole cells with the most powerful effect elicited by 1a. The 2'-fluoro derivative 3a was chemically phosphorylated much more cleanly and higher yield than 2a, without the formation of diphosphorylated by-products. This compound was found to be infinitely less sensitive to acid-catalyzed degradation than 2a. Since the substitution of fluorine for hydrogen had a slight potentiating effect on the dCMPD inhibitory activity while stabilizing the compound toward acid-catalyzed and enzymatic depyrimidination, compound 3b emerges as a very attractive tool for the pharmacological modulation of pyrimidine deaminase activity.

Cell Line↗
PubMed1994

Inhaled nitric oxide in congenital diaphragmatic hernia.

Pulmonary hypertension is a major complication of congenital diaphragmatic hernia (CDH). Inhaled nitric oxide (NO) is a selective pulmonary vasodilator because it produces vasodilatation of the pulmonary vasculature without systemic hypotension. In experimental and clinical studies, inhaled NO ameliorates pulmonary hypertension and improves gas exchange. The goal of the present study was to determine the extent to which infants with CDH respond to inhaled NO. Four newborn infants with CDH complicated by severe respiratory insufficiency and right-to-left shunting received inhaled NO. In three patients, postductal oxygenation improved in response to small concentrations of NO (5 to 10 ppm); two received NO after operative repair, and the third both before and after repair. However, tachyphylaxis developed in all cases within 1 to 6 days. A fourth patient received inhaled NO in an attempt at weaning from ECMO. He did not respond, remaining hypoxic despite 80 ppm NO, and continued to require ECMO. In the three patients who responded to inhaled NO, plasma nitrites and nitrates (stable oxidative end products of NO) accumulated over time, but not in the patient who did not respond. The accumulation of nitrite and nitrate in plasma may reflect alveolar-capillary NO absorption, and may identify patients who will respond to continued inhaled NO. Methemoglobin remained below 1.9% in all four babies. Selected infants with CDH may respond to NO, but the benefit may be temporary.

Administration, Inhalation↗
PubMed1994

Protracted venous infusion 5-fluorouracil and interferon-alpha in advanced and refractory colorectal cancer.

BACKGROUND: The management of patients with advanced colorectal cancer remains dependent on the optimal use of 5-Fluorouracil (5-FU). Enhanced 5-FU activity can be achieved by either adding a modulator or by altering the administration schedule, in particular using a protracted venous infusion. Based on encouraging phase II data using bolus 5-FU and interferon-alpha, we designed a study to investigate the activity of this modulator in patients with colorectal cancer refractory to protracted venous infusion 5-FU. PATIENTS AND METHODS: Patients with advanced colorectal cancer were treated with 5-FU (300 mg/m2/day) given as a protracted venous infusion via an indwelling central venous catheter and portable battery driven pump. At the time the tumour became refractory to 5-FU, interferon-alpha was added and further outcome evaluated. RESULTS: One hundred twenty-four patients were entered on the study, 118 of whom had measurable disease. Fifty-two patients had previously received chemotherapy. The overall tumour response rate with infusional 5-FU was 33% (38/118), however in previously untreated patients was 42% (29/69) and 18% in those given prior chemotherapy (9/49). At the point of refractory disease 64 patients had interferon-alpha added to the 5-FU. Five patients (8%) showed an objective partial response following interferon-alpha addition. Patient toxicities on infusional 5-FU included hand-foot erythroderma, stomatitis and diarrhoea. There were only 15 episodes of grade 3 or 4 toxicity. The addition of interferon-alpha gave fever, lethargy, myelosuppression and depression, but did not increase the incidence or severity of 5-FU related toxicities. Of 67 patients with tumour related pain, 53 (79%) had an improvement in their symptoms. Median survival of the whole group was 7.5 months. CONCLUSIONS: Protracted venous infusion 5-FU is an active and well tolerated palliative treatment for advanced colorectal cancer. The addition of interferon-alpha at the point of 5-FU refractory disease resulted in further significant response in a small number of patients. Further randomised studies, including quality-of-life end-points, are needed before the use of interferon-alpha can be recommended as a modulator of 5-FU in the clinical setting.

Adult↗
PubMed1994

A phase II study in advanced gastro-esophageal cancer using epirubicin and cisplatin in combination with continuous infusion 5-fluorouracil (ECF).

PURPOSE: A phase II study was performed in patients with unresectable or metastatic gastric cancer evaluating the efficacy of a new chemotherapy schedule combining epirubicin and cisplatin with a continuous ambulatory infusion of 5-fluorouracil (ECF). PATIENTS AND METHODS: One hundred thirty-nine consecutive, previously untreated patients were given ECF. Of these, 128 had measurable disease. Epirubicin (50 mg/m2 i.v.) and cisplatin (60 mg/m2 i.v.) were administered every three weeks for 8 cycles during a 21 week continuous i.v. infusion of 5-fluorouracil (200 mg/m2/day). In total 773 cycles of chemotherapy were given. RESULTS: Objective tumour responses was seen in 91 (71%) of the 128 patients with measurable disease, of which 15 (12%) had a complete response. Twenty patients with locally advanced disease responding to ECF had attempted resection of the primary--11 (55%) were completely removed, 4 of these had no residual tumour in the resected specimen. The overall median survival was 8.2 months with 1 and 2 year survivals of 30% and 10% respectively. Grade 3 or 4 emesis occurred in 13%, stomatitis in 7%, diarrhoea in 4%, infection in 6%, leucopenia in 21% and thrombocytopenia in 8% of patients. Myelosuppression delayed treatment in 39 (5%) of the 773 cycles. Six of the 139 patients (4.3%) had treatment related deaths. There was no measurable reduction in quality of life during chemotherapy, while 67% of the 66 patients with dysphagia had complete resolution of this symptom. CONCLUSIONS: The ECF regimen displays high anti-tumour activity with moderate toxicity in patients with gastric cancer and in some cases enabled resection of previously inoperable tumours.

Adenocarcinoma↗
PubMed1994

Bacterial meningitis in Swaziland: an 18 month prospective study of its impact.

STUDY OBJECTIVE: To describe the epidemiology, clinical features, and outcome of bacterial meningitis in Swaziland. DESIGN: Prospective study of patients diagnosed as having meningitis of nonviral aetiology during an 18 month period from February 1991 to July 1992. SETTING: Four regional hospitals covering the population of the four districts in Swaziland. SUBJECTS: All patients with non-viral meningitis admitted to hospital within the study period. MAIN RESULTS: Altogether 85 patients were reported to have bacterial meningitis: 48.3% were aged under 1 year. Causative organisms were identified in 60% of cases, and Streptococcus pneumoniae was found to be the commonest (49% of cases). Overall, case fatality was 38.8% for all age groups, and 62.5% (15 of 25) for adults. Neurological sequelae occurred in 22.4%. Three of the adult cases were HIV seropositive. Seizures, but not duration of symptoms before admission, were associated with a poor prognosis. There was a significant rise in incidence related to a period of drought. Fifteen patients were reported with tuberculous meningitis, of whom five were known to be HIV seropositive; the case fatality was 73.3%. CONCLUSIONS: The aetiology and age distribution of cases of meningitis differs greatly from that in developed countries. Rising HIV infection may have an important impact on the future incidence of meningitis. The high case mortality found should encourage efforts towards earlier diagnosis and treatment, and strengthens the need to develop appropriate vaccines.

Adolescent↗
PubMed1993

Resistance to cyclopentenylcytosine in murine leukemia L1210 cells.

Cyclopentenyl cytosine (CPEC) exhibits oncological activity in murine and human tumor cells and has now entered Phase I clinical trials. Its mode of action as an antitumor agent appears to be inhibition by its triphosphate (CPEC-TP) of CTP synthase, the enzyme which converts UTP to CTP. In an attempt to elucidate the mechanism of resistance to CPEC, a murine leukemia cell line resistant to CPEC (L1210/CPEC) was developed by N-methyl-N-nitro-N-nitrosoguanidine-induced mutagenesis and subsequent selection by cultivation of the L1210 cells in the presence of 2 microM CPEC. Resistant clones were maintained in CPEC-free medium for 6 generations before biochemical studies were performed. The resistant clone selected for further studies was approximately 13,000-fold less sensitive to growth inhibition by CPEC than the parental cells, and the concentration of CPEC required to deplete CTP in the resistant cells was 50-fold higher than in the sensitive cells. A comparison of the kinetic properties of CTP synthase from sensitive and resistant cells indicated alteration in the properties of the enzyme from the latter; the median inhibitory concentration for CPEC-TP increased from 2 to 14 microM, Km for UTP decreased from 126 to 50 microM, and Vmax increased 12-fold from 0.2 to 2.3 nmol/mg/min. Northern blot analyses of polyadenylated RNA from the resistant and sensitive cells indicated a 3-fold increase in transcripts of the CTP synthase gene in the resistant line. Consistent with these alterations in the properties of the enzyme, the resistant cells exhibited significantly expanded CTP and dCTP pools (4- 5-fold) when compared with the sensitive cells. No change was observed, however, in the properties of uridine-cytidine kinase, the enzyme responsible for the initial phosphorylation of CPEC; despite this, however, cellular uptake of CPEC was greatly decreased, and phosphorylation of CPEC and its incorporation into RNA were 10-fold less than in the parental cells. These latter observations are most readily explained by feedback inhibition by the increased CTP levels of the resistant cells of uridine-cytidine kinase and/or of the membrane transport process used for initial entry of CPEC.

Animals↗
PubMed1993

Measurement of cyclopentenyl cytosine 5'-triphosphate in vitro and in vivo by multidimensional high-performance liquid chromatography.

Cyclopentenyl cytosine 5'-triphosphate (CPEC-TP) is the active metabolite of the investigational drug cyclopentenyl cytosine (CPEC), a nucleoside analogue which exhibits noteworthy antineoplastic activity against several murine and human tumors in tissue culture, and which is now undergoing Phase I clinical trials. This study describes a method to measure the intracellular CPEC-TP levels in peripheral blood mononuclear cells (PBM cells) from patients treated with CPEC, without using radiolabeled drug. The method utilizes on-line multidimensional high-performance liquid chromatography (HPLC) with two columns of different retention mechanisms connected via an automated programmable switching valve. The elution fraction containing CPEC-TP is initially separated from cellular components using a gel sizing column (TSK-G2000-SW) and then rechromatographed by means of a reversed-phase column operated in an ion-pairing mode (YMC-A-312-ODS). The limit of quantitation of CPEC-TP by this method is 2.5 pmol per injection. When CPEC-TP levels were measured in PBM cells from 12 cancer patients after 20 h continuous infusion of CPEC at doses ranging from 3.5 to 5.9 mg/m2/h, the levels attained ranged from 1.4 to 13.4 microM (3.6 to 33.5 pmol/10(7) cells). However, wide variability in the concentrations of CPEC-TP achieved were evident at each dose and did not appear to correlate either with the CPEC dose or with CPEC plasma levels. This method was validated by a comparison of the quantitation of CPEC-TP in cultured PBM cells and Molt-4 cells (a human T-cell line adapted for growth in tissue culture) after incubation with both unlabeled and radiolabeled CPEC.

Animals↗
PubMed1993

Is early discharge following isolated splenic injury in the hemodynamically stable child possible?

Nonoperative treatment of splenic injury is well accepted. Two questions have not been answered. (1) What is the intensity of monitoring required in the hemodynamically stable patient? (2) How long do patients need to be hospitalized? Ninety-one patients having computed tomography (CT) or surgically proven splenic injury were treated between September 1986 and September 1991. Excluded from the study were 16 patients requiring operation and 22 patients having multiple system injuries. All operations occurred within 24 hours of admission. No transfusions were required later than 48 hours following admission. The remaining 53 patients (58%) constitute the study group. CT classification of Buntain indicated 6 class I, 21 class II, 24 class III, and 2 class IV injuries. The mean Injury Severity Score (ISS) for the group was 6.98 +/- 3.43. Serial hematocrits for the patients treated without transfusions were followed until three consecutive determinations showed no change. The lowest average hematocrit for the nontransfused group was 30.96% +/- 4.47% and occurred on day 2.06 +/- 0.76. Eleven patients (23%) had left-sided pleural effusions that resolved without intervention. One patient had an ileus for 3 days. CT or ultrasound examination was obtained on day 5 to 7 to document healing before the patient was allowed out of bed and discharged. The average hospital stay was 7.06 +/- 2.24 days. Twenty-two patients were initially observed in the intensive care unit (ICU). Clearly the interval between hematocrit stability (average, 2.06 days) and discharge (average, 7.06 days) constitutes a time of minimal nursing care while utilizing bed space and health care dollars.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

In vitro anti-human immunodeficiency virus (HIV) activities of transition state mimetic HIV protease inhibitors containing allophenylnorstatine.

Transition state mimetic tripeptide human immunodeficiency virus (HIV) protease inhibitors containing allophenylnorstatine [(2S,3S)-3-amino-2-hydroxy-4-phenylbutyric acid] were synthesized and tested for activity against HIV in vitro. Two compounds, KNI-227 and KNI-272, which were highly potent against HIV protease with little inhibition of other aspartic proteases, showed the most potent activity against the infectivity and cytopathic effect of a wide spectrum of HIV strains. As tested in target CD4+ ATH8 cells, the 50% inhibitory concentrations of KNI-227 against HIV type 1 LAI (HIV-1LAI), HIV-1RF, HIV-1MN, and HIV-2ROD were 0.1, 0.02, 0.03, and 0.1 microM, respectively, while those of KNI-272 were 0.1, 0.02, 0.04, and 0.1 microM, respectively. Both agents completely blocked the replication of 3'-azido-2',3'-dideoxythymidine-sensitive and -insensitive clinical HIV-1 isolates at 0.08 microM as tested in target phytohemagglutinin-activated peripheral blood mononuclear cells. The ratios of 50% cytotoxic concentrations to 50% inhibitory concentrations for KNI-227 and KNI-272 were approximately 2,500 and > 4,000, respectively, as assessed in peripheral blood mononuclear cells. Both compounds blocked the posttranslational cleavage of the p55 precursor protein to generate the mature p24 Gag protein in stably HIV-1-infected cells. The n-octanol-water partition coefficients of KNI-227 and KNI-272 were high, with log Po/w values of 3.79 and 3.56, respectively. Degradation of KNI-227 and KNI-272 in the presence of pepsin (1 mg/ml, pH 2.2) at 37 degrees C for 24 h was negligible. Current data warrant further careful investigations toward possible clinical application of these two novel compounds.

Antiviral Agents↗
PubMed1993

Bilateral carcinoma of the breast.

In a retrospective review of 2820 patients with breast carcinoma seen at the Combined Breast Clinic of St George's Hospital over a 23-year period 101 cases were bilateral of which 52 (1.8%) presented synchronously and 49 (1.7%) metachronously. Twenty deaths occurred in the synchronous group after a mean follow-up of 56.2 months and 15 deaths in the metachronous group after a mean follow-up of 48.5 months following diagnosis of the second tumour. If timed from initial presentation patients with metachronous tumours fared better than those with unilateral disease (P < 0.01). There was no significant difference in survival between patients with metachronous (if timed from the second tumour), synchronous or unilateral breast carcinoma.

Breast Neoplasms↗
PubMed1991

Cellular pharmacology of cyclopentenyl cytosine in Molt-4 lymphoblasts.

The toxicity, uptake, and metabolism of the oncolytic nucleoside cyclopentenyl cytosine (CPEC) have been examined in the Molt-4 line of human lymphoblasts. This compound is known to be converted to its 5'-triphosphate, which inhibits CTP synthetase and depletes the pools of cytidine nucleotides. In the Molt-4 system, the concentration of drug reducing proliferation by 50% in a 24-h incubation was between 50 and 100 nM. Cytidine, uridine, and nitrobenzylthioinosine almost fully prevented the cytotoxicity of CPEC when introduced shortly before or together with the drug, but only cytidine was effective as an antidote when added 12 h after 200 nM CPEC. Studies of the cellular entry of CPEC revealed that nitrobenzylthioinosine fully blocked this process over a 60-s interval and for as long as 2 h, suggesting that the initial interiorization was mediated by facilitated diffusion. In Molt-4 cells incubated with tritiated CPEC, 9 metabolites could be distinguished: prominent among these was cyclopentenyl uridine (CPEU), the deamination product of CPEC; other major metabolites included the 5'-mono-, di-, and triphosphates of CPEC, and of CPEU, along with two phosphodiesters provisionally identified as CPEC-diphosphate choline and CPEC-diphosphate ethanolamine. When the accumulation of CPEC-5'-triphosphate was measured as a function of concentration of the drug in the medium, the process was found not to be saturable by levels of CPEC up to 1000 nM. In cells incubated with 200 nM drug, CPEC-5'-triphosphate accumulated rapidly and linearly for approximately 4 h, the time for doubling of the concentration being 2 h. After a 16-h incubation with 100 nM CPEC, the concentration of CPEC-5'-triphosphate was 50-fold that of the parent drug in the medium and could be readily monitored spectrophotometrically in high-pressure liquid chromatography effluents without recourse to radiolabeled nucleoside. In 2-h incubations, the concentration of free CPEC required to reduce CTP by 50% was 150 nM; this corresponded to a CPEC-5'-triphosphate level of 750 nM. After washout of extracellular CPEC, CPEC-5'-triphosphate decayed with a half-life that ranged from 9 to 14 h. Twenty-four h after washout of 200 nM CPEC (the concentration of drug reducing proliferation by 80%), cells had not resumed proliferation, and CTP pools were still depressed by 90%. Cytidine, uridine, and nitrobenzylthioinosine all strongly repressed the anabolic phosphorylation of CPEC when added to Molt-4 cells along with the drug.(ABSTRACT TRUNCATED AT 400 WORDS)

Antineoplastic Agents↗