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Low-dose phosphonacetyl-L-aspartate (PALA) may potentiate both 5-fluorouracil (5-FU) incorporation into RNA and thymidylate synthase inhibition by 5-fluorodeoxyuridylate (5-FdUMP). The gastrointestinal toxicity of 5-FU is not increased by PALA administration. Exogenous leucovorin, on the other hand, which enhances thymidylate synthase inhibition, appears to increase the clinical toxicity of 5-FU in a dose-dependent manner. As a result, the clinical use of high-dose leucovorin requires a marked dose reduction of 5-FU. Extracellular leucovorin levels of 1 microM suffice to maximize the enhancement of thymidylate synthase inhibition in several models. We conducted a trial to add leucovorin to the PALA/5-FU regimen. We chose a leucovorin dose that was predicted to yield end-infusion total reduced folate concentrations of 1 microM. The major endpoint was to determine the maximum tolerated dose of 5-FU in this combination. The regimen consisted of 250 mg/m2 PALA given on day 1 and, 24 h later, escalating 5-FU doses ranging from 1,850 to 2,600 mg/m2 admixed with 50 mg/m2 leucovorin and given by 24-h infusion. Courses were repeated weekly. A total of 24 patients with a median performance status of 1 were entered at three dose levels. Diarrhea was dose-limiting; 6/13 patients had grade II or worse diarrhea at 2,600 mg/m2. Dose modification resulted in a mean dose intensity of 2,300 mg/m2 at both the 2,600- and 2,300-mg/m2 dose levels. The 2,300-mg/m2 dose is suitable for phase II testing of this regimen. Three patients (two with breast cancer and 1 with sarcoma) had a partial remission. We measured steady-state concentrations (Css) of 5-FU in 23 patients. The mean Css increased with dose from 0.738 to 1.03 micrograms/ml. Total body clearance did not vary with dose in this range. Patients with grade II or worse diarrhea had a higher mean Css (1.10 +/- 0.19) than those with grade O or I toxicity (0.835 +/- 0.25, P < 0.02). Total bioactive folates (bound and free) were measured using a biological assay. Pretreatment values ranged from 2 to 52 nM and were not predictive of toxicity. End-infusion (23-h) values were somewhat lower than predicted and ranged from 400 to 950 nM. The risk of diarrhea was positively correlated with end-infusion total folate values. In a logistic regression analysis, total folate values obtained at 23 h were a more powerful predictor of diarrhea than were 5-FU Css values.(ABSTRACT TRUNCATED AT 400 WORDS) [ABSTRACT FROM AUTHOR]

Children with acute lymphocytic leukemia (ALL) in remission were treated with overlapping sequential infusions of methotrexate (MTX) and 1-beta-D-arabinofuranosylcytosine (araC) as part of continuation therapy. The doses and the sequence were chosen to mimic conditions that produced greater than additive antineoplastic activity with these two drugs in preclinical studies. To assess the potential for the drug combination to exhibit greater than additive effect in vivo, we investigated several biochemical parameters that had been associated with synergism in vitro. Because the patients were in remission, the intracellular parameters could only be measured in cytologically normal hematopoietic cells. We observed that (1) the mean plasma concentrations of MTX and araC were above those required to obtain a greater than additive cytotoxicity with the two drugs in tissue culture; (2) MTX did not have a significant antipurine effect in bone marrow mononuclear cells; (3) the mean intracellular concentration of deoxycytidine triphosphate (dCTP) was significantly lower after treatment with the drug combination than after therapy with araC alone; and (4) the ratio of araC triphosphate (araCTP) to dCTP was 2.6 times higher after treatment with the combination than after araC alone. These results indicate that it is possible to achieve in patients the biochemical conditions associated with the greater than additive antineoplastic activity of MTX and araC in vitro. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the pharmacokinetics and toxicity of high-dose intravenous (i.v.) methotrexate (MTX) with leucovorin in patients with meningeal carcinomatosis., Methods: Of 16 eligible patients entered on this study, 13 with meningeal carcinomatosis from breast cancer, lung cancer, or osteosarcoma were treated with MTX at loading doses of 200-1500 mg/m2, followed by a 23-h infusion of 800-6000 mg/m2. Three patients without meningeal disease were also treated and the cerebrospinal fluid (CSF) MTX concentrations were compared in patients with and without central nervous system (CNS) disease., Results: Patients without CNS disease had lower CSF MTX concentrations relative to the plasma MTX levels than those with CNS disease, who all had CSF MTX concentrations above the target cytotoxic concentration (1 microM). The CSF MTX concentrations correlated better with the free and the total plasma MTX concentrations than with the doses. The mean half-life of CSF MTX was 8.7 +/- 3.4 h. The mean plasma clearance of MTX was not significantly different in patients with CNS disease (84 +/- 41 ml/min per m2) versus without CNS disease (59 +/- 38 ml/min per m2). All toxicities were grade 2 or less except grade 3 hematologic toxicity. No patient had an objective response in the CSF., Conclusion: This trial demonstrates that potentially cytotoxic CSF MTX concentrations (> 1 microM) are delivered safely by i.v. infusion, a less invasive and better distributed CSF therapy compared with intrathecal MTX. Because of the excellent pharmacokinetics and toxicity, high-dose i.v. MTX should be evaluated at a loading dose of 700 mg/m2 and a 23-h infusion of 2800 mg/m2 with leucovorin in less heavily pretreated patients with carcinomatous meningitis.

Lometrexol inhibits the first folate-dependent enzyme in de novo purine biosynthesis and is avidly polyglutamated and retained in tissues expressing folylpolyglutamate synthetase. Although clinical studies have been limited by cumulative toxicity, preclinical studies show that pretreatment with folic acid can protect normal tissue while maintaining tumor cytotoxicity. Therefore, a Phase I study of lometrexol every 21 days preceded by i.v. folic acid was initiated. Lometrexol was studied in six patients at 15 mg/m2, in six patients at 20 mg/m2, in three patients at 25 mg/m2, and in nine patients at 30 mg/m2. Patients received either 5 mg of folic acid 1 h before or 25 mg/m2 3 h before lometrexol. Blood samples were obtained around the first course and weekly thereafter for determination of plasma and erythrocyte (RBC) lometrexol concentrations. Bioactive folates in plasma and RBCs were determined in a subset of patients. Lometrexol pharmacokinetics were best described by a three-compartment model. Mean clearance and volume of distribution were 1.6 +/- 0.6 liters/h/m2 and 8.9 +/- 4.1 liters/m2. Mean half-lives were 0.23 +/- 0.1, 2.9 +/- 1.4, and 25.0 +/- 48.7 h. Pharmacokinetics were independent of either lometrexol or folic acid dose. In the weekly blood samples, RBC lometrexol levels rose, long after plasma lometrexol was undetectable. RBC lometrexol levels were independent of folic acid or lometrexol dose. Bioactive folates measured in plasma and RBCs during this same time period did not accumulate. Rising RBC levels were correlated with a fall in hematocrit, hemoglobin, and platelet count. This study indicates that the cumulative toxicity of lometrexol is related to tissue concentration and not plasma pharmacokinetics. RBC lometrexol may be an indicator of cumulative drug exposure and effect.

In this Phase I study, the maximally tolerated doses (MTDs) of i.p. iododeoxyuridine (IdUrd) alone and in combination with i.v. calcium leucovorin (LV) were determined. The pharmacokinetics and pharmacological advantage of IdUrd were evaluated, and flow cytometric analysis allowed examination of the extent of incorporation of IdUrd into tumor cells with and without the addition of i.v. LV. Thirty-nine patients with advanced neoplasms primarily confined to the peritoneal space were enrolled in a dose-escalation trial using 4-h dwells of IdUrd administered i.p. daily for 4 days with and without an i.v. infusion of LV 500 mg/m2/day for 4.5 days. Twenty-three patients received single-agent therapy, and 13 patients received i.p. IdUrd in combination with i.v. LV. The MTD of single-agent IdUrd administered on this schedule was 4125 mg/m2/day for 4 days; and that of the IdUrd in combination was 3438 mg/m2/day. Dose-limiting toxicities were myelosuppression and stomatitis. During the period of the dwell, the peritoneal AUC (area under the curve) of IdUrd exceeded the plasma AUC of IdUrd by one or two orders of magnitude in all patients at all doses tested; there was a possible effect of LV on peritoneal AUC. The geometric mean pharmacological advantage (AUCperitoneal/ AUCplasma) was 181 at 625 mg/m2/day and 90 at 4538 mg/m2/day. Flow cytometric analysis suggests saturation of IdUrd measured in DNA at the 2500-3125 mg/m2 dose level, without an increase after the addition of LV. Twelve patients received 4-12 courses of therapy. One patient with recurrent ovarian cancer who received 16 courses of therapy experienced complete resolution of her ascites, near normalization of CA-125 levels, and improved quality of life; two patients with high-risk tumors receiving "adjuvant" therapy are disease-free at 3 and 6 years after treatment; other patients experienced transient clearing of ascites. The recommended Phase II dose of i.p. IdUrd using a 4-h dwell daily for 4 days is 3750 mg/m2/day alone or 3125 mg/m2/day in combination with continuous i.v. LV at 500 mg/m2/day for 4.5 days. Although flow cytometric data suggest that DNA incorporation of IdUrd is not affected by the addition of LV, the cytotoxicity of the combination regimen may be increased due to LV-enhanced, IdUrd-related inhibition of thymidylate synthase. For this reason, we recommend that efficacy studies of the combination continue in parallel with studies of IdUrd alone.

A group of 18 patients with advanced cancer were entered on a phase I study of a 120-h continuous intravenous infusion of hydroxyurea. The dose of hydroxyurea was escalated in cohorts of patients from 1 to 2 to 3.2 g/ m2 per day. The primary dose-limiting toxicity was neutropenia, often accompanied by leukopenia, thrombocytopenia and generalized skin rash. Prophylactic treatment of patients with dexamethasone and diphenhydramine hydrochloride prevented the skin rash, but not the hematopoietic toxicities. The pharmacokinetics of hydroxyurea were studied in all patients. The steady-state concentrations of hydroxyurea were linearly correlated with the dose (R2 = 0.71, n = 18, P < 0.0001). The mean +/- SE concentrations were 93 +/- 16, 230 +/- 6 and 302 +/- 27 microM at 1, 2 and 3.2 g/m2 per day, respectively. The mean +/- SE renal and nonrenal clearances of hydroxyurea were 2.14 +/- 0.18 and 3.39 +/- 0.28 l/h per m2 (n = 16), neither of which correlated with the dose. The concentration of hydroxyurea in plasma decayed monoexponentially with a mean +/- SE half-life of 3.25 +/- 0.18 h (n = 17). The steady-state concentration of hydroxyurea was > 200 microM in all nine patients treated at 2 g/m2 per day, a dose which was well tolerated for 5 days. We recommend this dose for phase II trials in combination with other antineoplastic agents.

Twenty-seven patients with advanced cancer were entered in a phase I study of bolus i.v. 5-fluorouracil at a dose of 370 mg/m2/day for 5 days combined with a continuous i.v. infusion of (6S)-folinic acid for 5.5 days, starting 24 h in advance of the first 5-fluorouracil dose. The dose of (6S)-folinic acid was escalated in cohorts of patients from 250 mg/m2/day to a maximum of 1000 mg/m2/day. The pharmacokinetics of (6S)-folinic acid were studied in the 3 patients given 250 mg/m2/day and in 6 patients given 1000 mg/m2/day. The mean steady-state plasma concentrations of (6S)-folinic acid and its principal metabolite (6S)-5-methyltetrahydrofolate at the 250 mg/m2/day dose were 2.7 and 5.1 microM, respectively. Both concentrations were comparable to the concentrations produced when (6S)-folinic acid was administered as half of a (6R,S)-folinic acid mixture (E. M. Newman et al., Cancer Res., 49:5755-5760, 1989). At the 1000 mg/m2/day dose of (6S)-folinic acid, the concentration of (6S)-folinic acid was 15.3 microM, more than the 4-fold increase predicted by linear pharmacokinetics, while the concentration of (6S)-5-methyltetrahydrofolate was only 16.5 microM. The change in the ratio of the parent compound to its metabolite was accounted for by a decrease in the nonrenal clearance of (6S)-folinic acid, probably indicating saturation of its metabolism. The toxicities observed in this phase I trial, including stomatitis, diarrhea, neutropenia, and anemia, did not differ in nature or severity from those produced by 5-fluorouracil and (6R,S)-folinic acid when administered on the same schedule. Finally, the degree of toxicity did not appear to depend on the dose of (6S)-folinic acid over the range of doses tested.

Because of the synergy seen in adult trials when 5-fluorouracil is combined with leucovorin, we initiated a Phase I trial of this combination in children's refractory cancer. Leucovorin, an equal mixture of the (6R,S)-diastereoisomers, was administered p.o. for 6 consecutive days as 4 equal doses at 0, 1, 2, and 3 h totaling 500 mg/m2/day. 5-Fluorouracil was given daily on days 2 to 6 as an i.v. bolus immediately following the last dose of leucovorin. The leucovorin dose was held constant while the 5-fluorouracil dose was escalated in cohorts of patients from 300 mg/m2/day to its maximally tolerated dose. Thirty-five patients (19 with acute leukemia and 16 with solid tumors) were evaluable for toxicity. The maximally tolerated dose of FUra was 450 mg/m2/day for 5 treatments for patients with solid tumors and 650 mg/m2/day for 5 treatments for the children with leukemia. The dose-limiting toxicities were myelosuppression and stomatitis. Other side effects included transient, mild elevations of serum transaminases, mild nausea, vomiting, and diarrhea. The pharmacokinetics of high-dose p.o. leucovorin was studied in 23 children. There was considerable interpatient variability in the plasma concentrations of total bioactive folates (TBAF), (6S)-leucovorin, and (6S)-5-methyltetrahydrofolic acid. The maximum plasma concentration (Cmax) of TBAF was 821 +/- 97 (SE) nM, occurring at a median of 8 h; the Cmax of (6S)-leucovorin was 77 +/- 11 nM, occurring at 4 h. The TBAF concentration fell to 146 +/- 42 nM by 24 h. (6S)-5-Methyltetrahydrofolic acid accounted for 90 +/- 7% of the TBAF at the Cmax. The plasma concentration of (6R)-leucovorin, the unnatural isomer, was equal to that of TBAF. Thus, p.o. leucovorin reduced the 5-fold excess of (6R)-leucovorin over TBAF seen after i.v. doses. The relative amounts of the three major plasma species were approximately the same as in adults, even though the Cmax of each compound was lower.

The replication of Sarcoma 180 cells in culture was inhibited by 3,6-dihydroxy-4,5-dimethylphthalaldehyde (HMPA). The inhibition of growth caused by HMPA was evident after treatment of cells with drug for only 15 min. This exposure period caused decreased in (a) cloning efficiency, (b) transport and/or phosphorylation of [3H]thymidine and [3H]uridine, (c) incorporation of radioactive nucleosides into acid-insoluble material, and (d) incorporation of [3H]leucine into protein. Examination of the cytotoxicities of the model compounds 2,3,5,6-tetramethyl-1,4-dihydroquinone (durohydroquinone) and o-phthalaldehyde indicated that the dialdehyde portion of the molecule was responsible for the cytocidal effects of HMPA. The ratio of adenosine triphosphate to adenosine diphosphate in the acid-soluble fraction of Sarcoma 180 cells incubated in vitro with HMPA for 45 min was reduced in a concentration-dependent manner. The reduction in the ATP pool size produced by HMPA contrasts with the action of the periodate oxidation product of cytidine dialdehyde, which has been reported to increase the intracellular concentration of adenosine triphosphate.

Some properties of the human ovarian carcinoma line A2780 and a subline three times more resistant than the parent line to cisplatin are compared in this report. The rates of uptake and release of cisplatin were similar in the two cell lines. Resistance to cisplatin was associated with: (a) cross-resistance to 5-fluorouracil and methotrexate; (b) a 2.5-fold increase in thymidylate synthase, as measured by both enzyme activity and the capacity to complex 5-fluorodeoxyuridylate; and (c) an increase in the intracellular pools of 5,10-methylenetetrahydrofolate and tetrahydrofolate. These data suggest that cross-resistance to 5-fluorouracil and methotrexate in A2780 cells may be a consequence of increases in their respective target enzymes.

The pharmacokinetics of etoposide at doses of 1 gm/m2 to 3 gm/m2 were studied in patients with hematologic malignancies. The noncompartmental systemic clearance, mean residence time, steady-state volume of distribution, and elimination half-life were independent of the dose of etoposide, whereas the AUC was proportional to the dose. Comparison of these results with those reported previously indicates that etoposide exhibits linear pharmacokinetics over a thirtyfold range in doses (0.1 to 3 gm/m2).

The effects of amino acid deprivation and treatment with amino alcohols upon the growth, viability, and susceptibility to methotrexate (MTX) cytotoxicity were examined in BALB/3T3 cells and their virally transformed counterparts, SV-T2 cells. Cells were deprived of either histidine or tyrosine plus phenylalanine, or they were treated with amino alcohol analogues of histidine and tyrosine (histidinol and tyrosinol). When incubated in medium lacking histidine and supplemented with dialyzed serum (histidine-deficient medium), the BALB/3T3 cells remained viable for at least 3 days, but they ceased logarithmic growth, and the cell number reached an early plateau. In contrast, the SV-T2 cells continued to divide in histidine-deficient medium. Neither cell line ceased division in medium deficient in both phenylalanine and tyrosine. Incubation of the BALB/3T3 cells with 1.5 mM histidinol or 1.0 mM tyrosinol caused an early plateau similar to the effect of histidine deprivation. SV-T2 cells were not affected by these concentrations of histidinol or tyrosinol, but growth was arrested at higher concentrations. Any of the conditions used which caused a plateau in the number of BALB/3T3 cells substantially protected the treated cells from cell death caused by MTX. Therefore, pretreatment of BALB/3T3 cells with histidine deprivation, 1.5 mM histidinol, or 1.0 mM tyrosinol protected this cell line against MTX-induced cell death, while the same pretreatment conditions failed to protect SV-T2 cells. (SV-T2 cells were protected by 4.0 mM histidinol.) Thus, the ability of MTX to kill cells in vitro can be selectively modified by conditions which protect cells which retain normal growth control characteristics, but which do not protect virally transformed cells.

The pharmacokinetics of the active and inactive diastereoisomers of leucovorin and its active metabolite, 5-methyltetrahydrofolate (5-CH3-THF) were studied after iv injection of leucovorin in normal human subjects at a dose of 28 mg/m2, and in patients given 500 mg/m2 daily by constant iv infusion for a 5.5 day period. In both studies the plasma half-life (t1/2) of the active isomer, L-formyltetrahydrofolate (CHO-THF), was only 32 to 35 minutes, whereas the inactive isomer, D-CHO-THF had a plasma t 1/2 of 352 to 485 minutes. During constant infusion, the plasma levels reached plateaus of 2.33 and 37.5 microM for L-CHO-THF and D-CHO-THF, respectively. The inactive isomer was cleared from plasma only by urinary excretion of the unchanged drug. The active isomer was also excreted unchanged in the urine but in addition was extensively metabolized to the active metabolite L-5-CH3-THF. The active metabolite achieved a plasma level of 4.85 microM during constant infusion and appeared to have a longer t 1/2 after constant infusion than was observed after iv injection. Furthermore a larger apparent volume of distribution (Vd) of 5-CH3-THF was obtained in the constant infusion study. These findings suggest that constant iv infusion of large doses of leucovorin can considerably expand the intracellular pools of active folate. The consequence of the extensive accumulation of the inactive isomer, D-CHO-THF, is not known. However, the small Vd of D-CHO-THF suggests that it does not extensively accumulate in tissues.

A number of hydroquinone dialdehydes and structurally related compounds were synthesized and tested for antineoplastic efficacy against transplanted murine tumors. 3,6-Dihydroxy-4,5-dimethylphthalaldehyde,3,6-dihydroxy-4,5-dipropylphthalaldehyde, and 3,6-dihydroxy-4,5-dimethylphthalaldehyde hemialdal tetraacetate significantly prolonged the survival time of mice bearing either Sarcoma 180, Ehrlich carcinoma, or adenocarcinoma 755 ascites tumors. In addition, these agents were cytotoxic to Sarcoma 180 cells in culture at concentrations in the range of 25-30 microM.

M13 DNAs in which carbon 5 of each deoxycytidine residue in one strand is replaced with a bulky group are very good substrates for human DNA (cytosine-5) methyltransferase. Rate enhancements of up to 35 fold are obtained depending on the size of the moiety at C-5. The enzyme appears optimally suited to sense a methyl group in one strand at this position. Alkaline density gradient analyses of the distribution of methyl groups applied to 5-BrdCyd or 5-IdCyd substituted DNA reveal that these groups serve to direct the enzyme to methylate the unsubstituted strand.

The growth of auxotrophic bacteria remains the method of choice for the determination of biologically active folate metabolites in plasma. This report describes a microbiological assay for folates adapted to use disposable 96-well plates and an automatic plate reader. The modifications in the assay decreased reagent costs and made the analysis of hundreds of samples per day possible with a sensitivity limit of 10 fmol of (6S)-5-formyltetrahydrofolic acid. This limit compares favorably with that of previously reported, more laborious methods. The unnatural 6R diastereomer of 5-formyltetrahydrofolic acid did not interfere with the microbiological assay of the natural 6S diastereomer.