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In vitro and in vivo studies have been carried out in mouse and human tumors to investigate the biochemical and pharmacologic basis for the selectivity of 5-fluorouracil (FUra) action. Combination chemotherapy with FUra and thymidine was performed to determine the therapeutic relevance of 5-fluorouridine triphosphate (FUTP) incorporation into RNA. The results of these studies indicate that modulation of FUra cytotoxicity by deoxythymidine (dThd) did occur but failed to produce any significant therapeutic advantages in patients with advanced colorectal cancer. Modulation of FUra bioactivation via the deoxyribonucleotide pathway by coadministration of high-dose folinic acid resulted in enhanced therapeutic response rate of gastrointestinal tumor patients. This manuscript summarizes the preclinical and clinical findings on the metabolic modulation of FUra activity by dThd and folinic acid.

Plasma pharmacokinetics of high-dose (500 mg/m2) leucovorin calcium (dl-5-formyltetrahydrofolic acid [dl-CF]) and fluorouracil (FUra) have been evaluated in patients with advanced colorectal cancer treated with the combination of FUra and dl-CF by two different intravenous (IV) schedules: (A) In patients with no prior chemotherapy, dl-CF was administered by a two-hour IV infusion and FUra by rapid IV injection one hour after the start of the dl-CF infusion and (B) in previously treated patients, dl-CF and FUra were administered by five-day continuous IV infusion (CI). Following the two-hour infusion of dl-CF, mean peak plasma concentration and elimination half-life of I-5-formyltetrahydrofolic acid (I-CF) were 24 +/- 6 mumol/L and 0.8 +/- 0.1 hour, respectively. CI of dl-CF over five days yielded a mean steady-state plasma level of I-CF of only 1.2 +/- 0.5 mumol/L. Peak and steady-state plasma concentrations of the metabolite 5-methyl tetrahydrofolic acid were comparable in the two schedules (17 +/- 8 mumol/L for the two-hour infusion and 12 +/- 5 mumol/L for the CI). Areas under the concentration v time curve (AUC) of total reduced folates were significantly greater under conditions of CI: 89.0 v 16.7 mmol/L/min for the two-hour infusion. In tumor tissue, 5,10-methylenetetrahydrofolate increased eight-fold two to four hours following the two-hour infusion and two-fold during the CI of dl-CF and FUra. Inhibition of thymidylate synthase (dTMP-S) by the two-hour and CI infusion schedules were 66% v 39%, respectively. The observed differences in the intracellular dTMP-S folate cofactor pools and the degree of inhibition of dTMP-S achieved in patients treated by two different schedules may be due to differences in the biochemical properties and/or to differences in the modulation of FUra metabolism by folate of tumor tissues obtained from newly diagnosed and previously treated patients.

This study was designed to determine the role of immediate intravesical instillation of single dose thiotepa post transurethral resection of bladder tumor in the prevention of recurrence by tumor implantation, using murine bladder tumor line 2 and 201 C3H/He mice. Previous studies have suggested implantation may take place as early as the first hour and reach its maximum in 24 hours after resection of bladder tumor. An in vitro dose response curve of MBT2 to thiotepa was established by treatment with various concentrations of thiotepa of 0.00, 0.01, 0.21, 0.44, and 1.91 mg./ml. In a group of 201 mice, the bladder was catheterized with a 24G angiocatheter, and a fine copper wire was inserted through the lumen. The bladder was cauterized by touching the wire with a Bovie coagulator for four seconds at the lowest setting. All bladders were instilled with 1 x 10(6) cells of murine bladder tumor line 2, followed by instillation of 1.91 mg./ml. of thiotepa with various time delays per treatment group. The bladder implantation rates were 30.4% (17/56), 3.4% (2/59), 6.5% (2/31) and 26.9% (7/26) in the control, immediate, one-hour delay and 24-hour delay groups, respectively. The urethral implantation rates were 21.4% (12/56), 0% (0/59), 6.5% (2/31) and 0% (2/26), respectively. The overall implantation rates (bladder, urethra, or both) were 42.9% (24/56), 3.4% (2/59), 6.5% (2/31) and 25.9% (7/27), respectively. Implantation rates were significantly higher in the control and 24-hour delay groups than in the immediate and one-hour instillation groups (p less than 0.05, Fisher Exact Test). We conclude from this animal model that intravesical instillation of single dose thiotepa, to be effective, should be initiated within the first hour after tumor resection, since it dramatically decreased the incidence of bladder and urethral implantation.

A pilot study was conducted to determine the possible efficacy and the toxicities associated with the administration of four courses of intensive consolidation chemotherapy to patients with acute nonlymphocytic leukemia in remission. All therapy was completed within 6 months. The median duration of remission was 22 months, with 45+% of patients in remission at 3 years and few relapses to date thereafter. Sixty percent of patients experienced significant side effects after each course of therapy. The therapy appeared to be particularly efficacious for patients less than 45 years of age, since 65% are alive at 3 years and there is no projection for a median duration of remission as yet. The cytogenetic characteristics of the leukemic cells, the percentage of S phase cells, and the height of the WBC count were the most important prognostic characteristics at diagnosis.

Fifteen adult subjects comprised the study group; 2 were colon cancer patients. Total leucovorin (citrovorum factor; CF) doses of 200, 400, 800, and 1600 mg were equally subdivided and administered at 0, 1, 2, and 3 hours. Three of the subjects were fasting and the other 12 were not. Quantitation of serum L-CF by Pediococcus cerevisiae and total reduced folates (TRF) by radio-assay were performed in 10 samples from each subject drawn over a 12-hour period after initiation of CF dosing. The mean serum levels of L-CF remained greater than 0.1 microM at 3 hours and the TRF 3.5 microM at 5 hours, respectively, after termination of CF dosing in all subjects treated at the 800- and 1600-mg dose schedule. At all CF dosage schedules employed, peak serum concentrations were reached within 4 and 6 hours after initiation of oral CF. Peak TRF concentrations at the 200-, 400-, 800-, and 1600-mg doses were 3.42 +/- 0.65, 4.05 +/- 1.04, 4.81 +/- 0.14, and 5.11 +/- 1.81 microM, respectively. Peak L-CF levels at 200, 400, 800, and 1600 were 0.15 +/- 0.11, 0.21 +/- 0.14, 0.23 +/- 0.11, and 0.34 +/- 0.16 microM. Based upon these observations, the following conclusions were reached: 1) no significant differences were observed in serum concentrations of folates between the 800- and 1600-mg dose schedules; 2) at these doses serum concentrations of L-CF and TRF were achieved that warrant a phase I investigation of high-dose oral CF with standard dose FUra in patients with advanced colorectal carcinoma.

DMDP [N-(3,4-dimethoxyphenethyl)-N-methyl-2-(2-naphthyl-m-dithane- 2-propylamine] a recently developed calcium antagonist analogue, caused a greatly increased intracellular retention of adriamycin and concomitant enhanced cytotoxicity in adriamycin-resistant P388 leukemia cells in vitro. These effects of DMDP were greater than those of another calcium channel blocker, verapamil, and occurred at one-half the dosage levels. Only slight enhancement in adriamycin toxicity was observed for either of these agents in the adriamycin-sensitive parental cell line. However, no significant therapeutic potentiation of adriamycin activity occurred with either verapamil or DMDP treatment in vivo. In vivo maximum DMDP tumor intracellular concentrations, as analyzed by HPLC, were the same in vitro tumor cell levels required to overcome adriamycin resistance. This inability to overcome drug resistance in vivo at acceptable levels of host toxicity is not only a function of maintaining necessary calcium antagonist concentrations in resistant tumor cells.

The data from an ongoing 3-arm prospective study of 72 patients with advanced colorectal carcinoma is presented. The 3 regimens are as follows: Regime 1 (every 4 weeks)--5-fluorouracil (FUra) (450 mg/m2 iv bolus daily for 5 days, then 200 mg/m2 iv bolus every other day for 6 doses); regime 2 (every week for 4 weeks, then every other week)--methotrexate (MTX) (50 mg/m2 in a 4-hour infusion) followed by FUra (600 mg/m2 iv bolus); regime 3 (weekly for 6 weeks followed by a 2-week rest period)--D,L-leucovorin (D,L-CF) (500 mg/m2 in a 2-hour infusion) with FUra (600 mg/m2 iv bolus) 1 hour after the D,L-CF infusion began. All monitoring lesions except lung were documented by tissue biopsy. Thirteen of 18 patients in the FUra + D,L-CF arm were evaluable for response. Six of the 13 patients (46%) have had a partial response. The duration of the 6 responses has been 11, 8, 7, 4, 3 and 3 months. In patients with liver metastases as the monitoring lesion, a dramatic improvement in liver function tests has been seen during the first 2 courses (12 weeks) of treatment, but this was not sustained. The toxicity of FUra + D,L-CF was predominantly gastrointestinal; unlike with FUra alone, myelosuppression was not predominant.

Thirty specimens from 28 patients (15 previously treated, 13 previously untreated) with ovarian carcinoma were studied in a soft agar colony-forming assay to determine whether or not the assay could be useful for treatment planning. There were sufficient colonies for drug testing in 23 cases. An in vitro drug response was found in 12 of 106 drug tests. In vivo-in vitro correlations could be made for 28 drug trials in 16 patients. Eight patients were not evaluated for response because they were clinically disease free after debulking surgery. Single agents were evaluated in vitro, although most patients received combination chemotherapy. In 23 cases the tumor was resistant in vitro and in vivo. There were two false-negative and three false-positive results. Cell aggregates that may artificially increase growth rates and apparent in vitro drug resistance were a major problem technically. In view of the problems identified, the assay in its current form should not be used routinely to direct therapy.

Thirty-one evaluable patients with measurable advanced colorectal carcinoma were entered into a pilot study that used weekly fluorouracil (5-FU) at the dose of 600 mg/m2 by bolus infusion administered midway during a two-hour leucovorin calcium infusion of 500 mg/m2. This regimen was repeated weekly for six doses. Twenty-seven of these patients (87%) were considered to be refractory to prior 5-FU therapy and four (13%) were previously untreated. All 31 patients successfully completed at least one 6-week cycle of this regimen with acceptable toxicity. The combined complete (CR) and partial response (PR) rate was 45% with another 25% of patients remaining stable. The 95% confidence levels for the responding patients are 27.6% and 62.7%, respectively. The remaining 30% of the patients had all received prior 5-FU therapy and progressed. All of the responding patients and 80% of the patients with stable disease received two or more cycles of this regimen after a 3- to 4-week interval off therapy. The median time to disease progression was 16.1 months for responding patients and 6.7 months for those patients with stable disease. The median survival for the responders was 20.6 months and for those with stable disease 9.8 months. The median survival for the nonresponding patients was 3.9 months. Toxicity included diarrhea in 70% of patients, skin rash (erythema) in 10%, stomatitis in 15%, nausea and vomiting in 25%, and myelosuppression in 10%. This study confirms and extends previous observations that demonstrate the improved efficacy of 5-FU when used with high-dose leucovorin in advanced colorectal carcinoma.

Patients with acute nonlymphocytic leukemia were given remission induction therapy consisting of cytosine arabinoside and an anthracycline. Those patients who experienced complete remission received two courses of consolidation therapy and were randomized to receive maintenance therapy consisting of either daily chemotherapy with reinforcements every 3 mo or reinforcement therapy only every 6 wk. The overall complete remission rate was 66%, with 80% complete remission for previously untreated patients less than 60 yr of age who did not have a prior history of malignancy. Remission durations were the same for patients treated with both maintenance regimens. The major determinant for successful remission induction therapy was patient age, with older patients frequently succumbing to intercurrent infection. Documented leukemic cell resistance to the therapy employed was only rarely encountered. Once remission was achieved, age was no longer a determinant of patient survival, since duration of remission was independent of age. Remission durations were directly related to leukemic cell retention of cytosine arabinoside triphosphate. Hence therapy for acute nonlymphocytic leukemia can be divided into two separate areas: remission induction and remission maintenance.