Classification of anticancer chemotherapeutic drugs according to their immunopotentiating activity

Both melphalan (L-PAM: L phenylalanine mustard) and 5-fluorouracil (5-FU) expressed a cytotoxic effect in vitro on MOPC-315 plasmacytoma tumour cells. However, they differed in their chemotherapeutic effectiveness in BALB/c mice bearing large MOPC-315 plasmacytoma tumours. Therapy with L-PAM, 7.5 mg/kg induced permanent regression of tumours, whereas regression induced by 5-FU, 200 mg/kg, was only transient and the mice dies finally with tumours. Moreover, spleen cells of tumour bearing mice treated with L-PAM exhibited high specific cytotoxic potential in vitro whereas spleen cells from tumour bearing 5-FU treated mice were devoid of cytotoxic potential. Effectiveness of chemotherapy with L-PAM was antagonized by treatment in combination with 5-FU. L-PAM, but not 5-FU potentiated cell mediated contact sensitivity response in vivo and impaired induction of T-suppressor cells by ConA. The parameters mentioned above indicate that L-PAM behaves as an "immunopromoting" drug and 5-FU as a "nonimmunopromoting" drug.     

Bioavailability of cyclophosphamide in the CMF regimen

Cyclophosphamide (CY) was administered to 22 breast cancer patients treated routinely according to the CMF regimen: 75 mg/m3/d x 14 d p.o. CY, 30 mg/m2 days 1 and 8 i.v. methotrexate (MTX) and 500 mg/m2 days 1 and 8 i.v. 5-Fluorouracil (5-FU). The sequence of drug administration was always the same: 1) CY, 2) MTX; and 3) 5-FU. Capillary gas chromatography was performed for determination of CY in blood. Bioavailability (F) could be determined in 14 patients since CY was also administered intravenously in the same dose. The data of systemic exposure of oral CY in the other 8 patients were matched to those of the first 14 in whom bioavailability could be determined. Mean F was 0.85 +/- 0.22 (85% +/- 22%); in 1 patient F was 0.43 (43%). Furthermore, 3 patients treated with only p.o. CY had low estimated F values: 0.45, 0.49 and 0.50. In comparing patient characteristics with pharmacokinetic data, it was concluded that age might have a predictive value for elimination half-life t 1/2 z of i.v. CY. The youngest patients showed shortest t1/2 z and were also amongst those with the lowest F. This indication requires an extension of the study as well as monitoring of CY metabolism as a function of age. For the premenopausal patients this might be of particular importance, since this group is known to be prone to benefit from chemotherapeutic treatment according to the CMF regimen.     

Combination therapy of CPT-11, a camptothecin derivative, with various antitumor drugs against L 1210 leukemia

Antitumor effect of CPT-11 in combination with cyclophosphamide (CY), nimustin hydrochloride (AC-NU), thio-TEPA (TESPA), methotrexate (MTX), 5-fluorouracil (5-FU), cytosine arabinoside (ara-C), thioinosine (6-MPR), adriamycin (ADM), bleomycin (BLM), mitomycin C (MMC), actinomycin D (ACT-D), vincristine sulfate (VCR), etoposide (VP-16) or cisplatin (CDDP) against L 1210 murine leukemia was investigated. The combination treatment of CPT-11 with CY, ACNU, ADM, CDDP, TESPA and ACT-D showed synergistic effects and significantly prolonged the survival time of L 1210-inoculated mice compared with CPT-11 alone or antitumor drug alone. Although the combination with 5-FU, 6-MPR, VP-16, MMC or VCR had synergistic effect for some schedules exceptionally with ara-C, MTX or BLM had slight synergistic effect against L 1210.     

Schedule-dependent potentiation of chemotherapeutic drugs by the bioreductive compounds NLCQ-1 and tirapazamine against EMT6 tumors in mice

PURPOSE: Comparisons of schedule-dependent interactions between the hypoxic cytotoxins NLCQ-1/ tirapazamine (TPZ) and various chemotherapeutic drugs in BALB/c mice bearing EMT6 tumors. METHODS: The antitumor effects of the single or combined drugs were assessed with various administration time intervals using the in vivo-in vitro clonogenic assay as the endpoint. The chemotherapeutic drugs tested were cisplatin (cisDDP), melphalan (L-PAM), cyclophosphamide (CPM), 5-fluorouracil (5-FU), doxorubicin (Doxo), etoposide (VP-16) and Taxol at doses of 8, 5, 100, 150, 12, 35 and 20 mg/kg, respectively. NLCQ-1 was given at 10 mg/kg (28% of its single LD50 value) and TPZ was given at 30 mg/kg (38% of its single LD50 value). All drugs were given by i.p. injection in saline or as commercially available pharmaceutical solutions. RESULTS: Schedule-dependent synergistic interactions with different patterns for each bioreductive drug were observed with almost all of the chemotherapeutic agents examined. Potentiation accounting for more than 25% of the total tumor cell killing was observed with NLCQ-1/TPZ and cisDDP, L-PAM, CPM, 5-FU and Taxol at the optimal administration intervals. Potentiation accounting for 70% of the total tumor cell killing was found with NLCQ-1 and CPM. CONCLUSIONS: These results suggest a potential clinical use of NLCQ-1/TPZ as adjuvants to certain chemotherapeutic agents.     

Modulation of cytotoxicity of cytostatic drugs by hemodialysis in vitro and in vivo

For most cytotoxic substances there are no established guidelines on how to deal with overdosage. Little is known about the dialysability of cytostatic drugs. To obtain further information, human plasma was incubated with cytostatic drugs and dialysed in vitro, using 'minimodules' with capillaries identical to those in clinical use. Cytotoxicity before and after dialysis was measured in a biological test system using permanent human lymphoblast cultures (LS2). The 20 cytostatic drugs studied were categorized as follows: (1) Dialysability in vitro. Good: methotrexate (MTX), 5-fluorouracil (5-FU/5-FUdR), cytarabine (ARAC), actinomycin D (DACT), mitomycin C (MMC), 4-OH-cyclophosphamide (4-OH-CPM), ifosfamide (IFO), melphalan (L-PAM), dacarbazine (DTIC), cisplatin (DDP). Intermediate: Adriamycin (ADM), 4'-epi-doxorubicin (4'-EA), carmustine (BCNU). Ineffective: daunorubicin (DNR), vincristine (VCR), vinblastine (VBL), vindesine (VDS), etoposide (VP-16), teniposide (VM-26), mitoxantrone (MITOX). These in vitro results cannot be transferred automatically into the in vivo situation because of specific drug distribution and metabolic rates. Considering pharmacokinetic data from the literature, the following recommendations can be made for practical clinical purposes. (2) Detoxification by hemodialysis in vivo. Possibly effective: MTX, 5-FU, MMC, CPM, IFO, L-PAM, BCNU, DTIC. Ineffective: ADM, 4'-EA, DNR, MITOX, DACT, VP-16, VM-26, VCR, VBL, VDS, ARAC, DDP.     

Antagonism of HSV-tk transfection and ganciclovir treatment on chemotherapeutic drug sensitivity

Our study focused on the influence of herpes simplex virus thymidine kinase (HSV-tk) expression and ganciclovir (GCV) treatment on the sensitivity of C6 glioma cells to frequently used chemotherapeutic drugs, i.e. adriamycin (ADR), cisplatin (CDDP), 5-fluorouracil (5-FU), and methotrexate (MTX). Transfection with HSV-tk revealed an increased sensitivity to GCV and CDDP and a decreased sensitivity to ADR and MTX. No significant differences were found in sensitivity to 5-FU. Combined treatment in a HSV-tk negative cell line revealed an additive effect when GCV was combined with ADR, whereas an antagonistic effect was found when GCV was combined with CDDP, 5-FU, or MTX. Comparable results were obtained in an HSV-tk positive cell line, apart from CDDP, which showed an additive effect. In conclusion, both HSV-tk transfection and subsequent GCV treatment can influence the sensitivity of tumor cells to various chemotherapeutic drugs in an antagonistic manner. Therefore, combining HSV-tk/GCV gene therapy with chemotherapy might not always be beneficial.     

Effect of clinical levels of misonidazole on the response of tumour and normal tissues in the mouse to alkylating agents.

Experiments were carried out to determine whether the enhancement of alkylating-agent cytotoxicity seen after large single doses of misonidazole (MISO) in mouse tumours can also be achieved by prolonged exposure to low MISO levels similar to those which can be tolerated clinically. The level in mouse blood plasma could be maintained at about 100 micrograms/ml for 7 h by injecting small doses of MISO every 1/2 h. The effect of this treatment in combination with cyclophosphamide (CY) or melphalan (L-PAM) was studied in the RIF-1 tumour, using regrowth delay and cell-survival cloning assays. In each case, prolonged exposure to low levels of MISO gave enhancement ratios very close to those obtained with a large single dose. ERs of 1.6-2.0 were obtained with CY and 1.8-2.2 with L-PAM over the range of alkylating-agent doses used. In experiments with CY the response of 2 normal-tissue systems, marrow and WBC count, was also studied. No significant enhancement of CY damage occurred in either case. In the L-PAM experiments the LD50/30 and WBC counts were determined as normal-tissue end points. Multiple MISO had no effect. Our results show that levels of MISO which can be achieved safely in man yield good enhancement of the tumour cytotoxicity of 2 widely used chemotherapeutic agents without increasing the damage to normal tissues.     

Fluorouracil catabolism in the combination treatment of cyclophosphamide, methotrexate and fluorouracil.

The CMF-regimen is amongst the most effective chemotherapeutic approaches in the treatment of breast cancer. It is generally accepted that the efficacy of the combination of the three agents used in the regimen, i.e., cyclophosphamide (CY), methotrexate (MTX) and fluorouracil (FUra), is based on interactions between the drugs at the intratumoral level. In WAG/Rij rats we previously demonstrated that change of FUra clearance at the first day of the CMF-regimen occurs owing to concomitant CY + MTX. In the present study clearance of FUra and the first product of FUra catabolism, FUraH2, were monitored at day 1 and day 8 of the regimen upon treatment with single agent FUra (F), MTX + FUra (MF), CY + FUra (CF), and CY + MTX + FUra (CMF). At the first day of treatment, FUra and FUraH2 systemic exposure was demonstrated to be increased in CMF-treated rats owing to concomitant CY+MTX. At the eighth day of treatment it was found that repeated CY administration during the previous seven days in CF-treated rats resulted in increased FUra and FUraH2 systemic exposure and therefore increased the dose of FUra artificially. It is concluded that altered FUra clearance owing to extratumoral interactions by concomitant CY and MTX contributes to the efficacy of the CMF-regimen.     

Antagonism of HSV-tk Transfection and Ganciclovir Treatment on Chemotherapeutic Drug Sensitivity

Abstract

Our study focused on the influence of herpes simplex virus thymidine kinase (HSV-tk) expression and ganciclovir (GCV) treatment on the sensitivity of C6 glioma cells to frequently used chemotherapeutic drugs, i.e. adriamycin (ADR), cisplatin (CDDP), 5-fluorouracil (5-FU), and methotrexate (MTX). Transfection with HSV-tk revealed an increased sensitivity to GCV and CDDP and a decreased sensitivity to ADR and MTX. No significant differences were found in sensitivity to 5-FU. Combined treatment in a HSV-tk negative cell line revealed an additive effect when GCV was combined with ADR, whereas an antagonistic effect was found when GCV was combined with CDDP, 5-FU, or MTX. Comparable results were obtained in an HSV-tk positive cell line, apart from CDDP, which showed an additive effect. In conclusion, both HSV-tk transfection and subsequent GCV treatment can influence the sensitivity of tumor cells to various chemotherapeutic drugs in an antagonistic manner. Therefore, combining HSV-tk/GCV gene therapy with chemotherapy might not always be beneficial.     

Fluorouracil Catabolism in the Combination Treatment of Cyclophosphamide, Methotrexate and Fluorouracil

The CMF-regimen is amongst the most effective chemotherapeutic approaches in the treatment of breast cancer. It is generally accepted that the efficacy of the combination of the three agents used in the regimen, i.e., cyclophosphamide (CY), methotrexate (MTX) and fluorouracil (FUra), is based on interactions between the drugs at the intratumoral level. In WAG/Rij rats we previously demonstrated that change of FUra clearance at the first day of the CMF-regimen occurs owing to concomitant CY+MTX. In the present study clearance of FUra and the first product of FUra catabolism, FUraH₂, were monitored at day 1 and day 8 of the regimen upon treatment with single agent FUra (F), MTX + FUra (MF), CY + FUra (CF), and CY + MTX + FUra (CMF). At the first day of treatment, FUra and FUraH₂ systemic exposure was demonstrated to be increased in CMF-treated rats owing to concomitant CY + MTX. At the eighth day of treatment it was found that repeated CY administration during the previous seven days in CF-treated rats resulted in increased FUra and FUraH₂ systemic exposure and therefore increased the dose of FUra artificially. It is concluded that altered FUra clearance owing to extratumoral interactions by concomitant CY and MTX contributes to the efficacy of the CMF-regimen.     

5-Fluorouracil and methotrexate administered simultaneously as a continuous infusion. A phase I study

Infusion delivery systems have been evaluated for administration of many individual chemotherapeutic agents including 5-fluorouracil (5-FU) and methotrexate (MTX). This study combined the two drugs as an admixture, and in a Phase I trial design established a useful dose schedule for each of the component drugs. 5-FU at a fixed dose rate of 300 mg/M2/day was delivered with methotrexate (MTX) at four different dose rates (0.75, 1.0, 1.5, or 2.0 mg/M2/day, respectively). The drug solution was delivered via a subclavian venous access with a portable infusion pump in an ambulatory setting. Twenty-nine patients received a total of 38 courses of the two-drug infusion: 21 courses were delivered with the two agents admixed constantly throughout treatment (Schedule A) and 17 were administered the treatment with 5-FU delivered continuously and MTX added to the 5-FU for alternate 14-day cycles (Schedule B). For the former schedule, dose-rate-limiting toxicity was related to MTX and included stomatitis developing at days 8 to 14 (median, day 8) with the higher dose rates (1.5-2.0 mg/M2/day) and thrombocytopenia developing at days 11 to 56 (median, day 14) at the lowest dose rates (1.0 mg/M2/day). For Schedule B, dose-rate-limiting toxicity was similarly due to the MTX with thrombocytopenia and/or chemical hepatitis developing in six of seven courses of MTX at 1.0 mg/M2/day and in five of ten courses delivered at 0.75 mg/M2/day. On Schedule B the MTX-associated toxicities were reversed when the MTX administration was interrupted and in the face of continued 5-FU infusion. A reasonable dose rate and schedule for continuous infusion of 5-FU combined with MTX is: 5-FU 300 mg/M2/day X 28 days and MTX 0.75 mg/M2/day for days 1 to 14, with cycles administered consecutively each 28 days.     

Implications for improved high-dose methotrexate therapeutic effects in cultured human breast cancer and bone marrow cells

The cytotoxicity of high-dose methotrexate (MTX), 10 and 100 microM, and 5-fluorouracil (5-FU) combinations is independent of sequence in human MDA-MB-436 breast carcinoma cells. The growth inhibitory effects of 10 and 100 microM MTX are 22.54+/-1.56% and 16.20+/-0.74%, respectively, of the control rate. When the MTX and 5-FU concentrations are 10 microM, antiproliferative effects of MTX 2 hr before 5-FU (MTX/5-FU) and 5-FU 2 h before MTX (5-FU/MTX) are 25.17+/-1.23% and 25.60+/-1.28% of the control rate, respectively. The percentage of control rates for 5-FU alone is 94.89+/-1.35%. The growth rates of MDA-MB-436 cells in 100 microM MTX and 10 microM 5-FU are 15.19+/-0.62% (MTX/5-FU) and 16.53+/-0.85% (5-FU/MTX) of the control rate. The growth of cancer cells in the presence of 5-FU alone is 93.82+/-1.69% of the control rate. A comparison of the cell-killing effects of MTX and the nonpolyglutamable antifolate trimetrexate (TMQ) alone and in combination with 5-FU was performed to indirectly explore the role of polyglutamylation in breast cancer and bone marrow cells. The comparisons were made in equitoxic concentrations (10 microM) of MTX and TMQ and the time of exposure was the same. The inhibitory effects of TMQ, TMQ/5-FU, and 5-FU/TMQ in breast cancer cells were identical, but significantly less than MTX, MTX/5-FU, and 5-FU/MTX. The interaction between TMQ and MTX, TMQ/5-FU and MTX/5-FU, and 5-FU/TMQ and 5-FU/MTX was quantitatively similar in bone marrow. (Significant protection occurred in bone marrow cells exposed to 5-FU/TMQ and 5-FU/MTX.) Because the effects of 5-FU/MTX and 5-FU/TMQ on bone marrow were the same, it is unlikely that polyglutamylation plays a significant role in the protective effects of 5-FU. However, the greater inhibitory effect of MTX or MTX and 5-FU combinations, when compared with TMQ or TMQ and 5-FU, suggests that polyglutamylation of MTX may contribute to the cytotoxicity of this antifolate to breast cancer cells. Hence, these studies suggest that a priming and nontoxic dose of 5-FU before high-dose MTX sustains MTX cytotoxicity in breast cancer and protects against MTX toxicity to bone marrow progenitor cells.     

Local- and systemic-mediated suppression of contact hypersensitivity in mice by several structurally unrelated classes of tumor promoters

Several structurally unrelated classes of chemicals defined as promoters in the murine skin multistage carcinogenesis protocol were surveyed for their abilities to modify contact hypersensitivity (CHS) responses in SENCAR mice. Sensitization of dorsal skin with 2,4-dinitrofluorobenzene (DNFB) and subsequent challenge of ears 5 days later with DNFB resulted within 24 h in ear swelling. Pretreatment of dorsal skin with multiple applications (2 x/week for 2 weeks) of promoting doses of 12-O-tetradecanoylphorbol-13-acetate (TPA), anthralin, butylated hydroxytoluene hydroperoxide, n-dodecane and ethyl phenylpropionate (EPP) prior to sensitization with DNFB inhibited, to a comparable extent, the subsequent induction of CHS by DNFB challenge. Pretreatment of dorsal skin with promoting doses of benzoyl peroxide resulted in reproducible, but diminished suppression of CHS, relative to that mediated by the other chemical promoters. Application of promoting doses of TPA, anthralin and EPP, but not the other chemicals, to ventral skin prior to DNFB sensitization of dorsal skin also significantly inhibited DNFB-induced CHS. However, suppression of CHS mediated by ventral application of these three chemicals was quantitatively less than that occurring when the chemicals were applied to the site of DNFB sensitization. Collectively, these studies demonstrate that various classes of structurally unrelated tumor promoters have in common the ability to suppress CHS, a cell-mediated immune response. Furthermore, some tumor promoters exert their suppressive effects through both local and systemic processes.     

5-fu dose-dependency in mtx/s-fu sequential therapy assessed by in-vitro assay using gastric-cancer cell-lines

The sequential administration of methotrexate (MTX) and 5-fluorouracil (5-FU) (MTX/5-FU therapy) on gastric cancers has shown higher response rates than standard chemotherapy. The response rate of these cancers, however, still showed from 18 to 48%. The purpose of this study was to determine the appropriate interval time and doses of MTX/5-FU therapy using a panel of 4 cell lines originated from the poorly-differentiated gastric cancers. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used as the chemosensitivity test. The sequential administration of MTX and 5-FU inhibited the growth of 2 cell lines more than 5-FU alone. In one cell line (GCIY), it inhibited the growth 6 times, and the longest interval time (6 h) was the most effective. In the other cell line (KATOIII), it inhibited growth 3 times, and the shortest interval time (O h) was the most effective. The growth inhibition in these cases did not depend on the dose of MTX (0.01 mu g/ml to 100 mu g/ml), but on the dose of 5-FU. In conclusion, 2 out of 4 cell lines showed a synergic effect between MTX and 5-FU. While the appropriate interval time between the two drugs varied between two cell lines, 5-FU dose was more critical than that of MTX. If 5-FU dose were to be increased in future trials with MTX, its efficacy might be higher. This model should also be good to screen other anti cancer drugs combined with MTX/5-FU therapy.     

Combination therapy with methotrexate and 5-fluorouracil: a prospective randomized clinical trial of order of administration

Because of biochemical and tissue culture evidence casting doubt on the physiologic relevance of reported synergy afforded by sequential administration of methotrexate (MTX) followed by 5-fluorouracil (5-FU), a randomized controlled clinical trial was conducted in 108 patients with advanced cancer, including 70 with squamous cell carcinoma (SCC) of the head and neck, nine with SCC of other primary sites, 24 with colorectal, and five with gastric adenocarcinomas. Patients were randomized to receive weekly therapy consisting of MTX followed one hour later by 5-FU, or 5-FU followed one hour later by MTX. There was a trend to higher tumor response rates in patients treated with MTX before 5-FU (45% v 33% overall; 65% v 39% in patients with previously untreated head and neck cancer), but these differences were not significant, either by chi-square test or by multivariate stepwise logistic regression. The trend in survival favoring the reverse sequence of 5-FU before MTX was not significant in univariate analyses. Stepwise multivariate Cox model analysis showed that Eastern Cooperative Oncology Group performance status at study entry was the major prognostic factor for survival (P less than 0.001), but among the 70 patients with head and neck cancer, the sequence of drug administration was the only other significant prognostic factor for survival, and favored the sequence of 5-FU followed by MTX (P less than 0.025).     

Leucovorin enhances cytotoxicity of trimetrexate/fluorouracil, but not methotrexate/fluorouracil, in CCRF-CEM cells.

BACKGROUND: Increased response rates in studies of patients with colon cancer have indicated that the cytotoxic effects of fluorouracil (5-FU) are potentiated by leucovorin (LV) and by methotrexate (MTX). However, preliminary studies using a sequential combination of MTX, LV, and 5-FU showed no additional potentiation. PURPOSE: We hypothesized that the lack of additional cell kill with this combination could be due to competition of LV with MTX for cellular uptake and reduced folate polyglutamylation. We have tested this possibility by comparing the cytotoxicity of drug combinations containing MTX with that of drug combinations containing trimetrexate (TMTX), an antifolate that does not compete with LV for uptake or polyglutamylation. METHODS: Human lymphocytic leukemia CCRF-CEM cells were exposed to MTX or TMTX for 24 hours and to 5-FU during the last 4 hours of antifolate exposure. LV was administered 30 minutes before 5-FU. RESULTS: After 20 hours of exposure to TMTX or MTX, intracellular levels of phosphoribosyl pyrophosphate were elevated to a similar degree, and these levels did not decrease after a 30-minute exposure to LV. No additional cell kill was observed when LV was added to the MTX/5-FU combination, but cytotoxicity was enhanced when LV was added to the TMTX/5-FU combination. CONCLUSIONS: This study supports the hypothesis that the lack of additional cell kill when high-dose LV is added to the MTX/5-FU combination may be due to competition of MTX with LV for cellular uptake and/or competition of MTX or its polyglutamates with polyglutamylation of reduced folates. Inasmuch as TMTX does not compete with LV and reduced folates for uptake and polyglutamylation, the synergy obtained with the combination of TMTX plus 5-FU and high-dose LV further supports this hypothesis.     

Improving the anti-tumor activity of 5-fluorouracil by methotrexate

The first clinical application of biochemical modulation (BCM) of 5-fluorouracil (5-FU) was the sequential MTX/5-FU regimen proposed in 1977 by Bertino for the treatment of colorectal cancer. In Japan, sequential MTX/5-FU therapy was mainly used as a new method of treating gastric cancer, and attracted a great deal of attention because it proved effective in many cases of advanced gastric cancer that had been unresponsive to the previous chemotherapy, particularly scirrhous gastric cancer with poor prognosis. Its therapeutic efficacy varied according to histologic type, it was effective in cases of peritoneal dissemination and disseminated intravascular coagulopathy (DIC), it was associated with fewer adverse effects, and it was a multidrug chemotherapy based on a clear rationale. With sequential MTX/5-FU therapy as a starting point, fundamental studies of BCM and its clinical applications have expanded rapidly in Japan. This paper provides an outline of sequential MTX/5-FU therapy from the aspects of its mechanism of action, indications, therapeutic efficacy, relevance to adjuvant therapy, counter-measures to adverse effects, and emergence of resistance to the drugs involved. The high therapeutic efficacy of this therapy in certain histologic types is also discussed, and its combined use with other forms of BCM, as in triple BCM (LV/5-FU + CDDP/5-FU + MTX/5-FU), is introduced.     

The CMF-regimen. Modulation of cyclophosphamide uptake and clearance by methotrexate and fluorouracil

Influence of the 2 antimetabolites used in the CMF-regimen, methotrexate (MTX, M) and fluorouracil (FUra, F) on in vivo pharmacokinetics of orally administered cyclophosphamide (CY, C), were studied in WAG/Rij rats. Blood plasma concentrations of CY following oral administration were monitored in single-agent CY, in CY + MTX (CM), in CY + FUra (CF) and in CY + MTX + FUra (CMF) treatments. Each treatment group consisted of at least 10 rats. CY was determined in 50 microliters of plasma by capillary gas chromatography on the first day of chemotherapy. Statistical analysis of blood plasma concentration data revealed a significant influence of both MTX and FUra on CY input/output function (p:0.01). MTX and FUra significantly increased the area under the plasma concentration time-curve, whereas tmax was significantly prolonged in CF and CMF treatment groups (p:0.01). It is suggested that MTX and FUra interact at the site of CY pre-systemic metabolism, including first-pass metabolism, subsequently resulting in prolonged absorption.     

Azidothymidine and dipyridamole as biochemical response modifiers: synergism with methotrexate and 5-fluorouracil in human colon and pancreatic carcinoma cells.

Azidothymidine (AZT), inhibiting thymidine kinase (EC 2.7.1.21) (Weber, G. et al., Cancer Commun. 2:129-133, 1990) and dipyridamole, inhibiting nucleoside transport (Zhen, Y.-s. et al., Cancer Res. 43:1616-1619, 1983) exert blocking action on the activities of salvage pathways of nucleotide biosynthesis. Determined by clonogenic assay in human colon cancer HT-29 cells, the cell survivals for AZT, 10 microM, dipyridamole, 5 microM, and methotrexate (MTX), 0.025 microM, were 90, 82, and 62%, respectively; while the combinations of AZT + MTX, dipyridamole + MTX and AZT + dipyridamole + MTX, reduced survivals to 36, 4.3, and 0.7%. AZT or dipyridamole was synergistic with MTX, whereas AZT plus dipyridamole showed an even more marked potentiation of MTX activity. The survivals for 5-fluorouracil (5-FU), 0.5 microM, alone, AZT + 5-FU, dipyridamole + 5-FU, and AZT + dipyridamole + 5-FU were 86, 47, 29 and 5.1%, respectively. Similar results were observed in human pancreatic carcinoma BxPC-3 and PANC-1 cells. AZT markedly enhanced the inhibitory effect of dipyridamole in reversing the thymidine-hypoxanthine rescue from MTX cytotoxicity. AZT inhibited [14C]thymidine incorporation into DNA in HT-29 cells and strongly enhanced the effect of dipyridamole. The results indicate that combinations composed of AZT, dipyridamole, and antimetabolites, such as MTX and 5-FU, are potentially effective in the chemotherapy of human neoplasias.     

Resistance to chemotherapeutic antimetabolites: a function of salvage pathway involvement and cellular response to DNA damage.

The inherent or acquired (induced) resistance of certain tumours to cytotoxic drug therapy is a major clinical problem. There are many categories of cytotoxic agent: the antimetabolites, e.g. methotrexate (MTX), N-phosphonacetyl-L-aspartate (PALA), 5-fluorouracil (5-FU), 6-mercaptopurine (6-TG), hydroxyurea (HU) and 1-beta-D-arabinofuranosylcytosine (AraC); the alkylating agents, e.g. the nitrogen mustards and nitrosoureas; the antibiotics, e.g. doxorubicin and mitomycin C; the plant alkaloids, e.g. vincristine and vinblastine; and miscellaneous compounds, such as cisplatin. There are also many mechanisms of drug resistance elucidated principally from in vitro studies. These include mutation of target genes, amplification of target and mutated genes, differences in repair capacity, altered drug transport and differences in nucleoside and nucleobase salvage pathways (Fox et al, 1991). The aim of the present review is to evaluate in detail the mechanisms of response of both normal and tumour cells to three chemotherapeutic antimetabolites, MTX, PALA and 5-FU, which are routinely used in the clinic either alone or in combination to treat some of the commonest solid tumours, e.g. breast, colon, gastric and head and neck. The normal and tumour cell response to these agents will be discussed in relation to the operation of the known alternative ''salvage pathways'' of DNA synthesis and current theories of DNA damage response.