Topical delivery of 5-fluorouracil (5-Fu) by 3-alkylcarbonyl-5-Fu prodrugs

The solubilities in isopropyl myristate (SIPM) and pH 4.0 buffer (SAQ) and the partition coefficients between IPM and pH 4.0 buffer (KIPM:AQ) have been measured for a series of 3-alkylcarbonyl-5-fluorouracil prodrugs (3-AC-5-FU). The 3-AC-5-FU prodrugs were all 100 times more soluble in IPM and the first two members of the series were also more soluble in pH 4.0 buffer than 5-FU. The abilities of the 3-AC-5-FU prodrugs to deliver total 5-FU species through hairless mouse skin from IPM suspensions (Ji) were also measured. The 3-propionyl derivative 3, which exhibited the highest SAQ in the series, gave the highest Ji value. The SIPM, SAQ and molecular weights (mw) of the 3-AC-5-FU series correctly predicted the rank order and very closely (0.10 log units) predicted the absolute values for logJi using the transformed Potts-Guy equation. Although the series of 3-AC-5-FU prodrugs was generally quite effective at increasing Ji (2-20 times), the best 3-AC-5-FU prodrug was not as effective as the best 1-alkylcarbonyl-5-FU prodrug (1-AC-5-FU) at increasing Ji and the ability of the 3-AC-5-FU prodrugs to increase the concentration of total 5-FU species in the skin was 2-5 times less than the 1-AC-5-FU prodrugs. Thus, the 1-AC-5-FU prodrugs remain as the best prodrugs with which to enhance the topical delivery of 5-FU.     

Topical delivery of 5-fluorouracil (5-FU) by 1,3-bisalkylcarbonyl-5-FU prodrugs.

The solubilities in isopropyl myristate (S(IPM)) and pH 4.0 buffer (S(AQ)) and the partition coefficients between IPM and pH 4.0 buffer (K(IPM:AQ)) have been measured for a series of 1,3-bisalkylcarbonyl-5-fluorouracil prodrugs (1,3-AC-5-FU). The 1,3-AC-5-FU prodrugs were each over 500 times more soluble in IPM, but all members of the series, whose solubilities could be estimated, were much less soluble in pH 4.0 buffer than 5-FU. The abilities of the 1,3-AC-5-FU prodrugs to deliver total 5-FU species through hairless mouse skin from IPM suspensions (J(i)) were also measured. The 1,3-diacetyl derivative 2, which exhibited the highest S(AQ) in the series, gave the highest J(i) value. Although the series of 1,3-AC-5-FU prodrugs was generally effective at increasing J(i) (three to ten times), the best 1,3-AC-5-FU prodrug was not as effective as the best 1- or 3-alkylcarbonyl-5-FU prodrug (1- or 3-AC-5-FU) at increasing J(i) and their ability to increase the concentration of total 5-FU species in the skin was generally less than that of the 1-AC-5-FU prodrugs, but greater than that of the 3-AC-5-FU prodrugs. Thus, the 1-AC-5-FU prodrugs remain the best prodrugs with which to enhance the topical delivery of 5-FU.     

Topical delivery of 5-fluorouracil (5-FU) by 3-alkylcarbonyloxymethyl-5-FU prodrugs

The 3-alkylcarbonyloxymethyl-5-fluorouracil (3-ACOM-5-FU) prodrugs have been characterized by their solubilities in isopropyl myristate (S(IPM)) and partition coefficients between IPM and pH 4.0 buffer (K(IPM:AQ)). Estimated S(AQ) values have been obtained from S(AQ) = S(IPM)/K(IPM:AQ.) The abilities of the prodrugs to deliver total 5-FU species from IPM suspensions through hairless mouse skin (J(i)) have been evaluated in diffusion cell experiments. All of the prodrugs were much more soluble in IPM than 5-FU, and the propionyloxymethyl (C2) member of the series was almost twice as soluble in pH 4.0 buffer. Except for the acetyloxymethyl (C1) member of the series, the 3-ACOM-5-FU prodrugs exhibited greater S(IPM) and S(AQ) values than the corresponding 1-alkylcarbonyloxymethyl (1-ACOM-5-FU) prodrugs. The 3-ACOM-5-FU prodrugs that exhibited greater S(IPM) and S(AQ) values than the 1-ACOM-5-FU prodrugs also exhibited greater J(i) values, except for the C2 member. The C2 member also gave the largest error in predicting J(i) using the transformed Potts-Guy equation. All of the 3-ACOM-5-FU prodrugs delivered more 5-FU as a percentage of J(i) than the 1-ACOM-5-FU prodrugs but were not more effective as a series at targeting dermal as opposed to transdermal delivery.     

DNA repair pathways involved in repair of lesions induced by 5-fluorouracil and its active metabolite FdUMP

5-Fluorouracil (5-FU) is an antitumor antimetabolite that can be converted into fluoronucleotides and FdUMP. Fluoronucleotides are incorporated into DNA and RNA, while FdUMP results in nucleotide pool imbalance. Saccharomyces cerevisiae is unable to convert 5-FU into FdUMP, making yeast a unique model system to study the cellular effects of 5-FU and FdUMP independently. A panel of repair-deficient yeast strains was used to identify the DNA repair pathways needed for repair of lesions generated by 5-FU or FdUMP. This included yeast deficient in base excision repair (BER), nucleotide excision repair (NER), translesion synthesis (TLS), mismatch repair (MMR), post-replication repair (PRR), homologous recombination (HR) and non-homologous end-joining (NHEJ). The results revealed an important role of BER, since BER-mutants (ntg1, ntg2, apn1, apn2) showed pronounced sensitivity to both 5-FU and FdUMP. MMR mutants also showed high sensitivity to both compounds. In contrast, deficiencies in NER, NHEJ and TLS repair had only minor influence on the sensitivity to FU and FdUMP. Interestingly, deficiencies in HR (rad52) and PPR (rad6, rad18) were associated with increased sensitivity to 5-FU, but not to FdUMP. Taken together, our study reveals an important contribution of DNA repair pathways on the sensitivity to 5-FU and its active metabolite FdUMP. Importantly, the repair mechanisms differed for the 2 antimetabolites since lesions induced by 5-FU were repaired by BER, MMR, HR and PRR, while only BER and MMR were required for repair of FdUMP-induced lesions.     

Antitumor effect and tumor level of 5-fluoro-2'-deoxyuridylate following oral administration of tetradecyl 2'-deoxy-5-fluoro-5'-uridylate.

The antitumor effect and tumor levels of 5-fluoro-2'-deoxyuridylate (FdUMP) following oral administration of tetradecyl 2'-deoxy-5-fluoro-5'-uridylate (TT-62) were compared with those attained following intravenous (i.v.) or intraperitoneal (i.p.) administration of 5-fluorouracil (5-FU) or 5-fluoro-2'-deoxyuridine (FUdR) in BDF1 mice bearing murine mammary adenocarcinoma 755 and athymic mice bearing the transplantable human colon adenocarcinoma LS174T. Oral administration of TT-62 showed a stronger antitumor effect against adenocarcinoma 755 than FUdR. The maximum effect of TT-62 was similar to that of 5-FU. However, TT-62 and FUdR treatments were more effective than i.v. administration of 5-FU against LS174T. Thus, oral administration of TT-62 showed marked antitumor activity in both tumor systems. The maximum tolerated dose of FUdR resulted in a much higher level of free FdUMP in the LS174T tumor than that obtained with 5-FU. After oral administration of TT-62 the levels of FdUMP in the tumor were about 10 times those attained with 5-FU, but significantly lower than the levels obtained following i.v. administration of FUdR. With TT-62 the levels of FdUMP in the tumor reached their peak at 60 min following the administration and gradually decreased thereafter. However, FdUMP levels after administration of FUdR decreased rapidly. Three hours after the administration of TT-62 and for up to 24 h the FdUMP levels in the LS174T tumor were almost the same as after administration of FUdR, i.e. effective levels of FdUMP were maintained for a long time with TT-62.     

In-vitro differential metabolism and activity of 5-fluorouracil between short-term, high-dose and long-term, low-dose treatments in human squamous carcinoma cells

Although continuous infusion of 5-fluorouracil (5-FU) has been clinically demonstrated to be superior to bolus administration, the mechanistic difference between the treatments still remains unclear. Here, we investigated in vitro whether there were any differences in the metabolism and activity of 5-FU between these schedules. To simulate bolus and infusional treatments of 5-FU, HST-1 human squamous carcinoma cells were treated with short-term, high-doses and long-term, low-doses so that the area under the curve (AUC) of 5-FU became equivalent between both schedules, and compared the cytotoxicity, fluorinated RNA (F-RNA) levels, 5-fluorodeoxyuridine monophosphate (FdUMP) content and thymidylate synthase (TS) activity. F-RNA and FdUMP were measured by capillary gas chromatography-mass spectrometry and competitive ligand-binding assay, respectively. The [H]FdUMP binding site in TS was determined as an index of the amount of TS using the radio-binding assay. Long-term, low-dose treatment of 5-FU was found to be 1.3-1.7 times more cytotoxic than the short-term, high-dose treatment. F-RNA content increased as the AUC of 5-FU was increased and was 2-4 times significantly higher in the cells treated with the long-term, low-dose than those with the short-term, high-dose schedule, indicating that the levels of F-RNA are AUC and schedule dependent. In contrast, there were no significant differences in FdUMP levels, TS activity and TS inhibition rate between the schedules. These data suggest that the superior activity of 5-FU administered long-term, low-dose over short-term, high-dose could be explained by more 5-FU incorporated into RNA during a long-term, low-dose exposure, thus providing a strategic rationale for the clinical advantage of continuous infusion over bolus administration.     

Genetic and biochemical modulation of 5-fluorouracil through the overexpression of thymidine kinase: an in-vitro study

The pro-drug 5-fluorouracil (5-FU) exerts its anti-proliferative action after conversion into cytotoxic metabolites. We previously demonstrated that the anti-cancer action of 5-FU could be enhanced by boosting thymidine phosphorylase (TP) activity in cancer cells, the first step of the DNA pathway, that yields the critical anti-thymidylate synthase (TS) fluorodeoxyuridine monophosphate (FdUMP) metabolite. In the present study, we further studied to what extent 5-FU activity could be optimized by overexpressing cancer cell thymidine kinase (TK), the second step of the DNA pathway, for which controversial data have been published so far. Additionally, screening of biochemical modulators likely to contribute to 5-FU activation was also carried out. TK-overexpressing colorectal cells were obtained after designing vectors harboring viral and human cDNA, and performing stable transfection in the human HT29 cell line. Anti-proliferative assays were subsequently performed so as to evaluate change in cell sensitivity to 5-FU, and metabolism monitoring was carried out to follow drug activation and FdUMP formation after cellular uptake. Finally, TS inhibition was assessed as a pharmacological endpoint. Results showed that overexpression of TK led to a marked desensitization of our model. A negative correlation (r = 0.87) was found between the level of TK activity and 5-FU anti-proliferative action - the higher the activity, the lower the sensitivity. Of the various drugs screened as putative modulators, only those involved in TP activity proved to enhance 5-FU efficacy via optimized FdUMP formation. Conversely, genetically increasing TK activity did not modify 5-FU activation pathway nor subsequent TS inhibition in our model. Therefore, our results indicate that TK is not a limiting step in the production of anti-TS FdUMP and that tumor cells overexpressing TK are likely to resist 5-FU-based chemotherapies.     

Tumor 5-fluorodeoxyuridylate concentration as a determinant of 5-fluorouracil response

The antitumor activity of 5-fluoruoracil (5-FU) for two murine colonie adenocarcinomas was correlated with the concentration and the clearance of the active antimetabolite, 5-fluorodeoxyuridylate (FdUMP). Mice inoculated with a cell suspension of murine colonic adenocarcinomas 38 and 51 were treated with 5-FU (100 mg/kg i.p.) on 3 day post-transplantation. For mice bearing adenocarconoma 38, treatment with 5-FU was associated with a 97 per cent reduction in mean tumor weight a day 30 and a 77 per cent reduction at day 37 of tumor growth. In contrast, mice bearing colonic adenocarcinoma 51, treated with the same dose schedule of 5-FU did not demonstrate a reduction in the rate of tumor growth in vivo. Two hr after i.p. injection of 5-FU (100 mg/kg) the intracellular concentration of free FdUMP in the sensitive tumor 38 was 560 fmoles/μg of DNA. The active antimetabolite was maintained at a concentration in excess of 100 fmoles/μg of DNA for 72 hr. In contrast, the 2-hr free FdUMP concentration in the resistant tumor line 51 was 240 fmoles μg of DNA(P < 0.005), and a concentration in excess of 100 fmoles/μg of DNA was maintained for only 24 hr. There was no difference in the rate of progressive accumulation of the competitive metabolite, deoxyuridine monophosphate (dUMP), during the first 24 hr of the study. Two hr after i.p. injection of 5-FU (100 mh/kg), [³H] deoxyuridine ([³H]Udr) incorporation into DNA was reduced in both tumor lines to below 3 per cent of control. However, in the sensitive tumor, adeno-carcinoma 38, DNA synthesis was maximally inhibited for 72 hr, compared to 24 hr in the resistant adenocarcinoma 51. The reinitiation of DNA synthesis corresponded to the reduction of free FdUMP concentration to less than 100 fmoles/μg of DNA. There was no linear relationship between the FdUMP/ dUMP ratio and [³H]UdR incorporation into DNA in either tumor line. These data demonstrate that the peak tumor FdUMP concentration and the kinetics of its clearance correlated with the responsiveness of the two specific murine tumors to 5-FU. The measure of peak FdUMP level should be tested for its potential clinical application as a means of selecting patients with gastrointestinal and breast cancer to be treated with this agent.     

Synthesis and evaluation of N-acyl-2-(5-fluorouracil-1-yl)-D,L-glycine as a colon-specific prodrug of 5-fluorouracil.

N-nicotinyl-2-(5-fluorouracil-1-yl)-D,L-glycine (NFG) and N-isonicotinyl-2-(5-fluorouracil-1-yl)-D,L-glycine (INFG) were synthesized as colon-specific prodrugs of 5-fluorouracil (5-FU). As N-aromatic acyl amides of glycine, they are expected to be stable in the upper intestine and delivered to the colon as an intact form if they are nonabsorbable. Microbial hydrolysis of amide bond in the colon will give 2-(5-fluorouracil)-D,L-glycine, which releases 5-FU by spontaneous decomposition. NFG and INFG were soluble in water and stable in pH 1.2 and 7.4 buffer solutions. The apparent partition coefficient of NFG or INFG in 1-octanol/pH 7.4 phosphate buffer solution at 37 degrees was 0.025 or 0.024, respectively. On incubation with cecal contents of rats, conversion of NFG or INFG proceeded only 9 or 5% in 8 h, respectively, producing 5-FU and a metabolite. The metabolite formation was inhibited in the presence of diazouracil, a dihydrouracil dehydrogenase inhibitor. The HPLC retention time of the metabolite from the incubation of 5-FU, NFG, or INFG with cecal contents was identical to dihydro-5-fluorouracil (dihydro-5FU). When N-nicotinyl-2-hydroxy-D,L-glycine methyl ester (NHGM) was incubated with the cecal contents, the extent of amide bond hydrolysis was 85% in 24 h. The result suggested that steric hindrance imposed by 5-FU at 2-position of glycine retarded the hydrolysis of the amide bond in NFG or INFG and suppressed the prodrug conversion.     

Lack of interaction between bropirimine and 5-fluorouracil on human dihydropyrimidine dehydrogenase

1. Bropirimine (2-amino-5-bromo-6-phenyl-4-pyrimidinone) is a member of a class of antineoplastic agents that are administered concomitantly or sequentially with anticancer 5-fluorouracil (5-FU) prodrugs in clinical patients. Interactions between bropirimine and 5-fluorouracil (5-FU) were investigated on dihydropyrimidine dehydrogenase (DPD) activity, the rate-limiting enzyme of 5-FU metabolism, in human liver cytosol. Apparent DPD activity was determined by measuring the recovery of [14C]5-FU by HPLC. 2. The apparent activity of 5-FU metabolism (2.1-100 microM) showed a linear relationship in the Eadie-Hofstee plot in the pooled cytosol, suggesting that a single enzyme is responsible for apparent 5-FU metabolism. Km and Vmax were estimated to be 23 microM and 0.32 nmol min(-1) mg(-1) protein, respectively. Apparent DPD activity for 5-FU (25 microM) in the cytosol from 12 individual donors ranged from 0.017 to 0.39 (0.16 +/- 0.12) nmol min(-1) mg(-1) protein, indicating a large intersubject variance. 3. The suicidal inactivators of the DPD enzyme, (E)-5-(2-bromovinyl)uracil and 5-bromouracil (6.3-50 microM), illustrated concentration-dependent inhibition on DPD activity. Isocytosine (6.3-100 microM), used as a negative control, did not affect DPD activity. Bropirimine (6.3-100 microM) also did not show any inhibition of DPD activity. Therefore, bropirimine is unlikely to cause increases in 5-FU levels in clinical patients after co-administration of bropirimine with 5-FU prodrugs.     

5-Fluorouracil derivatives: a patent review

INTRODUCTION: The fluorinated analog of uracil 5-FU is an antimetabolite, active against a wide range of solid tumors. The main mechanism of action consists in interfering with DNA synthesis and mRNA translation. However, patients treated with 5-FU display several side effects, a result of its nonspecific cytotoxicity for tumor cells. Numerous modifications of the 5-FU structure have been performed in order to overcome these disadvantages. AREAS COVERED: In this review, the metabolic pathways, pharmacokinetics and clinical pharmacology of 5-FU are briefly introduced. Moreover, several derivatives developed and patented, including oral 5-FU prodrugs and combinations with other active compounds, are presented. Finally, new innovative methods for administration and vehiculization of 5-FU and its derivatives are described. EXPERT OPINION: The search for less toxic 5-FU derivatives, which diminish or circumvent some of its disadvantages, has allowed the development of selective antitumor prodrugs and novel methods for tissue-specific drug delivery. Although some of these oral prodrugs are being used clinically, either alone or in combination therapy with other anticancer agents, it seems that the potential of personalized medicine, including pharmacogenomics and targeted therapy with novel 5-FU derivatives, will improve the management and clinical responses of patients treated with 5-FU-based therapy.     

Synthesis and properties of N-nicotinoyl-2-(5-fluorouracil-1-yl)-D,L-glycine ester as a prodrug of 5-fluorouracil for rectal administration.

N-Nicotinoyl-2-(5-fluorouracil-1-yl)-D,L-glycine (NFG) methyl-(NFGM), ethyl-(NFGE) and isopropyl esters (NFGIp) were synthesized and their potential as a prodrug of 5-fluorouracil (5-FU) for rectal administration was investigated. Chemical conversion proceeded either by elimination of (5-FU) or by hydrolysis of ester group. 5-FU was released from NFGIp, NFGE and NFGM 90.5%, 71.3% and 48.5% of the dose, respectively, in 80% human plasma and 79.8%, 56.3% and 31.6%, respectively, in pH 7.4 buffer solution after 48 h of incubation at 37 degrees C. Release of 5-FU occurred mainly from NFG esters but very slightly from NFG, which suggested that release of 5-FU was greatly dependent on the stability of the ester group against hydrolysis. Solubility (M) in pH 7.4 buffer solution was 0.13, 0.09 and 0.04 and apparent partition coefficient in 1-octanol/pH 7.4 buffer solution was 0.76, 1.61 and 4.2, respectively, for NFGM, NFGE and NFGIp, which were in the ranges suitable for rectal absorption. Plasma concentration (microg/mL) of NFGM, NFGE and NFGIp at 50 min after rectal administration to rats was 1.9, 4.6 and 6.7, respectively, and that for 5-FU was below the limit of detection. Their potential as prodrugs of 5-FU for rectal administration is suggested.     

From a classic approach in cancer chemotherapy towards differentiation therapy: acyclic and cyclic seven-membered 5-fluorouracil O,N-acetals

Novel derivatives of 5-fluorouracil (5-FU) possessing a broader spectrum of antitumor activity and fewer toxic side effects than 5-FU have been sought. Herein, we report three different types of 5-FU O,N-acetals: a) a novel class of 5-fluorouracil-containing acyclonucleosides. The antitumor activities of such compounds were assessed against HEp human cells showing that (RS)-1-?[3-(2-hydroxyethoxy)-1-cyclopentoxy]propyl?-5-fluorouracil 3c is 4-fold more active than 5-FU. (RS)-1-?[3-(2-hydroxyethoxy)-1-isopropoxy]propyl?-5-fluorouracil 3b has important potential advantages over 5-FU because of its lower toxicity and its ability to induce myogenic differentiation in rhabdomyosarcoma cells. Our results suggest that this drug may be useful for differentiation therapy in this type of tumor; b) within the cyclic prodrugs of 5-FU, a series of new ring-expanded isosteres (1,4-oxaheteroepanes) of Ftorafur were synthesized. The level of diastereoselectivity in the preparation of cis and trans 1-(3-chloromethyl)-1,4-dioxepan-5-yl)-5-fluorouracil, although modest, suggests a potentially general approach for controlling the stereochemistry of this unexplored class of reactions involving the preparation of 5-FU seven-membered O,N-acetals; c) new 5-FU acyclic analogs containing two 5-FU moieties at both ends of the molecules with a linker having two amide bonds have been designed and synthesized. These bis(5-FU-O,N-acetals) show interesting antineoplastic activities against the HT-29 cell line.     

Parenteral nutrition decreases hepatic dihydropyrimidine dehydrogenase activity and modulates catabolism of 5-fluorouracil in rats

BACKGROUND: Dihydropyrimidine dehydrogenase (DPD) is a rate-limiting enzyme in the catabolism of 5-fluorouracil (5-FU). The effect of parenteral nutrition (PN) on hepatic DPD activity and metabolism of 5-FU remains unknown. MATERIALS AND METHODS: Rats were divided into two groups: a sham-operated oral feeding group (FED) and a PN group. After 7-day PN infusion, hepatic DPD activity, serum 5-FU levels and thymidylate synthase (TS) levels in the jejunum and tumor were measured. RESULTS: PN administration significantly decreased hepatic DPD activities. After infusion of 5-FU (40 mg/kg body), the serum 5-FU concentration and 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP)-bound TS levels in the jejunum were significantly higher in the PN group than the FED group (156.8 +/- 51.9 vs 100.5 +/- 51.9 ng/ml, p < 0.001 and 38.55 +/- 7.61 vs 22.89 +/- 4.46 pmol/g of tissue, p < 0.01, respectively). In Yoshida sarcoma-bearing rats, the FdUMP-bound TS level in the tumor did not differ significantly between the PN and FED rats. CONCLUSION: PN decreases hepatic DPD activity, which may lead to increased toxicity of 5-FU.     

Deoxyuridylate effects on thymidylate synthase-5-fluorodeoxyuridylate-folate ternary complex formation

The competitive basis and specificity of deoxyuridylate (dUMP)-mediated decreases in thymidylate synthase-5'-fluorodeoxyuridylate-folate (TS-FdUMP-folate) ternary complex formation at low concentrations of folates were investigated using charcoal isolation of protein-bound [3H]FuUMP ligand. Reaction conditions used 0.02 microM TS (Lactobacillus casei) and 0.10 microM [3H]FdUMP incubated for 10 min at 37 degrees and pH 7.4. Decreases in counts below control (C) values in dUMP-added samples (S) were expressed as C/S ratios. At CH2--H4PteGlu1 or H4PteGlu1 concentrations below 10 microM, highly linear relationships were found to exist between C/S value and dUMP concentrations, expressed as dUMP/FdUMP ratios. For H4PteGlu1, maximal C/S values for dUMP interference occurred at the lowest H4PteGlu1 concentrations, approaching the value of the TS-FdUMP binary complex. The efficiency of ternary complex formation by H4PteGlu1 was 28 +/- 5% of CH2--H4PteGlu1 values at concentrations below 1.0 microM. The protective effect of increasing H4PteGlu1 against dUMP interference resulted in a linear relationship between the logarithm of H4PteGlu1 concentration and the slope of dUMP interference (C/S vs dUMP/FdUMP). In contrast, the results with CH2--H4PteGlu1 were biphasic. At concentrations of CH2--H4PteGlu1 lower than 0.5 microM, C/S values were greater than those for binary complex alone, a result related to CH2--H4PteGlu1 consumption based on [5-3H]dUMP tritium-release studies. At concentrations of CH2--H4PteGlu1 above 1.0 microM, however, dUMP interference was nearly abolished. Kinetic analysis of the data suggests that this effect of the 5,10-methylene moiety may result in part from positive allosteric effects of first site TS-FdUMP-CH2--H4PteGlu1 ternary complex binding on acceleration of second site binding, in addition to slowed rates of dissociation. Other folylmonoglutamates showed relatively poor TS-[3H]FdUMP-folate complex formation: at 500 microM folate, as a percentage of CH2--H4PteGlu1 values, these were 29.6% for dihydrofolate, 7.5% for 5-CH3--H4PteGlu1, 3.0% for CH = H4PteGlu1, 1.6% for folic acid, 1.1% for 5-CHO--H4PteGlu1 (leucovorin) and 0.9% for 10-CHO--H4PteGlu1. Inhibitory effects by dUMP were consistent with binary complex effects alone for these folates. Study of methotrexate, as the monoglutamate and the hexaglutamate, suggested that ternary complexes with dUMP are favored over those with FdUMP at high concentrations of the antifolate. Our results indicate that activation of leucovorin to over 0.5 microM in intracellular CH2--H4PteGlu1 equivalents may be a requirement for achieving complete TS inhibition by FdUMP in the presence of excess conce     

Lack of interaction between bropirimine and 5-fluorouracil on human dihydropyrimidine dehydrogenase

1. Bropirimine (2-amino-5-bromo-6-phenyl-4-pyrimidinone) is a member of a class of antineoplastic agents that are administered concomitantly or sequentially with anticancer 5-fluorouracil (5-FU) prodrugs in clinical patients. Interactions between bropirimine and 5-fluorouracil (5-FU) were investigated on dihydropyrimidine dehydrogenase (DPD) activity, the rate-limiting enzyme of 5-FU metabolism, in human liver cytosol. Apparent DPD activity was determined by measuring the recovery of [¹⁴C]5-FU by HPLC.

2. The apparent activity of 5-FU metabolism (2.1 - 100 μm) showed a linear relationship in the Eadie-Hofstee plot in the pooled cytosol, suggesting that a single enzyme is responsible for apparent 5-FU metabolism. K_m and V_max were estimated to be 23 μm and 0.32 nmol min^?1 mg^?1 protein, respectively. Apparent DPD activity for 5-FU (25 μm) in the cytosol from 12 individual donors ranged from 0.017 to 0.39 (0.16 ± 0.12) nmol min^?1 mg^?1 protein, indicating a large intersubject variance.

3. The suicidal inactivators of the DPD enzyme, (E)-5-(2-bromovinyl)uracil and 5- bromouracil (6.3 - 50 μm), illustrated concentration-dependent inhibition on DPD activity. Isocytosine (6.3 - 100 μm), used as a negative control, did not affect DPD activity. Bropirimine (6.3 - 100 μm) also did not show any inhibition of DPD activity. Therefore, bropirimine is unlikely to cause increases in 5-FU levels in clinical patients after coadministration of bropirimine with 5-FU prodrugs.     

Tetrahydro-2H-1,3,5-thiadiazine-5-(4-pyridylcarboxamide)-2-thione derivatives as prodrugs for isoniazid; synthesis, investigations and in vitro antituberculous activity

3-Substituted-5-(4-pyridylcarboxamido)tetrahydro-2H-1,3,5-thiad iazine-2- thione derivatives 5a-e were synthesized as prodrugs for isoniazid (INH) to overcome the resistance developed with its therapeutic use. These prodrugs revealed higher lipophilicity compared with INH. Their degradation kinetics were studied in vitro using aqueous buffer solutions of pH values 1.2 and 7.4 was well as biological media of human plasma and rat liver homogenate at 37 degrees C. They were more stable toward enzymatic degradation in biological than in chemical media. Release of INH from these derivatives was detected as a result of both chemical and enzymatic hydrolysis by HPLC. The antimycobacterial activity of the synthesized compounds and INH was tested in vitro against human type of Mycobacterium tuberculosis. They exhibited a greater antitubercular activity than the parent drug. This result is considered as an indicator for an improved permeation of the synthesized prodrugs through mycobacterial cell membranes relative to INH.     

Novel derivatives of 5-fluorouridine and 5-fluorouracil having potent antitumor and lower immunosuppressive activities.

We studied the biological activities of several 5-fluorouridine (5-FUR) and 5-fluorouracil (5-FU) derivatives to find novel antitumor drugs with lower immunosuppressive effects. We examined 5-FUR and 5-FU derivatives acylated with (2-n-propyl-n-pentanoyl)glycine (KN-539). Among the examined compounds, we found satisfactory activities in a derivative of 5-FUR, 2',3',5'-tris-O-[N-(2-n-propyl-n-pentanoyl)glycyl]-5-fluorouridine (UK-21), and a derivative of 5-FU, 1-(6-[N-(2-n-propyl-n-pentanoyl)glycyl] amino-n-hexylcarbamoyl)-5-fluorouracil (UK-25). UK-21 (0.05-0.2 mmole/kg, p.o., 10 days) and UK-25 (0.1-0.4 mmole/kg, p.o., 10 days) suppressed Meth A and E.L.4 tumor growths in the corresponding syngeneic hosts (BALB/c mice and C57BL/6 mice, respectively) without decreasing body weight and blood leukocyte count. UK-21 and UK-25 suppressed the proliferation of KB tumor cells in vitro (IC50: 3.0 x 10(-11) M and 4.4 x 10(-7) M, respectively) at concentrations almost equivalent to those of 5-FUR and 5-FU, respectively. These results suggest that UK-21 and UK-25 express their antitumor activity as 5-FUR and 5-FU, respectively. Neither UK-21 nor UK-25 suppressed thymus weight and humoral antibody production against sheep red blood cells (SRBC) in ddY mice, although 1-(2-tetrahydrofuryl)-5-fluorouracil (FT-207) and 5-FU suppressed them in their respective therapeutic dose ranges for tumors. Thus, UK-21 and UK-25 are expected to develop into anticancer drugs with lower immunotoxicological effects.     

Synthesis,in vitro aerobic and hypoxic cytotoxicity and radiosensitizing activity of novel metronidazole tethered 5-fluorouracil

Background and the purpose of the study

Several 2, 4-dinitrophenyl and 2,4-dinitrophenylamine tethered 5-FU (5-fluorouracil) compared to their components have shown minimal or no cytotoxicity to HT-29 cell line under aerobic conditions but high cytotoxicity and radiosensitizing effects under hypoxic conditions. In the present study the cytotoxicity and radiation potentiation of three novel analogues of these compounds by replacing 2,4-dinitrophenyl moiety with 2-methyl-5-nitroimidazole, a known radiosensitizer and cytotoxic agent was investigated.

Methods

Tethered compounds 7–9 were prepared by the reaction of 1-(t-butoxycarbonyl)-5-fluorouracil 6 with metronidazole esters 2–4 followed by removal of the t-butoxycarbonyl protecting group. Cytotoxicity of compounds in HT-29 cells with or without radiation were determined by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), propidium iodide (PI)-digitonin and clonogenic assays.

Results

Tethered compounds 7–9 induced time-and concentration–dependent cytotoxicity under hypoxia but had no significant effect under aerobic conditions. These compounds also showed selective and concentration- dependent radiosensitization effects under hypoxic conditions.

Conclusion

Tethered compounds 7–9 compared to 5-FU 5 showed minimal cytotoxicities under aerobic and selective radiosensitizing activities under hypoxic conditions. Also effects of these compounds were higher than those of metronidazole 1 which is a known cytotoxin and radiosensitizer under hypoxic conditions.     

Effects of antifolates on the binding of 5-fluoro-2'-deoxyuridine monophosphate to thymidylate synthase

Folate based inhibitors of thymidylate synthase (TS) might facilitate binding of 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP) to TS similar to the natural reduced folate 5,10-methylenetetrahydrofolate (CH(2)-H(4)-folate). We studied the lipophilic, non-polyglutamatable antifolates Nolatrexed (NTX) and AG331 and antifolates, that can have a polyglutamate side chain like the natural folate CH(2)-H(4)-folate; GW1843U89, Raltitrexed (RTX) and Multi-targetted antifolate (MTA) and pentaglutamates (RTX-Glu(5) and MTA-Glu(5)). The capacity of these compounds to facilitate the binding of [(3)H]FdUMP to Lactobacillus casei TS and an ammoniumsulphate precipitate of human TS was investigated. Only NTX, RTX-Glu(5) and MTA-Glu(5) facilitated FdUMP binding to L. casei TS and their dissociation constant K(d) (0.2-0.7 microM) was low compared to CH(2)-H(4)-folate (2.0 microM). The small lipophilic molecule NTX was favorable to the larger AG331. Polyglutamylation, as indicated by the difference in effect of RTX vs. RTX-Glu(5) and MTA vs. MTA-Glu(5), seems to be important for a classical antifolate to facilitate binding of FdUMP to bacterial TS. Effects of antifolates on FdUMP binding to human TS were different. At a low concentration (0.05 microM) NTX, RTX-Glu(5) and MTA-Glu(5) facilitated 3-5 times higher binding of [(3)H]FdUMP to TS than CH(2)-H(4)-folate. At higher concentrations (0.3-5 microM) of NTX, RTX-Glu(5) and MTA-Glu(5) the FdUMP binding decreased. The complex remained stable in the absence of (anti)folate for at least 24hr. The K(d) values of the antifolates for human TS varied from 19 to 387 nM, while the K(d) of CH(2)-H(4)-folate for human TS was 351 nM. The Hill coefficients, which indicated the type of cooperativity of the antifolates in the binding of FdUMP to TS were positive (0.58-0.99) at low concentrations (<0.3 microM) and negative (-0.35 to -0.81) at concentrations >0.3 microM except for GW1843U89, which only showed negative cooperativity (-1.70). It was shown with [(14)C]NTX that when the binding of FdUMP decreased at high NTX concentrations, the binding of NTX to TS still increased. This also held for the natural substrate dUMP. The negative cooperativity of the antifolates was clearly concentration dependent. The difference between human and L. casei TS in the FdUMP binding assays with antifolates can possibly be explained by interaction of the two subunits of human TS, which was absent in L. casei TS. The binding of antifolates to one of the two subunits induced a conformational change of the other subunit. This change no longer allowed the binding of FdUMP or dUMP at the active site. In conclusion this study showed that antifolates enhanced the binding of FdUMP to TS, especially at low antifolate concentrations, that are also clinically achievable, e.g. in human plasma.