Plasma, intestine and tumor levels of 5-fluorouracil in mice bearing L1210 ascites tumor following oral administration of 5-fluorouracil, UFT (mixed compound of tegafur and uracil), carmofur and 5'-deoxy-5-fluorouridine.

Several 5-fluorouracil (5-FU) derivatives, 1-hexylcarbamoyl-5-fluorouracil (HCFU), 5'-deoxy-5-fluorouridine (5'-DFUR) and UFT (mixed compound of tegafur and uracil), have been developed and clinically widely used. However, comparative pharmacokinetic studies of the parent compound and other fluorinated drivatives have not been precisely reported. The dosage of the oral clinical use for human cancer of 5-FU, HCFU, 5'-DFUR and UFT as tegafur (FT) is 200-300mg/d, 600mg/d, 800-1,200mg/d and 300-600mg/d respectively. These amounts of the drugs are almost equimolar. Previously, we reported the effect of oral equimolar administration of each four drugs on thymidilate synthase activity, deoxyribonucleotide metabolism and cell cycle progression in L1210 ascites tumor. (1,2) In this study, we examined the antitumor effect and 5-FU concentration in the plasma, intestine and tumor after oral equimolar administrations of each drug using BDF1 mice bearing L1210 ascites tumor. In our study, UFT showed the best life prolongation among these four drugs. The intestine 5-FU level was highest by treatment with 5-FU during the initial 4 h. The plasma 5-FU level was highest by treatment with HCFU for 4 h. But the tumor 5-FU level was highest by treatment with UFT over the 24 h. In spite of the high plasma 5-FU concentration after the treatment with HCFU, the 5-FU concentration in the tumor was below the detectable level until 24 h. These findings suggested that the highest specific accumulation of 5-FU in tumor cells may explain the best therapeutic results of UFT.     

Discovery and development of novel anticancer drug capecitabine

Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a novel oral fluoropyrimidine carbamate, which was designed to be sequentially converted to 5-fluorouracil (5-FU) by three enzymes located in the liver and in tumors. N4-alkoxycarbonyl-5'-deoxy-5-fluorocytidine derivatives including capecitabine pass intact through the intestinal tract and are sequentially converted to 5-FU by a cascade of the three enzymes. The first step is the conversion to 5'-deoxy-5-fluorocytidine (5'-DFCR) by carboxylesterase located in the liver, then to 5'-deoxy-5-fluorouridine (5'-DFUR) by cytidine deaminase highly expressed in the liver and various solid tumors, and finally to 5-FU by thymidine phosphorylase (dThdPase) preferentially located in tumor tissues. Among large numbers of the derivatives, capecitabine was selected based on its susceptibility to hepatic carboxylesterase, oral bioavailability in monkeys and efficacy in a human cancer xenograft. Capecitabine given orally yielded substantially higher concentrations of 5-FU within tumors than in plasma or normal tissue (muscle). The tumor 5-FU levels were also much higher than those achieved by intraperitoneal administration of 5-FU at equi-toxic doses. This tumor selective delivery of 5-FU ensured greater efficacy and a more favourable safety profile than with other fluoropyrimidines. In 24 human cancer xenograft models studied, capecitabine was more effective at a wider dose range and had a broader spectrum of antitumor activity than 5-FU, UFT or its intermediate metabolite 5'-DFUR. The susceptibility of the xenografts to capecitabine correlated with tumor dThdPase levels. Moreover, the conversion of 5'-DFUR to 5-FU by dThdPase in tumor was insufficient in a xenograft model refractory to capecitabine. In addition, the efficacy of capecitabine was enhanced by dThdPase up-regulators, such as by taxanes and cyclophosphamide and by X-ray irradiation. The efficacy of capecitabine may, therefore, be optimized by selecting the most appropriate patient population based on dThdPase status and/or by combining it with dThdPase up-regulators. Capecitabine has additional characteristics not found with 5-FU, such as potent antimetastatic and anticachectic actions in mouse tumor models. With these profiles, capecitabine may have substantial potential in cancer treatment.     

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.     

Antineoplastic action of egg-white lysozyme on the growth of MCa mammary carcinoma and TLX5 lymphoma in the CBA mouse

The antitumor effects of egg-white lysozyme, at dosages between 25 and 100 mg/kg/day given for 5 to 14 days, was examined in CBA mice bearing MCa mammary carcinoma or TLX5 lymphoma. At early stages of tumor growth the antitumor action of lysozyme is statistically significant, independently from the route of administration (e.g., i.v. and oral admixed with food). With larger tumor masses, oral administration of lysozyme is effective on s.c. tumor growth but not on i.m. tumors. The effects of lysozyme in mice bearing TLX5 lymphoma consist of reduction of the capacity of tumor cells to form brain metastases: the effect is mediated by spleen cells. Dietary intake of lysozyme is also active in prolonging the survival time of animals treated with surgery and postsurgical cisplatin treatment. These effects indicate lysozyme to be an active substance, effective on the growth of malignant tumors and capable of synergizing with conventional therapies such as surgery plus cisplatin for the control of disseminated tumors in mice.     

Modulation of uridine phosphorylase gene expression by tumor necrosis factor-alpha enhances the antiproliferative activity of the capecitabine intermediate 5'-deoxy-5-fluorouridine in breast cancer cells

Uridine phosphorylase (UPase) has been shown to play an important role in the antineoplastic activity of 5-fluorouracil (5-FU) and in the anabolism of its oral prodrug, capecitabine, through the conversion of 5'-deoxy-5-fluorouridine (5'-DFUR) into 5-FU. In this study, we investigated the effect of tumor necrosis factor-alpha (TNF-alpha) on UPase gene expression and 5'-DFUR antiproliferative activity and elucidated the involved signal transduction pathway. Our data indicate that TNF-alpha significantly induced UPase mRNA expression and its enzymatic activity in EMT6 murine breast cancer cells, leading to an enhanced cytotoxicity of 5'-DFUR. This is further confirmed by an increased incorporation of 5'-DFUR-originated 5-FU nucleotides into nucleic acids. To clarify the mechanism of TNF-alpha-induced UPase expression, we first observed the effect of TNF-alpha on the UPase promoter activity with a series of 5'-deleted promoter-luciferase constructs. Transient transfection analysis showed that the TNF-alpha-inductive pattern in EMT6 cells was consistent with the presence of a nuclear factor-kappaB (NF-kappaB) binding element (-1332/-1312 bp) in the UPase promoter region. Furthermore, electrophoretic mobility shift assays, supershift, and cotransfection assays revealed that the activation of p65 was responsible for UPase induction by TNF-alpha. Finally, the induction of UPase by TNF-alpha could be suppressed by PS-341, a NF-kappaB inhibitor. In summary, TNF-alpha efficiently induces UPase gene expression through a NF-kappaB subunit p65-dependent pathway enhancing cell sensitivity to 5'-DFUR. The elucidation of this regulation mechanism may aid in the clinical use of 5-FU-based chemotherapy.     

杂环化合物取代的5-氟尿嘧啶衍生物的合成及抗肿瘤活性

杂环化合物取代的５氟尿嘧啶衍生物的合成及抗肿瘤活性毛曼君陈耀祖田（中科院兰州地质所；兰州大学化学系，兰州７３００００）杂环化合物大都有广泛的生物活性，据文献［１，２］报道，有巯基的嘧啶环系列化合物有抗癌活性和免疫增强作用。因而，设想给５氟尿...     

Antitumor activity of Klebsiella 03 lipopolysaccharide in mice

The antitumor activity of Klebsiella 03 lipopolysaccharide (KO3 LPS) isolated from the culture supernatant against S180 sarcoma, Ehrlich carcinoma, MM2 mammary carcinoma and Meth A fibrosarcoma in mice was investigated. KO3 LPS significantly prolonged the lifespan of S180-bearing ddY mice and MM2-bearing C3H/He mice by intraperitoneal pre- or postmedication at doses ranging from 0.1 to 1.0 mg/kg. The LPS also inhibited the growth of subcutaneously inoculated Ehrlich carcinoma in ddY mice and Meth A sarcoma in BALB/c mice by intraperitoneal, intravenous or intratumoral administration. The intratumoral injection of KO3 LPS was most effective and results by the intravenous and the intraperitoneal administrations followed in effectiveness, but the administration through the subcutaneous route was hardly effective. Thus, KO3 LPS was shown to have antitumor activity on both allogeneic tumors and syngeneic tumors. It was also indicated in this study that the lifeprolonging effect of KO3 LPS on S180 ascites type tumor-bearing mice was significantly minimized by pretreatment of cyclophosphamide and that the LPS did not influence the cell viability of HeLa cells, Ehrlich cells and MM2 cells in vitro. These results suggest that the antitumor activity of KO3 LPS is provided by host-mediated actions.     

Antitumor activity of biflorin, an o-naphthoquinone isolated from Capraria biflora

Pharmacological studies with an aqueous extract obtained from leaves of Capraria biflora showed potent cytotoxic, analgesic, antimicrobial and anti-inflammatory activities. It has been demonstrated that biflorin possesses an in vitro cytotoxic activity against tumor cells. The in vivo antitumor activity of biflorin was evaluated on two mouse models, sarcoma 180 and Ehrlich carcinoma. Biflorin was active against both tumors with a very similar profile. In addition, biflorin was also able to increase the response elicited by 5-FU in mice inoculated with both tumors. The results showed a decrease in Ki67 staining in tumor cells from treated-animals when compared with non-treated groups, which suggests an inhibition of tumor proliferation rate. Histopathological analysis from kidneys and liver showed that biflorin possessed weak and reversible toxic effects. It was also demonstrated that biflorin acts as an immunoadjuvant agent, rising the production of ovalbumin-specific antibodies and inducing a discreet increase of the white pulp and nest of megakaryocytic in spleen of treated mice, which can be related to its antitumor properties.     

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.     

Relationship between AUC of 5'-DFUR and toxicity of capecitabine, fluoropyrimidine carbamate analogs, and 5'-DFUR in monkeys, mice, and rats

Capecitabine is an oral fluoropyrimidine carbamate which is converted to 5-fluorouracil (5-FU) via 3 enzymatic step to 5'-deoxy-5-fluorocytidine (5'-DFCR), 5'-deoxy-5-fluorouridine (5'-DFUR), and finally 5-FU. We performed 4-week toxicity studies of capecitabine (N(4)-pentyloxycarbonyl-5'-deoxy-5-fluorouridine), galocitabine (trimethoxybenzyl-5'-deoxy-5-fluorocytidine), 4 different fluoropyrimidine carbamate analogs (R=butyl, isopentyl, propyl, or phenethyl), and 5'-DFUR in cynomolgus monkeys with toxicokinetic measurements of intact molecules, 5'-DFCR, and 5'-DFUR. Four-week toxicity data for capecitabine in rats and mice were also obtained for comparison. Capecitabine, galocitabine, butyl, and isopentyl analogs showed similar toxicities in hematopoietic and intestinal organs at 1.0 mmol/kg and the AUCs of 5'-DFUR were approximately 40 to 60 microg*hr/ml. These compounds showed slight toxicity at 0.5 mmol/kg and no toxicity at 0.1 mmol/kg, and AUCs of 5'-DFUR were approximately 30 and 5 microg*hr/ml, respectively. Propyl and phenethyl analogs showed slight toxicity at 1.0 mmol/kg and no toxicity at 0.5 mmol/kg, and AUCs of 5'-DFUR were approximately 30 and 10 microg*hr/ml, respectively. On the other hand, severe and slight-to-moderate toxicity was observed at 0.5 and 0.25 mmol/kg in 5'-DFUR-treated monkeys and AUCs of 5'DFUR were 35.6 and 5.2 microg*hr/ml, respectively. In mice and rats, the toxicity of capecitabine was less than in monkeys relative to dose, but 5'-DFUR AUCs were almost the same. In conclusion, 5'-DFUR AUC correlated with toxicity following oral administration of capecitabine and its analogs in monkeys, mice, and rats, although this relationship is not seen in humans. Capecitabine was less toxic in monkeys than oral 5'-DFUR according to dose (mmol/kg) and 5'-DFUR AUC.     

2-(芳基哌嗪)乙酰氨基-5-取代-苯并噻唑衍生物的合成及抗肿瘤活性

目的合成新型苯并噻唑衍生物并研究其抗肿瘤活性。方法以3-取代苯胺为原料合成系列2-（芳基哌嗪）乙酰氨基-5-取代-苯并噻唑衍生物,采用MTT法测试了化合物对肿瘤细胞的抑制作用。结果合成了12个新的苯并噻唑衍生物,化合物结构经’H-NMR、ESI-MS和元素分析确证。结论多数目标化合物对5种肿瘤细胞株具抗增殖作用,部分化合物显示出与阳性对照药物5-氟尿嘧啶相当的抗肿瘤活性。     

Lack of contribution of dihydrofluorouracil and alpha-fluoro-beta-alanine to the cytotoxicity of 5'-deoxy-5-fluorouridine on human keratinocytes

Capecitabine (Xeloda) is a very active oral fluoropyrimidine (colon and breast cancers) whose clinical use is complicated by the presence of hand-foot syndrome (HFS). This cutaneous toxicity is less frequently encountered with other oral fluoropyrimidines containing a dihydropyrimidine dehydrogenase (DPD) inhibitor. The HFS is thus attributed to the presence of the main 5-fluorouracil (5-FU) metabolites, dihydrofluorouracil (5-FUH2) and alpha-fluoro-beta-alanine (FBAL), but without strong pharmacological arguments. The aim of the present study was to closely examine this latter hypothesis. Capecitabine generates 5'-deoxyflourouridine (5'-DFUR) which is transformed into 5-FU at the cellular target site through the intermediary of thymidine phosphorylase (TP). The cytotoxic effects (MTT test, 4-day exposure) of 5'-DFUR, 5-FU, 5-FUH2 and FBAL were tested against the spontaneously immortalized human keratinocyte cell line (HaCaT) and the human cancer colon cell line WiDr as a control. Mean IC50s on HaCaT and WiDr were, respectively, 1.3 and 10 microM for 5'-DFUR, 0.2 and 3.3 microM for 5-FU, 13.4 and 560 microM for 5-FUH2, and greater than 650 and 6500 microM for FBAL. The respective 5'-DFUR IC50s values were not different when cells were exposed to 5'-DFUR alone or in combination with 5-FU, 5-FUH2 and FBAL in both cell lines, the relative proportion of each drug reflecting known pharmacokinetic data for capecitabine (5'-DFUR 12.4%, 5-FUH2 6.4%, 5-FU 1.2% and FBAL 80%). This latter finding demonstrates the relative lack of significant cytotoxic activity of 5-FUH2 and FBAL on human keratinocytes. TP activity was particularly high in HaCaT cells and DPD activity was very low in both cell lines. These data strongly suggest that the presence of 5-FU metabolites does not play a major role in the HFS generated by capecitabine and that it can probably be attributed to particularly high TP activity in keratinocytes. This observation may have important clinical consequences such as a possible local pharmacological inhibition of TP for controlling HFS.     

Development of 5-Fluorouracil derivatives as anticancer agents

5-Fluorouracil (5-FU) is one of the most potent antimetabolites which have been widely used in the treatment of advanced solid tumors. As an anticancer agent, because of its low efficacy and high toxicity, numerous modifications of 5-FU structure have been performed. A great number of novel 5-FU derivatives have been developed with highly efficient and much less toxic. In this paper, the recent development of novel 5-FU derivatives as potent antitumor agents is reviewed and discussed.     

Bioactivation of capecitabine in human liver: involvement of the cytosolic enzyme on 5'-deoxy-5-fluorocytidine formation.

Capecitabine, an anticancer prodrug, is thought to be biotransformed into active 5-fluorouracil (5-FU) by three enzymes. After oral administration, capecitabine is first metabolized to 5'-deoxy-5-fluorocytidine (5'-DFCR) by carboxylesterase (CES), then 5'-DFCR is converted to 5'-deoxy-5-fluorouridine (5'-DFUR) by cytidine deaminase. 5'-DFUR is activated to 5-FU by thymidine phosphorylase. Although high activities of drug metabolizing enzymes are expressed in human liver, the involvement of the liver in capecitabine metabolism is not fully understood. In this study, the metabolism of capecitabine in human liver was investigated in vitro. 5'-DFCR, 5'-DFUR, and 5-FU formation from capecitabine were investigated in human liver S9, microsomes, and cytosol in the presence of the inhibitor of dihydropyrimidine dehydrogenase, 5-chloro-2,4-dihydroxypyridine. 5'-DFCR, 5'-DFUR, and 5-FU were formed from capecitabine in cytosol and in the combination of microsomes and cytosol. Only 5'-DFCR formation was detected in microsomes. The apparent K(m) and V(max) values of 5-FU formation catalyzed by cytosol alone and in combination with microsomes were 8.1 mM and 106.5 pmol/min/mg protein, and 4.0 mM and 64.0 pmol/min/mg protein, respectively. The interindividual variability in 5'-DFCR formation in microsomes and cytosol among 14 human liver samples was 8.3- and 12.3-fold, respectively. Capecitabine seems to be metabolized to 5-FU in human liver. 5'-DFCR formation was exhibited in cytosol with large interindividual variability, although CES is located in microsomes in human liver. In the present study, it has been clarified that the cytosolic enzyme would be important in 5'-DFCR formation, as is CES.     

Tissue distribution and biotransformation of potassium oxonate after oral administration of a novel antitumor agent (drug combination of tegafur, 5-chloro-2,4-dihydroxypyridine, and potassium oxonate) to rats.

S-1, a new oral 5-fluorouracil (5-FU)-derivative antitumor agent, is composed of tegafur, 5-chloro-2,4-dihydropyridine, and potassium oxonate (Oxo). Oxo, which inhibits the phosphorylation of 5-FU, is added to reduce the gastrointestinal (GI) toxicity of the agent. In this study, we investigated the tissue distribution and the metabolic fate of Oxo in rats after oral administration of S-1. Oxo was mainly distributed to the intracellular sites of the small intestines in a much higher concentration than 5-FU, but little distributed to other tissues, including tumorous ones in which 5-FU was observed after oral administration of S-1. Plasma concentration-time profiles of Oxo and its metabolites after i.v. and oral administration of S-1 revealed that Oxo was mainly converted to cyanuric acid in the GI tract. Furthermore, the analysis of drug-related radioactivity in GI contents and in vitro studies suggested that Oxo was converted to cyanuric acid by two routes, the first being direct conversion by the gut flora in the cecum, and the second, conversion by xanthine oxidase or perhaps by aldehyde oxidase after degradation to 5-azauracil (5-AZU) by the gastric acid. These results indicate that, although a part of the administered Oxo was degraded in the GI tract, Oxo was mainly distributed to the intracellular sites of the small intestines in a much higher concentration than 5-FU and that little was distributed to other tissues, including tumors. We conclude that this is the reason why Oxo suppresses the GI toxicity of 5-FU without affecting its antitumor activity.     

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.     

Improvement of stability and bioavailability of 1-hexylcarbamoyl-5-fluorouracil (HCFU) by O-carboxymethyl-O-ethyl-beta- cyclodextrin]

The possible utility of O-carboxymethyl-O-ethyl-beta-cyclodextrin (CME-beta-CyD) as a novel drug carrier was studied in vitro and in vivo, by using 1-hexylcarbamoyl-5-fluorouracil (HCFU) as a model drug. The chemical instability of HCFU in solution and solid state was improved by CME-beta-CyD complexation. The in vitro release of HCFU from the CME-beta-CyD complex was decelerated in acidic solution, while accelerated at neutral pH regions, showing a typical delayed-release pattern. This pattern was clearly reflected in the blood levels after the oral administration of the complex to dogs, increasing the bioavailability. The present results suggested that CME-beta-CyD is useful as a delayed-release-type carrier for the oral administration of chemically labile HCFU.     

In vitro and in vivo antitumor effects of bisphosphonates

Bisphosphonates are powerful inhibitors of osteoclast-mediated bone resorption. They are currently used in the palliative treatment of bone metastases. However, bisphosphonates do not only act on osteoclasts. There is now extensive in vitro preclinical evidence that bisphosphonates can act on tumor cells: they inhibit tumor cell adhesion to mineralized bone as well as tumor cell invasion and proliferation. Bisphosphonates induce also tumor cell apoptosis and stimulate gammadelta T cell cytotoxicity against tumor cells. In vivo, bisphosphonates inhibit bone metastasis formation and reduce skeletal tumor burden. This may reflect direct antitumor effects and indirect effects via inhibition of bone resorption. In addition, bisphosphonates inhibit experimental angiogenesis in vitro and in vivo. Understanding the molecular mechanisms through which bisphosphonates act on tumor and endothelial cells will be undoubtedly an important task in the future. It will allow the design of clinical trials to investigate whether the antitumor activity of bisphosphonates can be realized in the clinical setting.     

Depression of phenytoin metabolic capacity by 5-fluorouracil and doxifluridine in rats

It has been found in clinical practice that the serum level of phenytoin, of which metabolism is mediated by hepatic CYP2C enzymes, was markedly elevated by co-administration of 5-fluorouracil (5-FU) and doxifluridine (5'-deoxy-5-fluorouridine; 5'-DFUR), a prodrug of 5-FU, but the detailed mechanisms are unclear. A study using rats was undertaken to examine the effects of 5-FU and 5'-DFUR on phenytoin metabolism in hepatic microsomes and phenytoin pharmacokinetics in-vivo. Neither 5-FU nor 5'-DFUR exhibited direct inhibitory effects on hepatic microsomal phenytoin p-hydroxylation, a major metabolic route catalysed by CYP2C in rats, as in humans. 5-FU and 5'-DFUR were injected intraperitoneally into male rats as single doses (1.68 mmol kg(-1)) and repeated doses (0.24 mmol kg(-1) for 7 days). Control rats received vehicle alone. A significant reduction in the activity of phenytoin p-hydroxylation was observed 4 days after the last administration irrespective of the agents and their treatment regimens, although the activity was unchanged on Day 1. Pharmacokinetic analysis of phenytoin revealed that the elimination rate constant and the total clearance was decreased by 70-75% in both the 5'-DFUR-treated and 5-FU-treated rats, indicating that the decrease in the metabolic capacity of phenytoin was responsible for the change in phenytoin disposition in-vivo. On the other hand, 5-FU significantly depressed the total P450 content, NADPH cytochrome c reductase activity and activities of progesterone hydroxylations. However, the depressive effects of 5'-DFUR were not very potent relative to those of 5-FU, which can be explained by the fact that 5-FU is derived from 5'-DFUR to only a small extent. According to a recent report, phenytoin p-hydroxylation and progesterone 2alpha-/21-hydroxylations share common CYP2C enzymes as their catalysts. Because there was a difference in the modulation profiles between phenytoin p-hydroxylation and progesterone 2alpha-/21-hydroxylations after exposure to 5'-DFUR, 5'-DFUR might modulate phenytoin metabolism without loss of catalytic ability for other substrates, unlike 5-FU. The present study suggested that the down-regulation of hepatic CYP2C enzymes occurs by 5-FU exposure even at a low level, and provided a fundamental explanation for the drug interaction encountered in clinical practice.