Search

DNA microarray analysis comparing human tumor tissues with normal tissues including hematopoietic progenitor cells resulted in identification of membrane dipeptidase as a prodrug activation enzyme. Novel prodrugs of 2'-deoxy-2'-methylidenecytidine (DMDC) including compound 23 that are activated by membrane dipeptidase (MDP) preferentially in tumor tissue were designed and synthesized to generate the active drug, DMDC, after hydrolysis of the dipeptide bond followed by spontaneous cyclization of the promoiety.

Capecitabine is an orally available fluoropyrimidine and is finally converted to 5-FU selectively in tumor tissues. In our study, we examined whether the antitumor activity of capecitabine is directly affected by a modulation of dihydropyrimidine dehydrogenase (DPD). The modulations were carried out by the overexpression of DPD in tumor cells and by tumor selective DPD inhibition. The DPD-overexpressing cells were obtained by transfection of human DPD cDNA into HCT116 human colorectal cancer cells. The HCT116 cells bearing DPD cDNA expressed about 13 times higher DPD activities than the parental HCT116 cells, and they became significantly less susceptible to capecitabine than the parental cells when transplanted into nude mice. Administration of RO0094889 that is converted to a DPD inhibitor 5-vinyluracil selectively in tumor tissues restored the antitumor activity of capecitabine against the tumor of the HCT116 cells carrying DPD cDNA and various tumors expressing DPD. As compared to 5-ethynyluracil or 5-vinyluracil, which inhibited DPD not only in tumor tissues but also in other non-cancerous tissues, the effective dose range of RO0094889 in augmenting the efficacy of capecitabine was much broader. These results indicate that the antitumor activity of capecitabine is directly affected by DPD activities in tumor tissues and therefore, the combination of capecitabine and a tumor selective DPD inhibitor, RO0094889, will be beneficial to patients who have tumors with high levels of DPD., (Copyright 2003 Wiley-Liss, Inc.)

A series of tumor-activated prodrugs of the inhibitors of dihydropyrimidine dehydrogenase (DPD), an enzyme catabolizing 5-fluorouracil (5-FU: 4g), has been designed and synthesized. RO0094889 (11c) is a prodrug of 5-vinyluracil (4c), a known DPD inhibitor, and was designed to generate 4c selectively in tumor tissues by sequential conversion of 11c by three enzymes: esterase, cytidine deaminase and thymidine phosphorylase, the latter two of which are known to be highly expressed in various tumor tissues. When capecitabine (1), a tumor-activated prodrug of 5-FU, was co-administered orally with 11c, 5-FU in tumor tissues was significantly increased with only a slight increase of 5-FU in plasma as compared with oral capecitabine alone.

Purpose: To identify the factors governing the dose-limiting toxicity in the gastrointestine (GI) and the antitumor activity after oral administration of capecitabine, a triple prodrug of 5-FU, in humans., Method: The enzyme kinetic parameters for each of the four enzymes involved in the activation of capecitabine to 5-FU and its elimination were measured experimentally in vitro to construct a physiologically based pharmacokinetic model. Sensitivity analysis for each parameter was performed to identify the parameters affecting tissue 5-FU concentrations., Results: The sensitivity analysis demonstrated that (i) the dihydropyrimidine dehydrogenase (DPD) activity in the liver largely determines the 5-FU AUC in the systemic circulation, (ii) the exposure of tumor tissue to 5-FU depends mainly on the activity of both thymidine phosphorylase (dThdPase) and DPD in the tumor tissues, as well as the blood flow rate in tumor tissues with saturation of DPD activity resulting in 5-FU accumulation, and (iii) the metabolic enzyme activity in the GI and the DPD activity in liver are the major determinants influencing exposure to 5-FU in the GI. The therapeutic index of capecitabine was found to be at least 17 times greater than that of other 5-FU-related anticancer agents, including doxifluridine, the prodrug of 5-FU, and 5-FU over their respective clinical dose ranges., Conclusions: It was revealed that the most important factors that determine the selective production of 5-FU in tumor tissue after capecitabine administration are tumor-specific activation by dThdPase, the nonlinear elimination of 5-FU by DPD in tumor tissue, and the blood flow rate in tumors.

The nonlinear pharmacokinetics of capecitabine, a triple prodrug of 5-FU preferentially activated in tumour tissues, was investigated in human cancer xenograft models. A physiologically based pharmacokinetic (PBPK) model integrating the activation process of capecitabine to 5-FU and 5-FU elimination was constructed to describe the concentration/time profiles of capecitabine and its three metabolites, including 5-FU, in blood and organs. All the biochemical parameters (enzyme kinetic parameters, plasma protein binding and tissue binding of capecitabine and its metabolites) integrated in this model were measured in vitro. The simulated curves for the blood and tumour concentrations of capecitabine and its metabolites can basically describe the observed values. A simple prodrug of 5-FU, doxifluridine, is known to be activated to 5-FU to some extent in the gastrointestinal (GI) tract, causing diarrhoea, which is the dose limiting side effect of doxifluridine. Consequently, the therapeutic index (the ratio of 5-FU AUC in the tumour to that in GI) after the administration of effective dose capecitabine was predicted by this PBPK model and found to be five times and 3000 times greater than that of doxifluridine and 5-FU, respectively. This was compatible with the previous result for the difference in the ratio of the toxic dose to the minimum effective dose between capecitabine and doxifluridine, suggesting that 5-FU preferentially accumulates in tumour tissue after oral administration of capecitabine compared with the other drugs (doxifluridine and 5-FU). The 5-FU AUC in tumour tissue of human cancer xenograft models at the minimum effective dose was comparable with those estimated for humans at the clinical dose. In addition, the predicted therapeutic indices at the respective doses were correlated well between humans and mice (xenograft model). These results suggest that the 5-FU AUC in human tumour tissue at its clinically effective dose can be predicted based on the PBPK model inasmuch as the 5-FU AUC in a human cancer xenograft model at its effective dose may be measured or simulated., (Copyright 2001 John Wiley & Sons, Ltd.)

Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a novel fluoropyrimidine carbamate, which was designed to be sequentially converted to 5-fluorouracil (5-FU) by three enzymes located in the liver and in tumors; the final step is the conversion of 5'-deoxy-5-fluorouridine (5'-DFUR) to 5-FU by thymidine phosphorylase (dThdPase) in tumors. In human cancer xenograft models, 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 intravenous administration of 5-FU at equitoxic doses. Capecitabine and its intermediates are not cytotoxic by themselves, but become effective after their conversion to 5-FU. This tumor selective delivery of 5-FU ensured greater efficacy and a more favorable 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 taxanes and cyclophosphamide. 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 this profile, capecitabine may have substantial potential in cancer treatment.

To identify an orally available fluoropyrimidine having efficacy and safety profiles greatly improved over those of parenteral 5-fluorouracil (5-FU: 1), we designed a 5-FU prodrug that would pass intact through the intestinal mucisa and be sequentially converted to 5-FU by enzymes that are highly expressed in the human liver and then in tumors. Among various N4-substituted 5'-deoxy-5-fluorocytidine derivatives, a series of N4-alkoxycarbonyl derivatives were hydrolyzed to 5'-deoxy-5-fluorocytidine (5'-DFCR: 8) specifically by carboxylesterase, which exists preferentially in the liver in humans and monkeys. Particularly, derivatives having an N4-alkoxylcarbonyl moiety with a C4-C6 alkyl chain were the most susceptible to the human carboxylesterase. Those were then converted to 5'-deoxy-5-fluorouridine (5'-DFUR: 4) by cytidine deaminase highly expressed in the liver and solid tumors and finally to 5-FU by thymidine phosphorylase (dThdPase) preferentially located in tumors. When administered orally to monkeys, a derivative having the N4-alkoxylcarbonyl moiety with a C5 alkyl chain (capecitabine: 6) The highest AUC and Cmax for plasma 5'-DFUR. In tests with various human cancer xenograft models, capecitabine was more efficacious at wider dose ranges than either 5-FU or 5'-DFUR and was significantly less toxic to the intestinal tract than the others in monkeys.

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.

Thymidine phosphorylase (dThdPase) is an essential enzyme for the activation of the cytostatics capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) and its intermediate metabolite 5'-deoxy-5-fluorouridine (5'-dFUrd) to 5-fluorouracil (5-FUra) in tumors. We observed previously that several cytokines and cytostatics up-regulated dThdPase expression and consequently enhanced the efficacy of capecitabine and 5'-dFUrd. In the present study, we found that X-ray irradiation also up-regulated dThdPase expression in several human cancer xenografts. A single-dose local irradiation at 5 Gy increased dThdPase levels by up to 13-fold at 9 days after the irradiation. Whole-body irradiation also up-regulated dThdPase in a tumor, but it did not increase the enzyme level in the liver. We also observed that the irradiation increased the levels of human tumor necrosis factor alpha (TNF-alpha), which is an up-regulator of dThdPase, prior to the dThdPase up-regulation. These results indicate that X-ray irradiation might increase dThdPase levels indirectly through the human TNF-alpha in the tumor tissue. In the WiDr colon and MX-1 mammary human cancer xenograft models, the combination of a single local X-ray irradiation with either capecitabine or 5'-dFUrd was much more effective than either radiation or chemotherapy alone. In contrast, treatment with X-ray irradiation and 5-FUra in combination showed no clear additive effects. Combined modality treatment of cancer patients with cape-citabine and X-ray irradiation would have greater potential usefulness than conventional radiochemotherapy with 5-FUra.

Thymidine phosphorylase (dThdPase) is an essential enzyme for the activation of the oral cytostatic drugs capecitabine (N(4)-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine, Xeloda(trade mark)) and its intermediate metabolite doxifluridine [5'-deoxy-5-fluorouridine (5'-dFUrd, Furtulon((R)))] to 5-fluorouracil (5-FUra) in tumors. In a previous study, we found that several cytostatics were able to up-regulate tumor levels of dThdPase in a human colon cancer xenograft model. In the present study, we confirmed that the administration of cytostatics used for breast cancer treatment, such as taxanes and cyclophosphamide (CPA), up-regulated the tumor level of dThdPase in mammary tumor models as well. Because the dThdPase up-regulation was observed even when CPA was given orally, we investigated further the usefulness of combination therapy with the 2 oral drugs, 5'-dFUrd/capecitabine and CPA in mammary tumor models. Daily oral administration of CPA up-regulated human dThdPase levels in the tumor tissue of mice bearing a human mammary tumor xenograft, MX-1, whereas in the small intestine and liver, it did not affect levels of pyrimidine nucleoside phosphorylases (PyNPase) including dThdPase and uridine phosphorylase. The preferential up-regulation of PyNPase activity in the tumor by CPA administration was also confirmed in mice bearing a syngeneic murine mammary adenocarcinoma, A755. In both models, combination therapy of 5'-dFUrd/capecitabine with CPA showed synergistic antitumor activity, without significant potentiation of toxicity. In contrast, treatment with CPA and either 5-FUra or UFT (a mixture of tegafur and uracil) in combination showed only additive activity. Our results suggest that CPA and capecitabine/5'-dFUrd, both available for oral administration, would be good partners, and that clinical trials with this drug combination against breast cancer are warranted., (Copyright 1999 Wiley-Liss, Inc.)

Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a novel oral fluoropyrimidine carbamate, which is converted to 5-fluorouracil (5-FU) selectively in tumours through a cascade of three enzymes. The present study investigated tissue localisation of the three enzymes in humans, which was helpful for us to design the compound. Carboxylesterase was almost exclusively located in the liver and hepatoma, but not in other tumours and normal tissue adjacent to the tumours. Cytidine (Cyd) deaminase was located in high concentrations in the liver and various types of solid tumours. Finally, thymidine phosphorylase (dThdPase) was also more concentrated in various types of tumour tissues than in normal tissues. These unique tissue localisation patterns enabled us to design capecitabine. Oral capecitabine would pass intact through the intestinal tract, but would be converted first by carboxylesterase to 5'-deoxy-5-fluorocytidine (5'-dFCyd) in the liver, then by Cyd deaminase to 5'-deoxy-5-fluorouridine (5'-dFUrd) in the liver and tumour tissues and finally by dThdPase to 5-FU in tumours. In cultures of human cancer cell lines, the highest level of cytotoxicity was shown by 5-FU itself, followed by 5'-dFUrd. Capecitabine and 5'-dFCyd had weak cytotoxic activity only at high concentrations. The cytotoxicity of the intermediate metabolites 5'-dFCyd and 5'-dFCyd was suppressed by inhibitors of Cyd deaminase and dThdPase, respectively, indicating that these metabolites become effective only after their conversion to 5-FU. Capecitabine, which is finally converted to 5-FU by dThdPase in tumours, should be much safer and more effective than 5-FU, and this was indeed the case in the HCT116 human colon cancer and the MX-1 breast cancer xenograft models.

Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a novel fluoropyrimidine carbamate that was synthesized for the purpose of finding antitumor drugs with improved safety and efficacy profiles compared with those of 5-fluorouracil (5-FUra) and doxifluridine (5'-deoxy-5-fluorouridine, 5'-dFUrd). The present study compared the antitumor activities of the compound with those of other fluoropyrimidines in 12 human cancer xenograft models and their antimetastatic activities in murine tumor models. The antitumor efficacy of capecitabine was greater than those of 5'-dFUrd, UFT (a mixture of tegafur and uracil) and 5-FUra. Capecitabine was also much safer, particularly much less toxic to the intestinal tract, than the other compounds, indicating higher therapeutic indices. The therapeutic indices of capecitabine, 5'-dFUrd and 5-FUra were >40, >20 and 2.0 against the human CXF280 colon cancer xenograft, the most sensitive line to the fluoropyrimidines so far tested, and 5.1, 1.5, and <1.5 against the human HCT116 colon cancer xenograft with ordinary sensitivity, respectively. In addition, capecitabine, as well as 5'-dFUrd, selectively suppressed the spontaneous metastasis of mouse Lewis lung carcinoma in mice at extremely low doses, 32-64 fold lower than their minimum effective dose (MED) against the primary tumor growth. Capecitabine was even more antimetastatic than 5'-dFUrd. These results indicate that capecitabine has high therapeutic potential.

Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a novel fluoropyrimidine carbamate that is converted to 5-fluorouracil (5-FUra) by three enzymes located in the liver and tumors; the final step is the conversion of 5'-deoxy-5-fluorouridine (5'-dFUrd) to 5-FUra by thymidine phosphorylase in tumors. The present study compared the efficacy of capecitabine and 5-FUra at their maximum tolerated doses in CXF280, HCT116, COLO205, and WiDr human colon cancer xenograft models, and measured subsequent 5-FUra and 5'-dFUrd levels in tumors and in the plasma and muscle. Capecitabine was effective in the first three models, whereas 5-FUra was effective only in CXF280, which is a cell line highly susceptible to fluoropyrimidines. In the three susceptible models, 5-FUra AUCs in tumors after capecitabine administration were 210 to 303 nmol x hr/g, whereas those after 5-FUra administration were 8.54 to 13.1 nmol x hr/g. In addition, capecitabine gave higher levels of 5-FUra AUC in tumors than in plasma (114- to 209-fold higher) and muscle (21.6-fold higher), whereas 5-FUra was not selectively distributed to tumors. In the refractory model, WiDr, 5-FUra AUC in tumors after capecitabine administration was only 62.8 nmol x hr/g, although the level of the intermediate metabolite 5'-dFUrd was high (AUC: 695 nmol x hr/g). The ratio of 5-FUra/5'-dFUrd levels in the WiDr tumors was 0.09, which was 23.8-fold lower than that in the HCT116 tumors. The mechanism of resistance would be the inefficient conversion of 5'-dFUrd to 5-FUra by thymidine phosphorylase in tumors. Thus, capecitabine might show its high efficacy as a result of delivering high levels of 5-FUra selectively to the tumors.

We showed that the efficacy of the new 2'-deoxycytidine (2'-dCyd) analogue antimetabolite 2'-deoxy-2'-methylidenecytidine (DMDC) correlates well with tumor levels of cytidine (Cyd) deaminase in human cancer xenograft models. DMDC was highly effective in tumors with higher levels of Cyd deaminase, whereas lower levels yielded only slight activity. In contrast, gemcitabine (2',2'-difluorodeoxycytidine), which has action mechanisms similar to those of DMDC, is only slightly active in tumors with higher levels of the enzyme. In the present study, we investigated the roles of Cyd deaminase in the antitumor activity of the two 2'-dCyd antimetabolites in 13 human cancer cell lines. Tetrahydrouridine, an inhibitor of Cyd deaminase, reduced the antiproliferative activity of DMDC (P = 0.0015). Furthermore, tumor cells transfected with the gene of human Cyd deaminase become more susceptible to DMDC both in vitro and in vivo. These results indicate that Cyd deaminase is indeed essential for the activity of DMDC. In contrast, the antiproliferative activity of gemcitabine was increased to some extent by tetrahydrouridine (P = 0.0277), particularly in tumor cell lines with higher levels of Cyd deaminase. This suggests that higher levels of Cyd deaminase may inactivate gemcitabine. Among nucleosides and deoxynucleosides tested, only dCyd, a natural substrate of both Cyd deaminase and dCyd kinase, suppressed the antiproliferative activity of DMDC by up to 150-fold. Because the Vmax/Km of DMDC for dCyd kinase was 8-fold lower than that for dCyd, the activation of DMDC to DMDC monophosphate (DMDCMP) by dCyd kinase might be competitively inhibited by dCyd. In addition, the dCyd concentrations in human cancer xenografts were inversely correlated with levels of Cyd deaminase activity. It is therefore suggested that higher levels of Cyd deaminase reduce the intrinsic cellular concentrations of dCyd in tumors, resulting in efficient activation of DMDC to DMDCMP by dCyd kinase. These results indicate that the efficacy of DMDC may be predicted by measuring the activity of Cyd deaminase in tumor tissues before treatment starts and that DMDC may be exploited in a new treatment modality: tumor enzyme-driven cancer chemotherapy.

Capecitabine (N4-pentyloxycarbonyl-5'-deoxy-5-fluorocytidine) is a new fluoropyrimidine carbamate, which is converted to 5-fluorouracil (5-FUra) selectively in tumors through the intermediate metabolite 5'-deoxy-5-fluorouridine (5'-dFUrd, doxifluridine). 5'-dFUrd is metabolized to 5-FUra by thymidine phosphorylase (dThdPase) located in high levels in various types of solid tumors from patients, whereas 5-FUra generated is catabolized to dihydrofluorouracil by dihydropyrimidine dehydrogenase (DPD). The present study investigated whether the efficacy of capecitabine and its intermediate metabolite 5'-dFUrd correlates with levels of these enzymes in various human cancer xenograft models. Capecitabine and 5'-dFUrd were highly effective and inhibited tumor growth by more than 50% in 18 of 24 xenograft lines (75%) and 15 of 24 xenograft lines (63%), respectively, whereas 5-FUra and a mixture of tegafur and uracil were effective only in 1 of 24 (4.2%) and 5 of 24 (21%), respectively. The efficacy of capecitabine correlated with dThdPase activity. However, capecitabine was effective even in tumors with lower levels of dThdPase if DPD levels were also lower. In contrast, it was not as effective even in tumors with sufficient levels of dThdPase if DPD levels were very high. The efficacy of capecitabine consequently correlated very well with and depended on the ratio of these two enzymes in tumors. These results indicate that capecitabine might exert its efficacy through 5-FUra generated in tumor tissues but not through that generated in normal organs. On the other hand, there was no correlation between the efficacy of a mixture of tegafur and uracil and these enzyme activities in tumors. The efficacy of capecitabine would be optimized by selecting patients who have tumors with a high ratio of dThdPase to DPD activities.

2'-Deoxy-2'-methylidenecytidine (DMDC) is a new 2'-deoxycytidine (dCyd) antimetabolite. The present study compared its antitumor activities with those of 2',2'-difluorodeoxy-cytidine (gemcitabine) in 15 human cancer xenograft models. DMDC was highly resistant to cytidine (Cyd) deaminase, which deaminates the dCyd analogues to inactive molecules, whereas gemcitabine was susceptible to the enzyme. Given p.o., high antitumor activity with therapeutic index of more than 10 was found with DMDC in 7 of 15 xenograft lines. In contrast, gemcitabine given i.v. or p.o. was highly effective in 4 of 15 human cancer xenograft lines. The antitumor spectrum of these compounds was quite different, although their molecular targets are reported to be similar. DMDC was highly effective in tumors with higher levels of Cyd deaminase activity, whereas it showed only slight activity in those with lower levels of Cyd deaminase. In contrast, gemcitabine appeared to be less effective in tumors with high levels of Cyd deaminase. We also investigated the correlation with the susceptibility to the two dCyd antimetabolites and dCyd kinase activity in tumors, but none was observed. Cyd deaminase activity was found to be high in tumor tissues from various types of human cancers thus far tested, such as colorectal cancer and non-small cell lung cancer. Such cancer types or individual patients who have tumors with high activity of the enzyme may be targets for DMDC therapy.

N4-Trimethoxybenzoyl-5'-deoxy-5-fluorocytidine (Ro 09-1390), a new prodrug of 5'-deoxy-5-fluorouridine (5'-dFUrd), was synthesized for the purpose of finding a drug with less intestinal toxicity than the parent compound. The present study compared the antitumor activity and immunotoxicity of Ro 09-1390 with those of 5'-dFUrd, 5-fluorouracil (5-FUra) and tegafur in various transplantable tumor models. The antitumor efficacy of Ro 09-1390 was comparable to 5'-dFUrd and these two agents were much more effective than the others. However, Ro 09-1390 was much less toxic to the intestinal tract and less immunosuppressive in both humoral and cellular immune reactions than 5'-dFUrd. Consequently, Ro 09-1390 showed higher therapeutic indices and higher efficacy than 5'-dFUrd at high dosages. The antitumor spectrum of Ro 09-1390 was somewhat different from that of 5'-dFUrd, though it shows the efficacy after it converts to 5'-dFUrd. The activity of Ro 09-1390 was partly associated with cytidine deaminase in the tumors treated. Ro 09-1390 appeared to be more effective against tumors with a high concentration of the enzyme by which the major metabolite 5'-deoxy-5-fluorocytidine (5'-dFCyd) is metabolized to 5'-dFUrd.

N4-Trimethoxybenzoyl-5'-deoxy-5-fluorocytidine (Ro 09-1390), a prodrug of the cytostatic 5'-deoxy-5-fluorouridine (5'-DFUR), was synthesized with the aim of reducing of the dose-limiting toxicity of 5'-DFUR, which is diarrhea. In mice bearing Lewis lung carcinoma, 5'-DFUR given po produced a substantial amount of 5-fluorouracil (5-FU) in the intestinal tract as well as tumors, where the enzyme pyrimidine nucleoside phosphorylase, essential for conversion of 5'-DFUR to 5-FU, is predominantly located. With the oral administration of Ro 09-1390 only a small amount of 5-FU was formed in the intestine; however, the administration of Ro 09-1390 and 5'-DFUR at the same dose produced similar amounts of 5-FU in tumor tissues. These differences in metabolism were reflected in their toxicity and antitumor efficacy. The administration of 5'-DFUR resulted in damage to the intestinal mucosal membrane and diarrhea in normal mice, whereas Ro 09-1390 was much less toxic to the intestinal tract. As regards antitumor activity, Ro 09-1390 and 5'-DFUR at equivalent doses inhibited the growth of Lewis lung carcinoma to similar extents. Since Ro 09-1390 was much less toxic to the intestinal tract than 5'-DFUR, mice bearing Lewis lung carcinoma could be given Ro 09-1390 daily over a longer period and at a higher dose, resulting in a longer survival time.