Setsuo Takeda

Antitumor activity and low intestinal toxicity of S-1, a new formulation of oral tegafur, in experimental tumor models in rats

Abstract S-1, a new oral antitumor agent, is composed of 1-(2-tetrahydrofuryl)-5-fluorouracil (Tegafur, FT), 5-chloro-2,4-dihydroxypyridine (CDHP) and potassium oxonate (Oxo) in a molar ratio of 1 : 0.4 : 1. FT which is a masked compound of 5-fluorouracil (5-FU) acts as an effector, while both CDHP and Oxo which do not have antitumor activity themselves act as modulators. In this study, the antitumor activity and intestinal toxicity of S-1 were investigated using experimental tumor models in rats, and compared with those of other oral fluoropyrimidines, namely 5-FU, FT, FCD (1 M FT/0.4 M CDHP) and UFT (combination of FT and uracil). In rats bearing subcutaneous Yoshida sarcoma, S-1 inhibited tumor growth at the lowest dose (ED50 value: S-1 5, UFT 22, FT 82, FCD 5, and 5-FU 19 mg/kg per day), and induced the least host body weight suppression, leading to the highest therapeutic index (TI) (S-1 4.5, UFT 1.4, FT 1.8, FCD 2.0, and 5-FU 1.4). S-1 also showed a higher therapeutic effect than UFT against AH-130 and Sato lung carcinoma. After administration of S-1 and UFT at equitoxic doses, S-1 showed a higher and more prolonged concentration of 5-FU than UFT both in plasma (AUC0-∞: S-1 28 nmol h/ml, UFT 15 nmol⋅h/ml) and in tumor tissue (AUC0-∞: S-1 95 nmol h/g tissue, UFT 52 nmol h/g tissue), leading to a higher 5-FU level incorporated into the RNA fraction (F-RNA level) in tumor tissue (AUC0-24: S-1 7.0 nmol h/mg RNA, UFT 4.3 nmol h/mg RNA) and 5–8% higher thymidylate synthase (TS) inhibition in tumor tissue at every time-point through 24 h. Compared with other oral fluoropyrimidines after administration of the maximal tolerable dose (MTD), S-1 caused the lowest rates of intestinal toxicities, such as diarrhea and occult blood in feces. S-1 also showed a higher antitumor effect on Yoshida sarcoma implanted intracolonically than UFT at an equitoxic dose (tumor weight: S-1 64±30 mg, UFT 133±52 mg; P<0.05). These results suggest that CDHP, which is a potent inhibitor of 5-FU degradation, increases the antitumor activity of FT, and that Oxo, which is an inhibitor of 5-FU phosphorylation, locally protects the gastrointestinal tract from 5-FU-induced toxicity without decreasing the antitumor activity.

TAT-59, a new triphenylethylene derivative with antitumor activity against hormone-dependent tumors

The antiestrogenic action of TAT-59 [(E)-4-[1-[4-[2-(dimethylamino)ethoxy]-phenyl]-2-(4-isopropyl) phenyl-1-butenyl]phenyl monophosphate] was characterized and compared with that of Tamoxifen (TAM). Its active metabolite, 4-OH-TAT-59, had a high binding affinity to estrogen receptor (ER), present in the cytosol of the uterus of immature rat, similar to estradiol. TAT-59 and 4-OH-TAT-59 inhibited in vitro estrogen-stimulated proliferation of MCF-7 cells at a lower concentration than TAM. In the absence of estradiol, TAT-59 and 4-OH-TAT-59 were effective at a lower concentration than that of 4-OH-Tamoxifen (4-OH-TAM), the active metabolite of TAM. In uterine growth inhibition, the effective dose of TAT-59 was about 3-6-fold lower than that of TAM, in various administration schedules. The minimum effective dose of TAT-59 against in vivo MCF-7 cells was about 3-fold lower than that of TAM. In DMBA-induced rat mammary tumors, TAT-59 inhibited the growth of existing tumors at about a 10-fold lower dose than TAM. Especially in the tumors with low ER levels (10-20 fmol/mg protein), TAT-59 showed a significantly stronger inhibitory effect than TAM. These experiments showed that TAT-59 was more effective in lower doses than TAM, even against the tumors with low ER content.

Interaction of DP-TAT-59, an active metabolite of new triphenylethylene-derivative (TAT-59), with estrogen receptors

DP-TAT-59, (Z)-2-(4-(1-(4-hydroxyphenyl)-2-(4-isopropylphenyl)-1-butenyl) phenoxy)-N, N-dimethylethylamine, has been reported to inhibit estrogen-stimulated growth of MCF-7 cells as well as rat uterus at lower concentrations than the hydroxymetabolite of tamoxifen (4-OH-TAM). In the present study, the growth of mouse Leydig cell tumor, B-1F cells were also more effectively inhibited by DP-TAT-59 than 4-OH-TAM. Additionally, the expression of estrogen responsive element ligated CAT gene transfected into B-1F cells was also suppressed by DP-TAT-59. Thus, the interaction of DP-TAT-59 with estrogen receptor (ER) was characterized and compared with that of 4-OH-TAM using immature rat and bovine uteri. The dissociation constant of DP-TAT-59 to ER of immature rat uterus was 0.24 nM and was similar to that of 4-OH-TAM (Kd = 0.20 nM) and estradiol (Kd = 0.29 nM). Using sucrose density gradients, the sedimentation constant of DP-TAT-59 with bovine uterus was 4.9S, which was similar to that of estradiol (5.1S) and 4-OH-TAM (5.3S). However, the elution profile of the DP-TAT-59-ER complex from a DEAE-Sephadex column was different for both estradiol-and 4-OH-TAM-ER complexes. These results suggest that ER forms different complexes with DP-TAT-59 than estradiol or 4-OH-TAM, while the ER binding affinity of these compounds are similar to each other.

Prolongation of survival period and improvement of cancer cachexia by long term administration of UFT

We assayed the antitumoral and anticachectic activity of an oral fluoropyrimidine, UFT using the Colon-26-bearing murine cachexia model in terms of the survival period and parameters corresponding to clinical symptoms. Tumor growth was inhibited by UFT dose-dependently at the dose range of 12.5-25.0 mg/kg per day. Although UFT did not show significant growth inhibition at 15.0 and 12.5 mg/kg to which UFT gave little toxicity, the survival period was shown to be superior to the case of maximum tolerated dose (25.0 mg/kg per day). Next, we compared the maximum increase of life span (ILS) value for an administration schedule of continuous 9 days and 5 weeks which mimics the clinical schedule and found that the ILS value in the latter group was superior to the former and UFT improved cachexia, in the same manner. In the following experiments, we have clarified that UFT decreased the level of both plasma interleukin-6 (IL-6) and tumorous prostaglandin E2 (PGE2) and it highly accelerated IL-6 production from Colon-26. These findings suggest that UFT therapy, in low-toxic dose, could be useful to cachectic patients with poor performance status.

Menogaril, an anthracycline compound with a novel mechanism of action: Cellular pharmacology

Menogaril, an anthracycline compound possessing a significant antitumor activity after both po and iv administration, has been introduced into clinical trials. However, its mechanism of action has not been clarified yet. This study revealed that its cytotoxicity correlated very well with the inhibition of macromolecular synthesis, indicating the involvement of interaction with DNA. The spectrophotometric study showed a weaker binding of this compound to calf thymus DNA when compared to that of doxorubicin (adriamycin). Despite the lower binding affinity of menogaril to DNA, pronounced DNA cleavage was observed in an intact cell system, indicating that the character of the interaction with DNA is different from intercalation. In contrast to doxorubicin, menogaril is extensively localized in the cytoplasm. The cytoplasmic localization prompted us to study its effect on cytoskeleton proteins. It was found that menogaril inhibited the initial polymerization rate of tubulin, indicating a possible contribution of this process to the overall cytotoxicity of menogaril.

Preliminary study on the optimal dosage schedule for oral tegafur/uracil (UFT) chemotherapy

BackgroundWe evaluated a new dose-intensive schedule for oral UFT (tegafur and uracil in a molar ratio of 1:4) administered for 5 consecutive days followed by 2 drug-free days (weekly-5-method), in comparison with conventional daily administration (weekly-7 method), in Yoshida-sarcoma-bearing rats.MethodsThe single dose of 20 mg/kg of UFT for rats corresponds to the human single dose when converted to dose per unit of body-surface area. The drug was administered 3 times a day for the weekly-5 method and twice a day for the weekly-7 method. A 7-day period was considered 1 course. The total doses per course were almost the same in both methods. Antitumor efficacy and survival effect were evaluated after 3 courses. Body weight changes and food consumption were also measured as indices of toxicity. The plasma pharmacokinetics were analyzed by simulating dosage patterns.ResultsSignificant tumor-growth inhibition was seen with both the weekly-5 and the weekly-7 methods as compared to the control. Moreover, the weekly-5 method showed higher tumor-growth inhibition and a better survival effect than the weekly-7 method. These results appear to be related to the duration of plasma concentrations of 5-FU being maintained above a certain concentration for a longer time with the weekly-5 method. Food consumption with the weekly-5 method recovered to the control level after the drug-free period, and body weight gain was also favorable.ConclusionThe results of this study suggest that the dose-intensive method of administering UFT orally for the weekly-5 method is a useful dosage schedule. Thus, this dosage schedule is recommended for use in clinical trials.

Potentiation of the antitumor activity of 5-trifluoromethyl-2'-deoxyuridine by the use of depot forms of the parent compound.

Summary5-Trifluoromethyl-2′-deoxyuridine (CF3dUrd), an antitumor agent, is known to be short-lived in human plasma. Since its rapid elimination from the blood-stream seems to have descouraged the clinical evaluation of this drug, we explored the potential use of masked derivatives of CF3dUrd as “depot” forms of the parent compound. First, we observed that the toxicity of CF3dUrd against HeLA cells in culture was 104 times greater for a 24-h treatment as compared with a 1-h treatment at identical concentrations of the drug, which suggests the importance of using a prolonged treatment period. In fact, the divided dosing of CF3dUrd to L1210-bearing mice was markedly more effective than its single administration. 5′-O-Hexanoyl-,N3-p-butylbenzoyl-, 5′-O-benzyloxymethyl-, and 3′-O-benzyl-CF3dUrd were found to be effective in maitaining the CF3dUrd concentration in plasma. The oral doses of these agents required to achieve 50% growth inhibition (ED50) in mice bearing sarcoma 180 tumors were 19, 34, 10, and 13 mg kg−1 day−1, respectively, whereas that of CF3dUrd was 63 mg kg−1 day−1. The ED50 values for these compounds were inversely correlated with the residence time of CF3dUrd in plasma. The therapeutic indices of these compounds, calculated as the dose producing a 50% inhibition of body-weight gain (IB50) divided by the ED50 value (1.89, 1,21, 1.40, and 2.15, respectively), were significantly higher than that of CF3dUrd (0.78). Consequently, these depot forms of CF3dUrd, particularly 3′-O-benzyl-CF3dUrd, are expected to be more useful than the parent compound as antitumor agents.

Antitumor activity of FTC-092, a masked 5-trifluoromethyl-2′-deoxyuridine derivative

Summary1-(3-O-Benzyl-2-deoxy-β-d-ribofuranosyl)-5-trifluoromethyl-2,4(1H,3H)-pyrimidinedione (FTC-092), a fluorinated pyrimidine derivative, appeared to be effective against various transplantable tumors in mice following oral administration, and its activity was superior to that of several other antitumor fluorinated pyrimidines. The ED50 value for FTC-092 the dose effective in achieving 50% inhibition of tumor growth against the solid form of sarcoma 180 was 13.3 mg/kg daily, whereas those for 5-trifluoromethyl-2′-deoxyuridine (CF3dUrd), the parent compound of FTC-092, for 1-(2-tetrahydrofuryl)-5-fluorouracil (Tegafur, FT), the prodrug of 5-fluorouracil (FUra), and for FUra were 64.1, 122, and 28 mg/kg daily, respectively. The therapeutic indices (LD10/ED50) of FTC-092, CF3dUrd, FT, and FUra were 4.39, 1.7, 1.35, and 1.65, respectively. FTC-092 itself is not an active agent. After it has been absorbed from the gastrointestinal tract, FTC-092 undergoes a gradual biotransformation, mainly via the action of liver microsomes, releasing CF3dUrd over a long period. The levels of CF3dUrd in the stomach and small intestine of mice after the oral administration of FTC-092 were undetectable, whereas those following the administration of CF3dUrd at the same dose were high for a period of several hours. In contrast, the CF3dUrd level generated in plasma after the administration of FTC-092 remained at a high level for a longer period than did that observed on the administration of CF3dUrd. The low levels of CF3Urd measured in stomach and small-intestine tissues and the maintenance of CF3dUrd in blood over long periods after the administration of FTC-092 are features that favor the possible clinical application of FTC-092.