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Biomedical subjects

T Shirasaka

Publications and source records attributed to T Shirasaka.

At least 55 records · Page 3Linked to original sources
PubMed1998

Anticancer activity and toxicity of S-1, an oral combination of tegafur and two biochemical modulators, compared with continuous i.v. infusion of 5-fluorouracil.

S-1 is an oral combined form of 1 M tegafur [a prodrug of 5-fluorouracil (5-FU)], 0.4 M 5-chloro-2,4-dihydroxypyridine (a reversible inhibitor of dihydropyrimidine dehydrogenase) and 1 M potassium oxonate (an inhibitor of orotate phosphoribosyltransferase). S-1 has been shown to exert a potent antitumor effect with low gastrointestinal toxicity in experimental tumor models. We have therefore compared the antitumor effect of oral S-1 with that of continuous infusion of 5-FU in rats bearing transplants of human and murine tumors. Almost complete inhibition of the tumor growth was obtained on 7 day schedules in Yoshida sarcoma-bearing rats by consecutive administration of 30 mg/kg/day of oral S-1 and 40 mg/kg/day infusion of 5-FU. However, a significant difference between the incidence of toxicities of S-1 and 5-FU, including body weight loss and diarrhea, was noted. The rats given the 5-FU infusion had marked weight loss and severe diarrhea, while those given oral S-1 had neither. Although about 50% inhibition of the tumor growth was attained with 15 mg/kg/day of oral S-1 and 30 mg/kg/day infusion of 5-FU in nude rats with xenografted human colon cancer (KM12C), the rate of body weight loss in the 5-FU-treated group was distinctly higher than in the S-1-treated group. The ratio of the 5-fluoronucleotide concentrations in gastrointestinal tissue to that in the tumor was lower in the S-1-treated rats than in the 5-FU-treated rats. In conclusion, the results suggest that oral S-1 might be more effective in the treatment of cancer patients than continuous infusion of 5-FU, from the standpoint of antitumor potency and toxicity.

Administration, Oral↗
PubMed1998

Preclinical antitumor efficacy of S-1: a new oral formulation of 5-fluorouracil on human tumor xenografts.

S-1 is a new oral formulation of 5-fluorouracil (5-FU) consisted of 1M tegafur, 0.4M 5-chloro-2,4-dihydroxypyridine that inhibits a degradation of 5-FU, and 1M potassium oxonate that regulates the phosphorylation of 5-FU in the gastrointestinal tract, and has shown excellent antitumor efficacy against various murine tumors in rodents, compared to the oral tegafur-based antitumor drug, UFT (1M tegafur plus 4M uracil), which is used clinically in Japan. To assess the possibility of clinically using S-1, we investigated the antitumor effect of S-1 on various human solid tumor xenografts in athymic rats and mice. In the nude rat system, S-1 was significantly effective against all 12 tumor xenografts tested when its minimum toxic dose (15 mg/kg) was administered for 14 days. Three tumors, stomach (H-81), colon (KM12C) and breast (H-31) markedly regressed in response to treatment with S-1 but not with UFT. The antitumor potency of S-1 was weak against human tumors xenografted into nude mice and likely similar to that of UFT. The reason of the discrepancy in the efficacy of S-1 between rats and mice was found to be that the 5-FU levels in the blood and tumor tissue of rats after oral administration of S-1 persisted much longer than in mice, and this prolonged maintenance of plasma 5-FU levels was significantly related to the potent antitumor activity of S-1. In conclusion, the results of this study suggested that based on its biological and pharmacokinetic characteristics, oral S-1 should be active against various human cancers.

Administration, Oral↗
PubMed1998

[Invention of a tumor-selective 5-fluorouracil derivative named S-1 by biochemical modulation of 5-fluorouracil].

A new oral type of 5-fluorouracil (5-FU) derivative possessed of both potent antitumor activity and less gastrointestinal (GI) toxicity was investigated and developed in the form of a combination of tegafur (FT), a masked form of 5-FU, and its two peculiar biochemical modulators. One is 5-chloro-2,4-dihydroxypyridine (CDHP), a new potent inhibitor of 5-FU degradation in vivo, and another is potassium oxonate (Oxo), a characteristic inhibitor of 5-FU phosphorylation, which distributes much higher in GI tract after p.o. administration. 5-FU levels in blood of rats following administration of FT, were markedly elevated and persisted for a long-time by co-oral CDHP corresponding to over 0.4 molar ratio to FT, like the case in continuous infusion of 5-FU, which resulted in an augmentation of antitumor efficacy in Yoshida sarcoma-bearing rats, although severe GI toxicity simultaneously occurred. To reduce 5-FU-induced toxicities such as diarrhea and body weight loss and to maintain the augmented antitumor activity, 0.5 to 2 molar Oxo was orally given to rats with one molar FT plus 0.4 molar CDHP. As a result, both severe GI injury and body weight loss were markedly inhibited by coadministration of 0.5 to 1.0 molar Oxo while high antitumor efficacy (about 90% inhibition of tumor growth) was maintained. However, such almost complete antitumor effect was reduced to about 50% inhibition of tumor growth by over 2 molar Oxo combined with one molar FT plus 0.4 molar CDHP. Based on these results, a novel 5-FU derivative, named S-1, was composed of one molar FT, 0.4 molar CDHP and one molar Oxo. S-1 showed an antitumor activity over 3-fold stronger than UFT (one molar FT plus 4 molar uracil) against Yoshida sarcoma and Sato lung carcinoma in rats and human colon carcinoma (KM12C) xenografted in nude rats when its minimum toxic dose was administered. Co-oral Oxo also significantly reduced the incidence of diarrhea and stomatitis induced by administration of FT-CDHP in beagle dogs. These results suggest that high antitumor activity and less GI toxicity of S-1 was brought about by the elevation in blood and tumor tissues and by selective decrease of 5-fluoronucleotides, an active metabolite of 5-FU, in GI tract.

Animals↗
PubMed1998

[Epidemiological studies on tobacco smoking and dependence in Hokkaido prefecture--relation to alcoholism].

Self-report symptom profiles for nicotine psychic dependence and nicotine physical dependence were examined in data obtained from 363 male and 82 female smokers. The subjects consisted of 363 healthy volunteer and 82 alcoholics. The questionnaire used in this study, consisted of items of the ICD-10 and DSM-IV. The ratio of nicotine dependence diagnosed according to the ICD-10 criteria was lower in alcoholics (22.0%) than in non-alcoholics (54.4%). A total of 19.4% of alcoholics experienced "progressive neglect of alternative pleasures or interest in favour of smoking"; however, only 2.2% of non-alcoholics had the same experience. Although the ratio of nicotine physical dependence diagnosed using the DSM-IV criteria (nicotine withdrawal), was 4.9% in alcoholics, only 0.3 % of non-alcoholics exhibited nicotine physical dependence. These results indicate that the potential for nicotine dependence is not higher than that for other drug dependence and suggested that nicotine physical dependence potential is not much stronger than that reported among social smokers.

Adult↗
PubMed1997

Continuous infusion of 5-fluorouracil and low dose cisplatin infusion for the treatment of advanced and recurrent gastric adenocarcinoma.

BACKGROUND: Several chemotherapy studies have suggested that continuous infusion of 5-fluorouracil (5-FU) is more effective than bolus 5-FU. In addition, 5-FU and cis-Diamminedichloroplatinum-II (cisplatin) in combination have been shown to have synergistic cytotoxicity against several human neoplasms. In this study, the authors evaluated the efficacy and toxicity of continuous infusion of 5-FU and low dose cisplatin infusion (FP therapy) in the treatment of advanced and recurrent gastric adenocarcinoma. The relationship between the response to FP therapy and several factors was also examined. METHODS: A total of 26 patients fulfilling standard eligibility criteria were enrolled in the trial. FP therapy consisted of 5-FU (350 mg/m2/day every day by continuous infusion) and cisplatin (7.5 mg/m2/day in 100 mL of normal saline infused over 1 hour on Days 1-5 every week) for 4 weeks. RESULTS: A complete response was observed in 2 cases and a partial response in 11 cases, for an overall response rate of 50%. Patients with good performance status (PS) (0-1) and differentiated histologic type showed higher response rates (50.0% and 63.6%, respectively) than patients with poor PS (2 or 3) and undifferentiated histologic type (28.6% and 35.3%, respectively), although there were no significant differences. Patients with low serum levels of immunosuppressive acidic protein (IAP) showed a significantly higher response rate (71.4%) than those with high IAP levels (0%). Toxic effects included leukopenia, thrombocytopenia, nausea, and vomiting; these were not life-threatening and did not require treatment interruption. CONCLUSIONS: FP therapy is a promising regimen for patients with advanced and recurrent gastric adenocarcinoma. Serum levels of IAP may predict chemosensitivity.

Adenocarcinoma↗
PubMed1997

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

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-infinity: S-1 28 nmolh/ml, UFT 15 nmol.h/ml) and in tumor tissue (AUC0-infinity: S-1 95 nmolh/g tissue, UFT 52 nmolh/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 nmolh/mg RNA, UFT 4.3 nmolh/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.

Animals↗
PubMed1997

Continuous infusion of 5-fluorouracil plus low-dose cisplatin in tumor-bearing mice.

Combination chemotherapy with 5-fluorouracil (5-FU) and cisplatin is widely used but the optimal daily dose of the latter has not been established. The present study was designed to determine the pharmacodynamic interaction and antitumor effect of these drugs when used at clinically relevant doses in animals. Male ddY mice were injected with Sarcoma 180 cells and then given a continuous infusion of 5-FU (10 mg/kg/day) for 5 days (via an implanted micropump) +/- cisplatin 1 mg/kg by i.p. bolus (pharmacodynamic study). Alternatively, mice were given 5-FU +/- cisplatin (0.2 mg/kg/day), cisplatin alone for 5 days or no treatment (anti-tumor effect study). Tissue and serum samples were taken for analysis. No significant differences in serum pharmocokinetics were observed between the groups at any timepoint but 0.5 h after the start of infusion, where the serum 5-FU concentration was lower with monotherapy than with combination therapy. 5-FU alone had a slight antitumor effect, while low-dose cisplatin alone had no noticeable effect. 5-FU + cisplatin produced a favorable response, with a significantly lower treated/control tumor weight ratio than in the non-treated and cisplatin monotherapy groups (p < 0.05), although this was not significantly different from the response to 5-FU monotherapy. In conclusion, the dose of cisplatin used in the present study was insufficient to generate a significant tumor response alone but it did tend to enhance the antitumor efficacy of 5-FU. Continuous 5-FU infusion plus low-dose daily cisplatin may become clinically useful after further investigation.

Animals↗
PubMed1997

[Comparison of epidural versus intravenous administration of fentanyl during epidural block].

Effects of epidural anesthesia induced with bupivacaine alone (group C), bupivacaine and fentanyl (group E), or bupivacaine and intravenous fentanyl (group I) on the onset and spread of cold sensory block, the onset of analgesia and the degree of motor block were compared. Seventy-five patients undergoing lower limb or abdominal surgery were allocated to three groups of 25; patients of group C received 15 ml of 0.5% bupivacaine and 2 ml of 0.9% saline epidurally, patients of group E received 15 ml of 0.5% bupivacaine and 2 ml of fentanyl epidurally, and patients of group I received 2 ml of fentanyl intravenously and 15 ml of 0.5% bupivacaine and 2ml of 0.9% saline epidurally. The onset time of cold sensory block at T11 was significantly shorter in groups E (6.8 +/- 1.9 (SD) min) and I (7.3 +/- 1.7 min) than in group C (9.3 +/- 1.9 min). The onset time of analgesia was also significantly shorter in groups E and I than in group C. The segmental spread of cold sensory block at 20 min after initial injection was significantly larger in groups E and I than in group C. There was no significant difference in motor block at 20 min among the three groups. Respiratory depression appeared more frequently in group I than in groups C and E. These results suggest that epidural administration of fentanyl offers a clinical advantage over intravenous administration for analgesia during epidural block.

Adult↗
PubMed1997

[Combination chemotherapy of continuous infusion 5-fluorouracil and daily low-dose cisplatin in advanced gastrointestinal and lung adenocarcinoma].

Continuous intravenous infusion (c.v.i.) of 5-fluorouracil (5-FU) plus daily low-dose cisplatin (CDDP) was evaluated in 45 patients with advanced and recurrent unresected colorectal, lung, gastric and pancreatic adenocarcinoma. 5-FU was given at a dose of 320 mg/m2/day, c.v.i. for 4 weeks, and CDDP between 3.5 to 7 mg/m2/day, infused for one hour five times a week for 4 weeks. Patients received 1 to 3 cycles of treatment (average 1.5 cycle). Pancreatic cancer cases needed longer treatment periods (2.25 cycles). The response rate of colorectal cancer cases was 57.7% (15/26), pancreas cancer 40%, gastric cancer 62.5%, and lung cancer 66.7%. The overall response rate was 57.8%. No severe side effects occurred in any of these cases. These data indicate that this combination 5-FU + daily low-dose CDDP chemotherapy is effective in the treatment of advanced gastrointestinal and lung adenocarcinoma.

Adenocarcinoma↗
PubMed1997

[Antitumor effect of S-1 and cisplatin treatment against human gastric cancer xenografted in nude mice].

The enhanced effects due to the combined use of oral administration of S-1 and intraperitoneal administration of Cisplatin (CDDP) were examined with gastric cancer xenografts (NUGC 4). S-1, a new anticancer drug, was daily administered at 10 mg/kg (qld x 5 x 3 weeks). 5-FU level in blood was 1 microgram/ml at two hours after the treatment. Antitumor activity was not found in mice with only the CDDP treatment. But antitumor activity by S-1 and daily low-dose (1 mg/kg) or intermittent treatment (5 mg/kg) of CDDP showed better results than daily S-1 treatment. The daily low-dose CDDP treatment showed similar efficacy to the intermittent administration at the same total dose, but the daily low-dose CDDP treatment was better in the light of toxicities. These results suggest that treatment with S-1 and daily low-dose CDDP was effective for gastric cancer.

Administration, Oral↗
PubMed1997

[Clinical manifestation of volatile solvent psychosis].

To identify symptomatological characteristics of solvent psychosis, 9 cases of chronic thinner intoxication with psychitaric evidence during the abstinent period are studied. The results were as follows: 1) During intoxication, 7 cases had visual hallucinations and 3 cases had auditory hallucinations. 2) Eight cases had irritabilities or mood disturbances without thinner intoxication. 3) Four cases had convulsions or delirium which were observed only in the withdrawal period, suggesting that these symptoms might be withdrawal signs of thinner dependence. 4) Six cases had Schneiderian first rank symptoms such as auditory hallucinations (i.e. voices commenting, voices arguing), delusions of control (withdrawal of thought, thought insertion, influence of thought) and delusional perception. Hallucinations that appeared in acute intoxication with thinner in 5 of the 6 cases, were second rank symptoms. Five of the 6 cases did not show negative symptoms (i.e. blunting of thought) and they could maintain good emotional contact with other. Symptoms of these 5 cases were different from those of schizophrenia or the flashback phenomenon of thinner dependence. These cases suggest that Schneiderian first rank symptoms and maintenance of emotional contact are important for diagnosis of volatile solvent psychosis.

Adolescent↗
PubMed1997

[Intravenous neostigmine enhances the analgesic effect of epidural anesthesia].

A single-blind trial of the intravenous neostigmine on epidural anesthesia was carried out on 75 patients undergoing lower limb or lower abdominal surgery. They were allocated to three groups of 25: patients of group C received 2 ml of 0.9% saline, patients of group AN 1 ml (0.5 mg) of atropine and 2 ml (1 mg) of neostigmine, and patients of group N 2 ml (1 mg) of neostigmine, intravenously 5 min before epidural injection of 15 ml of 2% mepivacaine solution without epinephrine. We assessed the onset and spread of cold sensory block and analgesia, and the degree of motor block and sedation. The onset time of analgesia at T 11 was significantly shorter in group N [6.2 +/- 2.0 (SD) min] than in groups C (8.5 +/- 2.6 min) and AN (8.7 +/- 2.4 min). The segmental spread of analgesia 10 and 20 min after epidural injection was significantly larger in group N (10.8 +/- 3.9 and 15.4 +/- 2.7 seg, respectively) than in groups C (7.6 +/- 3.4 and 12.8 +/- 3.5 seg, respectively) and AN (7.8 +/- 3.6 and 13 +/- 3.4 seg, respectively). There were no differences in the onset and spread of cold sensory block, and the degree of motor block and sedation among the three groups. The incidence of bradycardia and fecal incontinence was significantly higher in group N than in groups C and AN. These results demonstrate that intravenous neostigmine potentiates the analgesic effect of epidural anesthesia mediated by a cholinergic muscarinic mechanism. However, in clinical practice, it does not seem to be useful, because of the side effects.

Adolescent↗
PubMed1997

[Current status of low-dose CDDP. 5-FU therapy for solid malignant tumors--nationwide questionnaire survey].

A nation-wide questionnaire survey was undertaken concerning low-dose anticancer therapy of CDDP plus 5-FU, which involves (5-10 mg CDDP/body/day + 300-500 mg/body/day) for 4-6 weeks. Out of 1,525 cases from 130 institutions, 847 cases with evaluable lesions were collected from 79 institutions. The response rate was 56.4% in esophageal cancer, 34.3% in gastric cancer, 35.3% in colorectal cancer, 47.2% in liver cancer and 35.9% in lung cancer, respectively. Adverse effects were found to be fewer and compliance was much better than the conventional therapy. Such figures suggest that the present regimen may be more effective than any so far. Problems for medical administration such as unlicensed CDDP for colorectal cancer were pointed out, which hinder the forthcoming third phase study.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1996

Antitumor activity of 1 M tegafur-0.4 M 5-chloro-2,4-dihydroxypyridine-1 M potassium oxonate (S-1) against human colon carcinoma orthotopically implanted into nude rats.

The purpose of this study was to establish a nude rat orthotopic (organ-specific) human colorectal cancer model as an in vivo secondary screen for general evaluation of new anticancer agents against colorectal cancer and to evaluate practically the antitumor activity of 1 M tegafur-0.4 M 5-chloro-2,4-dihydroxypyridine-1 M potassium oxonate (S-1), a new p.o. fluoropyrimidine, in comparison to 1 M tegafur-4 M uracil [(UFT) effective on colorectal tumor in clinical]. After implantation of KM12C, a human colorectal cancer cell line, into the subserosal layer of the colon as a single-cell suspension, extensive local tumor growth and invasion to both the mucosal and the serosal sides were observed in all rats. Metastatic foci were also formed in both lymph nodes and lungs following local tumor growth in all of them. Using this method, an equitoxic dose of S-1 (15 mg/kg/day) and UFT (30 mg/kg/day) was administered p.o. for 14 consecutive days from 7 days after tumor cell implantation. S-1 showed a higher tumor growth inhibition than UFT did [S-1, 57% (significantly different from the tumor weight of the untreated group at P < 0.05) and UFT, 18% (P > 0.05)]. When both drugs were administered to nude rats bearing KM12C injected into the cecal wall for 28 consecutive days at equitoxic doses, the mean survival in the S-1 group was 16 days longer than that in the untreated group (P < 0.01) but that in the UFT group was only 8 days longer (P > 0.05). After the administration of an equitoxic dose of both drugs, S-1 gave the higher levels than UFT in various pharmacokinetic parameters as follows: area under the curve 0-24 h of 5-fluorouracil in plasma (3.5-fold), area under the curve 0-24 h of 5-fluorouracil incorporated into RNA in the tumor (1.3-fold), and thymidylate synthase inhibition rate (percentage) in the tumor (about 20%). Collectively, these findings suggested that this orthotopic human colorectal tumor model in nude rats is useful to evaluate the clinical therapeutic efficacy of drugs or therapies for colorectal cancer, and that S-1 had a higher therapeutic effect on human colorectal tumor than UFT did.

Adenocarcinoma↗
PubMed1996

Development of a novel form of an oral 5-fluorouracil derivative (S-1) directed to the potentiation of the tumor selective cytotoxicity of 5-fluorouracil by two biochemical modulators.

We have focused our attention on the development of a novel form of a tegafur-based [FT; a prodrug of 5-fluorouracil (5-FU)] antitumor agent. We have used two biochemical and pharmacological modulators of 5-FU to improve its overall activity. To potentiate the antitumor activity of FT, 5-chloro-2,4-dihydroxypyridine (CDHP) was used as a potent reversible inhibitor of 5-FU degradation. The reduction of gastrointestinal (GI) toxicity, induced in the host by 5-FU, was modulated by potassium oxonate (Oxo), an inhibitor of orotate phosphoribosyltransferase that catalyzes the phosphorylation of 5-FU, a process believed to be responsible for the toxic effects of 5-FU. When CDHP and FT were simultaneously given orally to Yoshida sarcoma-bearing rats in various molar ratios, the antitumor effect of FT was significantly potentiated by the combination consisting of at least a 0.2 versus 1 molar ratio of CDHP to FT, respectively. This augmentation of an antitumor activity was supported by potent and prolonged inhibition of dihydrouracil dehydrogenase activity (5-FU degrading activities) in the liver of tumor-bearing rats after oral CDHP (0.2:0.8 molar ratio) and furthermore by elevation and over 12 h retention of 5-FU levels in the tumors following combined administration of FT and CDHP at a molar ratio of 1:0.4, respectively. Moreover, to reduce the severe GI injury and subsequent loss of body weight, observed in parallel with an increased antitumor efficacy, Oxo was given orally to Yoshida sarcoma-bearing rats and nude rats xenografted with H-81 human gastric carcinoma, during consecutive administration of the FT-CDHP mixture. Combined treatment with Oxo and FT (1:2 molar ratio) supplemented with 0.4 molar CDHP resulted in protection of body weight loss without affecting the high antitumor efficacy of the FT-CDHP mixture. When [2-14C]FT plus CDHP was administered with Oxo, the 14C-labeled fluoronucleotide content was objectively decreased in the GI tract of the tumor-bearing rats but not in the tumor and bone marrow, which supports our initial hypothesis. Based on these promising data, we propose a suitable formulation of a FT-based anticancer drug, called S-1, and consisting of FT, CDHP and Oxo at a 1:0.4:1 molar ratio and showing tumor-selective cytotoxicity of 5-FU.

Animals↗
PubMed1996

[Estimation of pathways of 5-fluorouracil anabolism in human cancer cells in vitro and in vivo].

Possible pathways of intracellular phosphorylation of 5-fluorouracil (5-FU) in human cancer cells were investigated in vitro and in vivo. We used two inhibitors which regulate the anabolism of 5-FU for the purpose of elucidation of its pathways; one is oxonic acid (Oxo), an inhibitor of orotate phosphoribosyltransferase (OPRTase), catalizing a formation of FUMP from 5-FU, and another is 2, 6-dihydroxypyridine (DP), an inhibitor of uracil ribosyltransferase which catalizes a conversion of 5-FU to 5-fluorouridine. Although the pathway of 5-FU phosphorylation in murine tumor cells was varied, about 80% of human cancer cells tested were found to utilize the first pathway in which 5-FU was converted to FUMP by OPRTase. Thus, the phosphorylation of 5-FU via the first pathway was markedly inhibited by Oxo in 4 strains of 5 gastric cancer cells, 7 of 8 colorectal cancer cells and 3 of 4 lung cancer cells. In xenografts of human gastric and colorectal adenocarcinoma in which 5-FU phosphorylation is regulated by Oxo in vitro, the production of 5-fluoronucleotides and its incorporation into RNA after iv administration of 5-FU significantly decreased by co-administration of Oxo, suggesting that the nature of an anabolic pathway of 5-FU in the tumor cells in vitro reflects in vivo behavior. We also confirmed that the phosphoribosylpyrophosphate level in tumor cells was importantly related to determination of the metabolic pathway of 5-FU. These results would suggest that possible modulation of 5-FU lies on the augmentation of 5-FU efficacy.

Animals↗
PubMed1995

Enzymatic characterization of human immunodeficiency virus type 1 reverse transcriptase resistant to multiple 2',3'-dideoxynucleoside 5'-triphosphates.

A set of five mutations (A62V, V75I, F77L, F116Y, and Q151M) in the polymerase domain of reverse transcriptase (RT) of human immunodeficiency virus type 1 (HIV-1), which confers on the virus a reduced sensitivity to multiple therapeutic dideoxynucleosides (ddNs), has been identified. In this study, we defined the biochemical properties of RT with such mutations by using site-directed mutagenesis, overproduction of recombinant RTs, and steady-state kinetic analyses. A single mutation, Q151M, which developed first among the five mutations in patients receiving therapy, most profoundly reduced the sensitivity of RT to multiple ddN 5'-triphosphate (ddNTPs). Addition of other mutations to Q151M further reduced the sensitivity of RT to ddNTPs. RT with the five mutations proved to be resistant by 65-fold to 3'-azido-2',3'-dideoxythymidine 5'-triphosphate (AZTTP), 12-fold to ddCTP, 8.8-fold to ddATP, and 3.3-fold to 2',3'-dideoxyguanosine 5'-triphosphate (ddGTP), compared with wild-type RT (RTwt). Steady-state kinetic studies revealed comparable catalytic efficiency (kcat/Km) of RTs carrying combined mutations as compared with that of RTwt (< 3-fold), although a marked difference was noted in inhibition constants (Ki) (e.g. Ki of a mutant RT carrying the five mutations was 62-fold higher for AZTTP than that of RTwt). Thus, we conclude that the alteration of RT's substrate recognition, caused by these mutations, accounts for the observed multi-ddN resistance of HIV-1. The features of multi-ddNTP-resistant RTs should provide insights into the molecular mechanism of RT discriminating ddNTPs from natural substrates.

Antiviral Agents↗