Ability of sera from mice treated with Ge-132, an organo-germanium compound, to inhibit experimental murine ascites tumors

Serum specimens from mice treated orally with Ge-132 (100 mg/kg) exhibited antitumor activity against Ehrlich (allogeneic) and RL 1 (syngeneic) ascites tumors in BALB/c mice. Sera obtained from mice 24 hours after Ge-132 administration displayed the highest antitumor effect and the antitumor activity was dose-dependent. Sera prepared from mice 12, 36 or 48 hours after Ge-132 treatment had no protective effect. Circulating interferon (IFN) was induced at 24 hours after administration. The antiviral activity of serum from Ge-132-treated mice was inactivated by treatment with trypsin, low pH, and anti-IFN-gamma antiserum. The inactivated preparations of serum IFN induced by Ge-132 did not show antitumor activity when administered to mice bearing Ehrlich ascites tumors. These results suggest that the antitumor activity in the sera of Ge-132-treated mice may have been expressed through IFN-gamma which was induced by Ge-132.     

Antitumor activity of Ge-132, a new organogermanium compound, in mice is expressed through the functions of macrophages and T lymphocytes

The antitumor activity of Ge-132 against a variety of allogeneic and syngeneic murine ascites tumors was first evaluated. The antitumor effects of Ge-132 were observed when mice inoculated with Ehrlich carcinoma (allogeneic) or RL male 1 leukemia (syngeneic) cells were treated orally. However, Ge-132 had no activity on a T-cell lymphoma (EL 4, syngeneic) or a methylcholanthrene-induced fibrosarcoma (Meth-A, syngeneic). The antitumor effect of Ge-132 in mice was related to the dose administered as well as the administration schedule. The antitumor activity of Ge-132 was next studied in mice pretreated with some blockers against immunocompetent cells. The antitumor efficacy of Ge-132 was not observed when tumor-bearing mice were treated with trypan blue and carrageenan or monoclonal anti-Thy 1.2 antibody. However, when natural killer cells were eliminated from mice bearing RL male 1 or Ehrlich ascites tumors by treatment with anti-asialo GM 1 antiserum, the antitumor efficacy of the compound was unchanged. These results suggest that Ge-132 is effective against certain ascites tumors regardless of whether the tumor is syngeneic or allogeneic. Further, its effect might be expressed through host defense mechanisms, including macrophages and/or T lymphocytes.     

Suppression of tumor growth by peritoneal macrophages isolated from mice treated with carboxyethylgermanium sesquioxide (Ge-132)

In a murine model it has been shown that the antitumor activity of carboxyethylgermanium sesquioxide (Ge-132) can be depleted by administration of macrophage (M phi) blockers. In the present study, the role that M phi play in the antitumor activity of the compound was investigated. Oral administration of Ge-132 in mice was demonstrated to be effective in activating M phi (Ge-132-cytotoxic M phi), and the cytotoxic activity of these M phi appeared in the peritoneal cavity of mice 48 hours after the oral administration of the compound. Co-cultivation of RL male-1 leukemia or Ehrlich carcinoma cells with Ge-132-cytotoxic M phi in vitro resulted in marked suppression of the growth of tumor cells. The transfer of peritoneal exudate cells (PEC), or purified M phi fractions of PEC from Ge-132-treated mice to mice bearing Ehrlich or RL male-1 ascites tumors resulted in significant protection. However, when the cytotoxic M phi were depleted by carbonyl-iron treatment in vitro, no antitumor effect was demonstrated in mice bearing Ehrlich or RL male-1 ascites tumors. Macrophage fractions obtained from PEC of Ge-132-treated mice exhibited an inhibitory effect against certain tumors both in vivo and in vitro suggesting that the antitumor effect of Ge-132 observed in vivo resulted from the activation of M phi.     

Antitumor effect in mice of an organic germanium compound (Ge-132) when different administration methods are used

The antitumor effect of an organic germanium compound, carboxyethylgermanium sesquioxide (Ge-132), was examined in mice using two systems: one, the ascitic form of Ehrlich carcinoma in DDI mice, and the other, the solid form of Meth-A fibrosarcoma in BALB/c mice. In the mice with Ehrlich ascitic tumors, a remarkable prolongation in life span was observed after intraperitoneal (i.p.) or per oral (p.o.) administration of Ge-132 (300 mg/kg), but not after intravenous (i.v.) injection of the same compound. Following i.p. or p.o. administration, cytotoxic macrophages (M?) were induced in the peritoneal cavity after 48 h. although this was not the case after i.v. injections. When the in vivo effect of these in vitro active M? was examined after adoptive transfer to mice bearing Ehrlich ascitic tumor cells, a significant antitumor effect was noted. In the mice bearing solid Meth-A tumors, i.v. injections of Ge-132 (100 mg/kg) were found to inhibit tumor growth remarkably, although i.p. and p.o. administrations did not have the same result. This inhibitory effect of Ge-132 by i.v. administration was explained by the continued augmentation of NK activity in peripheral blood, which was followed by the induction of specific killer cells appearing in the spleen. When the mice which had recovered from Meth-A tumor growth, following i.v. injections of Ge-132, were challenged with the same tumor on day 30, all mice were able to tolerate the challenge, but not a challenge of RL male 1 tumor cells. These observations may indicate that the differing antitumor effects of Ge-132 produced when different administration methods are used can be explained by the variation in effector cells induced by such different administration routes.     

Anticancer treatment with a combination of antimetabolites of polyamine and pyrimidine

A combined efficacy of the polyamine antimetabolites, alpha-difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG) with two fluorinated pyrimidines was studied. DFMO, MGBG, 5-FU and 5'-deoxy-5-fluorouridine (5'-DFUR) were administered intraperitoneally to BALB/c nu/nu mice bearing xenotransplanted human gastric cancer for 5 consecutive days. Similar antitumor efficacies were observed in 3 groups treated with DFMO plus MGBG, DFMO, MGBG plus 5-FU as well as DFMO, MGBG plus 5'-DFUR. The two groups on 5-FU or 5'-DFUR alone did not differ in antitumor effects from the control, although reasonable levels of 5-FU were involved in tumor tissues. Hepatic and splenic 5-FU levels after 5-FU administration were significantly higher than those after 5'-DFUR, and marked decrease in mouse body weight was caused by 5-FU alone as well as 5-FU plus polyamine antimetabolites for 5 consecutive days. DNA biosynthesis and spermine levels in the tumor tissues on day 2 after cessation of the treatments dropped in 3 groups with DFMO plus MGBG, DFMO, MGBG plus 5'-DFUR as well as DFMO, MGBG plus 5-FU, while on day 6 there was little difference between the control and treated groups. These data suggest that combination with 5-FU or 5'-DFUR does not enhance the antitumor activity of polyamine antimetabolites by this experimental regimen.     

Antitumor mechanisms of carboxyethyl-germanium sesquioxide (Ge-132) in mice bearing Ehrlich ascites tumors

The administration of IFN-containing sera (Ge-sera) obtained from Ge-132-treated mice (Ge-mice) or the passive transfer of macrophages (M phi) to mice bearing ascites tumors resulted in the inhibition of tumor growth. The cooperative role of Ge-sera and Ge-M phi in the display of Ge-132-antitumor activity was studied. When mice were pretreated with antimouse IFN gamma antiserum, no IFN-inducing or antitumor activities of the compound were detected. Cytotoxic activities were detected in peritoneal M phi of mice treated with Ge-sera, and passive transfer of these M phi to tumor-bearing mice resulted in the inhibition of tumor growth. When tumor-bearing mice were pretreated with substances toxic to M phi, no antitumor activity of Ge-sera was observed. However, Ge-132 antitumor activity was observed in mice depleted of T-cells, even though the antitumor effects of the compound itself were not demonstrable in T-cell-depleted mice. Therefore, a part of the antitumor activity of Ge-132 appears to be expressed as follows: Ge-132 stimulates T-cells to produce circulating lymphokine(s) which are inactivated by anti-IFN gamma treatment; activated M phi are generated from resting M phi by these lymphokine(s); the transplanted tumors are inhibited by these M phi.     

Importance of T-cells and macrophages in the antitumor activity of carboxyethylgermanium sesquioxide (Ge-132)

The purpose of this study was to investigate the effective mechanisms of Ge-132, an organogermanium compound with immunomodulatory activity, on experimental murine ascites tumors. The antitumor effects of Ge-132 were observed when mice inoculated with Ehrlich carcinoma (allogeneic) or RL male 1 leukemia (syngeneic) cells were treated orally. However, Ge-132 had no activity on EL-4 lymphoma (syngeneic) or Meth A fibrosarcoma (syngeneic). The antitumor activity of Ge-132 was not observed when tumor-bearing mice were treated with trypan blue, carrageenan, or monoclonal anti-Thy 1.2 antibody. However, when natural killer (NK) cells were eliminated from mice bearing RL male 1 or Ehrlich ascites tumors by treatment with anti-asialo GM1 antiserum, the antitumor activity of the compound was unchanged. This suggests that Ge-132 was effective against certain ascites tumors regardless of whether the tumor was syngeneic or allogeneic. Furthermore, its effect might be expressed through host defense mechanisms, including macrophages and/or T-cells.     

Cooperation of lymphokine(s) and macrophages in expression of antitumor activity of carboxyethylgermanium sesquioxide (Ge-132)

The administration of IFN containing sera (Ge-sera) obtained from Ge-132-treated mice (Ge-mice) or the passive transfer of macrophages (M phi) to mice bearing ascites tumors resulted in the inhibition of tumor growth. The cooperative role of Ge-sera and Ge-M phi in the display of Ge-132-antitumor activity was studied. When mice were pretreated with antimouse IFN gamma antiserum, no IFN-inducing and antitumor activities of the compound were detected. Cytotoxic activities were detected on peritoneal M phi of mice treated with Ge-sera, and passive transfer of these M phi to tumor-bearing mice resulted in the inhibition of tumor growth. When tumor-bearing mice were pretreated with substances toxic to M phi, there was no antitumor activity of Ge-sera observed. However, there was antitumor activity of Ge-sera in mice depleted of T-cells, even though the antitumor effects of the compound itself were not demonstrable in T-cell depleted mice. Therefore, a part of the antitumor activity of Ge-132 may appear to be expressed as follows: (1) Ge-132 stimulated T-cells to produce circulating lymphokine(s) which were inactivated by anti-IFN gamma treatment; (2) activated M phi were generated from resting M phi by such lymphokine(s); (3) the transplanted tumors were inhibited by these M phi.     

Comparison between continuous intravenous and oral administration of 5-FU with LV

In case of 5-fluorouracil (5-FU)/leucovorin (LV) treatment, which is one of the most effective forms of chemotherapy for colorectal carcinoma, 5-FU is usually continuously infused from the venous route. However, since this continuous infusion limits the patients' active daily life, oral administration is preferable. In the present study, we evaluated the efficacy and side effects of orally administered 5-FU/LV. MATERIAL AND METHODS: In the continuous intravenous infusion group (civ group), colon 26 bearing mice were cannulated into central vein from external jugular vein. From this route, either 5, 10, or 20 mg/kg of 5-FU was continuously infused for 7 days (n = 6). In another group, either 10, 20, 40 mg/kg of 5-FU was infused orally (po group, n = 6). The other 6 animals were used for the non-treatment group. In the next series, 100 mg/kg of LV was added for each group above. Tumor volume, thymidylate synthase inhibition rate (TSIR) and body weight were measured at the end of infusion. During the experimental period, mice had free access to chow and water. RESULTS: The tumor/control (T/C) volumes ratio showed that approximately twice the orally administered 5-FU dose had an anti-tumor effect equal to that of 5-FU administered intravenously. Synergic antitumor effects by LV were only revealed in the civ group. Significant body weight loss was recognized only in the po group at a 5-FU dose of more than 20 mg/kg. In summary, since the modulation effect of LV was recognized only with continuously intravenous infusion of 5-FU, further improvement of oral administration is required in the LV/5-FU combination therapy.     

Antitumor drug toxicity in tumor-free and tumor-bearing mice

Summary This report summarizes studies of the toxicology of two antitumor drugs, l-phenylalanine mustard (l-PAM) and 5-fluorouracil (5-FU), administered singly and in combination to tumor-free and tumor-bearing mice. The purpose was to obtain data that might reveal the effect of disease on standard endpoints of drug toxicity. Young adult female B6C3F1 mice free of tumor or bearing murine mammary adenocarcinoma 16/C were treated with various dosages or combinations of l-PAM and 5-FU. All experiments included diluent control groups, and treatments were all administered IP daily for 5 days. Tumor size, body weight, hematology, clinical chemistry, and histopathology data were obtained on days 19, 21, 24, 28, 32, and 39 (day of tumor implantation = day 1; treatment on days 14–18), or on the corresponding post-treatment days in tumor-free mice. Tumor-bearing mice exhibited notable abnormalities in peripheral hematologic values and in concentrations of plasma urea nitrogen. If no drug treatment was administered, persistent reticulocytosis, granulocytosis, and uremia occurred in these mice. These abnormalities seemed to be related to tumor growth; drug treatment that produced partial regressions temporarily moderated cell counts and urea nitrogen concentrations. In general, these effects were observed in tumor-bearing mice receiving the highest doses in each experiment, suggesting that tumor-bearing mice are less sensitive than tumor-free mice to the effects of drugs on vital normal cells. Our data suggest that in the case of the particular tumor, host strain, and drugs studied here, distinct qualitative and quantitative differences in toxicity are obserbed when responses of tumor-free and tumor-bearing mice are compared.     

AK细胞及环磷酰胺治疗肝癌的实验研究

为研究１ 种新的过继免疫化疗治疗肝癌的方法,采用肝癌细胞株Ｈ２２ 接种于近交系Ｂａｌｂ／ｃ 小鼠皮下,制成肿瘤模型。使用ＩＬ２ 、肿瘤活化的杀伤细胞（ＡＫ细胞）及环磷酰胺（Ｃｙ） 进行治疗,检测小鼠脾淋巴细胞ＮＫ、ＬＡＫ及ＣＴＬ 活性,用流式细胞仪检测Ｌ３Ｔ４ 亚群及Ｌｙｔ２ 亚群含量。结果表明在过继免疫化疗组小鼠ＬＡＫ 及ＣＴＬ活性明显高于其它治疗组（Ｐ＜ ０．０１）,荷瘤小鼠肿瘤结节生长较ＩＬ２ 组及Ｃｙ 组明显缓慢（Ｐ＜ ０．０１）,生存期也明显高于其它各治疗组（Ｐ＜０ ．０１）。该研究表明过继免疫化疗有较强的抗肿瘤作用。     

Ability of sera from mice treated with Ge-132, an organic germanium compound, to inhibit experimental murine ascites tumours

Sera from C57Bl/6 mice treated orally with Ge-132 exhibited antitumour activity against Ehrlich (allogeneic) and RL male 1 (syngeneic) ascites tumours in BALB/c mice. Sera obtained from mice 24 h after Ge-132 administration displayed the greatest antitumour effect and this was dose dependent. Sera prepared from mice 12, 36, or 48 h after Ge-132 treatment had no protective effect. Circulating interferon (IFN) was induced at 24 h after administration of Ge-132 but was not detected in the sera at 12, 36, or 48 h after administration. The antiviral activity of sera from Ge-132-treated mice was inactivated by treatments with trypsin, low pH, and anti-IFN gamma antiserum. The inactivated preparations of serum IFN induced by Ge-132 did not exhibit antitumour activity when administered to tumour-bearing mice. These results suggest that antitumour activity in the sera of Ge-132-treated mice may be expressed through activities of Ge-132-induced lymphokine(s), such as IFN gamma.     

Characteristics in antitumor effects of organic silicon related compounds

To investigate the characteristics in antitumor effects of 2-trimethylsilylethylthioethylamine(KAS-010) and its conjugate with 5-FU (KAS-011), the antitumor and immunomodulating activities of these silicon compounds were examined with various systems. Both KAS-010 and KAS-011 administered orally was found to be effective to B 16 melanoma, Meth A sarcoma and MM 46 mammary carcinoma in vivo. On the other hand, KAS-011 administered orally exhibited a marked antitumor activity against L 1210 leukemia bearing mice. Furthermore, these silicon compounds inhibited significantly metastases to the lymph nodes and lung of Lewis lung carcinoma implanted id into the right ear of BDF1 mice. Especially, KAS-011 in combination with tumor amputation resulted in a remarkable prolongation of the survival time (% ILS: 93.8%) in this antimetastatic model. The cell killing effect was mainly dependent on the exposure time of these silicon compounds in cultured KB and human lung cancer (OAT) cells. Moreover, a significant increase of delayed type hypersensitivity reaction (DTHR) to sheep red blood cell (SRBC) induced by KAS-010 was seen in old aged mice. The DTHR in B 16 melanoma and Ehrlich carcinoma bearing mice treated with KAS-010 was significantly higher than those of non-treated tumor bearing mice, indicating an enhanced cellular immunity to KAS-010 possibly resulting in a remarked antitumor effect. We also found that tumor free mice treated these silicon compounds were acquired specific tumor immunity to Meth A sarcoma and MM 46 mammary carcinoma.     

Antitumor effect of intralesional injection with formalin-fixed Toxoplasma gondii organisms on Lewis lung carcinoma in Toxoplasma-infected mice

The antitumor effect of formalin-fixed Toxoplasma organisms (f-Tp) as an immunostimulant was examined in Toxoplasma-infected female C57BL/6 mice using a syngeneic Lewis lung carcinoma (3LL). Toxoplasma-infected mice, intradermally inoculated with the tumor cells mixed with 10(5), 10(6) or 10(7) f-Tp, developed a marked antitumor effect, inhibition of tumor growth and prolongation of life-span, in direct relation to the strength of the delayed-type hypersensitivity (DTH) reaction induced by f-Tp. The antitumor effect could also be observed even if an intralesional injection with f-Tp was performed 1, 3 or 5 days after the tumor inoculation. In a control, the injection with 2.5 X 10(6) live Mycobacterium bovis (BCG) in BCG-sensitized mice induced a significant antitumor effect, only when the BCG was injected in the mixture of tumor cells. These results demonstrate that the injection with f-Tp can induce a potent antitumor activity in mice with Toxoplasma infection.     

Corticotropin-releasing factor reduces tumor volume,halts further growth,and enhances the effect of chemotherapy in 4T1 mammary carcinoma in mice

The present study examines the effect of the endogenous neuroendoccrine factor, corticotropin-releasing factor (CRF), alone or in combination with 5-fluorouracil (5-FU), on 4T1 mammary tumor cells in vitro and in vivo. CRF has been detected in breast cancer tissues; however, the biological effects reported in the literature are sparse and variable. We found that exogenously administered CRF significantly reduced tumor growth without influencing angiogenesis or cell death. Furthermore, CRF reduced tumor interstitial fluid pressure (P_if) and potentiated the effect of 5-FU. These results show that CRF has antitumor effect on mammary carcinoma in mice.     

In vivo antitumor effects of fluoropyrimidines on colon adenocarcinoma 38 and enhancement by leucovorin.

Antitumor effect and active metabolites of fluoropyrimidines were examined in mice with transplantable colon adenocarcinoma 38 (Co 38). 5-Fluoro-2'-deoxyuridine (FUdR) treatment resulted in a much higher level of free 5-fluoro-2'-deoxyuridine-5'-monophosphate in the tumor than 5-fluorouracil (5-FU) did, and thymidylate synthase was almost completely inhibited after FUdR treatment, but FUdR showed weaker antitumor activity than 5-FU did. Moreover, 5-fluorouridine (FUR) also hardly inhibited tumor growth. A more marked tumor inhibition was obtained when FUdR and FUR were administered together. The antitumor activity of 5-FU was similar to that of the combination of FUdR and FUR. In combination with 2,2'-anhydro-5-ethyluridine, a uridine phosphorylase inhibitor, FUdR lost its antitumor activity, but that of FUR was somewhat potentiated. On the other hand, in combination with leucovorin (LV), 5-FU showed markedly potentiated antitumor activity, while the antitumor activity of FUdR or FUR was not potentiated. Addition of LV to the combination of FUdR and FUR enhanced the inhibitory effect of the drugs. From these results, the combination of FUdR and FUR together with LV, and the combination of 5-FU and LV seem to be highly efficacious against Co 38.     

In vivo Antitumor Effects of Fluoropyrimidines on Colon Adenocarcinoma 38 and Enhancement by Leucovorin

Antitumor effect and active metabolites of fluoropyrimidines were examined in mice with transplant-able colon adenocarcinoma 38 (Co 38). 5-Fluoro-2'-deoxj uridine (FUdR) treatment resulted in a much higher level of free 5-fluoro-2'-deoxyuridine-5'-monophosphate in the tumor than 5-rluorouracil (5-FU) did, and thymidylate synthase was almost completely inhibited after FUdR treatment, but FUdR showed weaker antitumor activity than 5-FU did. Moreover, 5-fluorouridine (FUR) also hardly inhibited tumor growth. A more marked tumor inhibition was obtained when FUdR and FUR were administered together. The antitumor activity of 5-FU was similar to that of the combination of FUdR and FUR. In combination with 2,2'-anhyilro-5-ethyluridine, a uridine phosphorylase inhibitor, FUdR lost its antitumor activity, but that of FUR was somewhat potentiated. On the other hand, in combination with leucovorin (LV), 5-FU showed markedly potentiated antitumor activity, while the antitumor activity of FUdR or FUR was not potentiated. Addition of LV to the combination of FUdR and FUR enhanced the inhibitory effect of the drugs. From these results, the combination of FUdR and FUR together with LV, and the combination of 5-FU and LV seem to be highly efficaceous against Co 38.     

羧乙基锗倍半氧化物抗移植瘤实验

将移植了ＨｅｐＡ鼠肝癌的ＮＩＨ鼠随机分为四组，一组作对照组，另三组分别给予Ｇｅ－１３２、ＣＹ、Ｇｅ－１３２＋ＣＹ治疗。２周后处死，测定血清中ＳＯＤ活性，对瘤体进行病理切片检查。结果表明：治疗组肿瘤重量较轻，ＳＯＤ活性较高（Ｐ＜０．０５）。Ｇｅ－１３２组的癌组织中白细胞浸润程度较高，细胞免疫力较强。对鼠肝癌的抑制率，Ｇｅ－１３２与ＣＹ合用有相加作用。     

Enhanced cytotoxic interaction between 5-fluorouracil and 4-hydroperoxycyclophosphamide against L1210 murine leukemic cells: applicability to ex vivo purging.

Eradication of contaminated tumor cells in bone marrow is a matter of utmost concern in the setting of autologous bone marrow transplantation. 4-Hydroperoxycyclophosphamide (4-HC) is often used for ex vivo chemical purging of contaminated tumor cells in bone marrow. The marrow from patients pretreated with 5-fluorouracil (5-FU) is enriched with multifactor-responsive high proliferative potential colony-forming cells. To develop an efficient ex vivo chemical purging system, we evaluated interaction between 4-HC and 5-FU. We investigated the antitumor effect of cyclophosphamide, a mother compound of 4-HC, and 5-FU against L1210 ascites tumor in B6D2F1 mice. The median lifespan of the mice treated with 4-HC or 5-FU alone was 8 and 12 days, respectively. The combination of both drugs significantly extended the median lifespan to 18.5 days. The median effect plot analysis indicated a synergistic cytotoxic interaction between 5-FU and 4-HC in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl terazolium bromide (MTT) assay. Clonogenic assay also showed that combination of 4-HC and 5-FU significantly reduced L1210 leukemic colonies to 20% of untreated control. Bone marrow cells from the mice treated with 5-FU at 150 mg/kg body weight was resistant to 4-HC at concentrations as high as 0.2 microgram/ml, which was more than 70% inhibitory concentration for colony formation in L1210 leukemic cells. Findings suggest that sequential treatment with in vivo 5-FU followed by ex vivo 4-HC could selectively enhance antitumor effects of 4-HC in tumor cells remaining in bone marrow.     

Enhanced antitumor effect of 5'-deoxy-5-fluorouridine by oral administration with L-cysteine

When given orally in combination with L-cysteine, 5'-deoxy-5-fluorouridine (DFUR) brought about a significant reduction in the growth of adenocarcinoma 755 and a significant prolongation of life-span in mice bearing Lewis lung carcinoma without increased toxicity to the host as compared with DFUR alone, though L-cysteine alone did not show an appreciable antitumor activity. Moreover, the combination of DFUR and L-cysteine resulted in a marked retardation of growth of human colon tumor LS174T transplanted into nude mice. Thus, the potency of DFUR was increased by L-cysteine. Pharmacokinetic studies revealed that after DFUR administration, plasma DFUR and 5-fluorouracil (5-FU) levels rapidly declined, but that, in the combination with L-cysteine, the plasma clearances of DFUR and 5-FU were slowed down considerably. In the tumor, DFUR and 5-FU levels were similar to those in the plasma. Such a prolongation of DFUR and 5-FU levels in plasma and tumor may produce the enhancement of antitumor effect seen with the combination of DFUR and L-cysteine.