Sex Hormone Dependency of Diethylnitrosamine-induced Liver Tumors in Mice and Chemoprevention by Leuprorelin

The prevalence of liver tumors throughout the world makes it imperative to seek chemopreventive agents. This tumor appears to be hormone-responsive and hormonal manipulations may therefore be beneficial. On this basis, both sexes of 12-day-old B6C3FJ mice were injected i.p. with diethylnitrosamine (DEN) at the dose of 2.5 μg/g body weight and observed for 32 weeks (males) or 36 weeks (females). In 100% of male mice, liver tumors were observed with an average diameter of 2.72 mm and multiplicity of 60.8. Orchidectomy at 6 weeks of age in these mice inhibited the incidence, multiplicity and size to 63%, 5.6 and 1.54 mm, respectively. By further implantation with an E₂ pellet at monthly intervals, these parameters were reduced to 26%, 0.6 and 0.61 mm, respectively. Administration of a gonadotropin-blocking chemical, leuprorelin, to DEN-treated male mice significantly reduced the multiplicity and size of tumors to 18.3 and 2.54 mm ( P <0.01 compared to those of DEN only). In female mice, the incidence of liver tumor was significantly smaller than that of males. However, ovariectomy and/or testosterone supplement significantly increased the occurrence of liver tumor. An anti-estrogen, toremifene, caused a marked further decrease of liver tumors. Mitotic indices with bromodeoxyuridine in tumor tissues paralleled the occurrence of liver tumors. Serum testosterone levels were significantly reduced by orchidectomy or by leuprorelin administration. These results further confirm that liver tumor is testosterone-responsive and hormonal manipulation by surgical orchidectomy or by chemical orchidectomy i.e. by leuprorelin, could substantially prevent the appearance of liver tumors.     

Influence of Paternal 252Cf Neutron Exposure on Abnormal Sperm, Embryonal Lethality, and Liver Tumorigenesis in the F1 Offspring of Mice

Experiments were conducted to determine whether neutron-induced genetic damage in parental germline cells can lead to the development of cancer in the offspring. Seven-week-old C3H male mice were irradiated with ²⁵²Cf neutrons at a dose of 0, 50, 100, or 200 cGy. Two weeks or 3 months after irradiation, the male mice were mated with virgin 9-week-old C57BL females. Two weeks after irradiation, the irradiated male mice showed an increased incidence of sperm abnormalities, which led to embryo lethalities in a dose-dependent manner when they were mated with unirradiated female mice. Furthermore, liver tumors in male offspring of male mice in the 50 cGy group were significantly increased in 19 of 44 (43.2%) animals, in clear contrast to the unirradiated group (1 of 31; 3.2%) ( P < 0.01). In the 100 cGy group, 6 of 39 (15%) mice had lesions. At 3 months after irradiation abnormal sperm and embryonal lethality were not significantly increased. The incidences of liver tumors in male offspring from the 50 cGy, 100 cGy and 200 cGy groups were 6 of 20 (30%), 5 of 22 (23%) and 1 of 19 (5%), respectively, which are not significantly increased compared with the control. It is concluded that increased hepatic tumor risk in the F₁ generation may be caused by genetic transmission of hepatoma-associated trait(s) induced by ²⁵²Cf neutron irradiation.     

Induction of Intestinal Tumors and Lymphomas in C57BL/6N Mice by a Food-borne Carcinogen, 2-Amino-l-methyl-6-phenylimidazo[4,5-b]pyridine

2-Amino-l-methyl-6-phenylimidazo[4,5- b ]pyridine (PhIP) is the most abundant heterocyclic amine contained in cooked meat and fish. Although PhIP has been demonstrated to induce various types of tumors in rats, lymphomas predominated in mice using the CDF1 strain. To investigate the carcinogenic activity of PhIP on other organs in mice with a different genetic background, PhIP was administered to C57BL/6N mice. After a 40-week administration of 300 ppm of PhIP in a high-fat diet followed by continuous feeding with a high fat diet, C57BL/6N mice developed adenomas and adenocarcinomas in the small intestine, the incidences being 52% in males and 68% in females at weeks 95 and 70, respectively. Lymphomas of B-cell origin also developed in both sexes as frequently as in the CDF1 strain, incidences being 48% in males and 32% in females. Although the incidence in PhIP-treated female mice did not differ from that in the control mice, lymphomas developed significantly earlier in the PhIP-treated mice. The present study demonstrated that the intestinal tract is another potential target of PhIP-induced carcinogenesis in mice, and that the carcinogenic activity of PhIP could be affected by the genetic background of the animals.     

Protection against Malignant Progression of Spontaneously Developing Liver Tumors in Transgenic Mice Expressing O6-Methylguanine-DNA Methyltransferase

To study the effect of O⁶-methylguanine-DNA methyltransferase (MGMT) on carcinogenesis, we have previously generated MGMT transgenic mice overexpressing the bacterial MGMT gene, ada , and demonstrated that high MGMT levels in the liver suppress induction of liver tumors after treatment with an alkylating hepatocarcinogen. To examine the effects of life-long elevation of MGMT activity on mouse spontaneous liver tumor development, ada-transgenic and control nontransgenic mice were compared. We also examined mutations at codon 61 of the H-ras oncogene, reported as a hot spot in mouse liver tumors, using a direct DNA sequencing method. The results revealed no significant difference in tumor incidence or mutation spectrum, but interestingly, ada-transgenic mice were found to have fewer malignant tumors and survived longer, indicating a possible protective role of MGMT against malignant conversion.     

小鼠结肠腺癌肝转移模型的建立

目的　建立结肠癌肝转移的动物模型 ,用于肿瘤转移防治的实验研究。方法　对BALB/c小鼠 ,经脾脏注入指数生长期的小鼠结肠腺癌细胞 (CT2 6 )悬液 0 .1ml,含细胞 1× 10 6个 ,保留脾脏。观察接种后小鼠的生存期 ,小鼠分别于接种后第 7、10、15天及自然死亡后剖腹 ,观察腹腔内肿瘤生长情况 ,留标本作病理检查和流式细胞术 (FCM )倍体检测。结果　小鼠平均自然生存时间为 (18.2± 1.8)天 ,尸解发现接种动物的肝脏表面均有灰白色转移结节形成 ,脾脏上有结节形成 ,其他脏器未见转移病灶。病理结果示肝转移瘤细胞与脾脏肿瘤细胞结构相似 ,符合低分化腺癌的特征。FCM倍体检测结果示肝转移瘤为四倍体肿瘤 ,与CT 2 6细胞倍体检测结果一致。结论　经脾脏注入CT 2 6细胞是建立结肠癌肝转移的可靠模型 ,具有潜伏期短、可重复的高转移发生率的特点 ,有较好的应用价值。     

Induction of Renal Cell Tumors in Rats and Mice, and Enhancement of Hepatocellular Tumor Development in Mice after Long-term Hydroquinone Treatment

Hydroquinone (HQ) was administered to F344 rats and B6C3F₁ mice of both sexes at a level of 0.8% in the diet for two years. This treatment induced renal tubular hyperplasia as well as adenomas, predominantly in males of both species, and was associated with chronic nephropathy in rats. In addition, the occurrence of epithelial hyperplasia of the renal papilla was increased in male rats. Foci of cellular alteration of the liver were significantly reduced in number by HQ in rats, but in contrast, were increased in mice, where development of hepatocellular adenoma was also enhanced in males. The incidence of squamous cell hyperplasia of the forestomach epithelium was significantly higher in mice of both sexes given HQ than in the controls, but no corresponding increase in tumor development was observed. The present study strongly indicates potential renal carcinogenicity of HQ in male rats and hepatocarcinogenicity in male mice. Thus, it is possible that HQ, which is present in the human environment, may play a role in cancer development in man.     

Rare Activation of the Human c-Ha-ras Transgene of Mice in Hemangioendothelial Sarcomas and Liver Tumors Induced by Glu-P-1

A transgenic mouse (Tg), having the human c-Ha- ras proto-oncogene, has been demonstrated to develop hemangioendothelial sarcomas (HESs) which are associated with the transgene mutation, but not to develop liver tumors. In this study, we examined the effects of 2-amino-6-methyldipyrido [1,2- a :3',2'- d ] imidazole (Glu-P-1), a food-borne carcinogen, which has been demonstrated to induce HESs and liver tumors in CDF₁ mice, on Tg mice. Chronic administration of 0.05% Glu-P-1 in the diet induced HESs in Tg (7/17), but not in 18 non-transgenic mice (N-Tg). With basal diet, two out of 17 Tg but none of 22 N-Tg, developed HESs. In contrast, Glu-P-1 administration induced liver tumors, both in Tg and in N-Tg; 16/17 in Tg and 13/18 in N-Tg. The incidence of hepatocellular carcinomas in Tg was higher than that in N-Tg (8/17 versus 3/18). With basal diet, only one out of 17 Tg and none of 22 N-Tg developed liver tumors. The Ha- ras mutation in tumors developed by the groups administered Glu-P-1, was examined. No mutations were detected in the transgene and mouse c-Ha- ras genes in all three HESs examined. In contrast, when 29 liver tumors taken from Tg were examined, two mutations of the transgene were detected in two HCCs. No mouse c-Ha- ras gene mutations were detected in any of the 47 liver tumors examined, which had developed in Tg and N-Tg mice. These results suggest that the transgene plays a role in the development of HESs induced by Glu-P-1, but not as a result of its mutation. Futher, the transgene plays no significant role in the development of liver tumors induced by Glu-P-1, but does play a role in the malignant conversion of some liver tumors, as a result of its mutation.     

Long-term Exposure to the Anti-inflammatory Agent Phenylbutazone Induces Kidney Tumors in Rats and Liver Tumors in Mice

Long-term toxicity and carcinogenicity of phenylbutazone, a nonsteroidal anti-inflammatory drug, were evaluated in F344/N rats and B6C3F1 mice. In 2-year studies, phenylbutazone was given in corn oil by gavage 5 days per week to groups of 50 rats of each sex at doses of 0, 50, or 100 mg/kg body weight, and to groups of 50 mice at doses of 0, 150, or 300 mg/kg body weight. Body weights and survival were similar among groups. Major target organs are kidneys in rats, and liver in mice. Kidney: inflammation, papillary necrosis, and mineralization in both sexes of rats, and hyperplasia and dilatation of the pelvis epithelium, and cysts in female rats. Uncommon tubular cell tumors of the kidney were found in 13 exposed rats: 5 in the 50 mg group and 4 in the 100 mg group of males; 4 in dosed female rats; none in controls. In female rats, dose-related increases in hyperplasia of the pelvis transitional epithelium, and 2 carcinomas were discovered. Urinary bladder: papillomas of the transitional epithelium were seen in 2 low-dose male and in 1 low-dose female rats. Forestomach: ulcers in rats, with acanthosis, hyperkeratosis, and basal cell hyperplasia in female rats; however, no neoplasms were associated with these lesions. Liver: primarily in male mice exposed to. phenylbutazone, hemorrhage, centrilobular cytomegaly and karyomegaly, fatty metamorphosis, cellular degeneration, and coagulative necrosis were seen; clear cell foci were observed in male mice. In summary, under the conditions of these 2-year oral intubation studies, phenylbutazone is associated with renal carcinogenicity in rats, as evidenced by increases in tubular cell neoplasms in both sexes. Evidence of carcinogenicity for male mice was shown by increased incidences and multiplicity of liver tumors. No carcinogenic activity was found for female mice.     

Kinetic Evaluation of 11C-1-Aminocyclopentane Carboxylic Acid in Rabbits Bearing VX-2 Tumors Using Positron Emission Tomography

Tumor detection with ¹¹C-1-aminocyclopentane carboxylic acid (¹¹-ACPC) showed that this amino acid has a high affinity for malignant tumors. We studied the kinetics of intravenously injected ¹¹C-ACPC in the rabbit VX-2 tumor using positron emission tomography. Three female rabbits bearing VX-2 tumor in the thighs were used. High uptake of ¹¹C-ACPC was seen in the tumor and liver. ¹¹-ACPC in plasma decreased rapidly after injection and its activity in the tumor increased with time. The kinetic evaluation of ACPC uptake into the tumor was performed using the unidirectional transport model. The average values of the transfer constant of ¹¹C-ACPC for VX-2 tumor were 0.030±0.002 ml/min/g. This preliminary result may form the basis for a quantitative analysis of the in vivo distribution of ¹¹C-labeled ACPC in tumors.     

超声造影在肝脏局灶性病灶良恶性肿瘤鉴别诊断中的应用价值

目的：探讨在肝脏局灶性良恶性肿瘤鉴别诊断中超声造影技术的应用价值。方法回顾性分析91例接受超声造影检查的肝脏肿瘤患者93个病灶的临床诊断资料,对肝脏不同病变的超声造影表现情况进行比较。结果在本次研究中,共有89个超声造影结果准确,诊断率为95．7％。在93个肝脏肿瘤病灶中,有78个恶性肿瘤病灶,有15个良性肿瘤病灶。超声造影回声增强程度、增强均匀度、消退快慢和增强快慢在肝脏良恶性肿瘤中存在统计学差异（P＜0．05）。在本次研究中,有肝转移癌（ metastatic liver carcinoma ,MLC）病灶26个,有肝细胞癌（ hepato cellular carcinoma , HCC）病灶52个,HCC和MLC在超声造影增强程度和增强均匀度上差异明显（P＜0．05）,在增强快慢和消退快慢上无明显差异（P＞0．05）。结论在肝脏良恶性肿瘤的鉴别中超声造影有很重要的应用价值。     

Strain Differences in Susceptibility to 2-Acetylaminofluorene and Phenobarbital Promotion of Rat Hepatocarcinogenesis in a Medium-term Assay System: Quantitation of Glutathione S-Transferase P-positive Foci Development

Strain differences in susceptibility to promotion by the liver carcinogens 2-acetylaminofluorene (2-AAF) and phenobarbital (PB) were examined in the medium-term bioassay system initially developed in our laboratory using male F344 rats as the test animal and glutathione S -transferase placental form (GST-P)-positive foci as the lesion end-point. Numbers and areas per cm² of induced GST-P-positive hepatocellular foci were compared in LEW, F344, NAR, SD, WBN, SHR, Wistar and ODS rats initiated with diethylnitrosamine (DEN) and subjected to partial hepatectomy during subsequent administration of 2-AAF or PB. LEW, SD, WBN, and F344 rats were most susceptible to hepatopromotion by both compounds, with a hundred fold increase in lesion area being observed for 2-AAF in the LEW case. NAR and SHR strains demonstrated an intermediate response, while Wistar and, in particular, the related ODS rats demonstrated very low susceptibilities. The obvious strain differences could be expressed in terms of comparative indices of promoting effects of 2-AAF and PB as well as DEN itself regarding each of the 8 strains tested. The use of F344 rats for the bioassay model was validated by the relatively high sensitivity to both DEN and 2-AAF initiation as well as second-stage promotion stimulus exhibited.     

Electron-equivalent Dose for the Effect of Gadolinium Neutron Capture Therapy on the Growth of Subcutaneously-inoculated Ehrlich Tumor Cells in Mice

The present in vivo study estimates the dose resulting fromthe gadolinium neutron capture reaction and the gadolinium enhancementextent of the thermal neutron effect. The assay is based onthe time required from cell inoculation to the formation oftumors with an arbitrary size of 200 mm². Mice were inoculatedsubcutaneously with Ehrlich tumor cells with or without megluminegadopentetate (1.2 mg ¹⁵⁷Gd/0.2 ml), and were exposed to 1.1x10¹² thermal neutrons cm^–2(n 8), or 3 MeV electrons atthree dose levels (each n 10). To reach 200 mm² in size, ittook 18.8 days for tumors treated with neutrons only and 34.7days for those treated with gadolinium and neutrons. From thetime-dose relation obtained with 3 MeV electrons, the equivalentdoses corresponding to delays of 34.7 and 18.8 days were 15.0and 7.4 Gy, respectively. Thus, gadolinium enhanced the thermalneutron effect two-fold (15.0/7.4) in the present study.     

The Roles of CD8+ and CD4+ Cells in Tumor Rejection

In vivo administrations of anti-Lyt-2.2 (CDS) mAb and anti-L3T4 (CD4) mAb selectively eliminated CD8⁺ cells amd CD4⁺ cells, respectively. The relative potencies of CD8⁺ cells and CD4⁺ cells and their roles in primary tumor rejections were studied by investigating the effects of these mAbs on tumor growth. CD8⁺ cells were themselves fully capable of mediating rejection in 5 different tumor rejection systems: two radiation leukemia virus (RadLV)-induced leukemias, B6RV2 and BALBRVD, a radiation-induced leukemia BALBRL♂1, and a plasmacytoma BALBMOPC-70A in CB6F₁ mice, and a Friend virus-induced leukemia B6FBL-3 in B6 mice. On the other hand, CD4⁺ cells were capable of resisting tumor growth of B6FBL-3, but not of the other four tumors. Furthermore, for efficient rejection of CB6F₁UV+^˚l sarcoma by CB6F₁ mice, synergy of CDS⁺ and CD4⁺ cells was necessary. Blocking of UV+^˚ 1 rejection was abrogated by delayed administration of anti-L3T4 (CD4) mAb but not anti-Lyt-2.2 (CDS) mAb, indicating the involvement of CD4⁺ cells in only the initial phase of rejection.     

The Effects of Boron Neutron Capture Therapy on Liver Tumors and Normal Hepatocytes in Mice

To explore the feasibility of employing boron neutron capture therapy (BNCT) to treat liver tumors, the effects of BNCT were investigated by using liver tumor models and normal hepatocytes in mice. Liver tumor models in C3H mice were developed by intrasplenic injection of SCCVII tumor cells. After borocaptate sodium (BSH) and boronophenylalanine (BPA) administration, ¹⁰B concentrations were measured in tumors and liver and the liver was irradiated with thermal neutrons. The effects of BNCT on the tumor and normal hepatocytes were studied by using colony formation assay and micronucleus assay, respectively. To compare the effects of BSH-BNCT and BPA-BNCT, the compound biological effectiveness (CBE) factor was determined. The CBE factors for BSH on the tumor were 4.22 and 2.29 using D ₁₀ and D ₀ as endpoints, respectively. Those for BPA were 9.94 and 5.64. In the case of hepatocytes, the CBE factors for BSH and BPA were 0.94 and 4.25, respectively. Tumor-to-liver ratios of boron concentration following BSH and BPA administration were 0.3 and 2.8, respectively. Considering the accumulation ratios of ¹⁰B, the therapeutic gain factors for BSH and BPA were 0.7-1.3 and 3.8-6.6, respectively. Therefore, it may be feasible to treat liver tumors with BPA-BNCT.     

Metabolism of Tegafur in Rat Liver Observed by in vivo 19F Magnetic Resonance Spectroscopy and Chromatography

Metabolism of tegafur in the rat liver was observed by in-vivo ¹⁹F magnetic resonance spectroscopy (MRS). After MRS observation, tegafur and q-fluorouracil (S-FU) in the liver were determined by a shromatographic method for comparison with the results of ¹⁹F-MRS. Rats were divided into 3 groups: 1) CCl4-induced liver injury group, 2) uracil combined group, 3) control group. Catabolism to fluoro-β-alanine was suppressed in both the liver injury group and the uracil combined group. Low peaks of 5-FU and fluoronucleotides could be found only in the uracil combined group. The result of ¹⁹F MRS observation of each group was in agreement with the result of determination of tegafur and 5-FU by chromatography. This showed that substances which could be observed by ¹⁹F-MRS were in proportion to all intracelluar fluoro-containing substances. ¹⁹F-MRS can provide direct information on the metabolism of fluoropyimidines non-invasivey and it might be a useful aid in choosing suitable shemotherapy for patients.     

Sex Differences in o-Phenylphenol and Sodium o-Phenylphenate Rat Urinary Bladder Carcinogenesis: Urinary Metabolites and Electrolytes under Conditions of Aciduria and Alkalinuria

F344 male and female rats were administered 1.25% o -phenylphenol (OPP) or 2% sodium o- phenylphenate (Na-OPP) in combination with 3% NaHCO₃ or 1% NI₄Cl for 8 weeks and changes in the urinary bladder histopathology and the urinary components were examined. Administration of OPP with NaHCO₃ resulted in marked urothelial liyperplasia in the urinary bladder of male rats, the response being less pronounced in females. OPP alone exerted no proliferative effect and NaHCO₃ induced only slight hyperplasia in males. Na-OPP alone induced mild hyperplastic lesions only in males, this being completely prevented by concomitant administration of NH₄C1. The findings thus demonstrated a clear correlation between hyperplastic response and reported carcinogenic potential of these treatments. Of the urinary factors examined, increases in levels of pH and sodium ion concentration were positively associated with proliferative lesions especially in males, although the findings failed to explain the sex difference. Urinary concentrations of non-conjugated forms of OPP metabolites were also not directly correlated with the development of hyperplasias. Thus, changes in individual urinary factors presumably affect nrothelial proliferation in combination rather than separately. The presence of OPP metabolites, including 2-phenyl-l,4-benzoquinone, in the urine may be unimportant in the OPP urinary carcinogenesis even under conditions of alkalinuria and high sodium ion concentration.     

Inhibitory Effects of Low-Dose Aloe-Emodin on the Development of Colorectal Tumors in Min Mice

Aloe-emodin (AE), a natural anthraquinone compound, has been reported to exhibit anticancer activityin various cancer cell lines and anti-inflammatory effects in murine macrophages. In the present study, weinvestigated the cancer chemopreventive effects of AE in an Apc-deficient Min mouse model. In the firstexperiment, male Min mice were fed a basal diet or diets containing 5 ppm AE and 10 ppm AE for 12 weeks.The dietary administration of 5 ppm AE significantly reduced the number of colorectal tumors. In a secondexperiment, we investigated the effects of AE on colitis-related colon carcinogenesis in Min mouse treated withdextran sodium sulfate (DSS). Female Min mice were administered 1% DSS in their drinking water for 7 days.AE was given to mice in their diet at a dose of 5 or 50 ppm for 5 weeks. Feeding with AE significantly reducedthe number of colorectal tumors. When proliferation of cells in normal-appearing colonic mucosa was assessedby monoclonal anti-rat Ki-67 antibody (MIB-5) immunohistochemistry in experiments 1 and 2, the AE treatmentsignificantly decreased the mean MIB-5-labeling index. These results suggest that the dietary administration oflow-dose AE may have chemopreventive effects against development of colorectal tumors in Min mice, possiblyin part by reducing cell proliferation in colorectal mucosa.     

Interleukin-12 Augments the Generation of Autologous Tumor-reactive CD8+ Cytotoxic T Lymphocytes from Tumor-infiltrating Lymphocytes

Human tumor-infiltrating lymphocytes (TIL) were obtained from breast cancer, renal cancer or neuroblastoma to investigate the generation of autologous tumor-reactive CD8⁺ cytotoxic T lymphocytes (CTL). When TIL were cultured with interleukin (IL)-2 (100 U/ml), the growth of TIL peaked around 8–10 days after the initiation of culture. In contrast, the proliferation of TIL cultured with IL-2 plus IL-12 peaked around 4–5 days after culture and tumor cells rapidly disappeared from the culture. To determine the generation of autologous tumor-reactive CD8⁺ CTL, TIL-derived CD8⁺ T cells were separated by FACStar. Both IL-2-activated and IL-2 plus IL-12-activated TIL-CD8⁺ T cells showed the same level of lymphokine-activated killer activity against a variety of tumor cells. However, TIL-CD8⁺ T cells activated with IL-2 plus IL-12 revealed greatly augmented cytotoxicity against autologous tumor cells compared with that induced by IL-2 alone. The autologous tumor cell-killing activity of TIL-CD8⁺ CTL was significantly inhibited by the addition of F(ab)₂ anti-CD3 monoclonal antibody, indicating that these CTL recognize autologous tumor antigen through T cell receptor. These results imply that IL-12 is a novel cytokine which facilitates the generation of autologous tumor-reactive CD8⁺ CTL from TIL.     

Comparative Studies on the Metabolism of New Fluorinated Pyrimidine Drugs in the Liver by in vivo19F Magnetic Resonance Spectroscopic Observation

1-Ethoxymethyl-5-fluorouracil (EM-FU) is a fluorinated pyrimidine derived from 5-FU, and 3-cyano-2,6-dihydroxypyridine (CNDP) is a chemical modulator which suppresses the catabolism of 5-FU by inhibiting dihydrouracil dehydrogenase in the liver. In this study, the metabolism of EM-FU and the suppression of 5-FU catabolism by CNDP were observed by in vivo ¹⁹F magnetic resonance spectroscopy in comparison with other similar drugs, because it is considered that the most effective mode of therapy using 5-FU is to suppress the catabolism of 5-FU in the liver and so to maintain for longer an effective blood level of 5-FU. The metabolism of EM-FU was very slow and the production of fluoro-β-alanine was very low as compared to the case of tegafur. The catabolic suppression by CNDP was much stronger than that of uracil. Therefore co-administration of EM-FU and CNDP should suppress catabolism and maintain an effective blood level of 5-FU for a long period of time.     

Selective Suppression of the Generation of Anti-tumor L3T4+ but Not of Lyt-2+ T Cell-mediated Immunity in the Tumor-hearing State

C3H/He mice hyperimmune against syngeneic MH134 hepatoma were prepared by intradermal (id) inoculation of viable tumor cells followed by surgical resection of the tumor and by repeated id challenges with viable tumor cells. Winn assays performed utilizing spleen cells from these mice have revealed that both Lyt-2⁺ and L3T4⁺ T cell subsets from MH134-hyperimmune mice produced complete tumor protection. The in vivo tumor-neutralizing activity was also found in spleen cells from tumor-bearing mice at various times after id implantation of MH134 tumor cells. However, in contrast to comparable tumor-neutralization by Lyt-2⁺ and L3T4⁺ T subsets from hyperimmune mice, only the Lyt-2⁺ T cell subset from tumor-bearing mice was capable of mediating the in vivo protective immunity. L3T4⁺ T cell-mediated immunity was not detectable in the tumor-bearing state irrespective of the length of the sensitization period with a primary growing tumor, but emerged in the mice which resisted the first tumor challenge after the resection of the primary tumor. These results indicate that the emergence of L3T4⁺ T cell-mediated anti-tumor immunity is stage-dependent and the Lyt-2⁺ T cells represent the main functional subset in the tumor-bearing state, although both subsets of T cells are potentially capable of effecting anti-tumor in vivo immunity. The results are discussed in relation to the selective suppression of the L3T4⁺ but not of Lyt-2⁺ T cell function in the tumor-hearing state.