Comparison of anti-arthritic properties of leflunomide with methotrexate and FK506: effect on T cell activation-induced inflammatory cytokine production in vitro and rat adjuvant-induced arthritis.

OBJECTIVE AND DESIGN: To examine the effect of leflunomide (LEF) on T cell activation-induced inflammatory cytokine production in human peripheral blood mononuclear cells (PBMC) and rat established adjuvant-induced arthritis (AIA), and compare these effects with methotrexate (MTX) and FK506 (tacrolimus), focusing on improvement of joint function in AIA. METHODS: Human PBMC were cultured with immobilized anti-CD3/CD28 monoclonal antibody to produce tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta and IL-6. The active metabolite of LEF was used in in vitro study. AIA was induced in female Lewis rats. Paw swelling and grip strength were measured as indicators of arthritis and joint function, respectively. Rats were therapeutically administered LEF (3.2-32 mg/kg) from days 15-24 by oral administration. RESULTS: LEF inhibited anti-CD3/CD28 induced production of TNF-alpha, IL-1beta and IL-6, with IC50 values of 27, 21 and 21 microg/ml, respectively. LEF also suppressed mouse bone marrow cell MTT conversion, with an IC50 value of 15 microg/ml. LEF significantly inhibited paw swelling and loss of grip strength in established AIA at 10 and 32 mg/kg. The inhibition of paw swelling and grip strength loss by LEF was more potent than MTX. However, maximum recovery of grip strength loss by LEF (23.5%) was less potent compared to that with FK506 (57.8%). CONCLUSIONS: LEF inhibited anti-CD3/CD28 induced inflammatory cytokine production in human PBMC at concentrations showing deleterious effects on bone marrow cell proliferation. LEF is superior to MXT in improving arthritis and joint function in established AIA, but is inferior to FK506 in recovering joint function, probably due to its anti-proliferative actions.

Anti-arthritic properties of FK506 on collagen-induced arthritis in rats.

OBJECTIVE AND DESIGN: To determine the effect of FK506 (tacrolimus) on paw inflammation, TNF-alpha expression in joint, and bone and cartilage destruction in type II collagen-induced arthritis (CIA) model in rats. METHODS: CIA was induced by immunization of female Lewis rats with an emulsion of bovine type II collagen and incomplete Freund's adjuvant. Paw inflammation was assessed by the increase in paw volume. Tumor necrosis factor (TNF) -alpha expression in hind knee joint was assessed by immunohistochemical analysis. Lesions of bone and cartilage were assessed on the basis of histological change in knee joint, radiographic analysis in hind paw, bone mineral density in femora and proteoglycan contents in the cartilage of femoral heads. FK506 at doses of 1, 1.8 and 3.2 mg/kg or its placebo formulation was orally administered to rats for 28 days from the day after immunization (n = 10). Effect of FK506 was compared with that of vehicle (distilled water). RESULTS: FK506 at a dose of 1.8 mg/kg significantly suppressed paw swelling (p < 0.01) and histological change in knee joint (p < 0.05). Tumor necrosis factor (TNF)-alpha was mainly expressed in the region with a marked infiltration of inflammatory cells in the hind knee joint. FK506 (3.2 mg/kg) markedly reduced TNF-alpha expression. FK506 at a dose of 1.8 mg/kg suppressed radiographic changes in hind paw (p < 0.05) and also recovered the decrease in bone mineral density in the femora (p < 0.05). Proteoglycan contents in the cartilage of femoral heads were determined to evaluate the cartilage destruction more quantitatively and found to significantly decrease in CIA rats. FK506 at a dose of 1.8 mg/kg recovered the loss of proteoglycan contents (p < 0.01). CONCLUSION: These results show that FK506 is effective in suppressing inflammation, TNF-alpha expression in joint, and damage to bone and cartilage in rat CIA, and may be useful in the treatment of rheumatoid arthritis.

FK506 is superior to methotrexate in therapeutic effects on advanced stage of rat adjuvant-induced arthritis.

OBJECTIVE AND DESIGN: The anti-arthritic properties of FK506 were compared with methotrexate (MTX) in established adjuvant-induced arthritis (AIA) in rats. MATERIAL: Female Lewis rats. TREATMENT: Arthritic rats were orally administered with FK506 (1-5.6 mg/kg) and MTX (0.1-1 mg/kg) from days 15-24. METHODS: Arthritis was induced by injection of Mycobacterium tuberculosis into the right hind footpad on day 0. Efficacy was determined on the basis of paw inflammation measured by paw volume and histological change, hyperalgesia and grip strength. Grip strength measurement was employed as an indication of function of paws in arthritic rats. Peripheral white blood cell (WBC) counts and thymus weights were measured, mainly as indicators of toxic side effects. RESULTS: FK506 suppressed paw inflammation and hyperalgesia without toxic effects on WBC and thymus in established AIA. MTX slightly suppressed paw inflammation and hyperalgesia at the highest dose (1 mg/kg). Toxic effects were observed at lower doses than the effective treatment dose with MTX. Grip strength was found to decrease during development of AIA. FK506, but not MTX, treated rats recovered grip strength loss. CONCLUSIONS: The results show that FK506 is more effective and less toxic than MTX in treating established AIA in rats.

Effects of FK506 and other immunosuppressive anti-rheumatic agents on T cell activation mediated IL-6 and IgM production in vitro.

The objective of this study was to investigate the therapeutic potential of FK506 and other immunosuppressive agents for the treatment of rheumatoid arthritis (RA), focusing on the effects on in vitro IL-6 production and IL-6-mediated immune response. We employed an in vitro model producing IL-6 via T cell activation in human PBMC, based on the hypothesis that T cells play a central role in the pathogenesis of RA. FK506 potently inhibited IL-6 production from PBMC stimulated with anti-CD3 and anti-CD28 monoclonal antibody (anti-CD3/CD28). Cyclosporin A (CsA) also inhibited the anti-CD3/CD28 induced IL-6 production but was about 100 times less potent than FK506. Dexamethasone (DEX) inhibited both anti-CD3/CD28 and LPS induced IL-6 production at almost the same concentration. Methotrexate (MTX) did not affect cytokine production. Anti-CD3/CD28 stimulated PBMC culture supernatants were found to enhance IgM production in SKW6.4 cells. The effects of anti-CD3/CD28 stimulated culture supernatants in the presence of agents on IgM production in SKW6.4 cells were investigated. FK506 and CsA led to suppression of IgM production induced by culture supernatants probably via inhibition of IgM inducible cytokine production from PBMC. DEX profoundly enhanced IgM production, although IL-6 production from PBMC was strongly inhibited by the agent. MTX decreased IgM production although it has no inhibitory effect on IL-6 production. The present study suggests that FK506 is the most effective among the four agents for the suppression of IL-6 production and IL-6-mediated autoantibody production in T cell activation related autoimmune diseases such as RA.

Cachexia induction by EL-4 lymphoma in mice and possible involvement of impaired lipoprotein lipase activity.

Several lines of evidence have postulated that reduction in the activity of lipoprotein lipase (LPL) is involved in cachexia induction in cancer patients. Recently we have demonstrated that murine melanoma B16 has the ability to reduce the LPL activity and thereby induce cachexia symptoms in mice following intraperitoneal inoculation. In order to further investigate the relationship between LPL activity and cachectic syndrome, cachexia models other than melanoma B16 are required. However, there are few animal cachexia models in which LPL activity is involved in the induction of cachectic symptoms. In this study, cachectic symptoms and plasma LPL activity were investigated in mice bearing EL-4 mouse lymphoma. In EL-4 bearing mice the body weight including tumor weight in the abdominal cavity was rather higher than that of normal mice without tumor, whereas weights of carcass wet and gastrocnemius muscle were significantly decreased in EL-4 bearing mice. Elevated blood levels of triglyceride and non-esterified fatty acid were observed in mice bearing EL-4, associated with the impaired plasma LPL activity. Overall, this study indicated that EL-4 lymphoma in mice results in a severe cachexia which is possibly related to impaired LPL activity and also provided a useful cachexia model for understanding the role of LPL in the development of cancer cachexia.

FK506 potently inhibits T cell activation induced TNF-alpha and IL-1beta production in vitro by human peripheral blood mononuclear cells.

The aim of this study was to elucidate the in vitro inhibitory potency of FK506 on production of the inflammatory cytokines, tumour necrosis factor (TNF)-alpha and interleukin (IL)-1beta, with a view to assessing this immunosuppressive agent as a potential anti-rheumatic drug. We employed an in vitro model which produces TNF-alpha and IL-1beta through T cell activation. Human peripheral blood mononuclear cells (PBMC) were cultured with immobilized anti-CD3/CD28 monoclonal antibody in this model. FK506 inhibited anti-CD3/CD28 induced TNF-alpha and IL-1beta production at concentrations less than 1 ng ml(-1). Flow cytometric analysis of intracellular TNF-alpha and IL-1beta positive cells showed that FK506 potently suppresses inflammatory cytokine production from CD14+ monocytes as well as from T cells. Cyclosporin A (CsA) and dexamethasone (DEX) also inhibited the anti-CD3/CD28 induced cytokine production, but were less potent than FK506. FK506 and CsA, but not DEX, specifically inhibited anti-CD3/CD28 induced inflammatory cytokine production without affecting the lipopolysaccaride (LPS) induced effect. Methotrexate (MTX) was completely inactive for suppressing cytokine production under either condition. Anti-CD3/CD28 stimulated PBMC culture supernatants were found to enhance the expression of adhesion molecules in human vascular endothelial cells. FK506, CsA and DEX led to the suppression of adhesion molecule expression probably by inhibiting cytokine production from PBMC. The inhibitory potency of agents on TNF-alpha and IL-1beta production was compared with cytotoxicity and FK506 was not cytotoxic at concentrations several orders of magnitude greater than those required for cytokine inhibition. These results strongly suggest that FK506 may be most effective to specifically prevent T cell activation mediated inflammatory cytokine production in a clinical setting.

Effects of a novel pyridylsulphonyl thiazole derivative, FR115092, on autoimmune and mitomycin C-induced thrombocytopenia in mice.

Dapsone (4,4'-diaminodiphenyl sulphone), an antileprotic and antimalarial drug, has been reported to be of therapeutic benefit in idiopathic thrombocytopenic purpura in the clinic. However, adverse reactions such as haemolytic anaemia have often been observed. In this study, we found that dapsone increased the number of platelets and decreased the number of red blood cells in male (NZWxBXSB)F1 (W/BF1) mice, an animal model of idiopathic thrombocytopenic purpura. In studies to prepare derivatives of dapsone with weaker side effects than the parent compound, FR115092 (2-[5-(2-pyridylsulphonyl)thiazolyl]amine) was discovered. The effect of FR115092 on the number of blood cells was studied and compared with dapsone in mice. FR 115092 increased the number of platelets without reducing the number of red blood cells in W/BF1 mice. This drug significantly suppressed the increase in circulating autoantibodies against platelets and increased the number of megakaryocytes. Furthermore, FR115092 inhibited the reduction of the number of platelets in mitomycin C-induced thrombocytopenic mice, as a consequence of its enhancement of growth and maturation of megakaryocytes. These findings suggest that FR115092 may be effective against various thrombocytopenias, without inducing haemolytic anaemia.

Ponalrestat, an aldose reductase inhibitor, inhibits cachexia syndrome in nude mice bearing human melanomas G361 and SEKI.

Our recent study has demonstrated that ponalrestat, an aldose reductase inhibitor, activates lipoprotein lipase (LPL) activity in the adipose tissue and alleviates the cachectic symptoms induced by B16 melanoma in mice. In this study, the effect of ponalrestat on cachexia symptoms in nude mice bearing human melanomas G361 and SEKI was investigated because it has been suggested that the suppression of LPL has an important role in cachexia induction by these two melanomas in nude mice. Mice bearing G361 subcutaneously did not gain weight and became cachectic, associated with the tumor growth. Tumor growth was not affected by ponalrestat, nevertheless treatment with ponalrestat resulted in an amelioration of the reduction in the weight of body mass, epididymal fat, gastrocnemius muscle, carcass and whole body lipid induced by the presence of G361. A severe weight loss observed in nude mice bearing SEKI was also partially attenuated by ponalrestat treatment. Overall, this study showed that ponalrestat is effective in the attenuation of the cachectic symptoms induced by human melanomas G361 and SEKI in nude mice, suggesting that ponalrestat has a potential usefulness for the treatment of cancer cachexia.

Ponalrestat, an aldose reductase inhibitor, inhibits cachexia syndrome induced by colon26 adenocarcinoma in mice.

Our recent study has demonstrated that ponalrestat, an aldose reductase inhibitor, activates lipoprotein lipase activity and alleviates B16 melanoma-induced cachexia in mice. In this study, the effect of ponalrestat on murine adenocarcinoma colon26-induced cachexia was investigated in mice. Mice bearing colon26 subcutaneously lost weight and became cachectic, associated with the tumor growth. Although tumor growth was slightly stimulated when tumor bearing mice were treated with ponalrestat: nevertheless, the drug attenuated the reduction in the weight of body mass, epididymal fat, gastrocnemius muscle and carcass induced by colon26, as well as significantly prolonged the survival of the colon26 bearing mice. Ponalrestat inhibited the production of interleukin-1 (IL-1) from human monocytes stimulated by Lipopolysaccharide (LPS) in vitro, and also suppressed LPS-induced increase of IL-1 in the blood in mice. Overall, this study showed that ponalrestat suppresses IL-1 production both in vitro and in vivo, and inhibits the cachectic symptoms induced by colon26 adenocarcinoma in mice, suggesting that ponalrestat has a therapeutic potential for the treatment of cancer cachexia.

Different effects of FK317 on multidrug-resistant tumor in vivo and in vitro.

FK317, a novel substituted dihydrobenzoxazine, was examined for antitumor effects on multidrug-resistant (MDR) tumor cells in vitro and in vivo. In nude mice, FK317 markedly inhibited the growth of s.c. implanted KB-V1 vinblastine (VLB)-resistant human epidermal carcinoma KB cells, as well as the parent cells (KB-3-1). However, KB-V1 showed much greater resistance to FK317 than to VLB and adriamycin (ADM) in the in vitro study. This resistance was reversed by the addition of verapamil, whereby intracellular accumulation of FK317 in the KB-V1 cells was also decreased. After incubation of FK317 in human and mouse blood, it was shown to be rapidly metabolized to a monodeacetylated form, and slowly metabolized further to a dideacetylated form. With the removal of the acetyl groups from FK317, resistance indexes in KB-V1 and SBC-3/ADM, ADM-resistant human lung carcinoma, decreased. In addition, photolabeling of P-glycoprotein with [3H]azidopine in KB-V1 plasma membrane was completely inhibited by FK317, but not by the deacetylated metabolites. These results indicate that FK317 is metabolized to deacetylated forms, which do not bind to P-glycoprotein and are incorporated into MDR cells, causing cytotoxic effects.

Cytotoxic mechanisms of FK317, a new class of bioreductive agent with potent antitumor activity.

FK317 is a member of a new class of bioreductive agents that exhibit strong cytotoxicity against various human cancer cells. The effect of FK317 was found to be stronger than that of mitomycin C (MMC), adriamycin (ADR) or cisplatin (CDDP). Alkaline elution analysis indicated that FK317 formed interstrand DNA-DNA and DNA-protein cross-links in cells. On the other hand, no DNA single-strand breaks were observed in the cells treated with FK317. In a cell-free system the deacetylated metabolites produced cross-linked DNA under reductive conditions, though FK317 itself did not form DNA-DNA cross-links. In order to elucidate the metabolic activation mechanisms, we established an FK317-resistant subline from human non-small cell lung cancer cells (Lu99) by stepwise and brief exposure (1 h) to FK317. The resistant subline (Lu99/317) showed cross-resistance to MMC and carboquone (CQ), but not to ADR or CDDP. DT-diaphorase, which is one of the activation enzymes of MMC and CQ, was deficient in Lu99/317 cells as determined by enzyme activity assay. However, the levels of NADPH:cytochrome P450 reductase, which is another activation enzyme for MMC and CQ, were comparable in resistant and parent cell lines. Treatment of the cells with dicumarol, an inhibitor of DT-diaphorase, reduced the cytotoxicity of FK317 to Lu99 cells, but not to Lu99/317 cells. These results indicate that deacetylation of FK317 is necessary for its reductive activation, and deacetylated FK317 is reduced by DT-diaphorase to form an active metabolite, which produces DNA-DNA interstrand and DNA-protein cross-links that lead to cell death.

FK317: a novel substituted dihydrobenzoxazine with potent antitumor activity which does not induce vascular leak syndrome.

PURPOSE: FK973, a substituted dihydrobenzoxazine, is an antitumor antibiotic which has shown high therapeutic efficacy in a phase I study, but its development has been abandoned because of the side effect of vascular leak syndrome (VLS) in the clinical study. This study was performed to investigate whether or not FK317, a new benzmethoxy derivative of FK973, retains the antitumor activity of FK973 without the side effect of VLS. METHODS: VLS was evaluated by the volume of pleural effusion in rats. Cytotoxic activities were determined by a tetrazolium-based colorimetric assay (MTT assay) against murine (B16, P388) and human (HeLa S3, KB) tumor cell lines. Antitumor activities against murine ascitic leukemia (P388, L1210), murine solid tumors (reticulum cell sarcoma M5076, Colon 38 carcinoma) and human xenografts (mammary carcinoma MX-1, lung carcinoma LX-1) were examined. RESULTS: FK973 (1.8 mg/kg) given i.v. to rats induced pleural effusion, one of the elements of VLS, 36 days after the first dosing, but did not 28 days after dosing. This model reflects clinical VLS delayed-type effusion with high protein concentrations. In contrast, FK317 (1.0-3.2 mg/kg) did not induce pleural effusion at all. FK317 had stronger cytotoxic effects against in vitro cultured B16, P388, HeLa S3 and KB tumor cell lines, and in in vivo experiments, FK317 showed equivalent antitumor activity against P388, M5076 and MX-1, and more potent antitumor activity against L1210, Colon 38 and LX-1 compared with FK973. CONCLUSION: These results suggest that FK317 retains the antitumor activity of FK973 and does not induce VLS, and FK317 is a drug with high clinical potential for treating tumors in humans.

Effect of FR143430, a novel cytokine suppressive agent, on adenocarcinoma colon26-induced cachexia in mice.

Cancer cachexia, characterized by weight loss and progressive tissue wasting, has been postulated to be mediated by cytokines. In this study the effect of FR143430, (2-(4-fluorophenyl)-4, 5, 6, 7-tetrahydro-3-(4-pyridyl)pyrazolo[1, 5-a]pyrimidine monohydrochloride), an inhibitor of Interleukin-1 and Tumor necrosis factor-a (TNF- a), on adenocarcinoma colon26-induced cachexia was investigated in mice. Tumor growth was not affected. Nevertheless, treatment with FR143430 (0.1 to lmg) into the tumor resulted in the attenuation of the reduction in body weight, food intake, epididymal fat and carcass weight, the decrease in the circulating levels of triglyceride and glucose, and the increase in the circulating levels of total cholesterol, non esterified free fatty acid (NEFA) and total protein, which were induced by the presence of the tumor. However, oral treatment with FR143430 failed to show an inhibitory effect on cachexia induction. Overall, this study demonstrated that the cachexia induced by colon26 was alleviated by the injection of FR143430 into the tumor in sufficient quantity, without any effect on tumor growth, suggesting the potential utility of cytokine suppressive agents e for the treatment of cancer cachexia.

Discovery of FR115092: a novel antinephritic agent.

A series of dapsone-related 4-aminopheynl and 2-aminothiazolyl derivatives was prepared, and their antinephritic activity and blood toxicity were evaluated. 5-(2-Pyridylsulfonyl)-2-thiazolamine (FR115092, 26) was effective against two nephritis models, namely graft-versus-host disease (GVHD) and autoimmune W/BF1 mice, and showed none of the blood toxicity observed with dapsone.

Synthesis and effects of novel thiazole derivatives against thrombocytopenia.

5-(2-Pyridylsulfonyl)-2-thiazolamine (2) was effective both in mitomycin C (MMC)-induced thrombocytopenia and in an animal model of idiopathic thrombocytopenic purpura (ITP). It also suppressed the increase of autoantibodies against platelets in the ITP model and showed no blood toxicity. Chemical modification of 2 led to the discovery of more potent compounds against MMC-induced thrombocytopenia.

Anti-cachectic effect of FK317, a novel anti-cancer agent, in colon26 and LX-1 models in mice.

The effects of FK317 (11-acetyl-8-carbamoyloxymethyl-4-formyl-6- methoxy-14-oxa-1,11-diazatetracyclo[7.4.1.0(2, 7). 0(10, 2] tetradeca-2,4,6-trien-9-yl acetate), a novel anti-cancer agent, on murine adenocarcinoma colon26- and human lung carcinoma LX-1-induced cachexia were investigated in mice. Mice bearing colon26 or LX-1 s.c. lost weight and became cachectic, associated with tumor growth. FK317 and mitomycin C (MMC) inhibited the growth of both tumors. FK317 ameliorated the weight loss induced by the presence of colon26 or LX-1, while MMC enhanced it. An attenuation of the reduction in the weights of epididymal fat, gastrocnemius muscle and carcass was observed in FK317-treated tumor-bearing mice in both cachexia models, but not in MMC-treated mice. The decreases in the circulating levels of triglyceride, glucose and non-esterified fatty acid, which were induced by the presence of colon26, was partially inhibited by treatment with FK317. Overall, this study revealed that FK317 is a potent anti-cancer drug with anti-cachectic activity, suggesting that FK317 has potential utility for the treatment of cancer.

FK317, a novel substituted dihydrobenzoxazine, exhibits potent antitumor activity against human tumor xenografts in nude mice.

The antitumor effects of FK317, a novel substituted dihydrobenzoxazine, were evaluated using human tumor xenografts (small cell lung cancer, non-small cell lung cancer, stomach cancer, colon cancer, pancreatic cancer, breast cancer, cervical cancer and ovarian cancer). Tumor growth-inhibitory effects and the effective dose-range of FK317 were much stronger and broader, respectively, than those of reference drugs such as mitomycin C, adriamycin, cisplatin, taxol and irinotecan. Furthermore, the body weight decrease and myelosuppression in FK317-treated mice were less than in the animals given any of the reference drugs. To explain this tumor selectivity, the distribution of FK317 was investigated after dosing tumor-bearing mice with the 14C-labelled compound. The concentration of FK317 in tumor tissues was relatively low, and long tumor retention was not observed. However, thin-layer chromatographic separation revealed that the radioactivity in the tumor resided mainly in strongly cytotoxic metabolites, while that in other tissues resided mainly in non-cytotoxic metabolites. These results suggest that FK317 shows strong antitumor activity without side effects, and one reason for this is its specific metabolite pattern. FK317 is now undergoing phase I clinical trials.

Increased frequency of HLA-DR4 allele in women with unexplained recurrent spontaneous abortions, detected by the method of PCR-SSP.

We investigated whether HLA-DR genes are associated with the etiology of unexplained recurrent spontaneous abortion (URSA), by using the polymerase chain reaction-sequence-specific primers (PCR-SSP) method, which is more accurate than serological typing. In women (n = 27) who experienced three or more consecutive spontaneous abortions in the first trimester, the frequency of the DR4 allele was significantly increased (relative risk = 4.25, P = 0.020) when compared with controls (n = 22) who experienced two or more full-term deliveries and no miscarriage. After high-resolutional analysis by a second PCR-SSP in positive cases for the DR4 allele phenotypic frequencies of HLA-DRB1*04 sub-alleles were disclosed. The most frequent sub-allele was DRB1*0405, followed by DRB1*0406 in both women with URSA and controls. However, none of the specific sub-alleles were attributed statistically to the increase in the DR4 allele in women with URSA.

[Characteristics of home parenteral nutrition and effectiveness of 3 way valved PICC in regional medical care].

Home medical care is becoming a greater matter of concern along with the increasing population of elderly persons. The various difficulties in home care are also found in regional care, and it could be said that in Japan regional care serves as an "advanced model" for home medical care. Ohya Town is located in the mountains of northern Hyogo Prefecture. It has a population of about 5,000 of which 32% is elderly people. There is no railroad, and it takes around 30 minutes to travel to the central hospital from the area. The three town clinics are in contact with each other and with the central hospital concerning medical information. The characteristics of Home Parenteral Nutrition in this underpopulated district are discussed and reported in reference mainly to cases in which the 3 way valved peripherally inserted central venous catheter (Groshong Catheter) is used, in comparison with HPN cases in the city university hospital.

A new aromatase inhibitor, FR901537. II. Pharmacological and antitumor effects.

The pharmacological and antitumor effects of FR901537, a new aromatase inhibitor, isolated from Bacillus sp. No. 3072, were studied. Treatment for four consecutive days with FR901537 inhibited the androstenedione-induced increase in the uterus weight in immature rats. FR901537 had no effect on the uterus, adrenal glands, ovary or pituitary weights in mature rats following 14 days of treatment. The antitumor activity of FR901537 on 7,12-dimethylbenz(a)anthracene-induced mammary tumors was studied in ovariectomized, testosterone propionate (TP)-treated rats as a postmenopausal tumor model. Ovariectomy caused the regression of the mammary tumors and the growth of tumors was remarkably stimulated following TP treatment. Further, in the rats treated with FR901537 and TP, the TP-induced tumor growth was significantly inhibited by FR901537. These results suggest that FR901537 is a promising drug in the treatment of estrogen-dependent mammary tumors in postmenopausal women.