In vitro response of a human colon tumor xenograft and a lung adenocarcinoma cell line to alpha-difluoromethylornithine alone and in combination with 5-fluorouracil and doxorubicin

We have investigated effects of alpha-difluoromethylornithine (DFMO), both as a single agent and in combination with 5-fluorouracil (5-FU) against a human colon tumor xenograft (T6) grown as primary tissue culture in serum-free medium and in combination with doxorubicin (DX) against a human lung adenocarcinoma cell line (A549). DFMO showed a dose-dependent growth-inhibitory effect against human colon tumor xenograft and lung adenocarcinoma cells. Growth-inhibitory activity of DFMO against T6 cells was reversed completely when the cells were treated simultaneously with putrescine (PU) (10(-6) M) and DFMO (10(-3) M). When 5-FU and DFMO were used in combination against T6 cells, no antagonism or synergism between the two drugs was seen. However, in the case of A549 cells, when DFMO was used in combination with DX, there was a consistent increase in growth inhibition that surpassed the inhibition of either agent given alone.     

Inhibition of ornithine decarboxylase with 2-difluoromethylornithine: reduced incidence of dimethylhydrazine-induced colon tumors in mice

2-Difluoromethylornithine (DFMO) was administered to 1,2-dimethylhydrazine (DMH)-treated mice to reduce colonic polyamine levels and mucosal hyperplasia. Mice received 1% DFMO in drinking water throughout the experiment and were given injections of DMH (20 mg/kg) weekly for 28 weeks. DFMO inactivated 93% of colonic ornithine decarboxylase activity. Although DMH treatment did not induce colonic ornithine decarboxylase activity by Week 28, the putrescine content was increased 31% in DMH-treated mice (p less than 0.01). Concurrent treatment with DFMO depressed putrescine content (42 to 63%) and spermidine content (27 to 38%), but it increased spermine content (18 to 22%). At Week 28 of treatment with DMH alone, RNA content was increased 8.6% (p less than 0.01), DNA content 10% (p less than 0.01), DNA specific activity 24% (p less than 0.01), and crypt depth 20% (p less than 0.01), but not in mice receiving DMH and DFMO. At 28 weeks, 13 of 17 mice (76%) treated with DMH alone had histologically confirmed colon cancers; of mice treated with DMH and DFMO, two of 18 (11%) had colonic tumors. Throughout the experiment, 50 colon cancers developed in 16 DMH-treated mice (mean, 3.12 tumors/mouse); three mice treated with DMH and DFMO developed three colon cancers total (p less than 0.001). Reduction of colonic polyamine levels after DFMO treatment prevents proliferative changes induced by DMH and reduces the incidence of tumors.     

Effects of DL-alpha-difluoromethylornithine on the growth and metastasis of B16 melanoma in vivo

The effects of DL-alpha-difluoromethylornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase, on the growth of experimental mouse B16-F10 melanoma cells were investigated. DFMO (3%) in drinking water was administered to B16-F10 melanoma-bearing mice. At 24 days, B16-F10 melanomas in DFMO-fed mice weighed 75% less than those in control mice (p less than 0.001). DFMO reduced putrescine and spermidine levels in B16-F10 melanoma by 98% and 84%, respectively, and prolonged the mean survival time from 25.9 +/- 1.2 to 35.7 +/- 2.2 days (p less than 0.001). The effects of DFMO on experimental metastasis were also investigated. DFMO treatment resulted in a significant decrease in pulmonary metastasis induced by i.v. injection of B16-F10 melanoma cells.     

多胺生物合成抑制剂DFMO抗裸鼠移植人大肠癌的实验研究

A human colon cancer cell line Hce-8693 was heterotransplanted in nude mice. polyamine biosynthesis inhibitor alpha-difluoromethylornithine (DFMO) showed a marked reproducible inhibition in this model. The size and weight of transplanted tumor in DFMO group were smaller than those of the control group and the average inhibition rate was 72.8% (P less than 0.001). DFMO showed higher tumor inhibitory rate than 5-Fu (35.4%) (P less than 0.001). Furthermore, DFMO demonstrated less severe bone marrow inhibition in the nude mice than 5-Fu (20.0% vs 53.2%, P less than 0.001). There was no synergistic action in these two drugs at the experimental doses. The concentration of putrescine and spermidine in the serum and tumor tissue in the DFMO group were 70% lower than those of the control group (P less than 0.001). These results indicate that the anti-tumor effect of DFMO might be explained by the inhibition of polyamine biosynthesis and this study provides an experimental basis for future clinical application of DFMO.     

Effects of alpha-difluoromethylornithine on the growth of experimental Wilms' tumor and renal adenocarcinoma

Because polyamines are essential for cellular growth and differentiation, and because human renal carcinomas have spermidine levels that are higher than those in normal renal tissue, effects of 2-difluoromethylornithine (DFMO) on the growth of experimental renal tumors were investigated. DFMO is a specific enzyme-activated irreversible inhibitor of ornithine decarboxylase, the rate-limiting enzyme controlling polyamine biosynthesis. DFMO (2%) in drinking water was administered to BALB/c mice with intrarenal transplants of a renal adenocarcinoma cell suspension and to Wistar/Furth rats with s.c. transplants of a Wilms' tumor. At 28 days, renal carcinomas in DFMO-fed mice weighed 72% less than those in control animals (p less than 0.001). Wilms' tumor weight was not affected by DFMO feeding. DFMO caused 72 to 75% inactivation of ornithine decarboxylase activity and reduced putrescine levels in renal carcinoma and Wilms' tumor, reduced spermidine levels in Wilms' tumor, and apparently raised spermine levels in the latter as a consequence. DNA content was not affected by DFMO feeding. The mean number of lung metastases in DFMO-fed, renal carcinoma-bearing mice was 0.1 and in controls was 1.4 (p less than 0.001). DFMO feeding increased survival of mice bearing renal carcinomas by 3.0 +/- 0.8 (S.E.) days (p less than 0.05), i.e., from 30.5 +/- 0.8 days to 33.5 +/- 1.2 days. DFMO did not affect the growth of Wilms' tumor; however, in renal adenocarcinoma, it reduced growth, prevented lung metastases, and increased survival.     

INHIBITORY EFFECT OF DEMO ON THE GROWTH OF TRANSPLANTED HUMAN COLON CANCER IN NUDE MICE

A human colon cancer cell line Hce- 8693 was heterotransplanted in nude mice. Polyamine blosythesis Inhibitor a- dlfiuoromethylomithine (DFMO ) show a marked reproducible inhibition in this model. The size and weight of transplanted tumor In DFMO group were smaller than those of the control group and the average inhibition rate was 72.8% (P < 0.001) . DFMO showed higher tumor inhibitory rate than 5-Fu (35. 4%) (P<0. 001) . Furthermore. DFMO demonstrated less severe bone marrow inhibition in the nude mice than 5-Fu (20. 0% Vs 53. 2%. P<0. 001) .There was no synergistic action in these two drugs at the experimental dose. The concentration of putrescine and spermidine in the plasma and tumor tissue in the DFMO group were 70% lower than those of the control group (P<0. 001) . These results indicate that the anti-tumor effect of DFMO might be explained by the inhibition of polyamine biosynthesis and this study provides an experimental basis for future clinical application of DFMO.     

Transferrin binding to two human colon carcinoma cell lines: characterization and effect of 60-Hz electromagnetic fields

125I-Labeled human transferrin was used to study the binding of transferrin to Colo 320 DM and Colo 205 human cell lines derived from adenocarcinomas of the colon. Although transferrin uptake was greater in both cases at 37 degrees than at 4 degrees it was found that slightly greater than two-thirds of the transferrin associated with the cells at 37 degrees was not bound to surface receptors but rather had been internalized by the cells. Subsequent analysis of true surface binding at 4 degrees by Scatchard analysis allowed determination of the number of transferrin receptors as well as association constants for the interaction. The number of transferrin receptors per cell was found to be inversely related to the cell density of the cultures from which cells were removed for study. Association constants were unaffected by cell density, with average values of 1.2 and 5.4 X 10(8) M-1 obtained for Colo 320 DM and Colo 205, respectively. Additionally, maximum theoretical numbers of receptors of 1.05 X 10(5)/cell for Colo 320 DM and 1.39 X 10(5)/cell for Colo 205 were determined. Furthermore, exposure of Colo 205 cells to three different experimental situations, i.e., 60 Hz-generated electric field only (E+, 300 mA/m2rms), magnetic field only (M+, 1.0 gauss rms), and combined electric + magnetic fields at these intensities (E+M+), altered the expression of transferrin receptors as compared to a concurrently run unexposed control population of cells (E-M-). In three separate experiments the number of transferrin receptors quantitated on both M+ and E+M+ cells was independent of cell culture density and was close to or exceeded the maximum theoretical number of receptors determined for this cell line. In contrast, E+ cells expressed fewer transferrin receptors than was predicted on the basis of cell culture density.     

in vivo effects of 4-amidinoindan-l-one 2′-amidinohydrazone (CGP 48664A) and α-difluoromethylornithine (DFMO) on L1210 growth,cell-cycle phase distribution and polyamine contents

We studied the in vivo effects of 4-amidinoindan-l-one 2′-amidinohydrazone (CGP 48664A), α-difluoromethylornithine (DFMO) and a combination of CGP 48664A-DFMO on tumor growth, cell-cycle phase distribution and polyamine contents. DBA-2 mice were inoculated i.p. with 10⁵ L1210 cells on day 0, treated i.p. on days 1–4 and killed on day 5. As compared to controls, CGP 48664A, DFMO and the CGP 48664A-DFMO combination reduced L1210 cell numbers by 33, 43 and 85%, respectively. CGP 48664A did not affect cell-cycle phase distribution. DFMO and the CGP 48664A-DFMO combination caused a moderate and a heavy accumulation in G₀/G₁- and G₂/M-phases, respectively. Compared with controls, the CGP 48664A-DFMO combination reduced putrescine, spermidine and total polyamines, but did not affect spermine. Compared with CGP 48664A, the CGP 48664A-DFMO combination caused lower putrescine and total polyamines, higher spermine, but no change in spermidine. Compared with DFMO, the CGP 48664A-DFMO combination caused higher putrescine and spermidine, lower spermine, but no change in total polyamine levels. We conclude that CGP 48664A potentiates the cystostatic effect of DFMO in vivo. The resulting growth inhibition is accompanied by an accumulation in G₀/G₁- and G₂/M-phases and a reduction of putrescine and spermidine. The data suggest that perturbed polyamine composition rather than reduced spermidine or total polyamine pool size causes a profound growth inhibition. © 1995 Wiley-Liss, Inc.     

Alterations in polyamine metabolism during continuous intravenous infusion of alpha-difluoromethylornithine showing correlation of thrombocytopenia with alpha-difluoromethylornithine plasma levels

Polyamine biosynthesis is important for cell proliferation and growth. The purpose of this study was to determine the biochemical and pharmacological parameters associated with host toxicity from a continuous infusion of alpha-difluoromethylornithine (DFMO). Twenty-five patients with metastatic carcinoma of the colon or rectum received continuous infusion of DFMO at a median dose of 8 g/m2/day (range, 6-14) for 28 days. DFMO plasma levels, RBC, plasma putrescine, spermidine, and spermine levels, and patient toxicities were evaluated. There was a significant decrease in RBC and plasma levels of putrescine, spermidine, and spermine following DFMO administration compared with the baseline RBC and plasma levels. Pearson correlation coefficient comparing nadir platelet count and steady-state DFMO level was statistically significant (n = 37; P less than 0.01; r = -0.53). Sustained suppression of circulating polyamine levels was also achieved with continuous DFMO infusion. The correlation between steady-state plasma DFMO levels and lowering of platelet count warrants prospective evaluation to determine its clinical usefulness.     

The antitumor effect of a novel differentiation inducer, 2, 2-Bis (4-(4-amino-3-hydroxyphenoxy) phenyl) adamantane (DPA), in combinatory therapy on human colon cancer

An adamantane derivative, 2, 2-Bis (4-(4-amino-3-hydroxyphenoxy) phenyl) adamantane (DPA), was found to inhibit the growth of several cancer cell lines in the National Cancer Institute (NCI) Anticancer Drug Screen system. Our previous study showed that DPA inhibited the growth of human colon cancer cell Colo 205 xenografts. DPA-treated cells were arrested at G(0)/G(1), and the DPA-induced cell growth inhibition was irreversible after removal of DPA. Moreover, no acute toxicity was observed after an intra-peritoneal challenge of DPA in nude mice weekly. In this study, we examined the in vivo therapeutic potential of DPA combined with clinical chemotherapeutic agent CPT-11 in Colo 205 cell xenografts. The in vitro cytostatic and differentiative effects of DPA on human colon cancer cells was also evaluated. DPA exerted growth inhibitory activities in vitro against three human colon cancer cell lines (Colo 205, HT-29, and HCT-15). DPA-treated cells showed a more adhesive epithelial phenotype. The differentiation markers of carcinoembryonic antigen (CEA) and fibronectin (FN) were significantly increased in colon cancer cells after treatment with DPA. Further studies showed the induction of p21/Cip1, p27/Kip1, E-cadherin and dephosphorylated p120ctn expression was involved in DPA-induced anticancer effects. Interestingly, DPA-induced elevation of p21/Cip1 was independent of the induction of p53 in Colo 205 cells. in vivo results demonstrated that DPA enhanced the in vivo anticancer activity of the chemotherapeutic agent, CPT-11, by elevation of p53-independent p21/Cip1 and p27/Kip1 expression. Our results suggest that DPA appears to be a new potentially less toxic modality of cancer combinatory therapy.     

Reduced cytocidal efficacy for adriamycin in cultured human carcinoma cells depleted of polyamines by difluoromethylornithine treatment

We have studied the effect of pretreatment with difluoromethylornithine (DFMO), an ornithine decarboxylase inhibitor, on the cytocidal responses of four human adenocarcinoma cell lines to Adriamycin (ADR). The cell lines utilized included HuTu-80 (duodenum), HT-29 (colon), ME-180 (cervix), and A-427 (lung). A 48-h DFMO pretreatment reduced putrescine and spermidine content to less than 10 and less than 1% of control levels and decreased spermine to between 70 and 30% of controls. Plating efficiency assays were used to generate ADR dose-response survival curves for DFMO-treated and control cultures. The DFMO pretreatment significantly protected human adenocarcinoma cells from the lethal effects of ADR. Addition of exogenous putrescine to the DFMO-treated cultures 24 h before treatment with ADR restored their cytocidal response to ADR to near control levels. Putrescine had no effect on cell survival in cultures that were not pretreated with DFMO. These observations suggest that DFMO-induced protection from ADR may be a specific consequence of DFMO-induced inhibition of polyamine biosynthesis. Alternatively, since ADR efficacy varies directly with cellular growth rates and DFMO inhibits proliferation, the protection may have resulted from DFMO-induced growth inhibition. Comparison of ADR uptake in DFMO-pretreated and control cells showed that the protection did not result from decreased intracellular accumulation of ADR.     

Docosahexaenoic acid enhances the susceptibility of human colorectal cancer cells to 5-fluorouracil

Purpose Powerful growth-inhibitory action has been shown for n-3 polyunsaturated fatty acids against colon cancer cells. We have previously described their ability to inhibit proliferation of colon epithelial cells in patients at high risk of colon cancer. In the work reported here we investigated the ability of docosahexaenoic acid (DHA) to potentiate the antineoplastic activity of 5-fluorouracil (5-FU) in p53-wildtype (LS-174 and Colo 320) and p53-mutant (HT-29 and Colo 205) human colon cancer cells.Methods When in combination with DHA, 5-FU was used at concentrations ranging from 0.1 to 1.0 M, much lower than those currently found in plasma patients after infusion of this drug. Similarly, the DHA concentrations (10 M) used in combination with 5-FU were lower than those widely used in vitro and known to cause peroxidative effects in vivo.Results Whereas the cells showed different sensitivity to the growth-inhibitory action of 5-FU, DHA reduced cell growth independently of p53 cellular status. DHA synergized with 5-FU in reducing colon cancer cell growth. The potentiating effect of DHA was attributable to the enhancement of the proapoptotic effect of 5-FU. DHA markedly increased the inhibitory effect of 5-FU on the expression of the antiapoptotic proteins BCL-2 and BCL-X_L, and induced overexpression of c-MYC which has recently been shown to drive apoptosis and, when overexpressed, to sensitize cancer cells to the action of proapoptotic agents, including 5-FU.Conclusion Our results indicate that DHA strongly increases the antineoplastic effects of low concentrations of 5-FU. Overall, the results suggest that combinations of low doses of the two compounds could represent a chemotherapeutic approach with low toxicity.     

Effects of alpha-difluoromethylornithine and methylglyoxal bis(guanylhydrazone) on the growth of experimental renal adenocarcinoma in mice

alpha-Difluoromethylornithine (DFMO) and methylglyoxal bis-(guanylhydrazone) (MGBG) were tested against a murine renal adenocarcinoma, because polyamines are necessary for neoplastic cell growth and because human renal adenocarcinomas contain higher levels of spermidine than do normal renal cells; MGBG inhibits spermidine synthesis and has some activity against human renal tumors; DFMO irreversibly inhibits ornithine decarboxylase, the first rate-limiting enzyme controlling polyamine biosynthesis; and DFMO promotes intracellular accumulation of MGBG in experimental tumor models and human leukemia. DFMO (2%) in drinking water, MGBG (15 mg/kg i.p.), or a combination of DFMO and MGBG was administered daily to BALB/c mice (n = 80) with intrarenal transplants of renal adenocarcinoma cells. At 28 days, renal carcinomas weighed 64 and 73% less, respectively, in DFMO- and DFMO-MGBG-treated mice than in control animals (p less than 0.01). MGBG alone had no antigrowth effect. DFMO-MGBG reduced the total metastatic index (total number of metastases/total number of animals) to 1.2 versus 3.6 in control animals (p less than 0.01) and increased survival by 12.3 +/- 1.5 (S.E.) days, from 30.8 to 42.5 days (p less than 0.05). Compared with control, DFMO-, or MGBG-treated animals, DFMO-MGBG exposure reduced tumor growth and the number of metastases, prevented metastases in some animals (47%), and increased survival of mice bearing renal adenocarcinomas. DFMO also appeared to selectively increase the uptake of [14C]MGBG by tumor tissue, which may help to explain the enhanced synergistic antigrowth effect of DFMO and MGBG against this murine renal adenocarcinoma.     

Polyamines as mediators of estrogen action on the growth of experimental breast cancer in rats

The role of polyamines as mediators of the mitogenic effect of 17 beta-estradiol (E2) was investigated in the N-nitrosomethylurea [(NMU) CAS: 684-93-5; N-methyl-N-nitrosourea]-induced Sprague-Dawley rat mammary tumor grown in the soft agar clonogenic assay under serum-free medium conditions. Inhibition of polyamine biosynthesis with alpha-difluoromethylornithine (DFMO) (1 mM), an irreversible inhibitor of ornithine decarboxylase, completely blocked the growth-promoting effect of E2 (10(-8) M) in this system. Exogenous administration of putrescine (2.5 mM), spermidine (0.1 mM), and spermine (0.1 mM) reversed the inhibitory effect of DFMO and completely restored the action of E2. These polyamines, however, had no effect on tumor growth when they were added alone in identical concentrations. The results indicate that polyamines are essential but probably not sufficient in mediating the E2 effect on the growth of the NMU-induced mammary tumor under these experimental conditions.     

Methylthiopropylamine, a potent inhibitor of spermidine synthase and its antiproliferative effect on human lymphoid leukemia Molt 4B cells

The catalytic activity of spermidine synthase isolated from rat ventral prostate was significantly inhibited by methylthiopropylamine (MTPA). Spermine synthase was almost insensitive to this inhibitor. Inhibition of spermidine synthase by MTPA was competitive with respect to a substrate putrescine (Ki, 3.3 = 10(-7) M), but not competitive with another substrate decarboxylated S-adenosylmethionine (dec AdoMet). MTPA inhibited the growth of human lymphoid leukemia Molt 4B cells. The spermidine content in the inhibitor-treated cells was dose-dependently depressed, whereas the putrescine content was increased concomitantly. In these spermidine depleted and growth retarded Molt 4B cells, the synthesis of protein, but not of DNA or RNA, was found to be significantly diminished.     

Estradiol control of ornithine decarboxylase mRNA,enzyme activity,and polyamine levels in MCF-7 breast cancer cells: therapeutic implications

Previous studies have shown that natural polyamines - putrescine, spermidine, and spermine - play a key role in the mechanism of action of estrogens in breast cancer. Ornithine decarboxylase (ODC) is the first enzyme of the polyamine biosynthetic pathway. To examine estrogenic regulation of polyamine biosynthesis in breast cancer, we measured ODC mRNA, ODC activity, and polyamine levels in G₁ synchronized MCF-7 cells. ODC mRNA and activity increased four-fold over that of cells in G₁ phase between 8 to 16 h after the addition of estradiol. Polyamine levels showed a sharp increase by 8 h after the addition of estradiol and decreased by 12 h. We further examined whether synthetic homologs of putrescine or spermidine could replace natural polyamines in supporting MCF-7 cell growth. Treatment of MCF-7 cells with 1 mM difluoromethylornithine (DFMO), an inhibitor of ODC, suppressed putrescine, spermidine, and spermine levels by 74, 78, and 10%, respectively, within 48 h. Cells treated with DFMO for 48 h were supplemented with either putrescine or its homologs or spermidine or its homologs. Diaminopropane, diaminobutane (putrescine), and diaminopentane were capable of fully or partially reversing the growth inhibitory effects of DFMO, whereas diaminoethane had no significant effect. Among a series of triamines, H₂N(CH₂)_nNH(CH₂)₃NH₂ (where n = 2 to 8; abbreviated as APn n = 4 for spermidine, or AP4), spermidine was most effective in reversing the effects of DFMO, whereas compounds with shorter or longer methylene bridging regions were less effective. AP8 was ineffective in reversing the growth inhibitory effects of DFMO. At 10 µM concentration, AP8 also inhibited DNA synthesis by 66%, as measured by [³H]-thymidine incorporation. These data show that MCF-7 cells have a strong requirement for polyamines for their growth and that estradiol stimulates the polyamine cascade by inducing the ODC mRNA level. Our results also suggest that polyamine homologs such as AP8 might be potentially useful in breast cancer therapy.     

Antitumor effects of two polyamine antimetabolites combined with mitomycin C on human stomach cancer cells xenotransplanted into nude mice

The antitumor effects of alpha-difluoromethylornithine (DFMO), methylglyoxal-bis-guanylhydrazone (MGBG) and mitomycin C (MMC), administered separately or in various combinations, on human stomach cancer cells xenotransplanted into BALB/c nude mice were studied using the protocol of Battelle's Columbus Laboratories (Ovejera et al., 1978). DFMO (1,000 mg/kg in 2 divided doses) and MGBG (50 mg/kg) were given intraperitoneally (i.p.) for 7 consecutive days from the time when the tumor weighed about 100 mg. MMC (2 mg/kg) was given i.p. every other day from the same time. Animals treated with either DFMO or MGBG alone displayed tumor growth comparable to that seen in untreated controls. In mice treated with DFMO plus MGBG with or without MMC, or in mice treated only with MMC, tumor growth was significantly lower than in untreated mice. In the group which received only combined DFMO/MGBG there was a rapid regrowth of the tumor after termination of therapy. Tumor putrescine levels decreased within 4 days following the administration of DFMO; however, spermidine levels did not decline with either DFMO or MGBG treatment even after 7 days. When combined DFMO/MGBG was given, there was a significant decline in spermidine levels 7 days after the initiation of treatment. In contrast, when MMC alone was administered, putrescine and spermidine levels in the tumor did not differ from those in control mice. Spermine decreased markedly in tumor with the combined administration of DFMO/MGBG as well as with combined DFMO/MGBG/MMC, but decreased only slightly when MMC alone or MMC plus either DFMO or MGBG was administered. By the 7th treatment day, DNA biosynthesis in the tumor had dropped markedly in all groups except those receiving DFMO or MGBG alone.     

Tumor angiogenesis and polyamines: alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, inhibits B16 melanoma-induced angiogenesis in ovo and the proliferation of vascular endothelial cells in vitro.

alpha-Difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, inhibited B16 melanoma-induced angiogenesis in chick embryo chorioallantoic membrane and subsequently the growth of the tumor on the chorioallantoic membrane. These inhibitions were reversed by exogenous putrescine and spermidine. DFMO also inhibited rapid neovascularization in yolk sac membrane of 4-day-old chick embryos and the inhibition was reversed by exogenous putrescine and spermidine. DFMO strongly inhibited DNA synthesis and proliferation of bovine pulmonary artery endothelial (BPAE) cells in culture and decreased their ornithine decarboxylase activity and intracellular polyamine concentrations. Addition of putrescine to the culture medium of DFMO-treated BPAE cells restored their intracellular putrescine and spermidine concentrations and their DNA synthesis and proliferation. Addition of spermidine to cultures of DFMO-treated BPAE cells restored their intracellular spermidine concentration and their DNA synthesis and proliferation. DFMO inhibited the proliferation of B16 melanoma cells in culture but the inhibitory effect was much less than that on BPAE cells. When one-half the monolayer of confluent cultures of BPAE cells had been peeled off, addition of DFMO to the cultures inhibited the proliferation and extension of the BPAE cells into the vacant area but had no effect on stationary cells in the remaining half of the monolayer, suggesting that it inhibited induction of proliferation of endothelial cells. These findings suggest that the antitumor activity of DFMO against solid tumors is probably due more to its inhibition of tumor-induced angiogenesis by inhibition of proliferation of endothelial cells induced by polyamine depletion than to a direct effect on tumor cell proliferation.     

Antitumor effect of 2'-deoxy-5-fluorouridine conjugates against a murine thymoma and colon carcinoma xenografts.

The conjugation of antineoplastic drugs to monoclonal antibodies reactive with tumor associated antigens conveys selective cytotoxicity, overcoming the systemic toxicities caused by drugs during standard chemotherapy. 2'-Deoxy-5-fluorouridine, a more potent derivative of 5-fluorouracil, is an antimetabolite which exerts its cytotoxic action by inhibiting the enzyme thymidylate synthetase and as a result inhibits DNA synthesis. 2'-Deoxy-5-fluorouridine was successfully conjugated to anti-Ly-2.1 reactive with the murine thymoma ITT(1)75NS E3, I-1, and 250-30.6 reactive with human colon cancer cells using the active ester of 2'-deoxy-5-fluoro-3'-O-succinoyluridine (5FdUrdsucc). In vitro, 5Fd-Urdsucc-anti-Ly-2.1 was selectively cytotoxic against ITT(1)75NS E3 murine thymoma cells at nanomolar concentrations. The human colon carcinoma cell LIM1899 was inhibited by 5FdUrdsucc-I-1 conjugates in the range of 10(-7)-10(-8) M, as were Colo 205 cells by 5FdUrdsucc-250-30.6 conjugates. In vivo, 5FdUrdsucc conjugates were more effective than equivalent amounts of free 5FdUrdsucc. Against the ITT(1)75NS E3 murine thymoma, a single dose of 100 micrograms (5FdUrdsucc equivalents) 5FdUrdsucc-anti-Ly-2.1 resulted in 85% tumor inhibition compared to mean tumor size of control mice. Irrelevant 5FdUrdsucc conjugates failed to inhibit tumor growth. Multiple doses of 5FdUrdsucc-I-1 conjugate produced 50% growth inhibition of the moderately differentiated tumor LIM1899. In contrast, the human colon carcinoma Colo 205 was relatively resistant to free 5FdUrdsucc and 5FdUrdsucc-250-30.6 conjugates.     

Phospho-sulindac (OXT-328) combined with difluoromethylornithine prevents colon cancer in mice

The nonsteroidal anti-inflammatory drug (NSAID) sulindac and the ornithine decarboxylase (ODC) antagonist difluoromethylornithine (DFMO), individually and together, are effective inhibitors of colon carcinogenesis. However, chronic use of sulindac is associated with significant side effects. We evaluated the chemopreventive efficacy of phospho-sulindac (P-S, OXT-328), an apparently safe derivative of sulindac, together with DFMO, in HT-29 human colon cancer xenografts. Nude mice were divided into four groups as follows: group 1 received vehicle (corn oil); group 2 received P-S (100 mg/kg/d) by oral gavage; group 3 received DFMO (2% in drinking water); and group 4 received P-S (100 mg/kg/d) by gavage plus DFMO (2% in drinking water; P-S/DFMO). Eighteen days after implantation, compared with controls, tumor volume was inhibited 65.9% by P-S, 52.9% by DFMO, and 70.9% by P-S/DFMO (P < 0.01 for all). P-S/DFMO reduced cell proliferation 27.1% and increased apoptosis 38.9% compared with controls (P < 0.05 for both). Compared with controls, P-S reduced the levels of thioredoxin-1 (Trx-1) and thioredoxin reductase (TrxR), whereas DFMO reduced polyamine content (putrescine and spermidine) and TrxR levels. Importantly, P-S/DFMO decreased putrescine and spermidine levels and the expression of Trx-1, TrxR, and cyclooxygenase (COX) 2. Of these molecular targets, TrxR most consistently correlated with tumor growth. Study results show that P-S/DFMO is an efficacious drug combination for colon cancer prevention and also show the safety of P-S, which may overcome the limiting side effects of conventional sulindac. P-S/DFMO has an intricate mechanism of action extending beyond polyamines and including the thioredoxin system, an emerging regulator of chemoprevention. P-S/DFMO merits further evaluation.