Metabolomic Analysis of Microcystis aeruginosa After Exposure to the Algicide L-Lysine

The widespread occurrence of cyanobacteria blooms damages the water ecosystem and threatens the safety of potable water and human health. Exogenous L-lysine significantly inhibits the growth of a dominant cyanobacteria Microcystis aeruginosa in freshwater. However, the molecular mechanism of how lysine inhibits the growth of M. aeruginosa is unclear. In this study, both non-target and target metabolomic analysis were performed to investigate the effects of algicide L-lysine. The results showed that 8 mg L^- 1 lysine most likely disrupts the metabolism of amino acids, especially the arginine and proline metabolism. According to targeted amino acid metabolomics analysis, only 3 amino acids (L-arginine, ornithine, and citrulline), which belong to the ornithine-ammonia cycle (OAC) in arginine metabolic pathway, showed elevated levels. The intracellular concentrations of ornithine, citrulline, and arginine increased by 115%, 124%, and 19.4%, respectively. These results indicate that L-lysine may affect arginine metabolism and OAC to inhibit the growth of M. aeruginosa.

Impairment of brain redox homeostasis caused by the major metabolites accumulating in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome in vivo

Ornithine, ammonia and homocitrulline are the major metabolites accumulating in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome, a genetic disorder characterized by neurological regression whose pathogenesis is still not understood. The present work investigated the in vivo effects of intracerebroventricular administration of ornithine and homocitrulline in the presence or absence of hyperammonemia induced by intraperitoneal urease treatment on a large spectrum of oxidative stress parameters in cerebral cortex from young rats in order to better understand the role of these metabolites on brain damage. Ornithine increased thiobarbituric acid-reactive substances (TBA-RS) levels and carbonyl formation and decreased total antioxidant status (TAS) levels. We also observed that the combination of hyperammonemia with ornithine resulted in significant decreases of sulfhydryl levels, reduced glutathione (GSH) concentrations and the activities of catalase (CAT) and glutathione peroxidase (GPx), highlighting a synergistic effect of ornithine and ammonia. Furthermore, homocitrulline caused increases of TBA-RS values and carbonyl formation, as well as decreases of GSH concentrations and GPx activity. Hcit with hyperammonemia (urease treatment) decreased TAS and CAT activity. We also showed that urease treatment per se was able to enhance TBA-RS levels. Finally, nitric oxide production was not altered by Orn and Hcit alone or in combination with hyperammonemia. Our data indicate that the major metabolites accumulating in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome provoke lipid and protein oxidative damage and a reduction of the antioxidant defenses in the brain. Therefore, it is presumed that oxidative stress may represent a relevant pathomechanism involved in the brain damage found in patients affected by this disease.

Chronic postnatal ornithine administration to rats provokes learning deficit in the open field task

Hyperornithinemia is the biochemical hallmark of hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, an inherited metabolic disease clinically characterized by mental retardation whose pathogenesis is still poorly known. In the present work, we produced a chemical animal model of hyperornithinemia induced by a subcutaneous injection of saline-buffered Orn (2-5 μmol/g body weight) to rats. High brain Orn concentrations were achieved, indicating that Orn is permeable to the blood brain barrier. We then investigated the effect of early chronic postnatal administration of Orn on physical development and on the performance of adult rats in the open field, the Morris water maze and in the step down inhibitory avoidance tasks. Chronic Orn treatment had no effect on the appearance of coat, eye opening or upper incisor eruption, nor on the free-fall righting reflex and on the adult rat performance in the Morris water maze and in the inhibitory avoidance tasks, suggesting that physical development, aversive and spatial localization were not changed by Orn. However, Orn-treated rats did not habituate to the open field apparatus, implying a deficit of learning/memory. Motor activity was the same for Orn- and saline- injected animals. We also verified that Orn subcutaneous injections provoked lipid peroxidation in the brain, as determined by a significant increase of thiobarbituric acid-reactive substances levels. Our results indicate that chronic early postnatal hyperornithinemia may impair the central nervous system, causing minor disabilities which result in specific learning deficiencies.

Polyamines upregulate the mRNA expression of cationic amino acid transporter-1 in human retinal pigment epithelial cells

We previously showed that ornithine was mainly transported via cationic amino acid transporter (CAT)-1 in human retinal pigment epithelial (RPE) cell line, human telomerase RT (hTERT)-RPE, and that CAT-1 was involved in ornithine cytotoxicity in ornithine-δ-aminotransferase (OAT)-deficient cell produced by a OAT specific inhibitor, 5-fluoromethylornithine (5-FMO). We showed here that CAT-1 mRNA expression was increased by ornithne in OAT-deficient RPE cells, which was reversed by an inhibitor of ornithine decarboxylase (ODC), α-difluoromethylornithine (DFMO). Polyamines, especially spermine, one of the metabolites of ODC, also enhanced the expression of CAT-1 mRNA. ODC mRNA expression was also increased by ornithine and polyamines, and gene silencing of ODC by siRNA decreased ornithine transport activity and its cytotoxicity. In addition, the mRNA of nuclear protein c-myc was also increased in 5-FMO- and ornithine-treated hTERT-RPE cells, and gene silencing of c-myc prevented the induction of CAT-1 and ODC. Increases in expression of CAT-1, ODC, and c-myc, and the inhibition of these stimulated expression by DFMO were also observed in primary porcine RPE cells. These results suggest that spermine plays an important role in stimulation of mRNA expression of CAT-1, which is a crucial role in ornithine cytotoxicity in OAT-deficient hTERT-RPE cells.

Ornithine transport via cationic amino acid transporter-1 is involved in ornithine cytotoxicity in retinal pigment epithelial cells

PURPOSE

A prior report showed ornithine cytotoxicity in ornithine-delta-aminotransferase (OAT)-deficient human retinal pigment epithelial (RPE) cells in an in vitro model of gyrate atrophy of the choroid and retina. This study was intended to clarify the mechanism of ornithine cytotoxicity and to determine the responsible amino acid transporters.

METHODS

The mRNA expression of amino acid transporters in human telomerase reverse transcriptase (hTERT)-RPE cells was examined by reverse transcription polymerase chain reaction (RT-PCR) and Northern blot analysis. Carrier-mediated ornithine transport via the L-type amino acid transporter (LAT)1, LAT2, cationic amino acid transporter (CAT)-1, and y(+)LAT2 systems was evaluated by short interfering (si)RNA-mediated gene silencing. The cytoprotective effect of CAT-1-specific siRNA on ornithine cytotoxicity was measured using quantitative analysis of cellular adenosine triphosphate (ATP) at 24 hours after treatment with ornithine in OAT-deficient RPE cells.

RESULTS

LAT1, LAT2, CAT-1, and y(+)LAT2 mRNA expression was detected by Northern blot analysis, whereas RT-PCR revealed that LAT1, LAT2, y(+)LAT1, y(+)LAT2, CAT-1, and b(0,+)AT mRNAs were expressed together with the heterodimeric glycoproteins 4F2hc and rBAT in hTERT-RPE cells. l-[(14)C]ornithine uptake in hTERT-RPE cells was decreased by 46.6% and 22.0% by CAT-1 and y(+)LAT2 siRNA, respectively, whereas LAT1 and LAT2 siRNA had no significant effect. Further, CAT-1 silencing by siRNA reduced ornithine cytotoxicity in OAT-deficient RPE cells.

CONCLUSIONS

The results suggest that ornithine transport via CAT-1 may play a crucial role in ornithine cytotoxicity in hTERT-RPE cells. Reduction of the ornithine transport via CAT-1 may be a new target for treatment of gyrate atrophy.

Cytotoxic Effect of Spermine on Retinal Pigment Epithelial Cells

PURPOSE

A prior study showed inactivation of ornithine-delta-aminotransferase (OAT)-deficient human retinal pigment epithelial (RPE) cells by a specific irreversible inhibitor (5-fluoromethylornithine; 5-FMO) leading to cell death, in an in vitro model of gyrate atrophy (GA) of the choroid and retina. In the present study, the cytotoxicity of metabolites of ornithine, especially spermine, in RPE cells was investigated, to clarify the mechanism of ornithine cytotoxicity in RPE cells.

METHODS

RPE cells were incubated with ornithine or compounds involved in ornithine metabolic pathways. The effects on RPE cell viability and proliferative activity were evaluated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric and [(3)H]thymidine incorporation assays. Incorporation of spermine into RPE cells was examined by using [(14)C]spermine and dansyl-spermine. To assess spermine-induced RPE cell death, cells were double stained with annexin V and propidium iodide and subjected to flow cytometry.

RESULTS

Ornithine, arginine, glutamate, proline, creatine, glycine, and putrescine exhibited no effects on the viability and proliferative activities of RPE cells, whereas spermidine and spermine (10 mM) inhibited [(3)H]thymidine incorporation by 13% and 89%, respectively. The inhibition of [(3)H]thymidine incorporation by spermine was dose dependent and was observed as early as 4 hours after addition. Further, spermine was incorporated and accumulated in the perinuclear region of RPE cells. Apoptotic RPE cell death was induced by spermine in a dose-dependent manner.

CONCLUSIONS

The present results demonstrated that excessive spermine is cytotoxic to RPE cells and suggest that metabolites of ornithine, especially spermine, may be involved in the mechanism of RPE degeneration in GA.

Effects of L-Ornithine on Metabolic Processes of the Urea Cycle in Human Keratinocytes

The complex metabolic function of L-ornithine has led to a great interest in studying its pharmacotherapeutic potential. L-Ornithine is known to be crucial for the metabolism of keratinocytes, especially in the synthesis of urea, polyamines and precursors of collagen synthesis. In this study, we investigated in vitro the cytotoxicity of L-ornithine, and its influence on urea synthesis and arginase expression in primary human keratinocytes. L-Ornithine (> or =1 mM) induced a decrease in the de novo urea synthesis of keratinocytes and an increase (> or =10 mM) in the expression of the urea-generating enzyme arginase. Up to 20 mM, L-ornithine showed no cytotoxic potential, whereas higher concentrations induced apoptosis in keratinocytes in a concentration- and time-dependent manner.

Prevention of Ornithine Cytotoxicity by Nonpolar Side Chain Amino Acids in Retinal Pigment Epithelial Cells

PURPOSE

To investigate the effect of amino acids on ornithine cytotoxicity in ornithine-delta-aminotransferase (OAT)-deficient human retinal pigment epithelial (RPE) cells as an in vitro model of gyrate atrophy (GA) of the choroid and retina.

METHODS

RPE cells were treated with 0.5 mM 5-fluoromethylornithine (5-FMOrn), a specific and irreversible OAT inhibitor. OAT-deficient RPE cells were incubated with 10 mM ornithine in the presence of 20 mM of 1 of 18 amino acids or 10 mM 2-amino-2-norbornane-carboxylic acid (BCH), a conventional inhibitor of the amino acid transporter system L. Ornithine cytotoxicity and cytoprotective effects of each amino acid was evaluated with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay 72 hours after treatment with ornithine in OAT-deficient RPE cells. Ornithine incorporation into RPE cells was evaluated using DL-[14C]ornithine.

RESULTS

An MTT colorimetric assay revealed that small and large zwitterionic amino acids, but not acidic or basic amino acids, decreased ornithine cytotoxicity in OAT-deficient RPE cells. Incorporation of DL-[14C]ornithine by RPE cells decreased to 79% of the control level after incubation for 48 hours with 20 mM leucine, the most effective cytoprotective amino acid. Further, BCH prevented ornithine cytotoxicity in a dose-dependent manner. Both light and heavy chains of L-type amino acid transporter (LAT)-1, LAT2, y+LAT1, and 4F2hc were expressed in RPE cells.

CONCLUSIONS

The present results demonstrate that L-type amino acid transporter(s) may be involved in protection against ornithine cytotoxicity in human RPE cells. Thus, amino acid transportation in RPE cells may be a good target for a new therapy for GA as well as other kinds of chorioretinal degeneration.

Prevention of ornithine cytotoxicity by proline in human retinal pigment epithelial cells

PURPOSE

To investigate the relationship between ornithine-delta-aminotransferase (OAT) deficiency and ornithine accumulation and the specific degeneration of retinal pigment epithelial (RPE) cells in gyrate atrophy.

METHODS

Human RPE cells, human hepatoma cells, and human fibroblast cells were treated with 5-fluoromethylornithine (5-FMOrn), a specific irreversible inhibitor of OAT. Ornithine cytotoxicity was determined by using a [3H]thymidine incorporation assay and immunohistochemical staining for cytokeratin. The effects of various metabolites of ornithine and arginine, such as creatine, creatine phosphate, I-delta 1-pyrroline-5-carboxylic acid (L-P5C), and proline, which may be deficient in gyrate atrophy on RPE cell damage by ornithine, were determined by the same procedures.

RESULTS

When the human RPE cells, HepG2 hepatoma cells, and WI-38 fibroblast cells were treated with 0.5 mM 5-FMOrn for 30 minutes, which inactivated OAT, ornithine exhibited severe time- and dose-dependent inhibition of DNA synthesis in the human RPE cells but not in the HepG2 hepatoma cells or WI-38 fibroblast cells. The inhibition of DNA synthesis was accompanied by drastic changes in morphologic appearance, disorganization of the cytoskeleton, and cell death. Ornithine or 5-FMOrn alone did not exhibit such cytotoxicity to the RPE cells. Proline prevented the cytotoxicity of ornithine.

CONCLUSIONS

These findings suggest that an elevated level of ornithine combined with an increased sensitivity to ornithine as a result of OAT deficiency may be crucial to the specific RPE degeneration in gyrate atrophy. They suggest also that abnormalities of proline metabolism may be involved in the progress of gyrate atrophy.

Apoptosis of photoreceptor cells in ornithine-induced retinopathy

BACKGROUND

The intravitreal injection of ornithine produces selective damage to the retinal pigment epithelium (RPE) and results in a loss of RPE, choriocapillaris and photoreceptor cells. To elucidate the mechanism of secondary retinal atrophy, we investigated the presence of apoptotic cells in a rat model of ornithine-induced retinopathy.

METHODS

At 6 and 12 h and 1, 2, 4, 7, 14 and 28 days after an intravitreal injection of L-ornithine hydrochloride in rat eyes, we removed the eyes and subjected them to histopathological examination. We detected apoptotic cells by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate digoxigenin nick end labeling (TUNEL) assay, which stains the 3'-OH ends of fragmented DNA. We used electron microscopy to detect the apoptotic cells morphologically.

RESULTS

RPE cells were selectively damaged immediately after ornithine administration. TUNEL-positive photoreceptor cells appeared exclusively in the photoreceptor cell layer 12 h after ornithine administration. The number of TUNEL-positive cells increased throughout the 2 days following the injection, then decreased markedly. TUNEL-positive cells remained until 28 days, when the photoreceptor cells had disappeared. The ganglion cell layer, inner nuclear layer and damaged RPE cells were negative for TUNEL staining during all stages. The electron microscopic study also revealed the pyknotic nuclei of apoptotic photoreceptor cells.

CONCLUSION

An intravitreal injection of ornithine caused primary damage to the RPE, and subsequently some of the photoreceptor cells revealed apoptosis by TUNEL assay. These findings suggest the dysfunction of the RPE causes photoreceptor cell death according to the intrinsic program of an apoptotic mechanism.

Effects of NO synthase inhibitors, arginine-deficient diet, and amiloride in pregnant rats

This study tests the hypothesis that nitric oxide synthase (NOS) inhibition is linked to NG-nitro-L-arginine methyl ester (L-NAME)-mediated intrauterine growth retardation (IUGR) and fetal limb reduction deficits (LRD) in pregnant dams. Administration of L-NAME (1 mg/ml) or aminoguanidine (AG, 500 micrograms/ml) in the drinking water or intraperitoneal administration of L-N5-(1-iminoethyl)-ornithine (L-NIO, 10 mg.kg-1.day-1) on gestational days 13-20 decreased nitrite and nitrate plus nitrate (RNI) levels in the urine and plasma and decreased RNI in incubates of aorta and fetal limbs compared with pregnant rats given amiloride (50 micrograms/ml) or water (control). Although all drugs caused fetal IUGR, only L-NAME and amiloride caused fetal deaths and LRD. Urine and tissue levels of RNI were unchanged in rats fed and arginine-free diet (AFD) on gestational days 13-20, and yet fetal IUGR, deaths, and LRD were prevalent. L-NAME potentiated the fetal abnormalities and resorptions. Plasma arginine concentrations decreased with AFD > > L-NAME > L-NIO. Plasma ornithine, a precursor for polyamine synthesis, decreased with AFD and increased with L-NAME. Thus inhibition of NOS is not linked to LRD. The ability of L-NAME and amiloride to produce fetal IUGR and LRD may result from L-NAME-mediated modulation of amino acid delivery to the fetus and amiloride-mediated inhibition of protein synthesis. Finally, IUGR appears unrelated to LRD.

[Ornithine induced retinopathy in rat--2. Process of disappearance of choriocapillaris]

We observed the process of disappearance of the choriocapillaris after loss of the retinal pigment epithelium (RPE) induced by intravitreal injection or ornithine. Three hours after administration of ornithine, the RPE cells swelled remarkably in the posterior pole, but, the endothelial cells of the choriocapillaris remained intact. At 3 days, the RPE cells became necrotic, but the choriocapillaris still preserved its in normal appearance. At 7 days, RPE disappeared completely in the posterior pole and the choriocapillaris displayed evidence of atrophy; the swollen lumen of the choriocapillaris became narrow the cytoplasm of the endothelium was swollen, and the number of fenestrae was reduced. On the other hand, these changes were not seen where the RPE remained. At 14 days, in the posterior pole, the lumen of the choriocapillaris occluded by the swollen endothelial cells. At 28 days, the choriocapillaris completely disappeared and the large choroidal vessel was directly in contact with Bruch's membrane. These results showed that the RPE is correlated with the presence of the choriocapillaris.

Hypothermic response of mice to ornithine-containing lipids and to endotoxin

The hypothermic response of mice to ornithine-containing lipids (Orn-Ls) of the form alpha-N-(3-acyloxyacyl)-ornithine and to endotoxin (Escherichia coli 0111:B4 lipopolysaccharide [LPS]) was studied. After the administration of Orn-L or LPS to C3H/HeSlc mice, body temperature decreases were determined at 30-min intervals by inserting a thermistor into the rectum of each mouse. When Orn-L (750 microg) or LPS (70 microg) was injected into the mice, body temperature decreases of 0.8 and 2.0 degrees C, respectively, occurred 1.8 to 2.0 h later. These body temperature decreases were completely suppressed by the preadministration of indomethacin. When anti-tumor necrosis factor alpha (TNF-alpha) antibody was administered before the administration of Orn-L or LPS, only the body temperature decrease by LPS was suppressed. The body temperature decrease by Orn-L was suppressed by anti-interleukin-1beta (IL-1beta) antibody preadministration. Next, in order to study IL-1beta and TNF-alpha mRNA expression in macrophages, peritoneal macrophages were collected 40 min after the administration of Orn-L or LPS to mice. The expression of IL-1beta mRNA by stimulation with Orn-L was as strong as that by stimulation with LPS, but the expression of TNF-alpha mRNA by stimulation with Orn-L was very weak. Our previous studies of in vitro macrophage activation by Orn-L proved that strong induction of IL-1 and prostaglandin E2 generation by Orn-L occurred (Y. Kawai and K. Akagawa, Infect. Immun. 57:2086-2091, 1989). From these experiments, the weak body temperature decrease in mice caused by Orn-L was found to be mediated by cytokines different from those which mediate the strong body temperature decrease caused by LPS. Namely, it was caused by prostaglandin E2 being mediated by IL-1 but not by TNF-alpha.

Nitric oxide synthase inhibitors. Preclinical studies of potential use for treatment of opioid withdrawal

Four inhibitors of nitric oxide synthase (NOS), administered as acute pretreatments, attenuated several signs of naloxone-precipitated opioid withdrawal in morphine-dependent rats. Profiles of these drugs for inhibiting the expression of withdrawal were similar to that of clonidine, a drug used clinically to treat opioid withdrawal. The nonselective NOS inhibitors, NG-nitro-L-arginine and NG-nitro-L-arginine methyl ester, and N(5)-(1-iminoethyl)-L-ornithine, a selective inhibitor of endothelial NOS, Increased blood pressure in awake, morphine-naive and morphine-dependent rats not undergoing withdrawal. 7-Nitroindazole, a selective inhibitor of neuronal NOS, did not elevate blood pressure. Insofar as hypertension is a component of opioid withdrawal in humans, the ability of 7-nitroindazole to attenuate morphine withdrawal in rats without eliciting a vasopressor response suggests that 7-nitroindazole may have human therapeutic potential. Research directions for the continued development of 7-nitroindazole as a therapeutic modality are discussed with respect to issues of physical dependence, tolerance, and safety.

Antifolates can potentiate topoisomerase II inhibitors in vitro and in vivo

Antifolates have been shown to increase the DNA strand breaks produced by the topoisomerase inhibitor etoposide. PT523 is a potent new antifolate that cannot be polyglutamated. Human SCC-25 squamous carcinoma cells were exposed to methotrexate, trimetrexate or PT523 at a concentration of 5 microM for 24 h along with various concentrations of etoposide or novobiocin during the final 2 h. Isobologram analysis of the treatment combinations indicated that exposure of the cells to PT523/etoposide, methotrexate/etoposide, PT523/novobiocin, methotrexate/novobiocin and trimetrexate/novobiocin resulted in greater than additive cytotoxicity. DNA alkaline elution studies with the same drug combinations indicated that there were three- to four-fold increases in the radiation equivalent (rad equivalent) strand breaks in the cellular DNA with etoposide or novobiocin along with the antifolate compared with the topoisomerase II inhibitors alone. Tumor growth delay studies were carried out in the murine SCC VII squamous carcinoma. PT523 (0.5 mg/kg) and methotrexate (2 mg/kg) were administered by 7-day continuous infusion while trimetrexate (3.75 mg/kg) was administered intraperitoneally daily on days 7-9. Etoposide (10 mg/kg) and novobiocin (100 mg/kg) were administered intraperitoneally on alternate days (7, 9, 11). The combinations of PT523 with etoposide or novobiocin were significantly more effective than methotrexate and etoposide or novobiocin, producing tumor growth delays of 8.4 days and 6.9 days, respectively. Overall, the antifolate/topoisomerase II inhibitor treatment combinations produced tumor growth delays that were apparently additive to greater than additive.

Some biochemical and pathophysiological aspects of long-term elevation of brain ornithine concentrations

Mice and chicken were given 5-fluoromethylornithine (5FMOrn), a selective inactivator of ornithine aminotransferase (OAT) over extended periods of time. This treatment allowed us to maintain elevated concentrations of ornithine in all tissues. Since gyrate atrophy, an autosomal recessive human disease, is characterized by the absence of OAT, special emphasis was put on the study of the visual system. Ophthalmoscopic and histologic examinations of the eye as well as electroretinograms and locomotor behaviour demonstrated an unimpaired visual system and brain. No toxic effects were observable in the treated mice. Likewise, chick embryo development was normal in spite of highly elevated brain and tissue ornithine concentrations. A likely explanation for the absence of toxic effects of 5FMOrn treatment, disregarding the non-toxicity of ornithine, is the fact that 10-20% of tissue OAT is refractory to inactivation by 5FMOrn. This residual activity may be sufficient to maintain vital functions.

[Changes in the intermediate stage of retinal degeneration after intravitreal injection of ornithine]

We reported previously that intravitreal injection of a small amount of 1-ornithine hydrochloride in monkey eyes damages the retinal pigment epithelium (RPE), selectively. At one year after administration, sharply demarcated chorioretinal atrophy was seen. This paper describes the intermediate stage of retinal degeneration caused by ornithine. Two weeks following intravitreal injection of ornithine, RPE cells at the equator became necrotic and disappeared. However RPE regenerated to cover Bruch's membrane at the border of RPE degenerated area. In 2 months at an area where RPE cells disappeared, the photoreceptors and choriocapillaris degenerated to disappear. However, in the area in where RPE regenerated, they maintained their structure. This report demonstrated that damage of RPE resulted in disappearance of the photoreceptor and choriocapillaris.

Protection of mice from lethal endotoxemia by use of an ornithine-containing lipid or a serine-containing lipid

The effects of an ornithine-containing lipid [alpha-N-(3-acyloxyacyl)-ornithine (Orn-L)] or a serine-containing lipid [alpha-N-(3-acyloxyacyl)-serine (Ser-L)] from Flavobacterium meningosepticum on lethal endotoxemia in mice were examined. When 500 micrograms of Orn-L was intravenously administered 1 h before intravenous administration of a lethal dose of endotoxin, none of the mice died. The protective effect of Ser-L was weaker than that of Orn-L. Light and electron microscopic studies demonstrated that necrosis of hepatocytes caused by endotoxin was prevented by pretreatment with Orn-L. Furthermore, Kupffer cells were activated morphologically 1 h after the administration of Orn-L or Ser-L, and the liposomes of the lipoamino acids were incorporated into phagolysosomes in activated Kupffer cells. The activity of tumor necrosis factor in sera of endotoxin-treated mice was decreased markedly by pretreatment of mice with Orn-L. In vitro, the lipoamino acids suppressed endotoxin-induced tumor necrosis factor generation but did not suppress tumor necrosis factor generation induced by zymosan and whole cells of Staphylococcus aureus. These results suggested that Orn-L and Ser-L can be used as specific blocking agents against endotoxin. The blocking mechanism may be antagonistic, because of the structural similarities between the lipoamino acids and endotoxin lipid A.

Polyamines and regulation of ornithine biosynthesis in Escherichia coli

The growth rate of several polyamine-deficient mutants of Escherichia coli was very low in minimal medium and increased markedly upon the addition of putrescine, spermidine, arginine, citrulline, or argininosuccinic acid. The endogenous content of polyamines was not significantly altered by the supplementation of polyamine-starved cultures with arginine or its precursors. In contrast, these compounds as well as putrescine or spermidine caused a 40-fold reduction in intracellular ornithine levels when added to polyamine-depleted bacteria. In vivo experiments with radioactive glutamic acid as a precursor and in vitro assays of the related enzymes showed that the decrease in ornithine levels was due to the inhibition of its biosynthesis rather than to an increase in its conversion to citrulline or delta 1-pyrroline-5-carboxylic acid and proline. High endogenous concentrations of ornithine were toxic for the E. coli strains tested. The described results indicate that the stimulatory effect of putrescine and spermidine on the growth of certain polyamine-starved bacteria may be partially due to the control of ornithine biosynthesis by polyamines.

Red blood cell polyamine levels and host toxicity during continuous alpha-difluoromethylornithine infusion

The dose effects of continuous alpha-difluoromethylornithine (DFMO) infusion on red blood cell (RBC) polyamine levels, host toxicity and tumor growth were determined. Male rats with and without a transplantable methylcholanthrene-induced sarcoma received intravenously either 0.45% NaCl or DFMO at 500 mg, 1,000 mg, or 2,000 mg/kg body wt/day for 6 or 12 days. Dose-related inhibition of tumor growth was noted after the 12-day treatment. There were no changes in host carcass weight, food intake, plasma albumin, hematocrit or white blood cell counts. Platelet suppression was associated with the 1,000- and 2,000-mg doses with the 12-day treatment. Morphometry of the small intestine revealed mild but significant shortening of villi in the duodenum and jejunum at the 2,000-mg dose, but none of the animals developed diarrhea. The 500-mg DFMO dose reduced the rate of tumor growth without inducing platelet suppression or altering intestinal morphology. A decrease in RBC putrescine levels was noted at all doses. RBC spermidine levels increased with the 500-mg dose. RBC spermine levels were higher at all doses compared with controls. These results suggest that thrombocytopenia is the major dose-limiting side-effect of continuous DFMO infusion but does not occur at a dose of 500 mg/kg body wt/day.

Inhibition of ornithine decarboxylase alters neurological responsiveness to a tremorigen

Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC; 200-800 mg/kg, s.c.), to rats has no detectable behavioral effects using a battery of tests to assess sensorimotor function. In contrast, the induction of tremor by chlordecone, a neurotoxic agent that affects neuronal ionic processes, is significantly attenuated by pretreatment with DFMO. The effects of DFMO on chlordecone-induced tremor were reversed by pretreatment with putrescine. DFMO had no effects on p,p'-DDT, a tremorigen having a mechanism of action different from chlordecone. These findings imply that polyamines may play a role in select neuronal processes.

Long-term maintenance therapy of established human small cell variant lung carcinoma implants in athymic mice with a cyclic regimen of difluoromethylornithine

We report that cyclic p.o. administration of alpha-difluoromethylornithine (DFMO), an inhibitor of polyamine biosynthesis, is an effective long-term (1-year) maintenance therapy for established implants of cultured human small cell lung carcinoma in athymic (nude) mice. Human small cell lung carcinoma cells, from a line which exhibited cell death in culture in the presence of DFMO, were inoculated into athymic mice and permitted to grow to palpable tumors (3-5-mm nodules with mean volume of 0.04 cm3). The animals were then randomized into untreated, continuous treatment and cyclic (3 weeks of 4 beginning 1 week after 8 weeks continuous) treatment groups. Treatment consisted of 3% DFMO in the drinking water (5.1 g/kg/day). The tumors in the untreated group grew to 27 cm3 by 8 weeks and the animals had a median survival of 7.6 weeks. Tumor growth was inhibited by 99% (0.3 cm3) in the continuous treatment group in comparison to untreated controls. Survival was prolonged with 93% survival at 10 weeks and a 101% increase in median survival to 15.3 weeks (P less than 0.05). The cyclic DFMO group had a 98.3% inhibition in tumor growth for longer than 1 year (0.56 cm3; P less than 0.05). Survival was also markedly prolonged compared to the untreated group with 100% survival up to 24 weeks and a median survival of 54.3 weeks (P less than 0.05). No significant toxicities were observed in the first 10 weeks of DFMO treatment even though antitumor effects were observed. With continuous DFMO treatment, the animals eventually became debilitated and developed marked weight loss and thrombocytopenia; by 20 weeks, mortality was 79%. With cyclic therapy, the animals resumed weight gain, recovered from thrombocytopenia and, at 20 weeks, had 0% mortality. By 55 weeks, mortality was 50% which, however, was not significantly different (P approximately 0.50) from mortality of a control group of nontumorous, athymic mice that had weekly body weight and skin fold measurements concurrently with the experimental, tumor-bearing animals. Thus, the observed mortality is ascribable to continuous encroachment on the normally sterile environment. These data suggest a role for DFMO in long-term therapy of sensitive human tumors such as small cell lung carcinoma, especially in patients with a low tumor burden. Furthermore, a cyclic regimen might be an important tool in maintaining clinical remissions induced by conventional combination chemotherapy.

The in vitro interaction of alpha-difluoromethyl ornithine (DFMO) and several interferons on human cell lines

The antiproliferative effects of six different human interferons were examined on two human cell lines--HM7 (human melanoma cell line) and MDA-MB-231 (human breast carcinoma cell line). A dose-response curve was developed for each interferon in which the maximum dose applied gave at least 30% growth inhibition of control values after 96-128 h of continuous exposure. An amount of alpha-difluoromethyl ornithine (DFMO) which caused 25% growth inhibition (0.01 mM for HM7 and 0.1 mM for MDA) was added to the cultures with various doses of each interferon. The inhibitory effects of DFMO and each interferon were additive at low concentrations. In no case was a synergistic effect observed. Unlike in the murine B-16 melanoma model, we could not show a synergistic inhibitory effect between DFMO and any of the six different interferons on two human epithelial tumor cell lines.

Effect of concentration of D,L-2-difluoromethylornithine on murine mammary carcinogenesis

The appearance of chemically induced mammary gland carcinomas in virgin female Sprague-Dawley rats was blocked by the administration of D,L-2-difluoromethylornithine (DFMO) in drinking water during the stage of tumor promotion. Rats were given injections s.c. at 50 days of age with either 35 mg of 1-methyl-1-nitrosourea (MNU) per kg of body weight or the 0.9% NaCl solution in which the carcinogen was dissolved. At 57 days of age, the rats were each randomly allocated to one of 14 treatment groups. Ten groups (five solvent treated and five MNU treated) were assigned to treatments consisting of 0.00, 0.0625, 0.125, 0.25, or 0.50% (w/v) solution of DFMO in their drinking water; two MNU-treated groups were placed on or removed from DFMO treatment (0.5%; w/v) at 90 days post-carcinogen exposure; and two carcinogen-treated groups received either putrescine (0.5-g/kg diet) or putrescine and DFMO (0.5%; w/v) throughout the experiment. The study was terminated 183 days after carcinogen treatment. All doses of DFMO exerted a protective effect against the induction of mammary cancer; however, only the feeding of the 0.125% and the 0.5% solutions of DFMO resulted in a significant reduction in cancer incidence. The average number of cancers per rat was reduced, and cancer-free time was extended at all concentrations of DFMO. The protective effect of DFMO was sustained following withdrawal of treatment at 90 days post-MNU injection. Feeding putrescine in conjunction with DFMO treatment partially blocked the inhibitory activity of DFMO. DFMO treatment did not affect food or water intake; body weight gain; the weight of ovaries, uterus, adrenal glands, liver, kidney, or spleen; or the periodicity of the estrous cycle. These data provide evidence of an inhibitory effect of DFMO against mammary cancer induced by MNU which cannot be attributed to a systemic toxic effect of this compound.

Convulsive syndrome induced by the intracerebroventricular injection of alpha-difluoromethylornithine in rats

In adult rats, the intracerebroventricular injection of alpha-difluoromethylornithine (DFMO), a polyamine antimetabolite which specifically inhibits ornithine-decarboxylase, induces a typical convulsive syndrome (ED50 = 100 micrograms/rat) and death (LD50 = 300 micrograms/rat). Histological lesions are seen only with the highest doses and are essentially restricted to the Ammon's horn neurones. Since DFMO is currently undergoing clinical trials for use in cancer chemotherapy, including brain tumours, its CNS toxicity should be carefully considered.

Disruption of the blood-brain barrier in hyperammonemic coma and the pharmacologic effects of dexamethasone and difluoromethyl ornithine

Both hyperammonemia and blood-brain barrier (BBB) breakdown have been implicated in the evolution of hepatic encephalopathy. To define a possible relationship, Swiss Albino mice were subjected to sublethal encephalopathic doses of ammonium acetate; the integrity of the BBB was determined grossly with Evans blue and quantitatively with [14C]-alpha-aminoisobutyrate (AIB). Some animals were injected with a dose of ammonium acetate sufficient to maintain coma for 1 hr (AC group). One group, termed stuporous (AS), received only enough ammonium acetate to interfere with grooming and exploratory activity; this dosage was insufficient to completely block the righting response, which was absent in the AC group. When compared to that of controls (CON) receiving normal saline instead of ammonium acetate, cerebral tissue from the AC group was stained blue and contained nearly double the amount of AIB; AS group brain tissue was unstained and the AIB content did not differ significantly from normal. Some of the AC group were pretreated with drugs known to retard BBB breakdown; one set received dexamethasone (AC-DXMN), another the ornithine decarboxylase inhibitor difluoromethyl ornithine (AC-DFMO), and a third L-ornithine (AC-ORN). Brain tissue from the AC-ORN group stained blue and AIB content did not differ significantly from that of the untreated AC group. Cerebral tissue of the AC-DXMN pretreatment group stained light blue; AIB content was significantly lower than in the AC group and greater than the CON group. The AC-DFMO brains were unstained and AIB content was significantly lower than in the AC group but did not differ significantly from CON. These results indicate that hyperammonemia may induce BBB breakdown but that the disruption of barrier integrity is not antecedent to the development of coma, although it seems to coincide with coma in time.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the irreversible ornithine decarboxylase inhibitor, alpha-difluoromethylornithine, aflatoxin B1, and choline deficiency on hepatocarcinogenesis

Liver carcinogenesis was induced in rats by aflatoxin B1 (AFB1) enhanced by a choline-deficient diet. In Experiment 1, the ornithine decarboxylase inhibitor, alpha-difluoromethylornithine (DFMO), was administered by gavage to one group only during AFB1 administration; another group received DFMO during AFB1 administration and for 2 months after carcinogen administration. These two groups were compared to two control groups, one given AFB1 and fed the choline-deficient diet and another fed the deficient diet only. In a second experiment, DFMO was administered at a concentration of 2% in the water for 3 weeks and then at 1% for the remainder of the study. Rats from each group in Experiment 1 were killed at 2, 8, and 10 months after AFB1 administration and the development of tumors was followed by histology; autoradiography of [3H]thymidine incorporation into DNA; enzyme histochemistry; and alpha-fetoprotein determination. The group given DFMO during AFB1 administration was not significantly different from the AFB1-treated control group at 2 and 8 months after AFB1 administration. However, at 10 months following AFB1 and DFMO administration, the [3H]thymidine-labeling index and glucose-6-phosphatase staining were significantly increased. This group had three animals bearing hepatocellular carcinomas as compared to none in the controls. The group given DFMO for 2 months after AFB1 administration had a significantly depressed growth rate 2 months later, but this difference was not apparent after 8 months. After 10 months, there was a significantly increased [3H] thymidine-labeling index and increased volume fraction of gamma-glutamyltranspeptidase in the AFB1-DFMO-treated group as compared to the controls. DFMO appeared to inhibit growth under some conditions, but if administration was discontinued after AFB1 exposure, it appeared to enhance tumorigenesis. In Experiment 2, where a larger dose of AFB1 was used and DFMO was administered in the water from start to finish of the experiment, DFMO inhibited tumor induction and depressed the appearance of markers examined during carcinogenesis. These data indicate that the regimen used for DFMO administration can markedly affect tumor induction.

Antitumor properties of (2R,5R)-6-heptyne-2,5-diamine, a new potent enzyme-activated irreversible inhibitor of ornithine decarboxylase, in rodents

(2R,5R)-6-Heptyne-2,5-diamine hydrochloride (MDL 72175) is a new, potent, and selective inhibitor of mammalian ornithine decarboxylase. MDL 72175 given p.o. in drinking fluid reduced by 80% the growth of EMT6 sarcoma in mice and of HTC hepatoma in rats. It prolonged the survival of mice bearing L1210 or P388 leukemias and inhibited the development of Lewis lung carcinoma in mice at doses 10- to 20-fold lower than those of alpha-difluoromethylornithine, the most widely used irreversible inhibitor of ornithine decarboxylase. MDL 72175 depleted putrescine and spermidine levels in the tumors to the same extent as did alpha-difluoromethylornithine. In the EMT6 sarcoma, MDL 72175 achieved at low doses a greater maximal antitumor effect than did alpha-difluoromethylornithine. In combination therapy, MDL 72175 plus Adriamycin gave at least additive antitumor effects on solid tumors and experimental leukemias in animals. The combination MDL 72175 plus methylglyoxal bis(guanylhydrazone) also gave additive antitumor effects on P388 leukemia, associated with an increased uptake of methylglyoxal bis(guanylhydrazone); in contrast, antagonistic effects were observed with this combination on EMT6 tumors in mice. Since MDL 72175 did not present toxicity at effective antitumor doses, this new ornithine decarboxylase inhibitor can be considered as a promising antitumor drug.

Inhibition of growth of human or hamster pancreatic cancer cell lines by alpha-difluoromethylornithine alone and combined with cis-diamminedichloroplatinum(II)

A major problem in the therapy of pancreatic adenocarcinoma is its inherent resistance to most chemotherapeutic agents. Previously, we have reported that the four pancreatic cancer cell lines studied here have elevated levels of ornithine decarboxylase, a growth-regulating enzyme, and further that the degree of elevation tends to parallel the degree of chemoresistance. On the basis of these prior findings, we investigated the effects of alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase, alone and in combination with cis-diamminedichloroplatinum(II) (cisplatin), to which two of the four cell lines display relative resistance. The cell lines studied were: two of human origin, PANC-1 and COLO-357; and two of hamster origin, WD PaCa and PD PaCa. Colony formation (clonogenic) assays were used to evaluate drug effects. Cells were exposed continuously to DFMO in medium. For the combined treatments, cells were exposed to cisplatin for 1 hr, washed, and then plated in DFMO-containing medium. The inhibitory effects of DFMO were predominantly cytostatic, were reversible by putrescine, and were roughly additive when combined with cisplatin. Our panel of cell lines responded heterogeneously to DFMO, with PANC-1 and WD PaCa showing the most sensitivity. The combination of DFMO and cisplatin appears to be a promising experimental approach to overcoming drug resistance in pancreatic cancer.

Induction of major chromosome aberrations in Chinese hamster ovary cells by alpha-difluoromethylornithine

DL-alpha-Difluoromethylornithine (DFMO) is a specific irreversible inhibitor of ornithine decarboxylase (EC 4.1.1.17) and has antitumor effects. In this paper, we show that DFMO inhibits the growth of and causes severe chromosomal damage in Chinese hamster ovary cell strain A7 which grows without serum but has deficient arginase activity and therefore requires ornithine or polyamines for continuous replication. In ornithine-containing medium, the A7 cells had very few chromosome aberrations, but incubation of these cells with 0.5 mM DFMO for 7 days induced chromosome aberrations in 12 to 46% of the mitoses. Depletion of polyamines by omitting ornithine from the medium also caused chromosome aberrations. The chromosomal damage found after DFMO treatment alone and ornithine deprivation alone were of similar nature. In addition to chromosome breaks, there were chromosome fragmentation and structurally changed chromosomes including rings, chromatid exchange configurations, and chromosome elongations. A phenomenon resembling premature chromosome condensation was also seen. Double-minute chromosomes were visible in some mitoses, and the chromosome elongations sometimes gave an impression of homogeneously staining regions.

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.

CNS toxicity and CSF pharmacokinetics of intraventricular DFMO and MGBG in beagle dogs

We have developed a beagle dog model to study the pharmacology and toxicology of anticancer drugs administered through the 3rd or lateral ventricles. A Foltz-type reservoir was implanted SC and connected by tube into a cerebral ventricle. Drugs were administered directly into the reservoir; CSF sampling of drugs administered into the ventricle was achieved directly by tapping the reservoir or by percutaneous puncture of the cisterna magna. In the current study, we evaluated the CSF pharmacokinetics and CNS toxicity of two inhibitors of polyamine metabolism, alpha-difluoromethylornitine (DFMO) and methylglyoxal bisguanylhydrazone (MGBG). Both drugs were judged too toxic to justify intrathecal or intraventricular studies with these agents in patients.

Reversal of the growth inhibitory effect of alpha-difluoromethylornithine by putrescine but not by other divalent cations

Treatment with alpha-difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of ornithine decarboxylase (ODC), depletes the putrescine and spermidine content, and reduces the growth rate of Ehrlich ascites tumor cells. The addition of putrescine, which is the immediate precursor of spermidine, promptly replenished the intracellular putrescine and spermidine pools and completely reversed the antiproliferative effect of DFMO. A sequential accumulation of spermine, spermidine and putrescine was observed. 1,3-diaminopropane, a lower homolog of putrescine, did not reverse the antiproliferative effect of DFMO, despite its structural similarity and identical positive charge. By inhibiting remaining ODC activity, resistant to 5 mM DFMO, and possibly by inhibiting spermine synthase activity, 1,3-diaminopropane produced a further decrease in total polyamine content by reducing the spermine content. Mg2+, which can replace putrescine in many in vitro reactions, completely lacked the capacity to reverse the antiproliferative effect of putrescine and spermidine deficiency.

Enhancement of 1,3-bis(2-chloroethyl)-1-nitrosourea-induced cytotoxicity and DNA damage by alpha-difluoromethylornithine in L1210 leukemia cells

Polyamine depletion by pretreatment with alpha-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase, potentiates the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in L1210 leukemia cells grown in a modified soft agar system. The dose enhancement ratio was 1.97 at a control colony formation level of 5%. The basis for this enhancement was investigated at the level of DNA damage using a modified fluorometric assay to quantitate the production of alkaline-labile strand breaks per relative DNA molecular mass. Pretreatment of cultured L1210 cells for 48 hr with 5 mM DFMO depleted intracellular putrescine and spermidine (but not spermine) pools and resulted in a 2.3-fold increase in BCNU-induced (10 micrograms/ml, 2 hr) DNA strand breaks per relative DNA molecular mass. The inclusion of 10 microM spermidine during the DFMO pretreatment fully prevented growth inhibition and enhancement of BCNU-induced DNA damage while maintaining cellular spermidine pools at control levels. The inclusion of 2 microM putrescine or spermidine also prevented growth inhibition and enhancement of DNA damage while maintaining spermidine pools at only 25 to 35% of control. Thus, the portion of spermidine essential for cell growth appears to be associated with DNA. BCNU itself was found to reduce cellular polyamine levels by causing their leakage from cells. In addition, BCNU was found to react directly with spermidine in a cell-free system, resulting in a major reaction product detectable by high-performance liquid chromatography. While decreased interaction of BCNU with polyamines could account, in part, for enhancement effects of DFMO, it is more probable that alterations in DNA structure secondary to polyamine depletion are responsible for these effects.

Effects of alpha-difluoromethylornithine and recombinant interferon-alpha 2 on the growth of a human renal cell adenocarcinoma xenograft in nude mice

The effects of human recombinant interferon-alpha 2 (IFN-alpha 2) and alpha-difluoromethylornithine (DFMO) as single agents and in combination were studied for efficacy against the renal cell adenocarcinoma (JDF-1) in an in vitro clonogenic assay and in vivo as xenografts in nude mice. In vitro studies showed dose-dependent inhibition of JDF-1 colony formation by IFN-alpha 2. DFMO alone did not significantly inhibit colony formation even though ornithine decarboxylase activity was significantly inhibited. The combination of IFN-alpha 2 and DFMO synergistically inhibited JDF-1 colony formation. The synergism was more readily observed at low IFN-alpha 2 concentrations. In vivo studies showed a similar tumor growth inhibition pattern. JDF-1 tumors were implanted s.c. in nude mice, and drugs were administered continuously by Alza minipumps (IFN-alpha 2) and in drinking water (DFMO) for 28 days. IFN-alpha 2 alone significantly inhibited JDF-1 growth, while DFMO alone had no significant inhibitory effect. The combination of IFN-alpha 2 and DFMO inhibited tumor growth in an apparent additive manner at the doses used. This was reflected in the mean tumor weights obtained at the termination of the experiment: control, 1484 +/- 187 (S.E.) mg; DFMO only, 1106 +/- 129 mg; IFN-alpha 2 only, 941 +/- 186 mg; and DFMO plus IFN-alpha 2, 620 +/- 109 mg. Assessment of mouse natural killer cell activity at the time of sacrifice showed that DFMO inhibited natural killer cell activity, while IFN-alpha 2 had no effect. DFMO was observed to inhibit ornithine decarboxylase activity in JDF-1 tumors by 78%, IFN-alpha 2 by 18%, and the combination by 78%. In addition, the drugs individually and in combination had similar inhibitory effects on JDF-1 spermidine content. One of the unexpected findings was the alteration in the spermine:spermidine ratio in the tumors treated with the combination of DFMO and IFN-alpha 2. The ratio in this group decreased to 0.44, while ratios for control, IFN-alpha 2 only, and DFMO only were 0.99, 0.66, and 0.88, respectively. These results clearly show that combined therapy with DFMO and IFN-alpha 2 is more effective than is single-drug therapy. The mechanism by which these drugs coordinately inhibit tumor growth is unclear but appears to be associated with direct inhibition of tumor cell proliferation, possibly by modulation of polyamine metabolism.

Synergistic antiproliferative activity of leukocyte interferon in combination with alpha-difluoromethylornithine against human cells in culture

alpha-Difluoromethylornithine, an enzyme-activated irreversible inhibitor of ornithine decarboxylase, was administered in combination with human leukocyte interferon to human lymphoblastoid (Daudi) cells in culture. True synergistic antiproliferative activity was observed at 72 hr after continuous exposure. This effect was observed regardless of the ratio of interferon to alpha-difluoromethylornithine concentrations. Although the mechanisms by which this effect occurs are unknown, these studies provide a rationale for combination clinical trials of alpha-difluoromethylornithine with leukocyte interferon.

Time dependence of the potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea cytotoxicity caused by alpha-difluoromethylornithine-induced polyamine depletion in 9L rat brain tumor cells

Treatment of 9L rat brain tumor cells with 1.0 mM alpha-difluoromethylornithine (DFMO) produced a time-dependent depletion of cellular putrescine and spermidine. An increase in the potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) cytotoxicity, measured with a colony-forming efficiency assay, followed the time course of polyamine depletion, reaching its maximum at 48 hr, the time at which maximum polyamine depletion was achieved. Treatment with DFMO at concentrations as low as 0.05 mM for 48 hr effectively depleted putrescine and spermidine and potentiated BCNU cytotoxicity. Treatment for 96 hr with 0.01 mM DFMO produced a partial decrease in putrescine and spermidine levels and a moderate potentiation of BCNU cytotoxicity. The amount of polyamine depletion in 9L cells treated with 0.05, 0.1, and 0.5 mM DFMO was identical at both 48 and 96 hr, but potentiation of BCNU cytotoxicity was greater at 96 hr than at 48 hr. When 9L cells were treated for 48 hr with 1 mM DFMO and DFMO was then removed from the cultures, polyamine levels did not reach control levels by 96 hr after change of medium. The potentiation of BCNU cytotoxicity during this 96-hr period correlated with the extent of polyamine depletion. When 100 microM putrescine was added to the culture medium after DFMO pretreatment (1 mM), polyamine levels approached those of control cells by 24 hr, and the amount of potentiation of DFMO cytotoxicity decreased. These results show that potentiation of BCNU cytotoxicity correlates closely with the amount of DFMO-induced polyamine depletion in 9L cells.

Antigrowth effect of polyamine biosynthesis inhibitors on the Dunning R 3327-G prostatic tumor

alpha-Difluoromethylornithine (DFMO) and methylglyoxal-bis-guanylhydrazone (MGBG), when administered simultaneously, inhibited growth and were highly toxic to the Dunning R 3327-G hormone-resistant prostatic adenocarcinoma transplanted into Copenhagen rats. Neither DFMO (2%) nor MGBG at a nontoxic dose (15 mg/kg) inhibited tumor growth, but total (47% early cure rate) or near total suppression of growth of established tumors was observed in rats receiving both treatments.

Decreased cytotoxicity of aziridinylbenzoquinone caused by polyamine depletion in 9L rat brain tumor cells in vitro

The in vitro cytotoxicity of aziridinylbenzoquinone (AZQ) used either alone or after induced intracellular polyamine depletion in 9L rat brain tumor cells was studied using a colony-forming efficiency assay. Used alone, AZQ was cytotoxic to 9L cells; however, depletion of intracellular putrescine and spermidine levels by treatment with 1 mM alpha-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, for 72 hr decreased significantly the cytotoxicity of AZQ. Dose modification factors were 1.9 and 1.8 at 10 and 1% survival levels, respectively. Decreased cytotoxicity could be almost completely prevented by addition of putrescine to polyamine-depleted cells 24 hr before AZQ treatment. Although AZQ alone was cytotoxic against 9L cells, metabolic activation by the S-9 rat liver microsomal fraction increased greatly the observed cytotoxicity. However, even with microsomal activation, pretreatment of cells with 1 mM alpha-difluoromethylornithine for 48 hr produced a significant decrease in AZQ cytotoxicity; dose modification factors were 2.4 and 2.2 at 10 and 1% survival levels, respectively. Addition of putrescine to polyamine-depleted cells 24 hr before AZQ treatment prevented the decrease in cytotoxicity. Pretreatment of 9L cells for 48 hr with 40 microM methylglyoxal bis(guanylhydrazone), a polyamine biosynthesis inhibitor that competitively inhibits S-adenosylmethionine decarboxylase, caused a decrease in the cytotoxicity of AZQ administered without microsomal activation. The dose modification factor was 1.6 at both 10 and 1% survival levels.

Biochemical and ultrastructural characterization of human cell variants resistant to the antiproliferative effects of methylglyoxal bis(guanylhydrazone)

Stable variants of the human cell line, VA2-B, have been developed which are 10- to 20-fold less sensitive to the antiproliferative effects of methylglyoxal bis(guanylhydrazone) (MGBG) than the parent cell lines and which are not drug transport deficient. The lines were characterized biochemically giving particular attention to parameters related to the two known sites of MGBG action, mitochondria and polyamine metabolism. Dose-response studies with MGBG (0 to 30 microM for 40 to 48 hr) revealed that, of the parameters related to polyamine metabolism (i.e., polyamine pools, S-adenosylmethionine, and ornithine decarboxylase activities), only spermine pool size reduction seemed to correlate with inhibition of cell growth by MGBG. By contrast, decreases in pyruvate oxidation (used here as a measure of mitochondrial function) closely paralleled growth inhibition in all cell lines. Similarly, MGBG-induced changes in mitochondrial ultrastructure were less conspicuous in the variants than in the parent cell line and also corresponded with growth inhibition. Respiration of isolated mitochondria from one of the variant lines was about 2-fold more resistant to the inhibitory effects of MGBG than mitochondria from the VA2 cells. Finally, treatment with alpha-difluoromethylornithine, a potent inhibitor of polyamine biosynthesis having no known effect on mitochondrial function, resulted in comparable inhibition of growth in variant and parent cell lines. Overall, the data suggest that a phenotypic alteration in mitochondrial function, rather than in polyamine metabolism, may represent the basis for MGBG resistance in these variant cell lines.

Intestinal changes caused by DL-alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase

Subacute (2 week) oral or intravenous administration of DL-alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), caused diarrhea and frequent emesis as early as 4 to 5 days in dogs (dose greater than or equal to 200 mg/kg/day). Diarrhea also occurred in monkeys after 1 week of treatment with an intravenous dose of 1000 mg/kg/day. Especially evident in the treated dogs with diarrhea were fluid loss, hemoconcentration, and decreased serum sodium and chloride which were findings totally reversible about 2 weeks after cessation of dosing. As a result of treatment with the highest intravenous dosage (1000 mg/kg/day), villous atrophy of the mucosa was observed by light and scanning electron microscopy in the canine small intestine. Transmission electron microscopy demonstrated that the most significant alterations of the canine intestinal tract involved the microvilli of epithelial cells which became shorter and were frequently less numerous or absent along focal areas of the plasma membrane. Intestinal mucosal levels of putrescine, especially in the duodenum and jejunum, were decreased as demonstrated in the monkeys following intravenous treatment with 100, 300, or 1000 mg/kg/day of DFMO. The results of this investigation are consistent with the hypothesis that the inhibition of ODC activity and subsequent altered polyamine metabolism may lead to delayed maturation of the intestinal epithelial cells and the impaired development of their microvilli, causing fluid loss due to reduced absorptive surface area.

Blood brain barrier breakdown in brain edema following cold injury is mediated by microvascular polyamines

A focal freeze injury to rat cerebral cortex induces an early (less than 5 min) increase in brain ornithine decarboxylase activity and an accumulation of polyamines involving cerebral microvessels. This polyamine synthesis correlates with the abnormal increase in microvascular permeability, monitored by uptake of Evans Blue and sod. fluorescein. The ornithine decarboxylase inhibitor alpha-difluoromethylornithine suppressed the injury-induced increment in spermidine and spermine and microvascular permeability. Putrescine nullified alpha-difluoromethylornithine inhibition and restored microvessel spermidine and spermine and the pathological increase in microvascular permeability. These results indicate that polyamine synthesis is obligatory for blood-brain barrier breakdown. alpha-Difluoromethylornithine may be useful in the treatment of vasogenic brain edema.

A mouse lymphoma cell mutant whose major protein product is ornithine decarboxylase

Mutant mouse lymphoma cells that overproduce ornithine decarboxylase have been generated by selection for resistance to difluoromethylornithine, an inhibitor of the enzyme. Starting with wild type S49 mouse lymphoma cells, sensitive to growth inhibition by 10 microM difluoromethylornithine, we obtained the Z.12 line, which is approximately 100 times more resistant to that drug (McConlogue, L., and Coffino, P. (1983) J. Biol. Chem. 258, 8384-8388). Subsequent selection for still higher levels of resistance was applied to the Z.12 cells and resulted in the generation of the D4.1 line, resistant to 10 mM difluoromethylornithine. The relative synthesis of ornithine decarboxylase in wild type, Z.12, and D4.1 cells was assessed by pulse labeling these cells with [35S]methionine and analyzing the radiolabeled proteins directly, or after immunoprecipitation, on sodium dodecyl sulfate-polyacrylamide gels. As shown previously, the rate of ornithine decarboxylase synthesis is augmented in Z.12 as compared to wild type. In D4.1 cells, the rate of synthesis of ornithine decarboxylase exceeds that of any other single protein; about 15% of total protein synthesis is devoted to the enzyme. The relative amounts of translatable ornithine decarboxylase mRNA in each cell line was determined by in vitro translation of extracted RNA. These results showed that the relative rate of synthesis in each cell line is a reflection of the cell's relative content of translatable ornithine decarboxylase mRNA. Examination of the chromosomes of wild type and D4.1 cells revealed that the former are pseudodiploid and the latter tetraploid. Two of the four chromosomes 14 in D4.1 contain large homogeneously staining regions, a finding consistent with the presence of regions of gene amplification.

Chinese hamster ovary cells resistant to alpha-difluoromethylornithine are overproducers of ornithine decarboxylase

The selection of Chinese hamster ovary cells resistant to ornithine analogues has been extended to very high levels of the suicide inhibitor alpha-difluoromethylornithine. Stepwise selections resulted in stepwise increases in the inducible levels of ornithine decarboxylase activity. The enzyme is shown by several criteria to be normal in every respect: regulation in the cell cycle, inhibition by antizyme, absolute specific activity as determined with the help of alpha-[3H]difluoromethylornithine. The enzyme has been highly purified from such overproducing cells. The subunit molecular weight of the mammalian enzyme has been confirmed to be approximately 54,000. The location of the enzyme in two-dimensional polyacrylamide gel electrophoresis was determined, and the protein could be detected on two-dimensional gels with extracts from our best overproducers.

Successful treatment with DL-alpha-difluoromethylornithine in established human small cell variant lung carcinoma implants in athymic mice

We report that p.o. administration of DL-alpha-difluoromethylornithine (DFMO), a specific inhibitor of polyamine biosynthesis, markedly inhibits the growth of established implants of cultured human small cell lung carcinoma (SCC) in athymic (nude) mice. Human SCC tumor cells, from a cell line which exhibited cell death in culture in the presence of DFMO, were inoculated s.c. into athymic mice. The tumors were permitted to grow until they became palpable (0.05 cu cm, 3- to 5-mm-diameter nodules). The animals were then randomized into control, and early (low tumor burden) and late (high tumor burden) treatment groups which received 3% DFMO in the drinking water (5.0 g/kg/day). The tumors in the untreated control group grew to a size of 29 cu cm by 9 weeks, and these animals had a median survival of 9 weeks. The late treatment group began DFMO treatment 3 weeks after clinical tumor engraftment, when mean tumor size was 1.5 cu cm (1.2- to 1.5-cm-diameter nodules). Tumor growth was inhibited by 60% (11.4 cu cm) by Week 9 and survival was prolonged, with 83% survival at 10 weeks and a 56% increase in median survival to 14 weeks (p less than 0.05). The early treatment group received the same dose of DFMO beginning 1 week after tumor engraftment, when their mean tumor size was 0.1 cu cm (4- to 6-mm-diameter nodules). The early DFMO group had a 99% inhibition in tumor growth (0.3 cu cm) (p less than 0.05). Survival was also prolonged compared to the untreated controls, with 83% survival at 10 weeks and a median survival of 15 weeks (p less than 0.05). In both the early- and late-DFMO-treatment groups, no significant clinical toxicities were observed in the first 10 weeks, during which antitumor therapeutic effects were seen. DFMO may have a potential role in the treatment of sensitive human tumors such as SCC. The data suggest that DFMO may be most useful clinically in patients with SCC who have a low tumor burden. Thus, DFMO might be an important tool to produce long-term maintenance of initial clinical remissions induced by combination chemotherapy.

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.

Effects of alpha-difluoromethylornithine and 5-fluorouracil on the proliferation of a human colon adenocarcinoma cell line

Because alpha-difluoromethylornithine (DFMO) reduces the incidence of experimental colon cancers, inhibits the growth of human lung cancer cells and human leukemia cells in culture, and in combination with methylglyoxal (bis)guanylhydrazone induces remission in children with leukemia, its effectiveness against a human colon adenocarcinoma cell line (Colo 205) was tested alone and in combination with 5-fluorouracil (5-FU). Both DFMO (2 X 10(-4) M) and 5-FU (10(-6) M) inhibited Colo 205 cell proliferation. Above 5 X 10(-4) M DFMO (p less than 0.001) and at 10(-4) M 5-FU (p less than 0.001), Colo 205 growth was completely inhibited. Although DFMO did not sensitize Colo 205 cells to a noninhibitory concentration of 5-FU, the effectiveness of inhibitory concentrations of 5-FU and DFMO in reducing Colo 205 cell growth was additive. DFMO (2 X 10(-4) M) caused 89 to 93% inhibition of ornithine decarboxylase activity (p less than 0.001) and reduced levels of putrescine (93%; p less than 0.01) and spermidine (57%; p less than 0.02). Growth rate and the intracellular putrescine and spermidine contents were restored by 10(-6) M putrescine. DFMO could be an effective chemotherapeutic agent against human colonic cancer because of its effects at such unusually low concentrations in vitro.

Effects of alpha-difluoromethylornithine alone and combined with adriamycin or vindesine on L1210 leukemia in mice, EMT6 solid tumors in mice, and solid tumors induced by injection of hepatoma tissue culture cells in rats

The effects of alpha-difluoromethylornithine (DFMO; RMI 71782) in combination with vindesine or Adriamycin were investigated in three different animal tumor models. When given in a concentration of 2% in drinking water to C57BL/6 X DBA/2 F1 mice inoculated i.p. with L1210 leukemia cells, DFMO prolonged the survival time 1,2-fold. Treatment with vindesine (0.1 mg/kg/week i.p. or Adriamycin (2.5 mg/kg/week i.p.) increased the mean survival time 1.4- and 2.3-fold, respectively. DFMO with vindesine doubled survival time, while DFMO with Adriamycin increased it 3.5-fold and yielded 30% long-term survivors. The growth of solid tumors induced in Buffalo rats by i.m. injection of hepatoma tissue culture cells was inhibited 65% after 2 weeks of DFMO treatment. Similar inhibition of growth could be achieved by weekly i.p. injections of vindesine (0.2 mg/kg) or Adriamycin (2.5 mg/kg). When the same doses of these drugs were administered in combination with DFMO, the growth of this hepatoma was completely arrested. Combined treatment of BALB/c mice bearing s.c. solid EMT6 tumors with DFMO and adriamycin or vindesine also resulted in enhanced inhibition of tumor growth compared to single-drug therapy. These results indicate that combination of DFMO with vindesine or Adriamycin is an effective approach to the treatment of several animal cancers.