Tumor suppression with a combination of alpha-difluoromethyl ornithine and interferon

Targeting ornithine decarboxylase reverses the LIN28/Let-7 axis and inhibits glycolytic metabolism in neuroblastoma

LIN28 has emerged as an oncogenic driver in a number of cancers, including neuroblastoma (NB). Overexpression of LIN28 correlates with poor outcome in NB, therefore drugs that impact the LIN28/Let-7 pathway could be beneficial in treating NB patients. The LIN28/Let-7 pathway affects many cellular processes including the regulation of cancer stem cells and glycolytic metabolism. Polyamines, regulated by ornithine decarboxylase (ODC) modulate eIF-5A which is a direct regulator of the LIN28/Let-7 axis. We propose that therapy inhibiting ODC will restore balance to the LIN28/Let-7 axis, suppress glycolytic metabolism, and decrease MYCN protein expression in NB. Difluoromethylornithine (DFMO) is an inhibitor of ODC in clinical trials for children with NB. In vitro experiments using NB cell lines, BE(2)-C, SMS-KCNR, and CHLA90 show that DFMO treatment reduced LIN28B and MYCN protein levels and increased Let-7 miRNA and decreased neurosphere formation. Glycolytic metabolic activity decreased with DFMO treatment in vivo. Additionally, sensitivity to DFMO treatment correlated with LIN28B overexpression (BE(2)-C>SMS-KCNR>CHLA90). This is the first study to demonstrate that DFMO treatment restores balance to the LIN28/Let-7 axis and inhibits glycolytic metabolism and neurosphere formation in NB and that PET scans may be a meaningful imaging tool to evaluate the therapeutic effects of DFMO treatment.

Polyamine-DNA Interactions: Possible Site of New Cancer Chemotherapeutic Intervention

The effects of polyamines on the structure of nucleic acids in cell-free systems and in cell culture systems are reviewed. Evidence suggests that polyamine depletion inhibits cell growth and may cause conformational changes in DNA. These effects may be exploited to cause changes in the action of drugs and may be used to advantage in combination treatment protocols. A discussion of theoretical models of the interactions, physicochemical evidence for conformational changes, and the effects of anticancer drugs in cells depleted of polyamines is presented.

Spermidine-analogous triamines suppressed the growth of Candida albicans

We examined the antifungal activity of various synthetic triamines on several fungi. Among various triamines having a general structure H2N(CH2)aNH(CH2)bNH2 (a=2-5, b=3-8), some triamines (a=4 or 5) showed inhibitory effect on the growth of Candida albicans and C. tropicalis. Determination of the minimum inhibitory concentrations (MICs) of these triamines on C. albicans showed that triamine 4-8 (a=4, b=8) and triamine 5-8 had strong antifungal activity. Further analysis revealed that the antifungal effect of triamine 4-8 was fungistatic and the antifungal effect was diminished by the addition of spermidine, a physiological triamine, to the medium. These results suggested that triamine 4-8 is antagonistic to spermidine and the antifungal activity is due to the suppression of the action of intrinsic polyamines. On the agar medium, C. albicans formed microcolonies even in the presence of triamine 4-8 by long cultivation. We then observed the form of C. albicans using microscope and found that the cells cultivated with triamine 4-8 were round, similar to the yeast form, while most of the cells on the agar medium without triamine 4-8 were hyphal form. Subsequently, we investigated the synergistic effect of two compounds with triamine 4-8, cyclohexylamine and dl-α-difluoromethylornithine which are inhibitors of enzymes involving in the biosynthesis of physiological polyamines such as spermidine. The results showed that the antifungal activity of triamine 4-8 increased by the addition of these enzyme inhibitors.

Revival of 2-(difluoromethyl)ornithine (DFMO), an inhibitor of polyamine biosynthesis, as a cancer chemopreventive agent

ODC (ornithine decarboxylase), a key enzyme of polyamine biosynthesis, is an inducible enzyme exhibiting high activity in tumour cells, suggesting ODC as a target for antineoplastic therapy. Among the inhibitors of polyamine-related enzymes, the ODC inactivator DFMO [2-(difluoromethyl)ornithine] became the most well-known. The drug is usually cytostatic and its effects on growth are reversed by micromolar concentrations of polyamines in the cellular environment. ODC inactivation is associated with decreased transcription of the growth-related c-myc and c-fos genes. DFMO used as a single drug has only minor effects on tumour growth. The low efficacy of the drug is due to the use of exogenous (gastrointestinal) polyamines by the mammalian organism. Although it was disappointing in most therapeutic attempts, DFMO showed potential in cancer chemoprevention based on its ability to lower polyamine levels in colorectal mucosa at low dosages with no demonstrable toxicity over long periods of use. DFMO in combination with other drugs prevents and inhibits the development of a variety of chemically induced cancers in animals with doses far lower than those administered for therapy. Low doses of several NSAIDs (non-steroidal anti-inflammatory drugs) and DFMO administered in combination have been shown to be more effective in inhibiting chemically induced colon tumours in rats than are high doses of these agents given individually. This combination has gained further interest after findings suggesting that ODC polymorphism is a genetic marker for colon cancer risk and supporting the use of DFMO and aspirin or other NSAIDs in combination as a strategy for colon cancer prevention.

Single-injection ornithine decarboxylase-directed antisense therapy using atelocollagen to suppress human cancer growth

BACKGROUND

Substantial evidence supports a direct role of ornithine decarboxylase (ODC) in the development and maintenance of human tumors. Although antisense oligonucleotide therapy targeting various genes are useful for cancer treatment, 1 of the major limitations is the problem of delivery. A novel antisense oligonucleotide delivery method is described that allows prolonged sustainment and release of ODC antisense oligonucleotides in vivo using atelocollagen.

METHODS

The effect of ODC antisense oligonucleotides in the atelocollagen on cell growth of gastrointestinal cancer (MKN 45 and COLO201) and rhabdomyosarcoma (RD) was studied in vitro using a cell-counting method with a hemocytometer. In vivo, the effect of intratumoral, intramuscular, and intraperitoneal single administration of ODC antisense oligonucleotides in the atelocollagen on tumor growth of MKN45, COLO201, and RD cells was studied. ODC activity and polyamine contents were measured.

RESULTS

In vitro, ODC antisense oligonucleotides in the atelocollagen remarkably suppressed MKN45, COLO201, and RD cell growth. A single administration of antisense oligonucleotides in the atelocollagen via 3 routes remarkably suppressed the growth of MKN45, COLO201, and RD tumor over a period of 35-42 days.

CONCLUSIONS

As various human cancers significantly express ODC, the results strongly suggest that this new antisense method may be of considerable value for treatment of human cancers.

Regulation of ornithine decarboxylase during oncogenic transformation: mechanisms and therapeutic potential

The activity of ornithine decarboxylase (ODC(1)), the first enzyme in polyamine biosynthesis, is induced during carcinogenesis by a variety of oncogenic stimuli. Intracellular levels of ODC and the polyamines are tightly controlled during normal cell growth, and regulation occurs at the levels of transcription, translation and protein degradation. Several known proto-oncogenic pathways appear to control ODC transcription and translation, and dysregulation of pathways downstream of ras and myc result in the constitutive elevation of ODC activity that occurs with oncogenesis. Inhibition of ODC activity reverts the transformation of cells in vitro and reduces tumor growth in several animal models, suggesting high levels of ODC are necessary for the maintenance of the transformed phenotype. The ODC irreversible inactivator DFMO has proven to be not only a valuable tool in the study of ODC in cancer, but also shows promise as a chemopreventive and chemotherapeutic agent in certain types of malignancies.

Effects of DFMO on glioma cell proliferation, migration and invasion in vitro

The polyamine inhibitor DL-alpha-difluoromethylornithine (DFMO) is a specific irreversible inhibitor of ornithine decarboxylase which is a rate-limiting enzyme in the polyamine bio-synthesis pathway. The present study describes the effects of DFMO on glioma cell proliferation, migration and invasion using multicellular spheroids from three glioma cell lines (GaMg, U-251 Mg and U-87 Mg). 10 mM DFMO reduced cell migration in the three cell lines by about 30-50%. 1 mM putrescine, added together with DFMO inhibited the DFMO effect. A stronger effect was observed in the growth assay where 10 mM DFMO reduced the spheroid growth, for all cell lines, by 90%. This effect was also reversed by adding 1 mM of putrescine. In vitro tumor cell invasion experiments indicated after 3 days of confrontation, an extensive invasion also after 10 mM DFMO treatment. The brain aggregate volumes were reduced to about the same extent as in the absence of drug, suggesting essentially no effects of DFMO on the invasive process. It is concluded that the tumor spheroids retained their ability to invade normal brain tissue even after DFMO exposure. However, DFMO inhibited spheroid growth and cell migration which supports the notion that cell growth, migration and invasion are biological properties that are not necessarily related to each other.

Influence of indomethacin and difluoromethylornithine on human tumour growth in nude mice

Biopsy material from six human colorectal carcinomas was transplanted to 114 nude mice. A treatment protocol was established which included no treatment (control, C), indomethacin (I), difluoromethylornithine (D) or a combination of both (ID). The influence of the various drugs on tumour weight and protein kinase CK2 activity was monitored. CK2 activity was measured because in all tumours examined so far the enzyme activity was found to be enhanced several-fold when compared to the non-neoplastic tissue of the same patient. More than half of the investigated tumours showed a conspicuous reduction in weight after drug treatment, and I and the combination of D/I were significantly effective using the mixed model analysis. Furthermore, we have tried to discover whether there is a change in the subcellular localisation of protein kinase CK2 subunits associated with drug treatment. We analysed the tumours and the non-neoplastic control tissues by immunohistochemistry using antibodies directed against the CK2 subunits and against the proliferation marker Mib. In addition, we have also investigated the behaviour of the nucleolar protein B23 which has also been shown to be enhanced several-fold in rapidly proliferating tissue and which is also a substrate for CK2. The immunohistochemical data suggest that, irrespective of the drug treatment and the observed reduction in CK2 activity, the CK2 subunits remain localised in the nucleus.

Antiproliferative effects of interferon gamma in combination with alpha-difluoromethylornithine on human carcinoma cell cultures

The antiproliferative effects of human recombinant interferon gamma (IFN gamma) in combination with alpha-difluoromethylornithine (DFMO) or as single agents were assessed on human cell cultures derived from carcinomas of the breast (MCF-7), the ovary (EFO-27) or the kidneys (EGI-4). Results were obtained in proliferation assays by direct cell counting. The cell lines differed considerably in their sensitivities to the antiproliferative effect of IFN gamma as compared by the 50% inhibition doses of the growth (ID50). In contrast to the findings with IFN gamma, similar antiproliferative effects resulted from the application of comparable doses of DFMO. While IFN gamma induced cytotoxic effects in EGI-4 cells, DFMO produced only cytostatic actions in the cell lines analyzed. Synergistic growth inhibition resulted from the combined application of IFN gamma and DFMO in EFO-27 cell cultures. This finding was most pronounced after treatment with IFN gamma or DFMO doses below the respective ID50 values. However, antagonistic effects occurred in cells of the line EGI-4 after DFMO had been combined with IFN gamma at concentrations below the cytotoxic dose range. Within the sensitivity of our proliferation assay, no synergistic interactions were found in MCF-7 cell cultures. In the cell lines tested, no relation between the sensitivity for the single agents and the effectivity of the drug combination was identified. Despite promising synergistic effects in the moderately IFN gamma-sensitive ovarian carcinoma cell line EFO-27, the efficacy of the IFN gamma/DFMO combination was restrained by possible antagonistic effects as demonstrated in the highly IFN gamma-sensitive EGI-4 renal carcinoma cell cultures. We conclude that the differential interaction patterns in the cell cultures analyzed preclude general suggestions for clinical studies using IFN gamma and DFMO.

Phase I study of combined alpha interferon, alpha difluoromethylornithine (DFMO), and doxorubicin in advanced malignancy

Interferon (IFN) and conventional cytotoxic chemotherapeutic agents have been successfully combined in various studies. Alpha difluoromethylornithine (DFMO) is a novel antitumor agent which is an inhibitor of polyamine metabolism. A phase I study of IFN 24 x 10(6) U/m2/day IM (days 3-7), DFMO 9 gm/m2 p.o. daily (days 1-7), and a variable dose of doxorubicin starting at 20 mg/m2 (day 6), of each 28 day cycle was performed. The aim of the study was to determine the maximally tolerable dose of doxorubicin in this combination. Three patients were treated with doxorubicin at 20 mg/m2 and six patients at 40 mg/m2. The dose limiting toxicities were neutropenia, fatigue and fever. All other toxicities were mild and there was no grade IV toxicity. A doxorubicin dose of 40 mg/m2 produced tolerable toxicity and is recommended for phase II studies. No major antitumor effects were seen.

Synergistic antiproliferative activity of human fibroblast interferon in combination with alpha-difluoromethylornithine against human gastric cancer cells in vitro

The author has studied the effects of alpha-difluoromethylornithine (alpha DFMO), an enzyme-activated irreversible inhibitor of ornithine decarboxylase; human fibroblast interferon (IFN beta); and their combination on human gastric cancer cell growth in vitro. alpha DFMO (from 0.1 to 4 mmol/l) inhibited cell growth in a dose-dependent manner. Both alpha DFMO (0.1 mmol/l) and higher doses of IFN beta (100 and 1000 IU/ml) caused only limited inhibition of cell growth. When alpha DFMO (0.1 mmol/l) was administered in combination with IFN beta (100 and 1000 IU/ml), synergistic antiproliferative activity was observed 7 days after continuous exposure. Although the mechanisms by which this effect occurs are unclear, it appears to be associated with direct inhibition of tumor cell proliferation, possibly by modulation of polyamine metabolism.

Alleviation of intestinal lesions by combined treatment with a 5-fluoro-2'-deoxyuridine (FUDR) derivative and alpha-difluoromethylornithine (DFMO)[correction of DMFO] in tumor-bearing mice

alpha-Difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, reduced intestinal lesions in tumor-bearing mice caused by treatment with N3-(3-methylbenzoyl)-3',5'-diacetyl [corrected]-FUDR (FF-705), a derivative of 5-fluoro-2'-deoxyuridine (FUDR). FF-705 at 32 mg/kg (the effective dose) suppressed tumor growth to about 40% of the control level. At this dose, body weight gain was suppressed slightly when FF-705 was given alone, and this change was milder in the DFMO-supplemented group. Intestinal lesions were suppressed almost completely by concomitant treatment with DFMO. The gross lesion index in the combined treatment group was similar to that in the controls and significantly smaller than in the FF-705-alone group (0.3 and 1.9, respectively). The histological lesion index in the combined treatment group was also significantly smaller than in the FF-705-alone group (7.9 and 23.8, respectively). When FF-705 was given at 64 mg/kg, the intestinal mucosal lesions were more severe, but DFMO supplementation reduced them by approximately 50%. Moreover, maltase and diamine oxidase activities of intestinal epithelium remained higher with combined treatment than with FF-705 alone. With FF-705 at 256 mg/kg (a toxic dose), DFMO had little protective effect against intestinal damage.

Prevention of metastasis of intraocular melanoma in mice treated with difluoromethylornithine

The antimetastatic potential of a novel chemotherapeutic agent, alpha-difluoromethylornithine (DFMO), was evaluated in a murine model of intraocular melanoma. In vivo studies demonstrated that DFMO retarded the growth and spontaneous metastasis of murine intraocular melanomas. Further studies indicated that oral DFMO also exercised antimetastatic effects against the blood-borne stage of melanoma metastases. In vitro studies revealed that DFMO exerted impressive antiproliferative effects on three murine melanoma cell lines, four human cutaneous melanoma cell lines, one human uveal melanoma cell line, and one conjunctival melanoma cell line. DFMO inhibited in vitro DNA synthesis in human cutaneous melanoma cell lines by 84%-98% and that in two human ocular melanoma cell cultures by 62% and 86%, respectively. DFMO possesses several characteristics that render it an attractive chemotherapeutic agent for potential use in the management of uveal melanoma. These include its antiproliferative effect against a wide range of murine and human melanomas, its extremely low toxicity, and its ease of administration.

Interactions between immunity and chemotherapy in the treatment of the trypanosomiases and leishmaniases

The immune status of a host infected with Trypanosoma spp. or Leishmania spp. can play an important role in successful chemotherapy. In animal models, treatment of African trypanosomiasis with difluoromethylornithine or melarsoprol requires an appropriate antibody-mediated immune response. An intact immune system is also necessary for rapid clearance of trypanosomes from the bloodstream following treatment with suramin or quinapyramine. Similarly, an efficient cell-mediated immune responses is required for maximal efficacy of pentavalent antimonials in the treatment of leishmaniasis. However, the potential relationship between parasite-induced or acquired immunosuppression and effective chemotherapy has been poorly studied. Macrophages which have been activated by bacterial cell wall components or gamma-interferon are known to display increased activity against Leishmania donovani or Trypanosoma cruzi. In experimental and clinical visceral leishmaniasis, use of macrophage activators together with pentavalent antimonials has lowered the dose of antimony required to cure the infection.

Polyamines: from molecular biology to clinical applications

The polyamines putrescine, spermidine and spermine represent a group of naturally occurring compounds exerting a bewildering number of biological effects, yet despite several decades of intensive research work, their exact physiological function remains obscure. Chemically these compounds are organic aliphatic cations with two (putrescine), three (spermidine) or four (spermine) amino or amino groups that are fully protonated at physiological pH values. Early studies showed that the polyamines are closely connected to the proliferation of animal cells. Their biosynthesis is accomplished by a concerted action of four different enzymes: ornithine decarboxylase, adenosylmethionine decarboxylase, spermidine synthase and spermine synthase. Out of these four enzyme, the two decarboxylases represent unique mammalian enzymes with an extremely short half life and dramatic inducibility in response to growth promoting stimuli. The regulation of ornithine decarboxylase, and to some extent also that of adenosylmethionine decarboxylase, is complex, showing features that do not always fit into the generally accepted rules of molecular biology. The development and introduction of specific inhibitors to the biosynthetic enzymes of the polyamines have revealed that an undisturbed synthesis of the polyamines is a prerequisite for animal cell proliferation to occur. The biosynthesis of the polyamines thus offers a meaningful target for the treatment of certain hyperproliferative diseases, most notably cancer. Although most experimental cancer models responds strikingly to treatment with polyamine antimetabolites--namely, inhibitors of various polyamine synthesizing enzymes--a real breakthrough in the treatment of human cancer has not yet occurred. It is, however, highly likely that the concept is viable. An especially interesting approach is the chemoprevention of cancer with polyamine antimetabolites, a process that appears to work in many experimental animal models. Meanwhile, the inhibition of polyamine accumulation has shown great promise in the treatment of human parasitic diseases, such as African trypanosomiasis.

Novel therapy for the treatment of human carcinoid

Development of effective treatment for patients with carcinoid tumors has been hampered by lack of an experimental model. The authors have established the only long-term cell line of a functioning human pancreatic carcinoid tumor (BON) that produces tumors in nude mice. In this study the authors examined the effect of three agents, alpha-interferon (IFN), a somatostatin analog, SMS 201-995 (SMS), and an inhibitor of polyamine biosynthesis, alpha-difluoromethylornithine (DFMO), on the growth of BON tumors. BON was implanted bilaterally as 3-mm2 pieces (subcutaneously [sc]) into male BALB/c nude mice. In the first study, 23 mice were randomized to four groups: control, IFN (1 x 10(6) units, sc, four times a day), IFN + SMS (300 micrograms/kg, intraperitoneally, three times a day), and IFN + 3% DFMO in drinking water. Treatments were initiated on day of tumor implantation. In the second study, mice were randomized to six groups: control, IFN, SMS, DFMO, IFN + SMS, IFN + DFMO, and IFN + SMS + DFMO. Treatments were started on day 15 after tumor implantation. Tumor area and body weights were measured weekly. In both studies mice were killed on day 28 after BON implantation and tumors removed, weighed, and analyzed for DNA and RNA content. In the first study, IFN either alone or in combination with SMS or DFMO suppressed BON tumor growth. When treatment was initiated after established tumor growth (study 2), however, the only effective treatments for suppression of growth of BON were IFN + DFMO and IFN + DFMO + SMS.(ABSTRACT TRUNCATED AT 250 WORDS)

Polyamine biosynthesis inhibitors combined with systemic hyperthermia in cancer therapy

A Phase I clinical trial has been initiated at the University of Arizona Cancer Center which combines escalating oral doses of the polyamine biosynthesis inhibitor alpha-difluoromethylornithine (DFMO), with systemic hyperthermia (approximately 41.5 degrees C) in the treatment of metastatic melanoma. The rationale for the combination of hyperthermia and polyamine biosynthesis inhibitors in the treatment of human cancers includes studies which show that depletion of endogenous polyamines, as a result of treatment with DFMO, sensitizes both rodent and human tumor cells to the cytotoxic effects of hyperthermia. Heat shock induces the first enzyme in polyamine catabolism, spermidine/spermine N1-acetyltransferase (N1-SAT). The consequently acetylated forms of spermidine and spermine are then constitutively oxidized by the enzyme polyamine oxidase (PAO). Both CHO and human A549 lung cancer cells exhibit heat-inducible polyamine acetylation, display potent heat sensitization after polyamine depletion, and ultimately reveal prolonged expression of thermotolerance. Conversely, HeLa cells do not demonstrate heat-inducible polyamine catabolism, are not sensitized to heat with DFMO, and display more rapid kinetics of thermotolerance decay. These laboratory studies suggest that enhancement of the cytotoxic action of hyperthermia by DFMO occurs as a consequence of the inhibition of polyamine catabolism, a heat-inducible process that affords some form of protection to cells undergoing heat stress. Human melanoma cultures demonstrate heat-inducible polyamine catabolism and are sensitized to hyperthermic cytotoxicity by DFMO. To date, 24 systemic hyperthermia treatments have been delivered to nine patients with metastatic melanoma in conjunction with oral DFMO under this Phase I clinical trial.

Metabolism and action of amino acid analog anti-cancer agents

The preclinical pharmacology, antitumor activity and toxicity of seven of the more important amino acid analogs, with antineoplastic activity, is discussed in this review. Three of these compounds are antagonists of L-glutamine: acivicin, DON and azaserine; and two are analogs of L-aspartic acid: PALA and L-alanosine. All five of these antimetabolites interrupt cellular nucleotide synthesis and thereby halt the formation of DNA and/or RNA in the tumor cell. The remaining two compounds, buthionine sulfoximine and difluoromethylornithine, are inhibitors of glutathione and polyamine synthesis, respectively, with limited intrinsic antitumor activity; however, because of their powerful biochemical actions and their low systemic toxicities, they are being evaluated as chemotherapeutic adjuncts to or modulators of other more toxic antineoplastic agents.

alpha-Difluoromethylornithine inhibits liver metastasis produced by intrasplenic injection of human tumor cells into nude mice

The purpose of these studies was to examine metastatic potentials of a human colon tumor xenograft (T6) and three different human tumor cell lines (LS174T, HT29 and A549) using the intrasplenic-nude mouse model system (ISMS model system). A further objective was to study the activity of alpha-difluoromethyl-ornithine (DFMO) against primary and metastatic growth of the xenograft and the three cell lines. DFMO is an irreversible inhibitor of ornithine decarboxylase, a rate-limiting step in polyamine biosynthesis. Tumor burdens in the liver of nude mice were observed 6 weeks after the intrasplenic injection with LS174T and 12-14 weeks after intrasplenic injections with T6, HT29 and A549. Most of the mice developed primary tumor growth in the spleens. DFMO showed significant activity against liver metastases but had little or no activity against primary tumor growth in the spleens of the ISMS model and against s.c. growth of the xenograft. The studies demonstrated that the ISMS model system is an excellent system for studying metastatic behavior of human tumors and for studying the antimetastatic activity of experimental drugs.

Urinary polyamine levels in cancer patients treated with D,L-alpha-difluoromethylornithine, an inhibitor of polyamine biosynthesis

The polyamine biosynthesis inhibitor D,L-alpha-Difluoromethylornithine hydrochloride monohydrate (DFMO) has cytostatic and cytotoxic effects against various human tumor cell lines in vitro. We measured levels of the polyamines putrescine and spermidine in the urine of cancer patients undergoing "conventional" chemotherapy in a two-arm randomized phase I-II study with and without additional DFMO administered orally at a dose of 1.7 g/sq.m. t.i.d. The study group included 38 patients with carcinoma of the breast, stomach, prostate, or female genital organs or metastatic carcinoma of unknown origin. A control group of 32 patients with similar malignancies received "conventional" chemotherapy without DFMO. Polyamine levels were determined periodically in the urine of all patients. In DFMO-treated patients, a significant decrease in putrescine and spermidine levels was observed after 3 weeks of DFMO therapy (the first time point evaluated) that usually persisted throughout the course of treatment. Significant differences in polyamine levels between DFMO-treated and control patients were observed for patients in remission. Less significant differences were noted, however, for patients with static or progressive disease between DFMO-treated and control groups. DFMO activity appears to be reflected by a long-term decrease in urinary polyamine levels.

The role of polyamines in interferon and retinoic acid mediated synergistic antiproliferative action

Retinoic acid alone has no effect on the human breast cancer cell line BT-20 but can amplify the antiproliferative action of interferon-gamma (IFN-gamma). In our system ornithine decarboxylase (ODC) activity correlates well with growth rate; it was investigated whether the antiproliferative effects of IFN-gamma and IFN-gamma plus retinoic acid could be attributed to suppression of ODC activity. The ODC inhibitor difluoromethylornithine (DFMO), which is active as a single agent did not enhance growth inhibition induced by the biological response modifiers. The substitution of the BT-20 cells with putrescine, the product of the enzymatic reaction mediated by ODC, reversed DFMO induced antiproliferative action. On the other hand putrescine did not affect the proliferation of BT-20 cells treated with interferon alone or in combination with retinoic acid.

Role of polyamines in the growth of hormone-responsive experimental breast cancer in vivo

We have provided evidence for a critical role of polyamines in the growth of the hormone-responsive N-nitrosomethyl-urea (NMU)-induced rat mammary tumor in vitro. The present experiments were designed to test whether polyamines are involved in the growth of this experimental tumor in vivo. To test this hypothesis, groups of rats bearing NMU-induced mammary cancers were randomly allocated to receive no treatment or escalating doses of the polyamine biosynthesis inhibitor alpha-difluoromethyl-ornithine (DFMO) (0.5%, 1%, 2%, 3% in drinking water). DFMO inhibited tumor growth in a dose-dependent fashion and consistently reduced tumor putrescine level. To evaluate the time dependency of this effect, additional groups of rats received either no treatment or 2% DFMO for 3, 7, 14, and 21 days. At all times DFMO suppressed tumor putrescine level as well as spermidine to spermine ratio. Finally, exogenous administration of putrescine (200 mg/kg/i.p./day x 21 days) given concomitantly with DFMO restored tumor growth, partially repleted tumor putrescine level, and raised the spermidine to spermine ratio to control levels. Putrescine, given alone, had no significant effect on either tumor polyamine levels or tumor growth. Except for modest weight loss, no major toxicity was encountered. These results indicate that polyamines play an important role in the growth of the NMU rat mammary tumor in vivo. The interaction between polyamines and hormones in supporting NMU mammary tumor growth in vivo remains to be elucidated.

Alterations in human circulating and bone marrow mononuclear cell polyamine levels in hematologic malignancies as a consequence of difluoromethylornithine administration

The effect of administering increasing intravenous doses of difluoromethylornithine on human tumor cell polyamine levels was determined in patients with hematologic malignancies. Difluoromethylornithine from 5.5. to 64 gm/m2 per day was administered to nine patients with refractory acute leukemia or multiple myeloma. Putrescine, spermidine, and spermine levels were determined on a daily basis in the circulating mononuclear cells and on a weekly basis in the mononuclear cells of the bone marrow. Tumor cell putrescine levels declined in 5 patients, spermidine levels declined in 4 patients, and spermine levels declined in 3 patients. Alterations in the polyamine levels of the bone marrow mononuclear cells paralleled those occurring in the peripheral blood mononuclear cells in the patients with leukemia. Seven to ten days of DFMO treatment were required for mononuclear cell polyamine levels to decrease. The higher drug doses were not significantly more effective than the lower doses in bringing about a decline in tumor cell polyamine levels, either with respect to treatment time required for onset of response or with respect to the ultimate extent of response.

Inhibition of mouse bladder tumor proliferation by alpha difluoromethylornithine and interferon in vitro and in vivo

Previous studies have reported that alpha difluoromethylornithine (DFMO), an enzyme-activated, irreversible inhibitor of ornithine decarboxylase (ODC), has anti-tumor activity in several tumor systems. Recently, investigations have revealed that combinations of DFMO and Interferon (IFN) are synergistic in inhibiting tumor cell growth. We tested the effects of DFMO and IFN alpha, beta alone and in combination on the growth of mouse bladder tumor (MBT-2) cells both in vitro and in vivo. MBT-2 cells were incubated for 72 hours in 96 well microtiter plates with DFMO, IFN alpha, beta and combinations of both agents and percentage inhibition was calculated. In vivo studies utilized the intravesical implantation method as well as subcutaneous implantation. DFMO was administered as a 1% solution in the drinking water. IFN alpha, beta was given bi-weekly by intravesical administration. DFMO effectively inhibited MBT-2 growth in vitro. The ID50 was 0.08 mM and peak inhibitory activity was reached at concentrations of 0.16 mM and remained constant with concentrations of up to 10 mM. IFN alpha, beta also inhibited the in vitro proliferation of MBT-2 with maximum inhibition (46%) at 2,000 U/ml. Combinations of DFMO and IFN alpha, beta showed increased anti-proliferative activity. The degree of enhancement varied with synergism, additivity, or sub-additivity at varying drug concentrations. In vivo, DFMO significantly retarded the growth of tumors implanted subcutaneously (p less than .05) and significantly delayed the outgrowth of tumors implanted intravesically (p less than .01). IFN alpha, beta alone was ineffective in vivo and produced no additive effect in vivo when used in combination with DFMO. Results of our investigation show that DFMO inhibits proliferation of MBT-2 cells in vitro and exhibits a similar effect in vivo against subcutaneous and intravesical tumor implants. IFN alpha, beta alone demonstrated anti-proliferative activity in vitro but did not affect MBT-2 growth in vivo. Although the combination of DFMO and IFN alpha, beta exhibited enhanced activity in vitro, no enhancement was observed with combination therapy in vivo.

Combined use of alpha-difluoromethylornithine and an inhibitor of S-adenosylmethionine decarboxylase in mice bearing P388 leukemia or Lewis lung carcinoma

The antitumor and antimetastatic effects of alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, combined with an inhibitor of S-adenosylmethionine decarboxylase, either methylglyoxal bis(guanylhydrazone) (MGBG) or ethylglyoxal bis(guanylhydrazone) (EGBG), were studied in mice bearing P388 leukemia or Lewis lung carcinoma. Although EGBG is a more specific inhibitor of polyamine biosynthesis than the widely used MGBG, the antitumor effect of the DFMO-EGBG combination on P388 leukemia-bearing mice was less than that of the DFMO-MGBG combination. The prolongation of survival time by the DFMO(1000 mg/kg)-MGBG(25 mg/kg) combination was 2.65-fold, while that of the DFMO(1000 mg/kg)-EGBG(50 mg/kg) combination was 1.34-fold. When mice were fed a polyamine-deficient diet, stronger antitumor effects were exerted; the prolongation of survival time by the DFMO-MGBG and the DFMO-EGBG combinations was 2.89-fold and 2.03-fold, respectively. The antitumor effect of combined use of the two polyamine antimetabolites with mice on normal and polyamine-deficient diets correlated with a decrease of polyamine charge contents in the tumor cells. The above in vivo results were confirmed clearly in the KB cell culture system. The antimetastatic activity of DFMO on Lewis lung carcinoma-bearing mice was strengthened by the addition of MGBG or EGBG. The antimetastatic activity of the DFMO-MGBG or DFMO-EGBG combination did not parallel the polyamine charge contents in the primary tumor and blood.

Ornithine decarboxylase activity in rabbit retina following treatment with alpha-difluoromethylornithine

The rabbit retina has been utilized as a model for the study of abnormal cellular proliferation on the retinal surface and into the vitreous, a process commonly initiated by trauma and generally leading to retinal detachment. This study characterizes the ability of alpha-difluoromethylornithine (alpha-DFMO), a suicide inactivator of L-ornithine decarboxylase (EC 4.1.1.17) to inactivate normal retinal ornithine decarboxylase (ODC) activity in the crude supernatant fraction after incubation with different concentrations of alpha-DFMO and at various times after intraocular administration. Partial inactivation of ODC activity occurred following preincubation of crude retinal supernatant fraction with 10(-5) M alpha-DFMO (N = 3; 34 +/- 6.9% of control), whereas preincubation with 10(-8) M alpha-DFMO did not alter ODC activity significantly (N = 3; 94 +/- 2% of control). Different concentrations of alpha-DFMO administered intraocularly inactivated retinal ODC activity to varying degrees with different rates of recovery. No gross toxicity occurred with ocular tissues following intravitreal administration of alpha-DFMO as determined by electrophysiologic measurements, by indirect examination of the retina, and by measurement of intraocular pressure. These results suggest that alpha-DFMO may be a useful tool in which to define the physiologic role of ODC and polyamines in intraocular cellular proliferative diseases.

Median effect and long term recovery analysis of biological modifier interactions with difluoromethylornithine on the proliferation of human melanoma cells

The ability of difluoromethylornithine (DFMO), a specific polyamine synthesis inhibitor, to interact with various biological modifiers to inhibit the colony-forming growth of human melanoma cells was determined by using the median effect principle to computer model the strength of two agent interactions. Either alpha- or gamma-IFN (interferon) in combination with DFMO resulted in a synergistic inhibition on human melanoma colony formation. For human melanoma cells which were not resistant to 13-cis RA (retinoic acid), an additive suppression on colony formation was obtained with the retinoid-DFMO combination. Dexamethasone (DEX) interacted with DFMO to yield a synergistic reduction in melanoma colony number on glucocorticoid sensitive cells and no growth enhancement with DFMO on glucocorticoid resistant melanoma lines. Human melanoma cells displayed differential long-term growth sensitivity to DFMO treatment. C8146C human melanoma cells were terminally growth-inhibited by a 96 h exposure to DFMO, in a manner which was concentration and time dependent. The proliferation of C82-7A melanoma cells was inhibited by 95% in presence of DFMO, but upon removal of DFMO the cells regained their ability to proliferate and form colonies. The simultaneous addition of DEX plus alpha-IFN plus 13-cis-RA with DFMO caused most of the human melanoma cells in these lines to become permanently growth arrested. Pre-treatment with DEX plus alpha-IFN plus 13-cis RA, but without DFMO, did not have any long term effect on the ability of melanoma cells to recover and proliferate in soft agar.(ABSTRACT TRUNCATED AT 250 WORDS)

Phase I-II clinical trial with alpha-difluoromethylornithine--an inhibitor of polyamine biosynthesis

Alpha-difluoromethylornithine (DFMO) is an enzyme-activated, irreversible inhibitor of ornithine decarboxylase, the first enzyme in the synthesis of the polyamines putrescine, spermidine and spermine. DFMO has been shown to have a cytostatic and cytotoxic effect against various human tumor cell lines. The present study was designed to evaluate the toxicity and efficacy of this compound when administered orally at a dose of 1.7 g/m sq. t.i.d. added to conventional chemotherapy to 38 patients with carcinoma of the breast, stomach, prostate, female genital organs or metastatic carcinoma of unknown origin. A control group of 32 patients with similar malignancies received conventional chemotherapy only. Gastrointestinal, hematologic and biochemical abnormalities caused by DFMO were negligible. Reasonable ototoxicity was the major toxic effect caused by DFMO and resulted in discontinuation of therapy in 6 of 38 patients (15.8%). No differences in disease progression were seen between those patients receiving DFMO plus conventional chemotherapy and those receiving only conventional chemotherapy.

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.

Polyamines in normal and cancer cells

Based on available evidence, it appears that polyamines are critical for proliferation of both normal and transformed cells. Although the requirement of polyamines for DNA replication and cell proliferation is established, the molecular events in which the polyamines are essential are yet unknown. Furthermore, transformed and cancer cells, possibly because of their higher proliferative rate, appear to be more dependent on polyamine metabolism than their normal counterparts. This has been shown by the in vivo response of tumor models and human tumor xenografts in nude mice to polyamine depletion by DFMO. Although there has been associated toxicity to the host, the inhibition of cell proliferation has been higher in the implanted tumors than in the host. DFMO, a specific irreversible inhibitor of ODC, has been used extensively in studies which have shed light on the role of polyamines in cell proliferation and differentiation. DFMO has shown interesting anti-tumor effect in a number of experimental tumor models. Currently, DFMO clinical trials are being completed, and it will be of interest to see whether this polyamine inhibitor, or other newer polyamine analogs and inhibitors, will find a place in the treatment of neoplastic disorders.

Effect of difluoromethylornithine on the antiglioma therapeutic efficacy of intra-arterial BCNU

In an attempt to improve glioma management, an animal model was developed to evaluate the therapeutic efficacy of intra-arterial 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Furthermore, the model was used to study the antitumor activity of D,L-alpha-difluoromethylornithine (DFMO), a polyamine-biosynthesis inhibitor, used both as a single agent and in combination with intra-arterial BCNU. An N-methylnitrosourea-induced gliosarcoma (T9) was transplanted stereotaxically into the right caudate nucleus of male Fischer 344 rats. Animals receiving a single low-dose (5 mg/kg) intracarotid injection of BCNU 9 days following tumor implantation had a 57% increase in life span compared with untreated control rats (p less than 0.001). Intracarotid drug delivery was more effective than systemic (intraperitoneal) administration of the same dose of BCNU. When given as a single agent, DFMO demonstrated dose-dependent effectiveness. As part of a combined regimen, DFMO enhanced the antitumor therapeutic activity of both systemic (intraperitoneal) and intra-arterial BCNU. Survival times of animals receiving combined DFMO and intra-arterial BCNU were almost double those of untreated controls, and were significantly better than survival times of animals receiving combined DFMO and intraperitoneal BCNU. These findings suggest methods to optimize current clinical chemotherapy for glioma.

Effects of human interferon and alpha-difluoromethylornithine on T47D cells

The effect of human interferon (IFN) and alpha-difluoromethylornithine (DFMO), an enzyme-activated irreversible inhibitor of eukaryotic ornithine decarboxylase, on the rate of DNA synthesis and the increase of ornithine decarboxylase activity of T47D cells was examined. It was found that IFN or DFMO alone causes little or appreciable inhibition of the [3H]thymidine incorporation, respectively. Each of the drugs alone has a significant inhibitory effect on ornithine decarboxylase activity. Combination of the two drugs has a synergistic effect and eliminates completely the [3H]thymidine incorporation and the activity of ornithine decarboxylase. The biological implication of IFN and DFMO is discussed with regard to the regulation of ornithine decarboxylase activity and the antiproliferative effects of the two drugs.

Inhibition by interferon (alpha + beta) of mouse liver regeneration and its reversal by putrescine

Mouse interferon (alpha + beta) given to mice by intraperitoneal injection suppressed both the accumulation of putrescine and stimulation of DNA synthesis in liver caused by partial hepatectomy. The suppression of DNA synthesis was completely reversed by exogenous putrescine. The same results were obtained when core 2',5'-oligoadenylate instead of interferon was given to partially hepatectomized mice. These results suggest that interferon inhibits putrescine formation through elevating the 2',5'-oligoadenylate level and thus inhibits DNA synthesis in the regenerating liver.

Difluoromethylornithine and leukocyte interferon: a phase I study in cancer patients

Difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, and human leukocyte interferon (IFN-alpha) have synergistic anti-tumor activities in vivo in B 16 melanoma and in vitro against several human cancer cell lines. We have, therefore, carried out a phase I combination study with DFMO plus alpha interferon in the following manner: DFMO was maintained at a steady dose for the first four levels, 1.5 g/m2 every 6 hr. IFN-alpha was given in 100% increments ranging from 0.4 X 10(6)U/m2 to 3.2 X 10(6)U/m2 i.m. daily. At the fifth dose level both IFN-alpha and DFMO were raised by 100 and 50% respectively. From levels one through four the combination was well tolerated with no dose interruptions required because of G.I. toxicity or myelosuppression. However, at dose level 5, one-third of the patients required dose cessation and decrease due to nausea, vomiting and diarrhea. We conclude that for phase II studies the maximal tolerated dose is 3.2 million units of IFN-alpha/m2 and 1.5 g/m2 of DFMO every 6 hr. Of 12 patients with metastatic melanoma, 2 had partial remissions lasting 58+ and 36+ weeks. Two additional patients had minor responses lasting 29 and 32+ weeks. Minor responses were observed in a patient with colon carcinoma and a patient with renal carcinoma. The clinical activity of the combination is currently being pursued in a phase II study among patients with metastatic malignant melanoma.

Ornithine decarboxylase activity during formation of experimental epiretinal membranes

This study demonstrates in a rabbit model of epiretinal membrane formation that retinal-associated ODC activity increases during this pathological process. These changes in retinal-associated ODC activity most likely occur in relationship to the proliferative lesion itself, since the retina consists primarily of nonproliferative tissues. Further knowledge of intraocular polyamine metabolism during epiretinal membrane formation which can result in retinal detachment may lead to the development of an effective pharmacological treatment.

Difluoromethylornithine enhances inhibition of melanoma cell growth in soft agar by dexamethasone, clone A interferon and retinoic acid

Five human melanoma cell lines (C8146C, C8161, C82-7A, C83-2CY and MIRW5) were shown to contain a significant number of melanoma colony-forming units resistant to single-agent treatment by dexamethasone, alpha-interferon and trans-retinoic acid. These biological modifiers were combined with difluoromethylornithine into a low-dose combination using concentrations below pharmacologically achievable levels. The suppression of melanoma colony formation induced by this combination was consistent and significantly higher than that seen with any single agent, colony formation being reduced by an average of 90%. Leaving either DEX or DFMO out of the 4-agent combination resulted in a significant decrease in the observed inhibition. This was also verified by the addition of putrescine which inhibited only the DFMO activity. Median effect analysis of the DFMO + IFN inhibition of C8161 cells demonstrated that the 2 agents interacted synergistically over the entire dose-response curve. Of the high-dose combination-treated melanoma colony-forming units, 97% did not form small growth units; most remained as arrested single cells, but the cells and small growth units could still metabolize tetrazolium stain after the experiment, suggesting that the high-dose combination arrested the growth of the melanoma colony-forming units via a non-cytotoxic mechanism.

The effect of alpha-difluoromethylornithine on natural killer cell and tumoricidal macrophage induction by interferon in vivo

The objective of the present investigation was to evaluate the effect of DFMO (DL-alpha-difluoromethylornithine HCl H2O) administration on tumoricidal effector cell generation by IFN or IFN inducers in vivo. DFMO administration reduces both splenic leukocyte and peritoneal macrophage polyamine levels. In tumor bearing (B16 melanoma) mice, DFMO administration did not impair splenic natural killer (NK) cell augmentation, assessed against NK sensitive YAC-1 target cells, by IFN alpha/beta or the IFN inducers tilorone and polyriboinosinic: polyribocytidilic acid (poly I:C). Tumoricidal macrophage activation by IFN alpha/beta was similarly uninhibited by DFMO. However, only tumoricidal macrophage not NK cell activity was observed which could kill the B16 melanoma target cells. These results indicate that DFMO is not immunosuppressive regarding antitumor cytolytic cell induction in vivo.

Human renal cell carcinoma xenograft: morphology, growth and chemosensitivities

A primary human renal clear cell carcinoma has been developed as a xenograft (JDF-1). Passage 7 of the JDF-1 tumor retained the microscopic morphology of the primary tumor, electron micrographs have confirmed its epithelial characteristics and karyotyping of a subsequent passage has proved it is not a murine hybrid. Immunoperoxidase studies using a panel of murine monoclonal antibodies demonstrate an antigenic phenotype specific for human renal cancer. In vitro chemosensitivities of the JDF-1 tumor were determined by the double-layer soft-agar clonogenic assay method. JDF-1 showed no significant sensitivities to several standard chemotherapeutic agents, but alpha-2-interferon and difluoromethylornithine in combination synergistically inhibited its growth by 74 per cent.

Consequences of ornithine decarboxylase inactivation by alpha-difluoromethylornithine and 5-fluorouracil on the growth of rabbit fibroblasts

The role of ornithine decarboxylase and polyamines in proliferative vitreoretinopathy (PVR) is ill-defined. An increase in the activity of this enzyme concurrent with an increase in polyamine levels may be essential in the process of intraocular cellular proliferation. Therefore, in this study, cultured rabbit fibroblasts were exposed to DL-alpha-difluoromethylornithine (alpha-DFMO), a mechanism-based irreversible inactivator of ornithine decarboxylase, alone and in combination with 5-fluorouracil (5-FU). Concentrations of 0.1mM alpha-DFMO and 0.125mM 5-FU decreased rabbit fibroblast cell number by 60% and 65%, respectively, after three days, while with either 5.0mM alpha-DFMO or 0.25mM 5-FU, cell number is decreased by 95%. The effectiveness of inhibitory concentrations of 5-FU and alpha-DFMO together in reducing cell number is additive.

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.

Potentiation by alpha-difluoromethylornithine of the activity of 3,4-dihydroxybenzylamine, a tyrosinase-dependent melanolytic agent, against B16 melanoma

Continuous exposure for 96 hr of B16 melanoma cells in culture to 2.5 mM alpha-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of ornithine decarboxylase, resulted in a marked increase in the activity of the enzyme tyrosinase, and also 20% cell kill as assessed by clonogenic assay. A 4-hr exposure to 0.4 mM 3,4-dihydroxybenzylamine (DHBA), a compound which is melanolytic due to its conversion to a cytotoxic quinone by the tumor specific enzyme tyrosinase, was found to be approximately equitoxic to 2.5 mM DMFO. However, a combination of DFMO (2.5 mM) and DHBA (0.4 mM) produced greater than 95% cell kill. This observed cytotoxicity with the combination suggests that induction of tyrosinase by DFMO sensitizes B16 melanoma cells to the melanolytic activity of DHBA. Oral administration of DFMO to mice bearing subcutaneous B16 melanomas also resulted in marked increases in the activity of tyrosinase in the tumor tissue. In mice inoculated intraperitoneally with 10(5) B16 melanoma cells, administration of DFMO via the drinking water (2%) increased the survival time by 8.5 days, whereas intraperitoneal administration of 300 mg/kg of DHBA for 14 days resulted in an increase in life span of 4.5 days compared to untreated controls. A combination of DFMO and DHBA prolonged the survival time by 14.6 days. These results indicate that DFMO in combination with an appropriate tyrosinase-dependent melanolytic agent might be useful in the chemotherapy of malignant melanomas.

Chemoprevention and chemotherapy by inhibition of ornithine decarboxylase activity and polyamine synthesis: colonic, pancreatic, mammary, and renal carcinomas

Specific, irreversible, inhibition of ODC activity with DFMO and resultant low levels of intracellular polyamines markedly suppress the induction of experimental colonic and mammary cancers and hold promise for augmenting the multidrug chemotherapy of established colonic, pancreatic, renal and mammary cancers without increasing systemic toxicity.

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.

Cytolytic activity of interferon-gamma and its synergism with 5-fluorouracil

Highly purified natural or recombinant human immune interferon (IFN-gamma) was found to be directly cytolytic to certain tumor cell lines in vitro. Out of 5 human tumor cell lines and one normal fibroblast line tested, the colon adenocarcinoma line HT-29 and the rhabdomyosarcoma line A673 were highly sensitive to cytolysis by interferon, as determined by 125I-iododeoxyuridine release in a 72 h microcytotoxicity assay. Cytolysis was marked at IFN-gamma concentrations of less than I U/ml, and it reached a near-maximal level at 6.4 U/ml. A synergistic cytolysis on HT-29 cells of IFN-gamma and 5-fluorouracil (5-FU) was observed at 5-FU concentrations ranging from 64 to 640 micrograms/ml. In contrast, no synergism was observed between IFN-gamma and mitomycin C. The direct cytolytic activity and synergistic cytolysis with 5-FU of the IFN-gamma preparations used in the present study were abolished completely by treatment with a neutralizing monoclonal antibody specific for human IFN-gamma.

Interferon--present and future prospects

The interferons are a group of proteins that have inspired a new era of investigation into biological modification. The interferons are now divided into subgroups characterized by chemical means and correspond to different biological responses which can be observed in terms of the inducer used, and the timing of the response. Identified originally as antiviral agents when homologous cell systems were treated prior to infection, new studies have extended these observations to place the interferons in a central role as a strong force in the regulation of immunologic responses. A marriage of interferonology and cell immunology is enlarging both our understanding of the action of these proteins and our ability to follow the course of an illness and eventually to control its outcome . Genetic engineering has provided a way to process quantities of interferon and provided the molecular sequence of all three classes of IFN including a model of the active site for IFN-alpha. The offshot of the technology developed to study the intracellular processes after interferon treatment have already led to increased sensitivity to detect virally treated diseases. Both the variety of the interferon inducers and the scope of parasites in which it can exert its influence provide a frontier of biological investigation which has at the root of its nature the very secret of life. In addition to cellular phenomena, the positive effects on tumor-bearing organisms and the ill effects on infant animals highlight the potential power of the interferons.