Inhibition of ornithine decarboxylase in human fibroblast cells by type I and type II interferons

Diverse Functions of Polyamines in Virus Infection

As obligate intracellular parasites, viruses rely on host cells for the building blocks of progeny viruses. Metabolites such as amino acids, nucleotides, and lipids are central to viral proteins, genomes, and envelopes, and the availability of these molecules can restrict or promote infection. Polyamines, comprised of putrescine, spermidine, and spermine in mammalian cells, are also critical for virus infection. Polyamines are small, positively charged molecules that function in transcription, translation, and cell cycling. Initial work on the function of polyamines in bacteriophage infection illuminated these molecules as critical to virus infection. In the decades since early virus-polyamine descriptions, work on diverse viruses continues to highlight a role for polyamines in viral processes, including genome packaging and viral enzymatic activity. On the host side, polyamines function in the response to virus infection. Thus, viruses and hosts compete for polyamines, which are a critical resource for both. Pharmacologically targeting polyamines, tipping the balance to favor the host and restrict virus replication, holds significant promise as a broad-spectrum antiviral strategy.

Evaluation of a short-term topical interferon α-2b treatment for histologically proven melanoma and primary acquired melanosis with atypia

OBJECTIVE

To evaluate the efficiency of series of 6-week treatments with brief intervals (6-week = 1 cycle) of topical Interferon α-2b (IFNα-2b) treatment in primary acquired melanosis (PAM) with atypia and melanoma of the conjunctiva.

PATIENTS AND METHODS

Five patients with biopsy-proven PAM with atypia and seven patients with melanoma of the conjunctiva, treated with topical IFNα-2b (1 million units/ml, 5 times daily), were included in the study. All patients had colour photographs and the tumour area was measured manually for each patient before and after treatment.

RESULTS

The median age of 12 patients at initiation of treatment was 61.5 years (range 39-75 years). The mean therapy duration was 2.4 cycles (range 1-6 cycle). Compared to pretreatment lesion dimension, the mean decrease in tumour size were after the first cycle 66% (range 18-98%; p = 0.004; n = 10 patients), after the second cycle 55% (range 10-100%; p = 0.016; n = 7 patients), and after the third cycle 74% (range 23-100%; n = 3 patients). In one patient 6 cycles of topical IFNα-2b were needed. The decrease in size was 22% after the 4(th) cycle, 34% after the 5(th) cycle, and 98% after the 6(th) cycle.

CONCLUSION

Our clinical experience demonstrates promising results of topical IFNα-2b treatment for PAM with atypia and melanoma of the conjunctiva without any local or systemic side effects. However, future multicenter prospective studies are recommended to confirm the efficiency and safety of topical IFNα-2b treatment.

A newly discovered function for RNase L in regulating translation termination

The antiviral and antiproliferative effects of interferons are mediated in part by the 2'-5' oligoadenylate-RNase L RNA decay pathway. RNase L is an endoribonuclease that requires 2'-5' oligoadenylates to cleave single-stranded RNA. In this report we present evidence demonstrating a role for RNase L in translation. We identify and characterize the human translation termination factor eRF3/GSPT1 as an interacting partner of RNase L. We show that interaction of eRF3 with RNase L leads to both increased translation readthrough efficiency at premature termination codons and increased +1 frameshift efficiency at the antizyme +1 frameshift site. On the basis of our results, we present a model describing how RNase L is involved in regulating gene expression by modulating the translation termination process.

Potential of interferon-alpha in solid tumours: part 1

Interferon-alpha (IFNalpha) is a pleiotropic cytokine with direct and indirect antitumour effects. These include prolongation of the cell cycle time of malignant cells, inhibition of biosynthetic enzymes and apoptosis, interaction with other cytokines, and immunomodulatory and antiangiogenic effects. The first clinical trials in solid tumours used crude preparations of natural IFNalpha and demonstrated that tumour regressions in solid tumours and haematological malignancies were possible. Since the advent of genetic engineering technology, recombinant (r) IFNalpha has been widely evaluated in solid tumours. This review discusses the use and potential of rIFNalpha in solid tumours; the first part focuses on malignant melanoma and metastatic renal cell carcinoma (RCC). In the adjuvant treatment of malignant melanoma, rIFNalpha has been tested in randomised trials in more than 6000 patients. High-dosage IFNalpha (> or =10MU) prolongs disease-free survival (DFS) but not overall survival (OS). Low-dosage IFNalpha (< or =3MU) has not been shown to prolong DFS or OS, and current data do not support its use outside clinical trials. The latest United Kingdom Co-ordinating Committee on Cancer Research meta-analysis of ten randomised trials that used adjuvant rIFNalpha has shown that there is a benefit in DFS but not OS. No conclusions can be reached for intermediate-dosage IFNalpha (5 to 10MU) until the mature results of the European Organization for Research and Treatment of Cancer (EORTC) study 18952 are available. In RCC, current evidence does not support the use of adjuvant IFNalpha. In metastatic malignant melanoma and RCC, reported response rates to rIFNalpha are approximately 15%. In a minority of responding patients, however, these responses can be long-standing. In metastatic malignant melanoma, IFNalpha combined with other cytotoxic agents with or without interleukin-2 has achieved high response rates but has not improved survival. In metastatic RCC, intermediate dosages of rIFNalpha should be used and therapy should probably be prolonged (>12 months); response depends on prognostic factors such as good performance status, whereas survival is affected by factors such as low tumour burden. Nephrectomy should therefore be considered in patients with good performance status prior to IFNalpha immunotherapy in advanced RCC, even in patients with metastatic disease. The toxicity of high-dosage IFNalpha and the lack of definite benefit on OS with high- or low-dosage IFNalpha do not support its use outside clinical trials. Data from the ongoing US Intergroup studies, the ongoing EORTC 18991 study (long-term therapy with pegylated IFNalpha) and mature data from EORTC 18952 (intermediate-dosage IFNalpha) will help establish the role of IFNalpha as adjuvant therapy in malignant melanoma.

Biological assays for interferons

Interferons (IFN) are potent biologically active proteins synthesised and secreted by somatic cells of all mammalian species. They have been well characterised, especially those of human origin, with respect to structure, biological activities, and clinical therapeutic effects. While structural differences are known to exist among the IFN species that constitute the "IFN family" and despite the existence of different receptors for type I and type II IFN, all species have been shown to exert a similar spectrum of in vitro biological activities in responsive cells. Principal among the biological activities induced by IFN is antiviral activity, the activity used to originally define IFN. Antiviral activity of IFN is mediated via cell receptors and is dependent on the activation of signalling pathways, the expression of specific gene products, and the development of antiviral mechanisms. Sensitivity of cells to IFN-mediated antiviral activity is variable, and depends on a number of factors including cell type, expression of IFN receptors and downstream effector response elements, effectiveness of antiviral mechanisms, and the type of virus used to infect cells. Nevertheless, by the judicious use of sensitive cell lines in combination with appropriate cytopathic viruses, effective assays to measure the antiviral activity have been developed. Historically, "antiviral assays" (AVA) were the first type of biological assays that were developed to measure the relative activity or potency of IFN preparations. However, the subsequent discoveries of several other biological activities of IFN has opened the way to the development of assays based on one or other of these activities. The latter include inhibition of cell proliferation, regulation of functional cellular activities, regulation of cellular differentiation and immunomodulation. More recently, the cloning of IFN responsive genes has led to the development of "reporter gene assays". In this case, the promoter region of IFN responsive genes is linked with a heterologous reporter gene, for example, firefly luciferase or alkaline phosphatase, and transfected into an IFN-sensitive cell line. Stably transfected cell lines exposed to IFN increase expression of the reporter gene product in direct relation to the dose of IFN, the readout being a measure of this product's enzymic action. The current review aims to give a critical overview of the development, specificity, standardisation and present use of the various biological assay methods now available for the quantification of IFN activity.

Cutaneous T-cell lymphoma. New immunomodulators

During the most recent decades, much knowledge has been gained concerning the immunologic and pathologic mechanisms of CTCL. The development of immunomodulators aimed at correcting aberrations in immunology and cellular growth and differentiation reflects this increased understanding. This review of the currently available immune-response modifying drugs shows that recombinant forms of natural cytokines and retinoids can be developed with tolerable toxicity profiles and substantial efficacy. Although milestone drugs such as bexarotene have been approved by the FDA- for treatment of CTCL, other agents such as IL-12 may also have a place in treatment of the disease. Even though unapproved, IFN-alpha may be the most active single immunomodulating agent against CTCL. It seems that further delineation of CTCL cytokine profile changes and immunologic aberrations are key in developing effective immunomodulators that are able to reverse these alterations.

Short-term treatment with interferon-alpha/beta promotes remyelination, whereas long-term treatment aggravates demyelination in a murine model of multiple sclerosis

The mechanisms by which type I interferons (IFN) reduce the rate and severity of exacerbations in multiple sclerosis are unknown. We utilized a model of multiple sclerosis to determine the extent of demyelination and remyelination in Theiler's murine encephalomyelitis virus (TMEV)-infected SJL/J mice treated with mouse IFN-alpha/beta for a short (5 weeks) or a long (16 weeks) period. All mice were chronically infected with TMEV to simulate the clinical situation in multiple sclerosis. Short-term IFN-alpha/beta treatment increased the percent of remyelinated spinal cord white matter by threefold when compared with phosphate-buffered saline (PBS) treatment (P < 0.02), but it did not affect the extent of demyelination. In contrast, long-term IFN-alpha/beta treatment increased the extent of demyelination by twofold (P < 0.03). Long-term treatment increased the absolute area of remyelination, but the percent remyelination as a function of area of demyelination was not changed because of increased demyelination. An immunomodulatory mechanism may have contributed to the effect of IFN-alpha/beta on white matter pathology because treated mice had higher anti-TMEV IgGs in serum and demonstrated decreased numbers of B and T lymphocytes infiltrating the central nervous system (CNS). There was no correlation between the level of anti- IFN-alpha/beta antibodies and the extent of demyelination or remyelination. These results indicate that the length of type I IFN treatment may have paradoxical effects on demyelination and remyelination.

Efficacy and safety of systemic recombinant interferon-alpha in Behçet's disease

OBJECTIVES

To evaluate the therapeutic efficacy and safety of systemic recombinant interferon alpha-2a (IFN-alpha) in patients with Behcet's disease (BD) and to determine the incidence of episodes in complete responders during the one-year pretreatment period and follow-up.

DESIGN

An open clinical study.

SETTING

Departments of Dermatology and Ophthalmology, University of Patras, Greece and Department of Dermatology, Heinrich-Heine University of Düsseldorf, Germany.

SUBJECTS

Twelve patients (aged 23-52 years) with active BD who had previously been unsuccessfully treated with systemic steroids and/or immunosuppressives.

INTERVENTIONS

IFN-alpha was administered subcutaneously at a dose of 6 X 10(6) IU per day 3 times per week for 2 months.

MAIN OUTCOME MEASURES

Change of area or number of mucocutaneous lesions, grading score for thrombophlebitis and ocular inflammation, haematological and biochemical parameters and number of episodes during the pretreatment period and the follow-up. Evaluation of IFN-alpha side effects.

RESULTS

Nine patients (75.0%) revealed a complete remission, two (16.6%) a partial remission and one patient (8.3%) showed no response. During the follow-up in five out of the nine complete responders (55.5%) no episodes of BD were seen, whereas, the other four patients (44.5%) had 1-2 episodes, as compared to 5-8 and 5-12 episodes, respectively, during the pretreatment period. An influenza-like syndrome (fever, nausea and myalgias) appeared during the early phase of therapy in all (but one) patients. No patient had to discontinue IFN-alpha because of intolerance.

CONCLUSIONS

Subcutaneous human recombinant interferon alpha-2a appears to be an effective and fairly well tolerated therapy for BD.

The biology of interferon-alpha and the clinical significance of anti-interferon antibodies

The therapeutic indications for Interferons (IFNs) have dramatically increased in number in recent years to include many different diseases of viral, malignant, angiogenic, allergic, inflammatory and fibrotic origin. In particular, the current pandemic of hepatitis C virus infection has further stimulated the requirement for a comprehensive understanding of both the mechanism of action of IFN and the reasons for therapeutic failure. The role of anti-IFN antibodies as a cause of treatment failure has been a particularly controversial area. In this review we will outline the biology and proposed mechanisms of action of IFN-alpha (IFN-alpha) and discuss the incidence, methods of detection and clinical significance of anti-IFN antibodies.

Interferons Alpha, Beta, and Omega

Interferon alpha (IFN-α) is a mixture of closely related proteins, termed “subtypes,” expressed from distinct chromosomal genes. Interferon β (IFN-β) is a single protein species and is molecularly related to IFN-α subtypes, although it is antigenically distinct from them. IFN omega (IFN-ω) is antigenically distinct from IFN-α and IFN-β but is molecularly related to both. The genes of three IFN subtypes are tandemly arranged on the short arm of chromosome 9. They are transiently expressed following induction by various exogenous stimuli, including viruses. They are synthesized from their respective mRNAs for relatively short periods following gene activation and are secreted to act, via specific cell surface receptors, on other cells. IFN-α subtypes are secreted proteins and as such are transcribed from mRNAs as precursor proteins, pre-IFN-α, containing N-terminal signal polypeptides of 23 hydrophobic amino acids (aa) mainly. Pre-IFN-β contains 187 aa, of which 21 comprise the N-terminal signal polypeptide and 166 comprise the mature IFN-β protein. IFN-ω contains 195 aa—the N-terminal 23 comprising the signal sequence and the remaining 172, the mature IFN-ω protein. At the C-terminus, the aa sequence of IFN-ω is six residues longer than that of IFN-α or IFN-β proteins. IFN-α, as a mixture of subtypes, and IFN-ω may be produced together following viral infection of null lymphocytes or monocytes/macrophages. The biological activities of IFNs are mostly dependent upon protein synthesis with selective subsets of proteins mediating individual activities. IFNs can also stimulate indirect antiviral and antitumor mechanisms, depending upon cellular differentiation and the induction of cytotoxic activity.

Interferon-beta inhibits progression of relapsing-remitting experimental autoimmune encephalomyelitis

The results of two phase III clinical trials have recently shown that interferon-beta (IFNbeta) is effective in the treatment of relapsing-remitting multiple sclerosis (RRMS). Treatment with IFNbeta results in a significant decrease in the rate of clinical relapse and a marked delay in progression to disability compared to placebo-treated control patients. In the present study, we demonstrate similar therapeutic effects after treating (SWR X SJL)F1 mice with IFNbeta at the onset of clinical signs of experimental autoimmune encephalomyelitis (EAE), a disease animal model widely used in MS studies. EAE was actively induced by immunization of (SWR X SJL)F1 mice with the immunodominant encephalitogenic peptide 139-151 of myelin proteolipid protein (PLP). In blinded testing, mice treated with IFNbeta at EAE onset showed a delay in progression to clinical disability as determined by marked improvement with time in mean clinical score, significant delay in onset of relapse, and significant decrease in exacerbation frequency compared to placebo-treated control mice. The therapeutic effect of IFNbeta was accompanied by a significant inhibition of delayed-type hypersensitivity (DTH) but not proliferation in response to the priming PLP 139-151. In addition, IFNbeta treatment resulted in an overall decrease in severity of both inflammation and demyelination in the central nervous system. These results mimic in an autoimmune animal model the effectiveness of IFNbeta treatment observed in MS. Moreover, our study suggests that anti-viral properties of IFNbeta are not essential for producing therapeutic effects in autoimmune demyelinating disease, and that the efficacy of IFNbeta in the treatment of MS may be due to inhibition of autoreactivity.

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.

Interferon beta decreases T cell activation and interferon gamma production in multiple sclerosis

Interferons (IFN) are biological molecules with anti-viral, anti-proliferative and immunomodulatory actions. There is evidence that IFN-gamma increases the frequency of exacerbations of multiple sclerosis (MS) whereas IFN-beta may reduce their frequency. Here we present evidence that IFN-beta significantly decreases concanavalin A (Con A)-induced proliferation of peripheral blood mononuclear cells (PBMC) of MS patients and healthy individuals. Similar results were obtained when PBMC were activated through the T cell receptor (TcR) by anti-CD3 monoclonal antibody or independently of it by phorbol ester and Ca2+ ionophore. These effects of IFN-beta were also noted when IFN-gamma and IFN-beta were added together. Furthermore, IFN-beta decreased proliferation when added to cells that were already pre-activated. Activated CD4+ and CD8+ T cells were downregulated to approximately the same extent. Analysis of cytokine production showed that IFN-gamma production by Con A activated PBMC was increased in MS when compared to controls. IFN-beta significantly decreased IFN-gamma production in MS patients and control individuals. Con A activated cultures treated with IFN-beta showed decreased IL2R expression and accumulation of IL2. These results show that IFN-beta decreases T cell activation and IFN-gamma production in vitro, effects that may be beneficial in MS.

Influence of interferon and radiation on serotonin content in primary carcinoid cell cultures

Carcinoids are in general thought to be radioresistent, and have not been subjected to radiation therapy, except for palliative purposes. Clinical experience has indicated that interferons might enhance radiation effect and toxicity. In order to examine the effect of radiation, the combination of radiation and interferon, and the usefulness of the main metabolic product of primary cell cultures--serotonin--as a response indicator, we exposed primary carcinoid cell cultures with and without interferon pretreatment to radiation (2 Gy and 8 Gy). Irradiation alone had no effect on the serotonin content of the medium at the low dose (2 Gy) and even at the high dose (8 gy) the effect was not significant. When cells were preincubated with 1,000 IU/ml alpha-interferon, however, irradiation with 8 Gy induced a significant reduction of the hormone concentration in the medium on day 12 to 54.9 +/- 8.0% of the control value (p = 0.026). We think our model may provide a useful tool for further exploration of these mechanisms.

Recombinant interferon-gamma inhibits the mitogenic effect of platelet-derived growth factor at a level distal to the growth factor receptor

Highly purified preparations of recombinant human interferons (rIFNs)-alpha A, -beta, and -gamma all inhibited platelet-derived growth factor (PDGF)-induced DNA synthesis in normal human dermal fibroblasts, as monitored by incorporation of [3H]-thymidine into trichloroacetic acid (TCA)-insoluble material. rIFN-gamma was the most potent, since it blocked the PDGF response by 50% at about 10 U/ml or 0.3 ng/ml, whereas with rIFN-alpha A and rIFN-beta 4000 U/ml and 600 U/ml, respectively (10 ng/ml in both cases), were required to achieve the same effect. There was a close parallelism between the ability of these rIFNs to inhibit PDGF mitogenic activity and their capacity to inhibit cell proliferation in serum-containing medium. None of the rIFNs inhibited specific binding of 125I-PDGF to fibroblasts, and none interfered with receptor internalization. The mechanism of action of rIFN-gamma was analyzed further. rIFN-gamma did not inhibit uptake of [3H]-thymidine into these cells. However, it shifted if the time point of initiation of DNA synthesis from about 14 h after stimulation with PDGF to about 18 to 21 h and decreased significantly the rate of the DNA synthesis. rIFN-gamma could be added up to 6 h following stimulation with PDGF with no loss of its inhibitory effect. rIFN-gamma also blocked the mitogenic activity of epidermal growth factor and basic fibroblast growth factor. Taken together these results implicate that rIFN-gamma exerts its antimitogenic effect by inhibiting a process that occurs late in the PDGF signaling pathway and onto which the activity pathways of other mitogens converge. In view of the important role PDGF may play in wound-healing and in the pathogenesis of the proliferative lesions of arteriosclerosis, these data point to a possible role IFN-gamma may play as a regulator of these processes in vivo.

Inhibition of ornithine decarboxylase induction of interferon (alpha + beta) and its reversal by dibutyryl adenosine 3',5'-monophosphate

Interferon (alpha + beta) given to C3H/HeN mice intraperitoneally inhibited increases in the activities of adenylate cyclase and ornithine decarboxylase after partial hepatectomy. The inhibition of ornithine decarboxylase was prevented by administration of dibutyryl cAMP. Core (2'-5')oligo(adenylate), i.e. A2'p5'A2'p5'A or (A2'p)2A, as well as interferon inhibited the increases in these two enzymes caused by partial hepatectomy. The inhibition by (A2'p)2A of ornithine decarboxylase activity was reversed by dibutyryl cAMP. These results suggested that the activity of interferon was similar to that of (A2'p)2A and that the inhibition of ornithine decarboxylase induction caused by these agents resulted from the inhibition of adenylate cyclase activity.

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.

Interferon-mediated inhibition of differentiation in a murine myoblast cell line

The effects of highly purified (greater than 5 X 10(7) IU/mg) murine beta-interferon (IFN) on a mouse myoblast line (MM14DZ) have been investigated to confirm and extend the previous observation that partially purified chicken interferon inhibits differentiation of cultured avian myoblasts (Lough et al., Biochem Biophys Res Commun 109:92, 1982). Cultures treated with 20-2,000 lU IFN/ml medium for 5 days exhibited dose-dependent 1) inhibition of differentiation, as indicated by reduced myotube formation and creatine kinase (CK) activity and 2) increases in DNA content, suggesting that the inhibitory effect was accompanied by continued proliferation of myoblasts. Mock-IFN had no such effects. Based on findings in other systems that IFN inhibits activity of ornithine decarboxylase (ODC), the polyamine products of which are required for myogenesis, the hypothesis that inhibition of differentiation was mediated by an effect of IFN on polyamine metabolism was tested. However, observations that 1) IFN-treated myoblasts retained control levels of ODC activity and 2) exogenous polyamines did not prevent IFN-inhibition did not indicate such a mechanism of action. On the other hand, treatment of control cultures with polyamines alone resulted in potentiation of myogenesis as revealed by precocious myotube formation and a marked increase in CK activity.

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.

Differential effects of pure human alpha and gamma interferons on fibroblast cell growth and the cell cycle

Pure human alpha and recombinant gamma interferons had differential effects on two strains of fetal lung fibroblasts in vitro. Alpha interferon had little effect on long-term cell growth, whereas gamma interferons, both glycosylated and non-glycosylated, were cytotoxic. However, when synchronized cells were studied, alpha interferon prolonged both G1 and S + G2 phases of the cell cycle, whereas gamma interferon only affected the G1 phase.

Interferon-mediated protein kinase activity in different fractions of mouse L-929 cells

The interferon (IFN)-mediated protein kinase activity in extracts from mouse L-929 cells is manifested by the phosphorylation of an endogenous 67 kD molecular weight (mw) protein in the presence of double-stranded (ds) RNA. This protein kinase activity can also be assayed after partial purification on poly(I) X poly(C)-Sepharose under phosphatase-free conditions. By the use of this latter technique, here we investigated the distribution of the protein kinase activity in different cellular compartments. Most of the protein kinase activity is found in the post-ribosomal supernatant (S100) fraction, while a small portion of it is associated with the ribosomal salt wash (RSW: 0.5 M KCl eluate of ribosomal pellet) and nuclear fractions. These results are in contrast to several observations in the literature in which the protein kinase activity is thought to be associated with the ribosomal pellet. This controversy results from the conditions used for assay of the protein kinase activity. In fact, when the kinase is assayed in crude extracts supplemented with dsRNA, very little kinase activity is detectable in the S100 fraction compared to the RSW fraction. The S100 fraction contains a high level of phosphatase(s) activity which interferes with the protein kinase assay and might account for the misinterpretation observed in the literature. Some recent results have implicated a correlation between the dsRNA-dependent protein kinase responsible for the phosphorylation of the 67 kD protein and a polyamine-dependent protein kinase which phosphorylates a similar molecular weight protein, subunit of ornithine decarboxylase (Orn Dcase). Here, we show that Orn Dcase does not bind to poly(I) X poly(C)-Sepharose and polyamines do not substitute the requirement of dsRNA for the phosphorylation of the 67 kD protein.