Augmentation of mouse natural killer cell activity by LS 2616, a new immunomodulator

The quinoline-3-carboxamide LS 2616 administered to mice in drinking water increased spontaneous cytotoxicity against YAC-1 cells in a dose-dependent manner. The enhancement of spontaneous cytotoxicity was found to be mediated by NK cells, as judged by their lack of adherence to nylon wool columns, relative resistance to treatment with antibodies to Thy-1.2 and complement, and almost total abrogation after depletion of asialo-GM1+ cells. Enhancement of NK activity was evident after 2 days of treatment, was maximal after 4 days, and remained elevated during the 14-day exposure period studied. NK activity returned to control levels 4 days after cessation of treatment. NK activity was significantly increased in spleen, peripheral blood, lymph nodes, and bone marrow of LS 2616-treated mice, while activity in peritoneal exudate cells and thymus remained low. LS 2616 was able to elevate NK activity in several mouse strains studied, including mice homozygous for the beige gene. Serum interferon levels were not increased during treatment with LS 2616. Combined injection of the interferon inducer Poly I:C and LS 2616 did not increase NK activity above that of animals injected with Poly I:C alone. However, Poly I:C, in contrast to LS 2616, increased NK activity in peritoneal exudate cells. Studies at the single cell level revealed that LS 2616 increased NK activity by increasing the number of lytically active cells via recruitment of new target-binding cells and not by increasing the lytic activity of pre-existing binders.     

Immunologic and toxicologic study of disaccharide tripeptide glycerol dipalmitoyl: a new lipophilic immunomodulator

A new lipophilic immunomodulator, disaccharide tripeptide glycerol dipalmitoyl (DTP-GDP), has been synthesized and evaluated for its immunologic activity and toxicology. DTP-GDP alone or in liposomes is more effective as an adjuvant and in activating macrophages compared with muramyldipeptide (MDP). Preclinical studies demonstrate no evidence of toxicity, including vasculitis. DTP-GDP in liposomes has shown antitumor activity in phase I clinical trials.     

Experience with mutagenicity testing of new drugs: viewpoint of a regulatory agency

Quality and quantity of mutagenicity testing were analyzed for drugs with new active compounds which were submitted for registration in the Federal Republic of Germany from mid 1982 to mid 1986. A large variety of deficiencies was found, applying to selection and number of mutagenicity tests as well as to test performances. Only 65 out of the 144 drugs submitted for registration were tested sufficiently in the initial phase of registration. From 1982 to 1986 this situation has not been changed markedly. Inadequate test performance still remains the main reason for insufficient testing, leading in some cases to artificially positive results. For in vivo tests the selection of test species was mainly motivated by technical reasons and not by characteristics of the test compound. Most of the insufficiencies were eliminated during the second phase of registration. In some cases insufficient mutagenicity testing led to consequences concerning risk-benefit assessment of the drug and its regulation.     

Comparison of the mutagenicity of amsacrine with that of a new clinical analogue, CI-921

The mutagenicity of CI-921, the 4-methyl-5-(N-methyl)carboxamide derivative of the clinical antileukaemia agent, amsacrine, has been assessed using both bacterial and mammalian cells. CI-921 is distinguished from amsacrine in its high activity against some experimental tumours and is currently undergoing phase I clinical trial. Like 9-aminoacridine and amsacrine, CI-921 is mutagenic to the Salmonella typhimurium frameshift tester strain TA1537, but shows no sign of inducing base pair changes in strain TA100. In Chinese hamster cell culture, however, it differs from 9-aminoacridine in causing extensive chromosomal aberrations and an increase in mutations at the hypoxanthine-guanine phosphoribosyltransferase locus. It induces the formation of tightly packed and multilayered colonies in treated cultures of C3H/10T1/2 cells, but its action differs from that of benzo[a]pyrene, which induces type III fibroblastic multilayered colonies. Side-by-side comparison of the mutagenic properties of CI-921 and amsacrine showed no substantial differences at similar toxicity, suggesting that the increased lipophilicity and DNA-binding affinity of CI-921, which are thought to contribute to its increased antitumour activity, do not concomitantly increase the efficiency of in vitro mutagenesis or cell transformation.     

Statins as a newly recognized type of immunomodulator

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, or statins, are effective lipid-lowering agents, extensively used in medical practice. Statins have never been shown to be involved in the immune response, although a report has indicated a better outcome of cardiac transplantation in patients under Pravastatin therapy. Major histocompatibility complex class II (MHC-II) molecules are directly involved in the activation of T lymphocytes and in the control of the immune response. Whereas only a limited number of specialized cell types express MHC-II constitutively, numerous other cells become MHC-II positive upon induction by interferon gamma (IFN-gamma). This complex regulation is under the control of the transactivator CIITA (refs 6,7). Here we show that statins act as direct inhibitors of induction of MHC-II expression by IFN-gamma and thus as repressors of MHC-II-mediated T-cell activation. This effect of statins is due to inhibition of the inducible promoter IV of the transactivator CIITA and is observed in several cell types, including primary human endothelial cells (ECs) and monocyte-macrophages (Mstraight phi). It is of note that this inhibition is specific for inducible MHC-II expression and does not concern constitutive expression of CIITA and MHC-II. In repressing induction of MHC-II, and subsequent T-lymphocyte activation, statins therefore provide a new type of immunomodulation. This unexpected effect provides a scientific rationale for using statins as immunosuppressors, not only in organ transplantation but in numerous other pathologies as well.     

Radioprotective effects of the immunomodulator AS101

Ammonium trichloro(dioxyethylene-O-O')tellurate (AS101) is a new synthetic compound previously described by us as having immunomodulating properties and minimal toxicity. Clinical trials are currently in progress with AS101 on AIDS and cancer patients. We found that AS101 was capable of inducing spleen cells and peritoneal exudate cells to secrete high quantities of CSF and IL-1. Because IL-1 has been previously described as a radioprotector and CSF may induce in vivo the proliferation of hemopoietic cells, we designed the present study in order to evaluate the effects of prolonged in vivo injections of AS101 on protection against lethal doses of irradiation, on the recovery pattern of precursor cells, and on the functioning of bone marrow (BM) and spleen cells of mice undergoing sublethal doses of treatment. We demonstrate that pretreatment with AS101 protects mice from lethal effects of ionizing radiation. AS101 was also found to significantly increase the number of BM and spleen cells, the absolute number of granulocyte macrophage-CFU and the secretion of CSF by BM cells. All were tested 9 days after sublethal dose of irradiation was administered. AS101 was found to have all of these radioprotective effects only when administered to mice before irradiation treatment. Moreover, the compound was found to enhance the proportion of CFU-S that enters the S phase of the cell cycle. These findings indicate that AS101 may be a promising agent to be used in reducing the time needed for reconstitution of hemopoietic cells after irradiation treatment.     

Toxicity and mutagenicity of plumbagin and the induction of a possible new DNA repair pathway in Escherichia coli.

Actively growing Escherichia coli cells exposed to plumbagin, a redox cycling quinone that increases the flux of O2- radicals in the cell, were mutagenized or killed by this treatment. The toxicity of plumbagin was not found to be mediated by membrane damage. Cells pretreated with plumbagin could partially reactivate lambda phage damaged by exposure to riboflavin plus light, a treatment that produces active oxygen species. The result suggested the induction of a DNA repair response. Lambda phage damaged by H2O2 treatment were not reactivated in plumbagin-pretreated cells, nor did H2O2-pretreated cells reactivate lambda damaged by treatment with riboflavin plus light. Plumbagin treatment did not induce lambda phage in a lysogen, nor did it cause an increase in beta-galactosidase production in a dinD::Mu d(lac Ap) promoter fusion strain. Cells pretreated with nonlethal doses of plumbagin showed enhanced survival upon exposure to high concentrations of plumbagin, but were unchanged in their susceptibility to far-UV irradiation. polA and recA mutants were not significantly more sensitive than wild type to killing by plumbagin. However, xth-1 mutants were partially resistant to plumbagin toxicity. It is proposed that E. coli has an inducible DNA repair response specific for the type of oxidative damage generated during incubation with plumbagin. Furthermore, this response appears to be qualitatively distinct from the SOS response and the repair response induced by H2O2.     

On the mutagenicity of nitroimidazoles

Regarding mutagenicity, metronidazole is one of the best-investigated compounds of the nitroimidazoles. This drug is mutagenic on bacteria, especially if base-pair tester strains are used and bacterial nitroreductases are present. The serum levels attained in man after intake of this drug are sufficient to cause mutations in bacteria. Furthermore, interaction with and binding to DNA occurs under anaerobic conditions and sometimes DNA breaks are observed. However, metronidazole does not show mutagenic activity in mammalian cells in vitro; the micronucleus test is negative and chromosome aberrations are only found under anaerobic conditions. With microbial systems the mutagenicity of 47 nitroimidazoles has been investigated. Only 4 compounds were always negative in the applied test systems. Because with base-pair tester strains mutagenicity was assessed, this class of compounds should be regarded as a base-pair mutagen. In fungi, some compounds (e.g. ZK 26173 and azathioprine) are potent mutagens, whilst with most investigated nitroimidazoles only a weak or no mutagenic activity could be detected. Somewhat similar observations have been made in tests with Drosophila melanogaster, a test for gene mutations in mammalian cells, the micronucleus test, cytogenic tests and the dominant lethal test. The reduction products of metronidazole, misonidazole and 1-methyl-2-nitro-5-vinylimidazole, cause DNA damage if the nitro group is reduced in the presence of DNA. Reduction products are formed by microbes in the gut or by mammalian cells under anaerobic conditions. No teratological effect due to metronidazole or most other nitroimidazoles has been observed. Metronidazole is carcinogenic in mice and rats, and dimetridazole in rats. Up to the present, no carcinogenic effects have been observed in man. Azathioprine is probably carcinogenic for man. It is unlikely that the therapeutic applications of the presently used nitroimidazoles, except for azathioprine, will cause an increase in the tumor incidence in man or will cause other genotoxic effects, although such effects cannot be excluded with certainty.     

On the mutagenicity of nitrofurans

UV (254 nm)-irradiated Tr phages infecting excision-repair-proficient E. coli cells undergo host-cell reactivation (HCR). Typically, the resulting survival curve is of a hetero-component type, i.e. extrapolation of the shallower curve component to zero UV dose gives ordinate values p < 1. This characteristics is accentuated if HCR is inhibited by UV irradiation of host cells prior to phage infection, or by the presence of caffeine or acriflavine. With increasing strenght of the inhibitory condition, p decreases and the slope of the steeper curve component increases, but the slope of the shallower curve component changes very little. In contrast, single-component curves are observed for Tr infecting excision-repair-deficient host cells, or for Tr undergoing photoenzymatic repair in these cells either with or without inhibition by caffeine or preirradiation of host cells. This indicates that throughout the population UV lesions are photorepaired or photorepair-inhibited independently of one another.Discussion of various possible interpretations of the hetero-component curves in the case of HCR suggests the existence of two modes of excision repair, one of them leading to a high degree of interdependence between repair events within individual phage particles. This mode of repair, which determines the slope and position of the shallower curve component, requires within an infected cell the occurrence of a “critical event”, whose probability is considerably lower than i and decreases with the strength of HCR inhibition. The other mode, leading to independent repair events, is of minor importance under our usual plating conditions, but plays a predominant role in liquid-holding recovery of the phage.     

Orthophenylphenol mutagenicity in a human cell strain

Orthophenylphenol (OPP), a widely used fungicide, induced ouabain-resistant (OuaR) mutants in a ultraviolet (UV)-sensitive human RSa cell strain and the frequencies increased in a dose-related fashion. OPP was a more potent mutagen than UV at doses related to equal survival. These results suggest that OPP has a mutagenic activity and that further experiments on this chemical are warranted.     

Investigation of the mutagenicity of ethylphenylglycidate

EPG and an in vitro digest of EPG by pepsin and pancreatin simulating mammalian digestion have been examined for genotoxicity in 4 mutagenicity tests employing different genetic endpoints. In the Salmonella reverse mutation assay, EPG showed only slight mutagenic activity against TA100, a strain responsive to base-pair exchange activity, in the presence of S9 mix. In vitro EPG was mutagenic for CHO-K1-BH4 cells with or without metabolic activation, the activity being greater in the presence of metabolic activation. In the in vitro SCE test, EPG was clastogenic for CHO-K1-BH4 cells independent of metabolic activation. EPG also induced transformation of C3H T10 1/2 mouse fibroblasts in vitro, producing both type II and type III foci. Subjecting an EPG solution to a simulated mammalian digestion process lowers the genotoxic activity of the solution.     

The testing of 4CMB, 4HMB and BC for mutagenicity in a new Neurospora crassa heterokaryon

This genetic system permits both point mutations and deletions to be detected in the same experimental material. 4CMB and BC are regarded as being mutagenic in this system. 4HMB induced mutations in only 1 of the 3 treatment protocols used, and its mutagenicity is questionable.     

Apparent mutagenicity of N-nitrosothiazolidine caused by a trace contaminant

The identification of N-nitrosothiazolidine (NTHZ) in smoked meat products prompted us to evaluate this compound for mutagenicity by the Salmonella assay. NTHZ was prepared in 99 + % purity by the nitrosation of the cysteamine-formaldehyde reaction mixture without isolation and purification of the resulting amine, and from thiazolidine, directly. Mutagenic activity was observed with TA100 without metabolic activation in the former, but not the latter preparation. An examination of the precursors, reaction intermediates, and HPLC separation of the NTHZ from the mutagenic product demonstrated that the genotoxic activity resulted from a synthesis-produced trace contaminant.