Protective activity of recombinant murine tumor necrosis factor-alpha and interferon-gamma against experimental murine lung carcinoma metastases.

A variety of biologic and synthetic agents protect BALB/c mice against experimental M109 micrometastases. We have presented evidence that eradication of these metastases is mediated by the activation of host macrophages to the tumoricidal state. We now present evidence that injection of H22, a neutralizing hamster IgG monoclonal antibody to murine interferon-gamma (IFN-gamma; macrophage activating factor), 2 days prior to i.v. tumor inoculation markedly increases the metastatic capacity of M109 lung carcinoma cells. Therefore, we tested several cytokines that induce or mediate macrophage-mediated cytotoxicity, including IFN-gamma, tumor necrosis factor-alpha, and interleukin-1 beta (IL-1 beta), for their ability to inhibit the development of experimental M109 lung metastases. Intraperitoneal treatment with recombinant murine (rMu) IFN-gamma (greater than or equal to 10,000 units/mouse) or recombinant murine TNF-alpha (greater than or equal to 10,000 units/mouse) produced greater than 60% inhibition of metastasis formation. Optimal therapy was observed when cytokines were administered 2 days prior to i.v. tumor cell inoculation. Neither IFN-gamma nor TNF-alpha inhibited colony formation of M109 cells in vitro, suggesting a host-mediated mechanism for antitumor activity. Peritoneal macrophages were primed for tumor cytotoxicity by treatment with either IFN-gamma or TNF-alpha. Intraperitoneal treatment with recombinant human IL-1 beta (1 X 10(5) units) lacked antimetastatic activity. The results further support the role of activated macrophages in the destruction of M109 micrometastases.

Modulation of interleukin-1 activity on murine thymocytes by various inhibitors of arachidonic acid oxygenation.

A variety of cyclooxygenase (FCO) and 5-lipoxygenase (5-LPO) inhibitors were tested for their ability to modulate murine thymocyte proliferation induced by IL-1 and suboptimal levels of the mitogen phytohemagglutinin (PHA). The contribution of drug toxicity to inhibition of 3H-thymidine incorporation was estimated by measuring MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) formazan production in the thymocyte cultures at the end of the assay. Cyclosporin A and dexamethasone, two positive control compounds, potently inhibited thymocyte proliferation at extremely low concentrations (0.01 and 0.001 micrograms/ml respectively), although activity roughly paralleled toxicity. In contrast, 5-LPO inhibitors (AA-861, BW-755c, and ETYA), but not selective FCO inhibitors (ibuprofen and indomethacin), suppressed lymphoproliferation at nontoxic concentrations, suggesting that products of the 5-LPO pathway may mediate the thymocyte proliferative response induced by IL-1/PHA. Attempts to counteract the suppressive activity of 5-LPO inhibitors by addition of leukotriene (LT) B4, LTC4, LTE4, 5-HETE, and 15-HETE were unsuccessful.

Studies of the antitumor activity of (2-alkoxyalkyl)- and (2-alkoxyalkenyl)phosphocholines.

Analogues of the synthetic antitumor phospholipid ALP (1-octadecyl-2-methyl-sn-glycero-3-phosphocholine; alkyl lysophospholipid) in which the 1-ether oxygen atom has been removed have been prepared and evaluated for in vitro and in vivo anticancer activity. Compounds are presented in which the saturated long chain varies in length from 8 to 25 carbon atoms. Sites of unsaturation are also incorporated into the framework in some examples. In particular, rac-(2-ethoxyeicosyl)phosphocholine (10) displays the best in vivo activity of the chemical series against a variety of transplanted tumors and activates murine peritoneal macrophages to express tumor cytotoxicity in vitro. However, 10 does not offer the wide spectrum of antitumor activity we feel necessary to warrant further study.

Inability of anti-asialo-GM1 and 2-chloroadenosine to abrogate maleic anhydride-divinyl ether-induced resistance against experimental murine lung carcinoma metastases.

Both macrophages and natural killer cells have been implicated in the antimetastatic activity of maleic anhydride-divinyl ether (MVE-5). In the present study, we attempted to utilize anti-asialo-GM1 antibody and 2-chloroadenosine, agents that kill natural killer (NK) cells and macrophages, respectively, to determine the relative contribution of each effector cell type to the overall host defense. These agents were tested in the M109 lung metastasis model in syngeneic BALB/c mice, and the cytotoxic activities of both peritoneal macrophages and splenic NK cells were followed. The most profound antitumor effect was observed when MVE-5 was given before rather than after i.v. tumor inoculation. Treatment i.p. with MVE-5 at 20 mg/kg produced greater than 98% inhibition of subsequent lung metastases when given 2 days prior to tumor. Anti-asialo-GM1 antibody (25 mg/kg, i.p.) and 2-chloroadenosine (50 mg/kg, i.p.) were administered concurrently with MVE-5. Although each agent exhibited greater selectivity for its respective target, the early (Day 2) inhibitory response was nonspecific. By Day 5 after MVE-5 treatment, 2-chloroadenosine only inhibited macrophage tumoricidal activity, and conversely, anti-asialo-GM1 antibody only inhibited NK reactivity. Despite the ability of these agents to increase survival of metastases in control animals, they only slightly abrogated the antimetastatic activity of MVE-5. Our data suggest that caution should be exercised in using these agents to discriminate macrophage and NK responses.

Macrophage involvement in the antitumor activity of a synthetic acyltripeptide (FK-565) against experimental lung carcinoma metastases.

Resident peritoneal macrophages can be activated to develop cytotoxicity against P815 mastocytoma target cells following incubation in vitro with either D-lactoyl-L-alanyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl-(L)-gl ycine (FK-156), heptanoyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl-(D)-alani ne (FK-565), or bacterial lipopolysaccharide (LPS) at a minimum concentration of 10 micrograms/ml. Subthreshold levels of hybridoma-derived macrophage activating factor (MAF) markedly potentiated this activity. In an experimental metastasis model, subcutaneous or intraperitoneal treatment with FK-565 (1 to 10 mg/kg) markedly inhibited lung metastasis formation when administered 2-4 days prior to i.v. tumor inoculation. Moreover, this protective activity could be abrogated by the selective macrophage inhibitor, 2-chloroadenosine, suggesting that activated macrophage were responsible for the antimetastatic activity of FK-565.

Effects of various inhibitors of arachidonic acid oxygenation on macrophage superoxide release and tumoricidal activity.

Macrophages release a variety of arachidonic acid metabolites after treatment with various membrane triggers or particulate stimuli. We examined the role of phospholipase and lipoxygenase inhibitors in the modulation of superoxide production and tumor cytolysis by murine macrophages. Superoxide was induced by the soluble stimulus, phorbol myristate acetate (PMA), and the particulate stimulus, opsonized zymosan, and was measured by the reduction of ferricytochrome c with the use of a micro ELISA reader. Macrophage-mediated tumor cytolysis was induced by hybridoma-derived, macrophage-activating factor (MAF) and was quantitated by 51Cr release from P815 target cells. In both assays, 72-hr peptone-elicited macrophages were used. Dexamethasone, and to a lesser degree hydrocortisone, inhibited superoxide release and MAF-induced tumor cytolysis. Inhibition in the superoxide assay required pretreatment with corticosteroid. Only the gold compound, auranofin, inhibited superoxide when given simultaneously with stimulant. Other phospholipase inhibitors, including mepacrine and 4-bromophenacyl bromide, and several lipoxygenase inhibitors, including BW755c, nordihydroguaiaretic acid (NDGA), and 5,8,11,14-eicosatetraynoic acid (ETYA), failed to modulate either macrophage response at nontoxic concentrations. At the concentrations tested in the tumoricidal and superoxide assays, mepacrine and 4-bromophenacyl bromide inhibited the release of 14C-arachidonic acid from macrophages stimulated with opsonized zymosan. Our data strongly suggest that corticosteroids suppress macrophage superoxide production and tumoricidal function by a nonphospholipase-dependent mechanism.

Comparison of various assays to quantitate macrophage activation by biological response modifiers.

Macrophages treated with various compounds that enhance host antitumor resistance exhibit measurable changes in metabolism, function, and surface antigens. In this study, murine peptone-induced peritoneal macrophages were stimulated in vitro by bacterial lipopolysaccharide (LPS), muramyl dipeptide (MDP), and poly I.poly C. They were subsequently compared in their ability to release superoxide and act as tumoristatic and tumoricidal effector cells. Superoxide generation was assayed by the reduction of ferricytochrome C. All three compounds failed to induce significant O2- release, unless the cells were also treated with phorbol myristate acetate (PMA). MDP was most active in potentiating the PMA response. In the tumor growth inhibition assay, cytostatic activity was comparable for all three compounds and did not exceed 32 percent. The combination of subthreshold levels of these compounds and hybridoma-derived MAF acted synergistically to induce potent cytostatic activity. In the chromium release assay, LPS and poly I.poly C rendered macrophages cytolytic for P815 target cells at concentrations greater than or equal to 1 microgram/ml. In contrast, significant cytolysis was observed with MDP only at 100 micrograms/ml. Defining precisely the effect of various biological response modifiers on several parameters of macrophage function may facilitate use of these agents in cancer therapy.

Potentiation of nonspecific immunotherapy of experimental lung metastases by indomethacin.

Intraperitoneal treatment with the interferon inducer, maleic anhydride-divinyl ether copolymer (MVE), has previously been demonstrated to effectively reduce metastatic growth in the lungs and prolong survival times of BALB/c mice bearing the syngeneic Madison lung (M109) carcinoma. Resistance to lung metastasis formation induced by MVE appears to result from an activation of alveolar macrophage function. Since E-type prostaglandins (PGE) suppress the cytotoxic activity of activated macrophages, we sought to determine the effect of indomethacin, a prostaglandin synthetase inhibitor, on the antimetastatic activity of MVE. An artificial metastasis model was developed in which single-cell suspensions of the M109 tumor were injected i.v. into BALB/c mice. A 52,600 molecular weight fraction of MVE (MVE-5) was administered i.p. at 20 mg/kg two days prior to tumor inoculation. MVE-5 treatment produced greater than 80 percent reduction in macroscopic lung lesion formation at Day 15 and Day 19 after tumor inoculation and a resultant 45 percent increase in lifespan. Chronic administration of indomethacin in the drinking water at 10 micrograms/ml potentiated the MVE-5 antitumor induced macrophage activation in vivo. In the absence of any evidence for an interaction between indomethacin and circulating M109 cells, it was felt that the potentiating effect could be best explained in terms of interference with PGE-mediated feedback inhibition of macrophage functional activity.