Polyinosinic-polycytidylic acid inhibits chemically induced tumorigenesis in mouse skin

Study on the Effect of Statolon on Methylcholanthrene Oncogenesis in Mice

Subcutaneous methylcholanthrene oncogenesis was produced in two strains of mice and statolon, an interferon inducer, was administered at different treatment regimens and at doses only just sufficient to induce an antiviral state in the host. No statistically significant extension of tumor appearance periods was observed.

Effect of Polyinosinic-polycytidylic Acid on Humoral and Cellular Immunity

Experiments have been performed to investigate the effects of polyinosinic-polycytidylic acid (Poly I:C) on humoral and cellular immunity in RFM/Un mice. Poly I:C, 0.1 mg i.p., administered 48 and 24 hours before 4 x 108 SRBC produced a marked reduction in direct PFC/106 cells and /spleen, and in the hemoagglutinin titre on the 3rd, 4th and 5th days after antigen inoculation. On the other hand, an increase in PFC and hemoagglutinin titre was observed on the 7th and 8th days. Histological examination revealed absence of germinal centers in the spleen on the 4th day. Poly I:C administered 24 and 48 hours after antigen produced an increase in direct PFC and hemoagglutinin titre on the 4th, 5th and 6th day. Histological examination disclosed evident germinal centers in the spleen on the 4th day after antigen. Poly I:C administered 5 to 1 days before antigen produced a markedly depressed direct PFC response in the groups injected 1 and 2 days before antigen. Recovery of the immune response was progressive and complete in groups injected 4 days before antigen. To study the effect of Poly I:C on secondary response to SRBC, two groups of animals injected with Poly I:C before or after antigen were reinjected with 2 x 108 SRBC. Secondary response evaluated by hemoagglutinin titre at varying intervals after the immunization disclosed in both groups a much higher antibody titre than that seen in controls receiving SRBC only. Mice injected with Poly I:C 48 or 24 hours before reimmunization with 2 x 108 SRBC were no different from controls on 3rd and 4th days in regard to number of indirect PFC as well as hemoagglutinin titre. Finally, mice immunized with two SRBC injections and then treated with Poly I:C on alternating days for 30 days had a much higher titre of hemoagglutinins than controls. In order to study the effect of Poly I:C on the cellular immune response, spleen cells from animals receiving Poly I:C 6–5 days before sacrifice were cultured in vitro with phytohemoagglutinin. DNA synthesis subsequent to PHA stimulation was evaluated by increase in 3HTdR incorporation. Cells from animals which had received Poly I:C demonstrated a remarkably higher 3HTdR uptake than cells from control animals. On the other hand, 5 x 106 spleen cells obtained from RFM/Un mice injected with Poly I:C as above were inoculated in 1–4 day old (RFM/Un x CBA/H)F1 hybrids. These were then sacrificed on day 8 and spleen indices calculated. Experimental animals disclosed GVH activity similar to that of controls (spleen index 2.3). From the results it is clear that if Poly I:C is injected before antigen the primary immune response is deppressed, whereas it is enhanced when Poly I:C is administered after antigen. On the other hand, the secondary response is generally enhanced regardless of the time of Poly I:C administration. Moreover, in Poly I:C –- treated animals there is an enhancement of PHA –- responsive cells while the GVH reactions is unchanged. As Poly I:C is capable of enhancing immune reactivity, the possibility of its use in antineoplastic chemotherapeutic protocols is suggested.

Comparison of Complete Carcinogenesis and Tumor Initiation and Promotion in Mouse Skin: The Induction of Papillomas by Tumor Initiation-Promotion a Reliable Short Term Assay

Skin tumors can be induced by the sequential application of a subthreshold dose of a carcinogen (initiation phase), followed by repetitive treatment with a weak or noncarcinogenic tumor promoter. Using a two-stage system to induce tumors in Senear mice there is a very good dose-response relationship between the induction of the number of papillomas per mouse at early times (10 to 20 weeks) and the final carcinoma incidence after longer latency (20 to 50 weeks). This system can be used not only to determine the tumor initiating and promoting activities of a compound but if the agent is given repeatedly by itself one can also determine if it is a complete carcinogen, i.e., if it has both tumor initiating and promoting activity. With the exception of a few pure tumor initiators, there is in general a good qualitative and quantitative correlation between the ability of a polycyclic aromatic hydrocarbon (PAH) to act as a complete carcinogen and to act as a tumor initiator in mouse skin. In addition, if the agent is given concurrently with a known complete carcinogen or a tumor initiator one can also determine if the agent has co-carcinogenic or co-tumor initiating activity or even possibly anticarcinogenic activity. Likewise, if the agent is given concurrently with a known tumor promoter one can determine if the agent has co-promoting or anti-pro-moting activity. There is a good correlation between the tumor-initiating activities of PAH and their abilities to bind covalently to DNA. In addition, various inhibitors of PAH tumor initiation show a strong correlation with their abilities to inhibit the binding of the PAH to DNA and their anti-tumor initiating activities. There is also a good correlation between the promoting abilities of phorbol esters to promote tumors and their abilities to induce ornithine decarboxylase (ODC), cell proliferation and dark basal keratinocytes. When other nonpromoting hyperplastic agents are used, only dark cell induction correlates with promotion. Certain polyamines and prostaglandins can enhance phorbol ester tumor promotion. Anti-inflammatory steroids, retinoids, and protease inhibitors are potent inhibitors of tumor promotion. They inhibit tumor promotion by inhibiting either the 12-0-tetradecanoylphorbol-13-acetate (TPA) induced cell proliferation, ODC and/or dark basal keratinocytes. Certain weak promoters such as mezerein which mimics TPA in many biochemical and morphological effects are potent second step promoters in a two-stage promotion regimen.

Toll-like receptor-agonists in the treatment of skin cancer: history, current developments and future prospects

This review will briefly cover some important aspects of skin structure and function before touching upon fundamental principles of neoplastic cell growth in the skin and some of the important molecular pathways involved. After presenting evidence for a role of the immune system in shaping the development of skin cancer, concepts for tumor immunotherapy with TLR-agonists are introduced from a historical point of view. Subsequently, the use of synthetic DNA, synthetic RNA and synthetic small immunostimulatory molecules for immunotherapy of early forms of epithelial carcinoma (actinic keratoses) and melanoma (lentigo maligna), as well as for advanced metastatic melanoma, is comprehensively presented. Finally, current developments and future prospects for immunotherapy of occult or unresectable melanoma metastastases, the most important clinical problem today, are discussed.

Interferon-alpha/beta can impede development of carcinogen-induced squamous-cell tumors in the esophagus of C57B1 mice

The effect of treatment with murine interferon-alpha/beta preparations on diethylnitrosamine-induced squamous-cell tumors in the esophagus of C57B1 mice was investigated. Diethylnitrosamine was administered in the drinking water for 18 weeks. Interferon was given intraperitoneally during the same 18 weeks or from the end of the period of carcinogen exposure until termination of the experiment. In mice given interferon and diethylnitrosamine synchronously, a significantly lower tumor index (number of tumors/cm of esophageal mucosa) was observed as compared to all control groups. Treatment with interferon after the administration of the carcinogen was terminated had no effect on the appearance of tumors. These data suggest that interferon therapy can exert certain effects on carcinogenesis.

Induction of suppressor T cells and inhibition of contact hypersensitivity in mice by 12-O-tetradecanoylphorbol-13-acetate and its analogs

12-O-tetradecanoylphorbol-13-acetate (TPA) and its analogs were surveyed for their abilities to modify contact hypersensitivity (CHS) responses in SENCAR mice. Sensitization of dorsal skin with 2,4-dinitrofluorobenzene (DNFB) and subsequent challenge of the ear 5 d later resulted within 24 h in ear swelling and increased vascular permeability (as measured by the extravasation of Evans Blue dye). Treatment of dorsal or ventral skin with TPA 4 times (application made every 3 or 4 d) prior to sensitization on the dorsum inhibited subsequent induction of CHS by DNFB challenge. Maximum suppression of CHS required sensitization at the site of TPA treatment. Suppression occurred over a narrow dose range of TPA (0.1-1.0 micrograms), and qualitatively correlated with the tumor incidences scored in an initiation-promotion multistage skin carcinogenesis experiment. Multiple applications (4x) of the promoters phorbol-12,13-dibenzoate (10 micrograms) and mezerein (2 micrograms) also suppressed CHS, whereas the non-promoter phorbol (20 micrograms) and the first stage tumor promoter 4-O-methyl TPA (20 micrograms) had no effect. Adoptive transfer of splenocytes isolated from mice pre-treated with TPA prior to DNFB sensitization inhibited the development of CHS in recipient mice that were sensitized and challenged with DNFB, but not oxazolone. Splenocyte preparations depleted of T lymphocytes prior to transfer could not suppress CHS in recipient mice. Conversely, suppressive activity was concentrated in splenocyte preparations depleted of adherent cells/monocytes. Collectively, these studies demonstrate that TPA treatment of murine epidermis prior to sensitization with hapten can inhibit subsequent hapten-dependent elicitation of CHS. This suppression is mediated in part by antigen-specific suppressor T cells. Furthermore, there is a qualitative correlation between the complete and second stage in vivo tumor-promoting activities of TPA and its analogs, and their abilities to inhibit CHS.

The effect of interferon on carcinogenesis by N-ethyl-N'-nitro-N-nitrosoguanidine in the duodenum of mice

The inhibitory effect of murine interferon alpha/beta (Mu-IFN) on the induction of adenocarcinoma of the duodenum in C57BL/6 mice given N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG) was examined. ENNG was given continuously in drinking water for 4 weeks and Mu-IFN was given intraperitoneally for 12 weeks. Then, the duodenal tumors of mice were examined stereomicroscopically and histologically. The level of IFN activity and natural killer (NK) activity were evaluated after an intraperitoneal single injection of Mu-IFN, and the level of NK activity was evaluated 2, 5 and 8 weeks after giving ENNG and Mu-IFN. In the mice given Mu-IFN, the incidence of duodenal tumors was significantly decreased (P less than 0.01), compared with that in mice given ENNG alone. Further, anti-asialo GM1 was given intraperitoneally every 5 days for 8 weeks to depress NK function and the incidence and size of duodenal tumors were examined. The results indicated that NK cells also have an important effect on the process of carcinogenesis. These data suggest that chemoprevention with IFN may be feasible.

The development of contact hypersensitivity in mouse skin is suppressed by tumor promoters

The ability of tumor promoters to suppress the development of contact hypersensitivity (CHS) was assessed by the mouse ear swelling assay. Application of the complete or second stage tumor promoters phorbol-12-myristate-13-acetate (PMA, 2 micrograms), croton oil (1%), benzoyl peroxide (20 mg), mezerein (2 micrograms), or phorbol-12-retinoate-13-acetate (PRA, 2 micrograms) to the abdominal surface of CF-1 female mice for 1 week (three treatments) prior to the sensitization of the same location with 0.5% 1-chloro-2,4-dinitrobenzene (DNCB) resulted in a 50% suppression (p less than 0.05) of the CHS response to DNCB. The first stage tumor promoters 4-O-Me-PMA (80 micrograms), calcium ionophore A23187 (80 micrograms), hydrogen peroxide (15%) and the non-promoting analogs phorbol-12,13-diacetate (PDA, 20 micrograms), phorbol (80 micrograms) or acetone did not suppress the response. The suppression of the development of CHS caused by PMA was dependent on the promoter being applied at the site of induction and was inhibited by application of the phospholipase A2 inhibitor dibromoacetophenone (100 micrograms), the lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA, 100 micrograms), or the antiinflammatory steroid fluocinolone acetonide (2 micrograms). Application of PMA or mezerein 24 h prior to challenge with DNCB, to the ears of mice previously sensitized with DNCB resulted in a significant enhancement of the ear swelling response by 60% and 110%, respectively, compared with controls. The results demonstrate that tumor promoters suppress the development of CHS, and suggest the possibility that second stage promotion may involve suppression of the development of a tumor specific immune response.

Indomethacin and poly I:C in the inhibition of carcinogen-induced bladder cancer in an experimental animal model

Fischer rats, in whom superficial transitional cell cancers of the urinary bladder were induced by the carcinogen N-[4-(5- nitrofuryl )-2-thiazolyl] formamide, were inoculated intraperitoneally with either phosphate buffered saline, indomethacin (a prostaglandin synthetase inhibitor), poly I:C (an interferon inducer), or indomethacin together with poly I:C. While indomethacin alone appeared to have a significant albeit variable inhibitory effect on tumor size, poly I:C had a far more pronounced significant inhibitory effect. The combination of poly I:C and indomethacin together, however, led to the greatest inhibition in tumor growth, and in some instances, to tumor regression. Splenic lymphocytes from the same animals demonstrated enhanced natural cytotoxicity after treatment with poly I:C. Surprisingly, levels of natural cytotoxicity seen in animals treated with indomethacin and poly I:C together were lower than those seen with poly I:C alone. No enhancement of cytotoxicity could be demonstrated in vitro in lymphocytes from indomethacin-treated animals. Macrophages were also treated in this system under identical conditions. However, the activity of macrophages alone and of macrophages and lymphocytes together did not appear to be modified either by indomethacin alone or by the combination of prostaglandin synthetase inhibition and interferon induction together, the combination of which in vivo was suggested to be most effective in controlling tumor progression. Further studies to determine timing of these interactions and doses of immune response modifiers in order to characterize mechanisms possibly at work in modifying tumor growth in this system therefore seem highly indicated.

Modulation of stimulatory effects of poly(I:C) on natural cytotoxicity by anti-interferon

The effect of polyinosinic . polycytidylic acid [poly(I:C)] on tumor inhibition in the context of natural cytotoxicity enhancement prompted further assessment of mechanisms underlying these effects. In vivo inoculations of poly(I:C) led to dose-dependent cytotoxicity enhancement in splenic lymphocytes and nonrecruited peritoneal exudate cells (monocytes). Although cytotoxicity of macrophages and lymphocytes together was less than that seen with lymphocytes alone, addition of indomethacin to these samples did not enhance cytotoxicity. In vivo inoculation of anti-interferon prior to poly(I:C) treatment prevented poly(I:C)-induced enhancement of natural cytotoxicity. Tumor growth was significantly inhibited by poly(I:C) treatment. Prior inoculation of anti-interferon antiserum partially prevented such tumor inhibition. Taken together, the tumor-inhibitory effect of poly(I:C) in this model may be mediated by interferon production and, at least in part, by interferon-induced enhancement of natural cytotoxicity.

Macrophage depletion and manipulation of enhanced immune response in an animal model of bladder cancer

In a transplantable model of bladder cancer the inhibition of tumor growth by polyinosinic:polycytidylic acid (poly(I:C], concomitant stimulation of natural killer cell activity, and inhibition of both effects by prior inoculation with anti-interferon antiserum have been previously observed. The possible role of macrophages in these interactions is explored. Depletion of peritoneal macrophages by silica at concentrations that did not markedly depress natural killer cell activity was found to inhibit the enhancement of natural killer cell activity by subsequent in vivo poly(I:C) inoculation. Inoculation with silica also seemed to abrogate the tumor inhibitory effect of poly(I:C) treatment. To determine whether effects of poly(I:C) on natural cytotoxicity and tumor growth were mediated through production of interferon, anti-interferon antiserum (alpha-IF) was inoculated prior to poly(I:C) therapy. Tumor growth appeared to be uneffected by this maneuver even though poly(I:C)-induced enhancement of natural cytotoxicity was inhibited. Taken together, both macrophages and interferon may play a pivotal role in the immune response in both a stimulatory and a suppressive capacity. Additional study on such influences may be important if in vivo manipulation of these regulatory effects is to be accomplished successfully.

Stimulation of cell proliferation by tumor-promoting phorbol esters and inhibition by some inhibitors of tumor promotion in suspension cultures of a human lymphoblastoid cell line

A human lymphoblastoid cell line, SCC-1, was established from the bone marrow of a patient with acute nonlymphocytic leukemia. 12-O-Tetradecanoylphorbol-13-acetate (TPA) enhanced cell proliferation of SCC-1 cells in suspension culture. A positive correlation was found between the tumor-promoting activities of several plant diterpenes and their enhancing effects on the growth of SCC-1 cells. Various compounds that inhibit tumor promotion were tested for their capacity to inhibit cell proliferation at a physiological concentration. These compounds were not cytotoxic but cytostatic even at high concentration.

Interferon and spontaneous cytotoxicity in man. I. Enhancement of the spontaneous cytotoxicity of peripheral lymphocytes by human leukocyte interferon

A purified preparation of human leukocyte interferon used at this hospital in the treatment of malignant diseases was tested for its ability to modify the spontaneous cytotoxicity of peripheral lymphocytes from healthy donors. The inhibitory effect of allogeneic lymphocytes on the (3H)thymidine incorporation of a lymphoblastoid cell line, Raji, was augmented by the presence of interferon or by pretreatment of the lymphocytes with interferon. This form of pretreatment also increased lymphocytes' capacity for reducing the number of surface-adherent tumor cells in a microassay. Moreover, lymphocytes treated with interferon exhibited an enhanced cytotoxic capacity for target cells on incubation with such cells labelled with 51CR.

Influence of immune stimulators on viral leukemogenesis

Injection of RNA, extracted from statolon by the SDS-phenol method, into FLV-infected mice 24 hours before SRBC immunization restored the immune response to SRBC to normal levels. Leukemosuppression was observed in 50% of the RNA-treated FLV-infected mice. These RNA-treated mice were clinically normal 25 days after infection, whereas all untreated infected mice developed erythroleukemia. Furthermore, all RNA-treated mice with suppressed erythroleukemia produced antibody which was cytotoxic for Friend leukemia cells. Our studies, and studies by others, indicate that the immunostimulatory and leukemosuppressive principle in statolon appears to be a dsRNA.

Viral interference and interferon

Viral interference is a phenomenon for which a cell infected by a virus becomes resistant toward a second outcoming infection by a superinfectant virus. Even though other mechanisms are known, it can be assumed that most cases of viral interference occurring in natural conditions are mediated by interferon, a low molecular weight protein produced by the infected cell in response to a stimulus provided by viral nucleic acid(s). The interferon produced by a cell can migrate to other cells not yet involved by the spreading infection, transmitting to them the antiviral-resistant state. Available evidence indicates that interferon acts by inducing the production of a second cellular protein, called antiviral protein, which is directly responsible for the antiviral state through some alterations of the cellular, virus-directed, proteosynthetic system. In addition to the antiviral activity, the interferon system can affect the growth of several nonviral organisms and that of tumour cells; rather controversial effects have been shown also on the immune responses; the mechanisms underlying these effects are still nuclear. However a relationship to the specific immune system is suggested also by the finding that interferon can be liberated by sensitized T-lymphocytes following antigenic stimulus. Activation of the interferon system can be operated in vitro and in vivo also by several non-viral substances of various nature, such as nucleic acids, polysaccharides, aromatic amines, etc. This fact, considering that interferon has been shown to play a critical role on the mechanisms of recovery from viral infections, may open new perspectives for their possible prophylactic and/or therapeutic use in viral diseases. This problem can be approached also by administering exogenous interferon. Encouraging preliminary results have so far been obtained either with interferon or its inducers. However, several problems of various nature have to be resolved before considering the actual use of interferon system as a wide range antiviral drug in natural viral diseases of man.

Poly(inosinic acid)-poly(cytidylic acid) inhibition of DNA synthesis in synchronized HeLa cells

Inhibition by double-stranded polyribonucleotides of DNA synthesis in synchronized HeLa cultures is dose- and time-dependent. Inhibition by poly(I.C) primarily affected late G(1) and early S phases of the cell cycle. Single-stranded polynucleotides, native calf-thymus DNA, and yeast RNA had no effect. Radioautography showed that after 2-hr exposure the synthetic polyribonucleotides were predominantly inside the nucleus. The results extend the spectrum of action of double-stranded RNA.

Protective Action of Polyinosinic-Polycytidylic Acid in Virus and Transplanted Leukemias of the Mouse

The inhibitory effects of polynucleotides on leukemia development and transplantability have been studied. RFM/Un mice, injected neonatally with leukemogenic Graffi virus, received 0.02 mg polyinosinic-polycytidylic acid (Poly I:C) intraperitoneally, twice a week, for two months starting 24 hrs after virus injection. Leukemia incidence in treated mice was significantly reduced, i.e., 56% with a mean latent period of 19 weeks as compared to 87% and 15 weeks latency in the control animals. RFM/Un adult mice, injected intravenously with different cell doses of two transplantable syngeneic leukemias, received four doses of 0.1 mg Poly I:C on alternate days starting 24 hrs after cell transplant. The evaluation of neoplastic nodules on the spleen surface according to the method of Bruce and Van Der Gaag (2) was the parameter of leukemic growth. Mice receiving Poly I:C showed a marked reduction in spleen nodule counts for all cell doses of both leukemia lines and histological examination of the spleen confirmed actual decrease in leukemic foci and disclosed enlargement of germinal centers and periarteriolar areas of lymphoid follicles. To investigate whether Poly I:C is capable of abolishing the state of immunological tolerance (operationally speaking) to cellular virus-induced antigens (CBA x C57BL)F1 adult mice, injected neonatally with Graffi virus, received 0.20 mg Poly I:C i.p. together with 104 or 105 cells from a syngeneic transplantable leukemia originally induced by Graffi virus. No differences in leukemic deaths were observed between Poly I:C treated virus-injected animals and controls, even though normal mice receiving Poly I:C and 10* cells showed 50% survival compared to 0% in control groups. Leukemic cells incubated in vitro in HE-MEM containing 0.1, 1, 10 or 100 μg Poly I:C/ml for 2, 4, 8 and 24 hrs (37 °C, 5% CO2) did not exhibit significant changes in viability as evaluated by phase contrast microscopy. On the basis of present and previous results (6), the possible mechanisms of antineoplastic action exerted by polynucleotides are discussed. It is concluded that while interferon production by synthetic RNAs may represent a major inhibiting factor in virus-induced tumors, non specific stimulation of immune reactivity and direct effect on cell metabolism and replication may play a significant role in other neoplastic conditions.

Inducers of interferon inhibit the mitotic response of liver cells to partial hepatectomy

Partially hepatectomized mice were injected with inducers of interferon, and the mitotic activity of liver cells was measured. The inducers were polyriboinosinic.polyribocytidylic acid, poly(I.C), Newcastle disease virus, and statolon. Each inhibited the mitosis of liver cells. Poly(I.C) was effective in doses as low as 1 mug per mouse. Polyriboinosinic acid, poly(I), had no inhibitory effect. These results extend the spectrum of action of inducers of interferon to inhibition of mitotic division of an aneoplastic, nonaneuploid mammalian cell.