Anti-tumor effects of interferon in mice injected with interferon-sensitive and interferon-resistant friend leukemia cells. IV. Definition of optimal treatment regimens

Type I and II IFNs inhibit Merkel cell carcinoma via modulation of the Merkel cell polyomavirus T antigens

Merkel cell carcinoma (MCC) is a rare and highly aggressive skin cancer associated with the Merkel cell polyomavirus (MCV). As MCC cell lines show oncogene addiction to the MCV T antigens, pharmacologic interference of the large T antigen (LTA) may represent an effective therapeutic approach for this deadly cancer. In this study, we investigated the effects of IFNs on MCC cell lines, especially on MCV-positive (MCV(+)) lines. Type I IFNs (i.e., Multiferon, a mix of different IFN-α subtypes, and IFN-β) strongly inhibited the cellular viability. Cell-cycle analysis showed increased sub-G fractions for these cells upon IFN treatment indicating apoptotic cell death; these effects were less pronounced for IFN-γ. Notably, this inhibitory effect of type I IFNs on MCV(+) MCC cell lines was associated with a reduced expression of the MCV LTA as well as an increased expression of promyelocytic leukemia (PML) protein, which is known to interfere with the function of the LTA. In addition, the intratumoral application of Multiferon resulted in a regression of MCV(+) but not MCV(-) MCCs in vivo. Together, our findings show that type I IFNs have a strong antitumor effect, which is at least in part explained by modulation of the virally encoded LTA.

IFN-alpha2b and thalidomide synergistically inhibit tumor-induced angiogenesis

Angiogenesis is an absolute requirement for tumor growth and metastasis. The purpose of this study was to evaluate the antiangiogenic activity of interferon-alpha2b (IFN-alpha2b) and thalidomide, as single agents and in combination. The murine dermis model was used to assess tumor-induced angiogenesis in nude mice. Human ACHN (renal), NIH-OVCAR-3 (ovarian), LNCaP (prostate), and SK-Mel-1 (melanoma) tumor cells were inoculated intradermally into the flanks of nude mice. IFN-alpha2b and thalidomide, administered daily, were effective inhibitors of angiogenesis induced by all four tumor types. The combination of IFN-alpha2b and thalidomide caused a synergistic decrease in mean vessel count in tumors that were resistant to the antiproliferative effects of IFN-alpha2b and thalidomide in vitro. This enhanced suppression of angiogenesis translated into synergistic antitumor activity in a xenograft model. Pegylated IFN-alpha (PEG-IFN-alpha2b) (10(6) U) administered once in 10 days was as effective as daily IFN-alpha2b treatment (10(6) U x 10 days). IFN-alpha2b and thalidomide have potentiated antiangiogenic activity when used in combination. A single dose of PEG-IFN-alpha2b (10(6) U) was as effective at suppressing vessel growth as an equivalent dose of IFN-alpha2b given daily for 10 days.

Interferon-alpha in tumor immunity and immunotherapy

Interferon-alpha (IFN-alpha) is a pleiotropic cytokine belonging to type I IFN, currently used in cancer patients. Early studies in mouse tumor models have shown the importance of host immune mechanisms in the generation of a long-lasting antitumor response to type I IFN. Recent studies have underscored new immunomodulatory effects of IFN-alpha, including activities on T and dendritic cells, which may explain IFN-induced tumor immunity. Reports on new immune correlates in cancer patients responding to IFN-alpha represent additional evidence on the importance of the interactions of IFN-alpha with the immune system for the generation of durable antitumor response. This knowledge, together with results from studies on genetically modified tumor cells expressing IFN-alpha, suggest novel strategies for using these cytokines in cancer immunotherapy and in particular the use of IFN-alpha as an immune adjuvant for the development of cancer vaccines.

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.

Host humoral and cellular immune mechanisms in the continued suppression of Friend erythroleukemia metastases after interferon alpha/beta treatment in mice

DBA/2 mice were injected intravenously with 2 x 10(6) 3C18 Friend erythroleukemia cells (FLC), a cell line resistant to interferon alpha/beta (IFN-alpha/beta). Although daily administration of mouse IFN-alpha/beta markedly increased the mean survival time, most IFN-treated mice continued to harbor FLC in different organs. To investigate the mechanisms responsible for this persistent suppression of FLC growth in IFN-treated mice, we undertook a series of adoptive transfer experiments with sera and spleen cells. Sera from FLC-injected, IFN-treated mice were very effective in conferring protection on DBA/2 mice even when injected systemically (intravenously) 18-24 h before intravenous challenge with FLC. These sera also exhibited antitumor activity when injected subcutaneously or intraperitoneally together with FLC. The protective factor in serum was shown to be an immunoglobulin. FLC-injected, IFN-treated mice developed antibodies to FLC demonstrable by radioimmunoassay and complement-dependent cytotoxicity. Sera from these mice recognized a specific 65-kD FLC membrane antigen(s) not detectable on membrane extracts from RBL-5 or ESb tumor cells, or on normal spleen cells. FLC-injected, IFN-treated mice also developed a specific cellular response demonstrable by transfer of protection with spleen cells injected intravenously or subcutaneously. Analysis of the responsible spleen cell populations indicated that the effector cells were neither T nor B cells. These results demonstrating the importance of host humoral and cellular immune mechanisms in the persistent suppression of FLC in IFN-treated mice may be relevant to the use of IFN-alpha/beta in patients in whom tumors may regress and tumor cells may then remain latent for extended periods of time.

Enhanced survival of IFN-alpha augmented IL-2 therapy of pulmonary metastases: efficacy comparable to interleukin-2 and lymphokine activated killer cells

Recently, we reported enhanced tumor reduction using recombinant interferon-alpha A/D (IFN) combined with interleukin-2 (IL-2). Similar synergism affecting survival was assessed in treatment of both early and advanced pulmonary metastases. This combination was compared with the current "standard" IL-2 and lymphokine activated killer (LAK) therapy in the treatment of early and advanced pulmonary metastases. C57BL/6 mice injected via tail vein with the weakly immunogenic methylcholanthrene-induced murine fibrosarcoma MCA-106 were treated intraperitoneally with IL-2 (50,000 units b.i.d.), IFN (50,000 units q.d.), LAK (2.5-10 x 10(7)), or various combinations of above. Treatment of both early Day 3 and advanced Day 10 metastases using IL-2/IFN reduced metastases and prolonged survival over both controls and IL-2 alone. It was superior to IFN, LAK, and IFN/LAK. Addition of LAK to IL-2/IFN demonstrated no added benefit. Although no mortality was observed during treatment of Day 3 metastases, treatment of Day 10 advanced pulmonary metastases for 9 days with IL-2/IFN resulted in early deaths (33%) without visible tumor, indicating possible toxicity of treatment. These results show survival benefit of IL-2/IFN over IL-2, IFN, or LAK treatment in the therapy of early and advanced pulmonary metastases, albeit with added toxicity. Its relative simplicity and comparable efficacy to the more complex and costly IL-2/LAK provide important advantages for potential clinical applications.

Anti-tumor effects of interferon in mice injected with interferon-sensitive and interferon-resistant Friend erythroleukemia cells. VIII. Role of the immune system in the inhibition of visceral metastases

DBA/2 mice were injected i.v. with IFN alpha/beta-resistant 3CI8 Friend erythroleukemia cells (FLC) which metastasize to the liver and spleen. IFN alpha/beta treatment of FLC-injected mice increased their survival time and these mice developed a resistance to a second challenge with FLC. The efficacy of IFN alpha/beta in increasing the survival time was compared between normal immunocompetent and immunodeficient mice. The anti-tumor action of IFN was markedly reduced or abolished in newborn DBA/2 mice, in adult athymic nu/nu and beige DBA/2 mice, and in BALB/c scid/scid mice. To determine the phenotype of the effector cells involved, FLC-injected DBA/2 mice were treated with antibodies to asialo-GMI, CD4, or CD8 antigens, or with cyclosporin A or silica. IFN alpha/beta treatment proved much less effective in these mice, indicating that a variety of effector cell types participated in the IFN-induced suppression of visceral metastases. Thus, an intact immune system appears to be essential to obtain optimal therapeutic effects of IFN alpha/beta in this experimental model.

In vivo antiproliferative effects of gamma-interferon and tumor necrosis factor alpha in a rat renal cell carcinoma model system

We have investigated the antiproliferative activities of recombinant rat-gamma-interferon and recombinant human tumor necrosis factor alpha in a rat renal cell carcinoma model system. The tumor was transplanted subcutaneously, the drugs were administered peritumorally. Gamma-interferon treatment starting two days after tumor implantation resulted in a dose-dependent growth inhibiting effect. Tumor necrosis factor alpha was only effective at the highest concentration. Different combinations of the drugs have additive or synergistic antiproliferative effects. The combination of both highest doses completely inhibited tumor growth without any obvious toxic effects on the rats. Rechallenge of the cured rats with a tumor piece in the contralateral flank did not result in a tumor specific immune response. Shortening of the treatment period to two weeks resulted in an increased lag-period, but finally all tumors started to grow. Furthermore, the anti-tumor effect was dependent on tumor volume at start of therapy. Monotherapy could not inhibit tumor growth of an established tumor. The combination with both highest doses, however, inhibited tumor growth even when treatment was started at a tumor volume of two to five cm3. Treatment with gamma-interferon and tumor necrosis factor is most effective at low tumor burden. These studies suggest that clinical application of these drugs is most effective in an adjuvant setting.

Natural resistance in mice against Friend leukemia cells. II. Studies with in vivo passaged interferon-sensitive and interferon-resistant cell clones

Experiments were designed to test the presence of antitumor natural resistance (NR) in DBA/2 mice against highly oncogenic in vivo passaged histocompatible Friend leukemia cells (FLC-V). NR was measured in vivo as rapid clearance of radiolabeled cells from different organs or as growth inhibition in lethally irradiated mice. Interferon-sensitive (745) or interferon-resistant (3C18) lines were used. Organ clearance studies showed that young recipients eliminate cells more rapidly than old mice. Moreover, depressive (e.g., cyclophosphamide or carrageenen) or enhancing (e.g., poly (I:C) or Friend leukemia virus infection) agents of NR function modulate accordingly leukemia cell clearance. Similar results were obtained testing tumor growth in lethally irradiated hosts, although modulating agents were substantially less effective in this system. Both FLC-745-V and FLC-3C18-V lines were equally susceptible to NR. Therefore, these data provide further support to the hypothesis that exogenous IFN capable of suppressing the growth of both lines could act via enhancement of the NR function.

Antitumor effects of interferon

Both natural and recombinant interferons have shown definite antitumor activity in some patients with some malignancies. The history of the development of interferon as an antitumor agent is reviewed, with special attention to its use in mice bearing 'spontaneously' appearing tumors and in mice injected with tumorigenic viruses or transplantable tumor cells. Interferon can inhibit the growth of primary tumors as well as the development of metastases. These experimental results have provided some indications as to the probable optimal regimens of interferon administration in man. Although the mechanisms of interferon's antitumor activity are unknown, it seems likely that interferon can act directly on the tumor cells as well as on the tumor bearing host.

Antibody to mouse interferon alpha/beta abrogates resistance to the multiplication of Friend erythroleukemia cells in the livers of allogeneic mice

Friend erythroleukemia cells (FLC) (H-2d) injected intravenously into adult syngeneic DBA/2 or allogeneic C57B1/6 (H-2b) or C3H (H-2k) mice lodge in the liver but only multiply in the liver of syngeneic mice. Our results indicated that endogenous IFN-alpha/beta was a crucial factor in preventing the multiplication of FLC in the liver of adult allogeneic mice. (a) Treatment of allogeneic adult C57B1/6 or C3H mice with polyclonal antibody to mouse IFN-alpha/beta (but not antibody to IFN-gamma) completely abrogated the resistance to the multiplication of FLC in the liver and 87% of tumor-injected, antibody-treated C57B1/6 mice died with extensive tumor involvement of the liver. In contrast, after intravenous inoculation FLC do not multiply at all (or very rarely) in the liver of adult C57B1/6 mice left untreated or treated with a variety of control globulins, and no deaths occurred. (b) 8 h after intravenous inoculation of FLC, poly(A)+ RNA hybridizable with specific DNA probes for mouse IFN-alpha or -beta (but not -gamma) was present in the liver of injected C57B1/6 mice. Using the expression of the Mx protein as an indicator of the presence of IFN-alpha/beta, we showed that Mx+ congenic C57B1/6 mice injected with FLC exhibited a marked increase in the expression of the Mx protein in the liver, spleen, kidney and lung, and this increase was blocked by treatment of mice with antibody to IFN-alpha/beta. The possibility that different host mechanisms are elicited depending on the site of tumor growth in allogeneic mice is discussed. IFN-alpha/beta appears to be of particular importance in determining the resistance of the liver to FLC in allogeneic mice.

Enhanced in vivo therapy of pulmonary metastases with interferon and interleukin-2

Interleukin-2 (IL-2) can mediate in vivo tumor regression at high doses. To enhance this efficacy, we studied the effect of adding a human hybrid recombinant interferon alpha A/D (rHuIFN-alpha-A/D) because of its known in vitro augmentation of immune-mediated tumoricidal activity. C56BL/6 mice bearing established pulmonary metastases induced by the iv injection of the methylcholanthrene-induced fibrosarcoma MCA 106 were treated for 12 days with intraperitoneal injections of (1) Hanks' balanced salt solution, (2) recombinant IL-2, (3) rHuIFN-alpha-A/D, and (4) a combination of IL-2 and HuIFN-alpha-A/D. IL-2 and interferon each had some antitumor activity. However, maximal reduction of pulmonary metastases consistently resulted from combining IL-2 with interferon. In two of four experiments, this combination was significantly better compared to either IL-2 or interferon treatment alone. The most potent regimen was 12 days of IL-2 (50,000 units bid) together with rHuIFN-alpha-A/D (50,000 units ip qd). No consistent pattern of proliferative or cytotoxic activity was found against a panel of stimulator and target cells. These results demonstrate enhanced antitumor efficacy of combining recombinant interferon alpha and IL-2 against established pulmonary metastases. Potential clinical applications are suggested by these data.

Interferon treatment markedly inhibits the development of tumor metastases in the liver and spleen and increases survival time of mice after intravenous inoculation of Friend erythroleukemia cells

To investigate the effect of interferon treatment on the development of tumor metastases, DBA/2 mice were injected i.v. with 2 X 10(6) Friend erythroleukemia cells (FLC) (equivalent to about 5 X 10(5) LD50). FLC multiplied rapidly in the liver and spleen and all untreated or control treated mice died between 7 and 12 days. Daily treatment of mice with potent preparations of mouse interferon alpha/beta was initiated 3 to 72 hr after i.v. inoculation of tumor cells, at times when FLC were already present in the liver and spleen. Interferon treatment resulted in a 100 to 1,000-fold inhibition of the multiplication of FLC in the liver and spleen and a marked increase in mean survival time. Small numbers of tumor cells persisted in the liver and spleen in some interferon-treated mice and could be recovered by bioassay several weeks after tumor inoculation. Most interferon-treated mice died with tumor in the ensuing months. Three of 34 interferon-treated mice were considered cured as they were alive at 386, 325 and 284 days after tumor inoculation. Daily treatment of tumor-inoculated mice with human recombinant interferons alpha D and alpha BDDD, which had antiviral activity on mouse cells in culture, also increased the survival time of mice injected i.v. with FLC. The use of the interferon-resistant 3C18 line of FLC suggests that the marked inhibition of development of established liver and spleen metastases was not due to a direct effect of interferon on the tumor cells, but was host-mediated.

Anti-tumor effects of interferon in mice injected with interferon-sensitive and interferon-resistant Friend leukemia cells. VI. Adjuvant therapy after surgery in the inhibition of liver and spleen metastases

Adult DBA/2 mice were injected s.c. with the highly malignant, interferon-resistant 3C18 line of Friend erythroleukemia cells (FLC). Eight or 9 days after established s.c. tumors had developed, the primary tumor was excised and mice were treated i.p. with either mouse interferon alpha/beta or a control preparation. At the time of surgery, mice already had tumor cells in the liver. All control-treated mice died in the ensuing 2 weeks with extensive tumor metastases in the liver and spleen. Interferon treatment resulted in an inhibition of the development of liver and spleen metastases and a markedly increased survival time. We conclude that interferon alpha/beta is effective as adjuvant therapy after surgery for metastatic disease in mice.