IFN-treatment of B16-F1 versus B16-F10: relative impact on non-adaptive and T-cell-mediated immune defense in metastatic spread

Activation of the cGAS-STING-IRF3 Axis by Type I and II Interferons Contributes to Host Defense

Interferons (IFNs) activate JAK-STAT pathways to induce downstream effector genes for host defense against invaded pathogens and tumors. Here both type I (β) and II (γ) IFNs are shown that can activate the transcription factor IRF3 in parallel with STAT1. IRF3-deficiency impairs transcription of a subset of downstream effector genes induced by IFN-β and IFN-γ. Mechanistically, IFN-induced activation of IRF3 is dependent on the cGAS-STING-TBK1 axis. Both IFN-β and IFN-γ cause mitochondrial DNA release into the cytosol. In addition, IFNs induce JAK1-mediated tyrosine phosphorylation of cGAS at Y214/Y215, which is essential for its DNA binding activity and signaling. Furthermore, deficiency of cGAS, STING, or IRF3 impairs IFN-β- or IFN-γ-mediated antiviral and antitumor activities. The findings reveal a novel IRF3 activation pathway parallel with the canonical STAT1/2 activation pathways triggered by IFNs and provide an explanation for the pleiotropic roles of the cGAS-STING-IRF3 axis in host defense.

Isotope tracing reveals distinct substrate preference in murine melanoma subtypes with differing anti-tumor immunity

BACKGROUND

Research about tumor "metabolic flexibility"-the ability of cells to toggle between preferred nutrients depending on the metabolic context-has largely focused on obesity-associated cancers. However, increasing evidence for a key role for nutrient competition in the tumor microenvironment, as well as for substrate regulation of immune function, suggests that substrate metabolism deserves reconsideration in immunogenic tumors that are not strongly associated with obesity.

METHODS

We compare two murine models: immunologically cold YUMM1.7 and immunologically-hot YUMMER1.7. We utilize stable isotope and radioisotope tracer-based metabolic flux studies as well as gas and liquid chromatography-based metabolomics analyses to comprehensively probe substrate preference in YUMM1.7 and YUMMER1.7 cells, with a subset of studies on the impact of available metabolites across a panel of five additional melanoma cell lines. We analyze bulk RNA-seq data and identify increased expression of amino acid and glucose metabolism genes in YUMMER1.7. Finally, we analyze melanoma patient RNA-seq data to identify potential prognostic predictors rooted in metabolism.

RESULTS

We demonstrate using stable isotope tracer-based metabolic flux studies as well as gas and liquid chromatography-based metabolomics that immunologically-hot melanoma utilizes more glutamine than immunologically-cold melanoma in vivo and in vitro. Analyses of human melanoma RNA-seq data demonstrate that glutamine transporter and other anaplerotic gene expression positively correlates with lymphocyte infiltration and function.

CONCLUSIONS

Here, we highlight the importance of understanding metabolism in non-obesity-associated cancers, such as melanoma. This work advances the understanding of the correlation between metabolism and immunogenicity in the tumor microenvironment and provides evidence supporting metabolic gene expression as potential prognostic factors of melanoma progression and may inform investigations of adjunctive metabolic therapy in melanoma.

TRIAL REGISTRATION

Deidentified data from The Cancer Genome Atlas were analyzed.

A Dual Promoter System to Monitor IFN-γ Signaling in vivo at Single-cell Resolution

IFN-γ secreted from immune cells exerts pleiotropic effects on tumor cells, including induction of immune checkpoint and antigen presentation, growth inhibition, and apoptosis induction. We combined a dual promoter system with an IFN-γ signaling responsive promoter to generate a reporter named the interferon sensing probe (ISP), which quantitates the response to IFN-γ by means of fluorescence and bioluminescence. The integration site effect of the transgene is compensated for by the PGK promoter-driven expression of a fluorescent protein. Among five potential IFN-γ-responsive elements, we found that the interferon γ-activated sequence (GAS) exhibited the best performance. When ISP-GAS was introduced into four cell lines and subjected to IFN-γ stimulation, dose-dependency was observed with an EC50 ranging from 0.2 to 0.9 ng/mL, indicating that ISP-GAS can be generally used as a sensitive biosensor of IFN-γ response. In a syngeneic transplantation model, the ISP-GAS-expressing cancer cells exhibited bioluminescence and fluorescence signals in an IFN-γ receptor-dependent manner. Thus, ISP-GAS could be used to quantitatively monitor the IFN-γ response both in vitro and in vivo.Key words: in vivo imaging, tumor microenvironment, interferon-gamma, dual promoter system.

Lopinavir-NO, a nitric oxide-releasing HIV protease inhibitor, suppresses the growth of melanoma cells in vitro and in vivo

We generated a nitric oxide (NO)-releasing derivative of the anti-HIV protease inhibitor lopinavir by linking the NO moiety to the parental drug. We investigated the effects of lopinavir and its derivative lopinavir-NO on melanoma cell lines in vitro and in vivo. Lopinavir-NO exhibited a twofold stronger anticancer action than lopinavir in vitro. These results were successfully translated into syngeneic models of melanoma in vivo, where a significant reduction in tumour volume was observed only in animals treated with lopinavir-NO. Both lopinavir and lopinavir-NO inhibited cell proliferation and induced the trans-differentiation of melanoma cells to Schwann-like cells. In melanoma cancer cell lines, both lopinavir and lopinavir-NO induced morphological changes, minor apoptosis and reactive oxygen species (ROS) production. However, caspase activation and autophagy were detected only in B16 cells, indicating a cell line-specific treatment response. Lopinavir-NO released NO intracellularly, and NO neutralization restored cell viability. Treatment with lopinavir-NO induced only a transient activation of Akt and inhibition of P70S6 kinase. The results of this study identify lopinavir-NO as a promising candidate for further clinical trials in melanoma and possibly other solid tumours.

Viral-mimicking protein nanoparticle vaccine for eliciting anti-tumor responses

The immune system is a powerful resource for the eradication of cancer, but to overcome the low immunogenicity of tumor cells, a sufficiently strong CD8(+) T cell-mediated adaptive immune response is required. Nanoparticulate biomaterials represent a potentially effective delivery system for cancer vaccines, as they can be designed to mimic viruses, which are potent inducers of cellular immunity. We have been exploring the non-viral pyruvate dehydrogenase E2 protein nanoparticle as a biomimetic platform for cancer vaccine delivery. Simultaneous conjugation of a melanoma-associated gp100 epitope and CpG to the E2 nanoparticle (CpG-gp-E2) yielded an antigen-specific increase in the CD8(+) T cell proliferation index and IFN-γ secretion by 1.5-fold and 5-fold, respectively, compared to an unbound peptide and CpG formulation. Remarkably, a single nanoparticle immunization resulted in a 120-fold increase in the frequency of melanoma epitope-specific CD8(+) T cells in draining lymph nodes and a 30-fold increase in the spleen, relative to free peptide with free CpG. Furthermore, in the very aggressive B16 melanoma murine tumor model, prophylactic immunization with CpG-gp-E2 delayed the onset of tumor growth by approximately 5.5 days and increased animal survival time by approximately 40%, compared to PBS-treated animals. These results show that by combining optimal particle size and simultaneous co-delivery of molecular vaccine components, antigen-specific anti-tumor immune responses can be significantly increased.

Targeted disruption of the 2B4 gene in mice reveals an in vivo role of 2B4 (CD244) in the rejection of B16 melanoma cells

Murine 2B4 (CD244) is a cell surface receptor expressed on all NK cells, gammadelta-T cells, a subset of CD8(+) T cells, and all CD14(+) monocytes. 2B4 binds to CD48 with high affinity, and cross-linking 2B4 with anti-2B4 Ab in vitro causes activation of NK cells. To study its physiological role, we have generated, by gene targeting, mice deficient in the expression of this cell surface molecule. The expression of lymphoid cell surface markers on PBMC and splenocytes of mice homozygous for the mutation in 2B4 (2B4(-/-)) is identical to that in wild-type mice. However, thymocytes from female 2B4(-/-) mice, but not male 2B4(-/-) mice, have an increase in the immature CD4(-)/CD8(-) population. To investigate the in vivo role of 2B4, wild-type and 2B4(-/-) mice were injected with CD48(+) and CD48(-) metastatic B16 melanoma cells. Wild-type mice rejected CD48(+) melanoma poorly compared with CD48(-) tumor cells, suggesting that ligation of 2B4 by CD48 on melanoma cells is inhibitory. In keeping with this, male 2B4(-/-) mice showed enhanced ability to reject CD48(+) melanoma cells. However, female 2B4(-/-) mice poorly rejected both CD48(+) and CD48(-) melanoma cells, revealing a gender-specific and CD48-independent defect in mice lacking 2B4. In vitro and in vivo experiments reveal a complex role of NK cells in gender specificity.

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.

Murine B16 melanoma vaccination-induced tumor immunity: identification of specific immune cells and functions involved

Vaccination using inactivated B16 melanoma cells that have been treated in vitro for > 2 weeks with interferon-alpha (IFN-alpha) (B16alpha cells) has been shown to elicit a protective host antitumor immunity. In these studies, vaccination with B16alpha cells has been shown to provide protection against primary B16 tumor challenge, established B16 tumors, and metastatic B16 tumors. Specific immune cells and factors that might mediate this tumor immunity have now been evaluated. Macrophage depletion studies suggest that macrophage function is required for expression of tumor immunity either for processing of antigen or for cytokine production but that macrophage function is not involved in direct cytotoxicity against the B16 challenge tumor. CD8(+) T cell depletion studies show that cytotoxic T cell function is required for expression of tumor immunity. Syngeneic knockout mouse experiments offer further insights into the immune cells and factors that mediate the development and expression of tumor immunity. First, interleukin-12 (IL-12) knockout mouse experiments identify IL-12 as an important cytokine in mediating the development of tumor immunity. Second, specific knockout mouse experiments show that tumor immunity requires the function of CD4(+) T cells, CD8(+) T cells, and natural killer (NK) cells. Third, specific knockout mouse experiments show that tumor immunity does not require the function of B cells. The results suggest that vaccination with inactivated B16alpha cells induces an active, cell-mediated immunity to B16 melanoma cells. The tumor vaccination protocol with B16alpha cell vaccinations establishes a potent tumor immunity against B16 melanoma tumors in mice and may serve as a model for induction of tumor immunity against primary or secondary melanoma tumors in humans.

Adenovirus-mediated expression of interleukin-12 induces natural killer cell activity and complements adenovirus-directed gp75 treatment of melanoma lung metastases

Based on the knowledge that adenovirus (Ad)-mediated expression of the murine gp75 melanoma antigen (Adgp75) will effectively immunize mice against H2-matched B16 melanoma cells, probably via cell- mediated immune mechanisms, we hypothesized that Ad-mediated delivery of the murine interleukin-12 (IL-12) complementary DNA heterodimer would have independent therapeutic effects on tumor growth, and that the combination of the two vectors would work synergistically to augment the antitumor response. We evaluated the therapeutic effect of each vector alone and in combination for efficacy in C57BL/6 mice with preestablished (2 d) B16 melanoma-derived pulmonary metastases, using the number of lung metastases as the efficacy parameter. Intraperitoneal administration of Adgp75 (10(8) PFU) reduced tumor burden to 45 +/- 7% of controls (P < 0.01), and AdIL12 administration (10(8) PFU, intraperitoneally) reduced the number of metastases to 43 +/- 7% of controls (P < 0.01). The combination of Adgp75 (10(8) PFU, intraperitoneally) and AdIL12 (10(8) PFU, intraperitoneally) provided further protection (15 +/- 3%; P < 0.01 as compared with naive control; P < 0.01 compared with Adgp75 or AdIL12 alone). Mice receiving AdIL12 showed increased natural killer cell (NK cell) function in an in vitro cytotoxicity assay, with a dose- dependent lysis of YAC-1 cells and, to a lesser extent, lysis of B16 cells. To assess the relative contribution of major histocompatibility complex I (MHC I) Dependent and Independent activity in combination therapy with Adgp75 plus AdIL12, we performed adoptive transfer experiments, using splenocytes from mice receiving Adgp75, AdIL12, or Adgp75 + AdIL12, from among which NK cells had been selectively depleted in vitro prior to adoptive transfer. Each group showed significant decreases in tumor burden resembling those with primary treatment. Interestingly, NK-cell depletion from among cells derived from the Adgp75- and AdIL12-treated mice significantly altered the therapeutic response (P < 0.01 compared with the Adgp75 + AdIL12 group), suggesting a significant role of NK-cell-mediated cytolysis in vivo, although there was still a significantly reduced tumor burden (P < 0.01 compared with that of naive controls). Collectively, these data support the concept that the combination of AdIL12 and Adgp75 provides additive effects against pulmonary metastases of B16 melanoma by MHC-independent (NK cell) means as well as MHC-dependent cytotoxic lymphocyte means, suggesting that this therapy may be a useful adjuvant in the treatment of metastatic melanoma.

Efficacy of B16 melanoma cells exposed in vitro to long-term IFN-alpha treatment (B16alpha cells) as a tumor vaccine in mice

B16 melanoma cells exposed to >2 weeks of in vitro interferon-alpha (IFN-alpha) treatment (B16alpha cells) were UV inactivated and used for vaccination. This vaccination was efficacious against challenge with parental B16 cells in the absence of adjuvant therapy. Vaccinations based on parental cells and B16 cells exposed to short-term in vitro IFN-alpha treatment were not effective. The efficacy of B16alpha vaccination was evaluated using three B16 tumor models. Using intraperitoneal (i.p.) tumor challenge given after vaccination, vaccination efficacy depended on the concentration of IFN-alpha to which B16alpha cells were exposed, the number of inactivated B16alpha cells inoculated, the number of inoculations administered, and the amount of tumor burden. A significant fraction (30%) of vaccinated mice surviving initial challenge had durable immunity against a second parental tumor challenge. This immunity increased to 92% with administration of a single booster vaccination. Using metastatic tumor challenge given after vaccination, vaccination reduced lung metastases by approximately 67%. Using vaccination begun 3 days after subcutaneous (s.c.) tumor challenge, regression of established tumor occurred when vaccination was given i.p. (39%) or contralaterally s.c. (53%). Taken together, the results suggest that vaccination with inactivated B16alpha cells may serve as a model for induction of host tumor immunity against primary or secondary tumors.

Enhanced in vivo sensitivity of in vitro interferon-treated B16 melanoma cells to CD8 cells and activated macrophages

Mouse B16 melanoma cells maintained in vitro in the presence of interferon (IFN)-alpha become resistant to the in vitro antiproliferative effects of IFN-alpha. However, IFN-alpha-treated mice inoculated with these in vitro IFN-treated cells (B16 alpha res cells) have significantly increased life spans (ILS) and significantly higher cure rates than IFN-alpha-treated mice inoculated with B16 cells. This unexpectedly greater sensitivity of B16 alpha res cells to the in vivo antitumor effects of IFN-alpha was evaluated by in vivo cell depletion experiments. Depletion of either activated peritoneal macrophages or cytotoxic T lymphocytes (CTL) reduced the ILS of IFN-treated B16 alpha res-inoculated mice to a level comparable to that of IFN-treated B16-inoculated mice. Depletion of natural killer (NK) cells did not affect the ILS for IFN-treated B16 alpha res-inoculated mice. These studies indicate that activated macrophage and CD8 cell function, but not NK cell function, is important for the enhanced antitumor effects induced by IFN-alpha against B16 alpha res cells. Macrophage killing was unlikely to be mediated by TNF-alpha or IL-1 as B16 and B16 alpha res cells were equally sensitive to TNF-alpha and insensitive to IL-1 in vitro. Further, H-2K antigen expression is significantly more readily inducible on B16 alpha res cells than on B16 cells, consistent with enhanced CD8-mediated killing due to increased MHC class I antigen expression.

Implicating a role for immune recognition of self in tumor rejection: passive immunization against the brown locus protein

The immune system can recognize differentiation antigens that are selectively expressed on malignant cells and their normal cell counterparts. However, it is uncertain whether immunity to differentiation antigens can effectively lead to tumor rejection. The mouse brown locus protein, gp75 or tyrosinase-related protein 1, is a melanocyte differentiation antigen expressed by melanomas and normal melanocytes. The gp75 antigen is recognized by autoantibodies and autoreactive T cells in persons with melanoma. To model autoimmunity against a melanocyte differentiation antigen, mouse antibodies against gp75 were passively transferred into tumor-bearing mice. Passive immunization with a mouse monoclonal antibody against gp75 induced protection and rejection of both subcutaneous tumors and lung metastases in syngeneic C57BL/6 mice, including established tumors. Passive immunity produced coat color alterations but only in regenerating hairs. This system provides a model for autoimmune vitiligo and shows that immune responses to melanocyte differentiation antigens can influence mouse coat color. Immune recognition of a melanocyte differentiation antigen can reject tumors, providing a basis for targeting tissue autoantigens expressed on cancer.

A detailed study of the effects of in vitro interferon treatment on the growth of two variants of the B16 mouse melanoma in the lungs: evidence for non-specific effects

Interferon treatment increases the ability of tumour cells to colonize the lungs. Although it has been suggested that this effect can be explained by increases in the expression of MHC molecules the precise mechanism is still uncertain. The growth in the lungs of a low (F1) and a high colonizing variant (BL6) of the B16 mouse melanoma have been studied after in vitro treatment with interferon. Interferon-gamma, but not interferon-alpha/beta, increased the number of lung colonies formed after intravenous injection, but not after subcutaneous administration. Treatment also increased the sizes of the lung colonies formed and the number of radiolabelled cells retained by the lungs. However, no clear relationship was observed between the number of colonies formed and the concentration of interferon used. The effect of interferon on F1 was greater than on BL6, but the overall number of colonies formed was very similar. These results suggest that interferon increases the adhesiveness of these cell lines in a fairly non-specific manner, that seems unlikely to involve MHC molecules. As a results of this and other studies the importance of interferon in the process of tumour spread seems very questionable.

In search of the 'missing self': MHC molecules and NK cell recognition

Natural killer (NK) cells can defend an organism against a variety of threats, probably using several different strategies to discriminate between normal and aberrant cells. According to the 'missing self' hypothesis, one function of NK cells is to recognize and eliminate cells that fail to express self major histocompatibility complex (MHC) class I molecules. In this article Hans-Gustaf Ljunggren and Klas Kärre review in vivo studies with H-2-deficient targets that support this hypothesis. In vitro studies, some of which have given conflicting results, are interpreted within a multiple choice model for NK cell recognition. The authors derive testable predictions for how MHC class I molecules act in cases where they control a rate-limiting step in the NK cell-target interaction.

Changes in adhesive properties of tumor cells do not necessarily influence metastasizing capacity

BSp6S and BSp73AS are two rat tumors which grow locally after intra-footpad (ifp) application. BSp73ASML and BSp6AS are variants, which metastasize via the lymphatics. Both variants have lost adherence properties, as shown by in vitro culture on plastic surfaces, suggesting that loss of adherence may be accompanied by increased metastasizing capacity. However, after growth of BSp6S and BSp73AS in vitro on poly(2-hydroxyethylmethacrylate) (polyHEMA)-coated plates, which resulted in loss of adherence and spreading, and subsequent intravenous (iv) or ifp injection of non-adherent tumor cells into syngeneic rats, metastasizing capacity was not increased. It is concluded that loss of adherence may facilitate metastatic spread, but certainly is not sufficient for initiation.