Enhanced in vivo sensitivity to interferon with in vitro resistant B16 tumor cells in mice

Adipose Tissue-Derived Mesenchymal Stem Cells Suppress Growth of Huh7 Hepatocellular Carcinoma Cells via Interferon (IFN)-β-Mediated JAK/STAT1 Pathway in vitro

Interferon (IFN)-β and/or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) secreted by adipose tissue-derived mesenchymal stem cells (ASCs) have been proposed as key mechanistic factors in anti-cancer efficacy in lung cancer and breast cancer cells, where they act through paracrine signaling. We hypothesized that IFN-β and TRAIL produced by ASCs suppress proliferation of hepatocellular carcinoma cells (HCCs). The present study evaluated the anti-cancer effects of ASCs on HCCs in vitro. We found that indirect co-culture with ASCs diminished growth of Huh7 hepatocellular carcinoma cells with increased protein levels of p53/p21 and phosphorylated STAT1 (pSTAT1), without apoptosis. Treatment with ASC-conditioned medium (ASC-CM) also decreased growth of Huh7 cells through elevated p53/p21 and pSTAT1 signaling. ASC-CM-mediated inhibition of cell growth was neutralized in Huh7 cells treated with anti-IFN-β antibody compared to that in ASC-CM-treated Huh7 cells incubated with an anti-TRAIL antibody. Treatment with JAK1/JAK2 inhibitors recovered inhibition of growth in Huh7 cells incubated in ASC-CM or IFN-β via down-regulation of pSTAT1/p53/p21. However, treatment of IFN-β resulted in no alterations in resistance of Huh7 cells to TRAIL. Our findings suggest that ASCs decrease growth through activated STAT1-mediated p53/p21 by IFN-β, but not TRAIL, in Huh7 cells.

Interferon Alpha Signalling and Its Relevance for the Upregulatory Effect of Transporter Proteins Associated with Antigen Processing (TAP) in Patients with Malignant Melanoma

INTRODUCTION

Interferon alpha (IFNα) is routinely used in the clinical practice for adjuvant systemic melanoma therapy. Understanding the molecular mechanism of IFNα effects and prediction of response in the IFNα therapy regime allows initiation and continuation of IFNα treatment for responder and exclusion of non-responder to avoid therapy inefficacy and side-effects. The transporter protein associated with antigen processing-1 (TAP1) is part of the MHC class I peptide-loading complex, and important for antigen presentation in tumor and antigen presenting cells. In the context of personalized medicine, we address this potential biomarker TAP1 as a target of IFNα signalling.

RESULTS

We could show that IFNα upregulates TAP1 expression in peripheral blood mononuclear cells (PBMCs) of patients with malignant melanoma receiving adjuvant high-dose immunotherapy. IFNα also induced expression of TAP1 in mouse blood and tumor tissue and suppressed the formation of melanoma metastasis in an in vivo B16 tumor model. Besides its expression, TAP binding affinity and transport activity is induced by IFNα in human monocytic THP1 cells. Furthermore, our data revealed that IFNα clearly activates phosphorylation of STAT1 and STAT3 in THP1 and A375 melanoma cells. Inhibition of Janus kinases abrogates the IFNα-induced TAP1 expression. These results suggest that the JAK/STAT pathway is a crucial mediator for TAP1 expression elicited by IFNα treatment.

CONCLUSION

We suppose that silencing of TAP1 expression provides tumor cells with a mechanism to escape cytotoxic T-lymphocyte recognition. The observed benefit of IFNα treatment could be mediated by the shown dual effect of TAP1 upregulation in antigen presenting cells on the one hand, and of TAP1 upregulation in 'silent' metastatic melanoma cells on the other hand. In conclusion, this work contributes to a better understanding of the mode of action of IFNα which is essential to identify markers to predict, assess and monitor therapeutic response of IFNα treatment in the future.

Enhancement of antiproliferative activity of interferons by RNA interference-mediated silencing of SOCS gene expression in tumor cells

The suppressor of cytokine signaling (SOCS) proteins, negative regulators of interferon (IFN)-induced signaling pathways, is involved in IFN resistance of tumor cells. To improve the growth inhibitory effect of IFN-beta and IFN-gamma on a murine melanoma cell line, B16-BL6, and a murine colon carcinoma cell line, Colon26 cells, SOCS-1 and SOCS-3 gene expression in tumor cells was downregulated by transfection of plasmid DNA expressing short hairpin RNA targeting one of these genes (pshSOCS-1 and pshSOCS-3, respectively). Transfection of pshSOCS-1 significantly increased the antiproliferative effect of IFN-gamma on B16-BL6 cells. However, any other combinations of plasmids and IFN had little effect on the growth of B16-BL6 cells. In addition, transfection of pshSOCS-1 and pshSOCS-3 produced little improvement in the effect of IFN on Colon26 cells. To understand the mechanism underlining these findings, the level of SOCS gene expression was measured by real time polymerase chain reaction. Addition of IFN-gamma greatly increased the SOCS-1 mRNA expression in B16-BL6 cells. Taking into account the synergistic effect of pshSOCS-1 and IFN-gamma on the growth of B16-BL6 cells, these findings suggest that IFN-gamma-induced high SOCS-1 gene expression in B16-BL6 cells significantly interferes with the antiproliferative effect of IFN-gamma. These results indicate that silencing SOCS gene expression can be an effective strategy to enhance the antitumor effect of IFN under conditions in which the SOCS gene expression is upregulated by IFN.

Effect of electrically mediated intratumor and intramuscular delivery of a plasmid encoding IFN alpha on visible B16 mouse melanomas

Interferon alpha may be used as a single agent therapy for metastatic malignant melanoma or as an adjuvant to chemotherapy. Delivery of interferon alpha by gene therapy offers an alternative to recombinant protein therapy. Electrically mediated delivery enhances plasmid expression in a number of tissues, for instance skin, liver, muscle and tumors including melanomas. Here we compare the effect of delivery of a plasmid encoding mouse interferon alpha on growth of visible B16 mouse melanomas following electrically mediated delivery to muscle or directly to the tumor. Intratumoral delivery of interferon alpha plasmid not only slows melanoma growth, but induces complete, long term, regression. This effect was not observed after intramuscular delivery.

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.

T Cell-Mediated, IFN-γ-Facilitated Rejection of Murine B16 Melanomas

The murine melanoma cell line B16.F10 (H-2b) was used to study specific T cell responses that reject tumors. Stable B16 transfectants were established that express viral Ags, either the hepatitis B surface Ag (HBsAg) or the large tumor Ag (T-Ag) of SV40. B16 cells and their transfected sublines were CD40+CD44+ but expressed no (or low levels of the) costimulator molecules CD154 (CD40L), CD48, CD54, CD80, and CD86. Surface expression of MHC class I (Kb, Db) and class II (I-Ab) molecules by B16 cells was low, but strikingly up-regulated by IFN-γ. CD95 (Fas) and CD95 ligand (CD95L (FasL)) were “spontaneously” expressed by B16 cells growing in vitro in serum-free medium; these markers were strikingly up-regulated by IFN-γ. B16 cells coexpressing CD95 and CD95L were irreversibly programed for apoptosis. In vitro, noninduced B16 transfectants stimulated a specific IFN-γ release response, but no cytolytic response (in a 4-h assay) in MHC class I-restricted CTL; in contrast, IFN-γ-induced B16 targets were efficiently and specifically lysed by CTL. In vivo, B16 transfectants were specifically rejected by DNA-vaccinated syngeneic hosts through a T-dependent immune effector mechanism. The tumors showed evidence of massive apoptosis in vivo during the rejection process. The data suggest that CTL-derived IFN-γ enhances an intrinsic suicide mechanism of these tumor cells in addition to facilitating lytic interactions of effectors with tumor targets.

Lack of mda-6/WAF1/CIP1-mediated inhibition of cyclin-dependent kinases in interferon-alpha resistant murine B16 melanoma cells

Previously we demonstrated that IFN-alpha augments mda-6/WAF1 and inhibits cyclin-dependent kinases in a p53-independent fashion in B 16 murine melanoma cells. On the other hand, IFN-gamma activates p53 expression without affecting the mda-6/WAF1 system. Combination of the two IFNs is additive. B16 cells acquire IFN-alpha resistant but IFN-gamma sensitive phenotype after long term IFN-alpha treatment (B16alpha cells). Here we demonstrate the absence of mda-6/WAF1-associated repression of cyclin-dependent kinases, but the existence of p53-dependent c-myc inhibition in IFN-gamma-treated B16alpha cells. Clearly, selective desensitization of IFN-alpha related growth regulation does not influence the IFN-gamma associated pathway. Our results further support the coexistence of distinct growth regulatory mechanisms in B16 cells that can be activated by different IFN-types independently of each other.

B16 melanoma cells exposed in vitro to long-term IFN-alpha treatment (B16 alpha cells) as activators of tumor immunity in mice

Mice inoculated with B16 melanoma cells exposed to long-term in vitro IFN-alpha treatment (> or = 14 days, B16 alpha cells) but not short-term in vitro IFN-alpha treatment (24 h) exhibited an enhanced survival time. Enhanced survival time also occurred when inactivated B16 alpha cells were inoculated at the same time as live B16 cells. Further, an even greater improvement in survival time was observed when the inactivated B16 alpha cells were inoculated before live B16 cell challenge. No enhancement in survival time was observed when mice were inoculated with inactivated, untreated B16 cells. Enhancement of survival time by B16 alpha cells was unrelated to retrovirus surface antigen expression. Long-lasting protective immunity to B16 cells was observed in mice that survived B16 alpha cell, but not normal B16 cell, challenge and subsequent IFN treatment. It is evident that inoculation with inactivated B16 alpha cells, but not with inactivated untreated B16 cells, was able to prolong significantly the survival time of mice either simultaneously or subsequently challenged with live B16 cells. Additionally, survival of B16 alpha-inoculated but not B16-inoculated mice was accompanied by a durable immunity. Inoculation of inactivated B16 alpha cells may serve as a model for the induction of host immunity to a parental primary or secondary tumor.

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.