Elevated expression of Fn14 in non-small cell lung cancer correlates with activated EGFR and promotes tumor cell migration and invasion

Alpha-Ketoglutarate Regulates Tnfrsf12a/Fn14 Expression via Histone Modification and Prevents Cancer-Induced Cachexia

Previous studies have shown that inhibition of TNF family member FN14 (gene: TNFRSF12A) in colon tumors decreases inflammatory cytokine expression and mitigates cancer-induced cachexia. However, the molecular mechanisms underlying the regulation of FN14 expression remain unclear. Tumor microenvironments are often devoid of nutrients and oxygen, yet how the cachexic response relates to the tumor microenvironment and, importantly, nutrient stress is unknown. Here, we looked at the connections between metabolic stress and FN14 expression. We found that TNFRSF12A expression was transcriptionally induced during glutamine deprivation in cancer cell lines. We also show that the downstream glutaminolysis metabolite, alpha-ketoglutarate (aKG), is sufficient to rescue glutamine-deprivation-promoted TNFRSF12A induction. As aKG is a co-factor for histone de-methylase, we looked at histone methylation and found that histone H3K4me3 at the Tnfrsf12a promoter is increased under glutamine-deprived conditions and rescued via DM-aKG supplementation. Finally, expression of Tnfrsf12a and cachexia-induced weight loss can be inhibited in vivo by DM-aKG in a mouse cancer cachexia model. These findings highlight a connection between metabolic stress and cancer cachexia development.

Deciphering a cell death-associated signature for predicting prognosis and response to immunotherapy in lung squamous cell carcinoma

BACKGROUND

Lung squamous cell carcinoma (LUSC) is a subtype of non-small cell carcinoma, accounting for about 30% of all lung cancers. Yet, the evaluation of prognostic outcome and therapy response of patients with LUSC remains to be resolved. This study aimed to explore the prognostic value of cell death pathways and develop a cell death-associated signature for predicting prognosis and guiding treatment in LUSC.

METHODS

Transcriptome profiles and corresponding clinical information of LUSC patients were gathered from The Cancer Genome Atlas (TCGA-LUSC, n = 493) and Gene Expression Omnibus database (GSE74777, n = 107). The cell death-related genes including autophagy (n = 348), apoptosis (n = 163), and necrosis (n = 166) were retrieved from the Kyoto Encyclopedia of Genes and Genomes and Gene Ontology databases. In the training cohort (TCGA-LUSC), LASSO Cox regression was used to construct four prognostic signatures of respective autophagy, apoptosis, and necrosis pathway and genes of three pathways. After comparing the four signatures, the cell death index (CDI), the signature of combined genes, was further validated in the GSE74777 dataset. We also investigated the clinical significance of the CDI signature in predicting the immunotherapeutic response of LUSC patients.

RESULTS

The CDI signature was significantly associated with the overall survival of LUSC patients in the training cohort (HR, 2.13; 95% CI, 1.62‒2.82; P < 0.001) and in the validation cohort (HR, 1.94; 95% CI, 1.01‒3.72; P = 0.04). The differentially expressed genes between the high- and low-risk groups contained cell death-associated cytokines and were enriched in immune-associated pathways. We also found a higher infiltration of naive CD4⁺ T cells, monocytes, activated dendritic cells, neutrophils, and lower infiltration of plasma cells and resting memory CD4⁺ T cells in the high-risk group. Tumor stemness indices, mRNAsi and mDNAsi, were both negatively correlated with the risk score of the CDI. Moreover, LUSC patients in the low-risk group are more likely to respond to immunotherapy than those in the high-risk group (P = 0.002).

CONCLUSIONS

This study revealed a reliable cell death-associated signature (CDI) that closely correlated with prognosis and the tumor microenvironment in LUSC, which may assist in predicting the prognosis and response to immunotherapy for patients with LUSC.

Fn14-Directed DART Nanoparticles Selectively Target Neoplastic Cells in Preclinical Models of Triple-Negative Breast Cancer Brain Metastasis

Triple-negative breast cancer (TNBC) patients with brain metastasis (BM) face dismal prognosis due to the limited therapeutic efficacy of the currently available treatment options. We previously demonstrated that paclitaxel-loaded PLGA-PEG nanoparticles (NPs) directed to the Fn14 receptor, termed "DARTs", are more efficacious than Abraxane─an FDA-approved paclitaxel nanoformulation─following intravenous delivery in a mouse model of TNBC BM. However, the precise basis for this difference was not investigated. Here, we further examine the utility of the DART drug delivery platform in complementary xenograft and syngeneic TNBC BM models. First, we demonstrated that, in comparison to nontargeted NPs, DART NPs exhibit preferential association with Fn14-positive human and murine TNBC cell lines cultured in vitro. We next identified tumor cells as the predominant source of Fn14 expression in the TNBC BM-immune microenvironment with minimal expression by microglia, infiltrating macrophages, monocytes, or lymphocytes. We then show that despite similar accumulation in brains harboring TNBC tumors, Fn14-targeted DARTs exhibit significant and specific association with Fn14-positive TNBC cells compared to nontargeted NPs or Abraxane. Together, these results indicate that Fn14 expression primarily by tumor cells in TNBC BMs enables selective DART NP delivery to these cells, likely driving the significantly improved therapeutic efficacy observed in our prior work.

Targeting fibroblast growth factor (FGF)-inducible 14 (Fn14) for tumor therapy

Fibroblast growth factor-inducible 14 (Fn14) is a member of the tumor necrosis factor (TNF) receptor superfamily (TNFRSF) and is activated by its ligand TNF-like weak inducer of apoptosis (TWEAK). The latter occurs as a homotrimeric molecule in a soluble and a membrane-bound form. Soluble TWEAK (sTWEAK) activates the weakly inflammatory alternative NF-κB pathway and sensitizes for TNF-induced cell death while membrane TWEAK (memTWEAK) triggers additionally robust activation of the classical NF-κB pathway and various MAP kinase cascades. Fn14 expression is limited in adult organisms but becomes strongly induced in non-hematopoietic cells by a variety of growth factors, cytokines and physical stressors (e.g., hypoxia, irradiation). Since all these Fn14-inducing factors are frequently also present in the tumor microenvironment, Fn14 is regularly found to be expressed by non-hematopoietic cells of the tumor microenvironment and most solid tumor cells. In general, there are three possibilities how the tumor-Fn14 linkage could be taken into consideration for tumor therapy. First, by exploitation of the cancer associated expression of Fn14 to direct cytotoxic activities (antibody-dependent cell-mediated cytotoxicity (ADCC), cytotoxic payloads, CAR T-cells) to the tumor, second by blockade of potential protumoral activities of the TWEAK/Fn14 system, and third, by stimulation of Fn14 which not only triggers proinflammtory activities but also sensitizes cells for apoptotic and necroptotic cell death. Based on a brief description of the biology of the TWEAK/Fn14 system and Fn14 signaling, we discuss the features of the most relevant Fn14-targeting biologicals and review the preclinical data obtained with these reagents. In particular, we address problems and limitations which became evident in the preclinical studies with Fn14-targeting biologicals and debate possibilities how they could be overcome.

Antibody–drug conjugates harboring a kinesin spindle protein inhibitor with immunostimulatory properties

Antibody–drug conjugates (ADCs) are used to target cancer cells by means of antibodies directed to tumor-associated antigens, causing the incorporation of a cytotoxic payload into target cells. Here, we characterized the mode of action of ADC costing of a TWEAKR-specific monoclonal antibody conjugated to a small molecule kinesin spindle protein (KSP) inhibitor (KSPi). These TWEAKR-KSPi-ADCs showed strong efficacy in a TWEAKR expressing CT26 colon cancer model in mice. TWEAKR-KSPi-ADCs controlled the growth of CT26 colon cancers in immunodeficient as well as in immunocompetent mice. However, when treated with suboptimal doses, TWEAKR-KSPi-ADCs were still active in immunocompetent but not in immunodeficient mice, indicating that TWEAKR-KSPi-ADCs act – in addition to the cytotoxic mode of action – through an immunological mechanism. Indeed, in vitro experiments performed with a cell-permeable small molecule KSPi closely related to the active payload released from the TWEAKR-KSPi-ADCs revealed that KSPi was capable of stimulating several hallmarks of immunogenic cell death (ICD) on three different human cancer cell lines: cellular release of adenosine triphosphate (ATP) and high mobility group B1 protein (HMGB1), exposure of calreticulin on the cell surface as well as a transcriptional type-I interferon response. Further, in vivo experiments confirmed that treatment with TWEAKR-KSPi-ADCs activated immune responses via enhancing the infiltration of CD4⁺ and CD8⁺ T lymphocytes in tumors and the local production of interferon-γ, interleukin-2, and tumor necrosis factor-α. In conclusion, the antineoplastic effects of TWEAKR-KSPi-ADCs can partly be attributed to its ICD-stimulatory properties.

High dimensionality reduction by matrix factorization for systems pharmacology

The extraction of predictive features from the complex high-dimensional multi-omic data is necessary for decoding and overcoming the therapeutic responses in systems pharmacology. Developing computational methods to reduce high-dimensional space of features in in vitro, in vivo and clinical data is essential to discover the evolution and mechanisms of the drug responses and drug resistance. In this paper, we have utilized the matrix factorization (MF) as a modality for high dimensionality reduction in systems pharmacology. In this respect, we have proposed three novel feature selection methods using the mathematical conception of a basis for features. We have applied these techniques as well as three other MF methods to analyze eight different gene expression datasets to investigate and compare their performance for feature selection. Our results show that these methods are capable of reducing the feature spaces and find predictive features in terms of phenotype determination. The three proposed techniques outperform the other methods used and can extract a 2-gene signature predictive of a tyrosine kinase inhibitor treatment response in the Cancer Cell Line Encyclopedia.

Identification of Pan-Cancer Biomarkers Based on the Gene Expression Profiles of Cancer Cell Lines

There are many types of cancers. Although they share some hallmarks, such as proliferation and metastasis, they are still very different from many perspectives. They grow on different organ or tissues. Does each cancer have a unique gene expression pattern that makes it different from other cancer types? After the Cancer Genome Atlas (TCGA) project, there are more and more pan-cancer studies. Researchers want to get robust gene expression signature from pan-cancer patients. But there is large variance in cancer patients due to heterogeneity. To get robust results, the sample size will be too large to recruit. In this study, we tried another approach to get robust pan-cancer biomarkers by using the cell line data to reduce the variance. We applied several advanced computational methods to analyze the Cancer Cell Line Encyclopedia (CCLE) gene expression profiles which included 988 cell lines from 20 cancer types. Two feature selection methods, including Boruta, and max-relevance and min-redundancy methods, were applied to the cell line gene expression data one by one, generating a feature list. Such list was fed into incremental feature selection method, incorporating one classification algorithm, to extract biomarkers, construct optimal classifiers and decision rules. The optimal classifiers provided good performance, which can be useful tools to identify cell lines from different cancer types, whereas the biomarkers (e.g. NCKAP1, TNFRSF12A, LAMB2, FKBP9, PFN2, TOM1L1) and rules identified in this work may provide a meaningful and precise reference for differentiating multiple types of cancer and contribute to the personalized treatment of tumors.

In silico analysis of STX2a-PE15-P4A8 chimeric protein as a novel immunotoxin for cancer therapy

Today, the targeted therapies like the use of immunotoxins are increased which targeted specific antigens or receptors on the surface of tumor cells. Fibroblast growth factor-inducible 14 (Fn14) is a cytokine receptor which involves several intercellular signaling pathways and can be highly expressed in the surface of cancer cells. Since the cleavage of enzymatic domain of Pseudomonas exotoxin A (PE) occurs in one step by furin protease, we fused enzymatic subunit of Shiga-like toxin type 2a (Stx2a) with domain II and a portion of Ib of PE to increase the toxicity of Stx. Then, we genetically fused the Fv fragment of an anti-Fn14 monoclonal antibody (P4A8) to STX2a-PE15 and evaluated the STX2a-PE15-P4A8 chimeric protein as a new immunotoxin candidate. In silico analysis showed that the STX2a-PE15-P4A8 is a stable chimeric protein with high affinity to the Fn14 receptor. Despite, the STX2a-PE15-P4A8 can be bind to the B cell receptor, but it has been weakly presented by major histocompatibility complex molecules II (MHC-II). So, it may have a little immunogenicity. On the basis of our in-silico studies we predict that STX2a-PE15-P4A8 can be a good candidate for cancer immunotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-021-00079-w.

Mechanisms of drugs-resistance in small cell lung cancer: DNA-related, RNA-related, apoptosis-related, drug accumulation and metabolism procedure

Small-cell lung cancer (SCLC), the highest malignant cancer amongst different types of lung cancer, has the feature of lower differentiation, rapid growth, and poor survival rate. Despite the dramatically initial sensitivity of SCLC to various types of treatment methods, including chemotherapy, radiotherapy and immunotherapy, the emergence of drugs-resistance is still a grandly clinical challenge. Therefore, in order to improve the prognosis and develop new therapeutic approaches, having a better understanding of the complex mechanisms of resistance in SCLC is of great clinical significance. This review summarized recent advances in understanding of multiple mechanisms which are involved in the resistance during SCLC treatment, including DNA-related process, RNA-related process, apoptosis-related mechanism, and the process of drug accumulation and metabolism.

Aging-associated genes TNFRSF12A and CHI3L1 contribute to thyroid cancer: An evidence for the involvement of hypoxia as a driver

The prevalence of thyroid cancer (TC) is high in the elderly. The present study was based on the hypothesis that genes, which have increased activity with aging, may play a role in the development of TC. A large-scale literature-based data analysis was conducted to explore the genes that are implicated in both TC and aging. Subsequently, a mega-analysis of 16 RNA expression datasets (1,222 samples: 439 healthy controls, and 783 patients with TC) was conducted to test a set of genes associated with aging but not TC. To uncover a possible link between these genes and TC, a functional pathway analysis was conducted, and the results were validated by analysis of gene co-expression. A multiple linear regression (MLR) model was employed to study the possible influence of sample size, population region and study age on the gene expression levels in TC. A total of 262 and 816 genes were identified to have increased activity with aging and TC, respectively; with a significant overlap of 63 genes (P<3.82×10⁻³⁵). The mega-analysis revealed two aging-associated genes (CHI3L1 and TNFRSF12A) to be significantly associated with TC (P<2.05×10⁻⁸), and identified the association with multiple hypoxia-driven pathways through functional pathway analysis, also confirmed by the co-expression analysis. The MLR analysis identified population region as a significant factor contributing to the expression levels of CHI3L1 and TNFRSF12A in TC samples (P<3.24×10⁻⁴). The determination of genes that promote aging was warranted due to their possible involvement in TC. The present study suggests CHI3L1 and TNFRSF12A as novel common risk genes associated with both aging and TC.

NF-κB signaling and crosstalk during carcinogenesis

Transcription factors (TFs) are proteins that control the transcription of genetic information from DNA to mRNA by binding to specific DNA sequences either on their own or with other proteins as a complex. TFs thus support or suppress the recruitment of the corresponding RNA polymerase. In general, TFs are classified by structure or function. The TF, Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), is expressed in all cell types and tissues. NF-κB signaling and crosstalk are involved in several steps of carcinogenesis including in sequences involving pathogenic stimulus, chronic inflammation, fibrosis, establishment of its remodeling to the precancerous niche (PCN) and transition of a normal cell to a cancer cell. Triggered by various inflammatory cytokines, NF-κB is activated along with other TFs with subsequent stimulation of cell proliferation and inhibition of apoptosis. The involvement of NF-κB in carcinogenesis provides an opportunity to develop anti-NF-κB therapies. The complexity of these interactions requires that we elucidate those aspects of NF-κB interactions that play a role in carcinogenesis, the sequence of events leading to cancer.

Pulmonary Manifestations of Predominantly Antibody Deficiencies

Predominantly antibody deficiencies (PADs) are the most frequent forms of primary immunodeficiency diseases (PIDs). Commonly accompanied with complications involving several body systems, immunoglobulin substitution therapy along with prophylactic antibiotics remained the cornerstone of treatment for PADs and related complications. Patients with respiratory complications should be prescribed an appropriate therapy as soon as possible and have to be adhering to more and longer medical therapies. Recent studies identified a gap for screening protocols to monitor respiratory manifestations in patients with PADs. In the present chapter, the pulmonary manifestations of different PADs for each have been discussed. The chapter is mainly focused on X-linked agammaglobulinemia, common variable immunodeficiency, activated PI3K-δ syndrome, LRBA deficiency, CD19 complex deficiencies, CD20 deficiency, other monogenic defects associated with hypogammaglobulinemia, immunoglobulin class switch recombination deficiencies affecting B-cells, transient hypogammaglobulinemia of infancy, and selective IgA deficiency.

miR-149-5p inhibits cell growth by regulating TWEAK/Fn14/PI3K/AKT pathway and predicts favorable survival in human osteosarcoma

MicroRNAs (miRNAs) as small non-coding RNAs act as either tumor suppressors or oncogenes in human cancers, of which miR-149-5p (miR-149) is involved in tumor growth and metastasis, but its role and molecular mechanisms underlying osteosarcoma growth are poorly understood. The correlation of miR-149 expression with clinicopathological characteristics and prognosis in patients with sarcoma was analyzed by The Cancer Genome Atlas (TCGA) RNA-sequencing data. Osteosarcoma cell growth affected by miR-149 was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and colony formation assays. As a result, we found that the expression level of miR-149 was markedly downregulated in human sarcoma samples and were negatively associated with tumor size, acting as an independent prognostic factor for overall survival of the sarcoma patients. Restoration of miR-149 expression suppressed osteosarcoma cell growth, while its knockdown reversed these effects. Furthermore, we identified TNFRSF12A (TNF receptor superfamily member 12A), also called fibroblast growth factor–inducible 14 (Fn14) as a direct target of miR-149, and TNFRSF12A and its ligand TNFSF12 (TNF superfamily member 12), also called tumor necrosis factor–related weak inducer of apoptosis (TWEAK), were both negatively correlated with miR-149 expression in sarcoma samples. Knockdown of TNFRSF12A suppressed cell growth, but its overexpression weakened the antiproliferative effects of miR-149 via the PI3K/AKT (AKT serine/threonine kinase) signaling pathway. Altogether, our findings show that miR-149 functions as a tumor suppressor in osteosarcoma via inhibition of the TWEAK–Fn14 axis and represents a potential therapeutic target in patients with osteosarcoma.

Enavatuzumab, a Humanized Anti-TWEAK Receptor Monoclonal Antibody, Exerts Antitumor Activity through Attracting and Activating Innate Immune Effector Cells

Enavatuzumab is a humanized IgG1 anti-TWEAK receptor monoclonal antibody that was evaluated in a phase I clinical study for the treatment of solid malignancies. The current study was to determine whether and how myeloid effector cells were involved in postulated mechanisms for its potent antitumor activity in xenograft models. The initial evidence for a role of effector cells was obtained in a subset of tumor xenograft mouse models whose response to enavatuzumab relied on the binding of Fc of the antibody to Fcγ receptor. The involvement of effector cells was further confirmed by immunohistochemistry, which revealed strong infiltration of CD45⁺ effector cells into tumor xenografts in responding models, but minimal infiltration in nonresponders. Consistent with the xenograft studies, human effector cells preferentially migrated toward in vivo-responsive tumor cells treated by enavatuzumab in vitro, with the majority of migratory cells being monocytes. Conditioned media from enavatuzumab-treated tumor cells contained elevated levels of chemokines, which might be responsible for enavatuzumab-triggered effector cell migration. These preclinical studies demonstrate that enavatuzumab can exert its potent antitumor activity by actively recruiting and activating myeloid effectors to kill tumor cells. Enavatuzumab-induced chemokines warrant further evaluation in clinical studies as potential biomarkers for such activity.

Identification of aurintricarboxylic acid as a selective inhibitor of the TWEAK-Fn14 signaling pathway in glioblastoma cells

The survival of patients diagnosed with glioblastoma (GBM), the most deadly form of brain cancer, is compromised by the proclivity for local invasion into the surrounding normal brain, which prevents complete surgical resection and contributes to therapeutic resistance. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK), a member of the tumor necrosis factor (TNF) superfamily, can stimulate glioma cell invasion and survival via binding to fibroblast growth factor-inducible 14 (Fn14) and subsequent activation of the transcription factor NF-κB. To discover small molecule inhibitors that disrupt the TWEAK-Fn14 signaling axis, we utilized a cell-based drug-screening assay using HEK293 cells engineered to express both Fn14 and a NF-κB-driven firefly luciferase reporter protein. Focusing on the LOPAC1280 library of 1280 pharmacologically active compounds, we identified aurintricarboxylic acid (ATA) as an agent that suppressed TWEAK-Fn14-NF-κB dependent signaling, but not TNFα-TNFR-NF-κB driven signaling. We demonstrated that ATA repressed TWEAK-induced glioma cell chemotactic migration and invasion via inhibition of Rac1 activation but had no effect on cell viability or Fn14 expression. In addition, ATA treatment enhanced glioma cell sensitivity to both the chemotherapeutic agent temozolomide (TMZ) and radiation-induced cell death. In summary, this work reports a repurposed use of a small molecule inhibitor that targets the TWEAK-Fn14 signaling axis, which could potentially be developed as a new therapeutic agent for treatment of GBM patients.

Correlation of EGFR Del 19 with Fn14/JAK/STAT signaling molecules in non-small cell lung cancer

Previous research has shown that p-EGFR (particularly mutated EGFR) may activate fibroblast growth factor-inducible 14 (Fn14) expression in non-small cell lung cancer (NSCLC), and the JAK/STAT signaling pathway may participate in this process. Thus, in order to verify this hypothesis, correlations among the expression levels of EGFR Del 19, Fn14 and JAK/STAT were detected and analyzed. The expression and location of these molecules were assessed using IHC, immunohistofluorescence, RT-qPCR and western blotting. The differences and correlations in the expression of these molecules and clinical pathological characteristics were statistically analyzed using Mann-Whitney U, Kruskal‑Wallis H and cross-table tests. Kaplan-Meier survival analysis and Cox proportional hazards models were used to estimate the effect of EGFR Del 19 and Fn14 expression on survival. Data showed that EGFR Del 19, Fn14 and JAK1/STAT1 expression was significantly related with differentiation, pTNM stage and lymphatic metastasis (P<0.01) and there was a marked correlation of EGFR Del 19, Fn14 and JAK1/STAT1 expression with histological type, differentiation, pTNM stage of NSCLC (P<0.05; rs>0.3). Immunohistofluorescence showed that there was a co-localization phenomenon between EGFR Del 19 and Fn14 expression. NSCLC patients with higher EGFR Del 19/Fn14 expression had a significantly worse prognosis than those with lower EGFR Del 19/Fn14 expression (P=0.0155/P=0.001; log-rank test). The multivariate analysis indicated that Fn14 expression may be an independent prognostic factor in NSCLC with EGFR Del 19 [hazard ratio (HR), 0.326; P=0.042]. Therefore, our results indicate that EGFR Del 19 may promote Fn14 and JAK1/STAT1 expression in NSCLC and Fn14 may serve as a prognostic biomarker in NSCLC with EGFR Del 19.

Fibroblast growth factor-inducible 14 regulates cell growth and multidrug resistance of small-cell lung cancer through the nuclear factor-κB pathway

Fibroblast growth factor-inducible 14 (Fn14) has been reported to play an oncogene role in many types of cancer. However, its biological functions in small-cell lung cancer (SCLC) remain unknown. The aim of this study is to investigate the roles of Fn14 in the cell growth and chemoresistance of SCLC and its possible molecular mechanism. Expression of Fn14 was examined in 51 cases of SCLC tissues by immunohistochemistry. Overexpression or knockdown of Fn14 was carried out in SCLC multidrug-resistant cell lines (H69AR and H446AR) and the parental cell lines (H69 and H446) to assess its influence on cell growth and chemoresistance. The results showed that Fn14 was expressed in 50.98% (26/51) of SCLC. Overexpression of Fn14 was associated with the poor pathologic stage of SCLC (P < 0.05 by the Fisher's exact test) and the shorter survival time (by the Kaplan-Meier method). Enforced expression of Fn14 in H69 and H446 cells promoted cell growth and enhanced multidrug resistance by decreasing cell apoptosis and increasing G2-phase cell accumulation. Inhibition of Fn14 expression using Fn14 shRNA in H69AR and H446AR cells inhibited cell growth and sensitized cancer cells to chemotherapeutic drugs by increasing drug-induced cell apoptosis accompanied by G1, S phase arrest. Furthermore, elevated expression of Fn14 in H69 and H446 cells can lead to increased expression of Bcl-xl and activity of nuclear factor-κB (NF-κB). Similar results were observed by Fn14 knockdown H69AR and H446AR cells. Bcl-xl expression regulated by Fn14 was dependent on NF-κB activation. Our results suggest that Fn14 modulates cell growth and drug resistance by upregulating Bcl-xl expression through the NF-κB pathway. All findings provide insight into the Fn14 signaling mechanism and Fn14 may be a potentially novel target for interfering with cancer growth and chemoresistance in SCLC.

TWEAKing for a fight with GVHD

In this issue of Blood, Chopra et al provide convincing evidence that tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) ligand acting through its receptor, fibroblast growth factor-inducible 14 (Fn14), is crucial to the intestinal apoptosis seen in graft-versus-host disease (GVHD) and associated mortality.

Exposure and Tumor Fn14 Expression as Determinants of Pharmacodynamics of the Anti-TWEAK Monoclonal Antibody RG7212 in Patients with Fn14-Positive Solid Tumors

PURPOSE

The TWEAK-Fn14 pathway represents a novel anticancer target that is being actively investigated. Understanding the relationship between pharmacokinetics of anti-TWEAK therapeutics and tumor pharmacodynamics is critical. We investigated exposure-response relationships of RG7212, an anti-TWEAK mAb, in patients with Fn14-expressing tumors.

EXPERIMENTAL DESIGN

Patients with Fn14-positive tumors (IHC ≥ 1+) treated in a phase I first-in-human study with ascending doses of RG7212 were the basis for this analysis. Pharmacokinetics of RG7212 and dynamics of TWEAK were determined, as were changes in tumor TWEAK-Fn14 signaling in paired pre- and posttreatment tumor biopsies. The objectives of the analysis were to define exposure-response relationships and the relationship between pretreatment tumor Fn14 expression and pharmacodynamic effect. Associations between changes in TWEAK-Fn14 signaling and clinical outcome were explored.

RESULTS

Thirty-six patients were included in the analysis. RG7212 reduced plasma TWEAK to undetectable levels at all observed RG7212 exposures. In contrast, reductions in tumor Fn14 and TRAF1 protein expression were observed only at higher exposure (≥ 300 mg*h/mL). Significant reductions in tumor Ki-67 expression and early changes in serum concentrations of CCL-2 and MMP-9 were observed exclusively in patients with higher drug exposure who had high pretreatment tumor Fn14 expression. Pretreatment tumor Fn14 expression was not associated with outcome, but a trend toward longer time on study was observed with high versus low RG7212 exposure.

CONCLUSIONS

RG7212 reduced tumor TWEAK-Fn14 signaling in a systemic exposure-dependent manner. In addition to higher exposure, relatively high Fn14 expression might be required for pharmacodynamic effect of anti-TWEAK monoclonal antibodies.

The TWEAK receptor Fn14 is a potential cell surface portal for targeted delivery of glioblastoma therapeutics

Fibroblast growth factor-inducible 14 (Fn14; TNFRSF12A) is the cell surface receptor for the tumor necrosis factor (TNF) family member TNF-like weak inducer of apoptosis (TWEAK). The Fn14 gene is normally expressed at low levels in healthy tissues but expression is significantly increased after tissue injury and in many solid tumor types, including glioblastoma (GB; formerly referred to as 'GB multiforme'). GB is the most common and aggressive primary malignant brain tumor and the current standard-of-care therapeutic regimen has a relatively small impact on patient survival, primarily because glioma cells have an inherent propensity to invade into normal brain parenchyma, which invariably leads to tumor recurrence and patient death. Despite major, concerted efforts to find new treatments, a new GB therapeutic that improves survival has not been introduced since 2005. In this review article, we summarize studies indicating that (i) Fn14 gene expression is low in normal brain tissue but is upregulated in advanced brain cancers and, in particular, in GB tumors exhibiting the mesenchymal molecular subtype; (ii) Fn14 expression can be detected in glioma cells residing in both the tumor core and invasive rim regions, with the maximal levels found in the invading glioma cells located within normal brain tissue; and (iii)

TWEAK

Fn14 engagement as well as Fn14 overexpression can stimulate glioma cell migration, invasion and resistance to chemotherapeutic agents in vitro. We also discuss two new therapeutic platforms that are currently in development that leverage Fn14 overexpression in GB tumors as a way to deliver cytotoxic agents to the glioma cells remaining after surgical resection while sparing normal healthy brain cells.

Blocking TWEAK-Fn14 interaction inhibits hematopoietic stem cell transplantation-induced intestinal cell death and reduces GVHD

Inhibition of the tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK)/fibroblast growth factor-inducible 14 (Fn14) system reduces intestinal cell death and disease development in several models of colitis. In view of the crucial role of TNF and intestinal cell death in graft-versus-host disease (GVHD) and the ability of TWEAK to enhance TNF-induced cell death, we tested here the therapeutic potential of Fn14 blockade on allogeneic hematopoietic cell transplantation (allo-HCT)-induced intestinal GVHD. An Fn14-specific blocking human immunoglobulin G1 antibody variant with compromised antibody-dependent cellular cytotoxicity (ADCC) activity strongly inhibited the severity of murine allo-HCT-induced GVHD. Treatment of the allo-HCT recipients with this monoclonal antibody reduced cell death of gastrointestinal cells but neither affected organ infiltration by donor T cells nor cytokine production. Fn14 blockade also inhibited intestinal cell death in mice challenged with TNF. This suggests that the protective effect of Fn14 blockade in allo-HCT is based on the protection of intestinal cells from TNF-induced apoptosis and not due to immune suppression. Importantly, Fn14 blockade showed no negative effect on graft-versus-leukemia/lymphoma (GVL) activity. Thus, ADCC-defective Fn14-blocking antibodies are not only possible novel GVL effect-sparing therapeutics for the treatment of GVHD but might also be useful for the treatment of other inflammatory bowel diseases where TNF-induced cell death is of relevance.

Minimizing the non-specific binding of nanoparticles to the brain enables active targeting of Fn14-positive glioblastoma cells

A major limitation in the treatment of glioblastoma (GBM), the most common and deadly primary brain cancer, is delivery of therapeutics to invading tumor cells outside of the area that is safe for surgical removal. A promising way to target invading GBM cells is via drug-loaded nanoparticles that bind to fibroblast growth factor-inducible 14 (Fn14), thereby potentially improving efficacy and reducing toxicity. However, achieving broad particle distribution and nanoparticle targeting within the brain remains a significant challenge due to the adhesive extracellular matrix (ECM) and clearance mechanisms in the brain. In this work, we developed Fn14 monoclonal antibody-decorated nanoparticles that can efficiently penetrate brain tissue. We show these Fn14-targeted brain tissue penetrating nanoparticles are able to (i) selectively bind to recombinant Fn14 but not brain ECM proteins, (ii) associate with and be internalized by Fn14-positive GBM cells, and (iii) diffuse within brain tissue in a manner similar to non-targeted brain penetrating nanoparticles. In addition, when administered intracranially, Fn14-targeted nanoparticles showed improved tumor cell co-localization in mice bearing human GBM xenografts compared to non-targeted nanoparticles. Minimizing non-specific binding of targeted nanoparticles in the brain may greatly improve the access of particulate delivery systems to remote brain tumor cells and other brain targets.

The TWEAK Receptor Fn14 Is an Src-Inducible Protein and a Positive Regulator of Src-Driven Cell Invasion

The TNF receptor superfamily member Fn14 (TNFRSF12A) is the sole signaling receptor for the proinflammatory cytokine TWEAK (TNFSF12).

TWEAK

Fn14 engagement stimulates multiple signal transduction pathways, including the NF-κB pathway, and this triggers important cellular processes (e.g., growth, differentiation, migration, and invasion). The TWEAK-Fn14 axis is thought to be a major physiologic mediator of tissue repair after acute injury. Various studies have revealed that Fn14 is highly expressed in many solid tumor types, and that Fn14 signaling may play a role in tumor growth and metastasis. Previously, it was shown that Fn14 levels are frequently elevated in non-small cell lung cancer (NSCLC) tumors and cell lines that exhibit constitutive EGFR phosphorylation (activation). Furthermore, elevated Fn14 levels increased NSCLC cell invasion in vitro and lung metastatic tumor colonization in vivo. The present study reveals that EGFR-mutant NSCLC cells that express high levels of Fn14 exhibit constitutive activation of the cytoplasmic tyrosine kinase Src, and that treatment with the Src family kinase (SFK) inhibitor dasatinib decreases Fn14 gene expression at both the mRNA and protein levels. Importantly, siRNA-mediated depletion of the SFK member Src in NSCLC cells also decreases Fn14 expression. Finally, expression of the constitutively active v-Src oncoprotein in NIH 3T3 cells induces Fn14 gene expression, and NIH 3T3/v-Src cells require Fn14 expression for full invasive capacity.

IMPLICATIONS

These results indicate that oncogenic Src may contribute to Fn14 overexpression in solid tumors, and that Src-mediated cell invasion could potentially be inhibited with Fn14-targeted therapeutics.

A phase I monotherapy study of RG7212, a first-in-class monoclonal antibody targeting TWEAK signaling in patients with advanced cancers

PURPOSE

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and fibroblast growth factor-inducible molecule 14 (Fn14) are a ligand-receptor pair frequently overexpressed in solid tumors.

TWEAK

Fn14 signaling regulates multiple oncogenic processes through MAPK, AKT, and NFκB pathway activation. A phase I study of RG7212, a humanized anti-TWEAK IgG1κ monoclonal antibody, was conducted in patients with advanced solid tumors expressing Fn14.

EXPERIMENTAL DESIGN

Dose escalations, over a 200- to 7,200-mg range, were performed with patients enrolled in weekly (QW), bi-weekly (Q2W), or every-three-week (Q3W) schedules. Primary objectives included determination of dose and safety profile. Secondary endpoints included assessments related to inhibition of

TWEAK

Fn14 signaling, tumor proliferation, tumor immune cell infiltration, and pharmacokinetics.

RESULTS

In 192 treatment cycles administered to 54 patients, RG7212 was well-tolerated with no dose-limiting toxicities observed. More than 95% of related adverse events were limited to grade 1/2. Pharmacokinetics were dose proportional for all cohorts, with a t1/2 of 11 to 12 days. Pharmacodynamic changes included clearance of free and total TWEAK ligand and reductions in tumor Ki-67 and TRAF1. A patient with BRAF wild-type melanoma who received 36 weeks of RG7212 therapy had tumor regression and pharmacodynamic changes consistent with antitumor effects. Fifteen patients (28%) received 16 or more weeks of RG7212 treatment.

CONCLUSION

RG7212 demonstrated excellent tolerability and favorable pharmacokinetics. Pharmacodynamic endpoints were consistent with reduced

TWEAK

Fn14 signaling. Tumor regression was observed and prolonged stable disease was demonstrated in multiple heavily pretreated patients with solid tumors. These encouraging results support further study of RG7212. Clin Cancer Res; 21(2); 258-66. ©2014 AACR.

The TWEAK-Fn14 system as a potential drug target

Fibroblast growth factor-inducible 14 (Fn14) is a member of the tumour necrosis factor (TNF) receptor family that is induced in a variety of cell types in situations of tissue injury. Fn14 becomes activated by TNF-like weak inducer of apoptosis (TWEAK), a typical member of the TNF ligand family. TWEAK is constitutively expressed by monocytes and some tumour cell lines and also shows cytokine inducible expression in various other cell types. Fn14 activation results in stimulation of signalling pathways culminating in the activation of NFκB transcription factors and various MAPKs but might also trigger the PI3K/Akt pathway and GTPases of the Rho family. In accordance with its tissue damage-associated expression pattern and its pleiotropic proinflammatory signalling capabilities, the TWEAK-Fn14 system has been implicated in a huge number of pathologies. The use of TWEAK- and Fn14-knockout mice identified the TWEAK-Fn14 system as a crucial player in muscle atrophy, cerebral ischaemia, kidney injury, atherosclerosis and infarction as well as in various autoimmune scenarios including experimental autoimmune encephalitis, rheumatoid arthritis and inflammatory bowel disease. Moreover, there is increasing preclinical evidence that Fn14 targeting is a useful option in tumour therapy. Based on a discussion of the signalling capabilities of TWEAK and Fn14, this review is focused on two major issues. On the one hand, on the molecular and cellular basis of the TWEAK/Fn14-related pathological outcomes in the aforementioned diseases and on the other hand, on the preclinical experience that have been made so far with TWEAK and Fn14 targeting drugs.

LKB1 inactivation sensitizes non-small cell lung cancer to pharmacological aggravation of ER stress

Five-year survival rates for non-small cell lung cancer (NSCLC) have seen minimal improvement despite aggressive therapy with standard chemotherapeutic agents, indicating a need for new treatment approaches. Studies show inactivating mutations in the LKB1 tumor suppressor are common in NSCLC. Genetic and mechanistic analysis has defined LKB1-deficient NSCLC tumors as a phenotypically distinct subpopulation of NSCLC with potential avenues for therapeutic gain. In expanding on previous work indicating hypersensitivity of LKB1-deficient NSCLC cells to 2-deoxy-D-glucose (2DG), we find that 2DG has in vivo efficacy in LKB1-deficient NSCLC using transgenic murine models of NSCLC. Deciphering of the molecular mechanisms behind this phenotype reveals that loss of LKB1 in NSCLC cells imparts increased sensitivity to pharmacological compounds that aggravate ER stress. In comparison to NSCLC cells with functional LKB1, treatment of NSCLC cells lacking LKB1 with the ER stress activators (ERSA), tunicamycin, brefeldin A or 2DG, resulted in aggravation of ER stress, increased cytotoxicity, and evidence of ER stress-mediated cell death. Based upon these findings, we suggest that ERSAs represent a potential treatment avenue for NSCLC patients whose tumors are deficient in LKB1.

FN14 expression correlates with MET in NSCLC and promotes MET-driven cell invasion

The five-year survival rate in advanced non-small cell lung cancer (NSCLC) remains below ten percent. The invasive and metastatic nature of NSCLC tumor cells contributes to the high mortality rate, and as such the mechanisms that govern NSCLC metastasis is an active area of investigation. Two surface receptors that influence NSCLC invasion and metastasis are the hepatocyte growth factor receptor (HGFR/MET) and fibroblast growth factor-inducible 14 (FN14). MET protein is over-expressed in NSCLC tumors and associated with poor clinical outcome and metastasis. FN14 protein is also elevated in NSCLC tumors and positively correlates with tumor cell migration and invasion. In this report, we show that MET and FN14 protein expressions are significantly correlated in human primary NSCLC tumors, and the protein levels of MET and FN14 are elevated in metastatic lesions relative to patient-matched primary tumors. In vitro, HGF/MET activation significantly enhances FN14 mRNA and protein expression. Importantly, depletion of FN14 is sufficient to inhibit MET-driven NSCLC tumor cell migration and invasion in vitro. This work suggests that MET and FN14 protein expressions are associated with the invasive and metastatic potential of NSCLC. Receptor-targeted therapeutics for both MET and FN14 are in clinical development, the use of which may mitigate the metastatic potential of NSCLC.

Roles of fibroblast growth factor-inducible 14 in hepatocellular carcinoma

The prognostic value of the fibroblast growth factor-inducible 14 (Fn14) expression in hepatocellular carcinoma (HCC) is unknown. Real-time PCR (RT-PCR), western blot assays and immunohistochemistry analysis were here performed in order to compare Fn14 expressions in paired liver samples of HCC and normal liver tissue. Most of the tumor tissues expressed significantly higher levels of Fn14 compared to adjacent non-tumor tissues, with Fn14High accounting for 54.6% (142/260) of all patients. The Pearson χ(2) test indicated that Fn14 expression was closely associated with serum alpha fetal protein (AFP) (P=0.002) and tumor number (p=0.019). Univariate and multivariate analyses revealed that along with tumor diameter and portal vein tumor thrombosis (PVTT ) type, Fn14 was an independent prognostic factor for both overall survival (OS) (HR=1.398, p=0.008) and recurrence (HR=1.541, p=0.001) rates. Fn14 overexpression HCC correlated with poor surgical outcome, and this molecule may be a candidate biomarker for prognosis as well as a target for therapy.

Mcl-1 mediates TWEAK/Fn14-induced non-small cell lung cancer survival and therapeutic response

Insensitivity to standard clinical interventions, including chemotherapy, radiotherapy, and tyrosine kinase inhibitor (TKI) treatment, remains a substantial hindrance towards improving the prognosis of patients with non-small cell lung cancer (NSCLC). The molecular mechanism of therapeutic resistance remains poorly understood. The TNF-like weak inducer of apoptosis (TWEAK)-FGF-inducible 14 (TNFRSF12A/Fn14) signaling axis is known to promote cancer cell survival via NF-κB activation and the upregulation of prosurvival Bcl-2 family members. Here, a role was determined for TWEAK-Fn14 prosurvival signaling in NSCLC through the upregulation of myeloid cell leukemia sequence 1 (MCL1/Mcl-1). Mcl-1 expression significantly correlated with Fn14 expression, advanced NSCLC tumor stage, and poor patient prognosis in human primary NSCLC tumors. TWEAK stimulation of NSCLC cells induced NF-κB-dependent Mcl-1 protein expression and conferred Mcl-1-dependent chemo- and radioresistance. Depletion of Mcl-1 via siRNA or pharmacologic inhibition of Mcl-1, using EU-5148, sensitized TWEAK-treated NSCLC cells to cisplatin- or radiation-mediated inhibition of cell survival. Moreover, EU-5148 inhibited cell survival across a panel of NSCLC cell lines. In contrast, inhibition of Bcl-2/Bcl-xL function had minimal effect on suppressing TWEAK-induced cell survival. Collectively, these results position TWEAK-Fn14 signaling through Mcl-1 as a significant mechanism for NSCLC tumor cell survival and open new therapeutic avenues to abrogate the high mortality rate seen in NSCLC.

IMPLICATIONS

The TWEAK-Fn14 signaling axis enhances lung cancer cell survival and therapeutic resistance through Mcl-1, positioning both TWEAK-Fn14 and Mcl-1 as therapeutic opportunities in lung cancer.

TWEAK/Fn14 Axis-Targeted Therapeutics: Moving Basic Science Discoveries to the Clinic

The TNF superfamily member TWEAK (TNFSF12) is a multifunctional cytokine implicated in physiological tissue regeneration and wound repair. TWEAK is initially synthesized as a membrane-anchored protein, but furin cleavage within the stalk region can generate a secreted TWEAK isoform. Both TWEAK isoforms bind to a small cell surface receptor named Fn14 (TNFRSF12A) and this interaction stimulates various cellular responses, including proliferation and migration. Fn14, like other members of the TNF receptor superfamily, is not a ligand-activated protein kinase. Instead, TWEAK:Fn14 engagement promotes Fn14 association with members of the TNFR associated factor family of adapter proteins, which triggers activation of various signaling pathways, including the classical and alternative NF-κB pathways. Numerous studies have revealed that Fn14 gene expression is significantly elevated in injured tissues and in most solid tumor types. Also, sustained Fn14 signaling has been implicated in the pathogenesis of cerebral ischemia, chronic inflammatory diseases, and cancer. Accordingly, several groups are developing TWEAK- or Fn14-targeted agents for possible therapeutic use in patients. These agents include monoclonal antibodies, fusion proteins, and immunotoxins. In this article, we provide an overview of some of the TWEAK/Fn14 axis-targeted agents currently in pre-clinical animal studies or in human clinical trials and discuss two other potential approaches to target this intriguing signaling node.

TWEAK/Fn14 signaling mediates gastric cancer cell resistance to 5-fluorouracil via NF-κB activation

Chemoresistance is one of the most serious problems in the treatment of cancer. In the present study, we show that Fn14 promotes resistance to 5-fluorouracil (5-FU) in gastric cancer (GC). We found that 5-FU treatment upregulated Fn14 expression in various cancer cell lines, including GC cell lines, and that knockdown of Fn14 using shRNA accelerated 5-FU sensitivity. In contrast, Fn14 overexpression or TWEAK treatment promoted resistance to 5-FU. Furthermore, we investigated the mechanisms underlying Fn14-mediated chemoresistance. We first revealed that 5-FU-mediated upregulation of Fn14 occurred as a result of NF-κB activation, indicating that 5-FU-mediated NF-κB activation was the principal event underlying Fn14 upregulation and 5-FU resistance in GC. Taken together, our results suggest that Fn14 is a novel therapeutic target and that inhibition of Fn14 combined with 5-FU treatment may be an effective molecular therapeutic strategy to treat 5-FU-resistant gastric cancers.

CRL4A-FBXW5-mediated degradation of DLC1 Rho GTPase-activating protein tumor suppressor promotes non-small cell lung cancer cell growth

DLC1 encodes a RhoA GTPase-activating protein and tumor suppressor lost in cancer by genomic deletion or epigenetic silencing and loss of DLC1 gene transcription. We unexpectedly identified non-small cell lung cancer (NSCLC) cell lines and tumor tissue that expressed DLC1 mRNA yet lacked DLC1 protein expression. We determined that DLC1 was ubiquitinated and degraded by cullin 4A-RING ubiquitin ligase (CRL4A) complex interaction with DDB1 and the FBXW5 substrate receptor. siRNA-mediated suppression of cullin 4A, DDB1, or FBXW5 expression restored DLC1 protein expression in NSCLC cell lines. FBXW5 suppression-induced DLC1 reexpression was associated with a reduction in the levels of activated RhoA-GTP and in RhoA effector signaling. Finally, FBXW5 suppression caused a DLC1-dependent decrease in NSCLC anchorage-dependent and -independent proliferation. In summary, we identify a posttranslational mechanism for loss of DLC1 and a linkage between CRL4A-FBXW5-associated oncogenesis and regulation of RhoA signaling.

Structural basis and targeting of the interaction between fibroblast growth factor-inducible 14 and tumor necrosis factor-like weak inducer of apoptosis

Deregulation of the TNF-like weak inducer of apoptosis (TWEAK)-fibroblast growth factor-inducible 14 (Fn14) signaling pathway is observed in many diseases, including inflammation, autoimmune diseases, and cancer. Activation of Fn14 signaling by TWEAK binding triggers cell invasion and survival and therefore represents an attractive pathway for therapeutic intervention. Based on structural studies of the TWEAK-binding cysteine-rich domain of Fn14, several homology models of TWEAK were built to investigate plausible modes of TWEAK-Fn14 interaction. Two promising models, centered on different anchoring residues of TWEAK (tyrosine 176 and tryptophan 231), were prioritized using a data-driven strategy. Site-directed mutagenesis of TWEAK at Tyr(176), but not Trp(231), resulted in the loss of TWEAK binding to Fn14 substantiating Tyr(176) as the anchoring residue. Importantly, mutation of TWEAK at Tyr(176) did not disrupt TWEAK trimerization but failed to induce Fn14-mediated nuclear factor κ-light chain enhancer of activated B cell (NF-κB) signaling. The validated structural models were utilized in a virtual screen to design a targeted library of small molecules predicted to disrupt the TWEAK-Fn14 interaction. 129 small molecules were screened iteratively, with identification of molecules producing up to 37% inhibition of TWEAK-Fn14 binding. In summary, we present a data-driven in silico study revealing key structural elements of the TWEAK-Fn14 interaction, followed by experimental validation, serving as a guide for the design of small molecule inhibitors of the TWEAK-Fn14 ligand-receptor interaction. Our results validate the TWEAK-Fn14 interaction as a chemically tractable target and provide the foundation for further exploration utilizing chemical biology approaches focusing on validating this system as a therapeutic target in invasive cancers.

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) promotes glioblastoma cell chemotaxis via Lyn activation

The long-term survival of patients with glioblastoma is compromised by the proclivity for local invasion into the surrounding normal brain, escaping surgical resection and contributing to therapeutic resistance. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK), a member of the tumor necrosis factor superfamily, can stimulate glioma cell invasion via binding to fibroblast growth factor-inducible 14 (Fn14) and subsequent activation of the Rho guanosine triphosphatase family member Rac1. Here, we demonstrate that TWEAK acts as a chemotactic factor for glioma cells, a potential process for driving cell invasion into the surrounding brain tissue. TWEAK exposure induced the activation of Src family kinases (SFKs), and pharmacologic suppression of SFK activity inhibited TWEAK-induced chemotactic migration. We employed a multiplexed Luminex assay and identified Lyn as a candidate SFK activated by TWEAK. Depletion of Lyn suppressed TWEAK-induced chemotaxis and Rac1 activity. Furthermore, Lyn gene expression levels increase with primary glioma tumor grade and inversely correlate with patient survival. These results show that TWEAK-induced glioma cell chemotaxis is dependent upon Lyn kinase function and, thus, provides opportunities for therapeutic targeting of this deadly disease.

TWEAK-independent Fn14 self-association and NF-κB activation is mediated by the C-terminal region of the Fn14 cytoplasmic domain

The tumor necrosis factor (TNF) superfamily member TNF-like weak inducer of apoptosis (TWEAK) is a pro-inflammatory and pro-angiogenic cytokine implicated in physiological tissue regeneration and wound repair. TWEAK binds to a 102-amino acid type I transmembrane cell surface receptor named fibroblast growth factor-inducible 14 (Fn14). TWEAK:Fn14 engagement activates several intracellular signaling cascades, including the NF-κB pathway, and sustained Fn14 signaling has been implicated in the pathogenesis of chronic inflammatory diseases and cancer. Although several groups are developing TWEAK- or Fn14-targeted agents for therapeutic use, much more basic science research is required before we fully understand the TWEAK/Fn14 signaling axis. For example, we and others have proposed that TWEAK-independent Fn14 signaling may occur in cells when Fn14 levels are highly elevated, but this idea has never been tested directly. In this report, we first demonstrate TWEAK-independent Fn14 signaling by showing that an Fn14 deletion mutant that is unable to bind TWEAK can activate the NF-κB pathway in transfected cells. We then show that ectopically-expressed, cell surface-localized Fn14 can self-associate into Fn14 dimers, and we show that Fn14 self-association is mediated by an 18-aa region within the Fn14 cytoplasmic domain. Endogenously-expressed Fn14 as well as ectopically-overexpressed Fn14 could also be detected in dimeric form when cell lysates were subjected to SDS-PAGE under non-reducing conditions. Additional experiments revealed that Fn14 dimerization occurs during cell lysis via formation of an intermolecular disulfide bond at cysteine residue 122. These findings provide insight into the Fn14 signaling mechanism and may aid current studies to develop therapeutic agents targeting this small cell surface receptor.

Antitumor activity of a humanized, bivalent immunotoxin targeting fn14-positive solid tumors

The TNF-like weak inducer of apoptosis (TWEAK; TNFSF12) receptor Fn14 (TNFRSF12A) is expressed at low levels in normal tissues but frequently highly expressed in a wide range of tumor types such as lung, melanoma, and breast, and therefore it is a potentially unique therapeutic target for these diverse tumor types. We have generated a recombinant protein containing a humanized, dimeric single-chain anti-fibroblast growth factor-inducible 14-kDa protein (Fn14) antibody fused to recombinant gelonin toxin as a potential therapeutic agent (designated hSGZ). The hSGZ immunotoxin is a highly potent and selective agent that kills Fn14-positive (Fn14(+)) tumor cells in vitro. Treatment of cells expressing the MDR protein MDR1 (ABCB1B) showed no cross-resistance to hSGZ. Induced overexpression of Fn14 levels in MCF7 cells through HER2 (ERBB2) signaling translated to an improved therapeutic index of hSGZ treatment. In combination with trastuzumab, hSGZ showed an additive or synergistic cytotoxic effect on HER2(+)/Fn14(+) breast cancer cell lines. Also, hSGZ treatment inhibited Erb3/Akt signaling in HER2-overexpressing breast cancer cells. Pharmacokinetic studies in mice revealed that hSGZ exhibited a biexponential clearance from plasma with a rapid initial clearance (t1/2α = 1.26 hours) followed by a seven-fold longer plasma half-life (t1/2β = 7.29 hours). At 24, 48, and 72 hours after injection, uptake of the hSGZ into tumors was 5.1, 4.8, and 4.7%ID/g, with a tumor-to-muscle ratio of 5.6, 6.2, and 9.0, respectively. Therapeutic efficacy studies showed significant tumor inhibition effects using an MDA-MB-231/Luc breast cancer xenograft model. Our findings show that hSGZ is an effective anticancer agent and a potential candidate for clinical studies.

Crystal structure of human TWEAK in complex with the Fab fragment of a neutralizing antibody reveals insights into receptor binding

The tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a multifunctional cytokine playing a key role in tissue regeneration and remodeling. Dysregulation of TWEAK signaling is involved in various pathological processes like autoimmune diseases and cancer. The unique interaction with its cognate receptor Fn14 makes both ligand and receptor promising targets for novel therapeutics. To gain insights into this important signaling pathway, we determined the structure of soluble human TWEAK in complex with the Fab fragment of an antibody selected for inhibition of receptor binding. In the crystallized complex TWEAK is bound by three Fab fragments of the neutralizing antibody. Homology modeling shows that Fab binding overlaps with the putative Fn14 binding site of TWEAK. Docking of the Fn14 cysteine rich domain (CRD) to that site generates a highly complementary interface with perfectly opposing charged and hydrophobic residues. Taken together the presented structure provides new insights into the biology of TWEAK and the TWEAK/Fn14 pathway, which will help to optimize the therapeutic strategy for treatment of related cancer types and autoimmune diseases.

IRS1 is highly expressed in localized breast tumors and regulates the sensitivity of breast cancer cells to chemotherapy, while IRS2 is highly expressed in invasive breast tumors

Insulin receptor substrate (IRS) proteins have been shown to play an important role in breast cancer by differentially regulating cancer cell survival, proliferation, and motility. Furthermore, the IL-4-induced tyrosine phosphorylation of the transcription factor STAT6 was shown to protect breast cancer cells from apoptosis. Here, we analyzed human breast cancer tissues for the expression of IRS1, IRS2, STAT6, and tyrosine phosphorylated STAT6 (pSTAT6). We found that IRS1 and pSTAT6 were both highly expressed in ductal carcinoma in situ (DCIS). On the other hand, IRS2 expression was low in DCIS, but increased significantly in relation to tumor invasiveness. We utilized cell lines with disparate IRS1 expression, MDA-MB-231, MCF7, and MCF7 cells with depleted IRS1 due to shRNA lentiviral infection, to examine the role of IRS1 and IRS2 in the responsiveness of breast cancer cells to chemotherapy. We report that high IRS1 sensitized MCF7 cells to specific chemotherapeutic agents. These results suggest that high IRS1 with low IRS2 expression may predict the effectiveness of specific types of chemotherapy in breast cancer.

The HER2- and heregulin β1 (HRG)-inducible TNFR superfamily member Fn14 promotes HRG-driven breast cancer cell migration, invasion, and MMP9 expression

HER2 overexpression occurs in 15% to 20% of all breast cancers and is associated with increased metastatic potential and poor patient survival. Abnormal HER2 activation, either through HER2 overexpression or heregulin (HRG):HER3 binding, elicits the formation of potent HER2-HER3 heterodimers and drives breast cancer cell growth and metastasis. In a previous study, we found that fibroblast growth factor-inducible 14 (Fn14), a member of the TNF receptor superfamily, was frequently overexpressed in human HER2+ breast tumors. We report here that HER2 and Fn14 are also coexpressed in mammary tumors that develop in two different transgenic mouse models of breast cancer. In consideration of these findings, we investigated whether HER2 activation in breast cancer cells could directly induce Fn14 gene expression. We found that transient or stable transfection of MCF7 cells with a HER2 expression plasmid increased Fn14 protein levels. Also, HRG1-β1 treatment of MCF7 cells transiently induced Fn14 mRNA and protein expression. Both the HER2- and HRG1-β1-induced increase in Fn14 expression in MCF7 cells as well as basal Fn14 expression in HER2 gene-amplified AU565 cells could be reduced by HER2 kinase inhibition with lapatinib or combined HER2 and HER3 depletion using siRNA. We also report that Fn14-depleted, HER2-overexpressing MCF7 cells have reduced basal cell migration capacity and reduced HRG1-β1-stimulated cell migration, invasion, and matrix metalloproteinase (MMP)-9 expression. Together, these results indicate that Fn14 may be an important downstream regulator of HER2/HER3-driven breast cancer cell migration and invasion.