Interferon Regulatory Factor-4 Levels Research Articles

Interferon Regulatory Factor 4 (IRF4) Plays a Key Role in Osteoblast Differentiation of Postmenopausal Osteoporosis.

Postmenopausal osteoporosis (PMOP) is a prevalent disease, which features decreased bone mass, bone weakness and deteriorated bone microstructure in postmenopausal women. Although many factors have been revealed to contribute to the occurrence of PMOP, its mechanism remains undefined. This work aimed to identify significant changes in gene expression during PMOP formation and to examine the most valuable differential genes in postmenopausal osteoporosis versus the control group. The GSE68303 dataset that contains 12 ovariectomize (OVX) experimental and 11 sham groups was downloaded and analyzed. The results indicated that interferon regulatory factor 4 (IRF4) might be a hub gene in the development of postmenopausal osteoporosis. Western blot and immunohistochemistry were carried out to evaluate IRF4 levels in thoracic vertebra extracts from OVX and Sham mice. To assess IRF4's impact on osteogenic differentiation in postmenopausal bone marrow mesenchymal stem cells (BM-MSCs), IRF4 overexpression (OV-IRF4) and knockdown (Sh-IRF4) plasmids were constructed. The results showed that comparing with the sham group, bone samples from the OVX group showed higher IRF4 expression. Alkaline phosphatase (ALP) staining revealed that IRF4 overexpression significantly inhibited ALP activity, while IRF4 knockdown promoted ALP activity in BM-MSCs. Simvastatin-treated OVX mice showed increased total bone volume/total tissue volume (BV/TV) and elevated Runx2 expression by immunohistochemical staining compared with the OVX group. This study demonstrated that IRF4 is associated with OVX induced osteoporosis, it can regulate bone stability by inhibiting the osteogenic differentiation BM-MSCs. This study may help enhance our understanding of the molecular mechanism of PMOP formation, providing new insights into estrogen defiance induced osteoporosis.

IRF4 affects the protective effect of regulatory T cells on the pulmonary vasculature of a bronchopulmonary dysplasia mouse model by regulating FOXP3

BackgroundBronchopulmonary dysplasia (BPD) is a common chronic lung disease in preterm infants, characterised by compromised alveolar development and pulmonary vascular abnormalities. Emerging evidence suggests that regulatory T cells (Tregs) may confer protective effects on the vasculature. Knockdown of their transcription factor, interferon regulatory factor 4 (IRF4), has been shown to promote vascular endothelial hyperplasia. However, the involvement of Tregs and IRF4 in the BPD pathogenesis remains unclear. This study aimed to investigate the regulation of Tregs by IRF4 and elucidate its potential role in pulmonary vasculature development in a BPD mouse model.MethodsThe BPD model was established using 85% hyperoxia exposure, with air exposure as the normal control. Lung tissues were collected after 7 or 14 days of air or hyperoxia exposure, respectively. Haematoxylin–eosin staining was performed to assess lung tissue pathology. Immunohistochemistry was used to measure platelet endothelial cell adhesion molecule-1 (PECAM-1) level, flow cytometry to quantify Treg numbers, and Western blot to assess vascular endothelial growth factor (VEGFA), angiopoietin-1 (Ang-1), forkhead box protein P3 (FOXP3), and IRF4 protein levels. We also examined the co-expression of IRF4 and FOXP3 proteins using immunoprecipitation and immunofluorescence double staining. Furthermore, we employed CRISPR/Cas9 technology to knock down the IRF4 gene and observed changes in the aforementioned indicators to validate its effect on pulmonary vasculature development in mice.ResultsElevated IRF4 levels in BPD model mice led to FOXP3 downregulation, reduced Treg numbers, and impaired pulmonary vascular development. Knockdown of IRF4 resulted in improved pulmonary vascular development and upregulated FOXP3 level.ConclusionIRF4 may affect the protective role of Tregs in the proliferation of pulmonary vascular endothelial cells and pulmonary vascular development in BPD model mice by inhibiting the FOXP3 level.

Inhibition of Rho-Associated Coiled-Coil Containing Protein Kinases with Belumosudil Mesylate Shows Anti-Tumor and Immune Modulatory Properties in Models of Multiple Myeloma

Background: Myeloma patient outcomes have continuously improved with the introduction of proteasome inhibitors (PIs), immunomodulatory drugs (IMiDs), monoclonal antibodies (mAbs) recognizing cell surface proteins and, most recently, B-cell maturation antigen (BCMA)-targeted bispecifics and chimeric antigen receptor (CAR)-guided T-cells. However, the prognosis in triple-class refractory (TCR) disease that is refractory to PIs, IMiDs, and CD38 mAbs remains poor and, since BCMA-targeted CAR-Ts and bispecifics are not curative, quadruple-class refractory (QCR) disease that progresses during or after these therapies is an emerging challenge, indicating a persistent need for novel agents. Rho-associated coiled-coil containing protein kinases (ROCK1 and ROCK2) may represent novel potential targets since ROCK1 has been associated with a plasma cell leukemia-like transcriptional profile and as a myeloma dependency. Moreover, ROCK2 mediates expression of Interferon regulatory factor 4 (IRF4) and c-MYC, as well as Th17 responses that may contribute to an immune suppressive microenvironment. Methods: To examine the central hypothesis that targeting ROCK1/2 could be a novel and effective approach to myeloma therapy, we performed pre-clinical studies with the ROCK1/2 inhibitor belumosudil mesylate using drug-naïve and drug-resistant myeloma cell lines in vitro. Also, in vivo studies with immune correlates were performed in the Vk*MYC immune-competent syngeneic myeloma model, which has been reported to have a 67% positive predictive value for clinical efficacy in humans. Results: Belumosudil mesylate as a single agent reduced the viability of a panel of myeloma cell lines representing different molecular subtypes in a time- and concentration-dependent manner, with median inhibitory concentrations from 618 to 1,114 nM at 72 hours. These represent clinically relevant concentrations as the mean steady state C max for belumosudil mesylate given with food in studies of chronic graft-versus-host disease patients was 4.36 mM. Staining of myeloma cells with Annexin V and propidium iodide (PI) demonstrated that belumosudil induced appearance first of Annexin +/PI - (early apoptotic) cells, followed later by Annexin +/PI + (late apoptotic) and Annexin -/PI + (necrotic) cells, in a concentration-dependent manner. Studies of myeloma resistance mechanisms showed belumosudil largely overcame adhesion-mediated drug resistance, and was active against MM.1S and RPMI 8226 cells that are considered daratumumab-resistant. Moreover, belumosudil showed equal or even, in some cases, higher potency against bortezomib-, carfilzomib-, dexamethasone-, iberdomide-, lenalidomide-, melphalan-, and mezigdomide-resistant cell lines compared to their drug-naïve counterparts. Belumosudil induced in vitro killing of myeloma cells in a time- and dose-dependent manner independent of the presence of natural killer (NK) cells. Notably, when used in combination with the CD38 mAb isatuximab and in the presence of NK cells, belumosudil enhanced myeloma cell killing and prevented isatuximab-induced loss of CD38 expression. Mechanistically, belumosudil induced a reduction in c-MYC, IRF4, and phospho-STAT3 levels, consistent with its action on the IRF4/c-MYC axis. Dosing of belumosudil in vivo at 50 mg/kg twice weekly for three weeks in Vk*MYC mice with paraprotein levels consistent with active myeloma produced a consistent decline in disease burden as determined by serum protein electrophoresis monitoring ( A) compared to vehicle controls. NanoString analysis of tumor samples from these mice ( B) found down-regulation of XBP1 (X-box binding protein 1) and SLAMF7 (Signaling lymphocytic activation molecule family member 7), consistent with the anti-tumor efficacy of belumosudil mesylate. In addition, up-regulation was seen of c- JUN and c- FOS, consistent with promotion of T-cell activation and clonal expansion, as well as effector differentiation of antigen-activated CD8 + T cells. Conclusions: These pre-clinical in vitro and in vivo data support the hypothesis that targeting of ROCK1 and ROCK2 with belumosudil mesylate may be a promising strategy for relapsed/refractory myeloma and provide a rationale for its translation to the clinic. Currently, clinical trials of belumosudil are planned.

IRF4 is required for migration of CD4+ T cells to the intestine but not for Th2 and Th17 cell maintenance.

The transcription factor Interferon Regulatory Factor 4 (IRF4) is central in control of T cell activation and differentiation. Deficiency of IRF4 results in severe immune deficiency and affects maturation and function of most if not all T cell subsets. Here we use mouse infection models for Citrobacter rodentium and Strongyloides ratti to analyze the function of IRF4 in T helper (Th) 17 and Th2 cell responses, respectively. IRF4 deficient mice were impaired in the control of both pathogens, failed to mount Th17 and Th2 cell responses and showed impaired recruitment of T helper cells to the intestine, the infection site of both pathogens. Compromised intestinal migration was associated with reduced expression of the intestinal homing receptors α4β7 integrin, CCR9 and GPR15. Identification of IRF4 binding sites in the gene loci of these receptors suggests a direct control of their expression by IRF4. Competitive T cell transfer assays further demonstrated that loss of one functional Irf4 allele already affected intestinal accumulation and Th2 and Th17 cell generation, indicating that lower IRF4 levels are of disadvantage for Th2 and Th17 cell differentiation as well as their migration to the intestine. Conversion of peripheral CD4+ T cells from an Irf4 wildtype to an Irf4 heterozygous or from an Irf4 heterozygous to a homozygous mutant genotype after C. rodentium or S. ratti infection did not reduce their capacity to produce Th17 or Th2 cytokines and only partially affected their persistence in the intestine, revealing that IRF4 is not essential for maintenance of the Th2 and Th17 phenotype and for survival of these T helper cells in the intestine. In conclusion, we demonstrate that the expression levels of IRF4 determine Th2 and Th17 cell differentiation and their intestinal accumulation but that IRF4 expression is not crucial for Th2 and Th17 cell survival.

Maggot treatment promotes healing of diabetic foot ulcer wounds possibly by upregulating Treg levels

PurposeThrough the study of regulatory T cells (Tregs), we found a possible way to promote the healing of diabetic foot ulcers (DFUs) with maggot treatment and investigated the associated mechanism. MethodsImmunohistochemistry was used to examinetissues from DFU patients treated with or without maggot debridement therapy (MDT). The expression of the signature Treg molecule Foxp3, interleukin-10 (IL-10), transforming growth factor-beta (TGF-β), and interferon regulatory factor 4 (IRF-4) in patients with DFU treated with or without MDT was tested by real-time PCR (RT-PCR). CD4+ T cells from mouse spleen cells were cocultured in vitro with maggot excretions/secretions (ES), and Foxp3, IL-10, TGF-β, and IRF-4 levels were measured by RT-PCR. ResultsFoxp3 expression was obviously increased in DFU patients treated using MDT but less pronounced in those treated without MDT (P < 0.05). Foxp3, IL-10, TGF-β, and IRF-4 gene expression levels were higher in DFU patients treated with MDT than in those treated without MDT. Moreover, in vitro coculture of mouse spleen cells with ESs produced results consistent with the in vivo results (P < 0.001). ConclusionMDT/ESs can obviously upregulate the Treg level and may affect DFU healing in different ways, suggesting a new direction for the future treatment of DFU.

IRF-4 deficiency reduces inflammation and kidney fibrosis after folic acid-induced acute kidney injury

The chronic phase following toxin-induced acute kidney injury (AKI) is characterized by robust inflammation and progressive kidney fibrosis. Interferon regulatory factor 4 (IRF-4) is a type of multifunctional transcription factor that has been deeply linked to inflammation and fibrotic diseases. However, the role of IRF-4 in kidney damage and renal fibrosis after toxin-induced AKI remain to be explored. In this work, we examined the effect of IRF-4 deficiency on inflammation and kidney fibrosis in an AKI-chronic kidney disease (CKD) transition model induced by folic acid (FA) injury. We showed that FA treatment resulted in severe acute tubular injury followed by inflammatory reaction and interstitial fibrosis in wild-type mice. A sharp elevation of IRF-4 levels was observed in FA-injured kidneys. IRF-4 knockout led to a substantial reduction of extracellular matrix (ECM) proteins deposition and inhibited myofibroblasts transformation in the kidneys of mice subjected to FA treatment. In addition, IRF-4 ablation impaired F4/80+ macrophages and CD3+ T lymphocytes infiltration into the FA-injured kidneys. Loss of IRF-4 reduced the production of inflammatory molecules such as CXCL16, IL-18, IL-6, and TGF-β1 in the kidneys in response to FA stress. Following FA injury, the kidneys of IRF-4 knockout mice had fewer bone marrow-derived myofibroblasts than wild-type controls. Moreover, IRF-4 disruption inhibited macrophages to myofibroblasts differentiation in the kidneys in response to FA stimuli. In vitro, IL-4 stimulated expression of α-smooth muscle actin and ECM proteins and promoted M2 macrophages to myofibroblasts transition in mouse bone marrow-derived monocytes, which was abolished in the absence of IRF-4. Thus, we identified an important role of IRF-4 in the pathogenesis of progressive CKD following FA-induced AKI.

IRF4 modulates the response to BCR activation in chronic lymphocytic leukemia regulating IKAROS and SYK.

Interferon regulatory factor 4 (IRF4) is a transcriptional regulator of immune system development and function. Here, we investigated the role of IRF4 in controlling responsiveness to B-cell receptor (BCR) stimulation in chronic lymphocytic leukemia (CLL). We modulated IRF4 levels by transfecting CLL cells with an IRF4 vector or by silencing using small-interfering RNAs. Higher IRF4 levels attenuated BCR signaling by reducing AKT and ERK phosphorylation and calcium release. Conversely, IRF4 reduction improved the strength of the intracellular cascade activated by BCR engagement. Our results also indicated that IRF4 negatively regulates the expression of the spleen tyrosine kinase SYK, a crucial protein for propagation of BCR signaling, and the zinc finger DNA-binding protein IKAROS. We modulated IKAROS protein levels both by genetic manipulation and pharmacologically by treating CLL cells with lenalidomide and avadomide (IMIDs). IKAROS promoted BCR signaling by reducing the expression of inositol 5-phosphatase SHIP1. Lastly, IMIDs induced IRF4 expression, while down-regulating IKAROS and interfered with survival advantage mediated by BCR triggering, also in combination with ibrutinib. Overall, our findings elucidate the mechanism by which IRF4 tunes BCR signaling in CLL cells. Low IRF4 levels allow an efficient transmission of BCR signal throughout the accumulation of SYK and IKAROS.

Antimyeloma Potential of Caffeic Acid Phenethyl Ester and Its Analogues through Sp1 Mediated Downregulation of IKZF1-IRF4-MYC Axis.

Caffeic acid phenethyl ester (CAPE, 2), a natural compound from propolis, is a well-documented antitumor agent with nuclear factor kappa B (NF-κB) inhibitory activity. Key transcription factors regulated by NF-κB, namely, interferon regulatory factor-4 (IRF4) and octameric binding protein-2 (OCT2), are implicated in the tumorigenesis of multiple myeloma (MM), an incurable bone marrow cancer. Adverse effects and resistance to current chemotherapeutics pose a great challenge for MM treatment. Hence, the structure-activity relationships of CAPE (2) and 21 of its analogues were evaluated for their antimyeloma potential. Preclinical evaluation revealed that CAPE (2) and the 3-phenylpropyl (4), 2,5-dihydroxycinnamic acid 3-phenylpropyl ester (17), and 3,4-dihydroxycinnamic ether (22) analogues inhibited human myeloma cell growth. Analogue 4 surpassed CAPE (2) and lenalidomide in showing strong apoptotic effects with a remarkable decrease in IRF4 levels. The analogue 17 exhibited the most potent anti-MM activity. The downregulation of specificity protein 1 (Sp1) and the IKZF1-IRF4-MYC axis by CAPE (2) analogues 4 and 17 revealed their novel mechanism of action. The analogues showed no adverse cytotoxic effects on normal human cells and exhibited appropriate in silico pharmacokinetic properties and drug-likeness. These findings suggest the promising application of CAPE (2) analogues to target Ikaros (IKZF1)/IRF4 addiction, the so-called Achilles heel of myeloma, for better treatment outcomes.

A High-Throughput Drug Screen Reveals a Novel Compound Class That Significantly Depletes IRF4 Expression in Multiple Myeloma

Introduction Multiple myeloma (MM) is an incurable hematological malignancy characterized by the clonal expansion of malignant plasma cells (PCs) within the bone marrow. MM is genetically heterogeneous with aberrations including hyperdiploidy and chromosomal translocations commonly involving the immunoglobulin heavy chain (IgH) region. Many transcription factors can revoke their normal processes and act as oncogenes when they are brought under the control of IgH regulatory regions by a chromosomal translocation. Interferon Regulatory Factor 4 (IRF4) is a transcription factor which controls plasma cell differentiation and possesses many regulatory roles including interferon response, immune cell response, cell proliferation, apoptosis, and metabolism. IRF4 has proven to be a genetic vulnerability in MM as silencing studies in a large panel of MM cell lines with various genetic etiologies have demonstrated IRF4 expression is essential for MM cell survival. Standard of care treatments that indirectly suppress IRF4 including Proteasome inhibitors and Cereblon modulators have provided the greatest clinical outcomes for patients. However, like many other transcription factors, IRF4 has been notoriously difficult to target due to the protein's lack of amenable binding pockets favored for small molecule inhibitor development. Thus, identifying novel mechanisms and compounds to target IRF4 (directly or indirectly) can provide significant clinical impacts for MM patients. Methods To discover compounds capable of depleting IRF4 levels, we performed a high-throughput drug screen utilizing the Selleckchem Drug Repurposing Library on a widely accepted IRF4-dependent cell line. This library consists of over 2,000 diverse compounds that have well validated mechanisms of actions and have additionally passed clinical phase 1 safety trials for accelerated translational use. MM.1S cells were treated for 48 hours in duplicate (n = 2) with 10 μM compound. Following treatment, the cells were fixed, permeabilized, and stained for viability and IRF4 levels. IRF4 expression and viability was acquired by using flow cytometry, with high dose lenalidomide and shRNA for IRF4 as positive controls. Compounds that reduced IRF4 levels and cell viability across both experimental runs were ranked and selected with a cutoff of 40% as promising candidate compounds for further validation. Results Our drug screen results revealed 20 compounds (undisclosed) which met our cutoff of a decrease of IRF4 levels by 40% or greater. Ten hits were selected as having greater or equal to IRF4 depleting properties of lenalidomide and moved forward to be validated by western blot. Six drugs were shown to deplete IRF4 by western blot in MM.1S and KMS-18 cells at 10 μM doses. Interestingly, 4 out of the 10 hits all belong to same compound class that selectively bind to the same target receptor (undisclosed). Additional experiments confirmed these class of compounds deplete IRF4 levels in a dose dependent manner (EC50 = 1 μM). A time course revealed that IRF4 levels decrease shortly after the binding of these drugs to their widely reported target receptor, suggesting this is a selective drug/target receptor-mediated mechanism directly altering levels of IRF4. In vitro studies demonstrated the ability to both halt cell growth and decrease the viability of a panel of 8 MM cell lines, with IC50's ranging from 1.6 - 8.5 μM. Synergy studies with Lenolidomide and Bortezomib are underway to determine any synergistic combinations with standard of care therapies. In vivo studies and RNA-sequencing are also currently underway to determine the impact of these compounds on MM tumor growth and overall survival, as well as better define the mechanism of action driving this novel class of IRF4 targeting compounds. Conclusions Despite knowledge that IRF4 is a biologically potent target in MM there have been no extensive studies highlighting drugs capable of targeting this transcription factor and its oncogenic signaling network. This screen has revealed novel compounds, some of which are clinically used, that are capable of depleting a highly dependent gene in MM. Notably, these compounds are able to deplete IRF4 in a novel mechanism which is capable of affecting survival of MM cell lines that represent the heterogeneity of myeloma, and thus holds potential for significant clinical impact. Disclosures Ghobrial: Amgen: Consultancy; Janssen: Consultancy; Celgene: Consultancy; Takeda: Consultancy; Sanofi: Consultancy; BMS: Consultancy.

Genetic variation in IRF4 expression modulates growth characteristics, tyrosinase expression and interferon-gamma response in melanocytic cells.

A SNP within intron4 of the interferon regulatory factor4 (IRF4) gene, rs12203592*C/T, has been independently associated with pigmentation and age-specific effects on naevus count in European-derived populations. We have characterized the cis-regulatory activity of this intronic region and using human foreskin-derived melanoblast strains, we have explored the correlation between IRF4 rs12203592 homozygous C/C and T/T genotypes with TYR enzyme activity, supporting its association with pigmentation traits. Further, higher IRF4 protein levels directed by the rs12203592*C allele were associated with increased basal proliferation but decreased cell viability following UVR, an etiological factor in melanoma development. Since UVR, and accompanying IFNγ-mediated inflammatory response, is associated with melanomagenesis, we evaluated its effects in the context of IRF4 status. Manipulation of IRF4 levels followed by IFNγ treatment revealed a subset of chemokines and immuno-evasive molecules that are sensitive to IRF4 expression level and genotype including CTLA4 and PD-L1.

Abstract 2323: Interferon regulatory factor-4 is transcriptionally regulated by NF-κB in peripheral T-cell lymphomas

Abstract Interferon regulatory factor-4 (IRF4) is a tightly-regulated transcription factor involved in growth and differentiation of normal lymphocytes. IRF4 is expressed in multiple lymphoid malignancies and its expression drives tumor growth. Thus, characterization of the molecular events regulating IRF4 levels is key to design any targeting strategy. Here, we define a novel regulatory mechanism controlling IRF4 expression in peripheral T-cell lymphoma (PTCL), an aggressive non-Hodgkin lymphoma with poor overall survival rates and high levels of this transcription factor. In normal T cells, IRF4 was induced upon external activation of protein kinase C (PKC) by phorbol myristate acetate and ionomycin, an effect reversed by the PKC inhibitor, enzastaurin. Unlike normal T cells, PTCL cells constitutively expressed IRF4 in the absence of external stimulation, and this expression was resistant to enzastaurin. To identify regulators of IRF4 expression in PTCL, we performed a pharmacological screen using inhibitors that targeted PKC-associated pathways, including mitogen-activated protein kinases, PI3K/AKT/mTOR, and NF-κB. Of the inhibitors tested, only the proteasome inhibitor, bortezomib, showed a decrease in IRF4 expression in a dose- and time-dependent manner. To confirm this result we used a more specific NF-κB inhibitor blocking IκB kinase, BMS-345541. This inhibitor dramatically reduced IRF4 expression by 95.6% (P&amp;lt;0.0001). We used cell-based assays to investigate further the role of NF-κB in the transcriptional regulation of IRF4. A reporter assay for the IRF4 promoter demonstrated reduced promoter activity by siRNA knockdown of RelB and p52 NF-κB subunits to 31.4% and 36.9% of control (P=0.009). IRF4 promoter activity also was inhibited 67.9% by IκBαΔN, a dominant negative inhibitor of NF-κB activity (P=0.002), and was increased 71% by siRNA knockdown of IκBα (P&amp;lt;0.05). Chromatin immunoprecipitation assays confirmed the occupancy of NF-κB subunits in the IRF4 promoter, and this interaction was diminished in the presence of BMS-345541. Finally, knockdown of RelB and p52 subunits had a tendency to decrease IRF4 gene expression by 24.4% and 27.3% (P=0.1). Taken together, these data demonstrate transcriptional regulation of IRF4 by the NF-κB family in PTCL, and suggest the NF-κB pathway may represent a therapeutic target for PTCLs with concurrent IRF4 and NF-κB expression. Citation Format: Rebecca L. Boddicker, N. Sertac Kip, Luciana L. Almada, Julie C. Porcher, Deanna M. Grote, Stephen M. Ansell, Martin E. Fernandez-Zapico, Andrew L. Feldman. Interferon regulatory factor-4 is transcriptionally regulated by NF-κB in peripheral T-cell lymphomas. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2323. doi:10.1158/1538-7445.AM2014-2323

Abstract B223: Selective downregulation of interferon regulatory factor 4 by generation 2.5 antisense oligonucleotides induces strong apoptosis and sensitizes multiple myeloma cells to lenalidomide or bortezomib.

Abstract Despite significant advances made recently in treating multiple myeloma (MM), MM patients are often either unresponsive to or develop resistance to the standard therapies. Therefore, the disease still remains incurable and new more efficacious therapies are needed. Interferon Regulatory Factor 4 (IRF4) is a transcription factor which plays a critical role in the differentiation of normal B and T cells, and is strongly implicated in the development of hematological malignancies, especially MM. Although recent publications have pointed IRF4 as a key driver in the progression of MM, it is considered an intractable target by convention approaches. We recently demonstrated preclinical and clinical activity of a next-generation constrained-ethyl (cEt) modified (Gen 2.5) antisense oligonucleotides (ASOs) targeting STAT3 mRNA (STAT3Rx/AZD9150). Systemic delivery of unformulated STAT3Rx/AZD9150 produced robust target RNA and protein reductions in a broad range of xenograft models (AACR 2013). More importantly, STAT3Rx/AZD9150 showed striking clinical activity in the phase I dose escalation study, producing anti-tumor activity in 4 out of 6 patients with advanced treatment-refractory lymphoma (ASCO 2013). In this study, we describe next-generation .Gen 2.5 ASOs targeting IRF4. We first investigated whether selective downregulaion of IRF4 could lead to the death of MM cells and enhance the sensitivity of the tumor cells to the treatment of either lenalidomide or bortezomib. IRF4 ASOs administered via ‘free-uptake’, (lipid-independent) to cells growing in culture reduced IRF4 levels in a dose-dependent fashion with a concomitant strong induction of apoptosis in multiple human MM cell lines including KMS-11 and H929 cells. c-Myc, a key oncogene in MM and an immediate target gene of IRF4, also decreased significantly following IRF4 knockdown as anticipated. Importantly, MM cells were sensitive to even modest depletion of IRF4 (&amp;lt;50%), suggesting the strong dependence of MM cells on IRF4 for their survival. The effects of IRF4 ASOs on cell death were specific to MM cells as the ASOs had little effect on the proliferation of most of non-MM types of tumor cells, further demonstrating the specificity of the compounds in targeting IRF4. Next, IRF4 ASOs strongly potentiated the antiproliferative effects of either lenalidomide or bortezomib on MM cells. In addition, we established bortezomib-resistant clones of KMS-11 cells from a long-term exposure to drug and these remained sensitive to IRF4 inhibition. Furthermore, the growth of subcutaneously implanted KMS-11 tumors was significantly delayed with the systemic administration of IRF4 ASO compared with control ASO and this activity correlated with IRF4 depletion. Finally, treatment of mice with mouse-selective IRF4 ASOs at 50 mg/kg, twice a week for 4 weeks was well tolerated in normal mice, which is consistent with the lack of phenotypes observed in IRF4 heterozygous animals. Taken together, these results suggest that MM cells rely heavily on the survival pathway mediated by IRF4 and that selective knockdown of IRF4 by ASOs might provide an efficacious option for treating MM either as a mono-therapy or in combination with other drugs currently in clinical use for MM. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B223. Citation Format: Tianyuan Zhou, Joanna Schmidt, Ari Jerue, Minji Jo, Youngsoo Kim, A. Robert MacLeod. Selective downregulation of interferon regulatory factor 4 by generation 2.5 antisense oligonucleotides induces strong apoptosis and sensitizes multiple myeloma cells to lenalidomide or bortezomib. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B223.

Lenalidomide downregulates the cell survival factor, interferon regulatory factor‐4, providing a potential mechanistic link for predicting response

Overexpression of the transcription factor interferon regulatory factor-4 (IRF4), which is common in multiple myeloma (MM), is associated with poor prognosis. Patients with higher IRF4 expression have significantly poorer overall survival than those with low IRF4 expression. Lenalidomide is an IMiD immunomodulatory compound that has both tumouricidal and immunomodulatory activity in MM. This study showed that lenalidomide downregulated IRF4 levels in MM cell lines and bone marrow samples within 8 h of drug exposure. This was associated with a decrease in MYC levels, as well as an initial G1 cell cycle arrest, decreased cell proliferation, and cell death by day 5 of treatment. In eight MM cell lines, high IRF4 levels correlated with increased lenalidomide sensitivity. The clinical significance of this observation was investigated in 154 patients with MM. Among MM patients with high levels of IRF4 expression, treatment with lenalidomide led to a significantly longer overall survival than other therapies in a retrospective analysis. These data confirm the central role of IRF4 in MM pathogenesis; indicate that this is an important mechanism by which lenalidomide exerts its antitumour effects; and may provide a mechanistic biomarker to predict response to lenalidomide.