Interferon regulatory factor 4 as a therapeutic target in adult T-cell leukemia lymphoma

Interferon regulatory factor 4 modulates epigenetic silencing and cancer-critical pathways in melanoma cells

Interferon regulatory factor 4 (IRF4) was initially identified as a key controller in lymphocyte differentiation and function, and subsequently as a dependency factor and therapy target in lymphocyte-derived cancers. In melanocytes, IRF4 takes part in pigmentation. Although genetic studies have implicated IRF4 in melanoma, how IRF4 functions in melanoma cells has remained largely elusive. Here, we confirmed prevalent IRF4 expression in melanoma and showed that high expression is linked to dependency in cells and mortality in patients. Analysis of genes activated by IRF4 uncovered, as a novel target category, epigenetic silencing factors involved in DNA methylation (DNMT1, DNMT3B, UHRF1) and histone H3K27 methylation (EZH2). Consequently, we show that IRF4 controls the expression of tumour suppressor genes known to be silenced by these epigenetic modifications, for instance cyclin-dependent kinase inhibitors CDKN1A and CDKN1B, the PI3-AKT pathway regulator PTEN, and primary cilium components. Furthermore, IRF4 modulates activity of key downstream oncogenic pathways, such as WNT/β-catenin and AKT, impacting cell proliferation and survival. Accordingly, IRF4 modifies the effectiveness of pertinent epigenetic drugs on melanoma cells, a finding that encourages further studies towards therapeutic targeting of IRF4 in melanoma.

Inhibition of interferon regulatory factor 4 orchestrates T cell dysfunction, extending mouse cardiac allograft survival

BACKGROUND

T cell dysfunction, which includes exhaustion, anergy, and senescence, is a distinct T cell differentiation state that occurs after antigen exposure. Although T cell dysfunction has been a cornerstone of cancer immunotherapy, its potential in transplant research, while not yet as extensively explored, is attracting growing interest. Interferon regulatory factor 4 (IRF4) has been shown to play a pivotal role in inducing T cell dysfunction.

METHODS

A novel ultra-low-dose combination of Trametinib and Rapamycin, targeting IRF4 inhibition, was employed to investigate T cell proliferation, apoptosis, cytokine secretion, expression of T-cell dysfunction-associated molecules, effects of MAPK and mammalian target of Rapamycin (mTOR) signaling pathways, and allograft survival in both in vitro and BALB/c to C57BL/6 mouse cardiac transplantation models.

RESULTS

In vitro, blockade of IRF4 in T cells effectively inhibited T cell proliferation, increased apoptosis, and significantly upregulated the expression of programmed cell death protein 1 (PD-1), Helios, CD160, and cytotoxic T lymphocyte-associated antigen (CTLA-4), markers of T cell dysfunction. Furthermore, it suppressed the secretion of pro-inflammatory cytokines interferon (IFN)-γ and interleukin (IL)-17. Combining ultra-low-dose Trametinib (0.1 mg·kg-1·day-1) and Rapamycin (0.1 mg·kg-1·day-1) demonstrably extended graft survival, with 4 out of 5 mice exceeding 100 days post-transplantation. Moreover, analysis of grafts at day 7 confirmed sustained IFN regulatory factor 4 (IRF4) inhibition, enhanced PD-1 expression, and suppressed IFN-γ secretion, reinforcing the in vivo efficacy of this IRF4-targeting approach. The combination of Trametinib and Rapamycin synergistically inhibited the MAPK and mTOR signaling network, leading to a more pronounced suppression of IRF4 expression.

CONCLUSIONS

Targeting IRF4, a key regulator of T cell dysfunction, presents a promising avenue for inducing transplant immune tolerance. In this study, we demonstrate that a novel ultra-low-dose combination of Trametinib and Rapamycin synergistically suppresses the MAPK and mTOR signaling network, leading to profound IRF4 inhibition, promoting allograft acceptance, and offering a potential new therapeutic strategy for improved transplant outcomes. However, further research is necessary to elucidate the underlying pharmacological mechanisms and facilitate translation to clinical practice.

Alvocidib inhibits IRF4 expression via super-enhancer suppression and adult T-cell leukemia/lymphoma cell growth

Adult T-cell leukemia/lymphoma (ATL) is an intractable hematological malignancy with extremely poor prognosis. Recent studies have revealed that super-enhancers (SE) play important roles in controlling tumor-specific gene expression and are potential therapeutic targets for neoplastic diseases including ATL. Cyclin-dependent protein kinase (CDK) 9 is a component of a complex comprising transcription factors (TFs) that bind the SE region. Alvocidib is a CDK9 inhibitor that exerts antitumor activity by inhibiting RNA polymerase (Pol) II phosphorylation and suppressing SE-mediated, tumor-specific gene expression. The present study demonstrated that alvocidib inhibited the proliferation of ATL cell lines and tumor cells from patients with ATL. RNA sequencing (RNA-Seq) and chromatin immunoprecipitation sequencing (ChIP-Seq) disclosed that SE regulated IRF4 in the ATL cell lines. Previous studies showed that IRF4 suppression inhibited ATL cell proliferation. Hence, IRF4 is a putative alvocidib target in ATL therapy. The present study revealed that SE-mediated IRF4 downregulation is a possible mechanism by which alvocidib inhibits ATL proliferation. Alvocidib also suppressed ATL in a mouse xenograft model. Hence, the present work demonstrated that alvocidib has therapeutic efficacy against ATL and partially elucidated its mode of action. It also showed that alvocidib is promising for the clinical treatment of ATL and perhaps other malignancies and neoplasms as well.

Hijacking Host Immunity by the Human T-Cell Leukemia Virus Type-1: Implications for Therapeutic and Preventive Vaccines

Human T-cell Leukemia virus type-1 (HTLV-1) causes adult T-cell leukemia/lymphoma (ATLL), HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) and other inflammatory diseases. High viral DNA burden (VL) in peripheral blood mononuclear cells is a documented risk factor for ATLL and HAM/TSP, and patients with HAM/TSP have a higher VL in cerebrospinal fluid than in peripheral blood. VL alone is not sufficient to differentiate symptomatic patients from healthy carriers, suggesting the importance of other factors, including host immune response. HTLV-1 infection is life-long; CD4+-infected cells are not eradicated by the immune response because HTLV-1 inhibits the function of dendritic cells, monocytes, Natural Killer cells, and adaptive cytotoxic CD8+ responses. Although the majority of infected CD4+ T-cells adopt a resting phenotype, antigen stimulation may result in bursts of viral expression. The antigen-dependent "on-off" viral expression creates "conditional latency" that when combined with ineffective host responses precludes virus eradication. Epidemiological and clinical data suggest that the continuous attempt of the host immunity to eliminate infected cells results in chronic immune activation that can be further exacerbated by co-morbidities, resulting in the development of severe disease. We review cell and animal model studies that uncovered mechanisms used by HTLV-1 to usurp and/or counteract host immunity.

Transient Viral Activation in Human T Cell Leukemia Virus Type 1-Infected Macaques Treated With Pomalidomide

Human T cell leukemia virus type 1 (HTLV-1) persists in the host despite a vigorous immune response that includes cytotoxic T cells (CTL) and natural killer (NK) cells, suggesting the virus has developed effective mechanisms to counteract host immune surveillance. We recently showed that in vitro treatment of HTLV-1-infected cells with the drug pomalidomide (Pom) increases surface expression of MHC-I, ICAM-1, and B7-2, and significantly increases the susceptibility of HTLV-1-infected cells to NK and CTL killing, which is dependent on viral orf-I expression. We reasoned that by restoring cell surface expression of these molecules, Pom treatment has the potential to reduce virus burden by rendering infected cells susceptible to NK and CTL killing. We used the rhesus macaque model to determine if Pom treatment of infected individuals activates the host immune system and allows recognition and clearance of HTLV-1-infected cells. We administered Pom (0.2 mg/kg) orally to four HTLV-1-infected macaques over a 24 day period and collected blood, urine, and bone marrow samples throughout the study. Pom treatment caused immune activation in all four animals and a marked increase in proliferating CD4⁺, CD8⁺, and NK cells as measured by Ki-67⁺ cells. Activation markers HLA-DR, CD11b, and CD69 also increased during treatment. While we detected an increased frequency of cells with a memory CD8⁺ phenotype, we also found an increased frequency of cells with a Treg-like phenotype. Concomitant with immune activation, the frequency of detection of viral DNA and the HTLV-1-specific humoral response increased as well. In 3 of 4 animals, Pom treatment resulted in increased antibodies to HTLV-1 antigens as measured by western blot and p24Gag ELISA. Consistent with Pom inducing immune and HTLV-1 activation, we measured elevated leukotrienes LTB4 and LTE4 in the urine of all animals. Despite an increase in plasma LTB4, no significant changes in plasma cytokine/chemokine levels were detected. In all cases, however, cellular populations, LTB4, and LTE4 decreased to baseline or lower levels 2 weeks after cessation of treatment. These results indicated that Pom treatment induces a transient HTLV-1-specific immune activation in infected individuals, but also suggest Pom may not be effective as a single-agent therapeutic.

The molecular basis for the development of Adult T-cell leukemia/lymphoma in patients with an IRF4K59R mutation

Interferon regulatory factor 4 (IRF4) is an essential regulator in the development of many immune cells, including B and T cells and has been implicated directly in numerous haematological malignancies, including Adult T-cell leukemia/lymphoma (ATLL). Recently, an activating mutation in the DNA binding domain of IRF4 (IRF4^K59R ), was found as a recurrent somatic mutation in ATLL patients. However, it remains unknown how this mutation gives rise to the observed oncogenic effect. To understand the mode of IRF4^K59R mediated gain of function in ATLL pathogenesis, we have determined the structural and affinity basis of IRF4^K59R /DNA homodimer complex using X-ray crystallography and surface plasmon resonance. Our study shows that arginine substitution (R59) results in the reorientation of the side chain, enabling the guanidium group to interact with the phosphate backbone of the DNA helix. This markedly contrasts with the IRF4^WT wherein the K59 interacts exclusively with DNA bases. Further, the arginine mutation causes enhanced DNA bending, enabling the IRF4^K59R to interact more robustly with known DNA targets, as evidenced by increased binding affinity of the protein-DNA complex. Together, we demonstrate how key structural features underpin the basis for this activating mutation, thereby providing a molecular rationale for IRF4^K59R -mediated ATLL development. This article is protected by copyright. All rights reserved.

Involvement of EZH2 inhibition in lenalidomide and pomalidomide-mediated growth suppression in HTLV-1-infected cells

Immunomodulatory imide drugs (IMiDs), such as lenalidomide and pomalidomide, exert pleiotropic effects, e.g., antitumor effects in multiple myeloma, by binding the protein Cereblon and altering its substrate specificity. Lenalidomide is approved for the treatment of adult T-cell leukemia/lymphoma (ATL) caused by human T-cell leukemia virus type 1 (HTLV-1), although the precise mechanisms responsible for its effectiveness have not been fully elucidated. Here, we used HTLV-1-infected cell lines to investigate how IMiDs exert anti-ATL effects. In three of four tested HTLV-1-infected cell lines, the cells treated with lenalidomide or pomalidomide exhibited mild growth suppression without apoptosis, which was associated with decreased IRF4, c-Myc, and phosphorylated STAT3 levels as well as enhanced SOCS3 expression. Additionally, the levels of enhancer of zeste homolog 2 (EZH2) and trimethyl histone 3 Lys27 (H3K27me3) were decreased following IMiD treatment in all three susceptible cell lines. An IMiD-mediated reduction of EZH2 and H3K27me3 levels was also observed in a multiple myeloma cell line. Furthermore, treatment with an EZH2-inhibitor reproduced the IMiD-mediated effects in HTLV-1-infected cells and multiple myeloma cells. These findings strongly suggest that a reduction of EZH2 expression is involved in the mechanism underlying the antitumor effects of IMiD.

Targeting NF-κB with Nanotherapy in a Mouse Model of Adult T-Cell Leukemia/Lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive, clonal malignancy of mature T cells caused by human T-cell leukemia virus type 1. Although it is a rare tumor type, it serves as an excellent model of a virus driven process that transforms cells and engenders a highly malignant tumor that is extraordinarily difficult to treat. The viral transcriptional transactivator (Tax) in the HTLV-1 genome directly promotes tumorigenesis, and Tax-induced oncogenesis depends on its ability to constitutively activate NF-κB signaling. Accordingly, we developed and evaluated a nano-delivery system that simultaneously inhibits both canonical (p65) and noncanonical (p100) NF-κB signaling pathways locally in tumors after systemic administration. Our results demonstrate that siRNA is delivered rapidly to ATLL tumors after either i.p. or i.v. injection. The siRNA treatment significantly reduced both p65 and p100 mRNA and protein expression. Anti-NF-κB nanotherapy significantly inhibited tumor growth in two distinct tumor models in mice: a spontaneous Tax-driven tumor model, and a Tax tumor cell transplant model. Moreover, siRNA nanotherapy sensitized late-stage ATLL tumors to the conventional chemotherapeutic agent etoposide, indicating a pleiotropic benefit for localized siRNA nanotherapeutics.