The rationale for development of ligelizumab in food allergy

Food allergy (FA) is a growing healthcare problem worldwide and the rising prevalence in many countries can be attributed to lifestyle, environmental, and nutritional changes. Immunoglobulin E (IgE)-mediated FA is the most common form of FA affecting approximately 3%-10% of adults and 8% of children across the globe. Food allergen-induced immediate hypersensitivity reactions mediated by IgE and high-affinity IgE receptor (FcεRI) complexes on mast cells and basophils are a major hallmark of the disease. FA can affect several aspects of health-related quality of life and impose a substantial financial burden on patients and healthcare systems. Although currently there is one United States Food and Drug Administration (FDA) and European Medicines Agency (EMA)-approved treatment for peanut allergy (Palforzia), the main treatment approaches are based on allergen avoidance and symptom management. Thus, there is an urgent need for more effective and ideally disease-modifying strategies. Given the crucial role of IgE in FA, anti-IgE monoclonal antibodies are considered promising therapeutic agents. Talizumab was the first humanized anti-IgE antibody to demonstrate substantial protection against allergic reactions from accidental peanut exposure by substantially increasing the peanut reactivity threshold on oral food challenge. However, development of talizumab was discontinued and further trials were performed using omalizumab. In double-blind, Phase 2, placebo-controlled trials in patients with multi-FAs, sustained dosing with omalizumab, or omalizumab in combination with oral immunotherapy, enabled rapid desensitization to multiple trigger foods. In this review, we describe the development of ligelizumab (a derivative of talizumab), a next generation, humanized monoclonal anti-IgE antibody, its existing clinical evidence, and its potential in the management of FA. When compared with omalizumab, ligelizumab binds with ∼88-fold higher affinity for human IgE and recognizes a different epitope that substantially overlaps with the binding site of FcεRI. These properties translate into a high potency to block IgE/FcεRI signaling in both in vitro and in vivo studies. Given its efficient suppression of IgE levels, good safety and pharmacokinetic/pharmacodynamic profile, ligelizumab clearly warrants further studies for the potential management of FA.

Identification and mechanistic characterization of low-molecular-weight inhibitors for HuR

Careful regulation of mRNA half-lives is a fundamental mechanism allowing cells to quickly respond to changing environmental conditions. The mRNA-binding Hu proteins are important for stabilization of short-lived mRNAs. Here we describe the identification and mechanistic characterization of the first low-molecular-weight inhibitors for Hu protein R (HuR) from microbial broths (Actinomyces sp.): dehydromutactin (1), MS-444 (2) and okicenone (3). These compounds interfere with HuR RNA binding, HuR trafficking, cytokine expression and T-cell activation. A mathematical and experimental analysis of the compounds' mode of action suggests that HuR homodimerizes before RNA binding and that the compounds interfere with the formation of HuR dimers. Our results demonstrate the chemical drugability of HuR; to our knowledge HuR is the first example of a drugable protein within the Hu family. MS-444, dehydromutactin and okicenone may become valuable tools for studying HuR function. An assessment of HuR inhibition as a central node in malignant processes might open up new conceptual routes toward combatting cancer.

oriP is essential for EBNA gene promoter activity in Epstein-Barr virus-immortalized lymphoblastoid cell lines

During Epstein-Barr virus latent infection of B lymphocytes in vitro, six viral nuclear antigens (EBNAs) are expressed from one of two promoters, Cp or Wp, whose activities are mutually exclusive. Upon infection, Wp is initially active, followed by a switch to Cp for the duration of latency. In this study, the region upstream of Cp was analyzed for the presence of cis elements involved in regulating the activities of the EBNA gene promoters in established in vitro immortalized lymphoblastoid cell lines (LCLs). It was determined that oriP, the origin for episomal maintenance during latency, is essential for efficient transcription initiation from either Cp or Wp in LCLs, as well as in some Burkitt's lymphoma cell lines. Deletion of the EBNA2-dependent enhancer located upstream of Cp resulted in a ca. two- to fivefold reduction in Cp activity in the LCLs assayed. More extensive deletion of sequences upstream of Cp, including the EBNA2-dependent enhancer, resulted in nearly complete loss of Cp activity. This loss of activity was shown to correlate with deletion of two CCAAT boxes, a proximal CCAAT box located at bp -61 to -65 and a distal CCAAT box located at bp -253 to -257, upstream of Cp. Site-directed mutagenesis of these cis elements demonstrated that Cp activity is highly dependent on the presence of a properly positioned CCAAT box, with the dependence on the distal CCAAT box apparent only when the proximal CCAAT box was deleted or mutated. Deletion of the glucocorticoid response elements located at ca. bp -850 upstream of Cp did not result in a significant loss in activity. In general, deletions which diminished Cp activity resulted in induction of Wp activity, consistent with suppression of Wp activity by transcriptional interference from Cp. The identification of oriP and the EBNA2-dependent enhancer as the major positive cis elements involved in regulating Cp activity in LCL suggests that EBNA gene transcription is largely autoregulated by EBNA 1 and EBNA 2.

Exclusive expression of Epstein-Barr virus nuclear antigen 1 in Burkitt lymphoma arises from a third promoter, distinct from the promoters used in latently infected lymphocytes

Epstein-Barr virus transformation of human B lymphocytes in vitro results in the expression of six viral nuclear antigens (EBNAs) and three viral membrane proteins. However, examination of viral gene expression in fresh Burkitt lymphoma isolates has revealed expression of only one of the nuclear antigens, EBNA-1. Previous transcriptional analyses of the EBNA-encoding genes demonstrated that all these genes are driven from one of two distal promoters located near the left end of the viral genome, raising the question of how exclusive expression of EBNA-1 occurs in Burkitt lymphoma tumors. Although most established Burkitt lymphoma cell lines (group 3) exhibit the full-expression pattern of viral antigens seen in lymphoblastoid cell lines, a few cell lines have been established that retain the restricted pattern of viral gene expression (group 1). In this paper we characterize transcription of the EBNA-1 gene in a group 1 Burkitt lymphoma cell line and show that (i) neither Cp nor Wp, the promoters involved in driving EBNA gene expression in lymphoblastoid cell lines, are active in this cell line; (ii) treatment of this cell line with 5-azacytidine, previously shown to induce expression of all EBNA genes, induced Cp and Wp activity; (iii) sizes of the EBNA-1 transcripts detected in two group 1 Burkitt lymphoma cell lines correlated with each other and were distinct from the size of the EBNA-1 transcript seen in lymphoblastoid cell lines; (iv) the EBNA-1 transcripts in the group 1 Burkitt lymphoma cell lines do not hybridize to a probe containing the common 5' exons present in all the EBNA transcripts from lymphoblastoid cell lines; and (v) anchored-PCR cloning the 5' region of the EBNA-1 transcript from one of the group 1 cell lines identified two exons, FQ and U, upstream of the EBNA-1 coding exon. The FQ exon lies just downstream of a TATAA box, which may represent the promoter for transcription of EBNA-1 in these cells. It is particularly noteworthy that an incomplete EBNA-1 cDNA clone from a nasopharyngeal carcinoma tumor line that expresses EBNA-1, but not the other EBNAs, has been characterized; this EBNA-1 transcript also contains the FQ/U splice junction, suggesting that the organization of exons upstream of the EBNA-1 coding exon is the same and that this organization may reflect a viral program for exclusive EBNA-1 expression.

Role for the Epstein-Barr virus nuclear antigen 2 in viral promoter switching during initial stages of infection

During latent Epstein-Barr virus (EBV) infection of human B lymphocytes, six viral nuclear antigen (EBNAs) are expressed from long primary transcripts by means of alternative splicing and alternative polyadenylylation sites. These transcripts initiate from one of two promoters, Cp or Wp, that function in a mutually exclusive fashion. Wp is exclusively utilized during the initial stages of infection of primary B lymphocytes, followed by a switch to Cp usage. These studies have been extended to show that (i) a mutant EBV strain lacking the gene encoding EBNA 2 fails to switch from Wp to Cp usage in primary B lymphocytes, although the virus contains a functional Cp; (ii) a region from -429 to -245 base pairs upstream of Cp is essential for Cp activity in B lymphocytes, but only in the context of upstream and downstream sequences; (iii) this region contains an EBNA 2-dependent enhancer; and (iv) DNase I protection employing nuclear extracts from B and T lymphocytes revealed a B-cell-specific footprint in the region of the EBNA 2-dependent enhancer. These results support a model for viral promoter switching during the initial stages of infection in which Wp activity leads to the expression of EBNA 2, followed by activation of Cp through the EBNA 2-dependent enhancer.

Alternative splicing dictates translational start in Epstein-Barr virus transcripts

Of the 10 viral genes known to be expressed during Epstein-Barr virus (EBV) latency, six encode nuclear antigens (EBNAs), all of which are expressed from a long primary transcript by means of alternative splicing and alternative polyadenylation sites. The primary transcript is generated by either of two promoters which operate in a mutually exclusive fashion in different clonal cell lines. All mRNAs from either promoter have exons in common from the BamHI W viral genomic fragment (the major internal repeat, IR1) which encode the N-terminal portion of one of the nuclear antigens (EBNA 4). In addition to the coding regions for EBNA 4, EBNA mRNAs encode another EBNA (i.e. EBNA 1, 2, 3A, 3B or 3C) downstream. We show that alternative splicing determines whether the translation initiation codon for EBNA 4 is present or absent, thus permitting the generation of mRNAs in which the first translation initiation codon is either that for the EBNA 4 gene or for the other EBNA gene encoded downstream. This mechanism presumably ensures efficient translation of all the EBNA genes.

Promoter switching in Epstein-Barr virus during the initial stages of infection of B lymphocytes

Transcription of the genes encoding the six viral nuclear antigens present in Epstein-Barr virus latently infected lymphocytes can be initiated from one of two promoters (Cp and Wp) mapping near the left end of the viral genome. These promoters are used in a mutually exclusive manner in clonal cell lines established from either Burkitt lymphoma tumors or in vitro infection of peripheral B lymphocytes. In this paper the role of Cp and Wp during viral latency is investigated. Cp appears to be the promoter normally employed during established latent infection. Analysis of two cell lines that use Wp revealed a deletion spanning Cp in the endogenous viral genomes, suggesting that cell lines exhibiting Wp activity harbor mutated viral genomes with a nonfunctional Cp. However, in contrast to the preferred usage of Cp exhibited by established Epstein-Barr virus-infected cell lines, Wp was shown to be exclusively utilized during the initial stages of viral infection. In addition to Wp activity, Cp usage was apparent by 6 days post-infection. A model is proposed involving B-lymphocyte differentiation-driven promoter switching during the establishment of viral latency.

Mutually exclusive use of viral promoters in Epstein-Barr virus latently infected lymphocytes

Of the eight viral antigens known to be expressed during Epstein-Barr virus latency, six are transcribed from a major rightward transcriptional unit, which gives rise to mRNAs containing common 5' exons. Analysis of cDNA clones has identified the use of two different promoters (Wp and Cp), located near the left-hand end of the viral genome, in generating these viral messages. Characterization of the activities of these two viral promoters in a number of Burkitt lymphoma and lymphoblastoid cell lines has revealed exclusive usage of only one of these promoters in all cell lines examined. Transfection of reporter constructs containing Wp and/or Cp linked to the bacterial chloramphenicol acetyltransferase gene into several different Epstein-Barr virus-infected cell lines generally supports a model in which the mutually exclusive use of Cp or Wp is determined by cellular factors and not by viral strain variation.