A human CD137×PD-L1 bispecific antibody promotes anti-tumor immunity via context-dependent T cell costimulation and checkpoint blockade

Immune checkpoint inhibitors demonstrate clinical activity in many tumor types, however, only a fraction of patients benefit. Combining CD137 agonists with these inhibitors increases anti-tumor activity preclinically, but attempts to translate these observations to the clinic have been hampered by systemic toxicity. Here we describe a human CD137xPD-L1 bispecific antibody, MCLA-145, identified through functional screening of agonist- and immune checkpoint inhibitor arm combinations. MCLA-145 potently activates T cells at sub-nanomolar concentrations, even under suppressive conditions, and enhances T cell priming, differentiation and memory recall responses. In vivo, MCLA-145 anti-tumor activity is superior to immune checkpoint inhibitor comparators and linked to recruitment and intra-tumor expansion of CD8 + T cells. No graft-versus-host-disease is observed in contrast to other antibodies inhibiting the PD-1 and PD-L1 pathway. Non-human primates treated with 100 mg/kg/week of MCLA-145 show no adverse effects. The conditional activation of CD137 signaling by MCLA-145, triggered by neighboring cells expressing >5000 copies of PD-L1, may provide both safety and potency advantages.

Abstract 952: The bispecific antibody MCLA-129 impairs NSCLC tumor growth by targeting EGFR and c-MET, inhibiting ligand-induced signaling and promoting ADCC and ADCP

MCLA-129 is an ADCC-enhanced common light chain bispecific human IgG1 Biclonics® antibody specifically targeting the receptor tyrosine kinases EGFR and c-MET. It inhibits activation and downstream signaling of EGFR and c-MET induced by their respective ligands EGF and HGF and promotes elimination of tumor cells via Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC) and Antibody-Dependent Cell-Mediated Phagocytosis (ADCP).

MCLA-129 was developed to overcome c-MET signaling-dependent EGFR TKI-resistance mechanisms and was identified during an unbiased screening campaign with a focus on inhibition of ligand-induced proliferation and migration of cancer cells. Selectivity of MCLA-129 for tumor cells is achieved by simultaneously targeting both EGFR and c-MET. MCLA-129 blocks EGF and HGF binding to EGFR and c-MET, respectively, and consequently inhibits their ligand-induced phosphorylation. MCLA-129 was shown to bind critical residues on EGFR and c-MET for EGF and HGF ligand binding.

GlymaxX® low fucose glycoengineering technology was used to enhance the mononuclear cell ADCC activity of the bispecific antibody. MCLA-129 demonstrated potent dose-dependent ADCC and ADCP against all NSCLC cell lines tested, which positively correlated with the EGFR and c-MET expression levels on the target cells. Significant inhibition of tumor growth of NCI-H1975EGFR L858R, T790M and HCC827/ER1EGFR del (E746, A750), c-MET amplified NSCLC cell line derived tumors was observed following MCLA-129 treatment.

MCLA-129 can overcome HGF-mediated EGFR-TKI resistance, as demonstrated by testing a non-ADCC enhanced version of this antibody in a panel of NSCLC cell lines in vitro and orthotopic tumors in vivo showing that it inhibits EGFR and c-MET activity. Significant tumor regression was observed following treatment of immunodeficient xenograft NSG-hHGFki mice bearing orthotopic tumors established from HCC827EGFR del (E746, A750) cells. In addition, in an acquired erlotinib EGFR TKI resistance model, treatment of mice harboring tumors as big as >500 mm3 led to significant reduction of tumor size which persisted after the treatment period.

Taken together these data demonstrate that MCLA-129 is a potent inhibitor of tumor growth applying various mechanisms of action, including inhibition of c-MET and EGFR signaling, ADCC and ADCP. MCLA-129 holds promise as a potential treatment for patients with NSCLC and other cancers, and warrants clinical evaluation.

Citation Format: David J. de Gorter, Alexandre Deshiere, Martijn van Rosmalen, Christian Wohn, Berina Eppink, Tristan Gallenne, Rinse Klooster, Li Mao, Wenxin Xu, Liang Deng, Qingyu Shu, Wei Liu, John de Kruif, Mario Di Matteo, Massimiliano Mazzone, Mark Throsby, Cecile A. Geuijen. The bispecific antibody MCLA-129 impairs NSCLC tumor growth by targeting EGFR and c-MET, inhibiting ligand-induced signaling and promoting ADCC and ADCP [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 952.

Abstract LB-C07: Preclinical evaluation of MCLA-129: A bispecific antibody targeting c-MET and EGFR

NSCLC is the most common form of cancer. Approximately 20% of NSCLC patients have mutations in the growth factor (GF) receptor EGFR. These patients respond to tyrosine kinase inhibitors (TKIs) that target mutant EGFR; however relapse eventually occurs. c-MET is one of the most common GF pathways upregulated in resistant patients. Met amplification is found in 5-10% of tumors that acquire resistance to EGFR TKIs in the first line of treatment and this frequency becomes higher in later lines of treatment. Preclinical studies have shown that co-inhibition of c-MET and EGFR inhibits growth and survival in these resistant tumors. We describe here an unbiased functional screen of bispecific antibodies (bAbs) targeting EGFR and c-MET to select MCLA-129 and its evaluation in an in vivo xenograft NSCLC model. Large collections of common light chain Fab binding ‘arms’ against EGFR and c-MET were derived from immunized MeMo® mice and used in different combinations (based on epitope and sequence diversity) to generate IgG1 Biclonics® bAbs. The panel of > 400 bAbs was screened for proliferation inhibition of the N87 cell line stimulated with EGF and/or HGF. Five bAbs inhibited N87 growth comparable to the combination of cetuximab and a MetMab analog (C+M). Two of the most potent Biclonics® bAbs were selected for further characterization and screened for inhibitory activity in NSCLC cell lines PC-9 and HCC827 that harbour an EGFR exon 19 deletion. The addition of HGF reversed the inhibitory effect of the EGFR TKI erlotinib and gefitinib in both cell lines. Combination of bAbs or C+M with erlotinib or gefinitinib resulted in inhibition of growth and downstream phosphorylation similar to erlotinib treatment without GF addition in both HGF alone or HGF + EGF culture conditions. The best bAb was as potent (PC-9) or more potent (HCC827) than C+M. The lead bAb, MCLA-129 was ADCC enhanced and shown to effectively mediate ADCC against NSCLC cell lines with both high and low affinity FcR bearing effector cells. MCLA-129 was then tested in an genetically engineered immunodeficient xenograft mouse model where endogenous mouse HGF promoter drives the expression of human HGF bypassing the problem of the low affinity binding of mouse HGF for human c-MET. Mice engrafted with HCC827 cells and treated with MCLA-129 (25 mg/kg) displayed significant tumor regression (below baseline) and a much slower tumor regrowth rate upon drug cessation and this activity was enhanced when combined with erlotinib (6mg/kg). This potent therapeutic activity was achieved without the contribution of ADCC and was not observed in mice that received only erlotinib, a bivalent c-MET antagonizing antibody or their combination. To model acquired resistance to EGFR TKI treatment, animals were treated with erlotinib until tumors were >500mm3, MCLA-129 was added to erlotinib in one randomized group. In this group, immediate tumor inhibition was observed, which persisted over the treatment period. In summary, MCLA-129 was synergistic with EGFR targeting TKI’s to reverse c-MET mediated resistance in NSCLC cell lines both in vitro and in vivo. The activity of MCLA-129 was superior to relevant comparator biologics that were combined to inhibit EGFR and c-MET signaling in the absence of functional immunity. These preclinical data suggest MCLA-129 could benefit NSCLC patients that become resistant to EGFR targeted therapies and warrants clinical evaluation.

Citation Format: Cecile Geuijen, Mario di Matteo, Tristan Gallenne, Sarah Trusso Cafarello, Roy Nijhuis, Therese Visser, Willem Bartelink, Carina Bartelink-Clements, Berina Eppink, Rinse Klooster, John dekruif, Massimiliano Mazzone, Mark Throsby. Preclinical evaluation of MCLA-129: A bispecific antibody targeting c-MET and EGFR [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr LB-C07. doi:10.1158/1535-7163.TARG-19-LB-C07

Abstract 541: An unbiased screen identifies a CD137xPD-L1 bispecific IgG1 antibody with unique T cell activation and binding properties

CD137 (4-1BB) is a transmembrane costimulatory receptor on T and NK cells that enhances adaptive immune responses and is a critical mediator of antitumor immunity. CD137 signaling requires receptor clustering normally facilitated by the trimeric CD137 ligand (CD137L). Alternatively, CD137 signaling can be triggered either directly by agonistic monoclonal antibodies (mAbs) or indirectly via crosslinking of CD137 binding mAbs by Fcγ receptors on neighboring cells. The development of CD137 targeted agents for cancer therapy has been hampered by on-target off-tumor toxicity in the case of agonist, monospecific, bivalent mAbs or limited antitumor activity in the case of crosslinking mAbs. To address the issues of toxicity and efficacy a highly selective and potent CD137xPD-L1 bispecific antibody (bAb) was identified by applying an unbiased functional screening approach. Collections of common light chain Fabs recognizing CD137 and PD-L1 were produced based on antibody panels from immunized MeMo® mice. A large and diverse panel of CD137xPD-L1 bAbs was then produced by combining different CD137 and PD-L1 Fabs based on epitope and sequence diversity in the IgG1 Biclonics® format. The bAbs were screened for activity in reporter cell lines expressing the receptors. This unbiased combinatorial screening identified a CD137xPD-L1 bAb (MCLA-145) for which CD137 mediated activation is dependent on the presence of PD-L1 on a neighboring cell and, as such, the antibody acts in ‘trans’. Flow cytometry experiments demonstrated that MCLA-145 is fully cross-reactive to cynomolgus monkey CD137 and PD-L1. The CD137 Fab arm blocks the interaction of CD137 with CD137L as demonstrated in a competition assay by flow cytometry. The PD-L1 Fab arm blocks the interaction between PD-1 and PD-L1 as demonstrated in ELISA. Binding epitopes were mapped by shotgun mutagenesis using a flow-based screen. In addition, hydrogen-deuterium exchange experiments were performed to map the binding domain on CD137. Data show that MCLA-145 binds the ligand binding domain of CD137 domain (CRDII). The PD-L1 Fab arm binds PD-L1 in the PD-1 binding N-terminal V domain. Both epitope mapping data sets are consistent with the CD137 and PD-L1 ligand blocking activity of MCLA-145. Monovalent binding affinities were measured by surface plasma resonance (SPR) and radioactive iodine labeling and demonstrated affinities in the low nM (CD137) and subnanomolar (PD-L1) range. SPR experiments also confirmed that MCLA-145 was able to bind simultaneously to both CD137 and PD-L1 recombinant proteins. The unique binding properties of MCLA-145 may result in an increased therapeutic window by specifically activating CD137 expressing cells in the tumor niche where PD-L1 is expressed while simultaneously blocking inhibitory input from the PD-1/PD-L1 axis.

Citation Format: Cecile A. Geuijen, Paul Tacken, Rinse Klooster, Horacio Nastri, Shaun Stewart, Jing Zhou, Steve Wang, Cheng-Yen Huang, Arjen Kramer, Linda Kaldenberg-Hendriks, John de Kruif, Renate den Blanken-Smit, Vanessa Zondag-van de Zande, Abdul Basmeleh, Willem Bartelink, Patrick Mayes, Gregory Hollis, Reid Huber, Mark Throsby. An unbiased screen identifies a CD137xPD-L1 bispecific IgG1 antibody with unique T cell activation and binding properties [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 541.

Abstract B088: Generation of immuno-modulatory receptor binding bispecific antibodies to modulate tumor immunity

Introduction: Monoclonal antibodies blocking CTLA-4 or PD-1 ligand interaction have been shown to induce durable clinical responses in a subset of melanoma and NSCLC patients. The clinical efficacy of these antibodies has been linked to their ability to restore robust anti-tumor immune responses. Based on clinical and preclinical data it is expected that combinations of antibodies blocking inhibitory and/or costimulatory molecules could benefit patients that do not respond to existing immunotherapies. However dual blockade of immuno-modulatory receptors (iMODs) has also been shown to increase immune-related toxicity as has been shown for a combination of CTLA-4 and PD-1 antibodies. Bispecific antibodies are a novel therapeutic modality capable of specifically binding two different targets. As such they may be ideally suited to address dual blockade of iMODs. Previous work on other cell surface targets has shown that bispecific antibodies can exert functional activities that cannot be reproduced by monoclonal antibody combinations. In addition, bispecific antibodies that more selectively target specific cell populations, based on the co-expression of the two targets, could have reduced safety liabilities in patients. We report here the generation and characterization of common light chain (cLC) Fab panels against PD-1, PD-L1, LAG-3, CD137, OX40 and TIM-3 for combination in a full length IgG1 bispecific antibody format and present the functional evaluation of some of these combinations in human in vitro functional assays.

Methods: Humanized cLC mice (MeMo®) were immunized with recombinant protein or DNA, and materials harvested from these mice were used to generate Fab regions against these antigens using phage display. Furthermore, large and diverse synthetic cLC Fab-phagemid libraries were used to select iMOD specific Fabs. The resulting cLC Fabs were cloned into bispecific antibody expression constructs for further testing. Recombinant proteins (both wild type and domain swapped orthologs) were generated for each target and used for binding and competition in both ELISA and FACS. Reporter assays using NFAT or NFkB-luc in Jurkat cells were used for each target to measure functional activity of antibodies. Furthermore, primary human assays using CD3 or SEB activation with cytokine release were used as a read-out of T cell activity.

Results: Two parallel strategies were applied to generate panels of cLC Fabs against PD-1, PD-L1, LAG-3, CD137, OX40 and TIM-3; mouse immunization and phage selection yielded >1350 specific Fab arms whereas synthetic library selections yielded >850 Fabs. Initial characterization and binning of representative clones were carried out in bispecific IgG format (iMOD specific Fabs combined with a Tetanus toxoid-specific control Fab arm) allowing for stringent ranking of the iMOD panels in a monovalent format for (domain) specificity, cynomolgus cross-reactivity, affinity, stability, and ligand blocking potency. The resulting characteristics of the identified bins were used to generate diverse bispecific antibody panels that combined different iMOD Fabs. These were first tested in reporter assays to select functional clones, that were then confirmed in a SEB driven T cell proliferation assay. Several bispecific candidates have been identified that show significantly increased cytokine production and other functional parameters compared to benchmark antibodies.

Conclusion: Large diverse Fab panels binding six different iMODs were generated for use in bispecific antibody combinations. Characterization and screening of large panels of bispecific IgG has been carried out in relevant functional assays. Results from the screening of bispecific antibodies targeting iMOD combinations support the concept of empirical screening to identify potent immunomodulatory combinations.

Citation Format: Rinse Klooster, Cecile Geuijen, Mark Throsby. Generation of immuno-modulatory receptor binding bispecific antibodies to modulate tumor immunity [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B088.

Isoaspartylation appears to trigger small cell lung cancer-associated autoimmunity against neuronal protein ELAVL4

Autoantibodies against SCLC-associated neuronal antigen ELAVL4 (HuD) have been linked to smaller tumors and improved survival, but the antigenic epitope and mechanism of autoimmunity have never been solved. We report that recombinant human ELAVL4 protein incubated under physiological conditions acquires isoaspartylation, a type of immunogenic protein damage. Specifically, the N-terminal region of ELAVL4, previously implicated in SCLC-associated autoimmunity, undergoes isoaspartylation in vitro, is recognized by sera from anti-ELAVL4 positive SCLC patients and is highly immunogenic in subcutaneously injected mice and in vitro stimulated human lymphocytes. Our data suggest that isoaspartylated ELAVL4 is the trigger for the SCLC-associated anti-ELAVL4 autoimmune response.

Longitudinal epitope mapping in MuSK myasthenia gravis: implications for disease severity

Muscle weakness in MuSK myasthenia gravis (MG) is caused predominantly by IgG4 antibodies which block MuSK signalling and destabilize neuromuscular junctions. We determined whether the binding pattern of MuSK IgG4 antibodies change throughout the disease course ("epitope spreading"), and affect disease severity or treatment responsiveness. We mapped the MuSK epitopes of 255 longitudinal serum samples of 53 unique MuSK MG patients from three independent cohorts with ELISA. Antibodies against the MuSK Iglike-1 domain determine disease severity. Epitope spreading outside this domain did not contribute to disease severity nor to pyridostigmine responsiveness. This provides a rationale for epitope specific treatment strategies.

Selection and characterization of llama single domain antibodies against N-terminal huntingtin

Huntington disease is caused by expansion of a CAG repeat in the huntingtin gene that is translated into an elongated polyglutamine stretch within the N-terminal domain of the huntingtin protein. The mutation is thought to introduce a gain-of-toxic function in the mutant huntingtin protein, and blocking this toxicity by antibody binding could alleviate Huntington disease pathology. Llama single domain antibodies (VHH) directed against mutant huntingtin are interesting candidates as therapeutic agents or research tools in Huntington disease because of their small size, high thermostability, low cost of production, possibility of intracellular expression, and potency of blood-brain barrier passage. We have selected VHH from llama phage display libraries that specifically target the N-terminal domain of the huntingtin protein. Our VHH are capable of binding wild-type and mutant human huntingtin under native and denatured conditions and can be used in Huntington disease studies as a novel antibody that is easy to produce and manipulate.

MuSK IgG4 autoantibodies cause myasthenia gravis by inhibiting binding between MuSK and Lrp4

Myasthenia gravis (MG) is a severely debilitating autoimmune disease that is due to a decrease in the efficiency of synaptic transmission at neuromuscular synapses. MG is caused by antibodies against postsynaptic proteins, including (i) acetylcholine receptors, the neurotransmitter receptor, (ii) muscle-specific kinase (MuSK), a receptor tyrosine kinase essential for the formation and maintenance of neuromuscular synapses, and (iii) low-density lipoprotein receptor-related protein 4 (Lrp4), which responds to neural Agrin by binding and stimulating MuSK. Passive transfer studies in mice have shown that IgG4 antibodies from MuSK MG patients cause disease without requiring complement or other immune components, suggesting that these MuSK antibodies cause disease by directly interfering with MuSK function. Here we show that pathogenic IgG4 antibodies to MuSK bind to a structural epitope in the first Ig-like domain of MuSK, prevent binding between MuSK and Lrp4, and inhibit Agrin-stimulated MuSK phosphorylation. In contrast, these IgG4 antibodies have no direct effect on MuSK dimerization or MuSK internalization. These results provide insight into the unique pathogenesis of MuSK MG and provide clues toward development of specific treatment options.

Antibodies to active zone protein ERC1 in Lambert-Eaton myasthenic syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is characterized by fluctuating muscle weakness and autonomic dysfunction. In 90% of the LEMS patients the disease is associated with auto-antibodies against the voltage-gated calcium channels (VGCC). Several auto-immune responses against other antigenic targets have been described to (co)-occur in LEMS patients. To identify new LEMS associated small cell lung cancer (SCLC) markers immunoprecipitation with a SCLC cell line was performed. We discovered strong immunoreactivity against the 120 kDa large ERC1 protein in one tumor-negative VGCC-positive LEMS patient. A recombinant ELISA assay and a cellular assay expressing GFP-tagged full length ERC1 were used to confirm the presence of auto-antibodies against ERC1 in this patient. Additional testing of 58 LEMS patients including 9 VGCC auto-antibody negative LEMS patients, 48 myasthenia gravis patients, 84 control patients with other diseases and 12 healthy controls revealed no other cases. ERC1 is therefore a new, but rare, antigen in LEMS.

Digenic inheritance of an SMCHD1 mutation and an FSHD-permissive D4Z4 allele causes facioscapulohumeral muscular dystrophy type 2

Facioscapulohumeral dystrophy (FSHD) is characterized by chromatin relaxation of the D4Z4 macrosatellite array on chromosome 4 and expression of the D4Z4-encoded DUX4 gene in skeletal muscle. The more common form, autosomal dominant FSHD1, is caused by a contraction of the D4Z4 array, whereas the genetic determinants and inheritance of D4Z4 array contraction-independent FSHD2 are unclear. Here we show that mutations in SMCHD1 (structural maintenance of chromosomes flexible hinge domain containing 1) on chromosome 18 reduce SMCHD1 protein levels and segregate with genome-wide D4Z4 CpG hypomethylation in human kindreds. FSHD2 occurs in individuals who inherited both the SMCHD1 mutation and a normal-sized D4Z4 array on a chromosome 4 haplotype permissive for DUX4 expression. Reducing SMCHD1 levels in skeletal muscle results in contraction-independent DUX4 expression. Our study identifies SMCHD1 as an epigenetic modifier of the D4Z4 metastable epiallele and as a causal genetic determinant of FSHD2 and possibly other human diseases subject to epigenetic regulation.

Long-lasting treatment effect of rituximab in MuSK myasthenia

OBJECTIVE

Rituximab has emerged as an efficacious option for drug-resistant myasthenia gravis (MG). However, reports published only describe the short-term follow-up of patients treated and little is known about their long-term clinical and immunologic evolution. Our objective was to report the clinical and immunologic long-term follow-up of 17 patients (6 MuSK+MG and 11 AChR+MG) and compare the response between AChR+MG and MuSK+MG patients.

METHODS

Myasthenia Gravis Foundation America postintervention status and changes in treatment and antibody titers were periodically determined. Lymphocyte subpopulations, total immunoglobulin, immunoglobulin G (IgG) anti-MuSK subclasses, and anti-tetanus toxoid IgG before and after treatment were also studied.

RESULTS

After a mean post-treatment period of 31 months, 10 of the AChR+MG patients improved but 6 of them needed reinfusions. In contrast, all MuSK+MG patients achieved a remission (4/6) or minimal manifestations (2/6) status and no reinfusions were needed. Consequently, in the MuSK+MG group, prednisone doses were significantly reduced and concomitant immunosuppressants could be withdrawn. Clinical improvement was associated with a significant decrease in the antibody titers only in the 6 MuSK+MG patients. At last follow-up MuSK antibodies were negative in 3 of these patients and showed a decrease of over 80% in the other 3.

CONCLUSION

In view of the long-lasting benefit observed in MuSK+MG patients, we recommend to use rituximab as an early therapeutic option in this group of patients with MG if they do not respond to prednisone.

CLASSIFICATION OF EVIDENCE

This study provides Class IV evidence that IV rituximab improves the clinical and immunologic status of patients with MuSK+MG.

Selection of VHH antibody fragments that recognize different Aβ depositions using complex immune libraries

Phage display technology is frequently used to obtain antigen specific binders with predetermined characteristics. Phage display libraries are often constructed from animals immunized with the antigen of interest. An important point of consideration when making immune libraries is the availability of an appropriate antigen sources. When available, often either the amount is not sufficient for immunization or it is expensive to obtain. To overcome this problem, these antigens are typically obtained by over expression in prokaryotic or eukaryotic expression systems. While this could solve the problem of obtaining sufficient quantities of antigen for a reasonable price and effort, correct folding and differences in posttranslational modification could potentially lead to binders that recognize the recombinant, but not the endogenous protein. In addition, selection of binders against specific modifications or structural epitopes could be missed.In this chapter we describe a particular selection of VHH antibody fragments from phage display libraries that were constructed from llamas immunized with different complex protein samples containing the antigen of interest. We show that this can result in binders that preferentially recognize the target of interest when present in specific structures depending on the antigen source.

Self-regulated alternative splicing at the AHNAK locus

AHNAK is a 700-kDa protein involved in cytoarchitecture and calcium signaling. It is secondarily reduced in muscle of dysferlinopathy patients and accumulates in muscle of calpainopathy patients, both affected by a muscular dystrophy. AHNAK directly interacts with dysferlin. This interaction is lost on cleavage of AHNAK by the protease calpain 3, explaining the molecular observations in patients. Currently, little is known of AHNAK regulation. We describe the self-regulation of multiple mRNA transcripts emanating from the AHNAK locus in muscle cells. We show that the AHNAK gene consists of a 17-kb exon flanked by multiple small exons. This genetic structure is shared by AHNAK2 and Periaxin, which share a common ancestor. Two major AHNAK transcripts are differentially expressed during muscle differentiation that encode for a small (17-kDa) and a large (700-kDa) protein isoform. These proteins interact in the cytoplasm, but the small AHNAK is also present in the nucleus. During muscle differentiation the small AHNAK is strongly increased, thereby establishing a positive feedback loop to regulate mRNA splicing of its own locus. A small 17-kDa isoform of Periaxin similarly traffics between the cytoplasm and the nucleus to regulate mRNA splicing. Thus, AHNAK constitutes a novel mechanism in post-transcriptional control of gene expression.

Facioscapulohumeral muscular dystrophy region gene 1 is a dynamic RNA-associated and actin-bundling protein

FSHD region gene 1 (FRG1) is a dynamic nuclear and cytoplasmic protein that, in skeletal muscle, shows additional localization to the sarcomere. Maintaining appropriate levels of FRG1 protein is critical for muscular and vascular development in vertebrates; however, its precise molecular function is unknown. This study investigates the molecular functions of human FRG1, along with mouse FRG1 and Xenopus frg1, using molecular, biochemical, and cellular-biological approaches, to provide further insight into its roles in vertebrate development. The nuclear fraction of the endogenous FRG1 is localized in nucleoli, Cajal bodies, and actively transcribed chromatin; however, contrary to overexpressed FRG1, the endogenous FRG1 is not associated with nuclear speckles. We characterize the nuclear and nucleolar import of FRG1, the potential effect of phosphorylation, and its interaction with the importin karyopherin α2. Consistent with a role in RNA biogenesis, human FRG1 is associated with mRNA in vivo and invitro, interacts directly with TAP (Tip-associated protein; the major mRNA export receptor), and is a dynamic nuclear-cytoplasmic shuttling protein supporting a function for FRG1 in mRNA transport. Biochemically, we characterize FRG1 actin binding activity and show that the cytoplasmic pool of FRG1 is dependent on an intact actin cytoskeleton for its localization. These data provide the first biochemical activities (actin binding and RNA binding) for human FRG1 and the characterization of the endogenous human FRG1, together indicating that FRG1 is involved in multiple aspects of RNA biogenesis, including mRNA transport and, potentially, cytoplasmic mRNA localization.

Clinical Dutch-English Lambert-Eaton Myasthenic syndrome (LEMS) tumor association prediction score accurately predicts small-cell lung cancer in the LEMS

PURPOSE

Approximately one half of patients with Lambert-Eaton myasthenic syndrome (LEMS) have small-cell lung carcinomas (SCLC), aggressive tumors with poor prognosis. In view of its profound impact on therapy and survival, we developed and validated a score to identify the presence of SCLC early in the course of LEMS.

PATIENTS AND METHODS

We derived a prediction score for SCLC in LEMS in a nationwide cohort of 107 Dutch patients, and validated it in a similar cohort of 112 British patients. A Dutch-English LEMS Tumor Association Prediction (DELTA-P) score was developed based on multivariate logistic regression.

RESULTS

Age at onset, smoking behavior, weight loss, Karnofsky performance status, bulbar involvement, male sexual impotence, and the presence of Sry-like high-mobility group box protein 1 serum antibodies were independent predictors for SCLC in LEMS. A DELTA-P score was derived allocating 1 point for the presence of each of the following items at or within 3 months from onset: age at onset ≥ 50 years, smoking at diagnosis, weight loss ≥ 5%, bulbar involvement, erectile dysfunction, and Karnofsky performance status lower than 70. The area under the curve of the receiver operating curve was 94.4% in the derivation cohort and 94.6% in the validation set. A DELTA-P score of 0 or 1 corresponded to a 0% to 2.6% chance of SCLC, whereas scores of 4, 5, and 6 corresponded to chances of SCLC of 93.5%, 96.6%, and 100%, respectively.

CONCLUSION

The simple clinical DELTA-P score discriminated patients with LEMS with and without SCLC with high accuracy early in the course of LEMS.

A unifying genetic model for facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is a common form of muscular dystrophy in adults that is foremost characterized by progressive wasting of muscles in the upper body. FSHD is associated with contraction of D4Z4 macrosatellite repeats on chromosome 4q35, but this contraction is pathogenic only in certain "permissive" chromosomal backgrounds. Here, we show that FSHD patients carry specific single-nucleotide polymorphisms in the chromosomal region distal to the last D4Z4 repeat. This FSHD-predisposing configuration creates a canonical polyadenylation signal for transcripts derived from DUX4, a double homeobox gene of unknown function that straddles the last repeat unit and the adjacent sequence. Transfection studies revealed that DUX4 transcripts are efficiently polyadenylated and are more stable when expressed from permissive chromosomes. These findings suggest that FSHD arises through a toxic gain of function attributable to the stabilized distal DUX4 transcript.

Comprehensive expression analysis of FSHD candidate genes at the mRNA and protein level

In facioscapulohumeral muscular dystrophy (FSHD) the majority of patients carry a D4Z4 macrosatellite repeat contraction in the subtelomere of chromosome 4q. Several disease mechanisms have been proposed to explain how repeat contraction causes muscular dystrophy. All proposed mechanisms foresee a change from a closed to a more open chromatin structure followed by loss of control over expression of genes in or proximal to D4Z4. Initially, a distance and residual repeat size-dependent upregulation of the candidate genes FRG2, FRG1 and ANT1 was observed, but most successive expression studies failed to support transcriptional upregulation of 4qter genes. Moreover, chromatin studies do not provide evidence for a cis-spreading mechanism operating at 4qter in FSHD. In part, this inconsistency may be explained by differences in the techniques used, and the use of RNA samples obtained from different muscle groups. The aim of this study is to comprehensively and uniformly study the expression of the FSHD candidate genes FRG1, FRG2, CRYM, ANT1, ALP, PITX1 and LRP2BP at the RNA and protein level in identically processed primary myoblasts, myotubes and quadriceps muscle. Expression was compared between samples obtained from FSHD patients and normal controls with samples from myotonic dystrophy type 1 patients as disease controls. No consistent changes in RNA or protein expression levels were observed between the samples. The one exception was a selective increase in FRG2 mRNA expression in FSHD myotubes. This study provides further evidence that there is no demonstrable consistent, large magnitude, overexpression of any of the FSHD candidate genes.

SOX antibodies in small-cell lung cancer and Lambert-Eaton myasthenic syndrome: frequency and relation with survival

PURPOSE

SOX1 antibodies are common in small-cell lung carcinoma (SCLC) with and without paraneoplastic syndrome (PNS) and can serve as serological tumor marker. Addition of other antibodies might improve its diagnostic power. We validated an enzyme-linked immunosorbent assay (ELISA) to assess the diagnostic value of serum antibodies in SCLC and Lambert-Eaton myasthenic syndrome (LEMS). Clinical outcome with respect to SOX antibodies was evaluated, as the SOX-related antitumor immune response might help to control the tumor growth.

PATIENTS AND METHODS

We used recombinant SOX1, SOX2, SOX3, SOX21, HuC, HuD, or HelN1 proteins in an ELISA to titrate serum samples and validated the assay by western blot. We tested 136 consecutive SCLC patients, 86 LEMS patients (43 with SCLC), 14 patients with SCLC and PNS (paraneoplastic cerebellar degeneration or Hu syndrome), 62 polyneuropathy patients, and 18 healthy controls.

RESULTS

Our ELISA was equally reliable as western blot. Forty-three percent of SCLC patients and 67% of SCLC-LEMS patients had antibodies to one of the SOX or Hu proteins. SOX antibodies had a sensitivity of 67% and a specificity of 95% to discriminate between LEMS with SCLC and nontumor LEMS. No difference in survival was observed between SOX positive and SOX negative SCLC patients.

CONCLUSION

SOX antibodies are specific serological markers for SCLC. Our assay is suitable for high throughput screening, detecting 43% of SCLC. SOX antibodies have diagnostic value in discriminating SCLC-LEMS from nontumor LEMS, but have no relation to survival in patients with SCLC.

Selection and characterization of KDEL-specific VHH antibody fragments and their application in the study of ER resident protein expression

Several diseases are caused by defects in the protein secretory pathway of the cell, particularly in the endoplasmic reticulum (ER). These defects are manifested by the activation of the unfolded protein response (UPR) that involves the transcriptional up-regulation of several ER resident proteins, the down-regulation of protein translation and up-regulation of ER associated degradation (ERAD). Although this transcriptional up-regulation of ER resident proteins during ER stress has been well described, data on differential protein expression of these same proteins are hardly available. Tools that would enable the simultaneous analysis of this set of proteins would be of high importance. Since the C-terminal KDEL sequence is a conserved epitope present in a large set of ER resident proteins, an antibody directed against this sequence would be such a tool. Using a carefully designed selection strategy, VHH antibody fragments from a non-immune phage display library were isolated that recognize the KDEL sequence at the C-terminus of proteins, irrespective of the protein context. In an accepted in vitro model for ER stress, this antibody was shown to be an excellent tool to study differences in ER resident protein expression. Furthermore, the application of this antibody showed differences in ER resident protein levels during replicative senescence of human umbilical vein endothelial cells (HUVECs), underlining its significance in biological research. The selection strategy used to obtain these KDEL-specific antibodies opens up ways to select antibodies to other conserved epitopes, such as the nuclear localization signal (NLS) or the peroxisomal targeting sequence, permitting the simultaneous analysis of specific groups of proteins.

Improved anti-IgG and HSA affinity ligands: clinical application of VHH antibody technology

Large scale, highly specific purification of valuable proteins from blood and removal of undesirable components promise to have wide therapeutic applications. Moreover, depletion of bulk proteins from blood is a prerequisite for clinical proteomics. Here we describe the development of specific, high affinity Camelid antibody fragments (VHH) derived from immune libraries for purification and depletion of the bulk protein HSA and IgG from human serum and plasma for therapeutic and research purposes. The anti-IgG VHH substantially improved depletion of IgGs from blood over the classical method based on protein A. To demonstrate the improved performance of VHH based IgG depletion, we analyzed the presence of auto-antibodies in human plasma before and after depletion from two groups of patients with auto-immune disease: Goodpasture syndrome (GP) and systemic lupus erythematosus (SLE). VHHs can be produced efficiently and cost effectively in Saccharomyces cerevisiae, a genetically regarded as safe (GRAS) microorganism. A good manufacturing process (GMP) for purification of these VHHs has also been developed. Moreover, as VHHs are single protein chains, they can be coupled relatively easily to solid matrices. These three factors are important for developing affinity purification medication.

Genotype-phenotype study in an FSHD family with a proximal deletion encompassing p13E-11 and D4Z4

BACKGROUND

In the majority of facioscapulohumeral muscular dystrophy (FSHD) cases, the molecular basis of the disease is due to loss of subtelomeric D4Z4 repeat units at 4q35. Occasionally, an apparent absence of the contracted D4Z4 repeat is associated with FSHD. One explanation for this finding is a deletion in the region proximal to the D4Z4 repeat array that encompasses the p13E-11 (D4F104S1) probe-binding site used in the DNA diagnosis. The frequency of such proximally extended deletions is unknown, and to date, few patients have been described due to the difficulties in the molecular identification of such cases.

METHODS

We describe a family (DUK 2531) in which a contracted D4Z4 allele and a large proximal deletion of approximately 75 kb are segregating to 11 individuals. This is the largest deletion identified to date. Family DUK 2531 was initially thought to have normal D4Z4 fragment size and therefore unlinked to the 4q35 region (FSHD1B).

RESULTS

Further molecular analysis of DUK 2531 reveals the presence of 10 repeat units (33 kb). The extended deletion includes the probe p13E-11 and B31 binding sites, the inverted repeat D4S2463, and genes FRG2 and TUBB4Q.

CONCLUSION

Despite the length of the proximal deletion in this family, the range and severity of the clinical manifestations are typical for the disorder. Because such deletions can lead to misinterpretation in the diagnostic setting, this suggests the need for additional diagnostic tests in facioscapulohumeral muscular dystrophy.

Phosphorylation of p42/44(MAPK) by various signal transduction pathways activates cytosolic phospholipase A(2) to variable degrees

Arachidonic acid has been implicated to play a role in physiological and pathophysiological processes and is selectively released by the 85-kDa cytosolic phospholipase A(2) (cPLA(2)). The activity of cPLA(2) is regulated by calcium, translocating the enzyme to its substrate, and by phosphorylation by a mitogen-activated protein kinase (MAPK) family member and a MAPK-activated protein kinase. In this study, the signal transduction pathways in growth factor-induced phosphorylation of p42/44(MAPK) and cPLA(2) activation were investigated in Her14 fibroblasts. p42/44(MAPK) in response to epidermal growth factor was not only phosphorylated via the Raf-MEK pathway but mainly through protein kinase C (PKC) or a related or unrelated kinase in which the phosphorylated p42/44(MAPK) corresponded with cPLA(2) activity. Serum-induced phosphorylation of p42/44(MAPK) also corresponded with cPLA(2) activity but is predominantly mediated via Raf-MEK and partly through PKC or a related or unrelated kinase. In contrast, activation of PKC by phorbol ester did not result in increased cPLA(2) activity, while p42/44(MAPK) is phosphorylated, mainly via Raf-MEK and through MEK. Moreover, p42/44(MAPK) phosphorylation is present in quiescent and proliferating cells, and p42/44(MAPK) is entirely phosphorylated via Raf-MEK, but it only corresponds to cPLA(2) activity in the former cells. Collectively, these data show that p42/44(MAPK) in proliferating, quiescent, and stimulated cells is phosphorylated by various signal transduction pathways, suggesting the activation of different populations of p42/44(MAPK) and cPLA(2).