Glutaminyl Cyclase Inhibitor 1

Glutaminyl cyclase is an enzymatic modifier of the CD47- SIRPα axis and a target for cancer immunotherapy

Cancer cells can evade immune surveillance through the expression of inhibitory ligands that bind their cognate receptors on immune effector cells. Expression of programmed death ligand 1 in tumor microenvironments is a major immune checkpoint for tumor-specific T cell responses as it binds to programmed cell death protein-1 on activated and dysfunctional T cells1. The activity of myeloid cells such as macrophages and neutrophils is likewise regulated by a balance between stimulatory and inhibitory signals. In particular, cell surface expression of the CD47 protein creates a 'don't eat me' signal on tumor cells by binding to SIRPα expressed on myeloid cells2-5. Using a haploid genetic screen, we here identify glutaminyl-peptide cyclotransferase-like protein (QPCTL) as a major component of the CD47-SIRPα checkpoint. Biochemical analysis demonstrates that QPCTL is critical for pyroglutamate formation on CD47 at the SIRPα binding site shortly after biosynthesis. Genetic and pharmacological interference with QPCTL activity enhances antibody-dependent cellular phagocytosis and cellular cytotoxicity of tumor cells. Furthermore, interference with QPCTL expression leads to a major increase in neutrophil-mediated killing of tumor cells in vivo. These data identify QPCTL as a novel target to interfere with the CD47 pathway and thereby augment antibody therapy of cancer.

Combining daratumumab with CD47 blockade prolongs survival in preclinical models of pediatric T-ALL

Acute lymphoblastic leukemia (ALL) is the most common malignant disease affecting children. Although therapeutic strategies have improved, T-cell acute lymphoblastic leukemia (T-ALL) relapse is associated with chemoresistance and a poor prognosis. One strategy to overcome this obstacle is the application of monoclonal antibodies. Here, we show that leukemic cells from patients with T-ALL express surface CD38 and CD47, both attractive targets for antibody therapy. We therefore investigated the commercially available CD38 antibody daratumumab (Dara) in combination with a proprietary modified CD47 antibody (Hu5F9-IgG2σ) in vitro and in vivo. Compared with single treatments, this combination significantly increased in vitro antibody-dependent cellular phagocytosis in T-ALL cell lines as well as in random de novo and relapsed/refractory T-ALL patient-derived xenograft (PDX) samples. Similarly, enhanced antibody-dependent cellular phagocytosis was observed when combining Dara with pharmacologic inhibition of CD47 interactions using a glutaminyl cyclase inhibitor. Phase 2-like preclinical in vivo trials using T-ALL PDX samples in experimental minimal residual disease-like (MRD-like) and overt leukemia models revealed a high antileukemic efficacy of CD47 blockade alone. However, T-ALL xenograft mice subjected to chemotherapy first (postchemotherapy MRD) and subsequently cotreated with Dara and Hu5F9-IgG2σ displayed significantly reduced bone marrow infiltration compared with single treatments. In relapsed and highly refractory T-ALL PDX combined treatment with Dara and Hu5F9-IgG2σ was required to substantially prolong survival compared with single treatments. These findings suggest that combining CD47 blockade with Dara is a promising therapy for T-ALL, especially for relapsed/refractory disease harboring a dismal prognosis in patients.

Human glutaminyl cyclase: Structure, function, inhibitors and involvement in Alzheimer's disease

Human glutaminyl cyclase (hQC) is an important enzyme for post-translational modification by converting the N-terminal glutaminyl and glutamyl into pyroglutamate (pGlu) through cyclization. The two isoforms of hQC, secretory glutaminyl cyclase (sQC) and golgi resident glutaminyl cyclase (gQC), are involved in various pathological conditions especially in Alzheimer's disease (AD). The sQC is known to mediate the formation of pyroglutamate containing amyloid beta (pGlu-Aβ) peptides while gQC mediates the maturation of C-C motif chemokine ligand 2 (CCL2). Therefore, hQC (both sQC and gQC) inhibition is considered to be an attractive strategy to prevent the formation of pGlu-Aβ and to reduce neuroinflammation and hence provides a new opportunity for the treatment of AD. In this review, we summarize our current understanding on the structure, function and inhibitors of hQC and its involvement in Alzheimer's disease.

A phase 1 study to evaluate the safety and pharmacokinetics of PQ912, a glutaminyl cyclase inhibitor, in healthy subjects

Introduction: Pyroglutamate-amyloid-β (pE-Aβ) peptides are major components of Aβ-oligomers and Aβ-plaques, which are regarded as key culprits of Alzheimer's disease (AD) pathology. PQ912 is a competitive inhibitor of the enzyme glutaminyl cyclase (QC), essential for the formation of pE-Aβ peptides.
Methods: A randomized, double-blind, placebo-controlled, single- and multiple-ascending oral dose study investigated the safety, pharmacokinetics, and pharmacodynamics of PQ912 in healthy nonelderly and elderly subjects.
Results: PQ912 was considered safe and well tolerated with dose-proportional pharmacokinetics up to doses of 200 mg. At higher doses up to 1800 mg, exposure was supraproportional and exposure in elderly subjects was approximately 1.5- to 2.1-fold higher. Exposure in cerebrospinal fluid (CSF) was approximately 20% of the unbound drug in plasma, and both serum and CSF QC activity was inhibited in a dose-related manner.
Discussion: This first-in-man study of a compound-targeting QC inhibition justifies further development of PQ912 for the treatment of AD.

Structural and kinetic characterization of Porphyromonas gingivalis glutaminyl cyclase

Porphyromonas gingivalis is a bacterial species known to be involved in the pathogenesis of chronic periodontitis, that more recently has been as well associated with Alzheimer's disease. P. gingivalis expresses a glutaminyl cyclase (PgQC) whose human ortholog is known to participate in the beta amyloid peptide metabolism. We have elucidated the crystal structure of PgQC at 1.95 ? resolution in unbound and in inhibitor-complexed forms. The structural characterization of PgQC confirmed that PgQC displays a mammalian fold rather than a bacterial fold. Our biochemical characterization indicates that PgQC uses a mammalian-like catalytic mechanism enabled by the residues Asp¹⁴⁹, Glu¹⁸², Asp¹⁸³, Asp²¹⁸, Asp²⁶⁷ and His²⁹⁹. In addition, we could observe that a non-conserved Trp¹⁹³ may drive differences in the binding affinity of ligands which might be useful for drug development. With a screening of a small molecule library, we have identified a benzimidazole derivative rendering PgQC inhibition in the low micromolar range that might be amenable for further medicinal chemistry development.