Benzenesulphonamide inhibitors of the cytolytic protein perforin

Approaches Towards Better Immunosuppressive Agents

Several classes of compounds are applied in clinics due to their immunosuppressive properties in transplantology and the treatment of autoimmune diseases. Derivatives of mycophenolic acid, corticosteroids and chemotherapeutics bearing heterocyclic moieties like methotrexate, azathioprine, mizoribine, and ruxolitinib are active substances with investigated mechanisms of action. However, improved synthetic approaches of known drugs and novel derivatives are still being reported to attempt better accessibility and therapeutic properties. In this review article, we present the synthesis of the designed chemical structures based on recent literature reports concerning novel compounds as promising immunosuppressive drugs. Moreover, some of the discussed derivers revealed also other types of activities with prospective medicinal potential.

Fragment-based and structure-guided discovery of perforin inhibitors

Perforin is a pore-forming protein whose normal function enables cytotoxic T and natural killer (NK) cells to kill virus-infected and transformed cells. Conversely, unwanted perforin activity can also result in auto-immune attack, graft rejection and aberrant responses to pathogens. Perforin is critical for the function of the granule exocytosis cell death pathway and is therefore a target for drug development. In this study, by screening a fragment library using NMR and surface plasmon resonance, we identified 4,4-diaminodiphenyl sulfone (dapsone) as a perforin ligand. We also found that dapsone has modest (mM) inhibitory activity of perforin lytic activity in a red blood cell lysis assay in vitro. Sequential modification of this lead fragment, guided by structural knowledge of the ligand binding site and binding pose, and supported by SPR and ligand-detected 19F NMR, enabled the design of nanomolar inhibitors of the cytolytic activity of intact NK cells against various tumour cell targets. Interestingly, the ligands we developed were largely inert with respect to direct perforin-mediated red blood cell lysis but were very potent in the context of perforin's action on delivering granzymes in the immune synapse, the context in which it functions physiologically. Our work indicates that a fragment-based, structure-guided drug discovery strategy can be used to identify novel ligands that bind perforin. Moreover, these molecules have superior physicochemical properties and solubility compared to previous generations of perforin ligands.

Effects of a Small-Molecule Perforin Inhibitor in a Mouse Model of CD8 T Cell-Mediated Neuroinflammation

BACKGROUND AND OBJECTIVES

Alteration of the blood-brain barrier (BBB) at the interface between blood and CNS parenchyma is prominent in most neuroinflammatory diseases. In several neurologic diseases, including cerebral malaria and Susac syndrome, a CD8 T cell-mediated targeting of endothelial cells of the BBB (BBB-ECs) has been implicated in pathogenesis.

METHODS

In this study, we used an experimental mouse model to evaluate the ability of a small-molecule perforin inhibitor to prevent neuroinflammation resulting from cytotoxic CD8 T cell-mediated damage of BBB-ECs.

RESULTS

Using an in vitro coculture system, we first identified perforin as an essential molecule for killing of BBB-ECs by CD8 T cells. We then found that short-term pharmacologic inhibition of perforin commencing after disease onset restored motor function and inhibited the neuropathology. Perforin inhibition resulted in preserved BBB-EC viability, maintenance of the BBB, and reduced CD8 T-cell accumulation in the brain and retina.

DISCUSSION

Therefore, perforin-dependent cytotoxicity plays a key role in the death of BBB-ECs inflicted by autoreactive CD8 T cells in a preclinical model and potentially represents a therapeutic target for CD8 T cell-mediated neuroinflammatory diseases, such as cerebral malaria and Susac syndrome.

Small Molecule Inhibitors of Lymphocyte Perforin as Focused Immunosuppressants for Infection and Autoimmunity

New drugs that precisely target the immune mechanisms critical for cytotoxic T lymphocyte (CTL) and natural killer (NK) cell driven pathologies are desperately needed. In this perspective, we explore the cytolytic protein perforin as a target for therapeutic intervention. Perforin plays an indispensable role in CTL/NK killing and controls a range of immune pathologies, while being encoded by a single copy gene with no redundancy of function. An immunosuppressant targeting this protein would provide the first-ever therapy focused specifically on one of the principal cell death pathways contributing to allotransplant rejection and underpinning multiple autoimmune and postinfectious diseases. No drugs that selectively block perforin-dependent cell death are currently in clinical use, so this perspective will review published novel small molecule inhibitors, concluding with in vivo proof-of-concept experiments performed in mouse models of perforin-mediated immune pathologies that provide a potential pathway toward a clinically useful therapeutic agent.

Preclinical Activity and Pharmacokinetic/Pharmacodynamic Relationship for a Series of Novel Benzenesulfonamide Perforin Inhibitors

Perforin is a key effector of lymphocyte-mediated cell death pathways and contributes to transplant rejection of immunologically mismatched grafts. We have developed a novel series of benzenesulfonamide (BZS) inhibitors of perforin that can mitigate graft rejection during allogeneic bone marrow/stem cell transplantation. Eight such perforin inhibitors were tested for their murine pharmacokinetics, plasma protein binding, and their ability to block perforin-mediated lysis in vitro and to block the rejection of major histocompatibility complex (MHC)-mismatched mouse bone marrow cells. All compounds showed >99% binding to plasma proteins and demonstrated perforin inhibitory activity in vitro and in vivo. A lead compound, compound 1, that showed significant increases in allogeneic bone marrow preservation was evaluated for its plasma pharmacokinetics and in vivo efficacy at multiple dosing regimens to establish a pharmacokinetic/pharmacodynamic (PK/PD) relationship. The strongest PK/PD correlation was observed between perforin inhibition in vivo and time that total plasma concentrations remained above 900 μM, which correlates to unbound concentrations similar to 3× the unbound in vitro IC₉₀ of compound 1. This PK/PD relationship will inform future dosing strategies of BZS perforin inhibitors to maintain concentrations above 3× the unbound IC₉₀ for as long as possible to maximize efficacy and enhance progression toward clinical evaluation.

Functional characterization and gene expression profile of perforin-2 in starry flounder (Platichthys stellatus)

The membrane attack complex/perforin (MACPF) superfamily consists of multifunctional proteins that form pores on the membrane surface of microorganisms to induce their death and have various immune-related functions. PFN2 is a perforin-like protein with an MACPF domain, and humans with deficient PFN2 levels have increased susceptibility to bacterial infection, which can lead to fatal consequences for some patients. Therefore, in this study, we confirmed the antimicrobial function of PFN2 in starry flounder (Platichthys stellatus). The molecular properties were confirmed based on the verified amino acid sequence of PsPFN2. In addition, the expression characteristics of tissue-specific and pathogen-specific PsPFN2 mRNA were also confirmed. The recombinant protein was produced using Escherichia coli, and the antimicrobial activity was then confirmed. The coding sequence of PFN2 (PsPFN2) in P. stellatus consists of 710 residues. The MACPF domain was conserved throughout evolution, as shown by multiple sequence alignment and phylogenetic analysis. PsPFN2 mRNA is abundantly distributed in immune-related organs such as the spleen and gills of healthy starry flounder, and significant expression changes were confirmed after artificial infection by bacteria or viruses. We cloned the MACPF domain region of PFN2 to produce a recombinant protein (rPFN2) and confirmed its antibacterial effect against a wide range of bacterial species and the parasite (Miamiensis avidus).

Perforins Expression by Cutaneous Gamma Delta T Cells

Gamma delta (GD) T cells are an unconventional T cell type present in both the epidermis and the dermis of human skin. They are critical to regulating skin inflammation, wound healing, and anti-microbial defense. Similar to CD8+ cytotoxic T cells expressing an alpha beta (AB) TCR, GD T cells have cytolytic capabilities. They play an important role in elimination of cutaneous tumors and virally infected cells and have also been implicated in pathogenicity of several autoimmune diseases. T cell cytotoxicity is associated with the expression of the pore forming protein Perforin. Perforin is an innate immune protein containing a membrane attack complex perforin-like (MACPF) domain and functions by forming pores in the membranes of target cells, which allow granzymes and reactive oxygen species to enter the cells and destroy them. Perforin-2, encoded by the gene MPEG1, is a newly discovered member of this protein family that is critical for clearance of intracellular bacteria. Cutaneous GD T cells express both Perforin and Perforin-2, but many questions remain regarding the role that these proteins play in GD T cell mediated cytotoxicity against tumors and bacterial pathogens. Here, we review what is known about Perforin expression by skin GD T cells and the mechanisms that contribute to Perforin activation.

Inhibition of the Cytolytic Protein Perforin Prevents Rejection of Transplanted Bone Marrow Stem Cells in Vivo

Perforin is a key effector protein in the vertebrate immune system and is secreted by cytotoxic T lymphocytes and natural killer cells to help eliminate virus-infected and transformed target cells. The ability to modulate perforin activity in vivo could be extremely useful, especially in the context of bone marrow stem cell transplantation where early rejection of immunologically mismatched grafts is driven by the recipient's natural killer cells, which overwhelmingly use perforin to kill their targets. Bone marrow stem cell transplantation is a potentially curative treatment for both malignant and nonmalignant disorders, but when the body recognizes the graft as foreign, it is rejected by this process, often with fatal consequences. Here we report optimization of a previously identified series of benzenesulfonamide-based perforin inhibitors for their physicochemical and pharmacokinetic properties, resulting in the identification of 16, the first reported small molecule able to prevent rejection of transplanted bone marrow stem cells in vivo by blocking perforin function.

Perforin inhibition protects from lethal endothelial damage during fulminant viral hepatitis

CD8 T cells protect the liver against viral infection, but can also cause severe liver damage that may even lead to organ failure. Given the lack of mechanistic insights and specific treatment options in patients with acute fulminant hepatitis, we develop a mouse model reflecting a severe acute virus-induced CD8 T cell-mediated hepatitis. Here we show that antigen-specific CD8 T cells induce liver damage in a perforin-dependent manner, yet liver failure is not caused by effector responses targeting virus-infected hepatocytes alone. Additionally, CD8 T cell mediated elimination of cross-presenting liver sinusoidal endothelial cells causes endothelial damage that leads to a dramatically impaired sinusoidal perfusion and indirectly to hepatocyte death. With the identification of perforin-mediated killing as a critical pathophysiologic mechanism of liver failure and the protective function of a new class of perforin inhibitor, our study opens new potential therapeutic angles for fulminant viral hepatitis.

CD8 T cells can protect the liver from viral infection, but can also result in severe liver damage and organ failure. Here, the authors develop a mouse model reflecting fulminant CD8 T cell mediated viral hepatitis, which occurs in a perforin-dependent manner that is protected by the use of perforin inhibitors.

The immunological synapse as a pharmacological target

The development of T cell mediated immunity relies on the assembly of a highly specialized interface between T cell and antigen presenting cell (APC), known as the immunological synapse (IS). IS assembly is triggered when the T cell receptor (TCR) binds to specific peptide antigen presented in association to the major histocompatibility complex (MHC) by the APC, and is followed by the spatiotemporal dynamic redistribution of TCR, integrins, co-stimulatory receptors and signaling molecules, allowing for the fine-tuning and integration of the signals that lead to T cell activation. The knowledge acquired to date about the mechanisms of IS assembly underscores this structure as a robust pharmacological target. The activity of molecules involved in IS assembly and function can be targeted by specific compounds to modulate the immune response in a number of disorders, including cancers and autoimmune diseases, or in transplanted patients. Here, we will review the state-of-the art of the current therapies which exploit the IS to modulate the immune response.

Substituted arylsulphonamides as inhibitors of perforin-mediated lysis

The structure-activity relationships for a series of arylsulphonamide-based inhibitors of the pore-forming protein perforin have been explored. Perforin is a key component of the human immune response, however inappropriate activity has also been implicated in certain auto-immune and therapy-induced conditions such as allograft rejection and graft versus host disease. Since perforin is expressed exclusively by cells of the immune system, inhibition of this protein would be a highly selective strategy for the immunosuppressive treatment of these disorders. Compounds from this series were demonstrated to be potent inhibitors of the lytic action of both isolated recombinant perforin and perforin secreted by natural killer cells in vitro. Several potent and soluble examples were assessed for in vivo pharmacokinetic properties and found to be suitable for progression to an in vivo model of transplant rejection.