Patent Application
20230181578
The invention is based on a method of modulating the activation or inhibition of Mixed lineage kinase domain-like (MLKL) protein, or a MLKL variant protein, via modulating the intramolecular interaction between the C-terminal helix (Hc) of the psK domain and a hydrophobic groove in the MLKL protein. The invention provides methods and compounds to selectively target the herein firstly disclosed intramolecular interaction of MLKL protein. Based on the herein disclosed essential intramolecular rearrangement of MLKL, the invention provides small molecules capable of specifically inhibiting mouse or human MLKL. The invention provides uses, including research and medical applications such as treatments, of MLKL driven conditions including necroptosis, cell trafficking, pathological immune responses and/or inflammation.
Cell death is fundamental for development, tissue homeostasis and immunity in multicellular organisms. Necroptosis is a form of regulated cell death that results in release of the inflammatory cellular contents after plasma membrane permeabilization, thereby triggering immune responses (1, 2). The medical importance of necroptosis has recently been illustrated by its connection to cancer (3, 4), inflammation (5), neurodegenerative diseases (6, 7) and pathogen infections (8, 9). Because of this, targeting necroptosis signaling is of great scientific and therapeutic interest and elucidating how it is regulated at the molecular level will help designing novel therapies for human health.
Necroptosis can be triggered via different receptors, including the toll-like receptors 3/4 (TLR3/4) and death receptors such as tumor necrosis factor receptor 1 (TNFR1), TRAIL receptors 1 and 2 (TRAIL-R1/2), and CD95 (Fas/APO-1) (10), and via the DNA-dependent activator of interferon-regulatory factors (DAI), under conditions of compromised caspase 8 activity. All these pathways converge in the formation of the necrosome, which contains active, phosphorylated Receptor-Interacting Protein kinase 3 (RIP3) and Mixed Lineage Kinase domain-Like (MLKL) (11-14). MLKL is essential for necroptosis and it is the most downstream effector of this form of cell death identified to date. RIP3-mediated phosphorylation activates MLKL and drives its oligomerization and translocation from the cytosol to the plasma membrane. Although activation of MLKL is essential for the key step of plasma membrane permeabilization and the execution of cell death (12, 15, 16), its mechanism of action remains unclear. Competing models propose that MLKL either indirectly (17, 18) or directly (19, 20) induces plasma membrane permeabilization to mediate cell death.
MLKL is a member of the pseudokinases family, a group of proteins that are catalytically deficient variants of kinases but keep the ability to bind ATP to exert signal transduction and scaffolding functions (21, 22). Solving the structure of MLKL by X-ray crystallography revealed an N-terminal four helix bundle domain (4HB), a C-terminal pseudokinase domain (psK) containing the RIP3 phosphorylation site and a brace region that bridges them (21). The 4HB of MLKL acts as the killer domain, whereas the psK domain is critical to restrain the death-inducing capacity of MLKL in healthy conditions (23, 24). Mechanistically, it has been shown that phosphorylation at defined sites in the psK domain is required to induce brace opening, 4HB exposure and cell death (23). However, how the psK domain regulates MLKL activation and the nature of the conformational changes in the psK that are enabled by phosphorylation remain unknown.
The interest in MLKL inhibition for blocking necroptosis has recently escalated because, to date, MLKL is the only effector solely implicated in this cell death pathway (13, 23, 25). Whereas inhibiting the kinase activity of RIP3 has been shown to block necroptosis, doing so fails to prevent cell death because it removes a RIP3-kinase-dependent regulatory control on caspase 8 activation, leading to aberrant apoptosis (26). Blocking the activity of the upstream kinase RIP1 has shown to be a promising therapeutic strategy for several indications (27-29). However, this strategy may not come without adverse effects, as it not only inhibits necroptosis, but also RIP1-kinase-dependent gene activation and/or apoptosis associated with its role as master regulator of all outputs of receptor-mediated signaling (30, 31). It is possible that inhibiting these additional RIP1-kinase-dependent pathways may act synergistically in certain diseases with the inhibition of necroptosis, yet this would be accidental. Hence, inhibiting the most downstream, possibly unique, sole necroptosis effector molecule MLKL would constitute the most specific means of necroptosis inhibition.
Uncovering the structural determinants required for MLKL regulation is key to discover new drugs interfering exclusively with necroptotic cell death. Targeting the ATP-binding site of the psK domain (23) is currently used as a strategy to develop new MLKL modulators. However, this approach suffers from low specificity because this pocket shares structural similarities with other (pseudo)kinases, which may cause undesirable off-target effects. Therefore, there is a need for the identification of alternative druggable sites on the structure of MLKL.
Thus, it is an objective of the invention to provide novel means and methods to modulate MLKL activity in order to devise their application not only in the modulation of necroptotic cell death, but also in the treatment or management of conditions associated with cell trafficking, pathological immune responses and/or inflammation.
Generally, and by way of brief description, the main aspects of the present invention can be described as follows:
In a first aspect, the invention pertains to a method for modulating the activation of Mixed lineage kinase domain-like (MLKL) protein, or a MLKL variant protein, wherein the MLKL protein, or MLKL variant protein, comprises at least an N-terminal four helix bundle (4HB) domain, a C-terminal pseudo kinase (psK) domain, connected by a brace region, and wherein the method comprises the modulation of the intramolecular interaction between the C-terminal helix (Hc) of the psK domain and a hydrophobic groove, and wherein the intramolecular interaction involves MLKL amino acid residues located in the 4HB domain, the brace region and the psK domain.
In a second aspect, the invention pertains to a method for modulating the activation capacity of necroptosis in a cell, the method comprising the step of contacting the cell with a dominant negative MLKL protein, a MLKL modulating compound or MLKL modulating composition, wherein said MLKL modulating compound or MLKL modulating composition when contacted with the cell modulates an intramolecular interaction between the C-terminal helix (Hc) of the psK domain and a hydrophobic groove wherein the intramolecular interaction involves MLKL amino acid residues located in the 4HB domain, the brace region and the psK domain of an MLKL protein, or a MLKL variant protein, in the cell.
In a third aspect, the invention pertains to a method for identifying a compound capable of modulating activation of MLKL, the method comprising
In a fourth aspect, the invention pertains to a method for identifying a compound capable of modulating activation of MLKL, the method comprising:
In a fifth aspect, the invention pertains to a method for identifying a compound capable of modulating activation of MLKL, the method comprising:
In a sixth aspect, the invention pertains to a method for treating a disease associated with necroptosis, inflammation, pathological immune response and/or trafficking in a subject, the method comprising performing in the subject a method according to any one of the preceding aspects, wherein the cell is a cell associated with the disease. In an alternative embodiment of the sixth aspect, the invention pertains to substance/composition for use in treating a disease associated with necroptosis, inflammation, pathological immune response and/or trafficking in a subject, wherein the substance or composition has an activity as a modulator of MLKL as disclosed herein.
In the following, the elements of the invention will be described. These elements are listed with specific embodiments; however, it should be understood that they may be combined in any manner and in any number to create additional embodiments. The variously described examples and preferred embodiments should not be construed to limit the present invention to only the explicitly described embodiments. This description should be understood to support and encompass embodiments which combine two or more of the explicitly described embodiments or which combine the one or more of the explicitly described embodiments with any number of the disclosed and/or preferred elements. Furthermore, any permutations and combinations of all described elements in this application should be considered disclosed by the description of the present application unless the context indicates otherwise.
In a first aspect, the invention pertains to a method for modulating the activation of Mixed lineage kinase domain-like (MLKL) protein, or a MLKL variant protein, wherein the MLKL protein, or MLKL variant protein, comprises at least an N-terminal four helix bundle (4HB) domain, a C-terminal pseudo kinase (psK) domain, connected by a brace region, and wherein the method comprises the modulation of the intramolecular interaction between the C-terminal helix (Hc) of the psK domain and a hydrophobic groove, and wherein the intramolecular interaction involves MLKL amino acid residues located in the 4HB domain, the brace region and the psK domain.
The method in some preferred aspects and embodiments is a non-therapeutic method. In addition, the term “non-therapeutic” in the present invention refers to a concept that does not include medical practice medical treatment of a human body or an animal body through therapy, such as the method for research purposes or for screening approaches.
The present invention is based on the surprising find that two murine isoforms of MLKL that molecularly only differ in the presence of an eight amino acid stretch at the C-terminal helix He are different in their function. When a known necroptosis trigger is applied, the MLKL version containing the insertion remains inactive, whereas the one devoid of this sequence is activated. Analyzing in detail the underlying molecular mechanism resulted in the discovery of a previously unrecognized interaction of He with a hydrophobic groove in MLKL that is essential for its capacity to induce necroptosis—this leads to the inventive aspects and embodiments of the present disclosure. This new insight further informed the design of a novel class of potent and species-specific inhibitors for both, murine and human MLKL, which are shown to substantially ameliorate necroptosis-driven dermatitis. The invention therefore provides a novel and highly specific strategy to prevent necroptosis therapeutically. The invention in certain of its aspects and embodiments is for use in medicine and in research.
In an alternative first aspect of the invention, there is provided a substance or composition for use in the method of the above first aspect, wherein said substance or composition is a modulator of said intramolecular interaction between the C-terminal helix (Hc) of the psK domain and a hydrophobic groove, and wherein the intramolecular interaction involves MLKL amino acid residues located in the 4HB domain, the brace region and the psK domain. Such use is preferably a use in medicine, for example, a use in the treatment and/or prevention of a disorder associated with MLKL activation (such as necroptosis).
In context of the present invention the term Mixed lineage kinase domain-like (MLKL) protein, shall refer to a protein as shown in SEQ ID NO: 1 or 2 (mouse MLKL isoforms 1 and 2) or SEQ ID NO: 3 or 4 (human MLKL isoforms 1 and 2). The protein identities can also be derived from the UniProt database in the version of February 2020 (www.uniprot.org). For the mouse MLKL isoform 1 under the accession number Q9D2Y4-1, for mouse MLKL isoform 2 under the accession number Q9D2Y4-2; for the human MLKL isoform 1 under the accession number Q8NB16-1, and for the human MLKL isoform 2 under the accession number Q8NB16-2.
In some preferred aspects and embodiments of the invention the MLKL protein, or a variant protein thereof, is a human MLKL protein.
The term “a MLKL variant protein”, or “variant MLKL protein” or similar expression, shall refer to any MLKL protein homologs, paralogs or orthologues of a human MLKL. In preferred embodiments a MLKL variant protein is a protein having an amino acid sequence with at least 50, 60, 70, 80, 85, 90, 95, 96, 97, 98, or 99 percent sequence identity to a sequence shown in one of SEQ ID NO: 1 to 4.
The term “modulating activation of MLKL” pertains to a change of activity of a MLKL protein selected from an activity as a necroptosis regulator, and without being bound to a specific theory, is being modulated by the modulation of a three-dimensional intramolecular conformation of the MLKL protein. The term “modulating” in this context preferably pertains to an “inhibition” of one or more activities of the MLKL protein, such as an inhibition of the necroptosis mediating function of the MLKL protein. Moreover, and in alternative or additional embodiments, the activity can be seen in the permeabilization of a cell plasma membrane induced by the MLKL protein. Furthermore, in additional or alternative embodiments, the activity of the MLKL protein of the invention is an interaction of the C-terminal helix (Hc) located in the pseudo kinase domain (psK) of the MLKL protein with the 4HB domain, preferably wherein the interaction of the He has a necroptosis agonistic activity. More specifically, the modulating includes a modulation of the intramolecular interaction of the He with a hydrophobic groove in the MLKL protein wherein the intramolecular interaction involves MLKL amino acid residues located in the 4HB domain, the brace region and the psK domain. Hence, in preferred embodiments of the invention the modulation of activation is a decrease in activation, or a decrease in the ability to be activated, and wherein the modulation of the intramolecular interaction is a reduced or impaired intramolecular interaction.
In yet preferred embodiments of the invention the modulation of the intramolecular interaction may involve any of the following procedures:
In the context of the present invention the term “hydrophobic groove” or “MLKL hydrophobic groove” pertains to a previously not defined structural motif of MLKL proteins, specifically of mouse or human MLKL proteins. Specifically, the hydrophobic groove comprises amino acid residues from the 4HB domain, the brace region and the psK domain, of the MLKL protein, and in the event the MLKL protein, or MLKL variant protein, is human MLKL1 (SEQ ID NO: 3), such amino acids are located between amino acid 80 and 100, more preferably 80 to 90, and most preferably are amino acids 81, 82, 83, 85, 86, 87, 89 or 90 from the 4HB; such amino acids are located between amino acid 120 and 190, more preferably 140 to 160, and most preferably are amino acids 148, 152, 155 or 156 from the brace region; such amino acids are located between amino acid 190 and 471, more preferably 300 to 450, and most preferably are amino acids 303, 307, 310, 311, 314, 315, 317, 318, 321, 322, 391, 392, 394, 395, 398, 402, 438, 440, 441, 443, 444, 445, 447 from the psK domain. Most importantly it is understood that the hydrophobic groove involves at least one amino acid of the aforementioned domain regions in the human MLKL protein. In the event the MLKL protein, or MLKL variant protein, is mouse MLKL2 (SEQ ID NO: 2), such amino acids are located between amino acid 20 and 100, more preferably 20 to 90, and most preferably are amino acids 23, 79, 80, 81, 84, 85, 86, 87, 88 or 89 from the 4HB; such amino acids are located between amino acid 120 and 190, more preferably 140 to 160, and most preferably are amino acids 147, 150, 151, 154 or 155 from the brace region; such amino acids are located between amino acid 190 and 464, more preferably 290 to 440, and most preferably are amino acids 296, 299, 300, 303, 304, 306, 307, 310, 311, 378, 382, 385, 389, 427, 428, 430, 431, 434 or 435 from the psK domain. Most preferably the present invention pertains to the human MLKL protein. It is understood that both for human and mouse MLKL proteins, the preferred embodiments include a combination of the most preferred amino acid positions of the 4HB, the brace region and the psK.
In some embodiments of the invention the He is located at the C-terminal end of the psK domain, and in the event the MLKL protein, or MLKL variant protein, is human MLKL1 (SEQ ID NO: 3), is between amino acids 400 to 471, preferably 450 to 471, most preferably between 460 to 471, and most preferably is between amino acid 458 to 468; and in the event the MLKL protein, or MLKL variant protein, is mouse MLKL2 (SEQ ID NO: 2), is between amino acids 400 to 464, preferably 420 to 464, most preferably between 430 to 460, and most preferably is between amino acids 445 to 455.
In preferred embodiments of the invention the modulating the intramolecular interaction comprises contacting the MLKL protein, or MLKL variant protein, with a compound selected from formula I or II, as well as derivatives, and solvates, salts, stereoisomers, complexes, polymorphs, crystalline forms, racemic mixtures, diastereomers, enantiomers, tautomers, isotopically labelled forms, prodrugs, and combinations thereof:
Preferably the above compound (i) [N-[3-[6-(4-methylpiperazin-1-yl)pyridazin-3-yl]phenyl]naphthalene-2-carboxamide] is an inhibitor of human MLKL protein (MBA-h1), and the above compound (ii) [N-(3-chloro-4-naphthalen-2-yloxyphenyl)-6-methoxy-2-methylquinolin-4-amine] is an inhibitor of mouse MLKL protein (MBA-m1).
In preferred embodiments of the invention said modulation of intramolecular interaction does not involve a modulation of interaction at the ATP-binding site or at the phosphorylation site within the MLKL protein, or MLKL variant protein; optionally, wherein the method additionally comprises an allosteric modulation of interaction at the ATP-binding site or at the phosphorylation site within the MLKL protein, or MLKL variant protein.
In a second aspect, the invention pertains to a method for modulating the activation capacity of necroptosis in a cell, the method comprising the step of contacting the cell with a MLKL modulating compound or MLKL modulating composition, wherein said MLKL modulating compound or MLKL modulating composition when contacted with the cell modulates an intramolecular interaction between the C-terminal helix (Hc) of the psK domain and a hydrophobic groove, wherein the hydrophobic groove is a 3 dimensional structural motif in the MLKL protein, or in the variant MLKL protein, that comprises and/or involves at least one amino acid residue from each of the 4HB domain, the brace region and the psK domain.
In preferred embodiments of the invention the impairment of the intramolecular interaction between the He and the hydrophobic groove of the MLKL protein, or the MLKL variant protein, in the cell impairs the activation capacity of necroptosis in the cell, for example impairs the permeabilization of the plasma membrane of the cell.
In another embodiment of the invention, the MLKL modulating compound or substance or MLKL modulating composition is selected from a polypeptide, peptide, glycoprotein, a peptidomimetic, an antigen binding construct (for example, an antibody, antibody-like molecule or other antigen binding derivative, or an or antigen binding fragment thereof), a nucleic acid such as a DNA or RNA, for example an antisense or inhibitory DNA or RNA, a ribozyme, an RNA or DNA aptamer, RNAi, siRNA, shRNA and the like, including variants or derivatives thereof such as a peptide nucleic acid (PNA), a genetic construct for targeted gene editing, such as a CRISPR/Cas9 construct and/or a guide nucleic acid (gRNA or gDNA) and/or tracrRNA, or a small molecular compound, preferably a small molecule having a molecular weight of less than 10 kD, more preferably of less than 2 kD, most preferably of less than 1 kD, or any combination of the above.
Preferably, the MLKL modulating compound or MLKL modulating composition is a compound/substance or composition of multiple compounds for the targeted introduction of mutations into the gene encoding the MLKL protein, or the MLKL variant protein, in the cell. For example, the targeted introduction of mutations comprises the targeted introduction of mutations into the sequence encoding the He and/or hydrophobic groove.
In preferred embodiments of this aspect, the He is located at the C-terminal end of the psK domain, and in the event the MLKL protein, or MLKL variant protein, is human MLKL1 (SEQ ID NO: 3), is between amino acids 400 to 471, preferably 450 to 471, most preferably between 460 to 471, most preferably is between amino acid 458 to 468; and in the event the MLKL protein, or MLKL variant protein, is mouse MLKL2 (SEQ ID NO: 2), is between amino acids 400 to 464, preferably 420 to 464, most preferably between 430 to 460, and most preferably is between amino acids 445 to 455.
In another preferred embodiment of this aspect, and the other aspects as well, the hydrophobic groove wherein the hydrophobic groove comprises at least one amino acid residue from each of the 4HB domain, the brace region and the psK domain, and
In a third aspect, the invention pertains to a method for identifying a compound capable of modulating activation of MLKL, the method comprising
In one preferred embodiment, the MLKL protein, or variant MLKL protein, is a constitutively active MLKL protein, for example a phosphorylated MLKL protein.
It may further be preferred that step (ii) of the above method of the third aspect is mandatory and comprises phosphorylation of the MLKL protein, or the MLKL variant protein; and/or comprises inducing necroptosis in the cell expressing the MLKL protein, or MLKL variant protein, or alternatively comprises trafficking, pathological immune responses and/or inflammation.
The method according to any one of claims 15 to 17, wherein the candidate compound is selected from a polypeptide, peptide, glycoprotein, a peptidomimetic, an antigen binding construct (for example, an antibody, antibody-like molecule or other antigen binding derivative, or an or antigen binding fragment thereof), a nucleic acid such as a DNA or RNA, for example an antisense or inhibitory DNA or RNA, a ribozyme, an RNA or DNA aptamer, RNAi, siRNA, shRNA and the like, including variants or derivatives thereof such as a peptide nucleic acid (PNA), a genetic construct for targeted gene editing, such as a CRISPR/Cas9 construct and/or a guide nucleic acid (gRNA or gDNA) and/or tracrRNA, or a small molecular compound, preferably a small molecule having a molecular weight of less than 5 kD, more preferably of less than 2 kD, most preferably of less than 1 kD, or any combination of the above.
In a fourth aspect, the invention pertains to a method for identifying a compound capable of modulating activation of MLKL, the method comprising:
In a fifth aspect, the invention pertains to a method for identifying a compound capable of modulating activation of MLKL, the method comprising:
In one embodiment the MLKL hydrophobic groove domain and/or the MLKL He domain are provided as full-length MLKL protein, or are provided as test proteins comprising the MLKL hydrophobic groove domain and/or the MLKL He domain, but not comprising the full psK and/or 4HB domain, more preferably the test protein is a MLKL mutant protein, such as a constitutively active MLKL protein, or a constitutively active MLKL variant protein.
In a sixth aspect, the invention pertains to a method for treating a disease associated with necroptosis, inflammation, pathological immune response and/or trafficking in a subject, the method comprising performing in the subject a method according to any one of the preceding aspects, wherein the cell is a cell associated with the disease. In an alternative embodiment of the sixth aspects, the invention pertains to substance/composition for use in treating a disease associated with necroptosis, inflammation, pathological immune response and/or trafficking in a subject, wherein the substance or composition has an activity as a modulator of MLKL as disclosed herein.
The method of treating a disease in preferred embodiments comprises a step of administering to the subject a therapeutically effective amount of the MLKL modulating compound or MLKL modulating composition.
In the various aspects and embodiments, the present invention pertains to a use in research or medicine, specifically in the prevention and/or treatment of a disease. In this context it is preferred that the disease is a disease associated with necroptosis and is preferably is selected from the group consisting of diseases of the bones, joints, connective tissue and cartilage, muscular diseases, skin diseases, cardiovascular diseases, circulatory diseases, hematological and vascular diseases, diseases of the lung, diseases of the gastro-intestinal tract, diseases of the liver, diseases of the pancreas, metabolic diseases, diseases of the kidneys, viral and bacterial infections, severe intoxications, degenerative diseases associated with the Acquired Immune Deficiency Syndrome (AIDS), disorders associated with aging, inflammatory diseases, auto-immune diseases, dental disorders, ophthalmic diseases or disorders, diseases of the audition tracts, diseases associated with mitochondria, and cancer, such as a solid cancer or lymphoid cancer, and cancer metastasis.
The terms “of the [present] invention”, “in accordance with the invention”, “according to the invention” and the like, as used herein are intended to refer to all aspects and embodiments of the invention described and/or claimed herein.
As used herein, the term “comprising” is to be construed as encompassing both “including” and “consisting of”, both meanings being specifically intended, and hence individually disclosed embodiments in accordance with the present invention. Where used herein, “and/or” is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example, “A and/or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein. In the context of the present invention, the terms “about” and “approximately” denote an interval of accuracy that the person skilled in the art will understand to still ensure the technical effect of the feature in question. The term typically indicates deviation from the indicated numerical value by ±20%, ±15%, ±10%, and for example ±5%. As will be appreciated by the person of ordinary skill, the specific such deviation for a numerical value for a given technical effect will depend on the nature of the technical effect. For example, a natural or biological technical effect may generally have a larger such deviation than one for a man-made or engineering technical effect. As will be appreciated by the person of ordinary skill, the specific such deviation for a numerical value for a given technical effect will depend on the nature of the technical effect. For example, a natural or biological technical effect may generally have a larger such deviation than one for a man-made or engineering technical effect. Where an indefinite or definite article is used when referring to a singular noun, e.g. “a”, “an” or “the”, this includes a plural of that noun unless something else is specifically stated.
It is to be understood that application of the teachings of the present invention to a specific problem or environment, and the inclusion of variations of the present invention or additional features thereto (such as further aspects and embodiments), will be within the capabilities of one having ordinary skill in the art in light of the teachings contained herein.
Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.
All references, patents, and publications cited herein are hereby incorporated by reference in their entirety.
The figures show:
The sequences show:
Certain aspects and embodiments of the invention will now be illustrated by way of example and with reference to the description, figures and tables set out herein. Such examples of the methods, uses and other aspects of the present invention are representative only, and should not be taken to limit the scope of the present invention to only such representative examples.
The examples show:
Mouse MLKL has three transcript variants produced by alternative splicing (
To evaluate the necroptotic potential of the different mMLKL isoforms, each of the three isoforms were re-expressed in NIH-3T3 MLKL knock out (ko) cells following induction of necroptosis with a mixture of TNF, a Smac mimetic compound (LCL-161) and the pan-caspase inhibitor zVAD (TSZ), which is the most commonly used necroptosis-inducing cocktail. The inventors quantified cell death by flow cytometry (
Surprisingly, mMLKL1 and mMLKL2 differed markedly in their capacity to induce necroptosis. Whereas mMLKL1 remained inactive following a stimulus that would normally trigger necroptosis, cells expressing mMLKL2 responded to treatment at the same levels as wild-type (wt), non-transfected NIH-3T3 cells. Specific expression of mMLKL2 in MLKL-deficient cells induced the typical necroptotic phenotype upon treatment: rounding up and detachment prior to plasma membrane breakdown. Similar results were obtained through the activation of the TNF pathway in L929 cells and in MLKL-deficient murine dermal fibroblasts (MLKL-ko MDFs) (not shown) or when necroptosis was triggered via TLR3/4 or DAI (
The stark difference in necroptotic activity despite the high sequence similarity between mMLKL1 and mMLKL2 raised the question about their distribution in nature. To examine the expression levels of mMLKL1 and mMLKL2 in different tissues and cell lines from mouse, the inventors performed quantitative RT-PCR, with primers that specifically detect the RNA of mMLKL1 or mMLKL2. It was found that necroptosis-inactive mMLKL1 is expressed in the heart, liver, kidney and cecum, as well as in bone-marrow-derived macrophages (BMDMs) and NIH-3T3 cells (
The finding that the presence of eight additional amino acids in mMLKL1, as compared to mMLKL2, completely abolishes the capacity of MLKL to induce necroptosis implied that this segment could be important for MLKL regulation. To guide the experimental design for testing the structure-to-function relationship of these extra residues located before the very last C-terminal helix (Hc), molecular dynamics (MD) simulations were used. The inventors built 3D models of mMLKL1 and mMLKL2 based on the crystal structure of full mouse MLKL2 (pdb: 4btf) (21). First, filled gaps were refined in missing regions connecting different secondary structure elements within the 4HB (S79-K94), brace (Y118-Q128), and psK (K351-S358 and V456-V464) domains of the full mMLKL2 structure, since the absence of structural information in the crystal about these segments could mask important interactions of the C-terminus with other protein regions. The segment S79-K94 was modeled based on the α-helix 4 of the human 4HB domain (pdb code: 2msv) (33), while the other unsolved regions were modeled ab initio. Next, the 3D structure of mMLKL1 was modeled based on the refined structure of mMLKL2. Considering that MLKL is activated upon phosphorylation by RIP3, the inventors also modeled phosphomimetic versions of mMLKL1 and mMLKL2 (pmMLKL1 and pmMLKL2) by mutating specific positions within the psK domain (S228E, S345D, S347D, T349D, and S352D) (34, 35). These residues are located opposite to the C-terminal segment of MLKL, in the N-lobe of the psK domain (
Comparative analysis of the structures of mMLKL1 and mMLKL2 phosphomutants predicted that the He of inactive mMLKL1, but not that of mMLKL2, is unfolded due to the presence of the extra eight amino acids. This suggested that the loss of secondary structure in He could be linked, perhaps even causally, to the lack of necroptosis activity of mMLKL1.
To assess experimentally whether the effect of this insertion was sequence-specific, different mutants were produced in which Ala-segments of different lengths (2, 4, 6, and 8 Ala) were inserted into mMLKL2 at the equivalent position of the extra eight amino acid sequence of mMLKL1 (
A previous study suggested that He could act as a suppressor of human MLKL activity by interacting with the α-helix 4 of the 4HB (36). To explore this possibility, the necroptotic activity of He deletion mutants was tested (
To predict the conformational changes that activate mMLKL2 upon phosphorylation, the inventors compared the MD simulations of mMLKL2 with its phosphomimetic version. To understand how the presence of the eight additional amino acids alters the structural dynamics of the protein, the inventors analyzed this for mMLKL1. An essential dynamics analysis was performed over the structural ensembles obtained through MD simulations. This method allows to predict differences in conformational dynamics among MLKL isoforms and the mutant structures in solution, which cannot be obtained from crystal structures (Amadei et al., 1993). As shown in
Inspection of the structure of mMLKL2 predicted that He is accommodated into a hydrophobic groove (
To test the hypothesis that He/groove association is essential for mMLKL2 activation, the double-mutant mMLKL2_L450R_S454R was designed. MD simulations predicted that replacement of Leu and Ser by the positively charged Arg would disrupt the He, thereby destabilizing its insertion into the groove and affecting the active conformation of mMLKL2 (
Human MLKL is annotated as two isoforms (hMLKL1 and hMLKL2) that share the N-terminal and the C-terminal sequences, although hMLKL2 lacks a major part of the psK domain (
Human and mouse MLKL orthologues strongly differ in their psK domain (22) and in the underlying mechanism that controls their regulation (32, 37). In fact, both orthologues are unable to induce necroptosis when their host cells are exchanged (24), which raised the question whether He would also be relevant for hMLKL activity. The inventors used MD simulations to generate a structural model of activatable hMLKL1 based on the NMR structure of the human 4HB domain (pdb: 2msv) (33), the crystal structure of its psK (pdb: 4mwi) (22), and the crystal structure of full length mouse MLKL (pdb: 4btf) (21). Phosphomimetic versions of human MLKL1 (phMLKL1) contained the mutations T357E and S358D (38). The MD simulations predicted that human MLKL1 sampled at least two conformational states (denoted as A and B), which were restricted to a single, different conformation in the phosphomutant (C) (
The role of Hc in hMLKL1 activity was explored experimentally by assessing the necroptosis potential of different mutants (
Cys86 was identified as a residue positioned at the core of the hydrophobic groove of hMLKL1 in the region comprising the α-helix 4 of the 4HB. The inventors evaluated the effect of exchanging Cys86 (either alone or together with Ser467 in the Hc) by negatively charged Asp (
We next sought to discern the hierarchy between the He/groove interaction and MLKL phosphorylation in the process of activation. The inventors evaluated experimentally the activity of phosphomimetic variants of mMLKL1 and mMLKL2 generated by substitution of Ser345 and Ser347 by Asp residues (
Based on the conserved relevance of the He/groove for MLKL function, the inventors predicted that it should be possible to find small chemical compounds that inhibit MLKL activity by disrupting the He/groove interaction. Indeed, the structural analysis provided here for the He/groove of activatable MLKL variants affords the ability to rationally screen for and optimize such necroptosis-inhibiting small compounds.
By screening the “Tres Cantos Antimalarial Set” (TCAMS) publicly available at the Chembl-NTD database (http://www.ebi.ac.uk/chemblntd) with the Autodock Vina software, the inventors identified putative blockers that target the He/groove of hMLKL1 or mMLKL2. Based on the scoring function of this initial analysis, the inventors selected the best-ranked commercially available compounds for human and mouse MLKL and tested them in necroptosis inhibition assays.
Thereby, the inventors identified two compounds, MBA-h1 and MBA-m1, that specifically inhibited necroptosis in human HT-29 (MBA-h1) and mouse NIH-3T3 WT cells (MBA-m1), respectively, in a dose-dependent manner (
To further characterize the mechanism by which MBA-h1 and MBA-m1 inhibit the necroptosis-inducing capacity of MLKL, the inventors assessed whether they affect MLKL phosphorylation and plasma membrane translocation, two hallmarks of MLKL activation. Western-blot analysis with antibodies against phosphorylated MLKL showed that none of the compounds blocked the phosphorylation of MLKL, implying they indeed act by solely blocking MLKL without affecting the upstream kinases RIP1 and RIP3 (
As MBA-m1 is the first specific inhibitor of mouse MLKL the inventors are aware of, the inventors sought to characterize its mechanism of inhibition in more detail. To obtain further evidence that MBA-m1 inhibits necroptosis by specifically targeting the He/groove of mMLKL2, the inventors took a rational approach to design mutations that affect the MBA-m1/MLKL interaction without altering the necroptosis-inducing capacity of mMLKL2. In cell death assays, the inventors confirmed that the mutant mMLKL2_I84A_F87A was as active as mMLKL2, but that it was inert to inhibition by MBA-m1 (
Finally, the inventors aimed to assess the efficacy of inhibiting necroptosis in vivo by specifically targeting the He/groove interaction of MLKL with MBA-m1 in a mouse model with proven necroptosis contribution to disease. the inventors recently showed that mice in which the keratinocyte-specific absence of the LUBAC component HOIP (HoipE-KO) is combined with constitutive deficiency for TNFR1 (Tnfr1KO) suffer from fatal skin inflammation at around day 70 after birth. This phenotype is substantially alleviated by constitutive deficiency in MLKL, showing that MLKL-dependent necroptosis contributes to the pathology (10). At around 30 to 40 days of age, the inventors treated Tnfr1KO;HoipEKO mice, which at this time suffer from mild dermatitis, with MBA-m1 daily for the next three weeks. Strikingly, this treatment significantly ameliorated dermatitis as assessed by a decrease in the severity score of skin lesions at the end of treatment (
The references are:
| Number | Date | Country | Kind |
|---|---|---|---|
| 20173672.5 | May 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/062355 | 5/10/2021 | WO |
