Secreted ORF8 induces monocytic pro-inflammatory cytokines through NLRP3 pathways in patients with severe COVID-19

Despite extensive research, the specific factor associated with SARS-CoV-2 infection that mediates the life-threatening inflammatory cytokine response in patients with severe COVID-19 remains unidentified. Herein we demonstrate that the virus-encoded Open Reading Frame 8 (ORF8) protein is abundantly secreted as a glycoprotein in vitro and in symptomatic patients with COVID-19. ORF8 specifically binds to the NOD-like receptor family pyrin domain-containing 3 (NLRP3) in CD14⁺ monocytes to induce inflammasomal cytokine/chemokine responses including IL1β, IL8, and CCL2. Levels of ORF8 protein in the blood correlate with severity and disease-specific mortality in patients with acute SARS-CoV-2 infection. Furthermore, the ORF8-induced inflammasome response was readily inhibited by the NLRP3 inhibitor MCC950 in vitro. Our study identifies a dominant cause of pathogenesis, its underlying mechanism, and a potential new treatment strategy for severe COVID-19.

The SARS-CoV-2 encoded ORF8 protein Stimulates Human Monocytes to Produce Pro-Inflammatory Cytokines

Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can result in a cytokine storm that is associated with poor outcomes in patients. The activation of a NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome following SARS-CoV-2 infection has been shown to play a major role in inflammatory immune responses. In this study, we show that open reading frame 8 (ORF8) protein is abundantly secreted as a glycoprotein in vitro. The glycosylated ORF8 stimulates human CD14+/CD16+ monocytes to cause upregulation of proinflammatory cytokine production and cell surface marker expression within 24 hours. The data suggests that stimulation of human monocytes by ORF8 is not receptor mediated. Rather, ORF8 is likely phagocytosed by human monocytes. ORF8 then stimulates the monocytes by independently binding to the NACHT and LRR domains of the NLRP3 protein. Pharmacologic inhibition of NLRP3 significantly diminished the production of pro-inflammatory cytokines from ORF8-stimulated human monocytes. Finally, this study shows that the ORF8 protein is also secreted in patients with newly diagnosed coronavirus disease 2019 (COVID-19). Levels of ORF8 in the blood of patients diagnosed with COVID-19 correlated with disease mortality and trajectory of disease. ORF8 stimulation of monocytes causes pro-inflammatory cytokine production that leads to the development of severe COVID-19.

Sustained, complete response to pexidartinib in a patient with CSF1R-mutated Erdheim-Chester disease

Erdheim-Chester disease (ECD) is a histiocytic neoplasm that predominantly harbors mitogen-activated protein kinase (MAPK) pathway variants. MAPK inhibitors typically are effective treatments, but mutations outside the MAPK pathway, such as CSF1R variants, may cause refractory ECD. We describe a patient with a novel somatic mutation in CSF1R (CSF1R^{R549_E554delinsQ} ) that resulted in refractory ECD affecting the central nervous system. Cell model studies, RNA sequencing analysis, and in silico protein modeling suggested that she had a gain-of-function mutation occurring in a region critical for autoinhibition. The patient was treated with pexidartinib, a CSF1R inhibitor, and has had a complete clinical and metabolic response lasting more than 1.5 years to date. To our knowledge, this is the first report to describe successful treatment of a patient with ECD by using an agent that specifically targets CSF1R. This case also highlights the critical role of individualized molecular profiling to identify novel therapeutic targets in ECD.

MCIR1: A patient-derived mantle cell lymphoma line for discovering new treatments for ibrutinib resistance

BACKGROUND

Despite the unprecedented success of ibrutinib in lymphoma therapy, the development of ibrutinib resistance due to acquired BTK or PLCγ2 mutations has become a new clinical problem. However, not all resistance is mediated by these mutations and these mechanisms are poorly understood due to a lack of study tools that truly recapitulate this clinical scenario.

METHODS

We established a novel patient-derived ibrutinib-resistant mantle cell lymphoma (MCL) line named MCIR1. Using immunological, molecular, and cytogenetic approaches, we comprehensively characterized MCIR1 and further demonstrated its utility in the study of resistance mechanisms and treatments to overcome this resistance.

RESULTS

We show that MCIR1 is a bona fide ibrutinib-resistant MCL cell line with normal BTK-/PLCγ2 but ibrutinib-resistant ERK1/2 and AKT1 signaling. RNA-Seq analysis revealed a robust non-canonical NF-kB signaling that drives the ibrutinib resistance. We also demonstrate the potential utility of a MCIR1-based cell and mouse model for the discovery of new treatments to overcome BTK inhibitor resistance.

CONCLUSIONS

We have established the first patient-derived ibrutinib-resistant MCL cell line MCIR1 that lacks BTK or PLCγ2 mutations but exhibits a hyperactive non-canonical NF-kB pathway. We further demonstrate its utility in the discovery and validation of new drugs to overcome this resistance.

Salicylates enhance CRM1 inhibitor antitumor activity by induction of S-phase arrest and impairment of DNA-damage repair

Chromosome region maintenance protein 1 (CRM1) mediates protein export from the nucleus and is a new target for anticancer therapeutics. Broader application of KPT-330 (selinexor), a first-in-class CRM1 inhibitor recently approved for relapsed multiple myeloma and diffuse large B-cell lymphoma, have been limited by substantial toxicity. We discovered that salicylates markedly enhance the antitumor activity of CRM1 inhibitors by extending the mechanisms of action beyond CRM1 inhibition. Using salicylates in combination enables targeting of a range of blood cancers with a much lower dose of selinexor, thereby potentially mitigating prohibitive clinical adverse effects. Choline salicylate (CS) with low-dose KPT-330 (K+CS) had potent, broad activity across high-risk hematological malignancies and solid-organ cancers ex vivo and in vivo. The K+CS combination was not toxic to nonmalignant cells as compared with malignant cells and was safe without inducing toxicity to normal organs in mice. Mechanistically, compared with KPT-330 alone, K+CS suppresses the expression of CRM1, Rad51, and thymidylate synthase proteins, leading to more efficient inhibition of CRM1-mediated nuclear export, impairment of DNA-damage repair, reduced pyrimidine synthesis, cell-cycle arrest in S-phase, and cell apoptosis. Moreover, the addition of poly (ADP-ribose) polymerase inhibitors further potentiates the K+CS antitumor effect. K+CS represents a new class of therapy for multiple types of blood cancers and will stimulate future investigations to exploit DNA-damage repair and nucleocytoplasmic transport for cancer therapy in general.

Abstract 650: MCIR1: A patient-derived ibrutinib-resistant mantle cell lymphoma line for the study of ibrutinib resistance and drug discovery

Constitutive activation of B-cell receptor (BCR) signaling is a major driving mechanism for the proliferation and survival of various B-cell lineage non-Hodgkin lymphomas (NHL). Blocking BCR signaling using the first-in-class Bruton's tyrosine kinase (BTK) inhibitor, ibrutinib, has proved effective and is currently FDA approved for the treatment of several B-cell lymphomas. Unfortunately, significant subsets of patients possess either primary or acquired resistance to ibrutinib, often resulting in worse prognosis and poorer responses to subsequent therapies. Therefore, overcoming ibrutinib resistance is an urgent clinical need requiring new tools to both delineate the molecular mechanisms of resistance and develop viable therapeutics.

To that end, we developed a mantle cell lymphoma (MCL) cell line, MCIR1, from a patient with clinically acquired ibrutinib resistance. MCIR1 is a bona fide MCL cell line featuring CD19+/CD5+/CD10-/CD23-/t(11;14)+/TP53+/-; and lacking the previously described mutations in BTK (C481S) and phospholipase C-gamma-2 (R665W, L845F). Importantly, MCIR1 cells possess hallmarks of ibrutinib resistance, including the insensitivity of ERK1/2 phosphorylation to ibrutinib in vitro, and the irresponsiveness of MCIR1 xenograft tumors to ibrutinib treatment in mice as compared with ibrutinib-sensitive Jeko-1 tumors. To delineate the molecular mechanism(s) of ibrutinib resistance, we identified by RNA-Seq analysis that MCIR1 cells possess robust activity of the non-canonical NFkB pathway and elevated expression of NFkB target genes, suggesting that this pathway likely drives their resistance to ibrutinib. Finally, we demonstrated the utility of MCIR1 as a tool for testing new drugs to combat ibrutinib resistance in vitro by showing its sensitivity to the anti-apoptotic B-cell lymphoma-2 (Bcl-2) protein inhibitor, venetoclax.

To our knowledge, MCIR1 is the first patient-derived ibrutinib-resistant cell line to be established. Hence, MCIR1 is especially useful because uniquely possesses the relevant clinical and biological features of patients with ibrutinib-resistant MCL. We propose MCIR1 as a tool to further the understanding of molecular mechanisms conferring ibrutinib resistance by providing a clinically relevant system with the capacity for molecular and genetic manipulations. Further, these features make MCIR1 an ideal model to screen drugs for combating ibrutinib resistance through both in vivo and in vitro approaches.

Citation Format: Kevin E. Nowakowski, Jithma P. Abeykoon, Mary J. Stenson, Michael M. Timm, Curtis A. Hanson, Daniel L. Van Dyke, Anne J. Novak, Xiaosheng Wu, Thomas E. Witzig. MCIR1: A patient-derived ibrutinib-resistant mantle cell lymphoma line for the study of ibrutinib resistance and drug discovery [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 650.