Efficacy and Safety of Etrasimod in Patients with Moderately to Severely Active Isolated Proctitis: Results From the Phase 3 ELEVATE UC Clinical Programme

BACKGROUND AND AIMS

Pivotal trials in ulcerative colitis have historically excluded patients with isolated proctitis. Etrasimod is an oral, oncedaily, selective sphingosine 1phosphate1,4,5 receptor modulator for the treatment of moderately to severely active ulcerative colitis. This post hoc analysis assessed efficacy and safety of etrasimod 2 mg once daily in patients with isolated proctitis (centrally read) from the phase 3 ELEVATE UC 52 and ELEVATE UC 12 trials.

METHODS

Patients, including those with isolated proctitis (<10 cm rectal involvement) who met all other inclusion criteria in ELEVATE UC 52 and ELEVATE UC 12, were randomised 2:1 to receive etrasimod or placebo. Primary, secondary and other identified efficacy endpoints and safety were assessed.

RESULTS

We analysed data from 64 and 723 patients at Week 12 (both trials pooled), and 36 and 397 patients at Week 52 (ELEVATE UC 52 only) with isolated proctitis and more extensive colitis (≥10 cm rectal involvement), respectively. Patients with isolated proctitis receiving etrasimod demonstrated significant improvements versus placebo, including clinical remission rates at Weeks 12 (42.9% vs 13.6%) and 52 (44.4% vs 11.1%), endoscopic improvement (52.4% vs 22.7%) at Week 12 and bowel urgency numerical rating scale score at Week 12 (all p<0.01). Generally similar trends were observed in patients with more extensive colitis. Safety was consistent across subgroups, with no new findings.

CONCLUSIONS

Etrasimod demonstrated significant improvements versus placebo in patients with isolated proctitis, and those with more extensive disease, in most efficacy endpoints at Week 12 and 52.

The Hedgehog pathway promotes blood-brain barrier integrity and CNS immune quiescence

The blood-brain barrier (BBB) is composed of tightly bound endothelial cells (ECs) and perivascular astrocytes that regulate central nervous system (CNS) homeostasis. We showed that astrocytes secrete Sonic hedgehog and that BBB ECs express Hedgehog (Hh) receptors, which together promote BBB formation and integrity during embryonic development and adulthood. Using pharmacological inhibition and genetic inactivation of the Hh signaling pathway in ECs, we also demonstrated a critical role of the Hh pathway in promoting the immune quiescence of BBB ECs by decreasing the expression of proinflammatory mediators and the adhesion and migration of leukocytes, in vivo and in vitro. Overall, the Hh pathway provides a barrier-promoting effect and an endogenous anti-inflammatory balance to CNS-directed immune attacks, as occurs in multiple sclerosis.

Angiotensin II controls occludin function and is required for blood brain barrier maintenance: relevance to multiple sclerosis

The blood-brain barrier (BBB) restricts molecular and cellular trafficking between the blood and the CNS. Although astrocytes are known to control BBB permeability, the molecular determinants of this effect remain unknown. We show that angiotensinogen (AGT) produced and secreted by astrocytes is cleaved into angiotensin II (AngII) and acts on type 1 angiotensin receptors (AT1) expressed by BBB endothelial cells (ECs). Activation of AT1 restricts the passage of molecular tracers across human BBB-derived ECs through threonine-phosphorylation of the tight junction protein occludin and its mobilization to lipid raft membrane microdomains. We also show that AGT knock-out animals have disorganized occludin strands at the level of the BBB and a diffuse accumulation of the endogenous serum protein plasminogen in the CNS, compared with wild-type animals. Finally, we demonstrate a reduction in the number of AGT-immunopositive perivascular astrocytes in multiple sclerosis (MS) lesions, which correlates with a reduced expression of occludin similarly seen in the CNS of AGT knock-out animals. Such a reduction in astrocyte-expressed AGT and AngII is dependent, in vitro, on the proinflammatory cytokines tumor necrosis factor-alpha and interferon-gamma. Our study defines a novel physiological role for AngII in the CNS and suggests that inflammation-induced downregulation of AngII production by astrocytes is involved in BBB dysfunction in MS lesions.

Death receptor expression and function at the human blood brain barrier

The blood brain barrier (BBB) is composed of specialized endothelial cells tightly anastomosed to one another and surrounded by a thick extracellular matrix, the basement membrane. Together these components restrict the diffusion of cells and molecules from the periphery into the central nervous system (CNS), providing immune privilege and homeostasis. Dysregulation of the BBB and trans-endothelial migration of immune cells are amongst the earliest CNS changes partaking in lesion formation in multiple sclerosis (MS). Death receptors are members of the tumor necrosis factor receptor (TNFR) super-family. They are expressed on a variety of tissues including endothelium, but the consequence of their triggering appears to be cell type specific. In this study, we describe the expression of death receptors TNFR1, Fas and DR5 on primary cultures of human BBB-derived endothelial cells (ECs), as well as the effects of receptor activation on human brain endothelial cell (HBEC) function. We show that HBECs are resistant to cell death mediated via TNFalpha, FasL and TRAIL and that neither receptor ligation induces cellular proliferation of HBECs. TNFR1 ligation induces NFkappaB activation and the upregulation of chemokines MCP-1 and IL-8, as well as adhesion molecules ICAM-1 and VCAM-1, while Fas and DR5 triggering activate the extracellular signal regulated kinases-1 and -2 (Erk 1/2, p42/44 MAPK) inducing the release of matrix metalloproteinase 9 (MMP9) by BBB-derived ECs.

Expression of the ATP-binding cassette membrane transporter, ABCG2, in human and rodent brain microvessel endothelial and glial cell culture systems

PURPOSE

The function of ABCG2 (BCRP), a member of the ATP-binding cassette (ABC) superfamily of membrane-associated drug transporters, at the blood-brain barrier remains highly controversial. This project investigates the functional expression of endogenous ABCG2 in cultures of human and rodent brain cellular compartments.

MATERIALS AND METHODS

RT-PCR, western blot and fluorescent immunocytochemical analyses were performed on ABCG2-overexpressing human breast cancer (MCF-MX100) cells, human and rat brain microvessel endothelial (HBEC and RBE4, respectively), and rat glial cells.

RESULTS

RT-PCR analysis detected ABCG2 mRNA in all the cell culture systems. Western blot analysis with anti-ABCG2 monoclonal BXP-21 antibody detected a robust band at approximately 72 kDa in the ABCG2-overexpressing MCF-MX100 cell line, whereas low expression was found in human and rat brain cell systems. Immunofluorescence microscopy detected predominant plasma membrane localization of ABCG2 in MCF-MX100 cells but weak signal in all brain cellular compartments. In the presence of ABCG2 inhibitors, the accumulation of (3)H-mitoxantrone and pheophorbide A, two established ABCG2 substrates, was significantly increased in MCF-MX100 cells but not in the human and rodent brain cell culture systems.

CONCLUSIONS

Our data show low endogenous ABCG2 protein expression, localization and activity in cultures of human and rat brain microvessel endothelial and glial cells.

Statins reduce human blood-brain barrier permeability and restrict leukocyte migration: Relevance to multiple sclerosis

OBJECTIVE

Dysregulation of the blood-brain barrier (BBB) and transendothelial migration of immune cells are among the earliest central nervous system changes partaking in lesion formation in both multiple sclerosis (MS) and its early clinical form, the clinically isolated syndrome. Evidence for the anti-inflammatory effects of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors within the central nervous system arose from studies demonstrating that statins improve clinical signs in the animal model of MS and reduce the number of gadolinium-enhancing lesions in MS.

METHODS

We sought to describe the impact of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor treatment on the physiology and immunology of human BBB-derived endothelial cells (ECs).

RESULTS

We demonstrate that lovastatin and simvastatin induce a 50 to 60% reduction in the diffusion rates of bovine serum albumin and [(14)C]-sucrose across human BBB-ECs in vitro through abrogation of isoprenylation processes, but independent of the expression of the tight junction molecules occludin, VE-cadherin, JAM-1, zonula occluden-1, and zonula occluden-2. Simvastatin and lovastatin were equipotent in reducing BBB permeability in vitro, with median effective concentration (EC(50)) of 9.5 x 10(-8) and 1.0 x 10(-7)M, respectively. We further demonstrate that lovastatin and simvastatin treatment of BBB-ECs significantly restricts the migration of clinically isolated syndrome-derived and MS-derived monocytes and lymphocytes across the human BBB in vitro, through a specific reduction in the secretion of the chemokines monocyte chemotactic protein-1/CCL2 and interferon-gamma-inducible protein-10/CXCL10 by BBB-ECs.

INTERPRETATION

Our data parallel the previously reported magnetic resonance imaging-based radiological findings and suggest an effect of statins that could be beneficial in early MS, restricting the diffusion of molecular tracers and the migration of immune cells across the human BBB.

Resistance of human adult oligodendrocytes to AMPA/kainate receptor-mediated glutamate injury

Multiple sclerosis is an inflammatory disease of the CNS leading to the destruction of oligodendrocytes (OLs), myelin sheaths and axons. The mediators of tissue injury remain unknown. Glutamate, which can be released by activated immune cells or produced within the CNS, has been implicated as a potential mediator of tissue injury in multiple sclerosis. alpha-Amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) and kainate are highly toxic when added to rodent OL cultures. Using OLs derived from human adult surgical specimens, we investigated AMPA/kainate receptor expression and the effects of receptor stimulation on the viability of human OLs. We find that human adult OLs in vitro express low levels of ionotropic glutamate receptors and are resistant to excitotoxicity mediated by high and sustained doses of AMPA or kainate, even when receptor desensitization is blocked. In contrast, rat OLs show strong AMPA receptor expression and are susceptible to excitotoxicity, as previously demonstrated. Furthermore, we show in human brain sections that OLs do not express AMPA receptors in situ and that glial expression of AMPA receptors is limited to astrocytes. The apparent lack of glutamate receptor expression on human OLs and their resistance to AMPA/kainate toxicity should be considered when postulating mechanisms of tissue injury in multiple sclerosis.

Impact of the coxsackie and adenovirus receptor (CAR) on glioma cell growth and invasion: Requirement for the C-terminal domain

Expression of the coxsackie and adenovirus receptor (CAR) is downregulated in malignant glioma cell lines and is barely detectable in high-grade primary astrocytoma (glioblastoma multiforme). We determined the effect of forced CAR expression on the invasion and growth of the human glioma cell line U87-MG, which does not express any CAR. Although retrovirally mediated expression of full-length CAR in U87-MG cells did not affect monolayer growth in vitro, it did reduce glioma cell invasion in a 3-dimensional spheroid model. Furthermore, in xenograft experiments, intracerebral implantation of glioma cells expressing full-length CAR resulted in tumors with a significantly reduced volume compared to tumors generated by control vector-transduced U87-MG cells. In contrast, U87-MG cells expressing transmembrane CAR with a deletion of the entire cytoplasmic domain (except for the first 2 intracellular juxtamembrane cysteine amino acids) had rates of invasion and tumor growth that were similar to those of the control cells. This difference in behavior between the 2 forms of CAR was not due to improper cell surface localization of the cytoplasmically deleted CAR as determined by comparable immunostaining of unpermeabilized cells, equivalent adenoviral transduction of the cells and similar extent of fractionation into lipid-rich domains. Taken together, these results suggest that the decrease or loss of CAR expression in malignant glioma may confer a selective advantage in growth and invasion to these tumors.

Oligodendrocyte injury in multiple sclerosis: a role for p53

Multiple sclerosis (MS) is a neurological disorder characterized by myelin destruction and a variable degree of oligodendrocyte death. We have previously shown that overexpression of the transcription factor p53 can induce oligodendrocyte apoptosis. We investigated the mechanism of p53-induced apoptosis using primary cultures of central nervous system-derived adult human oligodendrocytes. Adenovirus-mediated p53 overexpression resulted in up-regulation of the death receptors Fas, DR4 and DR5 with subsequent caspase-mediated apoptosis of the oligodendrocytes. The oligodendrocytes were protected from p53-induced cell death by blocking signaling through Fas and/or tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors. Although lower levels of p53 did not induce apoptosis, the increase in death receptor expression was sufficient to render the oligodendrocytes susceptible to apoptosis in the presence of exogenous Fas ligand and TRAIL. These ligands are present in the inflammatory milieu of active MS lesions. In situ analysis of active MS lesions revealed increased p53 expression in oligodendrocytes in lesions that featured oligodendrocyte apoptosis and cell loss. Our data provide evidence for a novel role for p53 in the pathogenesis of MS.

Differential effects of Th1 and Th2 lymphocyte supernatants on human microglia

We assessed the effects of soluble molecules (supernatants) produced by pro- (Th1) and anti- (Th2) inflammatory T-cell lines on the capacity of adult human CNS-derived microglia to express or produce selected cell surface and soluble molecules that regulate immune reactivity or impact on tissue protection/repair within the CNS. Treatment of microglia with supernatants from allo-antigen and myelin basic protein-specific Th1 cell lines augmented expression of cell surface molecules MHC class II, CD80, CD86, CD40, and CD54, enhanced the functional antigen-presenting cell capacity of microglia in a mixed lymphocyte reaction, and increased cytokine/chemokine secretion (TNFalpha, IL-6, and CXCL10/IP-10). These Th1-induced effects were not reproduced by interferon-gamma (IFNgamma) alone and were only incompletely blocked by anti-IFNgamma antibody. Th2 cell supernatant treatments did not alter costimulatory/adhesion molecule expression or induce cytokine/chemokine production by microglia. Th2 treatment, furthermore, failed to reduce the induction observed in response to Th1 supernatants. Neither Th1 nor Th2 supernatants induced production of the neurotrophin molecules, nerve growth factor, or brain-derived neurotrophic factor. Our results suggest that soluble molecules released by Th1 and not Th2 cells that infiltrate the CNS can stimulate resident microglia to acquire enhanced effector and accessory cell functions; the Th1-induced effects were not downregulated by Th2 supernatant-mediated bystander suppression.

Human brain endothelial cells supply support for monocyte immunoregulatory functions

Blood-derived monocytic cells comprise a significant component of most inflammatory responses that occur in the CNS. We utilized human brain-derived endothelial cells (HBECs) coated membranes in Boyden chambers to assess immune function related properties of human blood-derived monocytes following interaction with HBECs. Monocytes in contact with HBECs maintained functional antigen-presenting capacity and chemokine/cytokine production in contrast to monocytes that migrated through the HBEC barrier. These results indicate that HBECs, although themselves incapable of serving as competent antigen-presenting cells during the course of inflammatory CNS disorders, supply support needed for infiltrating perivascular monocytes to maintain their functions. Monocyte migration across HBECs was inhibited by interferon-beta.

Malignant glioma cells use MHC class II transactivator (CIITA) promoters III and IV to direct IFN-gamma-inducible CIITA expression and can function as nonprofessional antigen presenting cells in endocytic processing and CD4(+) T-cell activation

Malignant gliomas (MGs), lethal human central nervous system (CNS) neoplasms, contain tumor infiltrating lymphocytes (TIL). Although MHC class II molecules are frequently detected on MG cells, suggesting that they may be capable of antigen (Ag) presentation to CD4(+) T cells, deficiencies in CD4(+) T-cell activation are associated with these nonimmunogenic tumors. We evaluated regulation of the MHC class II transactivator (CIITA), the key intermediate that controls class II expression, in MG cells and tested whether MG cells could process native Ag. After interferon-gamma (IFN-gamma) stimulation, MG cells upregulated CIITA and class II molecules. IFN-gamma-inducible CIITA expression in MG cells, as well as primary human astrocytes, was directed by two CIITA promoters, pIV, the promoter for IFN-gamma-inducible CIITA expression in nonprofessional antigen-presenting cells (APC), and pIII, the promoter that directs constitutive CIITA expression in B cells. Both pIII and pIV directed CIITA transcription in vivo in MGs and ex vivo in IFN-gamma-activated primary MG cultures. We also demonstrate for the first time that MG cells can process native Ag for presentation to CD4(+) MHC class II-restricted Th1 cells, indicating that MG cells can serve as nonprofessional APC. CIITA may be a key target to modulate MHC class II expression, which could augment immunogenicity, Ag presentation, and CD4(+) T-cell activation in MG therapy.

Glial cell influence on the human blood-brain barrier

The blood-brain barrier (BBB) is a specialized structure of the central nervous system (CNS) that restricts immune cell migration and soluble molecule diffusion from the systemic compartment into the CNS. Astrocytes and microglia are resident cells of the CNS that contribute to the formation of the BBB. In this article, we consider the influence of these glial cells on the immune regulatory functions of the microvascular endothelium, with special emphasis on the human BBB. A series of in vitro studies demonstrate that soluble factors produced by glial cells, under basal culture conditions, help restrict development of inflammation within the CNS. These soluble factor effects include upregulating expression of molecules including HT7, UEA-1 lectin-binding sites, and angiotensin receptors that help define the phenotype of endothelial cells. These factors also induce tight junction formation between brain endothelial cells, contributing to the restricted permeability of the BBB. In contrast, these factors have little effect on expression of molecules by ECs that either promote lymphocyte migration, such as chemokines and adhesion molecules or molecules that are required for competent antigen presentation, such as MHC and co-stimulatory molecules. Glial cells that become activated in response to signals derived from the immune system or generated within the CNS, produce an array of inflammatory molecules that increase permeability and promote lymphocyte trafficking and persistence. These observations emphasize the bidirectional nature of neural-immune interactions; this dynamic system should be amenable to therapeutic interventions.

Caspase 8 expression and signaling in Fas injury-resistant human fetal astrocytes

Fas (APO-1/CD95) is a cell surface receptor initially identified in lymphoid cells, but more recently detected in the central nervous system under pathological, usually inflammatory, conditions. In most Fas expressing cells, triggering of Fas by its ligand or by antagonistic antibodies leads to apoptosis. Human fetal astrocytes (HFA) constitutively express Fas yet are resistant to cell death following Fas ligation. In the current study, using dissociated cultures of human fetal central nervous system-derived cells, we attempted to identify a basis for HFA resistance to Fas-mediated injury. We compared the components of the Fas signaling pathway of HFA to those of two human cell lines susceptible to Fas-mediated injury, U251 glioma and Jurkat T-cells. We found that HFA did not express caspase 8 (FLICE), the caspase primarily activated on Fas signaling. Although we could induce caspase 8 in HFA with the inflammatory cytokines IFNgamma and TNFalpha, HFA remained resistant to Fas-mediated injury. Addition of inflammatory cytokines to the extracellular milieu also increased FLIP mRNA (FLICE inhibitory protein). Furthermore, upon triggering of cytokine-treated cells with FasL, we observed upregulation of the cleavage product of FLIP (p43-FLIP) previously shown to associate with the DISC and to block caspase 8 recruitment, thereby inhibiting Fas-mediated death. Our findings indicate that caspase 8 and its regulators play a central role in determining the response to Fas ligation of HFA and support a role for Fas signaling in the developing central nervous system other than related to cytotoxicity.