Selectin-blocking semisynthetic sulfated polysaccharides as promising anti-inflammatory agents

A critical evaluation of crizanlizumab for the treatment of sickle cell disease

INTRODUCTION

P-selectin is a key adhesion molecule in the pathogenesis of sickle cell disease, including acute painful event(s). Many of the mediators activated in prototypical pain crisis are also involved in other complications seen in this population. Crizanlizumab is a monoclonal antibody approved in the US in 2019 for patients of all genotypes of sickle cell disease. By blocking P-selectin, it effectively prevents acute painful event(s) and has a manageable safety profile.

AREAS COVERED

In this review, we provide an overview of the (i) biology of P-selectin in sickle cell disease, (ii) various agents inhibiting P-selectin, (iii) pharmacology of crizanlizumab, (iv) preclinical and clinical data on crizanlizumab, and (v) its potential for other indications, ongoing studies, regulatory status, and cost issues. Further, we describe its position among other approved agents in sickle cell disease and project future directions as well.

EXPERT OPINION

Crizanlizumab holds great promise in modulating the natural history of sickle cell disease and may have pleotropic effects. Studies are ongoing to define its role in preventing other sickle cell-related complications, non-sickle cell inflammatory states, and thrombotic disorders.

P-Selectin Blockade in the Treatment of Painful Vaso-Occlusive Crises in Sickle Cell Disease: A Spotlight on Crizanlizumab

Microvascular vaso-occlusion driven pain crisis is the hallmark of sickle cell disease with profound morbidity and increased mortality. Selectins, most notably P-selectins have an integral role in this phenomenon. P-selection was first identified in 1989. In 2019, after 3 decades of basic, translational, and clinical work with this pathway, the US Food and Drug Administration approved a P-selectin antibody, crizanlizumab to reduce frequency of pain crisis in patients more than 16 years with sickle cell disease. We review the fundamentals of P-selectin pathobiology, P-selectin blocking agents, clinical data with the use of crizanlizumab and prospects of this novel class of drugs in the context of other treatments for painful vaso-occlusive episodes.

Adhesion of T Cells to Endothelial Cells Facilitates Blinatumomab-Associated Neurologic Adverse Events

Blinatumomab, a CD19/CD3-bispecific T-cell engager (BiTE) immuno-oncology therapy for the treatment of B-cell malignancies, is associated with neurologic adverse events in a subgroup of patients. Here, we provide evidence for a two-step process for the development of neurologic adverse events in response to blinatumomab: (i) blinatumomab induced B-cell-independent redistribution of peripheral T cells, including T-cell adhesion to blood vessel endothelium, endothelial activation, and T-cell transmigration into the perivascular space, where (ii) blinatumomab induced B-cell-dependent T-cell activation and cytokine release to potentially trigger neurologic adverse events. Evidence for this process includes (i) the coincidence of T-cell redistribution and the early occurrence of most neurologic adverse events, (ii) T-cell transmigration through brain microvascular endothelium, (iii) detection of T cells, B cells, and blinatumomab in cerebrospinal fluid, (iv) blinatumomab-induced T-cell rolling and adhesion to vascular endothelial cells in vitro, and (v) the ability of antiadhesive agents to interfere with blinatumomab-induced interactions between T cells and vascular endothelial cells in vitro and in patients. On the basis of these observations, we propose a model that could be the basis of mitigation strategies for neurologic adverse events associated with blinatumomab treatment and other T-cell therapies. SIGNIFICANCE: This study proposes T-cell adhesion to endothelial cells as a necessary but insufficient first step for development of blinatumomab-associated neurologic adverse events and suggests interfering with adhesion as a mitigation approach.

Bispecific T-Cell Engager (BiTE) Antibody Construct Blinatumomab for the Treatment of Patients With Relapsed/Refractory Non-Hodgkin Lymphoma: Final Results From a Phase I Study

PURPOSE

Blinatumomab is a CD19/CD3 BiTE (bispecific T-cell engager) antibody construct for the treatment of Philadelphia chromosome-negative acute B-lymphoblastic leukemia. We evaluated blinatumomab in relapsed/refractory B-cell non-Hodgkin lymphoma (NHL).

PATIENTS AND METHODS

This 3 + 3 design, phase I dose-escalation study determined adverse events and the maximum tolerated dose (MTD) of continuous intravenous infusion blinatumomab in patients with relapsed/refractory NHL. Blinatumomab was administered over 4 or 8 weeks at seven different dose levels (0.5 to 90 μg/m(2)/day). End points were incidence of adverse events, pharmacokinetics, pharmacodynamics, and overall response rate.

RESULTS

Between 2004 and 2011, 76 heavily pretreated patients with relapsed/refractory NHL, who included 14 with diffuse large B-cell lymphoma, were enrolled; 42 received treatment in the formal dose-escalation phase. Neurologic events were dose limiting, and 60 μg/m(2)/day was established as the MTD. Thirty-four additional patients were recruited to evaluate antilymphoma activity and strategies for mitigating neurologic events at a prespecified MTD. Stepwise dosing (5 to 60 μg/m(2)/day) plus pentosan polysulfate SP54 (n = 3) resulted in no treatment discontinuations; single-step (n = 5) and double-step (n = 24) dosing entailed two and seven treatment discontinuations due to neurologic events, respectively. Grade 3 neurologic events occurred in 22% of patients (no grade 4/5). Among patients treated at 60 μg/m(2)/day (target dose; n = 35), the overall response rate was 69% across NHL subtypes and 55% for diffuse large B-cell lymphoma (n = 11); median response duration was 404 days (95% CI, 207 to 1,129 days).

CONCLUSION

In this phase I study of relapsed/refractory NHL, continuous infusion with CD19-targeted immunotherapy blinatumomab at various doses and schedules was feasible, with an MTD of 60 μg/m(2)/day. Single-agent blinatumomab showed antilymphoma activity.

Cellular adhesion and the endothelium: P-selectin

P-selectin on endothelial cell surfaces is central to impaired microvascular blood flow in sickle cell disease (SCD). Restoration of blood flow is expected to provide therapeutic benefit for SCD patients, whatever the mechanism of action of the treatment. Long-term oral administration of a P-selectin-blocking agent potentially improves blood flow and averts acute painful vaso-occlusive crises in patients with SCD. This review focuses on the pathophysiology of the impairment of microvascular blood flow in SCD with an emphasis on the role of P-selectin and summarizes the status of development of antiselectin therapies as a means of improving microvascular flow.

Disruption of PF4/H multimolecular complex formation with a minimally anticoagulant heparin (ODSH)

Recent studies have shown that ultra-large complexes (ULCs) of platelet factor 4 (PF4) and heparin (H) play an essential role in the pathogenesis of heparin-induced thrombocytopenia (HIT), an immune-mediated disorder caused by PF4/H antibodies. Because antigenic PF4/H ULCs assemble through non-specific electrostatic interactions, we reasoned that disruption of charge-based interactions can modulate the immune response to antigen. We tested a minimally anticoagulant compound (2-O, 3-O desulfated heparin, ODSH) with preserved charge to disrupt PF4/H complex formation and immunogenicity. We show that ODSH disrupts complexes when added to pre-formed PF4/H ULCs and prevents ULC formation when incubated simultaneously with PF4 and UFH. In other studies, we show that excess ODSH reduces HIT antibody (Ab) binding in immunoassays and that PF4/ODSH complexes do not cross-react with HIT Abs. When ODSH and unfractionated heparin (UFH) are mixed at equimolar concentrations, we show that there is a negligible effect on amount of protamine required for heparin neutralisation and reduced immunogenicity of PF4/UFH in the presence of ODSH. Taken together, these studies suggest that ODSH can be used concurrently with UFH to disrupt PF4/H charge interactions and provides a novel strategy to reduce antibody mediated complications in HIT.

Junctional adhesion molecule (JAM)-B supports lymphocyte rolling and adhesion through interaction with alpha4beta1 integrin

Junctional adhesion molecule-A (JAM-A), JAM-B and JAM-C have been implicated in leucocyte transmigration. As JAM-B binds to very late activation antigen (VLA)-4, a leucocyte integrin that contributes to rolling and firm adhesion of lymphocytes to endothelial cells through binding to vascular cell adhesion molecule (VCAM)-1, we hypothesized that JAM-B is also involved in leucocyte rolling and firm adhesion. To test this hypothesis, intravital microscopy of murine skin microvasculature was performed. Rolling interactions of murine leucocytes were significantly affected by blockade of JAM-B [which reduced rolling interactions from 9.1 +/- 2.6% to 3.2 +/- 1.2% (mean +/- standard deviation)]. To identify putative ligands, T lymphocytes were perfused over JAM-B-coated slides in a dynamic flow chamber system. JAM-B-dependent rolling and sticking interactions were observed at low shear stress [0.3 dyn/cm(2): 220 +/- 71 (mean +/- standard deviation) versus 165 +/- 88 rolling (P < 0.001; Mann-Whitney rank sum test) and 2.6 +/- 1.3 versus 1.0 +/- 0.7 sticking cells/mm(2)/min (P = 0.026; Mann-Whitney rank sum test) on JAM-B- compared with baseline], but not at higher shear forces (1.0 dyn/cm(2)). As demonstrated by antibody blocking experiments, JAM-B-mediated rolling and sticking of T lymphocytes was dependent on alpha4 and beta1 integrin, but not JAM-C expression. To investigate whether JAM-B-mediated leucocyte-endothelium interactions are involved in a disease-relevant in vivo model, adoptive transfer experiments in 2,4,-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity reactions were performed in mice in the absence or in the presence of a function-blocking JAM-B antibody. In this model, JAM-B blockade during the sensitization phase impaired the generation of the immune response to DNFB, which was assessed as the increase in ear swelling in untreated, DNFB-challenged mice, by close to 40% [P = 0.037; analysis of variance (anova)]. Overall, JAM-B appears to contribute to leucocyte extravasation by facilitating not only transmigration but also rolling and adhesion.

Enhancing effects of new biological response modifier beta-1,3 glucan sulfate PS3 on immune reactions

Glucans have a long history as non-specific biological modulators; however, but the search for optimal chemical configuration is still on. The objective of this study was to evaluate intraperitoneal application of PS3, a sulfated derivative of a (1-->3)-beta-D-glucan isolated from sporophytes of Laminaria digitata. PS3 showed significant stimulation of phagocytic activity as well as potentiation of synthesis and release of IL-2 by splenocytes. In addition, PS3 increased NK cell-mediated killing of tumor cells both in vitro and in vivo. When combined, our observations suggest that PS3 is similarly effective as native non-sulfated (1-->3)-beta-D-glucan and is generally more active than lentinan.

Mesenchymal stem cells display coordinated rolling and adhesion behavior on endothelial cells

To explore the initial steps by which transplanted mesenchymal stem cells (MSCs) interact with the vessel wall in the course of extravasation, we studied binding of human MSCs to endothelial cells (ECs). In a parallel plate flow chamber, MSCs bound to human umbilical vein ECs (HUVECs) similar to peripheral-blood mononuclear cells (PBMCs) or CD34(+) hematopoietic progenitors at shear stresses of up to 2 dynes/cm(2). This involved rapid extension of podia, rolling, and subsequent firm adhesion that was increased when ECs were prestimulated with TNF-alpha. MSC binding was suppressed when ECs were pretreated with function-blocking anti-P-selectin antibody, and rolling of MSCs was induced on immobilized P-selectin, indicating that P-selectin was involved in this process. Preincubation of HUVECs with anti-VCAM-1 or of MSCs with anti-VLA-4 antibodies suppressed binding of MSCs to HUVECs but did not enhance inhibition by anti-P-selectin, indicating that both P-selectin and VCAM-1 are equally required for this process. Intravital microscopy demonstrated the capacity of MSCs to roll and adhere to postcapillary venules in vivo in a mouse model in a P-selectin-dependent manner. Thus, MSCs interact in a coordinated fashion with ECs under shear flow, engaging P-selectin and VCAM-1/VLA-4.

The influence of various structural parameters of semisynthetic sulfated polysaccharides on the P-selectin inhibitory capacity

Selectin-mediated leukocyte rolling along the endothelium is of key importance for maintaining the cellular immune response. The anti-inflammatory activities of heparin have partly been related to inhibition of P-selectin binding. Heparin, however, suffers from its heterogeneous variable structure, the animal origin and multiple in vivo effects. As P-selectin is a promising target for anti-inflammatory approaches, we focused on P-selectin inhibition by other sulfated polysaccharides and compared them with six heparins. We examined 15 structurally defined semisynthetic sulfated glucans, non-animal-derived from the linear glucans phycarin, curdlan or pullulan. The derivatives gradually differ in their degree of sulfation, molecular weight, and glycosidic linkage. The inhibitory capacity was analysed in a parallel plate flow chamber, detecting the rolling of U937 cells on P-selectin layers. Unfractionated heparins displayed variabilities between different preparations. Considering fractionated heparins, exceeding of a minimal mass is essential for activity. Comparing the glucan sulfates, charge density is the most important parameter for P-selectin binding. Highly sulfated derivatives are excellent inhibitors, the reduced cell binding up to 16.2+/-6.4% strongly exceeded the heparin activities. Molecular weight is of minor effects, while glycosidic backbone linkage holds certain importance. To check the P-selectin inhibition in vivo, heparin and one phycarin sulfate were tested using intravital microscopy of microvasculature in mice. Both compounds significantly reduced the rolling fractions of activated platelets on endothelium as effective as a blocking P-selectin antibody. Our study indicates that semisynthetic glucan sulfates with optimal structures block P-selectin excellently and might become promising candidates for anti-inflammatory drugs to replace heparin for certain applications.

CCR2 and CCR6, but not endothelial selectins, mediate the accumulation of immature dendritic cells within the lungs of mice in response to particulate antigen

Dendritic cells (DC) migrate from sites of inflammation to lymph nodes to initiate primary immune responses, but the molecular mechanisms by which DC are replenished in the lungs during ongoing pulmonary inflammation are unknown. To address this question, we analyzed the secondary pulmonary immune response of Ag-primed mice to intratracheal challenge with the particulate T cell-dependent Ag sheep erythrocytes (SRBC). We studied wild-type C57BL/6 mice and syngeneic gene-targeted mice lacking either both endothelial selectins (CD62E and CD62P), or the chemokine receptors CCR2 or CCR6. DC, defined as non-autofluorescent, MHC class II(+)CD11c(mod) cells, were detected in blood, enzyme-digested minced lung, and bronchoalveolar lavage fluid using flow cytometry and immunohistology. Compared with control mice, Ag challenge increased the frequency and absolute numbers of DC, peaking at day 1 in peripheral blood (6.5-fold increase in frequency), day 3 in lung mince (20-fold increase in total DC), and day 4 in bronchoalveolar lavage fluid (55-fold increase in total DC). Most lung DC expressed CD11c, CD11b, and low levels of MHC class II, CD40, CD80, and CD86, consistent with an immature myeloid phenotype. DC accumulation depended in part upon CCR2 and CCR6, but not endothelial selectins. Thus, during lung inflammation, immature myeloid DC from the bloodstream replace emigrating immature DC and transiently increase total intrapulmonary APC numbers. Early DC recruitment depends in part on CCR2 to traverse vascular endothelium, plus CCR6 to traverse alveolar epithelium. The recruitment of circulating immature DC represents a potential therapeutic step at which to modulate immunological lung diseases.

Dendrimer-like PEO glycopolymers exhibit anti-inflammatory properties

A new class of high molecular weight polysulfated PEO dendrimer-like glycopolymer has been synthesized by a combination of arm-first and core-first methodologies followed by trichloroacetimidate glycosidation as a facile bioconjugation strategy. An L-selectin antagonist was identified that exhibits 103-fold greater activity than other multivalent sLex glycopolymers and 20-50 times greater potency than other linear heparinoids. A significant reduction in inflammatory cell recruitment was observed in vivo.

Synthesis of Postulated Molecular Probes: Stereoselective Free-Radical-Mediated C-Glycosylation in Tandem with Hydrogen Transfer

Reported herein is a strategy employing an addition reaction in tandem with a hydrogen-transfer reaction for the elaboration of C-glycoside-based sialyl Lewis X (sLe(X)) analogues. Significant stereocontrol was noted when alkyl radicals were reacted with a series of alkoxytaconates. Transition states were proposed to explain the obtained selectivity. Further reaction between an anomeric-centered fucosyl-derived radical and a galactosylated hydroxytaconate provided easy access to C,O-diglycosides as mimics of sLe(X). In this case, two 1,3-distant stereocenters were created with high diastereoselectivity using free radical intermediates in a tandem process.

MR molecular imaging of early endothelial activation in focal ischemia

Focal ischemia followed by reperfusion initiates a harmful P- and E-selectin-mediated recruitment of leukocytes in brain microvasculature. In this study, we tested whether a novel magnetic resonance (MR) contrast agent (Gd-DTPA-sLe(x) A), which is designed to bind to activated endothelium could be detected by MR imaging (MRI) in a focal stroke mouse model. MRIs (9.4T) of the brain were acquired 24 hours after transient middle cerebral artery occlusion. T1 maps were acquired repeatedly before and up to 1.5 hours after the intravenous injection of either Gd-DTPA or Gd-DTPA-sLe(x) A. Analysis of images included a pixel-by-pixel subtraction of T1 maps from the precontrast T1 maps and quantification of T1 within the ischemic area. After injection of Gd-DTPA-sLe(x) A, T1 decreased compared with precontrast levels, and an interhemispheric difference between the pre-post contrast T1 developed within the stroke lesion at a mean time of 52 minutes after injection (p < 0.05). Animals injected with Gd-DTPA did not exhibit changes in T1 signal intensity between regions of the ipsilateral and contralateral hemispheres, indicating that the reductions in T1 observed with Gd-DTPA-sLe(x) A were unrelated to blood-brain barrier breakdown. Fluorescent-labeled sLe(x) A administered intravenously was observed to bind to the endothelium of injured but not control brain. The study suggests that the contrast agent Gd-DTPA-sLe(x) A can be used to visualize early endothelial activation after transient focal ischemia in vivo with MRI.