Spleen Tyrosine Kinase Inhibitor Fostamatinib Research Articles

Human dermal fibroblast subpopulations and epithelial mesenchymal transition signals in hidradenitis suppurativa tunnels are normalized by spleen tyrosine kinase antagonism in vivo.

Hidradenitis Suppurativa is a chronic inflammatory disease of which the pathogenesis is incompletely understood. Dermal fibroblasts have been previously identified as a major source of inflammatory cytokines, however information pertaining to the characteristics of subpopulations of fibroblasts in HS remains unexplored. Using in silico-deconvolution of whole-tissue RNAseq, Nanostring gene expression panels and confirmatory immunohistochemistry we identified fibroblast subpopulations in HS tissue and their relationship to disease severity and lesion morphology. Gene signatures of SFRP2+ fibroblast subsets were increased in lesional tissue, with gene signatures of SFRP1+ fibroblast subsets decreased. SFRP2+ and CXCL12+ fibroblast numbers, measured by IHC, were increased in HS tissue, with greater numbers associated with epithelialized tunnels and Hurley Stage 3 disease. Pro-inflammatory CXCL12+ fibroblasts were also increased, with reductions in SFRP1+ fibroblasts compared to healthy controls. Evidence of Epithelial Mesenchymal Transition was seen via altered gene expression of SNAI2 and altered protein expression of ZEB1, TWIST1, Snail/Slug, E-Cadherin and N-Cadherin in HS lesional tissue. The greatest dysregulation of EMT associated proteins was seen in biopsies containing epithelialized tunnels. The use of the oral Spleen tyrosine Kinase inhibitor Fostamatinib significantly reduced expression of genes associated with chronic inflammation, fibroblast proliferation and migration suggesting a potential role for targeting fibroblast activity in HS.

Fostamatinib or Thrombopoietin for the Treatment of Chronic Immune Thrombocytopenia in Adult Patients: A Real-World Assessment of Safety, Effectiveness and Cost

Introduction: Chronic immune thrombocytopenia purpura (ITP) in adults is a serious autoimmune disease in which platelets are prematurely destroyed, leaving the patient vulnerable to bruising and bleeding. Initial treatment starts with corticosteroids. In patients who become resistant or intolerant to corticosteroids, the thrombopoietic agents (TPOs), consisting of romiplostim (ROM), eltrombopag (ELT), and avatrombopag (AVA), or the spleen tyrosine kinase inhibitor fostamatinib (FOS), are appropriate next lines of therapy. In this study, the comparative safety, effectiveness, and cost of care between fostamatinib and the TPOs were evaluated in a real-world setting. Methods: A retrospective analysis of 17 community hematology practices across the USA was conducted to identify adult ITP patients who received one of the four agents. Data collection consisted of patient demographics, disease characteristics, as well as number and type of prior treatments. From the first day until the end of treatment, data were also collected on platelet (PLT) counts, adverse events, the use of rescue IVIG, platelet transfusions, and corticosteroids. Multivariable logistic regression analysis was used to compare PLT-related endpoints between agents. Results: A sample of 179 ITP patients who had received at least one of the four agents was identified. This resulted in a final sample of 51, 87, 127, and 44 patients who received FOS, ELT, ROM, or AVA, respectively. At month six, there were no significant differences between FOS and the TPOs in terms of the proportion of patients with the PLT count being ≥30 × 103/μL, ≥50 × 103/μL as well as the proportion of patients whose PLT levels doubled relative to baseline. The frequency of thromboembolic events (TEs) was 3.9% in FOS patients compared to 9.2%, 4.7%, and 11.4% in the ELT, ROM, and AVA groups. The mean cost per patient with FOS was $99,209 (95% CI: $59,595–$115,074), compared to $92,426 (95% CI: $68,331–$115,519), $108,482 (95% CI: $84,782–$132,182), and $131,050 (95% CI: $83,327–$179,897) for ELT, ROM, or AVA, respectively. Conclusions: In this real-world analysis, FOS was comparable to the TPOs in maintaining PLTs at clinically beneficial levels. Given these findings, the choice of therapy should be based on overall patient safety, preexisting risk factors for TEs, and cost effectiveness.

RWD137 A Real-World Comparative Effectiveness Analysis of Fostamatinib Vs. Thrombopoietic Receptor Agonists (TPOS) for the Treatment of Chronic Immune Thrombocytopenia in Adult Patients

Chronic immune thrombocytopenia purpura (ITP) is an acquired autoimmune disease characterized by antibody-induced platelet (PLT) destruction, leading to a reduction in the number of circulating PLTs. Initial treatment is with corticosteroids. In patients who become resistant to corticosteroids, the TPOs, consisting of romiplostim (ROM), eltrombopag (ELT) and avatrombopag (AVA) or the spleen tyrosine kinase inhibitor fostamatinib (FOS), are appropriate next lines of therapy. In this study, the comparative safety and effectiveness between fostamatinib vs. the TPOs was evaluated in a real-world setting.

A phase 1 study of the SYK inhibitor fostamatinib and weekly paclitaxel for recurrent platinum-resistant ovarian cancer.

5574 Background: Response to chemotherapy in patients (pts) with recurrent platinum-resistant ovarian cancer (PROC) is generally < 15%. Spleen tyrosine kinase (SYK) is overexpressed in PROC and is a key mediator of paclitaxel resistance in ovarian cancer cells. Fostamatinib (Fos), an orally available inhibitor of SYK, is currently FDA approved for the treatment of idiopathic thrombocytopenic purpura. The active form of Fos (R406) was shown to synergistically enhance taxane-mediated cytotoxicity in preclinical ovarian cancer models. This phase 1 study aimed to identify the maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D) of Fos when combined with standard weekly paclitaxel (wPac) for pts with PROC. Methods: Pts with PROC, defined as progression ≤6 months of last platinum, were eligible. A modified toxicity probability interval (mTPI) dose escalation design was used to determine the MTD/RP2D and response was assessed using RECISTv1.1 criteria. All pts received paclitaxel (wPac) 80mg/m2 intravenously on Days 1, 8, and 15, of a 28-day cycle. Fos was administered orally twice a day (BID) on a continuous schedule. Three dose levels (DL) were planned: DL1 - 100mg, DL2 - 150mg, and DL3 - 200mg. MTD was determined based on cycle 1 dose-limiting toxicities (DLTs) and responses were assessed every 2 cycles. A dose expansion cohort to further assess adverse events (AEs) and tolerability was performed. Results: 27 eligible pts, median age 62 years (range 35-79 years) with high-grade serous (n = 18), clear cell (n = 4), carcinosarcoma (n = 3), or other (n = 2) histology were treated at 3 centers. Twelve pts were treated in the dose escalation cohort (DL1 = 6, DL2 = 3, DL3 = 3). Common AEs at least possibly attributed to Fos, wPac, or both included diarrhea (70%), fatigue (52%), anemia (44%), neutropenia (33%), nausea (33%), hypertension (30%), and dysgeusia (30%). Treatment-emergent grade 3-4 AEs were neutropenia (37%), anemia (26%), and thromboembolic event (22%). During DL1, updated toxicity management guidelines not consistent with the original protocol were released and 2 of the 3 pts treated prior to the amendment were not considered evaluable for DLT. Thus 3 more pts were enrolled to DL1 after the amendment. Of the 10 pts evaluable for DLT in dose escalation, no DLTs were reported on any of the 3 DLs (DL1 = 4, DL2 = 3, DL3 = 3). DL3 was selected for dose expansion. One of 15 pts in the dose expansion cohort had a DLT (neutropenia) and one patient had a grade 5 infection. Of 18 pts treated at DL3, 7 (39%) had partial or complete response (95% CI: 17.3, 64.3%). Overall, 27 patients received a median of 3 cycles (range 0-10). Analysis of pharmacokinetic and correlative molecular studies of target expression are ongoing. Conclusions: The RP2D of Fos will be 200 mg orally BID when combined with wPac. AE profile of the combination was as expected and the combination demonstrated promising efficacy in pts with recurrent PROC. Clinical trial information: NCT03246074 .

1141. Phase 3 Trial (in progress) of the SYK Inhibitor Fostamatinib in Patients Hospitalized with COVID-19: Protocol and Study Implementation Updates

Abstract Background Immune dysregulation associated with COVID-19 includes immune cell activation, inflammatory cytokine release, and neutrophil extracellular trap release (NETosis), which are mediated by spleen tyrosine kinase (SYK) (Fig 1). Fostamatinib, an oral spleen tyrosine kinase (SYK) inhibitor, was approved for immune thrombocytopenia (ITP) in 2018, and the Phase 3 trials showed a lower than expected rate of thrombosis.1 Clinical studies showed a reduction in IL-6 in patients with rheumatoid arthritis.2 The active metabolite of fostamatinib (R406) protected against LPS-induced acute lung injury and thrombosis in mice3,4 and reduced MUC1 in a mouse model of ALI.5 Fostamatinib demonstrated abrogation of the hyperimmune response caused by anti-spike IgG,6 including reduction in hyperactivation of platelets7 and NETosis in neutrophils8 in in vitro studies using plasma from patients with severe COVID-19. A phase 2 study (NCT04579393) evaluated fostamatinib vs. placebo (all received standard of care [SOC]) in 59 hospitalized patients with COVID-19 and demonstrated reduction in mortality, ordinal scale scores, and number of days in the intensive care unit (ICU) as well as meeting the primary endpoint of safety.9 A phase 3 clinical study (NCT04629703) of fostamatinib for the treatment of COVID-19 is underway. Figure 1.Mechanism of Disease (COVID-19) and Role of SYK inhibition Methods A Phase 3, randomized, double-blind, placebo-controlled, adaptive design, multi-center study (NCT04629703) is underway to evaluate fostamatinib in 308 adult patients hospitalized with COVID-19 and on oxygen without intubation (Fig 2). Patients will receive fostamatinib 150 mg BID or placebo for 14 days; both arms receive SOC. At baseline, the clinical status score (8-point ordinal scale) had to be 5 or 6. Patients ≥ 65 years had to have ≥ 1 risk factor for severe disease and adults < 65 had to have ≥ 3. The primary outcome is days on oxygen (Day 1 to 29). Other endpoints include change in clinical status score, days in the ICU, time to hospital discharge, all-cause mortality, oxygen-free status and safety. Fostamatinib is investigational for COVID-19. Results Blinded data from this trial in progress are as of 2 December 2021. See Fig 3. Conclusion Final results of this Phase 3 trial are anticipated in 2022. Disclosures Lucy Yan, MD, PhD, Rigel Pharmaceuticals: Employee|Rigel Pharmaceuticals: Stocks/Bonds Ziad Mallat, MD, PhD, Rigel Pharmaceuticals: Advisor/Consultant Suzana Margareth Lobo, MD, PhD, Rigel Pharmaceuticals: Grant/Research Support Anuj Malik, MD, MS, Rigel Pharmaceuticals: Grant/Research Support Wolfgang Dummer, MD, PhD, Rigel Pharmaceuticals: Employee|Rigel Pharmaceuticals: Stocks/Bonds.

Evaluating fostamatinib disodium as a treatment option for immune thrombocytopenia in adult patients

ABSTRACT Introduction Immune thrombocytopenia (ITP) is an autoimmune bleeding disorder characterized by increased platelet destruction and decreased platelet production, leading to thrombocytopenia with or without bleeding manifestations. The majority of patients experiencing treatment need will eventually need secondary treatment following first-line therapy with steroids. In 2018, the oral spleen tyrosine kinase inhibitor fostamatinib received US Food and Drug Administration approval for ITP patients with an insufficient response to a previous treatment. Areas covered This review outlines pharmacological characteristics of fostamatinib and provides an overview of its efficacy and safety results in phase II and III trials, followed by the expert opinion of the authors. Expert opinion Increasing knowledge on the role of different players and mechanisms in the pathophysiology of autoimmune disorders, in general, and of ITP, in particular, has led to the development of several new treatment options, as illustrated by the introduction of fostamatinib in the treatment of ITP. However, lacking direct comparison with other recent treatment options (in particular, thrombopoietin receptor agonists), its use should be evaluated critically taking into account the unique toxicity and potential drug-drug interaction profile.

Inhibition of spleen tyrosine kinase decreases donor specific antibody levels in a rat model of sensitization

Antibody mediated rejection is a major cause of renal allograft loss. Circulating preformed donor specific antibodies (DSA) can result as a consequence of blood transfusion, pregnancy or prior transplantation. Current treatment strategies are limited due to partial or transient efficacy, adverse side-effects or patient unsuitability. Previous in vivo studies exploring autoimmune diseases have shown that spleen tyrosine kinase (SYK) signalling is involved in the development of pathogenic autoantibody. The role of SYK in allogenic antibody production is unknown, and we investigated this in a rodent model of sensitization, established by the transfusion of F344 whole blood into LEW rats. Two-week treatment of sensitized rats with selective SYK inhibitor fostamatinib strongly blocked circulating DSA production without affecting overall total immunoglobulin levels, and inhibition was sustained up to 5 weeks post-completion of the treatment regimen. Fostamatinib treatment did not affect mature B cell subset or plasma cell levels, which remained similar between non-treated controls, vehicle treated and fostamatinib treated animals. Our data indicate fostamatinib may provide an alternative therapeutic option for patients who are at risk of sensitization following blood transfusion while awaiting renal transplant.

Transitioning From Thrombopoietin Agonists to the Novel SYK Inhibitor Fostamatinib: A Multicenter, Real-World Case Series.

Fostamatinib is an oral spleen tyrosine kinase (SYK) inhibitor used for the treatment of adult patients with chronic immune thrombocytopenia (ITP) who have had an insufficient response to a previous treatment. Clinical and operational barriers may exist that warrant bridging or switching from thrombopoietin receptor agonists (TPO-RAs), such as volatility or unpredictability of platelets, adverse events, and quality of life or patient preference. While fostamatinib demonstrated durable platelet responses, the safety and efficacy in combination, bridging, and/or switching with TPO-RAs is not well documented. The objective of this article is to provide guidance from real-world case studies for a safe and effective strategy for the transitioning of patients from TPO-RAs to fostamatinib, with some degree of overlap between the two agents. Currently, the evidence does not exist to guide the safe and effective use of combination therapy or transition between therapies in ITP. This case series highlights the importance to further understand the complexities of managing this disease, as well as successfully combining, bridging, and/or switching patients over to fostamatinib without the need for rescue therapy or increase in adverse events. The need for real-world evidence that guides providers on the safety and efficacy of short- and long-term combination therapy of fostamatinib and TPO-RAs is crucial. The rationale for combination therapy is to target different pathways, platelet destruction, and production without added toxicities. Additionally, gradual tapering off of TPO-RAs may provide a more favorable clinical outcome when switching to fostamatinib. The need for additional data is necessary to provide clinicians with guidance when managing patients with ITP.

Long-Term Safety Profile of the Oral Spleen Tyrosine Kinase Inhibitor Fostamatinib in Immune Thrombocytopenia (ITP) and Other Diseases

Introduction: Fostamatinib is an oral, potent inhibitor of spleen tyrosine kinase (SYK) with proven efficacy and a manageable safety profile for the treatment of ITP. SYK is situated in an intracellular signaling pathway upstream of Bruton's tyrosine kinase (BTK). Long-term safety data on fostamatinib at various dosing regimens (up to 150 mg BID) has been collected in >4000 patients with ITP, rheumatoid arthritis (RA), and other autoimmune, allergic and neoplastic disorders. The safety and tolerability of fostamatinib were consistent across different patient populations (apart from disease specific events). We present a summary analysis of the fostamatinib safety data from the ITP and RA studies. Methods: Fostamatinib safety data from 2 randomized, double-blind, placebo-controlled, phase 3 studies and the long-term, open-label, extension (OLE) study in ITP were pooled and are based on a starting dose of 200 mg/day, which was increased to 300 mg/day after 4 weeks in 88% of patients. Fostamatinib safety data from 13 phase 2/3 studies in RA were pooled and are based on a dosing regimen of 100-150 mg/day (n=1232) or 200-300 mg/day (n=2205). Results: The pooled data set for ITP included 146 patients; 60% were female, and the median age was 53 years (range 20-88). The mean duration of fostamatinib treatment was 19 months (range <1-62 months), representing 229 patient exposure years. Adverse events (AEs) were reported in 87% of patients, and 63% were mild to moderate. Serious AEs were reported in 31% of patients. The incidence of diarrhea, hypertension, alanine aminotransferase increase (ALT), and aspartate aminotransferase (AST) increase was evaluated in 58 patients who received fostamatinib for ≥1 year. This enabled a comparison of the incidence of these AEs in quartiles over the first year to assess the cumulative effects of fostamatinib. The AEs were reported with decreasing frequency during the second, third, and fourth quarters of fostamatinib treatment compared with the first quarter of the initial year of treatment in the 58 patients (see Figure 1). In the same 58 patients, the use of rescue therapy decreased while median platelet counts increased each quarter of the first year. The pooled data set for RA included 3437 patients who received fostamatinib; 83% were female, and the median age was 54 (range 18 -87). The mean duration of treatment was 18 months (range <1-81) representing 5134 patient exposure years. AEs were reported in 86% of RA patients and were mild to moderate in 73% of RA patients. Serious AEs occurred in 14%. In the placebo-controlled RA studies, 2414 patients received fostamatinib with 823 patient exposure years and 1169 received placebo with 367 patient exposure years. Despite a two-fold (125%) increase in exposure with fostamatinib vs placebo (823 vs 367 patient exposure years), there was only a 26% increase in AEs with fostamatinib vs placebo (68% vs 54%). The most common events in the ITP and RA studies were diarrhea (36% and 24%), hypertension (22% and 19%) and nausea (19% and 8%), apart from disease-related AEs. Epistaxis (19% and 0.5%), petechiae (15% and 0.3%), contusion (12% and 2%), and fatigue (10% and 2%) are associated with ITP and were uncommon in the RA population. Rheumatoid arthritis was reported as an AE in 9% of patients with RA and in none with ITP. Some AEs may be dose-related, and one-third of the RA patients were on lower dosages (100-150 mg/day) than were generally given in the ITP trials (200-300 mg/day). Conclusions: Fostamatinib has been evaluated in >4000 patients across different disease populations. Fostamatinib has a consistent and manageable safety profile. No new safety signals and no cumulative toxicity were observed with up to 81 months (6.8 years) of continuous treatment. Figure 1 Disclosures Tong: Rigel: Current Employment, Current equity holder in publicly-traded company. Numerof:Rigel: Current Employment, Current equity holder in publicly-traded company. Datangel:Rigel: Current Employment, Current equity holder in publicly-traded company. Masuda:Rigel: Current Employment, Current equity holder in publicly-traded company.

SYK inhibition targets acute myeloid leukemia stem cells by blocking their oxidative metabolism

Spleen tyrosine kinase (SYK) is an important oncogene and signaling mediator activated by cell surface receptors crucial for acute myeloid leukemia (AML) maintenance and progression. Genetic or pharmacologic inhibition of SYK in AML cells leads to increased differentiation, reduced proliferation, and cellular apoptosis. Herein, we addressed the consequences of SYK inhibition to leukemia stem-cell (LSC) function and assessed SYK-associated pathways in AML cell biology. Using gain-of-function MEK kinase mutant and constitutively active STAT5A, we demonstrate that R406, the active metabolite of a small-molecule SYK inhibitor fostamatinib, induces differentiation and blocks clonogenic potential of AML cells through the MEK/ERK1/2 pathway and STAT5A transcription factor, respectively. Pharmacological inhibition of SYK with R406 reduced LSC compartment defined as CD34+CD38−CD123+ and CD34+CD38−CD25+ in vitro, and decreased viability of LSCs identified by a low abundance of reactive oxygen species. Primary leukemic blasts treated ex vivo with R406 exhibited lower engraftment potential when xenotransplanted to immunodeficient NSG/J mice. Mechanistically, these effects are mediated by disturbed mitochondrial biogenesis and suppression of oxidative metabolism (OXPHOS) in LSCs. These mechanisms appear to be partially dependent on inhibition of STAT5 and its target gene MYC, a well-defined inducer of mitochondrial biogenesis. In addition, inhibition of SYK increases the sensitivity of LSCs to cytarabine (AraC), a standard of AML induction therapy. Taken together, our findings indicate that SYK fosters OXPHOS and participates in metabolic reprogramming of AML LSCs in a mechanism that at least partially involves STAT5, and that SYK inhibition targets LSCs in AML. Since active SYK is expressed in a majority of AML patients and confers inferior prognosis, the combination of SYK inhibitors with standard chemotherapeutics such as AraC constitutes a new therapeutic modality that should be evaluated in future clinical trials.

Early atheroprotection by SYK inhibition fails in established disease when local macrophage proliferation dominates lesion progression

Macrophages in the arterial intima sustain chronic inflammation during atherogenesis. Under hypercholesterolemic conditions murine Ly6Chigh monocytes surge in the blood and spleen, infiltrate nascent atherosclerotic plaques, and differentiate into macrophages that proliferate locally as disease progresses. Spleen tyrosine kinase (SYK) may participate in downstream signaling of various receptors that mediate these processes. We tested the effect of the SYK inhibitor fostamatinib on hypercholesterolemia-associated myelopoiesis and plaque formation in Apoe−/− mice during early and established atherosclerosis. Mice consuming a high cholesterol diet supplemented with fostamatinib for 8 weeks developed less atherosclerosis. Histologic and flow cytometric analysis of aortic tissue showed that fostamatinib reduced the content of Ly6Chigh monocytes and macrophages. SYK inhibition limited Ly6Chigh monocytosis through interference with GM-CSF/IL-3 stimulated myelopoiesis, attenuated cell adhesion to the intimal surface, and blocked M-CSF stimulated monocyte to macrophage differentiation. In Apoe−/− mice with established atherosclerosis, however, fostamatinib treatment did not limit macrophage accumulation or lesion progression despite a significant reduction in blood monocyte counts, as lesional macrophages continued to proliferate. Thus, inhibition of hypercholesterolemia-associated monocytosis, monocyte infiltration, and differentiation by SYK antagonism attenuates early atherogenesis but not established disease when local macrophage proliferation dominates lesion progression.

The effects of the spleen tyrosine kinase inhibitor fostamatinib on ambulatory blood pressure in patients with active rheumatoid arthritis: results of the OSKIRA-ABPM (ambulatory blood pressure monitoring) randomized trial

Clinical trials of fostamatinib in patients with rheumatoid arthritis showed blood pressure (BP) elevation using clinic measurements. The OSKIRA-ambulatory BP monitoring trial assessed the effect of fostamatinib on 24–hour ambulatory systolic BP (SBP) in patients with active rheumatoid arthritis. One hundred thirty–five patients were randomized to fostamatinib 100 mg twice daily (bid; n = 68) or placebo bid (n = 67) for 28 days. Ambulatory, clinic, and home BPs were measured at baseline and after 28 days of therapy. Primary end point was change from baseline in 24–hour mean SBP. Fostamatinib increased 24–hour mean SBP by 2.9 mm Hg (P = .023) and diastolic BP (DBP) by 3.5 mm Hg (P < .001) versus placebo. Clinic/home-measured BPs were similar to those observed with ambulatory BP monitoring. After treatment discontinuation (1 week), clinic BP values returned to baseline levels. Fostamatinib induced elevations in 24–hour mean ambulatory SBP and DBP. BP elevations resolved with fostamatinib discontinuation.

The active metabolite of spleen tyrosine kinase inhibitor fostamatinib abrogates the CD4⁺ T cell-priming capacity of dendritic cells.

Spleen tyrosine kinase (SYK) is a core signalling protein that drives inflammatory responses and is fundamental to the propagation of signals via numerous immune receptors, including the B cell receptor and Fc receptors (FcRs). Fostamatinib, a small molecule SYK inhibitor, has shown evidence of ameliorating inflammation in RA patients. We sought to understand how the active metabolite of fostamatinib, R406, affects the inflammatory response at the cellular level. Antigen-specific in vivo systems and in vitro fluorescence microscopy were combined to investigate the effects of fostamatinib on antigen-specific interactions between dendritic cells (DCs) and CD4(+) T cells. Although it has previously been shown that R406 reduces the response of DCs to immune complexes (ICs), we found that fostamatinib failed to reduce specific CD4(+) T cell proliferation in mice after immunization with ICs. However, we observed in vitro that R406 reduces both the area and duration of cellular interactions between IC-activated DCs and specific CD4(+) T cells during the initial phase of cellular crosstalk. This led to diminished proliferation of antigen-specific CD4(+) T cells after R406 treatment compared with vehicle controls. This decreased proliferative capacity of CD4(+) T cells was accompanied by reduced expression of the co-stimulatory molecules, inducible T cell co-stimulator (ICOS) and PD-1, and abrogation of the production of inflammatory cytokines such as IFN-γ and IL-17. Our findings indicate a potential mechanism by which this compound may be effective in inhibiting FcR-driven CD4(+) T cell responses.

Fostamatinib Inhibits BCR Signaling, and Reduces Tumor Cell Activation and Proliferation in Patients with Relapsed Refractory Chronic Lymphocytic Leukemia.

Abstract 2882B-cell receptor (BCR) signaling contributes to the pathogenesis of chronic lymphocytic leukemia (CLL). Spleen tyrosine kinase (SYK) activated directly downstream of the BCR is essential for the induction of proliferation and survival pathways. The SYK inhibitor fostamatinib disrupts BCR signaling and was the first such inhibitor to show significant clinical activity in patients with mature B-cell malignancies. Fostamatinib has been shown to both induce apoptosis in unstimulated CLL cells as well as to inhibit BCR induced anti-apoptotic signals in vitro (Gobessi et al., 2009; Quiroga et al., 2009). Similarly, using the Eμ-TCL1 transgenic mouse model, fostamatinib has been shown to inhibit the growth of malignant B-cells without significant alteration of normal B-cells (Suljagic et al., 2010). In the first phase I/II clinical trial investigating fostamatinib in relapsed B-cell non-Hodgkin’s lymphoma (NHL) and CLL, clinical efficacy was observed in a variety of histologies with the highest response rate in CLL/SLL patients (Friedberg et al., 2010). Eleven CLL/SLL patients enrolled in this trial donated cellular material for correlative studies. Using these primary tumor samples, we evaluated the effects of fostamatinib on CLL cells in vivo after one cycle of treatment.We first validated the on-target effect of fostamatinib by using quantitative RT-PCR to measure expression of validated pathway specific gene signatures. Fostamatinib greatly down-regulated 12/12 evaluated BCR signature genes and significantly reduced the BCR gene signature score (computed as the average expression of the pathway specific genes; p=.002) Effective inhibition of BCR signaling was confirmed by a significant reduction in the phosphorylation of both BTK and ERK; two key BCR signaling molecules located downstream of SYK activation. Interestingly, BCR signaling was inhibited in CLL cells from all patients regardless of response to therapy. We next expanded our analysis to look at NF-κB and MYC gene signatures. We found that 11/11 representative NF-κB signature genes and 5/5 MYC signature genes were also down-regulated resulting in a significant reduction in both gene signature scores (p=.004 and p=.020, respectively). Confirming these results, we also observed a significant reduction in JUNB (p<.001) and MYC (p=.026) at the protein level. Interestingly, the reduction in NF-κB and MYC signature scores was highly correlated with the degree of reduction in BCR signaling suggesting that these pathways are linked. In addition to changes in the gene signatures we also observed a significant reduction in the cellular activation immunephenotype; CD69 and CD86 expression were significantly reduced by fostamatinib (p=.033 and p=.004, respectively). Further, we found that CD38 (an activation marker with prognostic significance) was also reduced on treatment although not to a significant extent. Finally, fostamatinib significantly reduced tumor proliferation as determined by the percentage of CLL cells expressing Ki67 (p=.005). Eight of the 11 patients in this study achieved a clinically significant response; interestingly however, the 3 non-responders demonstrated significantly brighter CD38 expression with an MFI up to 9-times the CD38 MFI in responders. A possible role of CD38 as a biomarker for response should be further explored in patients treated with BCR directed kinase inhibitors.In conclusion, fostamatinib and other inhibitors of BCR-related kinases constitute a major advance in the treatment of CLL. In vitro data with these compounds suggests that interruption of BCR signaling and survival pathways activated in the tissue microenvironments are likely responsible for the observed clinical response as only a moderate direct induction of apoptosis is seen in vitro. Here we demonstrate that inhibition of BCR-mediated signaling by fostamatinib results in a reduction in CLL proliferation and activation in vivo. Together these data provide a blueprint to further study the mechanism of action and resistance mechanisms of not only fostamatinib but also other BCR targeted therapeutics.This work was supported in part by the Intramural Research Program of the National, Heart, Lung and Blood Institute and by the University of Rochester SPORE in lymphoma P50 CA13080503, Rigel and the James P. Wilmot Foundation. Disclosures:Friedberg:Rigel: Research Funding.

The Oral Spleen Tyrosine Kinase Inhibitor Fostamatinib Attenuates Inflammation and Atherogenesis in Low-Density Lipoprotein Receptor–Deficient Mice

Spleen tyrosine kinase (SYK) has come into focus as a potential therapeutic target in chronic inflammatory diseases, such as rheumatoid arthritis and asthma, as well as in B-cell lymphomas. SYK has also been involved in the signaling of immunoreceptors, cytokine receptors, and integrins. We therefore hypothesized that inhibition of SYK attenuates the inflammatory process underlying atherosclerosis and reduces plaque development. Low-density lipoprotein receptor-deficient mice consuming a high-cholesterol diet supplemented with 2 doses of the orally available SYK inhibitor fostamatinib for 16 weeks showed a dose-dependent reduction in atherosclerotic lesion size by up to 59±6% compared with the respective controls. Lesions of fostamatinib-treated animals contained fewer macrophages but more smooth muscle cells and collagen-characteristics associated with more stable plaques in humans. Mechanistically, fostamatinib attenuated adhesion and migration of inflammatory cells and limited macrophage survival. Furthermore, fostamatinib normalized high-cholesterol diet -induced monocytosis and inflammatory gene expression. We present the novel finding that the SYK inhibitor fostamatinib attenuates atherogenesis in mice. Our data identify SYK inhibition as a potentially fruitful antiinflammatory therapeutic strategy in atherosclerosis.