ABSTRACT
Spleen tyrosine kinase (SYK) is an important regulatory molecule of signal transduction pathways involved in the pathogenesis of autoimmune diseases such as immune thrombocytopenia (ITP), and the SYK-signaling pathway has emerged as a potential target for the treatment of numerous diseases. The aim of this narrative review is to summarize the biological properties of SYK and its involvement in disease pathways, provide an update on SYK inhibitors in the treatment of ITP, and consider other potential applications. Fostamatinib, the only licensed SYK inhibitor to date, produces clinical response in ITP patients, including those who are refractory to other treatments. It appears to reduce the risk of thrombotic events and may therefore be a drug to consider for patients with an increased thrombotic risk. Encouraging results have also been obtained in the treatment of warm autoimmune hemolytic anemia. Several other SYK inhibitors have entered clinical trials for a range of indications, reflecting the ability of these drugs to affect multiple signaling pathways. SYK inhibitors have the potential to target several aspects of COVID-19 pathogenesis including thrombosis, without affecting normal hemostasis, and data from the first study of fostamatinib in COVID-19 are encouraging. It is hoped that ongoing trials in autoimmune indications other than ITP, as well as in hematological malignancies and other disorders, confirm the promise of SYK inhibitors. Immune thrombocytopenia (ITP) is an autoimmune disease that usually happens when your immune system mistakenly attacks and destroys platelets, which are cells that help blood to clot. Individuals with ITP can experience easy or excessive bruising and bleeding. Scientists have identified that an enzyme called spleen tyrosine kinase (SYK) is involved in numerous biological processes that are associated with the immune system response, inflammation, and some types of cancer in humans. Therefore, it has become a target for new drugs which inhibit the action of SYK. In this review article, the authors provide a summary of the biological properties and actions of SYK and its involvement in various diseases, discuss information about drugs that have been developed as SYK inhibitors for the treatment of ITP, and consider other potential uses for drugs that inhibit SYK. Although several drugs are being developed, the only SYK inhibitor that is currently available for the treatment of ITP is a drug called fostamatinib. In patients with ITP, including those who no longer respond to other treatments, fostamatinib has been shown to improve platelet counts and reduce bleeding events. Researchers are also currently investigating the use of drugs that inhibit SYK, including fostamatinib, for the potential treatment of other diseases associated with inflammation (e.g. rheumatoid arthritis, COVID-19), autoimmunity (e.g. warm autoimmune hemolytic anemia), and blood cancers (e.g. lymphoma, chronic lymphocytic leukemia, and acute myeloid leukemia). eng
ABSTRACT
Spleen tyrosine kinase (SYK) is an important regulatory molecule of signal transduction pathways involved in the pathogenesis of autoimmune diseases such as immune thrombocytopenia (ITP), and the SYK-signaling pathway has emerged as a potential target for the treatment of numerous diseases. The aim of this narrative review is to summarize the biological properties of SYK and its involvement in disease pathways, provide an update on SYK inhibitors in the treatment of ITP, and consider other potential applications. Fostamatinib, the only licensed SYK inhibitor to date, produces clinical response in ITP patients, including those who are refractory to other treatments. It appears to reduce the risk of thrombotic events and may therefore be a drug to consider for patients with an increased thrombotic risk. Encouraging results have also been obtained in the treatment of warm autoimmune hemolytic anemia. Several other SYK inhibitors have entered clinical trials for a range of indications, reflecting the ability of these drugs to affect multiple signaling pathways. SYK inhibitors have the potential to target several aspects of COVID-19 pathogenesis including thrombosis, without affecting normal hemostasis, and data from the first study of fostamatinib in COVID-19 are encouraging. It is hoped that ongoing trials in autoimmune indications other than ITP, as well as in hematological malignancies and other disorders, confirm the promise of SYK inhibitors.
ABSTRACT
Introduction: Cases of de novo immune thrombocytopenia (ITP), including a fatality following SARS-CoV-2 vaccination in a previously healthy recipient, led to studying its impact in pre-existing ITP. Published reports are limited but suggest that most patients with ITP tolerate the COVID-19 vaccines well without frequent ITP exacerbations (Kuter, BJH, 2021). Data regarding risk factors for exacerbation and relationship of response to first dose to that of second dose are limited. Methods: Data for patients with pre-existing ITP were obtained via 3 sources. First, via a ten-center retrospective study of adults with ITP who received a SARS-CoV-2 vaccine between December 2020 and March 2021 and had a post-vaccination platelet count (n=117);9 centers were in the United States. Eighty-nine percent of patients received mRNA-based vaccines. The second and third sources of data were surveys distributed by the Platelet Disorder Support Association (PDSA) and the United Kingdom ITP Support Association. A 'stable platelet count' was defined as a post-vaccination platelet count within 20% of the pre-vaccination level. ITP exacerbation was defined as any one or more of: platelet decrease ≥ 50% compared to pre-vaccination baseline, platelet decrease by >20% compared to prevaccination baseline with platelet nadir < 30x10 9/L, receipt of rescue therapy for ITP. Continuous variables were described as mean ±SD or median [interquartile range];categorical variables were described as n (%). Relative risks and 95% confidence interval were calculated to estimate strength of association. Results: Among 117 patients with pre-existing ITP from 10 centers who received a SARS-CoV-2 vaccine, mean age was 63±17 years, 62% were female, with median 12 [4-23] years since diagnosis of ITP;patients had received a median of 3 [2-4] prior medical treatments. Sixtynine patients were on ITP treatment at the time of vaccination (Table 1). There was an almost even distribution of platelet count response following each vaccine dose. In 109 patients with data for dose 1, platelet counts increased in 32 (29%), were stable in 43 (39%), and decreased in 34 (31%);in 70 patients following dose 2, platelet counts increased in 24 (34%), were stable in 25 (36%), and decreased in 21 (30%) (Figure 1). Nineteen (17%) patients experienced an ITP exacerbation following the first dose and 14 (20%) of 70 after a second dose. In total, fifteen patients received and responded to rescue treatments (n = 6 after dose 1, n = 8 after dose 2, n = 1 after both doses). Of 7 patients who received rescue treatment after dose 1, 5 received dose 2 and only 1/5 received rescue treatment again. Rescue consisted of increased dose of ongoing medication, steroids, IVIG, and rituximab. Splenectomized persons and those who received 5 or more prior lines of medical therapy were at highest risk of ITP exacerbation. Only 1 of 47 patients who had neither undergone splenectomy nor received 5 or more lines of therapy developed ITP exacerbation after dose 1. There were 14 patients offtreatment at the time of dose 1 and 7 patients at time of dose 2;1 patient in each group developed ITP exacerbation with both these having had normal counts prior to vaccination and having undergone splenectomy. In 43 patients whose platelet counts were stable or increased after dose 1 and received dose 2, only 6 (14%) had platelet decreases to <50 x10 9/L after dose 2. Age, gender, vaccine type, and concurrent autoimmune disease did not impact post-vaccine platelet counts. In surveys of 57 PDSA and 43 U.K. ITP patients, similar rates of platelet change were seen (33% of participants reported decreased platelet count in both surveys) and prior splenectomy was significantly associated with worsened thrombocytopenia in each. Conclusions: Thrombocytopenia may worsen in pre-existing ITP post-SARS-CoV2-vaccination but when ITP exacerbation occurred, it responded well to rescue treatment. No serious bleeding events were noted. Rescue treatment was needed in 13% of patients. Proactive vaccination surveillance of patien s with known ITP, especially those post-splenectomy and with more refractory disease, is indicated. These findings should encourage patients with ITP to not only be vaccinated, but to receive the second dose when applicable to ensure optimal immunization. Rituximab interferes with vaccination response and ideally would be held until a minimum of 2 weeks after completion of vaccination.
ABSTRACT
The high incidence of venous thromboembolism (VTE) and its consequent morbidity and mortality-along with an elevated risk for arterial thrombotic disease-was recognized early on by providers caring for individuals with coronavirus disease 2019 (COVID-19). Many hypotheses have been presented to explain the pathologic hypercoagulability seen in these patients. It has been difficult to determine how each potential risk factor contributes to the development of thrombotic complications, however. Patients hospitalized with COVID-19 typically have underlying medical conditions, and the illness affects multiple organs. The use of various therapeutic modalities to mitigate the systemic effects of the illness can further obscure the direct effects of COVID-19. At this time, physicians are searching for ways to predict which patients with COVID-19 are most likely to be affected by thrombosis. Identifying them is important because aggressive VTE prophylaxis may increase the rates of major bleeding complications and mortality, even as it reduces thrombogenesis. The concept of individualizing the dosing of low-molecular-weight heparin according to the severity of each patient's COVID-19 clinical status is emerging, and adaptive therapeutic trials are in progress. Until results are available, however, it is important to recognize potential risk factors for thrombosis. The following observational studies from the 62nd American Society of Hematology (ASH) Annual Meeting provide some insights on how to accomplish this.