Multiparameter Evaluation of the Platelet-Inhibitory Effects of Tyrosine Kinase Inhibitors Used for Cancer Treatment

Underlying Mechanisms of Thrombosis Associated with Cancer and Anticancer Therapies

OPINION STATEMENT

Cancer-associated thrombosis (CAT) has been identified as the second most prevalent cause of death after cancer itself. Moreover, the risk of thrombotic events in cancer patients increases due to anticancer drugs, such as tyrosine kinase inhibitors (TKIs). Venous thromboembolism (VTE) as well as arterial thromboembolic (ATE) events are present in CAT. Although VTE occurs more frequently, ATE events are very significant and in some cases are more dangerous than VTE. Guidelines for preventing thrombosis refer mainly VTE as well as the contribution of ATE events. Several factors are involved in thrombosis related to cancer, but the whole pathomechanism of thrombosis is not clear and may differ between patients. The activation of the coagulation system and the interaction of cancer cells with other cells including platelets, endothelial cells, monocytes, and neutrophils are promoted by a hypercoagulable state caused by cancer. We present an update on the pathomechanisms of CAT and the effect of anticancer drugs, mainly targeted therapies with a focus on TKIs. Considering the risk of bleeding associated with anticoagulation in each cancer patient, the anticoagulation strategy may involve the use of FXIa inhibitors, direct oral anticoagulants, and low-molecular-weight heparin. Further research would be valuable in developing strategies for reducing CAT.

Innovative strategies for measuring kinase activity to accelerate the next wave of novel kinase inhibitors

The development of protein kinase inhibitors (PKIs) has gained significance owing to their therapeutic potential for diseases like cancer. In addition, there has been a rise in refining kinase activity assays, each possessing unique biological and analytical characteristics crucial for PKI development. However, the PKI development pipeline experiences high attrition rates and approved PKIs exhibit unexploited potential because of variable patient responses. Enhancing PKI development efficiency involves addressing challenges related to understanding the PKI mechanism of action and employing biomarkers for precision medicine. Selecting appropriate kinase activity assays for these challenges can overcome these attrition rate issues. This review delves into the current obstacles in kinase inhibitor development and elucidates kinase activity assays that can provide solutions.

Modelling arterial thrombus formation in vitro

PURPOSE OF REVIEW

Models of arterial thrombus formation represent a vital experimental tool to investigate platelet function and test novel antithrombotic drugs. This review highlights some of the recent advances in modelling thrombus formation in vitro and suggests potential future directions.

RECENT FINDINGS

Microfluidic devices and the availability of commercial chips in addition to enhanced accessibility of 3D printing has facilitated a rapid surge in the development of novel in-vitro thrombosis models. These include progression towards more sophisticated, 'vessel on a chip' models which incorporate vascular endothelial cells and smooth muscle cells. Other approaches include the addition of branches to the traditional single channel to yield an occlusive model; and developments in the adhesive coating of microfluidic chambers to better mimic the thrombogenic surface exposed following plaque rupture. Future developments in the drive to create more biologically relevant chambers could see a move towards the use of human placental vessels, perfused ex-vivo. However, further work is required to determine the feasibility and validity of this approach.

SUMMARY

Recent advances in thrombus formation models have significantly improved the pathophysiological relevance of in-vitro flow chambers to better reflect the in-vivo environment and provide a more translational platform to test novel antithrombotics.

Patients Undergoing Systemic Anti-Cancer Therapy Who Require Surgical Intervention: What Surgeons Need to Know

As part of routine cancer care, patients may undergo elective surgery with the aim of long-term cure. Some of these patients will receive systemic anti-cancer therapy (SACT) in the neoadjuvant and adjuvant settings. The majority of patients, usually with locally advanced or metastatic disease, will receive SACT with palliative intent. These treatment options are expanding beyond traditional chemotherapy to include targeted therapies, immunotherapy, hormone therapy, radionuclide therapy and gene therapy. During treatment, some patients will require surgical intervention on an urgent or emergency basis. This narrative review examined the evidence base for SACT-associated surgical risk and the precautions that a surgical team should consider in patients undergoing SACT.

Differential Regulation of GPVI-Induced Btk and Syk Activation by PKC, PKA and PP2A in Human Platelets

Bruton's tyrosine kinase (Btk) and spleen tyrosine kinase (Syk) are major signaling proteins in human platelets that are implicated in atherothrombosis and thrombo-inflammation, but the mechanisms controlling their activities are not well understood. Previously, we showed that Syk becomes phosphorylated at S297 in glycoprotein VI (GPVI)-stimulated human platelets, which limits Syk activation. Here, we tested the hypothesis that protein kinases C (PKC) and A (PKA) and protein phosphatase 2A (PP2A) jointly regulate GPVI-induced Btk activation in platelets. The GPVI agonist convulxin caused rapid, transient Btk phosphorylation at S180 (pS180↑), Y223 and Y551, while direct PKC activation strongly increased Btk pS180 and pY551. This increase in Btk pY551 was also Src family kinase (SFK)-dependent, but surprisingly Syk-independent, pointing to an alternative mechanism of Btk phosphorylation and activation. PKC inhibition abolished convulxin-stimulated Btk pS180 and Syk pS297, but markedly increased the tyrosine phosphorylation of Syk, Btk and effector phospholipase Cγ2 (PLCγ2). PKA activation increased convulxin-induced Btk activation at Y551 but strongly suppressed Btk pS180 and Syk pS297. PP2A inhibition by okadaic acid only increased Syk pS297. Both platelet aggregation and PLCγ2 phosphorylation with convulxin stimulation were Btk-dependent, as shown by the selective Btk inhibitor acalabrutinib. Together, these results revealed in GPVI-stimulated platelets a transient Syk, Btk and PLCγ2 phosphorylation at multiple sites, which are differentially regulated by PKC, PKA or PP2A. Our work thereby demonstrated the GPVI-Syk-Btk signalosome as a tightly controlled protein kinase network, in agreement with its role in atherothrombosis.

Flow cytometry for evaluating platelet immunophenotyping and function in patients with thrombocytopenia

Platelets play an essential role in primary hemostasis through bleeding and thromboembolism. Thus, the diagnosis or evaluation of impaired hereditary, acquired, and drug-related platelet dysfunction has become imperative. The assessment of the platelet function is too complex for routine platelet function study. The major methods involved in platelet function study include platelet function analyzer testing, thromboelastography, thromboelastometry, light transmission aggregometry, and flow cytometry. The current review article focuses on the methods with flow cytometry for immunophenotyping of platelet and evaluating platelet function for platelet disorders, especially in patients with thrombocytopenia. According to the consensus published by the International Society on Thrombosis and Haemostasis, for inherited and acquired platelet disorders, the two major measures by which flow cytometry determines platelet function are glycoprotein IIb/IIIa/P-selectin (CD62p) expression and percentage of leukocyte-platelet aggregates. Using flow cytometry to determine platelet function has several advantages, including good sensitivity to low platelet counts, small blood volume required, and the nonnecessity of centrifugation. However, flow cytometry has still many limitations and challenges, with standardization for routine laboratory testing also proving difficult. Although flow cytometry is available for multipurpose and sensitive study of platelet functions at the same time, the challenging analysis gradually increases and needs to be addressed before reality.