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Updated: Apr 18, 2026
Ferric Chloride-induced Murine Thrombosis Models
Published on: September 5, 2016
Critical off-target effects of the widely used Rac1 inhibitors NSC23766 and EHT1864 in mouse platelets
S Dütting1, J Heidenreich, D Cherpokova
1Department of Experimental Biomedicine, University Hospital and Rudolf Virchow Center for Experimental Biomedicine, University of Würzburg, Würzburg, Germany.
Insights
Two common Rac1 inhibitors, NSC23766 and EHT1864, show significant off-target effects in platelet function studies. These findings question their use as specific Rac1 inhibitors and potential therapeutic agents.
Area of Science:
- Cardiovascular Biology
- Molecular Cell Biology
- Pharmacology
Background:
- Platelet aggregation is crucial for hemostasis but can cause pathological vessel occlusion.
- Rho GTPases, including Rac1, are key regulators of platelet cytoskeletal dynamics and activation.
- Rac1 inhibitors are explored for therapeutic benefits in cardiovascular disorders.
Purpose of the Study:
- To critically analyze the specificity of two Rac1 inhibitors, NSC23766 and EHT1864.
- To investigate potential off-target effects of these inhibitors in platelet function.
Main Methods:
- Assessed platelet function using flow cytometry and aggregometry in wild-type and Rac1-deficient mouse platelets.
- Analyzed platelet spreading via microscopy and effector molecule activation biochemically.
- Examined the impact of inhibitors on glycoprotein Ib-mediated signaling and Rac1 effector activation (PAK1/2).
Main Results:
- NSC23766 and EHT1864 exhibited potent Rac1-independent effects on platelet function at 100 μm.
- Both inhibitors impaired agonist-induced activation of Rac1-deficient platelets.
- Glycoprotein Ib signaling was significantly inhibited by NSC23766 in both wild-type and Rac1-deficient platelets.
Conclusions:
- NSC23766 and EHT1864 demonstrate significant off-target effects in mammalian cells at 100 μm.
- Their utility as specific Rac1/Rac inhibitors in biochemical studies is questionable at these concentrations.
- Concerns are raised regarding their potential as therapeutic agents due to observed off-target activities.
Background:
Platelet aggregation at sites of vascular injury is essential for normal hemostasis, but may also cause pathologic vessel occlusion. Rho GTPases are molecular switches that regulate essential cellular processes, and they have pivotal functions in the cardiovascular system. Rac1 is an important regulator of platelet cytoskeletal reorganization, and contributes to platelet activation. Rac1 inhibitors are thought to be beneficial in a wide range of therapeutic settings, and have therefore been tested in vivo for a variety of disorders. Two small-molecule inhibitors, NSC23766 and EHT1864, have been characterized in different cell types, demonstrating high specificity for Rac1 and Rac, respectively.
Objectives:
To analyze the specificity of NSC23766 and EHT1864.
Methods:
Platelet function was assessed in mouse wild-type and Rac1-deficient platelets by the use of flow cytometric analysis of cellular activation and aggregometry. Platelet spreading was analyzed with differential interference contrast microscopy, and activation of effector molecules was analyzed with biochemical approaches.
Results:
NSC23766 and EHT1864 showed strong and distinct Rac1-independent effects at 100 μm in platelet function tests. Both inhibitors induced Rac1-specific inhibition of platelet spreading, but also markedly impaired agonist-induced activation of Rac1(-/-) platelets. Furthermore, glycoprotein Ib-mediated signaling was dramatically inhibited by NSC23766 in both wild-type and Rac1-deficient platelets. Importantly, these inhibitors directly affected the activation of the Rac1 effectors p21-activated kinase (PAK)1 and PAK2.
Conclusions:
Our results reveal critical off-target effects of NSC23766 and EHT1864 at 100 μm in mammalian cells, raising questions about their utility as specific Rac1/Rac inhibitors in biochemical studies at these concentrations and possibly as therapeutic agents.
