Selective degradation of platelet BTK by PROTAC NX-5948 provides antithrombotic benefits without affecting hemostasis

Current antithrombotic therapies are effective in reducing thrombotic events but are limited by their associated risk of bleeding. Bruton tyrosine kinase (BTK) acts as a key signaling switch that drives platelet activation during thrombosis but is largely dispensable for routine hemostasis. It is an important nonredundant signaling mediator downstream of the glycoprotein VI and C-type lectin-like receptor 2 receptors and plays a key role in thrombosis with minimal involvement in hemostasis, making it an attractive antithrombotic target. Although BTK inhibitors effectively reduce thrombosis, their clinical use has been limited because of off-target effects. Protein degraders may overcome this limitation by enabling the ubiquitin proteasomal system to selectively target and degrade BTK. We here assessed the ability of the BTK degraders NX-2127 and NX-5948, currently in clinical trials for B-cell pathologies, to target platelet BTK for degradation. NX-2127 and NX-5948 induced concentration-dependent degradation of BTK in washed platelets, platelet-rich plasma, and whole blood. NX-5948 showed no hook effect and outperformed NX-2127 in potency, efficacy, and degradation kinetics. Proteomic analyses confirmed selective BTK degradation by NX-5948, with no evidence of major off-target effects. BTK degradation impaired collagen-related peptide (CRP)-mediated integrin αIIbβ3 activation, P-selectin expression, platelet aggregation, and in vitro thrombosis, with protease-activated receptor 1-mediated platelet function being left intact. Dosing mice with NX-5948 led to efficacious degradation of platelet BTK and impaired CRP-mediated, but not thrombin-mediated, ex vivo platelet function. In vivo, arterial thrombosis was markedly reduced, without an increase in bleeding time. Together, these results highlight NX-5948 as a potent, selective BTK degrader with antithrombotic potential and minimal hemostatic impact.