Targeting Thymidine Phosphorylase With Tipiracil Hydrochloride Attenuates Thrombosis Without Increasing Risk of Bleeding in Mice

Abstract

Objective: Current antiplatelet medications increase the risk of bleeding, which leads to a clear clinical need in developing novel mechanism-based antiplatelet drugs. TYMP (Thymidine phosphorylase), a cytoplasm protein that is highly expressed in platelets, facilitates multiple agonist-induced platelet activation, and enhances thrombosis. Tipiracil hydrochloride (TPI), a selective TYMP inhibitor, has been approved by the Food and Drug Administration for clinical use. We tested the hypothesis that TPI is a safe antithrombotic medication. Approach and Results: By coexpression of TYMP and Lyn, GST (glutathione S-transferase) tagged Lyn-SH3 domain or Lyn-SH2 domain, we showed the direct evidence that TYMP binds to Lyn through both SH3 and SH2 domains, and TPI diminished the binding. TYMP deficiency significantly inhibits thrombosis in vivo in both sexes. Pretreatment of platelets with TPI rapidly inhibited collagen- and ADP-induced platelet aggregation. Under either normal or hyperlipidemic conditions, treating wild-type mice with TPI via intraperitoneal injection, intravenous injection, or gavage feeding dramatically inhibited thrombosis without inducing significant bleeding. Even at high doses, TPI has a lower bleeding side effect compared with aspirin and clopidogrel. Intravenous delivery of TPI alone or combined with tissue plasminogen activator dramatically inhibited thrombosis. Dual administration of a very low dose of aspirin and TPI, which had no antithrombotic effects when used alone, significantly inhibited thrombosis without disturbing hemostasis. Conclusions: This study demonstrated that inhibition of TYMP, a cytoplasmic protein, attenuated multiple signaling pathways that mediate platelet activation, aggregation, and thrombosis. TPI can be used as a novel antithrombotic medication without the increase in risk of bleeding.

Thymidine Phosphorylase Is Increased in COVID-19 Patients in an Acuity-Dependent Manner

“…Based on the study from Manne et al (27), we speculate that SARS-CoV-2 can infect megakaryocytes and leads to the production of TYMP-overexpressing platelets. As mentioned above, our recent studies demonstrated that TYMP deficiency or inhibition significantly inhibited thrombosis in mice (12,13). Currently, no human study has been conducted to clarify the role of TYMP on thrombosis.…”

“…Administration of antiplatelet drugs to critical COVID-19 patients has achieved some clinical benefits (35). Our recent study has demonstrated that TPI is a rapidacting, safe antiplatelet medicine (13). As an auxiliary component of a novel anticancer drug, Lonsurf, TPI was approved by the FDA for clinical use.…”

“…Our recent study, for the first time, demonstrated that TYMP has a signaling function in platelets and plays a mechanistic role in platelet activation and thrombosis (12,13). Inhibition of TYMP with tipiracil hydrochloride (TPI), a selective, potent, and Food and Drug Administration-approved TYMP inhibitor, dramatically inhibits thrombosis in mice without increasing the risk of bleeding (13). Several inflammatory cytokines, including TNFα, IL-1, IL-6, IL-8, and IFN-γ induce TYMP expression (11,(14)(15)(16).…”

“…TYMP is also known as platelet-derived endothelial cell growth factor and is highly expressed in human platelets (11,12). Our recent study, for the first time, demonstrated that TYMP has a signaling function in platelets and plays a mechanistic role in platelet activation and thrombosis (12,13). Inhibition of TYMP with tipiracil hydrochloride (TPI), a selective, potent, and Food and Drug Administration-approved TYMP inhibitor, dramatically inhibits thrombosis in mice without increasing the risk of bleeding (13).…”

Thymidine Phosphorylase is Increased in Patients with Infection and Could be a Prognostic Marker for Sepsis and Disseminated Intravascular Coagulation

“…TYMP is an intracellular protein as it lacks a peptide sequence that is required for protein secretion [12]. By using platelets isolated from human and mice, Li et al, for the first time, demonstrated that TYMP has some signaling functions, and TYMP per se, can physically bind to Src family kinases, including Lyn, Fyn, and Yes, through which it regulates platelet activation and thrombosis [13,14]. In addition to platelets, TYMP is highly expressed by circulating cells involved in the innate immune system, including monocyte, granulocytes, natural killer cells, and dendritic cells [15].…”