Background: Doxorubicin is an effective chemotherapeutic drug used to treat patients with cancer. However, doxorubicin treatment is frequently associated with dose limiting cardiotoxicity. We previously reported that activation of protease activated receptor 1 (PAR1) contributes to doxorubicin-induced cardiac injury in mice. Proteolytic activation of PAR1 by the coagulation protease thrombin, at residue R41, or activated protein C (APC), at residue R46, can lead to downstream cytotoxic or cytoprotective signaling, respectively.

Aims: To determine if thrombin-mediated activation of PAR1 contributes to doxorubicin-induced cardiac injury.

Methods: PAR1^+/+, PAR1^-/-, PAR1^R41Q and PAR1^R46Q mice were subject to acute or chronic models of doxorubicin induced cardiac injury (one 20mg/g or five weekly 5mg/g i.p. injections). To inhibit PAR1/Gaq signaling in the acute model, mice were administered Q94 (5mg/g) twice daily by s.c. injection. Plasma extracellular vesicle tissue factor (EV-TF) activity was measured using an in-house assay. Plasma thrombin-antithrombin (TAT) complexes were assessed by immunoassay. Conscious echocardiography was used to assess cardiac function at day 5 in the acute model and day 35 in the chronic model.

Results: In the acute model, doxorubicin treatment significantly increased plasma levels of EV-TF activity and TAT complexes compared to controls at 24 hours (P<0.05). In both models a significant preservation in fractional shortening was observed in thrombin insensitive PAR1^R41Q and PAR1^-/- mice, but not in APC insensitive PAR1^R46Q mice, when compared to PAR1^+/+ controls (P<0.001). Selective inhibition of Gaq signaling downstream of PAR1 in PAR1^+/+ mice with Q94 significantly preserved fractional shortening compared to vehicle treated controls in the acute model (P<0.0001).

Conclusions: Our data demonstrates that administration of doxorubicin leads to generation of the PAR1 activating protease thrombin in vivo. Importantly, thrombin-mediated activation of PAR1 contributed to the cardiotoxic effect of doxorubicin in vivo. Selective inhibition of PAR1/Gaq signaling reduced doxorubicin-induced cardiotoxicity in mice.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/thrombin-mediated-activation-of-protease-activated-receptor-1-contributes-to-doxorubicin-induced-cardiac-injury/