PB1268 - Anti-Thrombotic Effects of the Proteasome Inhibitor Carfilzomib on the Endothelium

Background: Carfilzomib (CFZ) is a second-generation proteasome inhibitor used to treat multiple myeloma. Potent inhibition of the proteasome results in chronic proteotoxic endoplasmic reticulum (ER) stress, leading to apoptosis. While CFZ has improved survival rates in multiple myeloma, it is associated with an increased risk of cardiovascular adverse effects. While this has been putatively linked to cardiotoxicity, CFZ could potentially also exhibit adverse effects on the endothelium.

Aims: To investigate the effects of CFZ on the endothelium

Methods: HUVECS were treated with CFZ and expression of relevant markers of ER stress, inflammation and thrombosis measured. In some experiments cells were stimulated with TNF following CFZ treatment. Immunofluorescent staining was used to determine VWF string formation following drug treatment and turbidity and Factor X activation assays used to assess clot formation on endothelial cells.

Results: CFZ treatment of sub-confluent HUVECS induced BIP and ubiquitin expression indicating induction of ER stress, however CFZ treatment of confluent HUVECS did not induce ER stress indicating CFZ cannot induce ER stress in resting HUVECS. Interestingly, CFZ treatment induced the expression of eNOS, tissue plasminogen activator and thrombomodulin and was able to reduce TNF induced ICAM-1 and tissue factor expression, suggesting a potential protective effect on the endothelium. Consistent with these observations, CFZ reduced factor Xa generation and fibrin clot formation on the endothelium following TNF treatment and prevented the formation of VWF-platelet strings and leukocyte adhesion under shear stress.

Conclusion(s): This data demonstrates that CFZ is unable to induce ER stress in confluent resting endothelial cells and can conversely attenuate the pro-thrombotic effects of TNF on the endothelium. This study suggests that CFZ does not negatively alter HUVECS, and proteasome inhibition of the endothelium may offer a potential way to prevent thrombosis. Further studies are now required to establish the mechanisms behind these effects