Regression of Atherosclerosis in ApoE−/− Mice Via Modulation of Monocyte Recruitment and Phenotype, Induced by Weekly Dosing of a Novel “Cytotopic” Anti‐Thrombin Without Prolonged Anticoagulation

Abstract

Background Anticoagulants induce atherosclerosis regression in animal models but exploiting this clinically is limited by bleeding events. Here we test a novel thrombin inhibitor, PTL 060, comprising hirulog covalently linked to a synthetic myristoyl electrostatic switch to tether to cell membranes. Methods and Results ApoE−/− mice were fed chow or high‐fat diets, before transplantation of congenic aortic segments or injection of PTL 060, parental hirulog, control saline, or labeled CD 11b positive cells. Aortic transplants from transgenic mice expressing anticoagulants on endothelium did not develop atherosclerosis. A single intravenous injection of PTL 060, but not hirulog inhibited atheroma development by >50% compared with controls when assessed 4 weeks later. Mice had prolonged bleeding times for only one seventh of the time that PTL 060 was biologically active. Repeated weekly injections of PTL 060 but not hirulog caused regression of atheroma. We dissected 2 contributory mechanisms. First, the majority of CCR2+ (C‐C chemokine receptor type 2+) monocytes recruited into plaques expressed CCR7 (C‐C chemokine receptor type 7), ABCA1 (ATP‐binding cassette transporter – 1), and interleukin‐10 in PTL 060 mice, a phenotype seen in <20% of CCR2+ recruits in controls. Second, after several doses, there was a significant reduction in monocyte recruits, the majority of which were CCR2‐negative with a similar regression‐associated phenotype. Regression equivalent to that induced by intravenous PTL 060 was induced by adoptive transfer of CD 11b+ cells pre‐coated with PTL 060. Conclusions Covalent linkage of a myristoyl electrostatic switch onto hirulog in PTL 060 uncouples the pharmacodynamic effects on hemostasis and atherosclerosis, such that plaque regression, mediated predominantly via effects on monocytes, is accompanied by only transient anticoagulation.