Interleukin-2 receptor-specific fusion toxin inhibits barotrauma-induced arterial atherosclerosis

Immunocytochemical analyses of human plaques and experimental arterial lesions have implicated activated lymphocytes and monocytes in the pathogenesis of atherosclerosis, as demonstrated by the expression of interleukin-2 (IL-2) membrane receptors and major histocompatibility complex class II epitopes. The objective is to determine if targeting these cells with an IL-2 receptor-specific chimeric toxin, DAB₄₈₆-IL-2, can inhibit experimental post-angioplasty vascular neointimal thickening. Twenty-two atherogenically modeled rabbits were treated in vivo with DAB₄₈₆-IL-2 (0.1 mg/kg per day i.v.; n = 11) or placebo (n = 11) for 10 days following aortic balloon angioplasty (4 atm x 30 s each x 2 dilatations). In vitro ³H-leucine incorporation studies of mononuclear leukocyte and vascular smooth muscle cell protein synthesis inhibition by DAB₄₈₆-IL-2 were also performed. Angioplasty sites were examined for evidence of hyperproliferative atherosclerotic narrowing by quantitative angiography and histomorphometry of neointimal cross-sectional area at baseline and 6 weeks after injury. In vitro Concanavalin-A stimulated rabbit mononuclear leukocyte protein synthesis was 50% inhibited by DAB₄₈₆-IL-2 at a concentration (IC₅₀) of 6 x 10^-11 M. Rabbit vascular smooth muscle cells were ~ 150-fold less sensitive to DAB₄₈₆-IL-2 (IC₅₀ = 10^-8 M). In vivo studies showed no change in angioplasty site angiographic minimum luminal diameter at 6 weeks in DAB₄₈₆-IL-2 treated animals (from 2.96 ± 0.5 to 2.96 ± 0.48 mm; percent cross-sectional area reduction = 1 ± 10%; P = N.S.). In control animals, luminal diameter decreased from 2.79 ± 0.4 to 2.32 ± 0.52 mm at 6 weeks, and percent cross-sectional area was reduced by 34 ± 14% (P < 0.01 vs. placebo). Quantitative histomorphometric angioplasty segmental intimal cross-sectional area reduction of treated and placebo vessels also differed significantly (19 ± 16% vs. 31 ± 21%; P < 0.05). DAB₄₈₆-IL-2 caused no adverse effects on animal survival, weight or hepatic transaminase levels. We conclude that post-angioplasty administration of the chimeric toxin DAB₄₈₆-IL-2 inhibits angiographic narrowing and neointimal thickening in the atherogenic rabbit model. Although this IL-2 receptor-specific molecule was cytotoxic in vitro for activated mononuclear leukocytes and vascular smooth muscle cells, systemic toxicity did not occur in vivo at a dose comparable to that evaluated in clinical trials of this agent. Potential anti-proliferative effects of this chimeric toxin may be mediated by direct local inhibition of leukocyte-mediated inflammation, or through the indirect modification of vascular cell mitogenesis and cytokine release.