Salutary Effects of mTOR Inhibition on Deep Veins in Vivo: Results from the Sirolimus Trial with Drug-Eluting Balloon (STRIDE)

Objective: mTOR inhibitors have been shown to impact thrombotic, inflammatory, and fibrotic pathways in vitro. Drug-coated balloons (DCB) delivering mTOR inhibitors to the vessel wall have effectively reduced arterial intimal hyperplasia, but the utility in the venous system is unknown. This study aimed to develop a microsurgical technique for testing DCBs in the deep venous system in a rat model in vivo, and to characterize changes to the deep vein endothelium.

Methods: We developed a novel microsurgical model in anesthetized (isoflurane) Sprague Dawley rats (250-400g) consisting of exposure of the infrarenal IVC through a midline laparotomy, ligation of side branches, and cauterization of posterior branches. A sharpened guidewire was used to enter the infrarenal IVC with retrograde cannulation, a balloon advanced over the guidewire, inflated for 3 minutes and then removed, and a previously placed U-stitch tightened for hemostasis. A 3x10 mm DCB (sirolimus 3.0 μg/mm²) was inflated based on IVC diameter measured by ultrasound preoperatively to achieve a 15% overstretch between 6.5 to 16 atm. IVCs were harvested after 15 days to measure protein concentration locally. Local sirolimus concentration was measured by liquid chromatography (LC). ELISAs were performed for E-selectin, P-selectin, VEGF-a, MMP2, TIMP1, MCP-1, IL-6, and p-AKT.

Results:
We demonstrated the feasibility of a new in vivo microsurgical model for initial proof-of-concept venous endovascular experiments with a 99.96% survival rate (58 of 60, Figure 1A-B). Sirolimus uptake in the vein wall was confirmed by LC (Figure 1C) and subsequent inhibition of mTOR pathway confirmed by decrease in pAKT (Figure 1D). Uncoated balloon (UB) venoplasty compared to no treatment (Sham) resulted in significant increases in IL-6, MMP2, and TIMP1 expression. Compared to control and UB, IVCs treated with DCB had a significantly decreased expression of E-selectin and IL-6. No significant changes were found in MCP-1 and VEGF-a levels (data not shown).



Conclusions: Sirolimus DCB treatment of the venous endothelium inhibits endothelial cellular adhesive properties and inflammatory profile up to 15 days post-procedurally. Such modulation deserves further study in post thrombotic veins as potential measure to prevent sequelae such as recurrent venous thrombosis and fibrosis.