Secreted Matrix Metalloproteinase‑9 of Proliferating Smooth Muscle Cells as a Trigger for Drug Release from Stent Surface Polymers in Coronary Arteries

Cardiovascular
diseases are the leading causes of death in industrialized
countries. Atherosclerotic coronary arteries are commonly treated
with percutaneous transluminal coronary intervention followed by stent
deployment. This treatment has significantly improved the clinical
outcome. However, triggered vascular smooth muscle cell (SMC) proliferation
leads to in-stent restenosis in bare metal stents. In addition, stent
thrombosis is a severe side effect of drug eluting stents due to inhibition
of endothelialization. The aim of this study was to develop and test
a stent surface polymer, where cytotoxic drugs are covalently conjugated
to the surface and released by proteases selectively secreted by proliferating
smooth muscle cells. Resting and proliferating human coronary artery
smooth muscle cells (HCASMC) and endothelial cells (HCAEC) were screened
to identify an enzyme exclusively released by proliferating HCASMC.
Expression analyses and enzyme activity assays verified selective
and exclusive activity of the matrix metalloproteinase-9 (MMP-9) in
proliferating HCASMC. The principle of drug release exclusively triggered
by proliferating HCASMC was tested using the biodegradable stent surface
polymer poly-l-lactic acid (PLLA) and the MMP-9 cleavable
peptide linkers named SRL and AVR. The specific peptide cleavage by
MMP-9 was verified by attachment of the model compound fluorescein.
Fluorescein release was observed in the presence of MMP-9 secreting
HCASMC but not of proliferating HCAEC. Our findings suggest that cytotoxic
drug conjugated polymers can be designed to selectively release the
attached compound triggered by MMP-9 secreting smooth muscle cells.
This novel concept may be beneficial for stent endothelialization
thereby reducing the risk of restenosis and thrombosis.

心血管疾病是工业化国家的首要致死病因。动脉粥样硬化性冠状动脉病变通常采用经皮冠状动脉介入治疗，随后植入支架。该治疗方案已显著改善了临床预后，但被激活的血管平滑肌细胞（vascular smooth muscle cell, SMC）增殖会引发裸金属支架的支架内再狭窄。此外，药物洗脱支架因内皮化过程受到抑制，会导致支架血栓这一严重不良反应。本研究旨在开发并测试一种支架表面聚合物，该聚合物可将细胞毒性药物共价结合至支架表面，并通过增殖型平滑肌细胞选择性分泌的蛋白酶触发药物释放。研究筛选了静息状态与增殖状态的人冠状动脉平滑肌细胞（human coronary artery smooth muscle cell, HCASMC）及人冠状动脉内皮细胞（human coronary artery endothelial cell, HCAEC），以鉴定仅由增殖型HCASMC分泌的酶。通过表达分析与酶活性实验，证实了基质金属蛋白酶-9（matrix metalloproteinase-9, MMP-9）仅在增殖型HCASMC中表现出选择性且排他性的活性。本研究以可生物降解的支架表面聚合物聚乳酸（poly-l-lactic acid, PLLA）以及命名为SRL和AVR的MMP-9可裂解肽接头为材料，验证了仅由增殖型HCASMC触发药物释放的原理。通过偶联模型化合物荧光素（fluorescein），证实了MMP-9对肽链的特异性切割作用。在分泌MMP-9的HCASMC培养液中可检测到荧光素释放，而在增殖型HCAEC培养液中则未观察到此现象。本研究结果提示，可通过设计细胞毒性药物偶联聚合物，实现由分泌MMP-9的平滑肌细胞选择性触发结合药物的释放。这一全新概念有望促进支架内皮化，从而降低再狭窄与血栓形成的风险。