^99mTc-MAG3-Aptamer for Imaging Human Tumors Associated with High Level of Matrix Metalloprotease‑9

The human matrix metalloprotease 9 (hMMP-9) is involved in many physiological processes such as tissue remodeling. Its overexpression in tumors promotes the release of cancer cells thus contributing to tumor metastasis. It is a relevant marker of malignant tumors. We selected an RNA aptamer containing 2′-fluoro, pyrimidine ribonucleosides, that exhibits a strong affinity for hMMP-9 (<i>K</i>_d = 20 nM) and that discriminates other human MMPs: no binding was detected to either hMMP-2 or -7. Investigating the binding properties of different MMP-9 aptamer variants by surface plasmon resonance allowed the determination of recognition elements. As a result, a truncated aptamer, 36 nucleotides long, was made fully resistant to nuclease following the substitution of every purine ribonucleoside residue by 2′-<i>O</i>-methyl analogues and was conjugated to <i>S</i>-acetylmercaptoacetyltriglycine for imaging purposes. The resulting modified aptamer retained the binding properties of the originally selected sequence. Following ^99mTc labeling, this aptamer was used for ex vivo imaging slices of human brain tumors. We were able to specifically detect the presence of hMMP-9 in such tissues