CTT peptide

Matrix metalloproteinase 2 (MMP2 or gelatinase A), MMP9 (gelatinase B) and other MMPs including collagenases, stromelysins, and the membrane-type MMPs belong to a large family of endopeptidases involved in the degradation of extracellular matrix (ECM) proteins constituting the basement membrane barrier as well as cleavage of growth factor precursors, receptor tyrosine kinases, cell adhesion molecules, and other proteins. MMPs are involved in tumor growth, migration, invasion, and metastases as well as angiogenesis and tissue remodeling. Interestingly, MMP9 expression in the stromal cells but not in the breast cancer cells associated with poor prognosis. In an attempt to develop peptide-based gelatinase inhibitors to attenuate cancer progression, an in vitro phage display screen with purified MMP9 using a random peptide (CX5-8C) library was used to identify two cyclic decapeptides (CTTHWGFTLC (CTT) and CRRHWGFEFC) targeting MMP2 and MMP9. These peptides share the HWGF domain. The inhibitory effect of the peptides was analyzed in a 125I-gelatin degradation assay. CTT or CRRHWGFEFC inhibited the MMP9 activity with micromolar IC50 values while the control peptide (GACLRSGRGCGA) showed negligible effect. CTT also inhibited MMP2 with IC50 of 10 uM. CTT inhibits specifically the MMP2 and MMP9 activity while no inhibitory activity against MT1-MMP, MM8 or MM13 was detected. As a further modification, a CTT derived retro inverso peptide (D amino acids except glycine, L-Gly) was generated (cltfGwhttc) and it showed better inhibitory effect against MMP2 than the original CTT in vitro. However, it was not studied further due to its poor water solubility. When the gelatinase targeting CTT peptide was developed for radioimaging, it lost the inhibitory activity after conjugation to 125I, but not when conjugated to Technetium- 99m. Thus, the N-terminus of CTT was modified by the addition of two alanine and one tyrosine residues (AAY-CTT) followed by labeling with 125I (125I-AAY-CTT) to restore the inhibitory activity. The 125I-AAY-CTT as well as the CTT coated 125I-BSA encapsulated liposomes accumulated to the KS1767 Kaposi’s sarcoma tumors following the intravenous injections, unlike their non-targeting controls with some indication of homing also to metastatic lesions in the lung. In another study, CTT peptide conjugated to 64Cu through a DOPA (1,4,7,10-Tetraazacyclododecane- 1,4,7,10) chelator was tested in PET imaging. Even though the Cu (II)- DOTA-CTT inhibited MMP2 and MMP9 activities with binding affinities (EC50) of 8.7 uM and 18.2 uM, respectively, which are very similar to those of the original CTT (13.2 uM and 11.0 uM, respectively), it was not successful in in vivo tumor imaging. Stability and the gelatinase inhibition activity of the CTT peptide was increased by substituting the disulfide bond with an amide bond to form a c(KAHWGFTLD)NH2 peptide (C6). Cy5.5 fluorescein conjugated to the C6 peptide was taken up by MMP-2 expressing glioma cells in vitro and homed to both intratibial PC-3 prostate xenografts and orthotopic U87 glioma xenografts in vivo. In addition, C6 peptide conjugated to NOTA (1,4,7,10-Triazacyclononanetriacetic acid) chelator and radiolabeled with 68Ga (68Ga-NOTAC6) showed accumulation of the conjugate in subcutaneous ovarian cancer (SKOV3) xenografts. Several studies have since utilized CTT as an MMP2 inhibitor as vasorelaxant and imaging of gelatinase activity in tumors.