Multivalent dipeptidyl peptidase IV fragment-nanogold complex inhibits cancer metastasis by blocking pericellular fibronectin.

Inhibition of cancer metastasis is a fundamental challenge in cancer treatment. We have previously shown that metastasis of cancer cells in the lung is critically promoted by the interaction between the superficial dipeptidyl peptidase IV (DPP IV) expressed on lung endothelial cells and the pericellular polymeric fibronectin (polyFN) of circulating cancer cells. In the present study, we aimed to search for DPP IV fragments with high avidity to polyFN and develop FN-targeted gold nanoparticles (AuNPs) conjugated with DPP IV fragments for treating cancer metastasis. We first identified a DPP IV fragment encompassing amino acids 29-130 of DPP IV, designated DP4A, which contained FN-binding sites and could specifically bind to FN immobilized on gelatin agarose beads. Furthermore, we conjugated maltose binding protein (MBP)-fused DP4A proteins to AuNPs for fabricating a DP4A-AuNP complex and evaluated its FN-targeted activity in vitro and anti-metastatic efficacy in vivo. Our results show that DP4A-AuNP exhibited higher binding avidity to polyFN than DP4A by 9 folds. Furthermore, DP4A-AuNP was more potent than DP4A in inhibiting DPP IV binding to polyFN. In terms of polyFN-targeted effect, DP4A-AuNP interacted with FN-overexpressing cancer cells and was endocytosed into cells 10 to 100 times more efficiently than untargeted MBP-AuNP or PEG-AuNP with no noticeable cytotoxicity. Furthermore, DP4A-AuNP was superior to DP4A in competitive inhibition of cancer cell adhesion to DPP IV. Confocal microscopy analysis revealed that binding of DP4A-AuNP to pericellular FN induced FN clustering without altering its surface expression on cancer cells. Notably, intravenous treatment with DP4A-AuNP significantly reduced metastatic lung tumor nodules and prolonged the survival in the experimental metastatic 4T1 tumor model. Collectively, our findings suggest that the DP4A-AuNP complex with potent FN-targeted effects may have therapeutic potential for prevention and treatment of tumor metastasis to the lung.

Epitope analysis of the rat dipeptidyl peptidase IV monoclonal antibody 6A3 that blocks pericellular fibronectin-mediated cancer cell adhesion.

We previously showed that the rat dipeptidyl peptidase IV (rDPP IV) monoclonal antibody (mAb) 6A3 greatly inhibits the pericellular polymeric fibronectin-mediated metastatic cancer cell adhesion to rDPP IV. L(311)QWLRRI in rDPP IV has been proposed as the putative fibronectin-binding site. However, the inhibitory mechanism of 6A3 has been elusive. Epitope mapping of 6A3 may help to understand the interaction between fibronectin and rDPP IV. In the present study, we showed that 6A3 species-specifically recognized rDPP IV but inhibited fibronectin/rDPP IV-mediated cell adhesions of various cancer types and species, which was independent of rDPP IV enzymatic activity. The 6A3 epitope was stably exposed in both native and denatured rDPP IV. On the basis of the resolved structures and the species variations in DPP IV sequences, we finely mapped the 6A3 epitope to a surface-exposed Thr331-dependent motif D(329)KTTLVWN, only 11 amino acids away from L(311)QWLRRI on the same plane as the fifth beta-propeller blade. The functionality of 6A3 epitope in rDPP IV was ultimately demonstrated by the ability of 6A3-recognizable fragments to interfere with the inhibitory effect of 6A3 on full-length rDPP IV binding to pericellular polymeric fibronectin. On the basis of structural analysis, and the fact that the preformed fibronectin fragment/rDPP IV complex was co-immunoprecipitated by 6A3 and fixing the rDPP IV structure with paraformaldehyde did not avert the inhibitory effect, the mechanism of 6A3 inhibition may not be the result of complete competition or conformational change.