Blockage of the metastasis process remains a significant clinical challenge, requiring innovative therapeutic approaches. For this purpose, molecules that inhibit matrix metalloproteinases (MMPs) activity or induce the expression of their natural inhibitor, the tissue inhibitor of metalloproteinases (TIMPs), are potentially interesting. In a previous study, we have shown that synthetic ligands binding to cell surface nucleolin/nucleophosmin and known as HB 19 for the lead compound and NucAnt 6L (N6L) for the most potent analogue, inhibit both tumor growth and angiogenesis. Furthermore, they prevent metastasis in a RET transgenic mice model which develops melanoma. Here, we investigated the effect of N6L on the invasion capacity of MDA-MB 435 melanoma cells. Our results show that the multivalent pseudopeptide N6L inhibited Matrigel invasion of MDA-MB 435 cells in a modified Boyden chamber model. This was associated with an increase in TIMP-3 in the cell culture medium without change in TIMP-3 mRNA expression suggesting its release from cell surface and/or extracellular matrix (ECM). This may be explained by our demonstrated N6L interaction with sulfated glycosaminoglycans (GAGs) and consequently controlled the bioavailability of GAGs bound TIMP-3. The implication of TIMP-3 in N6L-induced inhibition of cell invasion was evidenced by siRNA silencing experiments showing that the loss of TIMP-3 expression abrogated the effect of N6L. The inhibition of tumor cell invasion by N6L demonstrated in this study, in addition to its previously established inhibitory effect on tumor growth and angiogenesis, suggests that N6L represents a promising anticancer drug candidate warranting further investigation.