Furin, a member the proprotein convertase (PC) family, processes inactive precursor proteins to functional proteins within the Golgi/trans-Golgi network secretory pathway. Furin and other PC family members (furin/PCs) activate proteins vital to proper physiological functioning, including growth factors and hormones, receptors, plasma proteins, and matrix metalloproteases (MMPs). Additionally, the expression and activity of furin/PC are necessary for processing substrates important for cell transformation and tumor progression, metastasis, and angiogenesis. Furin processing of the remodeling protease membrane type-1 matrix metalloproteinase (MT1-MMP) enhances cellular motility and invasiveness, contributing to aggression and metastatic potential cancer cells. Whereas overexpression and activity of furin/PC exacerbate the cancer phenotype, inhibition of its activity decreases or nullifies furin/PC-mediated effects, and thus, inhibition of furin may be a viable route to cancer therapy. Recently, we identified a small-molecule inhibitor of furin, named B3, by high-throughput screening with a K(i) and IC(50) of 12 microM. Here, we show that this cell-permeable, small-molecule compound inhibits furin-mediated cleavage of proMT1-MMP, resulting in decreased MMP-2 activation and cell motility in CHO cells expressing proMT1-MMP. Additionally, this molecule inhibited proMT1-MMP processing, complete MMP-2 maturation, and invasiveness of human fibrosarcoma cells (HT1080).