MMP9 and cancer: Some findings dictate emodin suppresses the activator protein Activator Protein-1 (AP-1) and NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) signaling [84, 85] pathways, respectively, thus inhibiting the expression of matrix metallopeptidase 9 (MMP-9) [85] as shown in Figure 2 and hence limiting the invasiveness in various cancer cells.