p-Cymene (4-isopropyltoluene) has been reported to have beneficial actions such as anti-inflammatory and antinociceptive activities. To evaluate whether p-cymene exhibits antitumor invasive actions, we examined the effects of p-cymene on the production of matrix metalloproteinase 9 (MMP-9)/gelatinase B and tissue inhibitor of metalloproteinases-1 (TIMP-1) in human fibrosarcoma HT-1080 cells. p-Cymene was found to dose-dependently inhibit the 12-O-tetradecanoylphorbol 13-acetate (TPA)-augmented production and gene expression of MMP-9 in HT-1080 cells. In contrast, p-cymene enhanced the TPA-augmented production and gene expression of TIMP-1 in HT-1080 cells. However, there was no change in the constitutive level of MMP-9 and TIMP-1 mRNAs and TIMP-1 protein in p-cymene-treated cells. In addition, we found that the in-vitro TPA-augmented invasiveness of HT-1080 cells was inhibited by p-cymene in a dose-dependent manner. Furthermore, p-cymene was found to suppress the constitutive and/or TPA-augmented phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase (MAPK) in HT-1080 cells. Thus, these results provide novel evidence that p-cymene is an effective candidate for the prevention of tumor invasion and metastasis through mechanisms that include the inhibition of MMP-9 expression and the augmentation of TIMP-1 production along with the suppression of ERK1/2 and p38 MAPK signal pathways in tumor cells.Key words p-cymene; tumor invasion; matrix metalloproteinase 9; tissue inhibitor of metalloproteinases-1; extracellular signal-regulated kinase 1/2 (ERK1/2); p38 mitogen-activated protein kinase (p38 MAPK)The proteolytic degradation of extracellular matrix (ECM) components in basement membranes and stroma tissues is requisite for progressing the invasion and metastasis of malignant tumor cells. Matrix metalloproteinases (MMPs) play a crucial role in ECM degradation, and different sets of MMPs concertedly act in ECM breakdown. 1,2) Gelatinase A (72-kDa type IV collagenase)/MMP-2 and gelatinase B (92-kDa type IV collagenase)/MMP-9 have been reported to facilitate tumor cell invasion and epithelial-mesenchymal transition as a promoter and/or modulator in normal and tumor cells in vivo and in vitro.3) On the other hand, the enzymic activity of MMPs and proteolytic activation of the MMP precursor (proMMP) have been reported to be controlled by endogenous inhibitors such as tissue inhibitors of metalloproteinases (TIMPs).4) Since four TIMPs have been identified, designated as TIMP-1, TIMP-2, TIMP-3, and TIMP-4, they inhibit MMPs by forming a strong noncovalent complex with a 1 : 1 stoichiometry. 4) Regarding the inhibitory properties among the TIMPs, TIMPs can bind to different sets of MMPs: e.g., the preference inhibition of TIMP-1 against MMP-9, MMP-3, and MMP-1, and that of TIMP-2 against MMP-2 rather than MMP-9.4,5) Therefore, the inhibition of expression and/or enzymic activity of MMP is likely to be an effective target(s) for preventing tumor invasion and metastasis.