Malolactomycin D, a potent inhibitor of transcription controlled by the Ras responsive element, inhibits Ras-mediated transformation activity with suppression of MMP-1 and MMP-9 in NIH3T3 cells

To search for anti-cancer agents, a screening system for Ras signal inhibitors was developed using a NIH3T3 cell Hue with an introduced reporter gene which is controlled by the Ras-responsive element (RRE). With this screening system, malolactomycin D was identified as a selective inhibitor of transcription from the RRE. This compound was found to preferentially inhibit the anchorage-independent growth rather than the anchorage-dependent growth of Ras-transformed NIH3T3 cells. The expression of matrix metalloproteinases MMP-1 and MMP-9, which have RRE in their promoters, were reduced by treatment with malolactomycin D at the translational and transcriptional levels. Analysis of the activity of mitogen-activated protein (MAP) kinases, which play important roles in transduction of the Ras signal, showed that malolactomycin D inhibits the activation of p38 MAP kinase and Jun N-terminal-kinase (JNK) but not extracellular signal-regulated kinase 1 or 2 (ERK1 or 2). These findings suggest that by inhibiting the pathway that leads to the activation of p38 MAP kinase and JNK, malolactomycin D suppresses the expression of MMPs. Since MMPs play important roles in metastasis and maintenance of the microenvironment of tumor cells, both of which facilitate tumor growth, the inhibition of MMPs by malolactomycin D is believed to contribute to its ability to inhibit Ras-mediated tumorigenesis.