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 inhibit ors was developed using a NIH3T3 cell Hue with an introduced reporter gene which is controlled by the Ras-responsive element (RRE). With this screenin g system, malolactomycin D was identified as a selective inhibitor of trans cription from the RRE. This compound was found to preferentially inhibit th e anchorage-independent growth rather than the anchorage-dependent growth o f Ras-transformed NIH3T3 cells. The expression of matrix metalloproteinases MMP-1 and MMP-9, which have RRE in their promoters, were reduced by treatm ent 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 malolac tomycin D inhibits the activation of p38 MAP kinase and Jun N-terminal-kina se (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 act ivation of p38 MAP kinase and JNK, malolactomycin D suppresses the expressi on of MMPs. Since MMPs play important roles in metastasis and maintenance o f the microenvironment of tumor cells, both of which facilitate tumor growt h, the inhibition of MMPs by malolactomycin D is believed to contribute to its ability to inhibit Ras-mediated tumorigenesis.