Ascochlorin is an isoprenoid antibiotic and antiviral that has diverse effects on mammalian cells. It suppresses PMA-induced invasion in renal carcinoma cells (IC50 = ~10 ?M) by inhibiting the expression of matrix metalloproteinase-9. At 2 ?M, ascochlorin profoundly increases the expression of p53 by increasing protein stability in cancer cells, and, at 50 ?m, it inhibits signaling through STAT3. Ascochlorin also binds and inhibits the mitochondrial cytochrome bc1 complex, blocking reduction of cytochrome b by ubiquinone.