Coumarins possess a wide array of therapeutic capabilities, but often with unclear mechanism of action. We tested a small library of 18 coumarin derivatives against human invasive breast ductal carcinoma cells with the capacity of each compound to inhibit cell proliferation scored, and the most potent coumarin analogues selected for further studies. Interestingly, the presence of two prenyloxy groups (5,7-diprenyloxy-4-methyl-...