An increasing amount of evidence suggests that the major culprit of cancer relapse is cancer stem cells (CSCs). Conventional chemotherapy appears to target bulk cancer cells, while CSCs on the other hand survive and may initiate new tumours. Thus, finding new therapies that target CSCs is important. In our research we are investigating the effect of a variety of molecules on bulk cancer cells and CSCs. Through cooperation with chemists, we have access to a library of salinomycin analogues. Salinomycin is a polyether antibiotic that was shown to be 100 times more efficient in inhibiting CSCs than the conventional chemotherapeutic drug paclitaxel. We have shown that synthetically modified salinomycin analogues are more efficient against CSCs than salinomycin and we are now evaluating the adverse outcome pathway of these compounds. We have cooperation with research groups in Bolivia and Ethiopia evaluating the cancer cell and CSC effect of compounds isolated from plants used in traditional medicine. As experimental system, we are using human cancer cell lines as well as normal cell lines. The concept of normal cell toxicity testing in vitro is central to our research and we think it is important to try to elucidate side effects before injecting toxic drugs into tumour bearing animals. We are in the process of developing a 3D system of electrospun fibers combined with extra cellular matrix components for co-cultivation of cancer cells and normal cells for drug testing.