Recent studies have revealed that elevated activity of various ALDHs is a hallmark of cancer stem cells and certain tumors.45,46 Moreover, correlations between ALDH expression and proliferation have been observed in normal and cancer cells as well.45,47–49 This offers an intriguing explanation for the observed bioactivity of acivicin and offers an opportunity to study the activity of selected enzymes using the diverse set of probes presented here. The gene discussed is LDHA; the disease is cancer.