- Natural products (NPs) encompass a rich source of bioactive chemical entities. Here, we used human cancer stem cells (CSCs) in a chemical genomics campaign with NP chemical space to interrogate extracts from diverse strains of actinomycete for anti-cancer properties. We identified a compound (McM25044) capable of selectively inhibiting human CSC function versus normal stem cell counterparts. Biochemical and molecular studies revealed that McM025044 exerts inhibition on human CSCs through the small ubiquitin-like modifier (SUMO) cascade, found to be hyperactive in a variety of human cancers. McM025044 impedes the SUMOylation pathway via direct targeting of the SAE1/2 complex. Treatment of patient-derived CSCs resulted in reduced levels of SUMOylated proteins and suppression of progenitor and stem cell capacity measured in vitro and in vivo. Our study overcomes a barrier in chemically inhibiting oncogenic SUMOylation activity and uncovers a unique role for SAE2 in the biology of human cancers.