Allelopathic compound 2-methoxy-1,4-naphthoquinone is broadly effective against pathogenic <i>Prototheca</i> species <i>in vitro</i> and <i>in vivo</i>

Unpigmented, yeast-like <i>Prototheca</i> algae are emerging pathogens responsible for unusual infections in humans and animals. Their treatment is often unsuccessful, as traditional antifungals and antibacterials show unsatisfactory activity against <i>Prototheca</i>. Therefore, the development of improved drugs that consider the peculiarities of algal biology is needed. Here, we describe a novel anti-<i>Prototheca</i> compound, the 2-methoxy-1,4-naphthoquinone, identified among molecules known to mediate plant and algal allelopathy. The 2-methoxy-1,4-naphthoquinone was highly active <i>in vitro</i> against a range of <i>Prototheca</i> isolates from different species, both planktonically and in biofilms. Its mode of action included the induction of toxic reactive oxygen species, and it targeted energy generation in the pathogen's mitochondria. It effectively treated <i>Prototheca bovis</i> skin infection in a mouse model, demonstrating translational potential. Altogether, this study not only identified a new effective anti-<i>Prototheca</i> compound, but also identified 1,4-naphthoquinone backbone as a lead structure for further therapeutic development and demonstrated the feasibility of exploring known anti-plant compounds as a source of anti-<i>Prototheca</i> treatments.