More than 180,000 people worldwide are affected by multiple myeloma (MM), a malignant and currently incurable bone marrow disease. Previous collaboration within the research team has led to the discovery of the cytotoxic potential of a compound mixture derived from Adriatic macroalgae, Cutleria multifida and Halopteris scoparia, against MM cells. This project aims to validate an innovative concept by developing and optimizing a (sub)fractionation process and identifying bioactive molecules with antitumor activity. The antitumor effects of the compounds will be confirmed in vitro using MM cell lines and in vivo in the zebrafish (Danio rerio) model organism. The identification of bioactive compound(s) with antitumor properties will contribute to the development of novel therapeutic strategies for MM.