Thiazole-fused androstenone and ethisterone derivatives: potent β- and γ-actin cytoskeleton inhibitors to treat melanoma tumors

Melanoma, the most fatal form of skin cancer, often becomes resistant to the current therapeutic approaches in most patients. To explore new treatment options, fused thiazole derivatives were synthesized, and several of these compounds demonstrated potent anti-melanoma activity both <i>in vitro</i> and <i>in vivo</i>. These compounds exhibited significant cytotoxicity against melanoma cell lines at low concentrations. The lead molecules induced apoptosis and caused G2/M phase cell cycle arrest to a lesser extent. These compounds also displayed remarkable antimetastatic activities in several cell-based and molecular assays, significantly inhibiting key processes of metastasis, such as cell migration and adhesion. mRNA sequencing revealed significant downregulation of β-actin (<i>ACTB</i>) and γ-actin (<i>ACTG1</i>) at the transcriptional level, and a similar effect was observed at the protein level by western immunoblotting and proteomics assays. Actin-rich membrane protrusions formation is crucial for facilitating metastasis by promoting cell migration. Fluorescence microscopy demonstrated that compounds E28 and E47 inhibited the formation of these membrane protrusions and impaired actin cytoskeleton dynamics. Docking studies suggested the lead compounds may suppress tumor proliferation and metastasis by targeting the mechanistic target of Rapamycin complex 2 (mTORC2). All these findings unanimously indicated the translational perspective of ethisterone and androstenone fused thiazole derivatives as potent antimetastatic and antimelanoma agents. In a preclinical mouse melanoma model, compounds E2 and E47 significantly reduced tumor growth and greatly improved overall mice survival, while showing a favorable safety profile based on a comprehensive blood plasma metabolite profile. These lead molecules also displayed promising physicochemical properties, making them strong candidates for further drug development studies.