Mechanisms of the Antineoplastic Effects of New Fluoroquinolones in 2D and 3D Human Breast and Bladder Cancer Cell Lines

Simple Summary Besides their antibacterial effects, fluoroquinolones possess other valuable properties such as immunomodulatory and anticancer activities. These features make fluoroquinolones ideal compounds for 'drug repositioning'. In the last decades, fluoroquinolone derivatives with improved anticancer effects have been synthesized. We have previously shown that certain ciprofloxacin and norfloxacin derivatives were more potent anticancer agents than their precursors. For this study, the mechanisms of action of the most active among these derivatives were evaluated in a panel of tumor cell lines, including particularly untreatable cancer forms (e.g., triple-negative breast cancer). The tested compounds exerted several well-known fluoroquinolone effects, like cell cycle arrest, apoptosis induction, migration, and topoisomerase II inhibition, along with rather unexplored mechanisms for fluoroquinolones, namely, alternative cell death and histone deacetylase inhibition. Our results delve deeper into the anticancer mechanisms of fluoroquinolone derivatives that, given their known tolerability, could represent a valid therapeutic option, even in poorly treatable tumors.Abstract Antibacterial fluoroquinolones have emerged as potential anticancer drugs, thus prompting the synthesis of novel molecules with improved cytotoxic characteristics. Ciprofloxacin and norfloxacin derivatives, previously synthesized by our group, showed higher anticancer potency than their progenitors. However, no information about their mechanisms of action was reported. In this study, we selected the most active among these promising molecules and evaluated, on a panel of breast (including those triple-negative) and bladder cancer cell lines, their ability to induce cell cycle alterations and apoptotic and necrotic cell death through cytofluorimetric studies. Furthermore, inhibitory effects on cellular migration, metalloproteinase, and/or acetylated histone protein levels were also evaluated by the scratch/wound healing assay and Western blot analyses, respectively. Finally, the DNA relaxation assay was performed to confirm topoisomerase inhibition. Our results indicate that the highest potency previously observed for the derivatives could be related to their ability to induce G2/M cell cycle arrest and apoptotic and/or necrotic cell death. Moreover, they inhibited cellular migration, probably by reducing metalloproteinase levels and histone deacetylases. Finally, topoisomerase inhibition, previously observed in silico, was confirmed. In conclusion, structural modifications of progenitor fluoroquinolones resulted in potent anticancer derivatives possessing multiple mechanisms of action, potentially exploitable for the treatment of aggressive/resistant cancers.