R5 and R7 positions on fluoroquinolone scaffolds drive F-actin filament disruption

Fluoroquinolones (FQs) are widely prescribed broad-spectrum antibiotics, with newer generations capable of crossing the blood brain barrier (BBB). Previous studies have reported the actin-destabilizing effects of FQs, suggesting their potential for drug repurposing. Actin-associated neuropathies are characterised by the formation of persistent, F-actin aggregates in neurons, which impair critical cellular functions. Therefore, identifying small molecules that can disrupt these actin filaments and aggregates can provide a promising therapeutic strategy. This research aims to map the direct interaction between FQs and F-actin to identify the structural basis for actin disruption. We demonstrated that FQs irreversibly disrupt F-actin filaments in a concentration-dependent manner using scattering-based assay. Electron microscopy and gel filtration confirmed generation-dependent disruption activity. In particular, Gen3 and Gen4 FQs reduced actin aggregates in more than 60% yeast cells. FQ treatment altered the thermal stability of F-actin at both 1:30 and 1:50 molar ratios with minor secondary structural changes. To explore the molecular insights of FQs interaction with F-actin, saturation transfer difference-NMR combined with complementary molecular dynamics simulations revealed the importance of the fluorinated quinolone core, which is common to all FQs. These studies highlight the involvement of an amino group at R5, and bulky piperazine, azabicyclo rings at the R7 position in driving F-actin disruption. We would like to propose that rational modifications at R5 and R7 positions can enhance both actin-disrupting potency and BBB permeability, thereby providing a basis for developing FQs derived therapeutics against actin-related neurodegenerative disorders.