Synthesis and biological assessment of ciprofloxacin-derived 1,3,4-thiadiazoles as anticancer agents

The quinolone-3-carboxylic acid scaffold is essential structure for Antibacterial activity of fluoroquinolones such as ciprofloxacin. Modification of 3-carboxylic functionality in this structure can be used for switching its activity from Antibacterial to Anticancer. Accordingly, a series of C-3 modified ciprofloxacin derivatives containing N-(5-(benzylthio)-1,3,4-thiadiazol-2-yl)-carboxamide moiety was synthesized as novel Anticancer agents. Most of compounds showed significant activity against MCF-7, A549 and SKOV-3 Cancer cells in the MTT assay. In particular, compounds 13a-e and 13g were found to be as potent as standard drug doxorubicin against MCF-7 cell line (IC₅₀s = 3.26-3.90 µM). Furthermore, the 4-fluorobenzyl derivatives 13h and 14b with IC₅₀ values of 3.58 and 2.79 µM exhibited the highest activity against SKOV-3 and A549 cells, being as potent as doxorubicin. Two promising compounds 13e and 13g were further tested for their Apoptosis inducing activity and cell cycle arrest. Both compounds could significantly induce Apoptosis in MCF-7 cells, while compound 13e was more potent Apoptosis inducer resulting in an 18-fold increase in the proportion of apoptotic cells at the IC₅₀ concentration in MCF-7 cells. The cell cycle analysis revealed that compounds 13e and 13g could increase cell portions in the sub-G1 phase, inducing oligonucleosomal DNA fragmentation and Apoptosis confirmed by comet assay.