Synthesis, characterization and in vitro extracellular and intracellular activity against Mycobacterium tuberculosis infection of new second-line antitubercular drug-palladium complexes Stefano Giovagnoli a , Maria Luisa Marenzoni b , Morena Nocchetti c , Claudio Santi a , Paolo Blasi a , Aurelie Schoubben a and Maurizio Ricci a a Department of Chemistry and Technology of Drugs, b Department of Pathology, Diagnostics and Clinical Veterinary, c Department of Chemistry, Perugia, Italy Keywords capreomycin; drug-palladium complexes; intracellular antitubercular activity; kanamycin; ofloxacin Correspondence Stefano Giovagnoli, Department of Chemistry and Technology of Drugs, Università degli Studi di Perugia, 06123 Perugia, Italy. E-mail: eureka@unipg.it Received April 20, 2013 Accepted September 16, 2013 doi: 10.1111/jphp.12162 Objectives The aim of this work was to characterize novel palladium (Pd) com- plexes with second-line antitubercular drugs, namely capreomycin (C), kanamycin (K) and ofloxacin (Ofx), and to address the in vitro extracellular and intracellular activity against Mycobacterium tuberculosis infection. Methods Synthesis reaction kinetics and complex properties were assessed. Kf was calculated from the transition state quasi-equilibrium approximation and Arrhenius plot. The complexes were characterized for qualitative solubility, stoichiometry, powder size and morphology, element analysis, and thermal behaviour. Structural analyses were performed by Fourier transform infrared spectroscopy and nuclear magnetic resonance. Activity was evaluated against H37Ra M. tuberculosis strain and in infected THP-1 cells, and compared with that of the parent drugs. Key findings The complexes showed log Kf of 6 for CPd and OfxPd, and 10 for KPd indicating good stability. Stoichiometry of 1 : 1, 2 : 3 and 1 : 3 resulted for OfxPd, KPd, and CPd. OfxPd structure matched that in literature, while K and C had more complex structures with possible multiple coexisting species. The com- plexes had extracellular activity comparable with drugs and an improved efficacy against intracellular infection of M. tuberculosis. Conclusions The novel anti-tuberculosis (TB) complexes had promising proper- ties, and extracellular and intracellular activity, which makes them potential tools for intracellular targeting of pulmonary TB. Introduction The lungs are a well-recognized site for drug administra- tion. [1] Properly tailored drug delivery systems can improve the treatment of lung infections by achieving higher local drug concentrations and reducing systemic exposure. [2,3] Among other treatments, tuberculosis (TB) therapy may benefit from this strategy. The efficient clearance of exogenous substances from the lungs complicates the successful development of suit- able pulmonary anti-TB drug delivery systems. Various approaches to this problem have been reported, such as the use of polymeric microparticles, [4–6] large porous particles, [7] liposomes [8–12] and polymeric nanoparticles. [13,14] These approaches are all aimed at enhancing infected alveolar macrophage targeting. In fact, the Mycobacterium tuberculosis can survive within cells inhibiting lysosome fusion, and this peculiarity makes the alveolar macrophages therapeutic targets. [15] However, the conventional TB the- rapy is not able to ensure adequate intracellular deliv- ery. [16,17] In this regard, inhalation may help overcome some of the well-known drawbacks of TB therapy, such as high dose and toxicity, by enhancing local drug accumulation. To do so, rapid drug absorption into the blood stream should be avoided. Beyond the aforementioned microencapsulation approaches, indeed modulation of drug water solubility is commonly used. Sparingly or highly water-soluble active molecules show often a high burst of drug release from pharmaceutical formulations as they solubilize fast in body fluids. This is the case of injectable second-line antituber- cular drugs (sl-ATDs), such as capreomycin (C) and kanamycin (K), and fluoroquinolones like ofloxacin (Ofx). And Pharmacology Journal of Pharmacy Research Paper © 2013 Royal Pharmaceutical Society, Journal of Pharmacy and Pharmacology, 66, pp. 106–121 106