International Journal of Antimicrobial Agents 33 (2009) 479–482 Contents lists available at ScienceDirect International Journal of Antimicrobial Agents j o u r n a l h o m e p a g e : h t t p : / / w w w . e l s e v i e r . c o m / l o c a t e / i j a n t i m i c a g Short communication SILA 421, an inhibitor of efflux pumps of cancer cells, enhances the killing of intracellular extensively drug-resistant tuberculosis (XDR-TB) Marta Martins a,b , Miguel Viveiros a , Jorge Ramos a , Isabel Couto a,c , Joseph Molnar d , Martin Boeree e , Leonard Amaral a,b,∗ a Unit of Mycobacteriology, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa (IHMT/UNL), Rua da Junqueira 96, 1349-008 Lisboa, Portugal b UPMM, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa (IHMT/UNL), Rua da Junqueira 96, 1349-008 Lisboa, Portugal c Centro de Recursos Microbiológicos (CREM), Faculdade de Ciências e Tecnologia, UNL, 2829-516 Caparica, Portugal d Department of Medical Microbiology and Immunology, Institute of Medical Microbiology, University of Szeged, H-6720, Szeged, Dom ter 10, Szeged, Hungary e University Lung Centre Dekkerswald, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands a r t i c l e i n f o Article history: Received 31 July 2008 Accepted 27 October 2008 Keywords: SILA compounds MDR-TB XDR-TB Macrophages Efflux pumps a b s t r a c t Multidrug-resistant and extensively drug-resistant tuberculosis (MDR/XDR-TB) are problematic to man- age, especially in patients with acquired immune deficiency syndrome (AIDS). There is therefore a dire need for effective anti-MDR/XDR-TB agents. We have previously shown that agents that inhibit the efflux pumps of MDR bacteria and cancer cells also enhance killing of intracellular mycobacteria, possibly by increasing the availability of K + and Ca 2+ needed for the activation of lysosomal enzymes of the phagolyso- somal unit. In this study, the newly synthesised and recently patented SILA 409 and 421 were tested for in vitro and ex vivo activity against XDR-TB. The minimum inhibitory concentration (MIC) of SILA compounds was determined by the BACTEC 460 TB system. The effect of each compound on the killing activity of human macrophages infected with XDR-TB was determined by exposing the macrophage that had phagocytosed the bacterium to the compounds and assessing the killing activity by colony-forming unit counting. Amongst the two compounds tested, SILA 421 was shown to have in vitro activity against XDR-TB (MIC < 3.5 mg/L) and to transform non-killing macrophages into effective killers of phagocytosed bacteria, without any cytotoxic activity. Because SILA 421 revealed good in vitro and ex vivo activities and is devoid of any cytotoxic activity, it is a potential candidate as an anti-MDR/XDR-TB drug. © 2008 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. 1. Introduction The rates of new cases of multidrug-resistant tuberculosis (MDR-TB) and now extensively drug-resistant tuberculosis (XDR- TB) continue to increase and this is now a major health concern [1]. Lisbon and Oporto, the two major cities of Portugal, are examples of where the rates of MDR-TB are exceedingly high [2],although with respect to Lisbon there has been a significant reduction in new cases of MDR-TB owing to the implementation of the Faster TB Track Programme and the ability of mycobacteriology laboratories in this area to identify within 1 day of receiving a positive acid fast- stained sputum specimen a patient infected with MDR-TB [3]. With respect to other cities that have not implemented this programme, the rates of new cases of MDR-TB continue to increase [2]. Regarding XDR-TB, retrospective evaluation of MDR-TB strains isolated from ∗ Corresponding author at: Unit of Mycobacteriology,Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa (IHMT/UNL), Rua da Junqueira 96, 1349-008 Lisboa, Portugal. Tel.: +351 21 365 2600; fax: +351 21 363 2105. E-mail address: lamaral@ihmt.unl.pt (L. Amaral). patients during the past 8 years clearly shows that a significant number are XDR-TB [2]. Undoubtedly, the laboratory plays a major role in the control of TB [1,3,4]. However, until TB is completely eliminated, effective therapy is an absolute requirement for con- trol of the disease. Although antibiotic-susceptible TB infections are not difficult to manage effectively under conditions that optimise therapy,inexperience of the physician or non-compliance of the patient contributes to the selection of antibiotic-resistant strains of Mycobacterium tuberculosis [1,4]. When the patient is infected with MDR-TB, therapy is problematic and cure rates are low [1]. To treat these MDR/XDR-TB infections, new and effective drugs are needed and, despite the fact that several are at phase II clinical trials, none are available at this time.We have previously demonstrated that phenothiazines used for the therapy of psychoses as well as their derivatives (i) have in vitro activity against a large range of bacteria, in particular M. tuberculosis [5–7], (ii) enhance the killing activity of infected macrophages [5] and (iii) cure mice infected with M. tuberculosis [8]. However, because thioridazine (TZ) as well as other neuroleptic phenothiazines cause arrhythmia and even ‘torsade de pointes’ (an uncommon variant of ventricular tachycardia), albeit at very low frequencies, there is resistance to employ these agents for 0924-8579/$ – see front matter © 2008 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. doi:10.1016/j.ijantimicag.2008.10.028