The human macrophage as a model to select compounds active against MDR/XDR-TB.

The emergence of Multi- and Extensively-Drug Resistant Mycobacterium tuberculosis(MDR/XDR-TB) represents a major threat to public health worldwide. Both infections result in high mortality, especially if the patient is co-infected with HIV. The selection of therapy for these multi-drug resistant infections is limited, and for most situations, ineffective as many of these strains are untreatable with the available drugs. Thus, there is an urgent need to design and develop new compounds against drug resistant M. tuberculosis that are effective within the main target of this infection, the human macrophage. We have recently demonstrated that efflux pumps inhibitors are activeagainst mycobacteria, by enhancing the killing activity of the human macrophage and may represent an alternative to the conventional antibiotherapy for the treatment of the MDR/XDR-TB infections.From previous studies we have demonstrated that thioridazine (TZ) enhances the killing of MDR-TB phagocytosed by human macrophages. However, the mechanism of action of TZ on these cells is not fully understood. We have studied the activity of TZ, several of its derivatives, organosilicon (SILA) compounds and other known inhibitors of K+ and Ca2+ transport (ouabain, reserpine and verapamil) on macrophages infected with MDR-TB and XDR-TB. After phagocytosis, the compounds were added to the macrophage cultures. Following incubation cells were lysed and the intracellular bac-terial concentration determined. Our results demonstrate that TZ, three of its derivatives and one SILA compound (SILA 421) enhanced substantially the macrophage killing activity. The killing activity of neutrophils is correlated with the K+ availability, which is dependent upontransport processes affected by agents that inhibit Ca2+-activated K+ pumps. Based on this and on our results, we postulate that the enhance-ment of the macrophage killing activity by these compounds could be due to the inhibition of Ca2+ and K+ transport that promotes the activation of hydrolases and the killing of intracellular bacteria. A model describing the sequence of events that lead to the killing of intracellular bacteria will be presented. Moreover, the ex-vivo testing of compounds using pa-the ex-vivo testing of compounds using pa-tient’s own macrophages in the clinical TB laboratory might allow screening the most effective compounds against MDR/XDR-TB providing the basis for the intelligent selection of drugs to be used in the therapy of these infections.