European Society of Mycobacteriology - Instituto Nacional de Saúde ...

PP-113
the human macrophage as a model to select
compounds active against MDR/XDR-TB
Marta Martins 1,2,* , Miguel Viveiros 1,3 , Isabel Couto 1,4 and Leonard Amaral 1,2,3 .
1 - Unit of Mycobacteriology, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa (IHMT/UNL), Lisbon, Portugal
2 - UPMM, IHMT/UNL, Lisbon, Portugal
3 - COST ACTION BM0701 (ATENS)
4 - Centro de Recursos Microbiológicos (CREM), Faculdade de Ciências e Tecnologia, UNL, Caparica, Portugal
* Corresponding author: Unit of Mycobacteriology and UPMM, Instituto de Higiene e Medicina Tropical, Universidade
Nova de Lisboa (IHMT/UNL), Rua da Junqueira, 96, 1349-008, Lisbon, Portugal; Telf: +351213652600; Fax: +351213632105;
e-mail: mmartins@ihmt.unl.pt
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 active against 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 Ca 2+
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 bacterial
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 upon transport processes
affected by agents that inhibit Ca 2+ -activated K + pumps. Based on this and on our results, we postulate that the enhancement
of the macrophage killing activity by these compounds could be due to the inhibition of Ca 2+ 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 patient’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.
European Society of Mycobacteriology | 30 th Annual Congress | July 2009 | Porto - Portugal
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