Thioridazine: resurrection as an antimicrobial agent?

Thioridazine cures extensively drug-resistant tuberculosis (XDR-TB) and the need for global trials is now!

Thioridazine (TDZ) has been shown to have in vitro activity against multidrug-resistant (MDR) and extensively drug-resistant (XDR) strains of Mycobacterium tuberculosis, to promote the killing of intracellular MDR and XDR strains and to cure the mouse of antibiotic-susceptible and -resistant pulmonary tuberculosis (TB) infections. Recently, TDZ was used to cure 10 of 12 XDR-TB patients in Buenos Aires, Argentina. At the time of writing, it is being used for the therapy of non-antibiotic-responsive terminal XDR-TB patients in Mumbai, India, on the basis of compassionate therapy and although it is too early to determine a cure, the patients have improved appetite, weight gain, are afebrile and free of night sweats, and their radiological picture shows great improvement. Because XDR-TB is essentially a terminal disease in many areas of the world and no new effective agents have yet to yield successful clinical trials, global clinical trials for the therapy of XDR-TB are urgently required.

Reversal of methicillin resistance in Staphylococcus aureus by thioridazine

OBJECTIVES

Thioridazine has been shown to reverse oxacillin resistance in methicillin-resistant Staphylococcus aureus (MRSA) in vitro. The aim of this study was to investigate whether thioridazine alone or in combination with oxacillin affects the transcription of the methicillin resistance gene mecA and the protein level of the encoded protein PBP2a.

METHODS

Viability of MRSA was determined in liquid media in the presence of oxacillin or thioridazine alone or in combination. Transcription of mecA was analysed by primer extension, and the protein level of PBP2a was analysed by western blotting in the presence of thioridazine and oxacillin.

RESULTS

We observed an increased susceptibility of MRSA towards oxacillin in the presence of thioridazine compared with bacteria grown with oxacillin or thioridazine alone. Transcription of mecA was reduced with increasing concentrations of thioridazine in the presence of a fixed amount of oxacillin. Furthermore, the protein level of PBP2a was reduced when bacteria were treated with the combination of oxacillin and thioridazine. The two drugs also affected the mRNA level of the beta-lactamase gene, blaZ.

CONCLUSIONS

The present study indicates that reversal of methicillin resistance by thioridazine in MRSA may be explained by a reduced transcription of mecA and blaZ, resulting in a reduced protein level of PBP2a.

Nitrate enhances the survival of Mycobacterium tuberculosis during inhibition of respiration

When oxygen is slowly depleted from growing cultures of Mycobacterium tuberculosis, they enter a state of nonreplicating persistence that resembles the dormant state seen with latent tuberculosis. In this hypoxic state, nitrate reductase activity is strongly induced. Nitrate in the medium had no effect on long-term persistence during gradual oxygen depletion (Wayne model) for up to 46 days, but significantly enhanced survival during sudden anaerobiosis. This enhancement required a functional nitrate reductase. Thioridazine is a member of the class of phenothiazines that act, in part, by inhibiting respiration. Thioridazine was toxic to both actively growing and nonreplicating cultures of M. tuberculosis. At a sublethal concentration of thioridazine, nitrate in the medium improved the growth. At lethal concentrations of thioridazine, nitrate increased survival during aerobic incubation as well as in microaerobic cultures that had just entered nonreplicating persistence (NRP-1). In contrast, the survival of anaerobic persistent (NRP-2) cultures exposed to thioridazine was not increased by the addition of nitrate. Nitrate reduction is proposed to play a role during the sudden interruption of aerobic respiration due to causes such as hypoxia, thioridazine, or nitric oxide.