Universitą degli studi di Pavia
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Degiacomi research activity
Identification of targets for new anti-TB drugs
Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb). TB remains a global health emergency, thriving on the spread of highly drug- resistant strains, the lack of vaccines and fast- acting drugs, and the co-epidemic with HIV. Indeed, about 3 billion people are latently infected and they serve as a reservoir for reactivating disease (WHO, 2010). Consequently, there is an urgent need of new antitubercular drugs.
This research is part of "New medicines for tuberculosis" project funded by EC-VI framework (2006-2011).
In 2009, two promising drugs, benzothiazinones (BTZ) and dinitrobenzamides (DNB), were found to be highly active against Mtb, including multidrug resistant (MDR) and extremely drug resistant (XDR) strains.
In our lab, it has been demonstrated that the target of BTZ is DprE1 enzyme, encoded by the Rv3790 or dprE1 gene, which works in concert with DprE2 (Rv3791 or dprE2 gene) to form the heteromeric decaprenylphosphoryl-β-D-ribose 2′- epimerase, involved in decaprenylphosphoryl-D- arabinose (DPA) biosynthesis. Moreover, it has been previously reported that DPA is the precursor of arabinogalactan, an essential component of the mycobacterial cell wall.
In all the Mtb and Mycobacterium smegmatis BTZ-resistant mutants found to date, missense mutations in dprE1 gene (or its ortholog) confer resistance to BTZ thanks to a common antibiotic resistance mechanism such as target modification. By enzymatic assay it was confirmed that the synthesis of DPA is inhibited in the presence of BTZs in wild type mycobacterial strains but not in BTZ spontaneous resistant mutants.
BTZs have a typical nitro group on the benzene ring. This substituent is essential for its antimycobacterial activity; in fact, the corresponding amino-derivative, found in the blood and urine of treated animals, is significantly less active in inhibiting both Mtb and M. smegmatis growths. Moreover, in M. smegmatis resistant strains, a nitroreductase, named NfnB, able to inactivate the BTZs, has been identified. In particular, an overexpression of NfnB, due to mutations in its transcriptional repressor (MSMEG_6503), caused the BTZ inactivation.
As well as BTZs, DNBs are nitro-aromatic compounds. Interestingly, it has been shown that incubation of Mtb with DNBs blocks the DPA biosynthesis, thus suggesting that both drugs could share the same target.
During my PhD, I have contributed to further validate DprE1 as a promising cellular target of BTZ and DNB drugs and demonstrated that these agents share common resistance mechanisms, involving target modification and drug inactivation. In addition, I contributed to further characterize DprE1 protein. Overall, these results gave more insights into BTZs and DNBs, and will be useful to design new and more effective antimycobacterial drugs. Until now, BTZs and DNBs were demonstrated to be highly promising for starting clinical trials.
The goals of the new project “More medicines for tuberculosis”, founded by EC-VII framework (2011-2016), are the discovery of five novel targets in Mtb and the selection of at least three anti-TB drugs active against replicant and dormant Mtb cells.
Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb). TB remains a global health emergency, thriving on the spread of highly drug- resistant strains, the lack of vaccines and fast- acting drugs, and the co-epidemic with HIV. Indeed, about 3 billion people are latently infected and they serve as a reservoir for reactivating disease (WHO, 2010). Consequently, there is an urgent need of new antitubercular drugs.
This research is part of "New medicines for tuberculosis" project funded by EC-VI framework (2006-2011).
In 2009, two promising drugs, benzothiazinones (BTZ) and dinitrobenzamides (DNB), were found to be highly active against Mtb, including multidrug resistant (MDR) and extremely drug resistant (XDR) strains.
In our lab, it has been demonstrated that the target of BTZ is DprE1 enzyme, encoded by the Rv3790 or dprE1 gene, which works in concert with DprE2 (Rv3791 or dprE2 gene) to form the heteromeric decaprenylphosphoryl-β-D-ribose 2′- epimerase, involved in decaprenylphosphoryl-D- arabinose (DPA) biosynthesis. Moreover, it has been previously reported that DPA is the precursor of arabinogalactan, an essential component of the mycobacterial cell wall.
In all the Mtb and Mycobacterium smegmatis BTZ-resistant mutants found to date, missense mutations in dprE1 gene (or its ortholog) confer resistance to BTZ thanks to a common antibiotic resistance mechanism such as target modification. By enzymatic assay it was confirmed that the synthesis of DPA is inhibited in the presence of BTZs in wild type mycobacterial strains but not in BTZ spontaneous resistant mutants.
BTZs have a typical nitro group on the benzene ring. This substituent is essential for its antimycobacterial activity; in fact, the corresponding amino-derivative, found in the blood and urine of treated animals, is significantly less active in inhibiting both Mtb and M. smegmatis growths. Moreover, in M. smegmatis resistant strains, a nitroreductase, named NfnB, able to inactivate the BTZs, has been identified. In particular, an overexpression of NfnB, due to mutations in its transcriptional repressor (MSMEG_6503), caused the BTZ inactivation.
As well as BTZs, DNBs are nitro-aromatic compounds. Interestingly, it has been shown that incubation of Mtb with DNBs blocks the DPA biosynthesis, thus suggesting that both drugs could share the same target.
During my PhD, I have contributed to further validate DprE1 as a promising cellular target of BTZ and DNB drugs and demonstrated that these agents share common resistance mechanisms, involving target modification and drug inactivation. In addition, I contributed to further characterize DprE1 protein. Overall, these results gave more insights into BTZs and DNBs, and will be useful to design new and more effective antimycobacterial drugs. Until now, BTZs and DNBs were demonstrated to be highly promising for starting clinical trials.
The goals of the new project “More medicines for tuberculosis”, founded by EC-VII framework (2011-2016), are the discovery of five novel targets in Mtb and the selection of at least three anti-TB drugs active against replicant and dormant Mtb cells.
