The
rise of drug-resistant Mycobacterium tuberculosis lends urgency to the need for new drugs for the treatment of tuberculosis
(TB). The identification of a serine protease, mycosin protease-1
(MycP1), as the crucial agent in hydrolyzing the virulence
factor, ESX-secretion-associated protein B (EspB), potentially opens
the door to new tuberculosis treatment options. Using the crystal
structure of mycobacterial MycP1 in the apo form, we performed
an iterative ligand- and structure-based virtual screening (VS) strategy
to identify novel, nonpeptide, small-molecule inhibitors against MycP1 protease. Screening of ∼485 000 ligands from
databases at the Genomics Research Institute (GRI) at the University
of Cincinnati and the National Cancer Institute (NCI) using our VS
approach, which integrated a pharmacophore model and consensus molecular
shape patterns of active ligands (4D fingerprints), identified 81
putative inhibitors, and in vitro testing subsequently
confirmed two of them as active inhibitors. Thereafter, the lead structures
of each VS round were used to generate a new 4D fingerprint that enabled
virtual rescreening of the chemical libraries. Finally, the iterative
process identified a number of diverse scaffolds as lead compounds
that were tested and found to have micromolar IC50 values
against the MycP1 target. This study validated the efficiency
of the SABRE 4D fingerprints as a means of identifying novel lead
compounds in each screening round of the databases. Together, these
results underscored the value of using a combination of in
silico iterative ligand- and structure-based virtual screening
of chemical libraries with experimental validation for the identification
of promising structural scaffolds, such as the MycP1 inhibitors.