Bioorganic & Medicinal Chemistry Letters 20 (2010) 3380–3383
Bioorganic & Medicinal Chemistry Letters
N-Hydroxybenzimidazole inhibitors of ExsA MAR transcription factor in
Pseudomonas aeruginosa: In vitro anti-virulence activity and metabolic stability
Mark C. Grier a, Lynne K. Garrity-Ryan a, Victoria J. Bartlett b, , Kevin A. Klausner a, Peter J. Donovan c,
,
Caroline Dudley a, Michael N. Alekshun d, , S. Ken Tanaka a, Michael P. Draper a, Stuart B. Levy a,
Oak K. Kim a,
*
a Paratek Pharmaceuticals, Inc. 75 Kneeland Street, Boston, MA 02111, United States
b Pfizer Research, 35 CambridgePark Drive, Cambridge, MA 02141, United States
c Akrivis Technologies, 1 Broadway, Cambridge, MA 02142, United States
d Merck, 2015 Galloping Hill Road, Kenilworth, NJ 07033, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 February 2010
Revised 4 April 2010
Accepted 7 April 2010
Available online 11 April 2010
ExsA is a multiple adaptational response (MAR) transcription factor, regulating the expression of a viru-
lence determinant, the type III secretion system (T3SS) in Pseudomonas aeruginosa. Non-cytotoxic, non-
antibacterial N-hydroxybenzimidazoles were identified as effective inhibitors of ExsA-DNA binding,
and their potential utility as anti-virulence agents for P. aeruginosa was demonstrated in a whole cell
assay. Select N-hydroxybenzimidazole inhibitors were stable in an in vitro human liver microsomal assay.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
MAR
Antivirulence
ExsA
Pseudomonas aeruginosa
N-Hydroxybenzimidazoles
Life-threatening infections caused by multi-drug resistant
(MDR) pathogens continue to present serious public health issues
worldwide. About half of MDR bacteria are Gram-negative, includ-
ing Pseudomonas aeruginosa, Escherichia coli, and Acinetobacter spp.
P. aeruginosa, in particular, are associated with hospital-acquired
pneumonia (HAP) as well as the chronic lung infections in cystic
fibrosis patients.1,2 Ventilator-associated pneumonia (VAP) espe-
cially poses great challenges in antimicrobial chemotherapy, be-
cause of the high frequency of MDR strains including P. aeruginosa.
Currently marketed antibiotics are becoming increasingly inac-
tive against MDR P. aeruginosa mainly because of resistance.3,4 The
next generation of antibiotic derivatives (e.g., carbapenems and
cephalosporins), demonstrating good activities against clinical iso-
lates of resistant P. aeruginosa, are in the late stage of clinical devel-
opment.5 However, given the same mechanism of action and the
similar chemical structures, these newer antibiotics would also
be subject to already existing resistance mechanisms. This situa-
tion has fostered interest in pursuing novel approaches as alterna-
tives to traditional antimicrobial chemotherapy.
Previously we reported MAR (multiple adaptational response)
technology in which we developed small molecule inhibitors for
bacterial transcription factors SoxS, MarA and Rob in E. coli, and
LcrF in Yersinia pseudotuberculosis.6,7 MAR proteins, a subgroup of
AraC family proteins, regulate the virulence gene expression in
many clinically important bacterial species. This novel strategy of
targeting bacterial virulence, as compared to traditional antibiotics
targeting bacterial growth or survival, may offer an opportunity to
circumvent resistance development issues. Given that MAR pro-
teins are not required for bacterial survival outside of a host, inhib-
itors of MAR proteins are less likely to apply the selection pressure
for resistance development.
ExsA is a MAR transcription factor in P. aeruginosa which regu-
lates the expression of a virulence determinant, the type III secre-
tion system (T3SS).8 The exsA null mutants do not express the T3SS
and exhibit substantially attenuated virulence in whole cell assays
and animal models of P. aeruginosa infection.9,10 Furthermore,
many clinically important P. aeruginosa strains express the T3SS,
which is correlated with the increased severity of clinical pneumo-
nia cases such as HAP/VAP.11,12 Therefore, developing anti-viru-
lence agents by targeting ExsA would be a viable approach to
prevent infections caused by P. aeruginosa, especially among pa-
tients in a high-risk environment such as receiving mechanical
ventilation.
* Corresponding author. Tel.: +1 617 275 0040; fax: +1 617 275 0039.
Present address.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.