Download Design, synthesis and screening of potential

Design, synthesis and screening of potential inhibitors of the enzyme New Delhi Metallo- -lactamase
Supervisor: http://www1.aston.ac.uk/lhs/staff/az-index/rathbodl/Dr Dan Rathbone
Associate supervisors Dr Tony Worthington and Dr Anthony Hilton
The latest “superbug” family to cause global concern achieves it mechanism of drug resistance through the
action of metallo- -lactamases capable of hydrolysing the  -lactam rings found in antibiotics such as
penicillins, cephalosporins and carbapenems. The most recent member of the family wields the particular
enzyme New Delhi Metallo- -lactamase (NDM-1). This monomeric enzyme has a molecular mass of 28 kDa
and can hydrolyze all  -lactams except aztreonam. It is of major concern that the gene coding for NDM-1 is
easily passed between microorganism species by promiscuous plasmid transfer. As a result the incidence of
observed resistance to carbapenems is increasing worldwide and in such cases treatment protocols are
severely limited.
This project will focus on combating drug resistance from microorganisms expressing the NDM-1 enzyme.
Initial in silico screening at Aston of recently published X-ray crystal structures of the NDM-1 enzyme with a
large database of drug-like molecules has revealed several structures that will potentially bind well to the
active site. These candidate structures that constitute the starting point for a programme to design and
synthesise potential inhibitors of the enzyme. The project will involve refinement of the computer models
for the enzyme and in silico screening of potential inhibitors. The most promising compounds will be
synthesised and tested against microorganisms (primarily E. coli) expressing the NDM-1 enzyme. The
organisms’ recovery of susceptibility to carbapenems will be taken as an indication of the effectiveness of
the putative NDM-1 inhibitor.
Antimicrob Agents Chemother. 2009 Dec;53(12):5046-54. Epub 2009 Sep 21.
http://www.ncbi.nlm.nih.gov/pubmed/19770275
NDM-1 shares very little identity with other MBLs, with the most similar MBLs being VIM-1/VIM-2, with
which it has only 32.4% identity. As well as possessing unique residues near the active site, NDM-1 also has
an additional insert between positions 162 and 166 not present in other MBLs. NDM-1 has a molecular
mass of 28 kDa, is monomeric, and can hydrolyze all beta-lactams except aztreonam. Compared to VIM-2,
NDM-1 displays tighter binding to most cephalosporins, in particular, cefuroxime, cefotaxime, and
cephalothin (cefalotin), and also to the penicillins. NDM-1 does not bind to the carbapenems as tightly as
IMP-1 or VIM-2 and turns over the carbapenems at a rate similar to that of VIM-2. In addit
doi: 10.1128/AAC.00774-09
Lancet Infect Dis. 2011 May;11(5):381-93.
Metallo-β-lactamases: a last frontier for β-lactams?
Cornaglia G, Giamarellou H, Rossolini GM.
Source
Department of Pathology and Diagnostics, University of Verona, Verona, Italy. [email protected]
Abstract
Metallo-β-lactamases are resistance determinants of increasing clinical relevance in Gram-negative
bacteria. Because of their broad range, potent carbapenemase activity and resistance to inhibitors, these
enzymes can confer resistance to almost all β-lactams. Since the 1990s, several metallo-β-lactamases
encoded by mobile DNA have emerged in important Gram-negative pathogens (ie, in Enterobacteriaceae,
Pseudomonas aeruginosa, and Acinetobacter baumannii). Some of these enzymes (eg, VIM-1 and NDM-1)
have been involved in the recent crisis resulting from the international dissemination of carbapenemresistant Klebsiella pneumoniae and other enterobacteria. Although substantial knowledge about the
molecular biology and genetics of metallo-β-lactamases is available, epidemiological data are inconsistent
and clinical experience is still lacking; therefore, several unsolved or debatable issues remain about the
management of infections caused by producers of metallo-β-lactamase. The spread of metallo-βlactamases presents a major challenge both for treatment of individual patients and for policies of infection
control, exposing the substantial unpreparedness of public health structures in facing up to this emergency.
Lancet Infect Dis 2010;
10: 597–602 Now, however,
clinical microbiologists increasingly agree that multidrugresistant
Gram-negative bacteria pose the greatest risk to
public health. Not only is the increase in resistance of
Gram-negative bacteria faster than in Gram-positive
bacteria,1,2 but also there are fewer new and developmental
antibiotics active against Gram-negative bacteria3–6 and
drug development programmes seem insuffi cient to
provide therapeutic cover in 10–20 years.7–9
The increase in resistance of Gram-negative bacteria is
mainly due to mobile genes on plasmids that can readily
spread through bacterial populations. Standardised
plasmid typing methods are enhancing our understanding
of the host ranges of these elements and their worldwide
distribution.10,11 Moreover, unprecedented human air
travel and migration allow bacterial plasmids and clones
to be transported rapidly between countries and
continents.12,13 Much of this dissemination is undetected,
with resistant clones carried in the normal human fl ora
and only becoming evident when they are the source of
endogenous infections. The CTX-M-15 extended-spectrum
β-lactamase (ESBL) encoded by blaCTX-M-15 was fi rst reported
in India in the mid-1990s.14,15 The gene jumped from the
chromosome of its natural hosts, Kluyvera spp, to
plasmids that have subsequently spread widely,10,16
establishing CTX-M-15 as the globally-dominant ESBL
and the primary cause of acquired resistance to thirdgeneration
cephalosporins in Entero bacteriaceae.17,18
Recent surveys have identifi ed ESBLs in 70–90% of
Enterobacteriaceae in India and; although these
collections might be a biased sample, they do suggest a
serious problem, making the widespread use of reserved
antibiotics such as carbapenems necessary.15,19 Rates of
cephalosporin resistance are lower in other countries but
the growing prevalence of ESBL producers is suffi cient to
drive a greater reliance on carbapenems. Consequently,
there is selection pressure for carbapenem resistance in
Enterobacteriaceae, and its emergence is a worldwide
public health concern since there are few antibiotics in
nzyme belongs to a group of enzymes (beta-lactamases) that are capable of breaking the chemical bonds of
a beta-lactam ring, which composes an important part of many antibiotics such as drugs of the penicillin,
cephalosporin, and carbapenem groups. Most of the beta-lactamase enzymes are effective on some or
most of the older antibiotics like penicillins and cephalosporins. NDM-1, however, is effective on both the
old and newer antibiotics (carbapenems such as imipenem) that contain a beta-lactam ring.