Mercapto-phosphonate compounds as broad-spectrum inhibitors of the metallo-beta-lactamases

Objectives: One of the emergent factors for the b-lactam antibiotic
resistance of pathogenic bacteria is the production of metallob-
lactamases (MBLs), which are able to hydrolyse the b-lactam ring
in a broad spectrum of substrates, particularly the carbapenems. MBLs
have been divided into three different sub-classes B1, B2 and B3 based
on sequence similarities [1]. In this report, we investigated the inhibitory
effect of mercapto-phosphonate derivatives against MBLs.
Methods: The laboratory of P Metzner (University of Caen, France)
synthesized 12 different mercapto-phosphonate compounds with the
ability to inhibit the subclass B1 VIM-4, the subclass B2 CphA and
the subclass B3 L1 MBLs respectively. Consequently, we determined
the competitive inhibition constant (Ki) as described by DeMester
et al. [2]. We also measured the minimal inhibition concentration (MIC)
for Escherichia coli recombinant strains producing VIM-4, CphA or L1,
for ampicillin or imipenem in the presence or absence of mercaptophosphonate
compounds.
Results: In the present study, we show that all the mercaptophosphonates,
with the exception of compound 1a, behaved as
good competitive inhibitors (Ki<15 mM) for CphA. Their activities
against the sub-classes B1 and B3 enzymes were more contrasted.
In addition, the presence of free Zn++ abolished the inhibitory
activity of compound 2b. The compound behaving as zinc chelator
could explain this phenomenon. Nevertheless, the (2-sulfanylphenyl)
phosphonic acid, the (4-bromophenyl)(sulfanyl)methyl phosphonic acid
and the [(2,4-dichlorophenyl)(sulfanyl)methyl] phosphonic acid were
good inhibitors (Ki<15 mM) against the different studied enzymes and
can be used as leads to the synthesis of new MBL inhibitors. Our tests
indicated that the presence of compounds 2b, 4a and mgfg decreased
the MIC value for imipenem.
Conclusion: In this study, we show that members of the phosphonates
group are able to enhance the inhibition of Zn b-lactamases. This is
the first report of new inhibitors possessing a strong activity against the
different sub-classes of MBLs. Reference(s)
[1] Galleni M, Lamotte-Brasseur J, Rossolini GM, Spencer J, Dideberg
O, Frere JM. Antimicrob Agents Chemother 2001; 45(3): 660−3.
[2] De Meester F, Joris B, Reckinger G, Bellefroid-Bourguignon C, Frere
JM, Waley SG. Biochem Pharmacol 1987 Jul 15; 36(14): 2393–403.