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Antimicrobial Agents and Chemotherapy, February 2002, p. 575-577, Vol. 46, No. 2
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.46.2.575-577.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Stability of New Carbapenem DA-1131 to Renal Dipeptidase (Dehydropeptidase I)
Sung Wook Park,1 Jeoung Soon We,1 Gye Won Kim,2 Seong Hak Choi,2 and Haeng Soon Park1*
Department of Pharmacy, College of Pharmacy, Chonnam National University, Kwangju,1
and Research Laboratory, Dong-A Pharmaceutical Co., Ltd., Yongin, Kyunggi-Do, Korea2
Received 7 September 2000/
Returned for modification 27 February 2001/
Accepted 4 November 2001

ABSTRACT
The stability of DA-1131 to renal dipeptidase (RDPase) (EC 3.4.13.19)
was compared with that of imipenem and meropenem by
Vmax/
Km ratios as an index of the enzyme's preference for substrates.
Our results showed a decreasing order of imipenem (6.24), meropenem
(2.41), and DA-1131 (1.39). The biochemical evaluation of DA-1131
as the least preferred substrate of RDPase suggests its potential
use as a novel ß-lactam antibiotic which may be usable
without coadministration of RDPase inhibitors once its clinical
suitability is proven.

INTRODUCTION
Imipenem (
N-formimidoylthienamycin), developed by Merck Sharp
& Dohme, West Point, Pa., was highly effective against bacterial
species resistant to most ß-lactam antibiotics with
unusually high potency against gram-positive as well as gram-negative
bacteria (
8,
21,
23). It is degraded, though, in the kidneys
of various animals, resulting in a reduced antibacterial activity.
The enzyme responsible for this metabolism was shown to be renal
dipeptidase (RDPase, also called renal dehydropeptidase I) (EC
3.4.13.19) located in the brush-border membrane of renal proximal
tubules (
8,
9,
20). Cilastatin,
Z-2-(2,2-dimethylcyclopropanecarboxamido)-2-butenoic
acid, is a specific competitive inhibitor of RDPase and is well
matched in its pharmacokinetic properties for coadministration
with imipenem (
8,
22). Therefore, imipenem is designed to be
coadministered with cilastatin to suppress RDPase for its clinical
use, and they are now manufactured in a 1:1 combination.
Meropenem, (-)-(4R,5S,6S)-3-[(3S,5S)-5-(dimethyl-carbamoyl)-3-pyrrolidinylthio]-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-1-azabicyclo[3,2,0]hept-2-ene-2-carboxylic acid, which was introduced in the late 1980s, though relatively less active against gram-positive bacteria than imipenem (1, 4, 6, 7), is stable in the presence of RDPase as judged by its Vmax/Km ratio. Thus, it is currently in clinical use without coadministration of an RDPase inhibitor.
DA-1131, (1R,5S,6S)-(2S,4S)-2-[(E)-3-methansulphonylamino-1-propenyl]-pyrrolidine-4-ylthiol-6-[(R)-1-hydroxyethyl]-1-methyl-1-carbapen-2-em-3-carboxylic acid, is a new carbapenem developed by the Research Laboratory at Dong-A Pharmaceutical Company, Yongin, Korea. It demonstrated a wide range of antibacterial activity against both gram-positive and gram-negative bacteria (G. W. Kim, M. S. Chang, K. W. Lee, Y. S. Chong, and J. Yang, Abstr. Annu. Meet. Korea Soc. Appl. Pharmacol., abstr. 232, 1996). It is also resistant to degradation by various bacterial ß-lactamases (S. H. Choi, G. W. Kim, J. Y. Kim, G. J. Lim, D. Y. Chung, W. B. Kim, and J. Yang, Abstr. Annu. Meet. Korea Soc. Appl. Pharmacol., abstr. 237, 1996). DA-1131 has been examined in many aspects, including pharmacokinetics under various conditions in animals (10, 12, 13, 16, 17, 18, 19), in the renal excretion mechanism (14, 15), and in nephrotoxicity-related studies (11).
We measured the kinetic parameters of imipenem, meropenem, and DA-1131 in relation to human RDPase and the RDPases of various animals to examine the stability of DA-1131 in reference to the two well-established ß-lactam antibiotics, imipenem and meropenem.
DA-1131 and meropenem were supplied by Dong-A Research Laboratory. Imipenem and cilastatin were obtained from Merck Sharp & Dohme. Human RDPase was purified to homogeneity with a 2,029-fold purification, and RDPases from animal sources were purified or partially purified according to the method previously described (24).
RDPase-catalyzed hydrolysis of imipenem, meropenem, and DA-1131 was measured in the presence and absence of cilastatin (0.15 µM) according to the method described by Kim and Campbell (9) by measuring the decrease in absorbance at 298 nm and 37°C as a function of time for 2.5 min. Substrate concentration was varied over a range of 1.25 to 3.3 mM in 3-(N-morpholino)propanesulfonic acid, pH 7.1. One microgram of purified RDPase was employed in a 250-µl reaction mixture, and 2-mm light path quartz cuvettes were used. The initial velocities are expressed as enzyme units (U) (micromoles of substrate hydrolyzed per minute) per milligram of protein with molar extinction coefficients at 298 nm for DA-1131, imipenem, and meropenem of 9.7314 x 10-3, 9.3222 x 10-3, and 1.0167 x 10-2 M-1 cm-1, respectively. Protein concentrations were determined according to the Bradford method (2) with bovine serum albumin as the standard protein.
The Lineweaver-Burk plots of imipenem (Fig. 1A),meropenem (Fig. 1B), and DA-1131 (Fig. 1C) identified cilastatin as a competitive inhibitor of RDPase-catalyzed hydrolysis in all plots shown by the crossings at the y axes.
The kinetic parameters and
Vmax/
Km ratios are summarized in
Table
1. The
Vmax/
Km ratio for each substrate has been used
as an index of the enzyme's preference for substrates (
3,
5).
The
Vmax/
Km ratio decreased in the order of imipenem (6.24),
meropenem (2.41), and DA-1131 (1.39), thus identifying DA-1131
as the least preferred substrate among the three, i.e., the
most stable compound against RDPase. The relative percent ratio
for DA-1131 was only 22.3% for imipenem and 57.7% for meropenem.
The
Ki values are 0.07 ± 0.02, 0.21 ± 0.04, and
0.35 ± 0.01 µM for imipenem, meropenem, and DA-1131,
respectively. Comparable
Ki values in such a close range indicate
that RDPase acts upon these carbapenems within the same catalytic
site (
9).
The kinetic parameters of these carbapenems in relation to the
RDPases of various animals were also determined, and the
Vmax/
Km ratios are summarized in Table
2. The
Vmax/
Km ratio for imipenem
was lower than that for meropenem in mouse and rabbit RDPase
but higher in rat, dog, and porcine RDPase. Thus, imipenem and
meropenem exhibited large variations in resistance to RDPase
depending on the enzyme source but the
Vmax/
Km ratio for DA-1131
was the lowest in all the tested animals. The
Vmax/
Km ratios
for meropenem (0.95) and DA-1131 (0.74) in the porcine enzyme
are significantly lower than for imipenem (19.75), thus suggesting
far more stability in the presence of RDPase than imipenem.
The relative ratios of DA-1131 to imipenem or meropenem were
less than 1.0 in all the tested animals, thus showing higher
resistance of DA-1131 to RDPase than to either antibiotic. Judging
from the
Vmax/
Km ratio, the susceptibility of carbapenems to
RDPase varied depending on the species (Tables
1 and
2). With
imipenem, the
Vmax/
Km ratio for human RDPase (6.24) was the
lowest while that of dog RDPase (39.02) was the highest. In
the case of meropenem, the porcine RDPase (0.95) exhibited the
lowest ratio and the rabbit RDPase (23.38) exhibited the highest,
although the ratio for mouse RDPase (21.14) was similarly high.
However, DA-1131 demonstrated the lowest ratio with porcine
RDPase (0.74) and the highest ratio with dog RDPase (12.56),
which was still significantly lower than that of either imipenem
(39.02) or meropenem (16.46).
Meropenem has been going through worldwide clinical trials since
1989, and it is now on the market as an effective ß-lactam
antibiotic. One of the most prominent fortes of meropenem is
in its relative stability to human RDPase; thus, it can be used
alone, without coadministration of any RDPase inhibitor. DA-1131
is even more stable against RDPase than meropenem in all species
tested so far, including humans, thus suggesting its high efficacy
without coadministration of an RDPase inhibitor once its suitability
is proven as a new antibiotic. DA-1131 is now being evaluated
in preclinical studies.

ACKNOWLEDGMENTS
This study was supported by the Korea Ministry of Science and
Technology.

FOOTNOTES
* Corresponding author. Mailing address: Department of Pharmacy, College of Pharmacy, Chonnam National University, Kwangju 500-757, Korea. Phone: 82 62 530-2923. Fax: 82 62 530-2949. E-mail:
haspark{at}chonnam.chonnam.ac.kr..


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Antimicrobial Agents and Chemotherapy, February 2002, p. 575-577, Vol. 46, No. 2
0066-4804/01/$04.00+0 DOI: 10.1128/AAC.46.2.575-577.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.