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K. Tuberculosis and other Mycobacterial Infections
Poster Session: Tuberculosis and other Mycobacterial Infections
Novel therapies for multidrug-resistant TB are needed and new BLIs could answer this call. Mtb encodes for BlaC, a class A β-lactamase. BlaC is inhibited by clavulanate (CLA) while the DBO avibactam (AVI) is an inefficient inhibitor (low k2/K value). Carbapenems are hydrolyzed slowly by BlaC (low kcat/Km value) making them “dual action” compounds that inhibit both BlaC and PG transpeptidases, the intended β-lactam targets. DBOs inhibit PG transpeptidases in other bacteria. To explore the therapeutic potential of new DBOs against Mtb, we compared the inhibitor activity of AVI, relebactam (REL), and durlobactam (DUR, formerly ETX2514) against BlaC and Mtb PG transpeptidases using a biochemical approach. We also investigated the ability of DUR to lower minimum inhibitory concentrations (MICs) of β-lactams against Mtb H37Rv.
Methods: Mass spectrometry was performed to capture acyl-enzyme complexes (AECs) of purified BlaC and PG transpeptidases (PonA1, LdtMt1, LdtMt2, LdtMt3, and LdtMt5) with β-lactams and BLIs. Steady-state enzyme kinetics were determined using nitrocefin as a substrate. MICs with amoxicillin (AMX), meropenem (MER), CLA, and DUR alone and in combination against Mtb H37Rv were assessed using a microdilution method.
Results: DUR alone had a MIC of 2 µg/mL with Mtb H37Rv (Table 1). BlaC formed AECs with all carbapenems and BLIs. BlaC had lower Ki app and higher k2/K with DUR than those with AVI and REL and comparable to those with CLA; however, with a period of pre-incubation, AVI fully inhibits BlaC (Table 2). The carbapenems and DUR formed the most AECs with PG transpeptidases of the β-lactams and BLIs respectively; PG transpeptidases had lower Ki app values with DUR than those with AVI (Table 3). Table 1. Minimum Inhibitory Concetrations for Mycobacterium tuberculosis H37RvTable 2.
Table 3
Conclusion:
: DUR alone has some antimicrobial activity against Mtb H37Rv. The likely mechanism that underlies this activity is inhibition of BlaC and several PG transpeptidases. Inhibition of enzyme targets with DUR was more potent and efficient than AVI and REL. DUR in combination with β-lactams lowered MICs but the DUR concentration used was higher than its MIC. Our findings support the exploration of novel BLIs against BlaC and PG transpeptidases with the ultimate goal of repurposing these drugs for the treatment of TB.
David Nguyen, MD
Fellow
University Hospitals Cleveland Medical Center/ Rainbow Babies & Children's Hospital
Cleveland, Ohio, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Christopher Bethel, MS
Research Assisitant
Louis Sokes Cleveland VA Medical Center
Cleveland, OH, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Magdalena A. Taracilla, MS
Researcher
Research Service, Louis Stokes Veterans Affairs Medical Center
Cleveland, OH, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Qing Li, n/a
Case Western Reserve University
Cleveland, Ohio, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Khalid M. Dousa, MD
Attending
Case Western Reserve University, Cleveland VA medical Center
Cleveland Heights, Ohio, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Sebastian G. Kurz, MD
Associate professor
Mount Sinai National Jewish Health Respiratory Institute
New York City, NY, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Liem Nguyen, PhD
Case Western Reserve University
Cleveland, Ohio, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Barry N. Kreiswirth, PhD
Professor
Hackensack Meridian Health
Nutley, New Jersey, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Wilem Boom, MD
Case Western Reserve University/ University Hospitals Cleveland Medical Center
Cleveland, Ohio, United States
Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.
Robert A. Bonomo, MD
Associate Chief of Staff for Academic Affairs
Louis Stokes Cleveland VA Medical Center
Cleveland, OH, United States
Disclosure: entasis (Research Grant or Support)Merck (Grant/Research Support)NIH (Grant/Research Support)VA Merit Award (Grant/Research Support)VenatoRx (Grant/Research Support)