709. In Vitro Antibacterial Activity and In Vivo Efficacy of Sulbactam–Durlobactam (ETX2514SUL) Against Pathogenic Burkholderia Species

Background The genus Burkholderia contains several pathogenic species with distinct etiologies, including Burkholderia pseudomallei the biothreat pathogen responsible for melioidosis and Burkholderia mallei which causes glanders. β-Lactams, such as ceftazidime and meropenem, are important therapeutic options for these infections. However, clinical resistance to β-lactams, which is primarily mediated by multiple types of β-lactamases in these species, is a growing concern. Durlobactam (ETX2514, DUR) is a novel β-lactamase inhibitor with broad-spectrum activity against Ambler class A, C, and D β-lactamases. Sulbactam (SUL) is an Ambler Class A β-lactamase inhibitor with intrinsic antibacterial activity against a limited number of species, including Acinetobacter spp. SUL-DUR is currently in Phase 3 clinical testing for the treatment of carbapenem-resistant infections caused by Acinetobacter spp. In this study, SUL-DUR was tested for in vitro antibacterial activity against B. pseudomallei and B. mallei as well as for in vivo efficacy in a preclinical model of melioidosis. Methods The antibacterial activity of SUL alone or in combination with DUR (fixed at 4 mg/L) against B. pseudomallei (n = 30) and B. mallei (N = 28) was determined following CLSI guidelines. In vivo efficacy was tested in an acute murine model of melioidosis in which 4 × 104 cfu Bp K96423 (SUL-DUR MIC = 1 mg/L) was administered intranasally to BalbC mice. SUL-DUR (100/200 or 400/200 mg/kg) was administered q4h subcutaneously 4 hours post-challenge for 6 days and murine survival was monitored for 45 days. Doxycycline (DOX) and ciprofloxacin (CIP) were dosed as positive controls at 40 mg/kg q12 h for 6 days. Results The addition of DUR effectively lowered the SUL MIC50/90 from 8/16 to 0.25/0.5 mg/L vs. B. pseudomallei and from 8/8 to 1/2 mg/L for B. mallei. All untreated mice in the melioidosis model succumbed to infection within 3 days of challenge. 60% survival was observed for both dose arms of SUL-DUR as compared with 40% survival observed for both CIP and DOX. Conclusion Preliminary preclinical data demonstrating robust in vitro and in vivo antibacterial activity of SUL-DUR against Burkholderia spp. suggests this combination may be an effective new therapy for the treatment of these challenging pathogens. Disclosures All authors: No reported disclosures.