AZD9773, a novel anti-TNFα immune Fab in development for severe sepsis and septic shock: demonstration of safety and efficacy in a murine CLP sepsis model

TNFα is thought to play a central role in the pathogenesis of sepsis and septic shock. AZD9773 is an ovine polyclonal anti-human TNFα immune Fab comprising TNFα-directed and nonspecific Fab populations. AZD9773 potency and pharmacokinetic attributes such as a shorter half-life distinguish it from anti-TNF monoclonal antibodies, which have been assessed previously in clinical sepsis models. Here we explore the preclinical safety/efficacy of AZD9773 in a mouse cecal ligation puncture (CLP) model. There are currently no reports of anti-TNF agent efficacy in mouse CLP; rather, TNFα neutralization is associated with minimal/no effect or increased mouse mortality. As AZD9773 is differentiated from other anti-TNFα agents based on neutralizing potency and pharmacokinetic attributes, we studied both the safety and efficacy of this product in mouse CLP models.

We studied AZD9773 (plus imipenem) effects in two mouse CLP models: a mild-grade model to explore the potential for AZD9773 to compromise mouse survival, and a severe-grade model to test AZD9773 efficacy. CLP (mild-grade sepsis) comprised 100% cecal ligation and single 20-gauge needle puncture, while CLP (severe-grade sepsis) comprised 100% cecal ligation and single 18-gauge needle puncture. Saline resuscitation and imipenem administration were included in both models. Since AZD9773 does not bind or neutralize murine TNFα, the CLP models were established in Tg1278/-/- (human TNFα transgene/mouse TNFα null) mice. An equivalent protein dose of DigiFab (plus imipenem) served as an irrelevant Fab control. Survival was monitored for 5 days.

The control severe-grade model resulted in approximately 20% survival at 5 days. Therapeutic i.p. dosing of AZD9773 bid from 24 to 60 hours (first dose 4,000 units/kg, second to fourth doses 2,000 units/kg) resulted in statistically significant increases in survival (>70%) compared with i.p. DigiFab control (n = 15 per group). The mild-grade model resulted in 63% survival with imipenem alone, 65% survival with AZD9773 and 69% survival with DigiFab at 5 days. Thus, therapeutic dosing of AZD9773 bid from 24 to 60 hours (schedule/dose/route as previously) did not result in significantly different survival outcomes versus either DigiFab or imipenem alone (n = 60 per group).

These data demonstrate for the first time that TNFα neutralization in a murine CLP model improves survival in a severe sepsis setting. Moreover, contrasting with previous reports, TNF suppression in mild-grade CLP models is not associated with increased mortality. These findings support the hypothesis that AZD9773 has potential to be differentiated from other anti-TNF agents as a therapeutic intervention in sepsis.

All authors are employees of AstraZeneca.