AZD9773 is a novel and potent anti-TNF-α polyclonal ovine immune Fab

The release of cytokines into the circulation is an essential part of the inflammatory cascade that underlies sepsis. Experimental and clinical data have shown that the pro-inflammatory cytokine, tumour necrosis factor-α (TNF-α), is a principal mediator of this cascade (Marshall 2003, Balk et al 1989, Bone et al 1989).
The investigational drug AZD9773, intended for intravenous infusion, contains ovine immune fragments (Fabs) of immunoglobulin G (IgG) that bind to human (hu)TNFα. Here we describe the in vitro and in vivo pharmacology of AZD9773.
AZD9773 binding to human TNF-α was assessed using surface plasmon resonance (SPR) technology. AZD9773 functional potency was profiled versus recombinant human (r-hu)TNFα and natural (WHO International Standard) (n)TNFα in TNF-α-mediated cytotoxicity assays using the L929 cell line. Finally, humanised mice (Tg1278/TNF-/-: hu-TNF-α transgenic, murine TNF-α null) were used to assess AZD9773 effects on endotoxin-induced serum cytokines, chemokines and related factors.

SPR assays revealed that r-hu-TNF-α bound to immobilised AZD9773 total Fabs with an equilibrium dissociation constant (K_d) of ~60 nM. AZD9773 neutralised both r-hu- and n-TNF-α biological activity in the L929 cytotoxicity assays. AZD9773 neutralised r-hu-TNF-α with an apparent inhibitory constant (K_i) of approximately 40 pM. In humanised mice, AZD9773 produced a statistically significant reduction in 29 out of 60 serum cytokines and related factors (including hu-TNF-α and murine interleukin (IL-6)).
AZD9773 is a potent TNF-α neutralising ovine immune Fab and, considering the modest AZD9773:TNF-α binding affinity, the data indicates that there is significant synergy in neutralising TNF-α bioactivity between the polyclonal anti-TNF-α species that comprise AZD9773. The in vivo suppression of 29 out of 60 induced serum cytokines, chemokines and related factors, confirms the significant role for TNF-α in eliciting acute endotoxin responsiveness.

All authors are current employees of AstraZeneca.