Tifacogin increases bacterial clearance from blood

Multiple animal studies show that tifacogin (rTFPI; Chiron Corp.) improves survival when administered after lethal challenge with bacteria. Since some anticoagulant agents fail to rescue challenged animals, this effect of tifacogin may be due to mechanisms beyond anticoagulant activity. Other data relevant to tifacogin action include: IL-6 levels decrease in tifacogin-treated animals, infused tifacogin circulates as fragments, domains essential for anticoagulation are confined to TFPI's N-terminus, the C-terminus of tifacogin binds to LPS and, in a preliminary experiment, we found that a tifacogin peptide (amino acids 255–276) inhibited LPS-induced IL-6 and TNF-α production. We hypothesize that tifacogin's C-terminus acts on the innate immune system to promote bacterial clearance. To test this we mixed C-terminal tifacogin peptides with whole blood inoculated with opsonization-resistant bacteria (Escherichia coli 018:K1:H7 or a clinical isolate of coagulase-negative Staphylococci ATCC 700583), and then assessed bacteria growth. Controls were: a scrambled peptide from tifacogin's C-terminus or cultures without fragments. Both controls supported vigorous bacterial growth. Peptide 255–276 almost eradicated E. coli at 3 μM but not at 300 nM. Peptide 242–268 eliminated most bacteria at 3 μM and 300 nM, and in separate experiments inhibited growth by 90% at 10–30 nM. This region of tifacogin is also associated with heparin binding. Not surprisingly, 3 U/ml heparin completely antagonized peptide 242–268's activity. Unlike the bactericidal peptide LL37, peptide 242–268 was unable to clear bacteria in the absence of whole blood. This suggests that tifacogin interacts with a blood component, such as cellular mediators of immunity. Similar results were obtained with Staphylococci. The finding that tifacogin has bacterial clearance activity in addition to its anticoagulant activity is additional support for the rationale underlying Chiron's ongoing phase III study of tifacogin in patients with severe community-acquired pneumonia.

Figure 1