Pharmacodynamic and antineoplastic activity of BI 836845, a fully human IGF ligand-neutralizing antibody, and mechanistic rationale for combination with rapamycin

Insulin-like growth factor (IGF) signaling is thought to play a role in the development and progression of multiple cancer types. To date, therapeutic strategies aimed at disrupting IGF signaling have largely focused on antibodies that target the IGF-I receptor (IGF-IR). Here, we describe the pharmacologic profile of BI 836845, a fully human monoclonal antibody that utilizes an alternative approach to IGF signaling inhibition by selectively neutralizing the bioactivity of IGF ligands. Biochemical analyses of BI 836845 demonstrated high affinity to human IGF-I and IGF-II, resulting in effective inhibition of IGF-induced activation of both IGF-IR and IR-A in vitro. Cross-reactivity to rodent IGFs has enabled rigorous assessment of the pharmacologic activity of BI 836845 in preclinical models. Pharmacodynamic studies in rats showed potent reduction of serum IGF bioactivity in the absence of metabolic adverse effects, leading to growth inhibition as evidenced by reduced body weight gain and tail length. Moreover, BI 836845 reduced the proliferation of human cell lines derived from different cancer types and enhanced the antitumor efficacy of rapamycin by blocking a rapamycin-induced increase in upstream signaling in vitro as well as in human tumor xenograft models in nude mice. Our data suggest that BI 836845 represents a potentially more effective and tolerable approach to the inhibition of IGF signaling compared with agents that target the IGF-I receptor directly, with potential for rational combinations with other targeted agents in clinical studies.

Wound healing and degradation of the fibrin sealant Beriplast P following partial liver resection in rabbits

The objective of this study was to investigate the degradation kinetics of the fibrin sealant (FS) Beriplast P in an experimental liver surgery model in rabbits. A partial liver resection was performed in 21 rabbits, and the wound area covered with Beriplast P to ensure hemostasis. Wound healing of the resection sites was evaluated morphologically over 11 weeks. Degradation of the FS was evaluated by measuring the thickness of the remaining fibrin layer. Plasma samples were analyzed for antibodies against fibrinogen, albumin, thrombin, fibrin, and factor XIII. No postoperative hemorrhage was observed, indicating successful hemostasis throughout. The FS was degraded with a half-life of about 25 days postapplication and was completely replaced by granulation tissue within 9 weeks. The FS degradation and tissue development followed the general stages of wound healing: inflammation and resorption, proliferation, organization and production of collagen, maturation, and scarring. An immune reaction was elicited against the main four human proteins of the FS. The antibody titers peaked on day 14, with a gradual decrease thereafter. We conclude that the FS accomplished hemostasis, facilitated healing in accordance with natural processes, and was completely degraded over time. In humans, the reduced immunogenicity of the FS would potentially increase its degradation half-life.

Hypotension with intravenous immunoglobulin therapy: importance of pH and dimer formation

Therapy with intravenous immunoglobulin preparations has been used effectively in a wide range of conditions. Although generally well tolerated, intravenous immunoglobulin preparations may be associated with transient hypotension in some patients. This study examined the role of different immunoglobulin G fractions in the development of intravenous immunoglobulin-induced hypotension in an anaesthetized rat model and assessed the effects of a new liquid immunoglobulin prepared at a low pH on both the formation of immunoglobulin G dimers and the development of hypotension. The effects of this new preparation in an experimental autoimmune encephalomyelitis model were also evaluated. Results from the haemodynamic studies indicated that immunoglobulin G dimers in polyclonal immunoglobulin G are responsible for the hypotensive events associated with some immunoglobulin preparations. They also showed that adjustment to an acidic pH results in the rapid dissociation of immunoglobulin G dimers and prevents the development of hypotension. Additional experiments demonstrated that only immunoglobulin G dimers with a functional Fc fragment can bind to Fcgamma receptors on macrophages to induce the release of blood pressure-lowering mediators. Moreover, essentially monomeric Fc fragments can block the blood pressure-lowering effects of immunoglobulin G dimers. Preparation of a new liquid intravenous immunoglobulin with the pH adjusted to 4.3 prevents the formation of immunoglobulin G dimers even over long-term storage and does not significantly affect blood pressure in a rat model. This preparation is as effective as other intravenous immunoglobulin preparations in ameliorating symptoms of experimental autoimmune encephalomyelitis. These results, like those from previous studies, indicate that preparation of intravenous immunoglobulin at a low pH substantially reduces immunoglobulin G dimerization; this effect significantly decreases the potential for intravenous immunoglobulin to induce hypotension without reducing its clinically relevant biological activity.

A comparison of fibrin sealants in relation to their in vitro and in vivo properties

INTRODUCTION

Fibrin sealants (FS) have been used for many years to facilitate hemostasis and to provide suture support and sealing/adhesion of tissues after surgery. While their composition is similar, different formulations, application devices, and varying concentrations of key components mean that the properties of clots formed by individual FS can be diverse.

MATERIALS AND METHODS

We performed several studies, including animal models, to compare the properties of 12 different commercially available FS/application device combinations using partial liver and kidney resection models to assess hemostatic efficacy and a novel pig skin model to measure adhesive clot strength. The quality of mixing was determined using colored spray images.

RESULTS

Although the FS tested shared the principle of combining fibrinogen and thrombin, major differences were found between the individual preparations with regard to hemostatic efficacy. Two pre-requisites for successful early hemostasis were identified--adequate clottable protein content and the ability of the application device to effectively mix the fibrinogen and thrombin components of the FS. Factor XIII activity was a key determinant in prevention of re-bleeding and premature clot lysis. Furthermore, FS lacking measurable factor XIII activity formed the weakest, softest clots.

CONCLUSIONS

Clearly, all FS are not the same, and their different characteristics may potentially translate into different clinical outcomes. In our studies, while all FS tested performed well on individual parameters, Beriplast P (Aventis Behring) was the foremost FS in consistently providing early hemostasis, minimizing the risk of re-bleeding, and providing strong adhesive clots capable of resisting mechanical forces.

The importance of factor XIII as a component of fibrin sealants

BACKGROUND

The need for factor XIII (FXIII) in fibrin sealant is subject to discussions. Some commercially available fibrin sealants (FS) contain high levels of FXIII (up to 70-80 U/mL) while others contain low levels or none. The objective of the present studies was to investigate the need for FXIII in FS.

MATERIALS AND METHODS

Beriplast P, a commercial FS containing 40-80 U/mL FXIII, was compared with FS with different concentrations of FXIII or FXIII depleted FS. In Study 1, Beriplast P or FS with 4 U/mL FXIII was allowed to cross-link for 0.25, 1, and 2 min and the resulting fibrin gamma- and beta-chains as well as gamma-gamma-chain dimers were analyzed by SDS-PAGE and densitometry. In Study 2, a series of six FS was prepared from fibrinogen containing 0 (FS-FXIII), 17.5, 35, 70, 140, and 280 U/mL FXIII. The intrasealant strength was determined using a biomechanical test (twin-bottle test). In Study 3, 18 rabbits underwent bilateral partial kidney resection (acute model); right (n = 18) and left (n = 18) kidneys were treated with Beriplast P or FS with 4 U/mL FXIII (FS + 4U FXIII). In Study 4, rabbits were randomly assigned to receive FXIII depleted FS (FS-FXIII) (n = 15); FS + 3 U/mL FXIII (n = 10); FS + 10 U/mL FXIII (n = 10); or Beriplast P (n = 15), after partial rabbit kidney resection (chronic model). The primary endpoint for Studies 3 and 4 was hemostasis.

RESULTS

In Study 1, Beriplast P produced significantly more fibrin gamma-chain cross-linking in the observed period than FS with 4 U/mL FXIII. In Study 2, fibrin clot strength increased as a function of FXIII concentration with a maximum of 70 U/mL. In Study 3, significantly more animals achieved hemostasis in the Beriplast P treated group than in the FS + 4U FXIII group (P = 0.03 at 15 s; P < 0.001 at 1 and 2 min). In Study 4, FS containing FXIII (all concentrations) achieved more efficient hemostasis and reduced the need for respray compared with FS-FXIII. Beriplast P was associated with a lower incidence of postoperative adhesions compared with the other treatment groups. At autopsy, the majority of clots formed from FXIII containing FS exhibited mild to moderate clot lysis, whereas the majority of clots in the FS-FXIII group showed severe lysis.

CONCLUSIONS

FXIII, when added to fibrinogen concentrate in FS, improved fibrin cross-linking and clot strength. FXIII containing FS achieved more effective hemostasis than FXIII depleted FS. FXIII is an essential component of commercial FS and should be present in FS at an optimal concentration of about 40-80 U/mL.

Treatment of porcine sepsis with high-dose antithrombin III reduces tissue edema and effusion but does not increase risk for bleeding

We evaluated the effectiveness of antithrombin III (AT III) infusions designed to achieve supraphysiologic plasma levels of this serine protease inhibitor in preventing vascular permeability and disseminated intravascular coagulation in a pig model of sepsis. In addition, we determined whether high AT III doses were associated with increased bleeding risk. Sepsis was induced in 18 pigs by injection of lipopolysaccharide (LPS) (0.25 microg/kg per h for 3 h). At 90 min after the start of LPS infusion, pigs were randomized (n = 6 per group) to receive either human serum albumin as a placebo, AT III 120/5 (120 U/kg, 30-min bolus + 5 U/kg per h for 240 min), or AT III 250/10 (250 U/kg + 10 U/kg per h). Three additional animals served as negative controls (no LPS, no AT III). Treatment with AT III significantly reduced the amount of effluents in body cavities and fibrin monomers. AT III did not significantly increase bleeding risk as determined by organ hemorrhage. An additional assessment of AT III's bleeding risk [skin bleeding time (SBT)] was carried out in 35 nonseptic pigs treated with either AT III alone (120/5 or 250/10) or in the combination with heparin. Heparin administration alone produced a dose-dependent increase in SBT, but AT III alone did not. Addition of AT III 120/5 to heparin did not induce a further increase in bleeding time over heparin alone. These results indicate that administration of AT III in doses designed to achieve very high plasma concentrations significantly ameliorates symptoms of sepsis-induced vascular leakage and disseminated intravascular coagulation without increasing bleeding risk.