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.

Aluminum hydroxide influences not only the extent but also the fine specificity and functional activity of antibody responses to tick-borne encephalitis virus in mice.

Aluminum hydroxide is the most widely used adjuvant in human vaccines and serves as a potent enhancer of antibody production. Its stimulatory effect strongly depends on the adsorption of the antigen to the adjuvant, which may influence antigen presentation and, as a consequence, the fine specificity of antibody responses. Such variations can have functional consequences and can modulate the effectiveness of humoral immunity. Therefore, we investigated the influence of aluminum hydroxide on the fine specificity of antibody responses in a model study in mice using an inactivated purified virus particle, the flavivirus tick-borne encephalitis (TBE) virus, as an immunogen. To dissect and quantify the specificities of polyclonal antibodies in postimmunization sera, we established a platform of immunoassays using recombinant forms of the major target of neutralizing antibodies (protein E) as well as individual domains of E (DIII and the combination of DI and DII [DI+DII]). Our analyses revealed a higher proportion of neutralizing than virion binding (as detected by enzyme-linked immunosorbent assay) antibodies after immunization with aluminum hydroxide. Furthermore, the induction of antibodies to DIII, a known target of potently neutralizing antibodies, as well as their contributions to virus neutralization were significantly greater in mice immunized with adjuvant and correlated with a higher avidity of these antibodies. Thus, our data provide evidence that aluminum hydroxide can lead to functionally relevant modulations of antibody fine specificities in addition to its known overall immune enhancement effect.

Involvement of lipids in different steps of the flavivirus fusion mechanism.

Flavivirus membrane fusion is triggered by acidic pH and mediated by the major envelope protein E. A structurally very similar fusion protein is found in alphaviruses, and these molecules are designated class II viral fusion proteins. In contrast to that of flaviviruses, however, alphavirus fusion has been shown to be absolutely dependent on the presence of cholesterol and sphingomyelin in the target membrane, suggesting significant differences in the fusion protein-membrane interactions that lead to fusion. With the flavivirus tick-borne encephalitis virus (TBEV), we have therefore conducted a study on the lipid requirements of viral fusion with liposomes and on the processes preceding fusion, specifically, the membrane-binding step and the fusion-associated oligomeric switch from E protein dimers to trimers. As with alphaviruses, cholesterol had a strong promoting effect on membrane binding and trimerization of the fusion protein, and-as shown by the use of cholesterol analogs-the underlying interactions involve the 3beta-hydroxyl group at C-3 in both viral systems. In contrast to alphaviruses, however, these effects are much less pronounced with respect to the overall fusion of TBEV and can only be demonstrated when fusion is slowed down by lowering the temperature. The data presented thus suggest the existence of structurally related interactions of the flavivirus and alphavirus fusion proteins with cholesterol in the molecular processes required for fusion but, at the same time, point to significant differences between the class II fusion machineries of these viruses.