To target IFNγ to HSC, we modified IFNγ with PDGFβR-recognizing cyclic peptide (PPB) using different conjugation strategies as illustrated in Fig. 1E. PPB was directly conjugated to IFNγ (IFNγ-PPB) or by way of a 2 kDa hydrophilic hetero-bifunctional PEG linker (IFNγ-PEG-PPB). In addition, we synthesized IFNγ-PEG as a control. The synthesis details are illustrated in Supporting Fig. 1. The synthesized conjugates were characterized by western blot analyses with anti-IFNγ and anti-PPB antibodies (Supporting Fig. 2). Because chemical modifications of cytokines can
diminish their biological activity, click here we examined the activity of the IFNγ conjugates compared to unmodified IFNγ
in mouse RAW macrophages. These cells express the IFNγR but lack PDGFβR. IFNγ and its constructs IFNγ-PPB, IFNγ-PEG, and IFNγ-PEG-PPB all induced a similar dose-dependent increase in nitric oxide (NOx) release in RAW cells (Fig. 1F). There was no significant difference in dose-response slopes, demonstrating that all IFNγ conjugates retained full biological activity. IFNγ binds to its receptor, which is strictly species-specific, whereas PDGFβR binding is not. In order to discriminate between IFNγR- and PDGFβR-mediated http://www.selleckchem.com/products/Lapatinib-Ditosylate.html bindings, we used mouse NIH3T3 fibroblasts, primary rat HSC, and human LX2 hepatic stellate cells. The results Thiamine-diphosphate kinase confirmed the species specificity of IFNγ; mouse IFNγ and mouse derived IFNγ-PEG showed binding to mouse 3T3 fibroblasts (Fig. 2A) but not to rat HSC and human HSC (Fig. 2B; Supporting Fig. 3). However, PPB-modified mouse IFNγ conjugates showed high binding to mouse, rat, and human cells (Fig. 2A,B; Supporting Fig. 3), which was almost completely blocked with anti-PDGFβR IgG (Fig. 2B). This demonstrates the
specific binding of PPB-modified IFNγ constructs to PDGFβR, which is species-nonspecific. Subsequently, we investigated the antifibrotic effects of the constructs in mouse 3T3 fibroblasts and in human HSC after their activation with TGFβ. Both mouse IFNγ and IFNγ conjugates induced significant reduction in collagen expression in mouse cells (Fig. 2C,D). In addition, mouse IFNγ and IFNγ conjugates inhibited PDGF-induced cell proliferation in 3T3 fibroblasts as assessed by thymidine incorporation assays (Fig. 2E). Interestingly, in human LX2 cells, TGFβ1-induced collagen expression was strongly inhibited by treatment with the PDGFR-specific IFNγ constructs (Fig. 2C,D), whereas unmodified mouse IFNγ and IFNγ-PEG did not induce any effect in human cells due to species differences. These results clearly demonstrate that mouse IFNγ, which is inactive in human cells, can become biologically active in other species by directing it to the PDGFβR.