Generation of monoclonal antibodies to chemokine receptors

A novel monoclonal antibody to fibroblast growth factor 2 effectively inhibits growth of hepatocellular carcinoma xenografts

Expression of fibroblast growth factor 2 (FGF2) is believed to be a contributing factor to the growth of a number of tumor types, including hepatocellular carcinoma (HCC). However, the potential of monoclonal antibodies that neutralize FGF2 for treatment of patients with cancer has not yet been explored in clinical trials. We therefore generated a novel monoclonal antibody (mAb), GAL-F2, specific for FGF2 and characterized its properties in vitro and in vivo. GAL-F2 binds to a different epitope than several previous anti-FGF2 mAbs tested. This novel epitope was defined using chimeric FGF1/FGF2 proteins and alanine scanning mutagenesis and was shown to comprise amino acids in both the amino and carboxy regions of FGF2. GAL-F2 blocked binding of FGF2 to each of its four cellular receptors, strongly inhibited FGF2-induced proliferation and downstream signaling in human umbilical vein endothelial cells, and inhibited proliferation and downstream signaling in two HCC cell lines. Moreover, GAL-F2, administered at 5 mg/kg i.p. twice weekly, potently inhibited growth of xenografts of the SMMC-7721, HEP-G2, and SK-HEP-1 human HCC cell lines in nude mice, and in some models, had a strong additive effect with an anti-VEGF mAb or sorafenib. Treatment with GAL-F2 also blocked angiogenesis and inhibited downstream cellular signaling in xenografts, indicating its antitumor mechanism of action. Our report supports clinical testing of a humanized form of the GAL-F2 mAb for treatment of HCC and potentially other cancers.

Isotype-dependent inhibition of tumor growth in vivo by monoclonal antibodies to death receptor 4

To explore an approach for death receptor targeting in cancer, we developed murine mAbs to human death receptor 4 (DR4). The mAb 4H6 (IgG1) competed with Apo2L/TNF-related apoptosis-inducing ligand (DR4's ligand) for binding to DR4, whereas mAb 4G7 (IgG2a) did not. In vitro, both mAbs showed minimal intrinsic apoptosis-inducing activity, but each triggered potent apoptosis upon cross-linking. In a colon tumor nude mouse model in vivo, mAb 4H6 treatment without addition of exogenous linkers induced apoptosis in tumor cells and caused complete tumor regression, whereas mAb 4G7 partially inhibited tumor growth. An IgG2a isotype switch variant of mAb 4H6 was much less effective in vivo than the parent IgG1-4H6, despite similar binding affinities to DR4. The same conclusion was obtained by comparing other IgG1 and IgG2 mAbs to DR4 for their anti-tumor activities in vivo. Thus, the isotype of anti-DR4 mAb may be more important than DR4 binding affinity for tumor elimination in vivo. Anti-DR4 mAbs of the IgG1 isotype may provide a useful tool for investigating the therapeutic potential of death receptor targeting in cancer.

Determination of Residues Involved in Ligand Binding and Signal Transmission in the Human IFN-α Receptor 2

The human IFN-α receptor (hIFNAR) is a complex composed of at least two chains, hIFNAR1 and hIFNAR2. We have performed a structure-function analysis of hIFNAR2 extracellular domain regions using anti-hIFNAR2 mAbs (1D3, 1F3, and 3B7) and several type I human IFNs. These mAbs block receptor activation, as determined by IFN-stimulated gene factor 3 formation, and block the antiviral cytopathic effects induced by type I IFNs. We generated alanine substitution mutants of hIFNAR2-IgG and determined that regions of hIFNAR2 are important for the binding of these blocking mAbs and hIFN-α2/α1. We further demonstrated that residues E78, W101, I104, and D105 are crucial for the binding of hIFN-α2/α1 and form a defined protrusion when these residues are mapped upon a structural model of hIFNAR2. To confirm that residues important for ligand binding are indeed important for IFN signal transduction, we determined the ability of mouse L929 cells expressing hIFNAR2 extracellular domain mutants to mediate hIFN signal. hIFN-α8, previously shown to signal a response in L929 cells expressing hIFNAR1, was unable to signal in L929 cells expressing hIFNAR2. Transfected cells expressing hIFNAR2 containing mutations at residues E78, W101, I104, or D105 were unresponsive to hIFN-α2, but remained responsive to hIFN-β. In summary, we have identified specific residues of hIFNAR2 important for the binding to hIFN-α2/1 and demonstrate that specific regions of the IFNAR interact with the subspecies of type I IFN in different manners.