The enlargement of the hormone immune deprivation concept to the blocking of TGFα-autocrine loop: EGFR signaling inhibition

Transforming growth factor alpha (TGFα) is a potent ligand of the epidermal growth factor receptor (EGFR). EGFR is frequently over-expressed in epithelial tumors and endogenous ligands, mostly TGFα, are frequently co-expressed with EGFR, potentially resulting in autocrine stimulation of tumor cell growth. Therefore, different therapeutic approaches aim for the inactivation of TGFα/EGF/EGFR signaling system, but no approach is based on TGFα as a target. The principal goal of this work was to assess the potential of an active specific immunotherapy approach to block the TGFα/EGFR autocrine loop. For the proof of the concept, a fusion protein between human TGFα (hTGFα) and P64k protein from Neisseria meningitidis was generated, and its immunogenicity characterized in a mouse model using different adjuvants. All immunogens were effective for the generation of specific humoral responses against hTGFα. The inmunodominant epitope of hTGFα when immunizing mice with the fusion protein involved the C-loop/C-terminal region. This region includes key residues for hTGFα binding to EGFR. The anti-hTGFα immune mice sera recognized the natural hTGFα precursor in A431 cells and hTGFα-transfected 3T3 fibroblasts as revealed by flow cytometry analysis and immunoblotting. They inhibited the binding of ¹²⁵I-TGFα to the EGFR, EGFR-autophosphorylation, and downstream activation of MAP kinases as well as proliferation of two EGFR-expressing human carcinoma cell lines. These data suggest that EGFR signaling activation by the hTGFα autocrine loop may be inhibited in vivo by induction of specifically blocking antibodies. The fusion protein reported in this paper could be a potential immunogen for the development of a new cancer vaccine.