Peptide Vaccines and Peptidomimetics of EGFR (HER-1) Ligand Binding Domain Inhibit Cancer Cell Growth In Vitro and In Vivo

Abstract

Epidermal growth factor receptor (EGFR) is a validated target for several cancers including lung, colorectal, and certain subtypes of breast cancer. Cetuximab targets ligand binding of EGFR, but major problems like high cost, short t1/2, toxicity, and emergence of resistance are associated with the drug. Immunization with EGFR B cell epitopes will train the immune system to produce specific Abs that can kill cancer cells. Also, therapy with stable, less-expensive, and nontoxic EGFR peptide mimics will block EGFR signaling and inhibit cancer growth. We designed three peptides based on the contact sites between EGF and EGFR. The B cell epitopes were synthesized alone and also linked with the measles virus T cell epitope to produce a chimeric peptide vaccine. The peptide vaccines were immunogenic in both mice and rabbits and Abs raised against the vaccine specifically bound EGFR-expressing cells and recombinant human EGFR protein. The peptide mimics and the anti-peptide Abs were able to inhibit EGFR signaling pathways. Immunization with the peptide vaccine or treatment with the B cell epitopes significantly reduced tumor growth in both transplantable breast and lung cancer models. Immunohistochemical analysis also showed significant reductions in microvascular density and actively dividing cells in the tumor sections after treatment in the FVB/n breast cancer model. The 418–435 B cell epitope was the best candidate both as a vaccine or peptide mimic because it caused significant inhibition in the two mouse models. Our results show that this novel EGFR B cell epitope has great potential to be used as a vaccine or treatment option for EGFR-expressing cancers.

IGF-1R peptide vaccines/mimics inhibit the growth of BxPC3 and JIMT-1 cancer cells and exhibit synergistic antitumor effects with HER-1 and HER-2 peptides

“…The 4 epitopes, IGF-IR-6-26, IGF-IR-26-42, IGF-IR-56-81, and IGF-IR-234-252, so named according to their epitope span,were chemically synthesized and characterized, as previously described. 32 Based on initial characterization in vitro, we selected 2 of the peptide sequences, IGF-1R-56-81 and IGF-1R-234-252 for integration into an engineered recombinant peptide with a "promiscuous" Measles virus fusion (MVF) T-cell epitope (KLLSLIKGVIVHRLEGVE) with a 4-residue (GPSL) linker sequence. We subsequently examined the immunogenicity of these peptide mimics in rabbits and mice, as previously described.…”

“…Our rationale for epitope design was based on the ligand-binding site of the receptor using crystallographic structures, mutagenesis studies, and models of the receptor-ligand complex. 37 The other HER-family receptor epitopes included herein encompassed HER-1-418, 32 HER-2-266, 33 and HER-2-597, 34 HER-1 and HER-2 targeting epitopes, previously synthesized and characterized for their respective antitumor properties in vitro and in vivo as potential cancer vaccine candidates.…”

“…37 Peptide synthesis was performed as previously described. 66 Briefly, synthesis was performed on a solid-phase peptide synthesizer using Fmoc chemistry; crude peptides were purified by reverse-phase HPLC, after which characterization was done by mass spectrometry. Amino acid sequences and molecular Table 1.…”

“…46 Furthermore, we recently demonstrated antitumor effects of HER-1 peptide vaccines and peptide mimics in breast cancer cells both in vitro and in vivo. 32 Combination treatment of JIMT-1 and BxPC3 cancer cells with HER-1-418 and either IGF-IR-56 or IGF-1R-234 peptides inhibited cell proliferation to a greater degree (*p < 0.001) than did single peptides (**p < 0.005) (Fig. 7A).…”

“…[32][33][34] Thus, we evaluated the effects of combining agents targeting the IGF-1R 56-81 epitope with those antagonizing the HER-1 418 epitope in breast and pancreatic cancers. Our results showed a significant decrease in proliferation and receptor phosphorylation when these epitopes were used in combination.…”