Novel monoclonal antibody specific for the de2‐7 epidermal growth factor receptor (EGFR) that also recognizes the EGFR expressed in cells containing amplification of the EGFR gene

Abstract

In some respects, the EGFR appears to be an attractive target for tumor-targeted antibody therapy: it is overexpressed in many types of epithelial tumor and inhibition of signaling often induces an anti-tumor effect. The use of EGFR specific antibodies, however, may be limited by uptake in organs that have high endogenous levels of the wild type EGFR such as the liver. The de2-7 EGFR (or EGFRvIII) is a naturally occurring extracellular truncation of the EGFR found in a number of tumor types including glioma, breast, lung and prostate. Antibodies directed to this tumor specific variant of the EGFR provide an alternative targeting strategy, although the lower proportion of tumors that express the de2-7 EGFR restricts this approach. We describe a novel monoclonal antibody (MAb 806 The delta 2-7 epidermal growth factor receptor (de2-7 EGFR) is a naturally occurring extracellular truncation of the EGFR found in a number of tumor types including glioma, breast, lung and prostate. [1][2][3][4] In adults, the expression of the de2-7 EGFR appears restricted to tumors exhibiting amplification of the EGFR gene. 5 Prostate cancer maybe an exception to this observation, as the expression level of de2-7 and wild type EGFR appear to be inversely related in this tumor type. 2 The rearrangement seen in the de2-7 EGFR results in an in-frame mature mRNA lacking 801 nucleotides spanning exons 2-7. 6 -9 The corresponding EGFR protein contains a 267 amino acid deletion and a novel glycine residue at the fusion junction. 9 Although this truncated receptor does not bind ligand, it does possess low constitutive activity and imparts a significant growth advantage to glioma cells grown as tumor xenografts in nude mice 10 and is able to transform NIH3T3 cells. 11 The cellular mechanisms utilized by the de2-7 EGFR in glioma cells are not fully defined but include a decrease in apoptosis 12 and a small enhancement of proliferation. 12 The aberrant splicing event that generates the de2-7 EGFR leads to the formation of an unique junctional peptide in the N-terminal of the extracellular domain. 13 As this peptide sequence is not found in the wild type EGFR, its expression is restricted to tumor cells making it an attractive target for antibody therapy. Indeed, the production of both polyclonal 14 and monoclonal 3,15,16 antibodies specific to this unique peptide have been described. One potential drawback in targeting of the de2-7 EGFR is that it is only expressed in a portion of tumors containing EGFR gene amplification. Expression of the de2-7 EGFR has been analyzed in glioma by a number of groups with most reporting that approximately 30% of gliomas express the mutant receptor 13 with expression being lowest in anaplastic astrocytomas and highest in glioblastoma multiforme. 17 The proportion of positive cells within de2-7 EGFR expressing gliomas has been reported to range from 37-86%. 1 A very recent report found that all high-grade prostate carcinomas expressed the de2-7 EGFR 2 although this observation has not been confirmed. Expression in ...

Targeting a Cancer-Specific Epitope of the Epidermal Growth Factor Receptor in Triple-Negative Breast Cancer

“…The amount of surface EGFR on MDA-MB-468 cells was approximately five-fold higher than on HCC70 cells (Figure 2, A and B). The 806-immunotoxin bound to MDA-MB-468 cells slightly better than the HCC70 cells, with 5% to 10% of total EGFR accessible to 806-PE38, similar to reports of parental m806 binding (18). 806-PE38D553 exhibited similar binding activity as the active immunotoxin.…”

“…The m806 antibody binds cells expressing misfolded, amplified, or overexpressed EGFR but not to cells expressing wildtype EGFR ( [16][17][18] ). The m806 epitope is not accessible when the receptor is in an inactive monomer or activated dimer but is exposed in the locally misfolded (transitional), or "untethered," conformation, which preferentially occurs under oncogenic conditions (19,20).…”

Characterization of ABT-806, a Humanized Tumor-Specific Anti-EGFR Monoclonal Antibody

“…The human tumor cell lines A431 (human vulvar squamous carcinoma), U87MG (human glioma), and U87MGde2-7 (engineered from U87MG to overexpress EGFRvIII) utilized in previous published work with mAb806 and ch806 were provided by the Ludwig Institute for Cancer Research (Melbourne, Victoria, Australia) in 2010 (9,13). SCC15 cells, human head and neck squamous cell carcinoma (HNSCC), were acquired from the ATCC in 2002.…”

“…The targeted epitope is accessible in tumors with wild-type EGFR amplification or in tumors that express EGFRvIII, the most common deletion mutant of EGFR that lacks the ligand-binding domain of exons 2-7 and retains constitutive kinase activity (8)(9)(10). Thus mAb806 has tumor-specific binding properties and would not be expected to elicit the side effects, including skin rash, observed with other cetuximab-like EGFR targeting (mAbs) associated with targeting of normal tissues.…”

Therapeutic Inhibition of the Epidermal Growth Factor Receptor in High-Grade Gliomas: Where Do We Stand?

“…Using conjugates specifically targeting EGFRvIII such as MAb 806 or 3C10 may offer an alternative way of destroying tumor cells with possible clinical utility in combination therapy, a prospect that has to be investigated in further clinical trials (91,92).…”