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

Abstract

Background: Triple-negative breast cancers (TNBCs) are typically more aggressive and result in poorer outcomes than other breast cancers because treatment options are limited due to lack of hormone receptors or amplified human epidermal growth factor receptor 2 (HER2). Many TNBCs overexpress the epidermal growth factor receptor (EGFR) or manifest amplification of the EGFR gene, supporting EGFR as a therapeutic target. While EGFR-directed small molecule inhibitors have shown limited effectiveness in clinical settings, use of EGFR as a mechanism of delivering enzymatic cytotoxins to TNBC has not been demonstrated. Methods: Using the single-chain variable fragment (scFv) of the 806 antibody that binds only cells with overexpressed, misfolded, or mutant variants of the EGFR, a recombinant immunotoxin was engineered through gene fusion with Pseudomonas aeruginosa Exotoxin A (806-PE38). The potency of 806-PE38 on reducing TNBC cell growth in vitro and in xenograft models (n 6) was examined for six TNBC cell lines. All statistical tests were two-sided. Results: 806-PE38 statistically significantly reduced the viability of all tested TNBC lines, with IC 50 values below 10 ng/mL for three of six cell lines, while not affecting cells with wild-type EGFR (IC 50 >300 ng/mL). Systemic treatments with 806-PE38 vs vehicle resulted in statistically significantly reduced tumor burdens (806-PE38 mean ¼ 128 mm 3 [SD ¼ 46 mm 3 ] vs vehicle mean ¼ 749 mm 3 [SD ¼ 395 mm 3 ], P ¼ .001) and increased median survival (806-PE38 median ¼ 82 days vs vehicle median ¼ 50 days, P ¼ .01) in a MDA-MB-468 TNBC mouse xenograft. Deletion of the catalytic residue eliminated both cytotoxic activity in vitro and the reduction in tumor burden and survival (P ¼ .52). Conclusions: These data support the further development of the 806-PE38 immunotoxin as a therapeutic agent for the treatment of patients with EGFR-positive TNBC. Follow-up experiments with combination therapies will be attempted to achieve full remissions.

The Therapeutic Potential of PI3K/Akt/mTOR Inhibitors in Breast Cancer: Rational and Progress

“…The addition of everolimus was well tolerated; however, it did not lead to any significant improvement in terms of RR (48% vs. 30% in favor of everolimus) and pathological CR (30% vs. 26% in favor of everolimus) [Gonzalez-Angulo et al, 2011]. Despite triple negative BC is HER2-, everolimus has been examined in a regimen with anti-HER2 agents since EGFR is high-amplified in $50% of triple negative BC tumors [Reis-Filho and Tutt, 2008;Simon et al, 2016], providing a robust rationale for exploration the association between an anti-EGFR and a mTOR inhibitor to determine overlap in the tumors that were refractory to anti-EGFR drugs [Gogineni and DeMichele, 2012;Passiglia et al, 2015]. Though the mTOR inhibitors paradoxically stimulate the AKT pathway [Sun et al, 2005], this activation could probably serve as a mechanism for resistance to mTOR inhibitors [Hahn et al, 2009;Jerusalem et al, 2014].…”

Anti-metastatic and anti-proliferative activity of eugenol against triple negative and HER2 positive breast cancer cells

“…Breast cancer is a heterogeneous complex of diseases [ 3 ] and can be classified into different subtypes based on biological characteristics (traditional classification systems), or gene expression patterns (molecular classification) [ 4 ]. Triple-negative breast cancer (TNBC) has a distinct aggressive molecular subtype, characterized by lack of progesterone receptor (PR), estrogen receptor (ER), and human epidermal growth factor receptor-2 (HER-2) expression [ 5 ] resulting in poorer outcomes than other subtypes [ 6 ]. Moreover, TNBC can be classified in different subtyping based on gene expression profiling into basal like1, basal-like 2, an immunomodulatory subtype, mesenchymal, mesenchymal stem cell-like and luminal androgen receptor subtype [ 7 ].…”

Targeting Receptors on Cancer Cells with Protein Toxins

“…Regarding triple-negative breast cancer, EGFR amplification has been reported to occur in approximately 60% of cases when analyzed by silver in situ hybridization, validating this receptor as a target in this malignancy [ 6 ]. The scFv of 806 was fused with PE38 to produce the 806-PE38 immunotoxin [ 33 ]. In vitro analysis indicated that it killed triple-negative breast carcinoma cell lines with EGFR overexpression but not lines that only expressed wildtype EGFR at normal levels [ 33 ].…”