Targeting epidermal growth factor receptor and SRC pathways in head and neck cancer

Epidermal growth factor receptor (EGFR), a member of the ErbB family of receptor tyrosine kinases (RTKs), is highly expressed in head and neck squamous cell carcinoma (HNSCC) where increased EGFR expression levels in tumors are associated with decreased survival. HNSCC patient responses to EGFR-targeted monotherapies in clinical trials, though significant, have been limited. Tumor signaling pathway components that work in cooperation with EGFR or provide compensation for the loss of EGFR-initiated signaling will be ideal targets for therapies to be used in combination with EGFR-targeted agents. Based on the current understanding of molecular signaling pathways and available agents, ErbB family-targeted and Src family-targeted agents represent strategies for further exploration. Here, we discuss agents targeting ErbB and Src family kinases in clinical development, provide an overview of completed and ongoing clinical trials, and outline a molecular rationale for combining ErbB- and Src-targeted therapeutics.     

Honokiol inhibits the growth of head and neck squamous cell carcinoma by targeting epidermal growth factor receptor

Here, we report the chemotherapeutic effect of honokiol, a phytochemical from Magnolia plant, on human head and neck squamous cell carcinoma (HNSCC). Treatment of HNSCC cell lines from different sub-sites, SCC-1 (oral cavity), SCC-5 (larynx), OSC-19 (tongue) and FaDu (pharynx) with honokiol inhibited their cell viability, which was associated with the: (i) induction of apoptosis, (ii) correction of dysregulatory cell cycle proteins of G0/G1 phase. Honokiol decreased the expression levels of epidermal growth factor receptor (EGFR), mTOR and their downstream signaling molecules. Treatment of FaDu and SCC-1 cell lines with rapamycin, an inhibitor of mTOR pathway, also reduced cell viability of HNSCC cells. Administration of honokiol by oral gavage (100 mg/kg body weight) significantly (P < 0.01-0.001) inhibited the growth of SCC-1 and FaDu xenografts in athymic nude mice, which was associated with: (i) inhibition of tumor cell proliferation, (ii) induction of apoptosis, (iii) reduced expressions of cyclins and Cdks, and (iv) inhibition of EGFR signaling pathway. Molecular docking analysis of honokiol in EGFR binding site indicated that the chemotherapeutic effect of honokiol against HNSCC is mediated through its firm binding with EGFR, which is better than that of gefitinib, a commonly used drug for HNSCC treatment.     

Targeting epidermal growth factor receptor signaling in the treatment of head and neck cancer

In this review, key aspects of epidermal growth factor receptor (EGFR) biology and the fruitful translation of these fundamental findings into recent treatment advances in head and neck squamous cell cancer (HNSCC) are highlighted. In contrast to a number of contemporary reviews of the EGFR, many of which focus on colorectal and nonsmall cell lung cancer, this review discusses the EGFR as a validated therapeutic target in HNSCC. Recent data confirm a survival advantage for the addition of the anti-EGFR monoclonal antibody cetuximab to definitive radiation therapy in locoregionally advanced HNSCC patients, as well as palliative benefits for patients with incurable recurrent and metastatic HNSCC. Small-molecule EGFR tyrosine kinase inhibitors also show considerable promise in this disease, both alone and in combination with radiation and chemotherapy. Both classes of anti-EGFR agent are generally well tolerated, with side effects (notably skin rash) that are distinct from the toxicities of conventional chemotherapy. Ongoing clinical trials will more clearly define the role for EGFR inhibitors in all treatment phases of HNSCC.     

Targeting epidermal growth factor receptor signaling in the treatment of head and neck cancer

In this review, key aspects of epidermal growth factor receptor (EGFR) biology and the fruitful translation of these fundamental findings into recent treatment advances in head and neck squamous cell cancer (HNSCC) are highlighted. In contrast to a number of contemporary reviews of the EGFR, many of which focus on colorectal and nonsmall cell lung cancer, this review discusses the EGFR as a validated therapeutic target in HNSCC. Recent data confirm a survival advantage for the addition of the anti-EGFR monoclonal antibody cetuximab to definitive radiation therapy in locoregionally advanced HNSCC patients, as well as palliative benefits for patients with incurable recurrent and metastatic HNSCC. Small-molecule EGFR tyrosine kinase inhibitors also show considerable promise in this disease, both alone and in combination with radiation and chemotherapy. Both classes of anti-EGFR agent are generally well tolerated, with side effects (notably skin rash) that are distinct from the toxicities of conventional chemotherapy. Ongoing clinical trials will more clearly define the role for EGFR inhibitors in all treatment phases of HNSCC.     

Cross-talk between G protein-coupled receptor and epidermal growth factor receptor signaling pathways contributes to growth and invasion of head and neck squamous cell carcinoma

G protein-coupled receptors (GPCR) and the epidermal growth factor receptor (EGFR) are often both overexpressed and contribute to the growth of cancers by activating autocrine pathways. GPCR ligands have been reported to trigger EGFR signaling via receptor cross-talk in cancer cells. Here, we show that GPCR ligands prostaglandin E2 (PGE2) and bradykinin (BK) activate EGFR signaling. Inhibition of EGFR using several strategies, including small-molecule inhibitors and an EGFR-specific antibody, resulted in partial attenuation of signaling downstream of EGFR. PGE2 and BK triggered EGFR signaling by increasing selective autocrine release of transforming growth factor-alpha (TGF-alpha). Inhibition of tumor necrosis factor-alpha-converting enzyme abrogated BK- or PGE2-mediated activation of EGFR signaling. Both PGE2 and BK stimulated head and neck squamous cell carcinoma (HNSCC) invasion via EGFR. Treatment of HNSCC cells with the BK antagonist CU201 resulted in growth inhibition. The combination of CU201 with the EGFR small-molecule inhibitor erlotinib resulted in additive inhibitory effects on HNSCC cell growth in vitro. Inhibition of the PGE2 synthesis pathway with sulindac induced HNSCC cytotoxicity at high doses (EC(50), 620 micromol/L). However, combined inhibition of both EGFR with the tyrosine kinase inhibitor erlotinib and GPCR with sulindac at low doses of 6 and 310 micromol/L, respectively, resulted in synergistic killing of HNSCC tumor cells. Combined blockade of both EGFR and GPCRs may be a rational strategy to treat cancers, including HNSCC that shows cross-talk between GPCR and EGFR signaling pathways.     

Insulin-like growth factor-I receptor/human epidermal growth factor receptor 2 heterodimerization contributes to trastuzumab resistance of breast cancer cells

The majority of breast cancer patients who achieve an initial therapeutic response to the human epidermal growth factor receptor 2 (HER-2)-targeted antibody trastuzumab will show disease progression within 1 year. We previously reported the characterization of SKBR3-derived trastuzumab-resistant pools. In the current study, we show that HER-2 interacts with insulin-like growth factor-I receptor (IGF-IR) uniquely in these resistant cells and not in the parental trastuzumab-sensitive cells. The occurrence of cross talk between IGF-IR and HER-2 exclusively in resistant cells is evidenced by the IGF-I stimulation resulting in increased phosphorylation of HER-2 in resistant cells, but not in parental cells, and by the inhibition of IGF-IR tyrosine kinase activity leading to decreased HER-2 phosphorylation only in resistant cells. In addition, inhibition of IGF-IR tyrosine kinase activity by I-OMe-AG538 increased sensitivity of resistant cells to trastuzumab. HER-2/IGF-IR interaction was disrupted on exposure of resistant cells to the anti-IGF-IR antibody alpha-IR3 and, to a lesser extent, when exposed to the anti-HER-2 antibody pertuzumab. Heterodimer disruption by alpha-IR3 dramatically restored sensitivity to trastuzumab and resistant cells showed a slightly increased sensitivity to pertuzumab versus parental cells. Neither alpha-IR3 nor pertuzumab decreased HER-2 phosphorylation, suggesting that additional sources of phosphorylation other than IGF-IR exist when HER-2 and IGF-IR are not physically bound. Our data support a unique interaction between HER-2 and IGF-IR in trastuzumab-resistant cells such that cross talk occurs between IGF-IR and HER-2. These data suggest that the IGF-IR/HER-2 heterodimer contributes to trastuzumab resistance and justify the need for further studies examining this complex as a potential therapeutic target in breast cancers that have progressed while on trastuzumab.     

Targeting the epidermal growth factor receptor. Trials in head and neck and lung cancer

The epidermal growth factor receptor (EGFR) promotes the growth of different cell types and has been implicated in tumorigenesis. The EGFR comprises a family of four structurally similar tyrosine kinases with a complex link to downstream signaling molecules that ultimately regulate key cell processes. Anti-EGFR agents have been developed as promising therapeutic anticancer targets, and some have been recently approved for the treatment of non-small-cell lung cancer and colon cancer. The two anti-EGFR therapies with the greatest clinical application are monoclonal antibodies that block the binding of ligands to EGFR and small-molecule tyrosine kinase inhibitors that inhibit the binding of adenosine triphosphate to the internal tyrosine kinase receptor of EGFR. We attempt to give an overview of the EGFR function and biology, focusing on the most important clinical findings and applications of EGFR inhibitors in lung and head and neck cancer.     

Epidermal growth factor receptor (EGFR) polymorphisms and survival in head and neck cancer patients

EGFR overexpression has been implicated in the development of head and neck squamous cell carcinoma (HNSCC). This study evaluates the prognostic ability of four polymorphisms in EGFR gene for patients diagnosed with HNSCC and treated with chemoradiation. EGFR polymorphisms in the promoter region were not associated with clinical or pathological characteristics. In relation to R497K polymorphism, patients with the Arg/Arg genotype showed the highest risk of disease-specificity mortality and none of the patients with the Lys/Lys genotype died throughout the follow-up period of the study. Patients with (CA)(n) repeats <17 in both alleles tended toward inferior overall survival compared with those with (CA)(n) repeats > or = 17 in both alleles (p=0.07). Moreover, the distribution of patients with any (CA)(n) repeats > or = 17 and both alleles <17 was statistically different across patients who were recorded as having partial response or no response to therapy (p=0.034). Combination analysis of both polymorphisms, (CA)(n) repeats and R497K, suggests that these polymorphisms may be associated with clinical outcome in patients treated with chemoradiation.     

Molecular mechanisms of resistance to therapies targeting the epidermal growth factor receptor.

Targeted therapies that inhibit the activity of tyrosine kinase receptors such as the epidermal growth factor receptor (EGFR) have shown activity against solid malignancies when used as single agents or in combination with chemotherapy. Although anti-EGFR therapies are active in some patients, eventually disease in nearly all patients will become refractory to therapy. Therefore, a better understanding of the mechanisms of resistance to anti-EGFR therapies is critical to further improve the efficacy of this class of agents. Mechanisms that mediate resistance to anti-EGFR therapies include the presence of redundant tyrosine kinase receptors, increased angiogenesis, and the constitutive activation of downstream mediators. Two recent landmark publications have also shown that specific mutations in the kinase domain of EGFR in some lung carcinomas are associated with markedly improved response rates to an EGFR tyrosine kinase inhibitor. Mutations in the EGFR receptor seem to play a significant role in determining the sensitivity of tumor cells to EGFR inhibitor therapy by altering the conformation and activity of the receptor. As the field of molecular therapeutics continues to evolve, a comprehensive understanding of resistance mechanisms will ultimately lead to refinements in our regimens to provide better care for patients with cancer.     

Intriguing issues of EGFR targeting in head and neck cancer

We have read the recent comprehensive review by Cruz et al.[1] regarding the targeting of receptor tyrosine kinases andtheir therapeutic perspectives in head and neck squamous cellcarcinomas (HNSCC). The major focus of this report was epidermalgrowth factor receptor (EGFR) biology and targeting. However,we feel     

Aberrant epidermal growth factor receptor signaling and enhanced sensitivity to EGFR inhibitors in lung cancer

Epidermal growth factor receptor (EGFR) is occasionally amplified and/or mutated in non-small cell lung cancer (NSCLC) and can be coexpressed with other members of the HER receptor family to form functional heterodimers. We therefore investigated lung cancer cell lines for alterations in EGFR gene copy number, enhanced expression of EGFR and other HER family members, and EGFR coding sequence mutations and correlated these findings with response to treatment with the EGFR inhibitors and the kinetics of ligand-induced signaling. We show here that somatic deletions in the tyrosine kinase domain of EGFR were associated with increased EGFR gene copy number in NSCLC. Treatment with the specific EGFR tyrosine kinase inhibitors (TKI) gefitinib or erlotinib or the EGFR inhibitory antibody cetuximab induced apoptosis of HCC827, a NSCLC cell line with EGFR gene amplification and an exon 19 deletion. H1819, a NSCLC cell line that expresses high levels of EGFR, ErbB2, and ErbB3 but has wild-type EGFR, showed intermediate sensitivity to TKIs. In both cell lines, ligand-induced receptor tyrosine phosphorylation was delayed and prolonged and AKT was constitutively phosphorylated (but remained inhibitable by EGFR TKI). Thus, in addition to EGFR mutations, other factors in NSCLC cells, such as high expression of ErbB family members, may constitutively activate AKT and sensitize cells to EGFR inhibitors.     

Oncogenic fingerprint of epidermal growth factor receptor pathway and emerging epidermal growth factor receptor blockade resistance in colorectal cancer

Epidermal growth factor receptor (EGFR) has been an attractive target for treatment of epithelial cancers, including colorectal cancer (CRC). Evidence from clinical trials indicates that cetuximab and panitumumab (anti-EGFR monoclonal antibodies) have clinical activity in patients with metastatic CRC. The discovery of intrinsic EGFR blockade resistance in Kirsten RAS (KRAS)-mutant patients led to the restriction of anti-EGFR antibodies to KRAS wild-type patients by Food and Drug Administration and European Medicine Agency. Studies have since focused on the evaluation of biomarkers to identify appropriate patient populations that may benefit from EGFR blockade. Accumulating evidence suggests that patients with mutations in EGFR downstream signaling pathways including KRAS, BRAF, PIK3CA and PTEN could be intrinsically resistant to EGFR blockade. Recent whole genome studies also suggest that dynamic alterations in signaling pathways downstream of EGFR leads to distinct oncogenic signatures and subclones which might have some impact on emerging resistance in KRAS wild-type patients. While anti-EGFR monoclonal antibodies have a clear potential in the management of a subset of patients with metastatic CRC, further studies are warranted to uncover exact mechanisms related to acquired resistance to EGFR blockade.     

Concurrent radiotherapy plus epidermal growth factor receptor inhibitors in patients with human papillomavirus-related head and neck cancer

Purpose

Concurrent radio-chemotherapy (RT-CT) is the standard treatment for locally advanced head and neck squamous cell carcinoma (LA-HNSCC), but RT plus epidermal growth factor receptor (EGFR) inhibitors is an effective option when CT is not appropriate. Human papillomavirus (HPV) is associated with an improved prognosis in LA-HNSCC; however, it has not been fully studied as a prognostic factor after RT + EGFR inhibitors.

Experimental design

Immunohistochemical expression of p16INK4A and PCR of HPV16 DNA were retrospectively analyzed in tumor blocks from 52 stage III/IV LA-HNSCC patients treated with RT + EGFR inhibitors. Disease-free survival (DFS) and overall survival (OS) were analyzed by the Kaplan–Meier method.

Results

DNA of HPV16 was found in six of 52 tumors (12 %) and p16 positivity in eight tumors (15 %). After a median follow-up time of 45 months (6–110), p16-positive patients treated with RT + EGFR inhibitors showed an improved DFS (2-year DFS 75 vs. 44 %, HR 0.25, 95 % CI 0.06–0.99, p = 0.047) compared with p16-negative patients. These differences were outperformed when compared by HPV16 status (2-year OS rates of 83 vs. 58 %, HR 0.17, 95 % CI 0.02–0.99, p = 0.049 and 2-year DFS rates of 83 vs. 45 %, HR 0.17, 95 % CI 0.02–0.99, p = 0.049). In the Cox regression analysis with OS as the end point, ECOG 0–1 was the only prognostic factor independently associated with a good prognosis in the multivariable analysis.

Conclusion

In this study, p16/HPV16-positive patients with LA-HNSCC treated with RT + EGFR inhibitors showed a better survival, not confirmed in multivariate analysis.     

Therapeutic targeting of the epidermal growth factor receptor in human cancer

The epidermal growth factor receptor (EGFR; also referred to as HER1 or ERBB1), is a member of the type 1 receptor tyrosine kinase family known as the ERBB family. Comprising 4 members-ERBB1, ERBB2 (also known as HER2), ERBB3 (HER3), and ERBB4 (HER4)-these receptors play a principal role in allowing cells to integrate and respond correctly to diverse external stimuli, ranging from soluble endocrine and paracrine factors to signaling molecules on neighboring cells. The cell must interpret these extracellular signals to produce an appropriate developmental or proliferative response, and aberrant activation of the kinase activity of these receptors, particularly EGFR and ERBB2, is important in the development and progression of human cancer. Given its roles in signal transduction and development of the malignant phenotype, EGFR has emerged as a critical target for therapeutic development against various forms of cancer. This review focuses on the current therapeutic approaches directed against EGFR, the emerging challenges of EGFR therapy resistance, and how our increasing knowledge of EGFR biology is driving more targeted or alternative approaches to cancer therapies.