Antitumor effect of vandetanib through EGFR inhibition in head and neck squamous cell carcinoma

There are over 30,000 new cases of head and neck squamous cell carcinoma (HNSCC) each year. Despite recent advances, the overall survival of HNSCC patients has remained unchanged in the past 30 years. Patients with recurrent or metastatic cancer have a poorer prognosis and a decreased overall survival. Surgical resection of these cancers often leads to severe permanent cosmetic deformities and functional deficits. Therefore, there is a critical need for more effective agents to treat HNSCC. The epidermal growth factor receptor (EGFR) has shown significant potential as a therapeutic target in solid malignancies, including those of the head and neck. Dys-regulation of EGFR contributes to HNSCC progression. EGFR is overexpressed in approximately 90% of HNSCC tumor specimens where increased expression is correlated with poor clinical outcome.1 Antitumor effects have been observed upon inhibition of the EGFR tyrosine kinase in both in vitro and in vivo models. Among the various approaches to EGFR inhibition, cetuximab (Erbitux, IMC-C225), a chimeric monoclonal antibody against EGFR, has been the most studied.2,3 The 2006 study reported by Bonner et al,3 which examined the efficacy of cetuximab when combined with radiotherapy in patients with locoregionally advanced head and neck cancer, led to the FDA approval of cetuximab for HNSCC. There have been parallel developments with targeted therapies that inhibit angiogenesis. A key regulator of angiogenesis is vascular endothelial growth factor (VEGF), which is secreted by tumor cells in hypoxic conditions. After VEGF is secreted, it binds its receptors (VEGFR1–3) on endothelial cells, leading to endothelial cell proliferation and tumor angiogenesis.4 Beva-cizumab (Avastin, Genentech), a recombinant human monoclonal antibody to VEGF, has been studied in many cancers and has been FDA-approved in colorectal and breast carcinomas.5 Inhibition of EGFR and/or VEGFR has individually shown promise as an anticancer strategy; thus, it is not surprising that the concomitant inhibition of both targets has been proposed as an anticancer therapy.6–8 Tonra et al6 showed that combined treatment with cetuximab and DC101, a humanized monoclonal antibody to VEGFR-2, had more significant antitumor effects in xenografts of colon and pancreatic cancer than each agent alone. AEE788, a small-molecule tyrosine kinase inhibitor (TKI) with dual specificity against EGFR and VEGFR, proved to be an effective therapeutic strategy in a murine oral cancer model.7 Bevacizumab in combination with erlotinib (a small-molecule inhibitor of the EGFR tyrosine kinase) has been studied in phase I/II clinical trials involving patients with recurrent HNSCC. Vokes et al9,10 showed that this combination treatment resulted in a response rate of approximately 70% of patients enrolled. A novel small-molecule TKI, vandetanib, ZD6474 (Astra-Zeneca, Macclesfield, UK), is an oral dual inhibitor of both EGFR and VEGFR developed by AstraZeneca.11 In non-small cell lung cancer, vandetanib showed promising results when used in combination with docetaxel, a anti-mitotic chemotherapy drug.12 Additionally, vandetanib is in an ongoing open-label phase I study in combination with radiation therapy with or without cisplatin for untreated, unresected, locally advanced HNSCC.13 The antitumor effects of EGFR inhibition on HNSCC have been well documented. It has also been observed in vitro that inhibition of EGFR on tumor cells decreases production of VEGF by tumor cells.8 Consistent with this observation, EGFR inhibitors such as gefitinib and cetuximab have shown antiangiogenic properties when used in vivo.14 In several cancer types, signal transducer and activator of transcription 3 (STAT3) has been shown to mediate VEGF production.15,16 STAT3 mediates intracellular signaling pathways in tumor cells that are downstream of EGFR via activation of STAT3 target genes including VEGF.17 It has been demonstrated that EGFR inhibition decreases STAT3 activity and that in vitro suppression of STAT3, in breast and cervical cancers, decreases VEGF production.16,18 Therefore, it is our hypothesis that EGFR inhibition in HNSCC using vandetanib will result in antitumor effects in vitro and in vivo, and these effects are mediated by the activation of STAT3. We hypothesize that the anti-tumor effects of EGFR inhibition will be exerted, in part, through the downregulation of STAT3 and the STAT3 target gene, VEGF. We also anticipate that the decreased production of VEGF will potentiate the effects of direct VEGFR inhibition on the tumor endothelium. HNSCC tumor cells express significant levels of EGFR, but VEGFR expression is limited primarily to the endothelium. Although the specificity of vandetanib to VEGFR is approximately 10-fold greater than that of EGFR, we hypothesized that vandetanib will still have a significant antitumor effect on HNSCC due to the high EGFR expression.19 In this study, we demonstrate that vandetanib exerts significant in vitro and in vivo antitumor effects via inhibition of the EGFR pathway.