Understanding the Role of EGFR in the Treatment of Head and Neck Squamous Cell Carcinoma

Sammanfattning: Head and neck squamous cell carcinoma (HNSCC) originates from the epithelial lining of the upper aerodigestive tract. It accounts for over 90 % of the malignancies found in the head and neck region. 600,000 new cases of HNSCC occur each year worldwide. Apart from causing painful lesions, HNSCC directly impacts the patient’s fundamental functions such as breathing and eating and also can disrupt the patient’s senses such as smell, taste, speech and even vision. Most cases of HNSCC require a combination of different treatments such as surgery, chemotherapy (primarily cisplatin based), and radiotherapy. Treatment decisions are largely based on the size of the tumor, the involvement of local lymph nodes, and distant spread. Treatment resistance and local recurrence are significant problems and to date no form of clinical treatment sensitivity  prediction is available.A majority of HNSCC tumors overexpresses the epidermal growth factor receptor (EGFR). This receptor is involved in proliferation and DNA repair and is the target of a monoclonal antibody named cetuximab that selectively binds and inhibits EGFR. It is the only targeted therapy available to HNSCC patients and reserved for late stage patients in  Sweden.Numerous investigators have searched for predictive markers and we hypothesized that since HNSCC is a very heterogeneous disease a single factor would not be able to predict the treatment outcome. In paper I we explore a panel of predictive factors using a point system, called the number of negative points (NNP), in which we could combine both proteins and genetic variations in an attempt to find a set of markers that could predict the intrinsic cisplatin sensitivity (ICS). The expression level of EGFR, Hsp70, Bax, Bcl-XL, survivin, and COX-2 was determined in 39 HNSCC cell lines. Moreover, the p53, MDM2, FGFR4, XPC, XPD, XRCC1, and XRCC3 genes were analyzed for the presence of specific single nucleotide polymorphisms (SNPs). Pearson’s correlation tests showed that EGFR was the only protein that alone correlated to ICS (r=0.388, P=0.015). The strongest correlation to ICS was found when combining SNPs in XRCC3 and XPD with the expression of EGFR, Hsp70, Bax, and Bcl-2 using the NNP system (r=0.614 P≤0.001).In paper II we assess the intrinsic radiosensitivity (IR), the ICS, and the intrinsic cetuximab sensitivity (ICmabS) as well as their combinations in 25 HNSCC cell lines established from HNSCC biopsies taken at the Department of Otorhinolaryngology and Head and Neck Surgery at Linköping University Hospital. Furthermore we investigate the EGFR status (consisting of EGFR gene copy number, EGFR mRNA, EGFR protein, pEGFR), pAkt and mRNA levels of the seven known EGFR ligands. No correlation was found between the different treatment sensitivities. Cetuximab treatment response was significantly correlated to epiregulin (EREG) mRNA expression (r=-0.408, P=0.043). Cetuximab resistant cell lines tended to have low levels of pEGFR (P=0.13) while resistant cell lines had a significantly lower expression of EGFR protein (P=0.04) and tended to have decreased levels of pAkt (P=0.13) and amphiregulin (AREG) mRNA (p=0.18).In paper III the functional importance of EGFR ligands in relation to proliferation and cetuximab sensitivity was investigated. Here we tried to diminish the tumor heterogeneity by selecting three cell lines that are derived from the same anatomical location but display different ICmabS. Signaling through the EGFR was stimulated with recombinant EGF, AREG or EREG or reduced by siRNA-mediated silencing of the aforementioned EGFR ligands. EGF downregulation suppressed the proliferation of all investigated tumor cell lines whereas the response to an increased level of EGF differed between EGFR overexpressing and EGFR non-overexpressing cell lines. Furthermore, tumor cells consistently displayed increased cetuximab resistance upon the addition of EGF, whereas EGF silencing was associated with an improved cetuximab response. The data regarding AREG and EREG were inconclusive.In paper IV we wanted to validate in vitro drug sensitivity testing of HNSCC cell lines in an in vivo xenograft model, and to identify treatment-induced changes in the EGFR signaling pathway that could be used as markers for cetuximab treatment response. In vitro ICmabS for the HNSCC cell lines UT-SCC-14 and UT-SCC-45 was established using a crystal violet assay. In order to determine the corresponding in vivo sensitivity, UT-SCC-14 and UT-SCC-45 xenografts were generated in female BALB/c (nu/nu) nude mice. Mice were given three injections of intraperitoneal cetuximab or PBS and the tumor volume was recorded continuously. The expression of EGFR, pEGFR, pSrc, and Ki67 in the tumor tissue was investigated by immunohistochemistry. The in vitro sensitivity was reproduced in the in vivo model. Furthermore a clear reduction of EGFR, pEGFR, and pSrc after cetuximab treatment was noted in UT-SCC-14, the cetuximab sensitive cell line while the cetuximab resistant UT-SCC-45 showed a slight increase in EGFR, pEGFR and pSrc.In conclusion, the EGFR ligand EGF is a potential predictive marker of poor cetuximab response and a possible treatment target. Moreover, treatment-induced downregulation of EGFR and pEGFR is associated with a good cetuximab response.