Novel treatments for head and neck squamous cell carcinoma: preclinical identification and clinical investigation

Head and neck cancer: the role of anti-EGFR agents in the era of immunotherapy

Head and neck cancers (HNC) represent the seventh most frequent cancer worldwide, with squamous cell carcinomas as the most frequent histologic subtype. Standard treatment for early stage diseases is represented by single modality surgery or radiotherapy, whereas in the locally advanced and recurrent or metastatic settings a more aggressive multi-modal approach is needed with locoregional intervention and/or systemic therapies. Epidermal Growth Factor Receptor (EGFR) plays an important role in HNC biology and has been studied extensively in preclinical and clinical settings. In this scenario, anti-EGFR targeted agent cetuximab, introduced in clinical practice a decade ago, represents the only approved targeted therapy to date, while the development of immune-checkpoint inhibitors has recently changed the available treatment options. In this review, we focus on the current role of anti-EGFR therapies in HNCs, underlying available clinical data and mechanisms of resistance, and highlight future perspectives regarding their role in the era of immunotherapy.

GANT61 and Lithium Chloride Inhibit the Growth of Head and Neck Cancer Cell Lines Through the Regulation of GLI3 Processing by GSK3β

Several signaling pathways are aberrantly activated in head and neck squamous cell carcinoma (HNSCC), including the Hedgehog-Gli (HH-GLI), WNT, EGFR, and NOTCH pathways. The HH-GLI pathway has mostly been investigated in the context of canonical signal transduction and the inhibition of the membrane components of the pathway. In this work we investigated the role of downstream inhibitors GANT61 and lithium chloride (LiCl) on cell viability, wound closure, and colony forming ability of HNSCC cell lines. Five HNSCC cell lines were treated with HH-GLI pathway inhibitors affecting different levels of signal transduction. GANT61 and LiCl reduce the proliferation and colony formation capabilities of HNSCC cell lines, and LiCl has an additional effect on wound closure. The major effector of the HH-GLI signaling pathway in HNSCC is the GLI3 protein, which is expressed in its full-length form and is functionally regulated by GSK3β. LiCl treatment increases the inhibitory Ser9 phosphorylation of the GSK3β protein, leading to increased processing of GLI3 from full-length to repressor form, thus inhibiting HH-GLI pathway activity. Therefore, downstream inhibition of HH-GLI signaling may be a promising therapeutic strategy for HNSCC.

Targeted Therapy in Locally Advanced and Recurrent/Metastatic Head and Neck Squamous Cell Carcinoma (LA-R/M HNSCC)

Surgery and radiotherapy are the standard treatment options for patients with squamous cell carcinoma of the head and neck (SCCHN). Chemoradiotherapy is an alternative for patients with locally advanced disease. In recurrent/metastatic disease and after progression to platin-based regimens, no standard treatments other than best supportive care are currently available. Most SCCHN tumours overexpress the epidermal growth factor receptor (EGFR). This receptor is a tyrosine-kinase membrane receptor that has been implicated in angiogenesis, tumour progression and resistance to different cancer treatments. In this review, we analysed the different drugs and pathways under development to treat SCCHN, especially recurrent/metastatic disease. Until now, the EGFR signalling pathway has been considered the most important target with respect to new drugs; however, new drugs, such as immunotherapies, are currently under study. As new treatments for SCCHN are developed, the influence of therapies with respect to overall survival, progression free survival and quality of life in patients with this disease is changing.

Dysregulation of splicing proteins in head and neck squamous cell carcinoma

Signaling plays an important role in regulating all cellular pathways. Altered signaling is one of the hallmarks of cancers. Phosphoproteomics enables interrogation of kinase mediated signaling pathways in biological systems. In cancers, this approach can be utilized to identify aberrantly activated pathways that potentially drive proliferation and tumorigenesis. To identify signaling alterations in head and neck squamous cell carcinoma (HNSCC), we carried out proteomic and phosphoproteomic analysis of HNSCC cell lines using a combination of tandem mass tag (TMT) labeling approach and titanium dioxide-based enrichment. We identified 4,920 phosphosites corresponding to 2,212 proteins in six HNSCC cell lines compared to a normal oral cell line. Our data indicated significant enrichment of proteins associated with splicing. We observed hyperphosphorylation of SRSF protein kinase 2 (SRPK2) and its downstream substrates in HNSCC cell lines. SRPK2 is a splicing kinase, known to phosphorylate serine/arginine (SR) rich domain proteins and regulate splicing process in eukaryotes. Although genome-wide studies have reported the contribution of alternative splicing events of several genes in the progression of cancer, the involvement of splicing kinases in HNSCC is not known. In this study, we studied the role of SRPK2 in HNSCC. Inhibition of SRPK2 resulted in significant decrease in colony forming and invasive ability in a panel of HNSCC cell lines. Our results indicate that phosphorylation of SRPK2 plays a crucial role in the regulation of splicing process in HNSCC and that splicing kinases can be developed as a new class of therapeutic target in HNSCC.

Cytotoxic Effect of Coscinium fenestratum on Human Head and Neck Cancer Cell Line (HN31)

Coscinium fenestratum is widely used as a medicinal plant in many Asian countries. This study aimed to investigate the cytotoxic effect of a crude water extract of C. fenestratum (CF extract) compared to 5-fluorouracil (5-FU) on human HN31 cell line, a metastatic squamous cell carcinoma of the pharynx. The results revealed that cell morphology visualized under inverted light microscopy was changed from flat with a polygonal appearance to round appearance after CF extract application. The cell viability assay (MTT test) showed that the concentration producing 50% growth inhibition (IC₅₀) at 48-hour incubation of CF extract on HN31 was 0.12 mg/mL, while the IC₅₀ of 5-FU was 6.6 mg/mL, indicating that CF extract has a higher potency. However, combining various concentrations of 5-FU and CF extract at IC₅₀ did not show synergistic effect. The CF extract dose dependently increased cell apoptosis determined by Annexin-V and propidium iodide staining. It decreased the phosphorylation of p38 MAPK and pAkt, while it increased the tumor suppressor protein p53. In conclusion, the cytotoxicity of CF extract was associated with the modulation of p38 MAPK, pAkt, and p53 signal molecules, leading to inhibiting cell survival and increasing apoptosis. No synergistic effects of CF extract and 5-FU were observed.