EGFR inhibition as a therapy for head and neck squamous cell carcinoma

The involvement of epidermal growth factor receptor/protein kinase B signaling in the tumor intrinsic PD-L1-induced malignant potential of oral squamous cell carcinoma

BACKGROUND

Various antigen-presenting cells and tumor cells-expressing PD-L1 inhibits antitumor immune responses in the tumor microenvironment. Recently, numerous studies have shown that tumor cell intrinsic PD-L1 also plays important roles in tumor growth and progression. On the other hand, oral squamous cell carcinoma (OSCC) cells overexpress epidermal growth factor receptor (EGFR) and EGFR signal pathway exacerbates tumor progression. Therefore, this study assessed whether tumor-intrinsic PD-L1 facilitates malignant potential of OSCC cells through regulation of EGFR signaling.

METHODS

Two OSCC cell lines, SAS and HSC-3, were transfected with PD-L1 and EGFR-specific small interfering RNA (siRNA). Influences of PD-L1 knockdown on malignant potentials of OSCC cells were examined by Cell Counting kit-8 assay, transwell assay, sphere formation assay, flow cytometry, and Western blot. Effects of PD-L1 and EGFR knockdown on each expression were examined by quantitative real-time PCR (qRT-PCR), Western blot, and flow cytometry.

RESULTS

Transfection of an PD-L1-siRNA into OSCC cells decreased the abilities of proliferation, stemness, and mobility of these cells significantly. PD-L1 knockdown also decreased EGFR expression through the promotion of proteasome- and lysosome-mediated degradation and following activation of the EGFR/protekin kinase B (AKT) signal pathway. Meanwhile, EGFR knockdown did not influence PD-L1 expression in SAS and HSC-3 cells, but treatment with a recombinant human EGF induced its expression. Treatment with erlotinib and cetuximab suppressed rhEGF-induced PD-L1 expression and localization in the cellular membrane of both OSCC cells.

CONCLUSION

OSCC cells-expressing PD-L1 induced by EGF stimulation may promote malignancy intrinsically via the activation of the EGFR/AKT signaling cascade.

Advances in radiotherapy and immunity in hepatocellular carcinoma

Primary liver cancer is one of the most common malignant tumours worldwide; it caused approximately 830,000 deaths in 2020. Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer, accounting for over 80% of all cases. Various methods, including surgery, chemotherapy, radiotherapy, and radiofrequency ablation, have been widely used in the treatment of HCC. With the advancement of technology, radiotherapy has become increasingly important in the comprehensive treatment of HCC. However, due to the insufficient sensitivity of tumour cells to radiation, there are still multiple limitation in clinical application of radiotherapy. In recent years, the role of immunotherapy in cancer has been increasingly revealed, and more researchers have turned their attention to the combined application of immunotherapy and radiotherapy in the hope of achieving better treatment outcomes. This article reviews the progress on radiation therapy in HCC and the current status of its combined application with immunotherapy, and discusses the prospects and value of radioimmunotherapy in HCC.

Epidermal growth factor/epidermal growth factor receptor signaling blockage inhibits tumor cell-derived exosome uptake by oral squamous cell carcinoma through macropinocytosis

Various cell types secrete exosomes into their surrounding extracellular space, which consequently affect the function and activity of recipient cells. Numerous studies have showed that tumor cell‐derived exosomes play important roles in tumor growth and progression. Although a variety of endocytic pathways are reportedly involved in the cellular uptake of exosomes, detailed mechanisms remain unknown. The present study demonstrated that treatment with recombinant epidermal growth factor (EGF) time‐ and dose‐dependently promoted cellular uptake of oral squamous cell carcinoma (OSCC) cell‐derived exosomes into OSCC cells themselves. Conversely, EGF receptor (EGFR) knockdown and treatment with EGFR inhibitors, including erlotinib and cetuximab, abrogated OSCC cell uptake of exosomes. The macropinocytosis inhibitor 5‐(N‐ethyl‐N‐isopropyl) amiloride (EIPA) blocked the effects of active EGF/EGFR signaling on uptake of OSCC cell‐derived exosomes. These EGFR inhibitors also suppressed OSCC cell‐derived exosome‐induced proliferation, migration, invasion, stemness, and chemoresistance of OSCC cells. Taken together, the data presented herein suggest that EGFR inhibitors might inhibit the malignant potential of OSCC cells through direct inhibition of not only EGFR downstream signaling pathway but also cellular uptake of OSCC cell‐derived exosomes through macropinocytosis.

Loss of CPAP causes sustained EGFR signaling and epithelial-mesenchymal transition in oral cancer

Higher epidermal growth factor receptor (EGFR) signaling can contribute to tumor metastasis and resistance to therapies in oral squamous cell carcinoma (OSCC). EGFR signaling can promote epithelial-mesenchymal transition (EMT) in OSCC. EMT is a process by which epithelial cells acquire invasive properties and it can contribute to tumor metastasis. Not only do the abnormal functions of microtubule and microtubule-organizing centers (MTOC) such as centrosomes lead to cancers, but also the malignant tissues are characterized by aberrant centriolar features and amplified centrosomes. Microtubule inhibition therapies increase the sensitivity to EGFR targeting drugs in various cancers. In this study, we show that the loss of expression of a microtubule/tubulin binding protein, centrosomal protein 4.1-associated protein (CPAP), which is critical for centriole biogenesis and normal functioning of the centrosome, caused an increase in the EGFR levels and its signaling and, enhanced the EMT features and invasiveness of OSCC cells. Further, depletion of CPAP enhanced the tumorigenicity of these cells in a xeno-transplant model. Importantly, CPAP loss-associated EMT features and invasiveness of multiple OSCC cells were attenuated upon depletion of EGFR in them. On the other hand, we found that CPAP protein levels were higher in EGF treated OSCC cells as well as in oral cancer tissues, suggesting that the frequently reported aberrant centriolar features of tumors are potentially a consequence, but not the cause, of tumor progression. Overall, our novel observations show that, in addition to its known indispensable role in centrosome biogenesis, CPAP also plays a vital role in suppressing tumorigenesis in OSCC by facilitating EGFR homeostasis.

Mitochondrial ROS1 Increases Mitochondrial Fission and Respiration in Oral Squamous Cancer Carcinoma

Simple Summary

The clinical efficacy of anti-epidermal growth factor receptor (EGFR) antibody cetuximab for oral squamous cell carcinomas (OSCCs) is low. We previously reported that an increased oncogenic ROS proto-oncogene 1 (ROS1) is responsible for the invasiveness and metastasis of OSCC. This study demonstrates for the first time that ROS1, a receptor tyrosine kinase, can localize to mitochondria. Mitochondrial ROS1 in the highly invasive OSCC promotes mitochondrial fission, enhances mitochondrial oxidative phosphorylation and ATP production but reduces mitochondrial biogenesis. These findings highlight the novel function of ROS1 in mitochondrial morphogenesis and metabolic adaptation to promote OSCC invasiveness.

Abstract

Increased ROS proto-oncogene 1 (ROS1) expression has been implicated in the invasiveness of human oral squamous cell carcinoma (OSCC). The cellular distribution of ROS1 has long-been assumed at the plasma membrane. However, a previous work reported a differential cellular distribution of mutant ROS1 derived from chromosomal translocation, resulting in increased carcinogenesis. We thus hypothesized that cellular distribution of upregulated ROS1 in OSCC may correlate with invasiveness. We found that ROS1 can localize to mitochondria in the highly invasive OSCC and identified a mitochondria-targeting signal sequence in ROS1. We also demonstrated that ROS1 targeting to mitochondria is required for mitochondrial fission phenotype in the highly invasive OSCC cells. OSCC cells expressing high levels of ROS1 consumed more oxygen and had increased levels of cellular ATP levels. Our results also revealed that ROS1 regulates mitochondrial biogenesis and cellular metabolic plasticity. Together, these findings demonstrate that ROS1 targeting to mitochondria enhances OSCC invasion through regulating mitochondrial morphogenesis and cellular respiratory.

EPS8 phosphorylation by Src modulates its oncogenic functions

Background

EPS8 is a scaffolding protein that regulates proliferation, actin dynamics and receptor trafficking. Its expression is increased in cancer, enhancing mitogenesis, migration and tumorigenesis. Src phosphorylates EPS8 at four tyrosine residues, although the function is unknown. Here we investigated the pro-oncogenic role of EPS8 tyrosine phosphorylation at Src target sites in HNSCC.

Methods

Plasmids expressing EPS8 Src-mediated phosphorylation site mutants (Y485F, Y525F, Y602F, Y774F and all four combined [FFFF]) were expressed in cells containing a normal endogenous level of EPS8. In addition, cells were treated with dasatinib to inhibit Src activity. EPS8 downstream targets were evaluated by western blotting. Wound closure, proliferation, immunofluorescence and tumorgenicity assays were used to investigate the impact of phenylalanine mutations on EPS8 biological functions.

Results

FOXM1, AURKA, and AURKB were decreased in cells expressing FFFF- and Y602F-EPS8 mutants, while cells harbouring the Y485F-, Y525F- and Y774F-EPS8 mutants showed no differences compared to controls. Consistent with this, dasatinib decreased the expression of EPS8 targets. Moreover, Y602F- and FFFF-EPS8 mutants reduced mitogenesis and motility. Strikingly though, FFFF- or Y602F-EPS8 mutants actually promoted tumorigenicity compared with control cells.

Conclusions

Phosphorylation of EPS8 at Y602 is crucial for signalling to the cell cycle and may provide insight to explain reduced efficacy of dasatinib treatment.

Molecular biology of oral cavity squamous cell carcinoma

Oral cavity squamous cell carcinoma (OCSCC) is a heterogeneous and complex disease that arises due to dysfunction of multiple molecular signaling pathways. Recent advances in high-throughput genetic sequencing technologies coupled with innovative analytical techniques have begun to characterize the molecular determinants driving OCSCC. An understanding of the key molecular signaling networks underlying the initiation and progression of is essential for informing treatment of the disease. In this chapter, we discuss recent findings of key genes altered in OCSCC and potential treatments targeting these genes.

ALPK1 Expression Is Associated with Lymph Node Metastasis and Tumor Growth in Oral Squamous Cell Carcinoma Patients

Oral squamous cell carcinoma (OSCC) is the most common malignant cancer, with high mortality rates in advanced stages. Recent studies have shown that the expression of ALPK1 mRNA and its inhibitory differentiation function are associated with cancer progression. However, the expression and clinicopathologic features of ALPK1 in OSCC remain unexplored. Herein, the authors investigated the expression patterns of ALPK1 in 39 matched OSCC patients and examined the relationship between ALPK1 protein expression and clinicopathologic factors using immunohistochemical scores. Using Western blot analysis, ALPK1 expression was found to be significantly higher in tumor tissues than that in nontumor tissues. Through an immunoreactive scoring system, a significantly higher number of advanced-stage tumor size T4 and lymph node metastasis N2 exhibited higher ALPK1 expression levels than that exhibited by T1/T2/T3 tumors and N0/N1. In addition, ALPK1 protein expression was aberrant in malignant oral cancer cell lines compared with that in pre-malignant oral epithelial cells, whereas minimal expression was observed in normal oral epithelial cells. Knockdown of ALPK1 resulted in a significant reduction in cell growth, migration, and invasion capacity in vitro. Consequently, expression of N-cadherin and vimentin decreased in ALPK1-deficient cells. Thus, these results suggest that ALPK1 serves as a potential biomarker and target for OSCC development in late stages.

Emerging Phytochemicals for the Prevention and Treatment of Head and Neck Cancer

Despite the development of more advanced medical therapies, cancer management remains a problem. Head and neck squamous cell carcinoma (HNSCC) is a particularly challenging malignancy and requires more effective treatment strategies and a reduction in the debilitating morbidities associated with the therapies. Phytochemicals have long been used in ancient systems of medicine, and non-toxic phytochemicals are being considered as new options for the effective management of cancer. Here, we discuss the growth inhibitory and anti-cell migratory actions of proanthocyanidins from grape seeds (GSPs), polyphenols in green tea and honokiol, derived from the Magnolia species. Studies of these phytochemicals using human HNSCC cell lines from different sub-sites have demonstrated significant protective effects against HNSCC in both in vitro and in vivo models. Treatment of human HNSCC cell lines with GSPs, (-)-epigallocatechin-3-gallate (EGCG), a polyphenolic component of green tea or honokiol reduced cell viability and induced apoptosis. These effects have been associated with inhibitory effects of the phytochemicals on the epidermal growth factor receptor (EGFR), and cell cycle regulatory proteins, as well as other major tumor-associated pathways. Similarly, the cell migration capacity of HNSCC cell lines was inhibited. Thus, GSPs, honokiol and EGCG appear to be promising bioactive phytochemicals for the management of head and neck cancer.

Eribulin sensitizes oral squamous cell carcinoma cells to cetuximab via induction of mesenchymal-to-epithelial transition

Inhibition of epidermal growth factor receptor (EGFR) signalling has emerged as a new treatment strategy for oral squamous cell carcinoma (OSCC). Previously, we found that loss of EGFR expression in OSCC was associated with epithelial-mesenchymal transition (EMT), and may have functional implications with regard to resistance to cetuximab, a monoclonal anti-EGFR antibody. Eribulin (a microtubule inhibitor) reportedly renders breast cancer less aggressive, and less likely to metastasise, by triggering mesenchymal-to-epithelial (MET) transition. In the present study we evaluated whether eribulin-induced MET was associated with re-sensitization of resistant OSCC cell lines to cetuximab. In vitro antiproliferative activities were determined in three human OSCC lines (OSC-20, OSC-19 and HOC313) treated with eribulin. These three human OSCC represented different EMT/MET states. Interestingly, HOC313 cells (mesenchymal phenotype) were highly sensitive to eribulin in comparison with other cell lines, and significantly enhanced the anti-proliferative effect of cetuximab in response to the drug. Eribulin also underwent a MET-associated gene switch that resulted in morphological changes and high EGFR expression in HOC313 cells, and abrogated a TGF-β-induced EMT gene expression signature. Eribulin-dependent sensitization of OSCC to cetuximab is likely due to induction of MET. Combination therapies based on eribulin and cetuximab have potential as a novel treatment regimen in OSCC.

Loss of epidermal growth factor receptor expression in oral squamous cell carcinoma is associated with invasiveness and epithelial-mesenchymal transition

Inhibition of epidermal growth factor receptor (EGFR) signaling has emerged as a novel therapeutic strategy for the treatment of oral squamous cell carcinoma (OSCC). The EGFR-directed inhibitor cetuximab is currently the only approved targeted therapy for the treatment of OSCC. EGFR status may affect the patient response to cetuximab treatment. In the present study, via analysis of the immunomarker for EGFR, it was revealed that 58.3% of the total cases investigated stained positively for EGFR expression, and furthermore, that invasiveness was inversely correlated with EGFR expression. Expression levels of EGFR were quantified, and the correlation between EGFR expression and cetuximab sensitivity was investigated using three varying grades of invasive human OSCC line. EGFR expression in high-grade invasive cells was significantly downregulated compared with that of low-grade invasive cells. There was no significant antiproliferative effect in the high-grade invasive cells treated with various concentrations of cetuximab. The EMT-associated genes, N-cadherin, vimentin and Snail, were upregulated in the high-grade invasive cells. The low-grade invasive cells exhibited characteristics of typical epithelial cells, including the expression of E-cadherin and absence of the expression of N-cadherin, vimentin and Snail. Transforming growth factor-β induced low-grade invasive cells to undergo an epithelial-mesenchymal transition (EMT)-associated gene switch, which resulted in low levels of EGFR expression. The results of the present study suggested that loss of EGFR expression in OSCC was associated with EMT, and may have functional implications with regard to tumor invasiveness and the resistance to cetuximab treatment.

2-Deoxy-d-glucose Suppresses the In Vivo Antitumor Efficacy of Erlotinib in Head and Neck Squamous Cell Carcinoma Cells

Poor tumor response to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) is a significant challenge for effective treatment of head and neck squamous cell carcinoma (HNSCC). Therefore, strategies that may increase tumor response to EGFR TKIs are warranted in order to improve HNSCC patient treatment and overall survival. HNSCC tumors are highly glycolytic, and increased EGFR signaling has been found to promote glucose metabolism through various mechanisms. We have previously shown that inhibition of glycolysis with 2-deoxy-d-glucose (2DG) significantly enhanced the antitumor effects of cisplatin and radiation, which are commonly used to treat HNSCC. The goal of the current studies is to determine if 2DG will enhance the antitumor activity of the EGFR TKI erlotinib in HNSCC. Erlotinib transiently suppressed glucose consumption accompanied by alterations in pyruvate kinase M2 (PKM2) expression. 2DG enhanced the cytotoxic effect of erlotinib in vitro but reversed the antitumor effect of erlotinib in vivo. 2DG altered the N-glycosylation status of EGFR and induced the endoplasmic reticulum (ER) stress markers CHOP and BiP in vitro. Additionally, the effects of 2DG + erlotinib on cytotoxicity and ER stress in vitro were reversed by mannose but not glucose or antioxidant enzymes. Lastly, the protective effect of 2DG on erlotinib-induced cytotoxicity in vivo was reversed by chloroquine. Altogether, 2DG suppressed the antitumor efficacy of erlotinib in a HNSCC xenograft mouse model, which may be due to increased cytoprotective autophagy mediated by ER stress activation.

Activation of MET pathway predicts poor outcome to cetuximab in patients with recurrent or metastatic head and neck cancer

BACKGROUND

Activation of the MET oncogene promotes tumor growth, invasion and metastasis in several tumor types. Additionally, MET is activated as a compensatory pathway in the presence of EGFR blockade, thus resulting in a mechanism of resistance to EGFR inhibitors.

METHODS

We have investigated the impact of HGF and MET expression, MET activation (phosphorylation), MET gene status, and MET-activating mutations on cetuximab sensitivity in recurrent or metastatic squamous cell carcinoma of the head and neck (HNSCC) patients.

RESULTS

A single-institution retrospective analysis was performed in 57 patients. MET overexpression was detected in 58% patients, MET amplification in 39% and MET activation (p-MET) in 30%. Amplification was associated with MET overexpression. Log-rank testing showed significantly worse outcomes in recurrent/metastatic, MET overexpressing patients for progression-free survival and overall survival. Activation of MET was correlated with worse PFS and OS. In multivariate logistic regression analysis, p-MET was an independent prognostic factor for PFS. HGF overexpression was observed in 58% patients and was associated with MET phosphorylation, suggesting a paracrine activation of the receptor.

CONCLUSIONS

HGF/MET pathway activation correlated with worse outcome in recurrent/metastatic HNSCC patients. When treated with a cetuximab-based regimen, these patients correlated with worse outcome. This supports a dual blocking strategy of HGF/MET and EGFR pathways for the treatment of patients with recurrent/metastatic HNSCC.

Unraveling the role of epidermal growth factor receptor in oral lesions: Key to non surgical treatment modes

Epidermal growth factor receptor (EGFR) is a transmembrane receptor with tyrosine kinase activity, mediating actions of various growth factors including EGF, transforming growth factor-α, and neuregulins. Protein binding to ligand induces receptor modification, tyrosine autophosphorylation leading to cell signaling resulting in cellular proliferation. This receptor plays diverse roles in maintaining homeostasis and recent molecular advances identify that EGFR mutations are linked to several carcinomas. EGFR plays important roles in the development and maintenance of various oral structures, tooth development, eruption and morphogenesis. EGFR expression has also been studied in diverse oral pathologies like squamous cell carcinomas, potentially malignant lesions, lichen planus, salivary gland tumors and odontogenic cysts and tumours. The present review delves into the various general features of EGFR with an insight into its physiological and pathological role in the oral cavity. The clinical implications and upcoming role of EGFR inhibitors in the nonsurgical treatment of oral lesions has also been discussed.

MyD88-Dependent Signaling Decreases the Antitumor Efficacy of Epidermal Growth Factor Receptor Inhibition in Head and Neck Cancer Cells

EGFR is upregulated in the majority of head and neck squamous cell carcinomas (HNSCC). However, many patients with HNSCC respond poorly to the EGFR inhibitors (EGFRI) cetuximab and erlotinib, despite tumor expression of EGFR. Gene expression analysis of erlotinib-treated HNSCC cells revealed an upregulation of genes involved in MyD88-dependent signaling compared with their respective vehicle-treated cell lines. We therefore investigated whether MyD88-dependent signaling may reduce the antitumor efficacy of EGFRIs in HNSCC. Erlotinib significantly upregulated IL6 secretion in HNSCC cell lines, which our laboratory previously reported to result in reduced drug efficacy. Suppression of MyD88 expression blocked erlotinib-induced IL6 secretion in vitro and increased the antitumor activity of erlotinib in vivo. There was little evidence of Toll-like receptor or IL18 receptor involvement in erlotinib-induced IL6 secretion. However, suppression of IL1R signaling significantly reduced erlotinib-induced IL6 production. A time-dependent increase of IL1α but not IL1β was observed in response to erlotinib treatment, and IL1α blockade significantly increased the antitumor activity of erlotinib and cetuximab in vivo. A pan-caspase inhibitor reduced erlotinib-induced IL1α secretion, suggesting that IL1α was released because of cell death. Human HNSCC tumors showed higher IL1α mRNA levels compared with matched normal tissue, and IL1α was found to be negatively correlated with survival in patients with HNSCC. Overall, the IL1α/IL1R/MYD88/IL6 pathway may be responsible for the reduced antitumor efficacy of erlotinib and other EGFRIs, and blockade of IL1 signaling may improve the efficacy of EGFRIs in the treatment of HNSCC.

Targeting EGFR-PI3K-AKT-mTOR signaling enhances radiosensitivity in head and neck squamous cell carcinoma

INTRODUCTION

Head and neck squamous cell carcinoma (HNSCC) is frequently characterized by high resistance to radiotherapy, which critically depends on both altered signaling pathways within tumor cells and their dynamic interaction with the tumor microenvironment.

AREAS COVERED

This review covers EGFR-phosphoinositide 3-kinase (PI3K)-protein kinase B (AKT)-mechanistic target of rapamycin (mTOR) signaling in HNSCC. The role of each pathway node in radioresistance is discussed. Preclinical and clinical innovative aspects of targeting EGFR-PI3K-AKT and mTOR are demonstrated. Ongoing clinical trials and future perspectives are presented.

EXPERT OPINION

Different cellular signaling pathways seem to mediate radioresistance in advanced HNSCC and various molecular targeted therapies are currently being investigated to sensitize tumor cells to radiotherapy. Recently, new insights in the mutational landscape of HNSCC unraveled critical alterations in putative oncogenes and tumor suppressor genes and have emphasized the importance of PI3K and the corresponding upstream and downstream signaling pathways in pathogenesis and treatment response. The frequent activation of the EGFR-PI3K-AKT-mTOR pathway in HNSCC and its implication in the context of radiosensitivity make this pathway one of the most promising targets in the therapy of HNSCC patients. Clinical studies targeting EGFR and mTOR in combination with radiotherapy are under investigation.

Phosphorylation of AKT(Ser473) serves as an independent prognostic marker for radiosensitivity in advanced head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is frequently characterized by high resistance to radiotherapy, which critically depends on both altered signaling pathways within tumor cells and their dynamic interaction with the tumor microenvironment. This study evaluated the prognostic value of the phosphorylation status of AKT on Ser473 and Thr308 for the clinical outcome of patients with advanced HNSCC on radiotherapy. Furthermore, we investigated the impact of AKT(Ser473) phosphorylation [p-AKT(Ser473)] in the context of radioresistance using ex vivo tissue cultures that resemble the complex tissue architecture and paracrine interaction with the tumor microenvironment. In a cohort of 120 patients with advanced HNSCC, who were treated with primary or adjuvant radiotherapy, a significant association was found between relative p-AKT(Ser473) levels and overall survival (p = 0.006) as well as progression-free survival (p = 0.021), while no significant correlation was revealed for relative p-AKT(Thr308) levels. In ex vivo tissue cultures p-AKT(Ser473) levels were increased upon irradiation and treatment with the PI3K inhibitor LY294002 inhibited both basal and irradiation induced AKT(Ser473) phosphorylation. Strikingly, pretreatment with LY294002 sensitized tissue cultures derived from primary and recurrent tumors to radiotherapy as determined by impaired tumor cell proliferation and enhanced DNA damage. In conclusion, phosphorylation status of AKT(Ser473) in tumor specimens serves as a novel biomarker to identify patients with advanced HNSCC at high risk for treatment failure following radiotherapy, and our data from ex vivo tissue cultures support the assumption that pharmacological inhibition of AKT(Ser473) phosphorylation might circumvent radioresistance to improve efficiency and reduce toxicity of current treatment modalities.

Axl mediates acquired resistance of head and neck cancer cells to the epidermal growth factor receptor inhibitor erlotinib

Elevated expression and activity of the epidermal growth factor receptor (EGFR) is associated with development and progression of head and neck cancer (HNC) and a poor prognosis. Clinical trials with EGFR tyrosine kinase inhibitors (e.g., erlotinib) have been disappointing in HNC. To investigate the mechanisms mediating resistance to these agents, we developed an HNC cell line (HN5-ER) with acquired erlotinib resistance. In contrast to parental HN5 HNC cells, HN5-ER cells exhibited an epithelial-mesenchymal (EMT) phenotype with increased migratory potential, reduced E-cadherin and epithelial-associated microRNAs (miRNA), and elevated vimentin expression. Phosphorylated receptor tyrosine kinase profiling identified Axl activation in HN5-ER cells. Growth and migration of HN5-ER cells were blocked with a specific Axl inhibitor, R428, and R428 resensitized HN5-ER cells to erlotinib. Microarray analysis of HN5-ER cells confirmed the EMT phenotype associated with acquired erlotinib resistance, and identified activation of gene expression associated with cell migration and inflammation pathways. Moreover, increased expression and secretion of interleukin (IL)-6 and IL-8 in HN5-ER cells suggested a role for inflammatory cytokine signaling in EMT and erlotinib resistance. Expression of the tumor suppressor miR-34a was reduced in HN5-ER cells and increasing its expression abrogated Axl expression and reversed erlotinib resistance. Finally, analysis of 302 HNC patients revealed that high tumor Axl mRNA expression was associated with poorer survival (HR = 1.66, P = 0.007). In summary, our results identify Axl as a key mediator of acquired erlotinib resistance in HNC and suggest that therapeutic inhibition of Axl by small molecule drugs or specific miRNAs might overcome anti-EGFR therapy resistance.

Antitumor effects of EGFR antisense guanidine-based peptide nucleic acids in cancer models

Peptide nucleic acids have emerged over the past two decades as a promising class of nucleic acid mimics because of their strong binding affinity and sequence selectivity toward DNA and RNA, and resistance to enzymatic degradation by proteases and nucleases. While they have been shown to be effective in regulation of gene expression in vitro, and to a small extent in vivo, their full potential for molecular therapy has not yet been fully realized due to poor cellular uptake. Herein, we report the development of cell-permeable, guanidine-based peptide nucleic acids targeting the epidermal growth factor receptor (EGFR) in preclinical models as therapeutic modality for head and neck squamous cell carcinoma (HNSCC) and nonsmall cell lung cancer (NSCLC). A GPNA oligomer, 16 nucleotides in length, designed to bind to EGFR gene transcript elicited potent antisense effects in HNSCC and NSCLC cells in preclinical models. When administered intraperitoneally in mice, EGFRAS-GPNA was taken-up by several tissues including the xenograft tumor. Systemic administration of EGFRAS-GPNA induced antitumor effects in HNSCC xenografts, with similar efficacies as the FDA-approved EGFR inhibitors: cetuximab and erlotinib. In addition to targeting wild-type EGFR, EGFRAS-GPNA is effective against the constitutively active EGFR vIII mutant implicated in cetuximab resistance. Our data reveals that GPNA is just as effective as a molecular platform for treating cetuximab resistant cells, demonstrating its utility in the treatment of cancer.

Regulation of epidermal growth factor receptor signaling and erlotinib sensitivity in head and neck cancer cells by miR-7

Elevated expression and activity of the epidermal growth factor receptor (EGFR)/protein kinase B (Akt) signaling pathway is associated with development, progression and treatment resistance of head and neck cancer (HNC). Several studies have demonstrated that microRNA-7 (miR-7) regulates EGFR expression and Akt activity in a range of cancer cell types via its specific interaction with the EGFR mRNA 3'-untranslated region (3'-UTR). In the present study, we found that miR-7 regulated EGFR expression and Akt activity in HNC cell lines, and that this was associated with reduced growth in vitro and in vivo of cells (HN5) that were sensitive to the EGFR tyrosine kinase inhibitor (TKI) erlotinib (Tarceva). miR-7 acted synergistically with erlotinib to inhibit growth of erlotinib-resistant FaDu cells, an effect associated with increased inhibition of Akt activity. Microarray analysis of HN5 and FaDu cell lines transfected with miR-7 identified a common set of downregulated miR-7 target genes, providing insight into the tumor suppressor function of miR-7. Furthermore, we identified several target miR-7 mRNAs with a putative role in the sensitization of FaDu cells to erlotinib. Together, these data support the coordinate regulation of Akt signaling by miR-7 in HNC cells and suggest the therapeutic potential of miR-7 alone or in combination with EGFR TKIs in this disease.

Bioactive phytochemical proanthocyanidins inhibit growth of head and neck squamous cell carcinoma cells by targeting multiple signaling molecules

Despite advances in surgical and medical therapies, approximate 50% survival rate of head and neck squamous cell carcinoma (HNSCC) has had marginal improvement in the last 30 years. Therefore, alternative strategies are required for the management of HNSCC. Here, we report the chemotherapeutic effect of proanthocyanidins on HNSCC cells using in vitro and in vivo models. Treatment of human HNSCC cell lines from different sub-sites, such as oral cavity (SCC1), larynx (SCC5), tongue (OSC19) and pharynx (FaDu), with grape seed proanthocyanidins (GSPs) reduced their cell viability and induced cell death in a dose- and time-dependent manner. GSPs induced inhibition of cell viability was associated with: (i) G1-phase arrest, (ii) inhibition of expressions of cyclins (cyclin D1 and Cyclin D2) and cyclin-dependent kinases (Cdk), (iii) increased expression of the Cdk inhibitory proteins (Cip1/p21, Kip1/p27), enhanced binding of Cdk inhibitors to Cdks, and downregulation of E2F transcription factor. GSPs significantly (P<0.05−0.001) increased apoptosis of SCC1 and OSC19 cells with induction of Bax, reduced expression of Bcl-2, and activation of caspase-3. GSPs also reduced the expression of epidermal growth factor receptor (EGFR), and treatment of SCC1 cells with erlotinib, an EGFR-targeting small molecule tyrosine kinase inhibitor, significantly (P<0.05−0.001) reduced cell viability and increased cell death. Dietary administration of GSPs (0.5%, w/w) in supplementation with AIN76A control diet inhibited the growth of SCC1 tumor xenografts in athymic nude mice, which was associated with: (i) inhibition of cell proliferation, (ii) induction of apoptosis of tumor xenograft cells, (iii) decreased expression of cyclins and Cdks, (iv) decreased expression of EGFR, and (v) increased expression of Cip1/p21 and Kip1/p27 proteins and their increased binding to Cdks in tumor xenograft samples. Together, these results suggest that GSPs may be a promising candidate for head and neck squamous cell carcinoma therapy.

EGFR status and EGFR ligand expression influence the treatment response of head and neck cancer cell lines

BACKGROUND

Combination treatment (chemoradiotherapy) is the standard treatment for locally advanced head and neck squamous cell carcinoma (HNSCC); however, treatment resistance and local recurrence are significant problems. A high level of epidermal growth factor receptor (EGFR) has been associated with a more aggressive phenotype as well as decreased responsiveness to radio- or chemotherapy. We examined the role of EGFR status and EGFR ligand expression for the treatment response.

METHODS

Intrinsic sensitivity to radiotherapy, cisplatin, and cetuximab treatments was investigated in 25 HNSCC cell lines. EGFR gene copy number, mRNA and protein expression, EGFR and Akt phosphorylation status, and mRNA expression of the EGFR ligands were analyzed using quantitative PCR and ELISA and assessed for their impact on treatment sensitivity.

RESULTS

Different treatment modalities yielded great diversity in outcome; of note, cetuximab treatment stimulated growth in one cell line. When treatments were combined primarily additive effects were observed. While radioresistance tended to be associated with a high level of phosphorylated EGFR (pEGFR; P = 0.09), cetuximab-resistant cells had low levels of pEGFR (P = 0.13). The three most cetuximab-sensitive cell lines had high EGFR gene copy numbers. Furthermore, cetuximab treatment response was significantly correlated with epiregulin mRNA expression (r = -0.408, P = 0.043). Cisplatin-resistant tumor cells expressed significantly lower levels of EGFR protein (P = 0.04) compared to cisplatin-sensitive cells and tended to have lower levels of phosphorylated Akt (pAkt; P = 0.13) and lower expression levels of amphiregulin (P = 0.18).

CONCLUSIONS

Epidermal growth factor receptor status and ligand expression influence the treatment sensitivity of HNSCC cells and may be useful as predictive markers.

Phthalocyanine-peptide conjugates for epidermal growth factor receptor targeting

Four phthalocyanine (Pc)-peptide conjugates designed to target the epidermal growth factor receptor (EGFR) were synthesized and evaluated in vitro using four cell lines: human carcinoma A431 and HEp2, human colorectal HT-29, and kidney Vero (negative control) cells. Two peptide ligands for EGFR were investigated: EGFR-L1 and -L2, bearing 6 and 13 amino acid residues, respectively. The peptides and Pc-conjugates were shown to bind to EGFR using both theoretical (Autodock) and experimental (SPR) investigations. The Pc-EGFR-L1 conjugates 5a and 5b efficiently targeted EGFR and were internalized, in part due to their cationic charge, whereas the uncharged Pc-EGFR-L2 conjugates 4b and 6a poorly targeted EGFR maybe due to their low aqueous solubility. All conjugates were nontoxic (IC(50) > 100 μM) to HT-29 cells, both in the dark and upon light activation (1 J/cm(2)). Intravenous (iv) administration of conjugate 5b into nude mice bearing A431 and HT-29 human tumor xenografts resulted in a near-IR fluorescence signal at ca. 700 nm, 24 h after administration. Our studies show that Pc-EGFR-L1 conjugates are promising near-IR fluorescent contrast agents for CRC and potentially other EGFR overexpressing cancers.

Therapeutic targets in head and neck squamous cell carcinoma: identification, evaluation, and clinical translation

Head and neck squamous cell carcinoma (HNSCC) encompasses a diverse group of malignancies originating in the oral cavity, oropharynx, larynx and hypopharynx. Although treatment modalities have improved, carefully designed biomarker-driven clinical trials will yield the best opportunities to enhance HNSCC therapy options in the future. Due to the heterogeneous nature of HNSCC, discovering a "silver bullet" for the treatment of HNSCC is unlikely. Consequently, impactful HNSCC clinical trials will require multiple assay platforms and expanded technical expertise. In this review, we will outline pathways critical to HNSCC oncogenesis and highlight signaling nodes within these pathways that represent biomarkers for prognosis and potential targeted therapies. All treatment modalities are subject to mechanisms of resistance; thus, lessons learned from HNSCC investigations and studies of similar targeted agents in other pertinent malignancies will be discussed.

Pathway profiling and rational trial design for studies in advanced stage cervical carcinoma: a review and a perspective

Multiple genetic abnormalities will have occurred in advanced cervical cancer and multiple targeting is likely to be needed to control tumor growth. To date, dominant therapeutic targets under scrutiny for cervical cancer treatment have been EGFR pathway and angiogenesis inhibition as well as anti-HPV vaccines. The potentially most effective targets to be blocked may be downstream from the membrane receptor or at the level of the nucleus. Alterations of the pathways involved in DNA repair and in checkpoint activations, as well as the specific site of HPV genome integration, appear worth assessing. For genetic mutational analysis, complete exon sequencing may become the norm in the future but at this stage frequent mutations (that matter) can be verified by PCR analysis. A precise documentation of relevant alterations of a large spectrum of protein biomarkers can be carried out by reverse phase protein array (RPPA) or by multiplex analysis. Clinical decision-making on the drug(s) of choice as a function of the biological alteration will need input from bio-informatics platforms as well as novel statistical designs. Endpoints are yet to be defined such as the loss (or reappearance) of a predictive biomarker. Single or dual targeting needs to be explored first in relevant preclinical animal and in xenograft models prior to clinical deployment.

An update on molecular diagnostics of squamous and salivary gland tumors of the head and neck

CONTEXT

Molecular testing in anatomic pathology is becoming standardized and can contribute valuable diagnostic, therapeutic, and prognostic information for the clinical management of patients. In head and neck pathology, recent advances in molecular testing have provided important targets in several different diagnostic areas, with particular emerging clinical applications in squamous and salivary gland pathology. In squamous mucosal-derived lesions, human papilloma virus has emerged as an important pathogenic etiology in a subset of oropharyngeal squamous cell carcinomas. Within the category of salivary gland tumors, 3 tumors have recently been recognized that contain oncogenic translocations.

OBJECTIVE

To describe the current state of information about the molecular alterations in squamous lesions and in salivary gland tumors of the head and neck.

DATA SOURCES

Published literature on squamous and salivary gland tumors of the head and neck.

CONCLUSIONS

The different approaches to identification of viral-associated tumors include assays using polymerase chain reaction, in situ hybridization, and immunohistochemistry. Most mucoepidermoid carcinomas harbor MECT1-MAML2 gene rearrangement. The MYB-NFIB translocations have recently been identified in adenoid cystic carcinomas. Finally, a newly described tumor of salivary gland, mammary analogue secretory carcinoma, harbors the ETV6-NTRK3 translocation. Although these translocations are just emerging as diagnostic targets, future roles may evolve as potential therapeutic targets.

Phosphoproteomic analysis of signaling pathways in head and neck squamous cell carcinoma patient samples

Molecular targeted therapy represents a promising new strategy for treating cancers because many small-molecule inhibitors targeting protein kinases have recently become available. Reverse-phase protein microarrays (RPPAs) are a useful platform for identifying dysregulated signaling pathways in tumors and can provide insight into patient-specific differences. In the present study, RPPAs were used to examine 60 protein end points (predominantly phosphoproteins) in matched tumor and nonmalignant biopsy specimens from 23 patients with head and neck squamous cell carcinoma to characterize the cancer phosphoproteome. RPPA identified 18 of 60 analytes globally elevated in tumors versus healthy tissue and 17 of 60 analytes that were decreased. The most significantly elevated analytes in tumor were checkpoint kinase (Chk) 1 serine 345 (S345), Chk 2 S33/35, eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) S65, protein kinase C (PKC) ζ/ι threonine 410/412 (T410/T412), LKB1 S334, inhibitor of kappaB alpha (IκB-α) S32, eukaryotic translation initiation factor 4E (eIF4E) S209, Smad2 S465/67, insulin receptor substrate 1 (IRS-1) S612, mitogen-activated ERK kinase 1/2 (MEK1/2) S217/221, and total PKC ι. To our knowledge, this is the first report of elevated PKC ι in head and neck squamous cell carcinoma that may have significance because PKC ι is an oncogene in several other tumor types, including lung cancer. The feasibility of using RPPA for developing theranostic tests to guide personalized therapy is discussed in the context of these data.

dPORE-miRNA: polymorphic regulation of microRNA genes

BACKGROUND

MicroRNAs (miRNAs) are short non-coding RNA molecules that act as post-transcriptional regulators and affect the regulation of protein-coding genes. Mostly transcribed by PolII, miRNA genes are regulated at the transcriptional level similarly to protein-coding genes. In this study we focus on human miRNAs. These miRNAs are involved in a variety of pathways and can affect many diseases. Our interest is on possible deregulation of the transcription initiation of the miRNA encoding genes, which is facilitated by variations in the genomic sequence of transcriptional control regions (promoters).

METHODOLOGY

Our aim is to provide an online resource to facilitate the investigation of the potential effects of single nucleotide polymorphisms (SNPs) on miRNA gene regulation. We analyzed SNPs overlapped with predicted transcription factor binding sites (TFBSs) in promoters of miRNA genes. We also accounted for the creation of novel TFBSs due to polymorphisms not present in the reference genome. The resulting changes in the original TFBSs and potential creation of new TFBSs were incorporated into the Dragon Database of Polymorphic Regulation of miRNA genes (dPORE-miRNA).

CONCLUSIONS

The dPORE-miRNA database enables researchers to explore potential effects of SNPs on the regulation of miRNAs. dPORE-miRNA can be interrogated with regards to: a/miRNAs (their targets, or involvement in diseases, or biological pathways), b/SNPs, or c/transcription factors. dPORE-miRNA can be accessed at http://cbrc.kaust.edu.sa/dpore and http://apps.sanbi.ac.za/dpore/. Its use is free for academic and non-profit users.

Phase II study of nimotuzumab, a humanized monoclonal anti-epidermal growth factor receptor (EGFR) antibody, in patients with locally advanced or metastatic pancreatic cancer

INTRODUCTION

Nimotuzumab is a humanized monoclonal antibody that binds to the EGFR. Based on phase I data, the recommended dose has been established at 200 mg weekly. This study was aimed at evaluating the safety and efficacy of nimotuzumab monotherapy in patients (pts) with locally advanced or metastatic pancreatic cancer.

METHODS

Pts who failed first line standard chemotherapy for advanced disease and had at least one measurable lesion were eligible for the study. Nimotuzumab was given intravenously at 200 mg once weekly for 6 weeks (wks). Follow up by CT scan was performed after 8 weeks. Pts continued receiving treatment 3-weekly until disease progression or unacceptable toxicity occurred. Endpoints included tumor response (RECIST), progression-free survival (PFS), and safety.

RESULTS

A total of 56 pts were enrolled for treatment (ECOG status of 1 [n = 41] or 0 [n = 15]), the majority (47 pts) had metastatic disease. Nearly half of the pts [n = 26] received ≥2 regimens. Pts evaluable for response: n = 36; CR: 0; PR: 0; SD: 6 pts. Median PFS for pts with SD was 19.2 weeks, for all pts 6.7 weeks (95% CI: 6.43-7.14 weeks). PFS after 1 year was 10.3% with a median overall survival of 18.1 weeks. Treatment-related adverse events were generally mild including rash grade 1 in 5 pts. After a single dose of 200 mg, the t(1/2) was calculated to 45 h.

CONCLUSION

These data confirm that nimotuzumab is safe and very well tolerated. To improve efficacy, a randomized, placebo-controlled trial with Gem has been initiated.

EGFR-PI3K-AKT-mTOR signaling in head and neck squamous cell carcinomas: attractive targets for molecular-oriented therapy

IMPORTANCE OF THE FIELD

Recent advances in the understanding of the oncogenesis of head and neck squamous cell carcinomas (HNSCC) have revealed multiple dysregulated signaling pathways. One frequently altered axis is the EGFR-PI3K-Akt-mTOR pathway. This pathway plays a central role in numerous cellular processes including metabolism, cell growth, apoptosis, survival and differentiation, which ultimately contributes to HNSCC progression.

AREAS COVERED IN THIS REVIEW

Books, journals, databases and websites have been searched to provide a current review on the subject.

WHAT THE READER WILL GAIN

This article reviews the current understanding of EGFR-PI3K-Akt-mTOR signaling in HNSCC, including the impact of both genetic and epigenetic alterations. This review further highlights the potential of targeting this signaling cascade as a promising therapeutic approach in the treatment of HNSCC.

TAKE HOME MESSAGE

Genetic alterations of several nodes within this pathway, including both genetic and epigenetic changes, leading to either oncogene activation or inactivation of tumor suppressors have frequently been implicated in HNSCC. Consequently, drugs that target the central nodes of this pathway have become attractive for molecular oriented cancer therapies. Numerous preclinical and clinical studies are being performed in HNSCC; however, more studies are still needed to better understand the biology of this pathway.

Honokiol inhibits epidermal growth factor receptor signaling and enhances the antitumor effects of epidermal growth factor receptor inhibitors

PURPOSE

This study aimed to investigate the utility of honokiol, a naturally occurring compound, in the treatment of head and neck squamous cell carcinoma (HNSCC) as well as its ability to target the epidermal growth factor receptor (EGFR), a critical therapeutic target in HNSCC, and to enhance the effects of other EGFR-targeting therapies.

EXPERIMENTAL DESIGN

Human HNSCC cell lines and the xenograft animal model of HNSCC were used to test the effects of honokiol treatment.

RESULTS

Honokiol was found to inhibit growth in human HNSCC cell lines, with 50% effective concentration (EC(50)) values ranging from 3.3 to 7.4 micromol/L, and to induce apoptosis, as shown through Annexin V staining. These effects were associated with inhibition of EGFR signaling, including downstream inhibition of mitogen-activated protein kinase, Akt, and signal transducer and activator of transcription 3 (STAT3), and expression of STAT3 target genes, Bcl-X(L) and cyclin D1. Furthermore, honokiol enhanced the growth inhibitory and anti-invasion activity of the EGFR-targeting agent erlotinib. Although HNSCC xenograft models did not show significant inhibition of in vivo tumor growth with honokiol treatment alone, the combination of honokiol plus cetuximab, a Food and Drug Administration-approved EGFR inhibitor for this malignancy, significantly enhanced growth inhibition. Finally, HNSCC cells rendered resistant to erlotinib retained sensitivity to the growth inhibitory effects of honokiol.

CONCLUSIONS

These results suggest that honokiol may be an effective therapeutic agent in HNSCC, in which it can augment the effects of EGFR inhibitors and overcome drug resistance.

Pharmacodynamic trial of nimotuzumab in unresectable squamous cell carcinoma of the head and neck: a SENDO Foundation study

PURPOSE

To assess the pharmacodynamic effects of nimotuzumab, an anti-epidermal growth factor receptor (EGFR) monoclonal antibody with intermediate affinity for the receptor, in skin and tumor tissues from head and neck cancer patients.

EXPERIMENTAL DESIGN

Pharmacodynamic study in patients with advanced squamous cell carcinoma of the head and neck, unsuitable for chemoradiotherapy, enrolled in a single-center trial. Patients received 8 weekly infusions of nimotuzumab. The first nimotuzumab infusion was administered 1 week before starting radiation, whereas the remaining doses were administered concomitantly with irradiation. Paired biopsies were taken from skin and primary tumors, before (pretherapy) and 1 week (on single-agent therapy) after first infusion. Immunohistochemistry was conducted to assay the effects of nimotuzumab on total and phosphorylated EGFR, phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2), p-AKT, and proliferation (Ki-67).

RESULTS

Nimotuzumab was well tolerated and there was no evidence of skin rash. Objective response was achieved in 9 of 10 patients. The pharmacodynamic assays showed inhibition of p-EGFR in both skin and tumor (P = 0.042 in skin and P = 0.034 in tumor). No significant changes in p-ERK1/2, p-AKT, or Ki-67 were detected in skin. In addition, lymphocytic infiltrates, folliculitis, or perifolliculitis were not observed. In tumor samples, there was an upregulation of p-AKT (P = 0.043), a reduction in proliferation index (P = 0.012), and a nonsignificant trend toward a decrease of p-ERK1/2 (P = 0.091).

CONCLUSIONS

The pharmacodynamic data confirmed the ability of nimotuzumab to decrease EGFR phosphorylation. Downstream effects were observed in tumor cells but not in skin, a finding that may help to explain the lack of skin rash in patients treated with nimotuzumab.

A mouse model for oral squamous cell carcinoma

Despite recent advances, the prognosis of oral squamous cell carcinoma is still poor. Therapeutic options such as radiotherapy, chemotherapy, surgery and the novel treatment option gene therapy are being investigated in animal models. Diverse models have been studied to induce oral squamous cell carcinomas. The carcinogenic 4-nitroquinoline-1-oxide (4NQO) model has proven to be successful although until now it is unknown at what time point the established tumor is a representative squamous cell carcinoma and has a suitable volume for scientific treatment. For this end we applied 4NQO 3 times a week during 16 weeks and measured the volume of tumor tissue each week until the end of the experiment at 40 weeks. Concurrent histopathology at different time points up to the end of the experiment revealed that all mice bearing oral tumors were diagnosed with squamous cell carcinoma. Immunohistochemistry with markers cyclin D1 and E-cadherin revealed that the generated mouse oral tumors showed strong similarities with the described immunopathology in human oral tumors. The 4NQO model is a suitable alternative for preclinical gene therapy experiments with primary oral tumors. Future survey of therapeutic options in the carcinogenic 4NQO model should be conducted around 40 weeks after the start of the treatment.

Current and potential inflammation targeted therapies in head and neck cancer

Inflammation often exists in the tumor microenvironment and is induced by inflammatory mediators (cytokines, chemokines, and growth factors) produced by the tumor, stroma, and infiltrating cells. These factors modulate tissue remodeling and angiogenesis and actively promote tumor cell survival and chemoresistance through autocrine and paracrine mechanisms. Head and neck squamous cell carcinomas (HNSCCs) are highly inflammatory and aggressive in nature, and they express a number of cytokines and growth factors involved in inflammation. These cytokines and growth factors activate important signal transduction pathways, including NF-kappaB, JAK/STAT, and PI3K/Akt/mTOR, which regulate the expression of genes controlling growth, survival, and chemosensitivity. This review provides an update on recent advances in the understanding of the mechanisms driving cancer-related inflammation in HNSCC and on molecular targeted therapies under preclinical and clinical investigation.

Synergistic combinations of signaling pathway inhibitors: mechanisms for improved cancer therapy

Cancer cells contain multiple signal transduction pathways whose activities are frequently elevated due to their transformation, and that are often activated following exposure to established cytotoxic therapies including ionizing radiation and chemical DNA damaging agents. Many pathways activated in response to transformation or toxic stresses promote cell growth and invasion and counteract the processes of cell death. As a result of these findings many drugs, predominantly protein and lipid kinase inhibitors, of varying specificities, have been developed to block signaling by cell survival pathways in the hope of killing tumor cells and sensitizing them to toxic therapies. Unfortunately, due to the plasticity of signaling processes within a tumor cell, inhibition of any one growth factor receptor or signaling pathway frequently has only modest long-term effects on cancer cell viability, tumor growth, and patient survival. As a result of this realization, a greater emphasis has begun to be placed on rational combinations of drugs that simultaneously inhibit multiple inter-linked signal transduction/survival pathways. This, it is hoped, will limit the ability of tumor cells to adapt and survive because the activity within multiple parallel survival signaling pathways has been reduced. This review will discuss some of the approaches that have been taken to combine signal transduction modulatory agents to achieve enhanced tumor cell killing.