PTEN expression is involved in the invasive properties of HNSCC: a key protein to consider in locoregional recurrence.

Specific phenotypic effects of PTEN in head and neck squamous cell carcinoma (HNSCC) remain poorly defined without a direct causal connection between the loss of PTEN function and the progression of cancer. Here, we describe a potential role for PTEN in cancer progression. Using an shRNA targeting PTEN in HNSCC cells, we show that the loss of PTEN expression is associated with a decrease of cell adhesion, a reduction in E-cadherin expression while cell migration is promoted. Together with the tissue organization and molecular markers expressed in tumors derived from shPTEN cells in vivo, this study indicates that HNSCC cells deficient in PTEN expression undergo an epithelial­mesenchymal transition (EMT). Additionally, our results suggest that both the low levels of expression and subcellular localization of PTEN are involved in the EMT phenotype, and ultimately in possible locoregional reccurences. We hypothesize that the loss of PTEN expression as well as the subcellular localization could be of interest as a predictive marker of recurrence in HNSCC.

Synergistic antitumor effect between gefitinib and fractionated irradiation in anaplastic oligodendrogliomas cannot be predicted by the Egfr signaling activity.

In high-grade gliomas, the identification of patients that could benefit from EGFR inhibitors remains a challenge, hindering the use of these agents. Using xenografts models, we evaluated the antitumor effect of the combined treatment "gefitinib + radiotherapy" and aimed to identify the profile of responsive tumors. Expression of phosphorylated proteins involved in the EGFR-dependent signaling pathways was analyzed in 10 glioma models. We focused on three models of anaplastic oligodendrogliomas (TCG2, TCG3 and TCG4) harboring high levels of phospho-EGFR, phospho-AKT and phospho-MEK1. They were treated with gefitinib (GEF 75 mg/kg/day x 5 days/week, for 2 weeks) and/or fractionated radiotherapy (RT: 5x2Gy/week for 2 weeks). Our results showed that GEF and/or RT induced significant tumor growth delays. However, only the TCG3 xenografts were highly responsive to the combination GEF+RT, with ∼50% of tumor cure. Phosphoproteins analysis five days after treatment onset demonstrated in TCG3 xenografts, but not in TCG2 model, that the EGFR-dependent pathways were inhibited after GEF treatment. Moreover, TCG3-bearing mice receiving GEF monotherapy exhibited a transient beneficial therapeutic response, rapidly followed by tumor regrowth, along with a major vascular remodeling. Taken together, our data evoked an "EGFR-addictive" behavior for TCG3 tumors. This study confirms that combination of gefitinib with fractionated irradiation could be a potent therapeutic strategy for anaplastic oligodendrogliomas harboring EGFR abnormalities but this treatment seems mainly beneficial for "EGFR-addictive" tumors. Unfortunately, neither the usual molecular markers (EGFR amplification, PTEN loss) nor the basal overexpression of phosphoproteins were useful to distinguish this responsive tumor. Evaluating the impact of TKIs on the EGFR-dependent pathways during the treatment might be more relevant, and requires further validation.

Tumor vascular responses to antivascular and antiangiogenic strategies: looking for suitable models.

Antiangiogenic and vascular disrupting agents are in the current cancer therapeutic armamentarium. A better understanding of the intricate mechanisms ruling neovessel survival within tumors during or after treatment is needed. Refinement of imaging and a growing knowledge of molecular biology of tumor vascularization provide new insights. It is necessary to define suitable methods for monitoring tumor response and appropriate tools to analyze data. This review compares most commonly used preclinical models, considering their recent improvements, and describes promising new approaches such as microfluidics, real-time electrical impedance based technique and noninvasive imaging techniques. The advantages and limitations of the in vitro, ex vivo and in vivo models are discussed. This review also provides a critical summary of emerging approaches using mathematical modeling.

Cellular response to cetuximab in PTEN-silenced head and neck squamous cell carcinoma cell line.

The implication of loss of PTEN expression in resistance to targeted therapy has already been described in many tumor types. The absence of response to anti-EGFR agents in PTEN-deficient tumors relies on persistent activation of signaling pathways downstream of pEGFR. To investigate the role of PTEN loss of expression in head and neck squamous cell carcinoma (HNSCC) response to cetuximab, we used siRNA in Cal 27 cells and then evaluated key signaling protein activation (pAKT and pERK 1/2) as well as cell viability and proliferation. PTEN silencing in Cal 27 cells led to a constitutive activation of signaling pathways evidenced by a strong increase in pAKT and pERK 1/2 expression. Moreover, PTEN-silenced cells did not show any significant changes either in cell viability or proliferation, only slight modifications on cell cycle. Additionally and unpredictably, our results indicated that PTEN silencing, led to a drastic reduction in pEGFR expression whereas total EGFR level did not significantly vary. Strikingly, despite this overactivation of signaling pathways ruling cell survival and proliferation in siPTEN cells, cetuximab fully exerted pAKT and pERK 1/2 inhibition of expression, similarly to its effect in untransfected Cal 27 cells. In conclusion, our study established that in Cal 27 cells, cetuximab keeps full ability to inhibit EGFR-dependent mechanisms, as shown by a decreased pAKT and pERK 1/2 level of expression, despite a strong PTEN silencing-induced overactivation. In Cal 27 cells, loss of PTEN expression does not lead to a loss of cetuximab efficacy in inhibiting EGFR-downstream signaling pathways, contrarily to data shown in previous works conducted in other tumor types.