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Heat shock protein 90 (HSP90), a molecular chaperone, has provoked great interest as a promising molecular target for cancer treatment, due to its involvement in regulating the conformation, stability and functions of key oncogenic proteins. At present, a variety of chemical compounds targeting HSP90 have been developed and have shown convincing anti-neoplastic activity in various preclinical tumor models. The aim of our study was to evaluate the antitumor effects of a novel HSP90 inhibitor, NVP-AUY922, in esophageal squamous cancer cells (ESCC). Four ESCC cell lines (TE-1, TE-4, TE-8, TE-10) were examined. NVP-AUY922 potently inhibited the proliferation of ESCC, particularly in PTEN-null TE-4 cells with a 2-3 times lower IC50 than the other three cell lines. Western blot analysis showed that PTEN-null TE-4 cells exhibited higher AKT and ERK activity, which contribute to cell proliferation and survival. NVP-AUY922 significantly suppressed the activity of AKT and ERK in TE-4 but not in PTEN-proficient TE-10 cells. Genetic modification experiments demonstrated that the sensitivity to NVP-AUY922 was decreased by exogenous transduction of PTEN in TE-4 and increased by silencing PTEN expression in intact PTEN-expressing TE-10, suggesting that the expression of PTEN may be associated with cell sensitivity in HSP90 inhibition. Furthermore, the enhanced activity of AKT in PTEN-silenced TE-10 was more easily suppressed by NVP-AUY922. Collectively, NVP-AUY922 exhibits a strong antiproliferative effect, revealing its potential as a novel therapeutic alternative to current ESCC treatment. The effect may be improved further by impeding PTEN expression.

The HSP90 molecular chaperone family is highly conserved and expressed in various organisms ranging from prokaryotes to eukaryotes. HSP90 proteins play essential housekeeping functions, such as controlling the activity, turnover and trafficking of various proteins, promoting cell survival through maintaining the structural and functional integrity of some client proteins which control cell survival, proliferation and apoptosis, and play an important role in the progression of malignant disease. HSP90 proteins are ATP-dependent chaperones and the binding and hydrolysis of ATP are coupled to conformation changes of HSP90, which facilitate client protein folding and maturation. Many natural and synthetic molecular compounds have been proposed as promising cancer therapy via disrupting the formation of complex ATP-HSP90-client proteins.

Autophagy is a cellular lysosomal degradation pathway involved in proteins and organelles recycling for promoting cell survival, development and homeostasis. It is a multistep process and genetic studies have identified many proteins that participate in autophagosome formation and fusion with lysosomes, and various signaling factors that associate with the regulation of autophagy. In general, autophagy acts as a cell protector and its dysfunction is correlated with diverse pathologies, such as neurodegeneration, liver, heart and muscle diseases, cancer, inflammation and ageing. However, its role in cell death increases the complexity of the autophagic degradation system. A broad understanding of autophagy, ranging from detailed processes, including induction, formation and degradation, to function in physiology and pathology, revealed by accumulating studies, may be helpful for formulating therapeutic strategies for autophagy-associated human diseases.

Esophageal cancer is one of the most frequently occurring cancers in the world. Targeting therapy strategy of cancer with specific inhibitors is developing and has showed promising antitumor efficacy. It is known that mTOR is an important controller of cell growth. RAD001 (everolimus) is a specific inhibitor of mTOR that can block the mTOR signaling pathway. The purposes of this study was to explore the inhibitory effects of RAD001 on mTOR signaling and the mechanism of cell growth suppression by RAD001. We examined both the expression of mTOR, p70S6K and S6 in SEG-1 esophageal cancer cells and KOB-13 normal esophageal epithelial cells and the efficacy of RAD001 against SEG-1 esophageal cancer cells. mTOR, p70S6K and S6 were overexpressed in SEG-1 esophageal cancer cells compared with KOB-13 normal esophageal epithelial cells. SEG-1 esophageal cancer cells were sensitive to RAD001. The survival rate of the cells treated with RAD001 over 0.33 microM was significantly different compared with that of control (P<0.01). RAD001 inhibited the phosphorylation of mTOR (Ser2448) and S6 (Ser240/244) in different grades and the expressions of mTOR, p70S6K and S6. As a result, RAD001 induced a dose-dependent decrease in cell proliferation, G1/S arrest and damage of cell shape. Taken together, these data showed that RAD001 can inhibit mTOR signaling and proliferation in SEG-1 esophageal cancer cells in vitro. It offers a therapeutic intervention through inhibition of mTOR as a potential strategy for esophageal cancer.

Focal adhesion kinase (FAK) is a 125-kDa non-receptor and non-membrane protein tyrosine. FAK can function with integrins and growth factor receptors to promote cell survival dependent kinase activity and nuclear FAK promotes cell proliferation and survival through FERM (FAK, ezrin, radixin, moesin) domain-enhanced p53 degradation independent kinase activity. Many previous studies have indicated that FAK plays a critical role in the biological processes of normal and cancer cells and FAK has been proposed as a potential target in cancer therapy. Small molecule inhibitors (PF-573,228; PF-562,271 and NVP-226) for use as potential cancer therapies have been developed. However, the detailed mechanism of the role for FAK in tumor cell generation and progression remain unclear, so future work is needed to explore these issues. New inhibitors that can be effectively inhibit the function of FAK still need to be explored due to the low specificity, and resistance.

There is currently no suitable animal model of metastasis using cultured human gastrointestinal stromal tumor cells even though the molecular mechanisms of c-KIT-mediated progression and metastasis should be clarified. Ba/F3 murine lymphocyte cells transduced with mutant c-KIT have been utilized to analyze some molecular mechanisms related to a constitutively activated c-KIT signaling and to assess the efficacy of molecular-targeted inhibitors. Using this cellular system, we coincidentally discovered the development of axillary and inguinal lymph node swelling three weeks after subcutaneous injection of Ba/F3 cells with c-KIT mutation into nude mice. Mutation-specific PCR detected c-KIT mutation in the swollen lymph nodes but not in unmetastasized normal lymph nodes, indicating that the lymph nodes contain tumor cells which should come from a primary subcutaneous tumor. Microscopic observation revealed tumor cells infiltrating through lymphatic follicles with Ki-67-positive staining to distinguish them from lymphocytes. The significance of this model is helpful to understand the molecular mechanisms of c-KIT-mediated metastasis and is useful for assessments of molecular therapeutics and in vivo imaging.

Esophageal cancer is one of the most aggressive cancers in the world. Novel preventive and therapeutic strategies tend to target the key molecules involved in the signaling transduction pathways for cell growth. It is known that FAK and mTOR are important controllers of cell growth. TAE226, a novel small molecule compound, is a potent ATP competitive inhibitor of FAK and IGF-IR. TAE226 can block FAK and IGF-IR signaling pathways. The purpose of this study was to explore the inhibitory effects on mTOR signaling and the mechanism of cell growth suppression by TAE226. We examined the expression of mTOR and S6 in esophageal cancer cells (SEG-1) and normal esophageal epithelial cells (KOB-13) and the efficacy of TAE226 against SEG-1 cells. mTOR and S6 were overexpressed in SEG-1 cells compared with KOB-13 cells. TAE226 inhibited the expression of mTOR, Akt, p70S6K and S6 as well as the phosphorylation of mTOR (Ser2448), Akt (Ser473), p70S6K (Thr389) and S6 (Ser240/244). As a result, TAE226 induced a dose-dependent decrease in cell growth (number) and damage in the cell shape. Together, these data show that TAE226 has potent inhibitory effects on mTOR signaling and esophageal cancer cell growth indicating that TAE226 has potential application in esophageal cancer treatment.