The cell surface proteins CD133, CD24 and CD44 are putative markers for cancer stem cell populations in colon cancer, associated with aggressive cancer types and poor prognosis. It is important to understand how these markers may predict treatment outcomes, determined by factors such as radioresistance. The scope of this study was to assess the connection between EGFR, CD133, CD24, and CD44 (including isoforms) expression levels and radiation sensitivity, and furthermore analyze the influence of AKT isoforms on the expression patterns of these markers, to better understand the underlying molecular mechanisms in the cell. Three colon cancer cell-lines were used, HT-29, DLD-1, and HCT116, together with DLD-1 isogenic AKT knock-out cell-lines. All three cell-lines (HT-29, HCT116 and DLD-1) expressed varying amounts of CD133, CD24 and CD44 and the top ten percent of CD133 and CD44 expressing cells (CD133high/CD44high) were more resistant to gamma radiation than the ten percent with lowest expression (CD133low/CD44low). The AKT expression was lower in the fraction of cells with low CD133/CD44. Depletion of AKT1 or AKT2 using knock out cells showed for the first time that CD133 expression was associated with AKT1 but not AKT2, whereas the CD44 expression was influenced by the presence of either AKT1 or AKT2. There were several genes in the cell adhesion pathway which had significantly higher expression in the AKT2 KO cell-line compared to the AKT1 KO cell-line; however important genes in the epithelial to mesenchymal transition pathway (CDH1, VIM, TWIST1, SNAI1, SNAI2, ZEB1, ZEB2, FN1, FOXC2 and CDH2) did not differ. Our results demonstrate that CD133high/CD44high expressing colon cancer cells are associated with AKT and increased radiation resistance, and that different AKT isoforms have varying effects on the expression of cancer stem cell markers, which is an important consideration when targeting AKT in a clinical setting.

Head and neck squamous cell carcinoma (HNSCC) of multi-factorial etiopathogenesis is rising worldwide. Treatment-associated toxicity problems and treatment failure in advanced disease stages with conventional therapies have necessitated a focus on alternative strategies. Molecular targeted therapy, with the potential for increased selectivity and fewer adverse effects, hold promise in the treatment of HNSCC. In an attempt to improve outcomes in HNSCC, targeted therapeutic strategies have been developed. These strategies are focusing on the molecular biology of HNSCC in an attempt to target selected pathways involved in carcinogenesis. Inhibiting tumor growth and metastasis by focusing on specific protein or signal transduction pathways or by targeting the tumor microenvironment or vasculature are some of the new approaches. Targeted agents for HNSCC expected to improve the effectiveness of current therapy include EGFR inhibitors (Cetuximab, Panitumumab, Zalutumumab), EGFR tyrosine kinase inhibitors (Gefitinib, Erloitinib), VEGFR inhibitors (Bevacizumab, Vandetanib), and various inhibitors of, e.g., Src-family kinase, PARP, proteasome, mTOR, COX, and heat shock protein. Moreover, targeted molecular therapy can also act as a complement to other existing cancer therapies. Several studies have demonstrated that the combination of targeting techniques with conventional current treatment protocols may improve the treatment outcome and disease control, without exacerbating the treatment related toxicities. Some of the targeted approaches have been proved as promising therapeutic potentials and are already in use, whereas remainder exhibits mixed result and necessitates further studies. Identification of predictive biomarkers of resistance or sensitivity to these therapies remains a fundamental challenge in the optimal selection of patients most likely to benefit from targeted treatment.