PIK 3 CA Mutations in Head and Neck Squamous Cell Carcinoma

Purpose: Recent studies have reported high frequencies of somatic mutations in the phosphoinositide-3-kinase catalytica (PIK3CA) gene in severalhuman solid tumors. Althoughgeneamplifications of PIK3CA have been reported in head and neck squamous cell carcinoma (HNSCC), small mutation of the gene has not been evaluated in HNSCC previously. In this study, we examined themutation frequency of PIK3CA in HNSCC. Experimental Design:More than 75% of the somatic mutations of PIK3CA are clustered in the helical (exon 9) and kinase domains (exon 20). To investigate the possible role of PIK3CA in HNSCC tumorigenesis, exons1, 4, 5, 6, 7, 9, and 20 of the gene were analyzed by direct genomic DNA sequencing in 38 HNSCC specimens. Results:We identified four missense mutations in the seven exons of PIK3CA from 38 HNSCC specimens (11%). Three of the four mutations (i.e., H1047R, E542K, and E545K) have been previously reported as hotspot mutations.The remaining novelmutation,Y343C, is identified at exon 4 nucleotide 1028 A! G. Three of the four mutations were shown to be somatic, whereas the fourth mutation (H1047R) was identified in a cell line. Interestingly, three of the four mutations identifiedwere in pharyngeal cancer samples. Conclusions:These data provide evidence that oncogenic properties of PIK3CA contribute to the carcinogenesis of human head and neck cancers, especially in pharyngeal cancer. A specific kinase inhibitor to PIK3CA may potentially be an effective therapeutic reagent against HNSCC or pharyngeal cancer in particular. The phosphatidylinositol 3-kinase (PI3K) signaling pathway regulates many normal cellular processes, such as cell proliferation, survival, and apoptosis (1–3). Dysregulation or genetic aberration of components of this pathway, including AKT, PTEN , and PIK3CA , has been associated with cancer development (4–12). PIK3CA is located on chromosome 3q26.32 and encodes for the catalytic subunit p110a of class IA PI3K. It has been implicated to function as an oncogene in human cancer because of its elevated kinase activity and genomic amplification in tumor samples (7–12). Recently, high frequencies of somatic mutations in the PIK3CA gene have been reported in several human cancer types, including colon, brain, stomach, breast, and ovary (13–18). More than 75% of these mutations are clustered in the helical (exon 9) and kinase domains (exon 20) of the gene (13). The three most frequently reported mutation hotspots in PIK3CA (i.e., E542K, E545K, and H1047R) have been shown to elevate its lipid kinase activity and lead to the activation of the downstream Akt signaling pathway (13, 19). Interestingly, PIK3CA mutations and PTEN loss are nearly mutually exclusive, suggesting that the homeostasis of phosphatidylinositol-3,4,5-triphosphate regulated by both PIK3CA and PTEN is critical to carcinogenesis (20). This further evinced the importance of the PI3K pathway in the tumorigenesis of many cancer types. Although the PIK3/AKT/PTEN pathway has been implicated in head and neck squamous cell carcinoma (HNSCC; refs. 12, 21–23), no genetic mutation of PIK3CA has been described to date. To investigate whether PIK3CA-activating mutation is a common mechanism involved in the tumorigenesis of HNSCC, we analyzed for genetic alterations of the PIK3CA gene in 38 HNSCC specimens, including eight cell lines, by direct genomic DNA sequencing. Only exons 1, 4, 5, 6, 7, 9, and 20 of the gene were sequenced in these specimens because they covered the most common PIK3CA mutations previously observed in human cancer (13–17, 24–26). Materials and Methods Tissue samples and cell lines. Eight HNSCC cell lines (RPMI 2650, A253, SW579, Detroit 562, FADU, CAL 27, SCC-15, and SCC-25) were purchased from the American Type Culture Collection (Rockville, MD). The cell lines were maintained as recommended by the American Type