Background: A somatic mutation of the PIK3CA (phosphatidylinositol 3-kinase catalytic subunit) gene has been found in human cancer patients. However, this mutation has not yet been extensively studied in esophageal squamous cell carcinomas.
Materials and methods: We analyzed a mutation of the PIK3CA gene in 88 Japanese cases of esophageal squamous cell carcinomas that had all undergone surgery at the Department of Surgery II, Nagoya City University Medical School, between 1996 and 2003. The TE and KYSE series of cell lines are human esophageal cancer cell lines. Two PIK3CA mutation hot spots (exon 9 and exon 20) were analyzed by a real time polymerase chain reaction (PCR)-based assay and the data were confirmed by direct sequencing. We performed a cell proliferation assay to determine the effects of a PI3K inhibitor LY294002.
Result: In exon 9, a somatic mutation was found in two patients (2.2%) and in two cell lines. The mutations included three E545K (G1633A) mutations and one E545Q (G1633C) mutation. However, in exon 20, no mutation was observed in our esophageal cancer patients. PI3K inhibitor (LY294002) inhibited the growth of an esophageal cancer cell line with a PIK3CA mutation (E545K) in vitro.
Conclusions: We found LY294002 to reduce the proliferation of the esophageal cancer cell line in vitro. Importantly, a cell line with a PIK3CA gene mutation was more susceptible to a PI3K inhibition than those without any such mutation. Further functional analyses of the PIK3CA mutations are warranted to determine whether or not they may be potentially useful targets of therapy for esophageal cancer.