Alterations in various signaling pathways can result in escape from normal cell cycle control, potentially leading to deregulated cell proliferation and thus cancer development. Among these is the PI3K-mTOR signaling pathway (including PTEN, Akt, and S6), which is deregulated in several cancer types. Currently, several kinase inhibitors targeting this pathway are being developed and tested in clinical trials. Evaluation of the expression profile of signaling molecules of the PI3K-mTOR pathway might guide the development of these targeted therapies. The availability of high quality biomarker assays utilizing highly specific primary antibodies is crucial for expression profile studies of the PI3K-mTOR signaling pathway. Here we report the use of 4 biomarker prototype assays (PTEN, pS473 Akt, pS240 S6, and Cyclin D1) in an expression study using breast cancer tissues. An immunohistochemical (IHC) prototype assay was established for each of the 4 antibodies (PTEN, pAkt, pS6, and Cyclin D1) using a polymer based detection system. The expression level of each biomarker was analyzed in 29 formalin-fixed paraffin-embedded ER positive breast cancer tissues using the prototype assays. A total of 27 of the 29 ER-positive breast cancer tissues were PR positive. All 29 tissues were positive for pS6 and Cyclin D1. 28/29 tissues were positive for pAkt and 25/29 tissues were PTEN positive. All 4 biomarkers showed a range of expression in the breast cancer tissues tested, with Cyclin D1 having a slightly higher (medium to high) expression range. PTEN negative and PTEN low expression tissues demonstrated mainly low to medium level of pAkt but medium to high level of pS6 and Cyclin D1 expression. The pAkt negative tissue showed low level PTEN and pS6 expression but high level Cyclin D1 expression.

Due to the small sample size in this study and the small number of PTEN null samples it was not possible to establish a correlation between the 4 biomarkers tested. However, all 4 PTEN null tissues demonstrated low to medium level pAkt and medium to high level pS6 and Cyclin D1 expression, indicating a possible link in their expression levels. A larger study using these prototype biomarker assays (PTEN, pS473 Akt, pS240 S6, and Cyclin D1) might be useful to further elucidate a possible interrelationship between these biomarkers in different tumor types.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA