PIK3CA as a molecular target in mantle cell lymphoma

Abstract

8612 Background: We sought to determine the contribution of PIK3CA gene alterations to the pathogenesis of mantle cell lymphoma (MCL). PIK3CA is known to be involved in the PI 3-kinase/AKT signaling pathway, which is activated in MCL. Methods: We analysed 35 primary MCL cases (14 frozen and 21 paraffin-embedded specimens) and 2 MCL cell lines (Granta, REC1). To search for PIK3CA mutations, we isolated genomic DNA from primary MCL cases and MCL cell lines and performed direct sequencing of the exons 9 and 20 of PIK3CA. We used real-time quantitative PCR to investigate genomic amplification of the PIK3CA gene. We also analyzed PTEN and phoshorylated Akt protein levels in primary cases and cell lines using western blotting and immunohistochemistry (IHC). Flow cytometry analysis was used to assess apoptosis after treatment of MCL cell lines and the Raji Burkitt lymphoma cell line with LY294002, a specific inhibitor of PI3KCA. Results: We found that 14 of 23 (58%) primary MCL cases with amplifiable β- globin and two of two cell lines harboured a gain (>3) of PIK3CA gene copy number. PIK3CA gene mutations were not identified. In addition, amplification of PIK3CA correlated with the status of Akt phosphorylation in 7 of 12 (58%) primary MCL cases and the two MCL cell lines. Inhibition of PIK3CA induced increased apoptosis in the MCL cell lines. PTEN protein expression was present in all 14 primary MCL cases and cell lines by western blotting whereas five of 33 (15%) cases tested by IHC had loss of PTEN protein expression. Only one of the 5 MCL cases with loss of PTEN expression harboured gain of PIK3CA gene copy number. Therefore, PI3KCA gene amplification and PTEN loss were nearly mutually exclusive. Conclusions: We conclude that PIK3CA is an oncogene in MCL and PIK3CA amplification may be linked to pathogenesis and survival in MCL. No significant financial relationships to disclose.