Phosphatidylinositol 3′-Kinase Catalytic Subunit α Gene Amplification Contributes to the Pathogenesis of Mantle Cell Lymphoma

Abstract

Purpose: Activation of phosphatidylinositol 3′-kinase pathway is implicated in the pathogenesis of mantle cell lymphoma (MCL). The genetic change in phosphatidylinositol 3′-kinase catalytic subunit α (PIK3CA) in MCL has not been identified. Experimental Design: Thirty-five primary MCL cases and 2 MCL cell lines (GRANTA-519 and Rec-1) were used to investigate somatic mutation and gene copy number of PIK3-CA. Gene copy number was determined using quantitative real-time PCR and fluorescence in situ hybridization. We used quantitative real-time reverse transcription-PCR to measure PIK3CA transcription levels. Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) and phoshorylated AKT protein levels were analyzed using Western blotting and immunohistochemistry. Flow cytometry was used to assess apoptosis after treatment of MCL cell lines and one control cell line with LY294002, a specific inhibitor of PI3KCA. Results: Fifteen of 22 (68%) MCL cases and the MCL cell lines harbored a gain (≥3) of PIK3CA gene copy number. In addition, cases with increased PIK3CA gene copy number had elevated PIK3CA mRNA levels. Furthermore, amplification of PIK3CA correlated with the status of AKT phosphorylation in 7 of 12 (58%) primary MCL cases. 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 5 of 33 (15%) cases tested by immunohistochemistry had loss of PTEN expression. Conclusions: We conclude that a gain of gene copy number of PIK3CA is frequent genetic alteration that contributes to MCL progression. PIK3CA is a promising therapeutic target in MCL. (Clin Cancer Res 2009;15(18):5724-32) Mantle cell lymphoma (MCL) is now recognized as a distinct clinicopathologic subtype of B-cell non-Hodgkin's lymphoma with well-characterized morphology, a distinct immunophenotypic profile, specific karyotypic abnormality, and even a unique underlying molecular alteration (1). MCL comprises approximately 3% to 10% of non-Hodgkin's lymphoma and is characterized by an aggressive clinical course and poor prognosis with a median survival of 3 to 5 years (2, 3). Although front therapy induces a high rate of complete remission, relapse is inevitable and new treatments are needed for relapsed MCL (4).The genetic hallmark of MCL is the chromosomal translocation t(11;14)(q13;q32), which results in deregulated aberrant expression of cyclin D1 (5-7). However, the concept that MCL represents a distinct clinicopathologic and molecularly defined entity does not preclude the existence of additional distinctive disease subsets that could define disease heterogeneity. The

P110α-mediated constitutive PI3K signaling limits the efficacy of p110δ-selective inhibition in mantle cell lymphoma, particularly with multiple relapse

“…In keeping with a previous report, 15 we found loss of PTEN expression in 17% of diagnostic (6/35) and 16% of all (22/138) biopsies ( Figure 2C). A higher proportion of tumors exhibiting blastoid morphology had loss of PTEN expression compared to cases with classical histology, but this was not statistically significant (20% vs 15%, P 5 .55 by Fisher's exact test).…”

“…3,15 Loss of PTEN expression is another mechanism leading to constitutive activation of the PI3K pathway, and studies in solid tumors have demonstrated a key role for p110b in PTEN-deficient tumors. [16][17][18] Loss of PTEN expression has been described in approximately 15% of MCLs.…”

“…[16][17][18] Loss of PTEN expression has been described in approximately 15% of MCLs. 15 Other mechanisms of PTEN inactivation that have been suggested in MCL include phosphorylation of PTEN and negative regulation by the microRNA-17-92 cluster. 4,19 More recently, activation of all 3 class IA isoforms has been described in association with somatic mutations in the gene encoding the regulatory p85a subunit (PIK3R1) in solid tumors.…”

“…Preclinical studies have demonstrated the potential of inhibiting the PI3K pathway in MCL, 3,4,15,21 but early-phase studies of the first p110d selective inhibitor, GS-1101, demonstrated more modest responses in patients with MCL compared with the impressive results seen in indolent non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia. 22 Because loss of PTEN expression (;15%) and gene amplification of p110a (;68%) have been described in MCL, 15 understanding the relative contribution of the class IA isoforms in this disease may help in targeting this important oncogenic pathway more effectively.…”

“…22 Because loss of PTEN expression (;15%) and gene amplification of p110a (;68%) have been described in MCL, 15 understanding the relative contribution of the class IA isoforms in this disease may help in targeting this important oncogenic pathway more effectively.…”