PI3K Inhibition As a Potential Therapeutic Strategy in Peripheral T-Cell Lymphomas,

Abstract 3493

Peripheral T-cell lymphomas (PTCL) are a heterogeneous group of very aggressive malignancies lacking efficient therapy. Unfortunately, there are neither animal models nor representative cell lines for most PTCL types, making functional and pharmacodynamic studies even more difficult. PI3K signaling is essential for cell proliferation and survival, is frequently altered in human cancer and seems to play a critical role in T-cell development and activation. The aim of this work is to determine the efficiency of PI3K inhibition in PTCL, looking for pharmacodynamic biomarkers, and to identify markers that could distinguish responders from non-responders.

Twenty two PTCL cases and seven reactive lymph nodes were studied using gene expression profiling. We performed an in silico analysis using the Connectivity Map program to identify drugs that could potentially reverse the PTCL gene expression signature. Among them, several PI3K/mTOR inhibitors were found.

Moreover, genomic studies using Gene Set Enrichment Analysis identified PIK3CD gene (encoding for the delta isoform of PI3K) to be the only one significantly correlated to the activation of CD40, NF-kB and TCR pathways. Quantitative RT-PCR confirmed the strong overexpression of PIK3CD in 6 PTCL-derived cell lines compared to normal T cells from healthy donors. Sequence analyses for the coding region of the PIK3CD gene identified a point mutation in one of these cell lines, described as activating in solid tumors.

A panel of 6 PTCL cell lines belonging to different PTCL subgroups was treated with 3 PI3K inhibitors (LY294002, ETP-45658, GDC-0941). Moreover, genetic inhibition was also carried out using small interference RNA to specifically abolish the expression of alpha and delta isoforms of PI3K (PIK3CA and PIK3CD genes, respectively).

In vitro studies showed very similar results with the three pharmacological PI3K inhibitors we used: they induced G1 cell cycle arrest in all cell lines, and apoptosis in some of them, in a time/dose-dependent manner. We also observed a decrease in the levels of pAKT(S473) in all cell lines, while pGSK3B(S9) and p-p70S6K(T389) were reduced after treatment only in sensitive cell lines.

Our results indicate that genetic inhibition of PI3K delta isoform could induce apoptosis in those PTCL cell lines that were sensitive to PI3K inhibitors, but not in the resistant cell lines; while genetic inhibition of PI3K alpha isoform did not display such effects.

Taken together these results could highlight the relevance of PI3K delta isoform in at least a subset of PTCL, indicating that PI3K inhibition, especially delta isoform, could be an effective therapeutic approach for PTCL and identifying potential markers for patients' stratification and pharmacodynamic assessment.