PIM as a Rational Target for B-Cell Lymphomas.

The Pim kinases are a family of serine/threonine kinases composed by three members: Pim1, Pim2 and Pim3, involved in the phosphorylation and regulation of several proteins that are essential for cell cycle progression, metabolism or apoptosis (BAD, p21, p27KIP, AKT, Mdm2 and cMyc, among them). Overexpression, translocation or amplification of Pim family have been described in many human cancers, including B-cell Non Hodgkin's Lymphoma, Multiple Myeloma, Prostate cancer and Pancreatic cancer. In addition, 50% of patients diagnosed with diffuse large B-cell Lymphoma (DLBCL) present somatic mutations in Pim1. Despite of its important role in cancer progression, very few chemical inhibitors have been described in the literature, being effective all of them in the high micromolar range.

Validating PIM as a rational therapeutic target in B-cell lymphoma, developing tools for patient stratification and pharmacodynamic studies on PIM inhibition.

Gene expression profiling and Copy Number data were obtained from a series of 94 B-cell Non-Hodgkin Lymphoma patients (DLBCL, FL, MALT, MCL and NMZL). The effect of Pim inhibition was checked on cell lines by using a novel specific inhibitor for the Pim family (ETP-39010). Newly produced antibodies and RT-PCR primers and protocols were standarized.

Gene expression data revealed high Pim isoforms expression in a subset of patients with Mantle cell lymphoma (MCL), and Diffuse Large B-cell lymphoma (DLBLC)-ABC type. CGH analysis focused on chromosomal regions containing Pim family and its main regulatory upstream pathway (JAK/STAT) was performed. Heterozygous gains of Pim1 (6p21.2) and Pim3 (22q13.33) were identified in 13.6% of DLBCL patients and in 4.2% of MCL. Alterations in JAK/STAT pathway were also detected in 59.1% of DLBCL patients, and 37.5% of MCL patients presented any alteration in JAK/STAT pathway, being frequent losses of JAK2 chromosomal region. Analysis of additional pathways involved in the up-stream regulation of Pim family disclosed heterozygous gains of PIK3C3 in 40.9% of DLBCL patients, and gains of PIK3CA in 45.9% of MCL patients.

Lymphoma cell lines (15) derived from both MCL (9) and ABC-DLBLC (6) subtype, have been analyzed by qRT-PCR and Western-blot, showing variable expression levels of Pim1, Pim2 and Pim3. IC50 obtained for the ETP-39010 compound is in the low micromolar range for the MCL (0.7-8.7 micromolar) and DLBCL-ABC (0.8-10.3 micromolar) cell lines. Since Pim kinase family phosphorilate multiple sites of Bad and AKT, we have checked the inhibition of its phosphorilation as molecular biomarkers for the ETP-39010 effect. Our data show an inhibition of at least 20% of pBad (S112) and almost a complete inhibition of pAKT (S473) 4h after treatment. In addition, cell cycle arrest at G1 and induction of apoptosis were observed 24h after the treatment.

Pim family genes are a rational therapeutic target in MCL and DLBCL-ABC lymphoma subtypes. Stratification and pharmacodynamic markers have been developed for PIM inhibition using a novel specific inhibitor compound -ETP-39010-.

No relevant conflicts of interest to declare.