Abstract 6719: Osteopontin-c is worse prognostic marker and mediate key steps associated with central nervous system infiltration in B-cell acute lymphoblastic leukemia cells

B-cell acute lymphoblastic leukemia (B-ALL) is the most common pediatric malignance, but 35% of patients still relapse after chemotherapy treatment, mainly in the central nervous system (CNS). In order to search for new biomarkers that could predict CNS infiltration and relapse, many studies are trying to find gene products aberrantly expressed in these patients, including osteopontin (OPN). The OPN primary transcript undergoes alternative splicing, generating at least five OPN splicing isoforms (OPN-SI), named OPNa, OPNb, OPNc, OPN4 and OPN5, that have tumor specific roles and have been reported as biomarkers in solid tumors. However, knowledge regarding OPN-SI in B-ALL is scarce. This study aimed to investigate the expression patterns and roles of OPN-SI in CNS infiltration in B-ALL. OPN-SI transcript levels were analyzed by quantitative real time PCR (qRT-PCR) assays using RNA extracted from 54 B-ALL pediatric patient blood samples or from RS4,11 cell line. OPNc transcript knock-down in RS4;11 cells (a B-ALL cell line containing the MLL gene fusion) was performed using anti-OPNc or control scrambled antisense DNA oligomers (anti-OPNc-ASOs and Scbl-ASO, respectively). These oligomers were transfected in RS4;11 cells and the in vitro effects of OPNc knock-down were evaluated by several functional assays, such as cell viability by MTT analysis, cell adhesion, and transmigration and invasion assays using a boyden chamber device. Among tested OPN-SI, OPNc is the most highly expressed OPN-SI in B-ALL patient samples containing the MLL fusion gene, when compared to those samples harboring the ETV6-RUNX1 fusion gene (p