Abstract 3119: Expression of OPN isoforms and its potential use on risk stratification in early childhood precursor B-acute lymphoblastic leukemia (pre-B ALL)

Abstract

Abstract Precursor-B cell acute lymphoblastic leukemia (Pre-B ALL) corresponds to most leukemia cases. Pre-B ALL in children younger than 12 months-old is characterized by a high total leukocytes count, central nervous system (CNS) infiltration and KMT2A rearrangements (KMT2A-r), whereby patients are directed to a high risk treatment protocol. Searching for new additional prognostic biomarkers, especially those that can better predict CNS involvement are needed. It has been reported that osteopontin (OPN) is able to anchor bone-marrow leukemic blasts, protecting these cells from chemotherapeutic cytotoxicity and that circulating OPN has been correlated to blast CNS infiltration. Until now, data regarding OPN in ALL and other non-solid tumors are only correlated to full lenght OPN. However, OPN suffers alternative splicing, generating three splicing isoforms (OPN-SI), named OPNa, OPNb and OPNc. This study aims to evaluate whether OPN-SIs could differently contribute to risk stratification of childhood Pre-B ALL harboring or not the KMT2A-r. This study included 34 childhood Pre-B ALL patients, whose several clinical data, including the status of KMT2A-r are available. Total RNA from bone marrow blast cells have been extracted using the RNeasy (QIAGEN) mini kit and then cDNA has been synthesized. OPN-SI expression has been analyzed by qualitative and quantitative RT-PCR using isoform specific oligonucleotides. Using the qualitative RT-PCR approach, we showed that most patient samples express the 3 OPN-SI (48.64%). Other 10.8% of these cases expressed OPNa and OPNb isoforms, while 13.51% expressed OPNa and OPNc. Only 8.1% of these samples expressed only OPNa or OPNc isoforms. These data showed that OPNa isoform is expressed in most patient samples, followed by OPNc. We also observed that OPNa expression seems to be correlated to the occurrence of KMT2A-r. Considering OPN-SI expression levels, most patient samples (47.05%) overexpress OPNa. Among those patients that harbor the KMT2A-r, 35.29% of them express similar OPN-SI expression levels, while 32.9% overexpress OPNa and 20% overexpress OPNc. Only 5.88% overexpress OPNb. Among those patient samples that lack KMT2A-r, a higher proportion overexpress OPNa, followed by those that overexpress OPNb, or OPNc or have similar levels of the 3 OPN splice variants. As a whole, our data demonstrate that OPNa isoform is the OPN splice variant expressed in most Pre-B ALL samples, besides being overexpressed in relation to OPNb and OPNc isoforms. Our data also provide evidence that OPNa splice variant expression data could contribute to risk stratification in Pre-B ALL patients, correlated to the occurrence of KMT2A-r, besides being the first study of OPN-SI in non-solid tumors, especially in ALL. Ongoing studies will better better investigate the correlation between OPN-SI expression and additional prognostic data, including KMT2A-r. Citation Format: Abigail Cristina da Silva Rezende Rezende, Mariana Emerenciano Cavalcante de Sa, Etel Rodrigues Pereira Gimba. Expression of OPN isoforms and its potential use on risk stratification in early childhood precursor B-acute lymphoblastic leukemia (pre-B ALL). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3119.