Inducing TCF3-PBX1B (t1;13)(q23;p13.3) Fusion Protein Influences Metabolism of Methotrexate in Human Acute Lymphoblastic Leukemia Cell Lines

Acute Lymphoblastic Leukemia (ALL) is the most widespread form of childhood cancer, and methotrexate (MTX) is one of the most commonly used chemotherapeutic agents used to treat pediatric ALL. The antileukemic effects of MTX is partially determined by intracellular concentrations of MTX polyglutamate (MTXPG), the active form of the drug. MTXPG inhibits the folate pathway, leading to cytotoxicity towards leukemic cells. It has been observed that MTXPG concentrations are lower in the Transcription Factor 3 - PBX Homeobox 1B (TCF3-PBX1B) subtype of leukemia patients as compared to other subtypes, but the mechanism through which this occurs is largely unknown. This study aims to establish the REH human ALL cell line as a viable cell line that accurately depicts pediatric ALL patients to allow for future studies to be performed to elucidate the mechanism of action of the TCF3-PBX1B fusion protein. Preliminary patient data has shown that folate pathway genes, folylpolyglutamate synthetase (FPGS) and reduced folate carrier (SLC19A1 or RFC) are positively correlated with MTXPG concentration. Further analysis has shown that transcription factors Notch Receptor 2 (NOTCH2) and SRY-Box Transcription Factor 11 (SOX11) have strong negative correlation with FPGS and SLC19A1. In our experiment, REH human ALL cells were transduced with either doxycycline-inducible LacZ (as control) or TCF3-PBX1, to determine whether the same trends seen in patients hold true in human leukemia cell lines. Data shows similar trends between patients and cell line and that the presence of TCF3-PBX1B fusion protein in REH cell line ultimately decreases intracellular MTXPG concentration. This establishes the REH human ALL cell line as a viable method of studying MTX metabolism in pediatric ALL patients, and future studies performed on the cell line can be incorporated into clinical care to create a personalized MTX treatment.