RESUMO
Splicing factor 3b subunit 1 (SF3B1) is the largest subunit and core component of the spliceosome. Inhibition of SF3B1 was associated with an increase in broad intron retention (IR) on most transcripts, suggesting that IR can be used as a marker of spliceosome inhibition in chronic lymphocytic leukemia (CLL) cells. Furthermore, we separately analyzed exonic and intronic mapped reads on annotated RNA-sequencing transcripts obtained from B cells (n = 98 CLL patients) and healthy volunteers (n = 9). We measured intron/exon ratio to use that as a surrogate for alternative RNA splicing (ARS) and found that 66% of CLL-B cell transcripts had significant IR elevation compared with normal B cells (NBCs) and that correlated with mRNA downregulation and low expression levels. Transcripts with the highest IR levels belonged to biological pathways associated with gene expression and RNA splicing. A >2-fold increase of active pSF3B1 was observed in CLL-B cells compared with NBCs. Additionally, when the CLL-B cells were treated with macrolides (pladienolide-B), a significant decrease in pSF3B1, but not total SF3B1 protein, was observed. These findings suggest that IR/ARS is increased in CLL, which is associated with SF3B1 phosphorylation and susceptibility to SF3B1 inhibitors. These data provide additional support to the relevance of ARS in carcinogenesis and evidence of pSF3B1 participation in this process.
RESUMO
Acute myeloid leukemia (AML) is an aggressive hematopoietic disease characterized by glutamine-dependent metabolism. A novel glutaminase (GLS) inhibitor, CB-839, is currently under evaluation for treatment of hematopoietic malignancies and solid tumors. Our purpose was to measure cellular changes in AML associated with CB-839 treatment and to test the ability of hyperpolarized pyruvate for interrogating these changes to OCI-AML3 cells. Our results show that treatment with CB-839 interfered with the citric acid cycle, reduced the NADH/NAD+ ratio and ATP levels, reduced cell proliferation and viability, and reduced the basal and maximal respiratory capacities [oxygen consumption rate (OCR)]. We observed a reduction of the conversion of hyperpolarized pyruvate to lactate in cell lines and in a mouse AML model after CB-839 treatment. Our in vitro and in vivo results support the hypothesis that, in AML, glutamine is utilized to generate reducing equivalents (NADH, FADH2) through the citric acid cycle and that reduction in redox state by GLS inhibition decreases the rate of pyruvate to lactate conversion catalyzed by lactate dehydrogenase. We propose hyperpolarized pyruvate/lactate measurement as a method for direct monitoring of metabolic changes occurring in AML patients receiving CB-839. With further optimization, this method may provide a noninvasive imaging tool to assess the early efficacy of therapeutic intervention with GLS inhibitors.