No abstract

Interactions between retinoic acid (RA) receptor ␣ (RAR␣) and coregulators play a key role in coordinating gene transcription and myeloid differentiation. In patients with acute promyelocytic leukemia (APL), the RAR␣ gene is fused with the promyelocytic leukemia (PML) gene via the t(15;17) translocation, resulting in the expression of a PML/RAR␣ fusion protein. Here, we report that topoisomerase II beta (TopoII␤) associates with and negatively modulates RAR␣ transcriptional activity and that increased levels of and association with TopoII␤ cause resistance to RA in APL cell lines. Knockdown of TopoII␤ was able to overcome resistance by permitting RA-induced differentiation and increased RA gene expression. Overexpression of TopoII␤ in clones from an RA-sensitive cell line conferred resistance by a reduction in RA-induced expression of target genes and differentiation. Chromatin immunoprecipitation assays indicated that TopoII␤ is bound to an RA response element and that inhibition of TopoII␤ causes hyperacetylation of histone 3 at lysine 9 and activation of transcription. Our results identify a novel mechanism of resistance in APL and provide further insight to the role of TopoII␤ in gene regulation and differentiation.

Investigating the mutations driving non Hodgkin lymphomas and developing plasma-based assays for tumour detection and monitoring) (R.D.M.); a post-doctoral fellowship from the Michael Smith Foundation for Health Research (H.-L.W.); and a Bio-Rad Droplet Innovation Award (M.A.). M.A., M.C., and K.B. contributed equally to this work. Disclosures: A part of this study was also funded by a Droplet Innovation Award given to M.A. by Bio-Rad.

Ultrasensitive methods for rare allele detection are critical to leverage the full potential offered by liquid biopsies. Here, we describe a novel molecular barcoding method for the precise detection and quantification of circulating tumor DNA (ctDNA). The major benefits of our design include straightforward and cost-effective production of barcoded adapters to tag individual DNA molecules before PCR and sequencing, and better control over cross-contamination between experiments. We validated our approach in a cohort of 24 patients with a broad spectrum of cancer diagnoses by targeting and quantifying single-nucleotide variants (SNVs), indels and genomic rearrangements in plasma samples. By using personalized panels targeting a priori known mutations, we demonstrate comprehensive error-suppression capabilities for SNVs and detection thresholds for ctDNA below 0.1%. We also show that our semi-degenerate barcoded adapters hold promise for noninvasive genotyping in the absence of tumor biopsies and monitoring of minimal residual disease in longitudinal plasma samples. The benefits demonstrated here include broad applicability, flexibility, affordability and reproducibility in the research and clinical settings.