The determination of human peripheral blood mononuclear cell counts using a genomic DNA standard and application in tenofovir diphosphate quantitation.

A fluorescent quantitation method to determine PBMC-derived DNA amounts using purified human genomic DNA (gDNA) as the reference standard was developed and validated. gDNA was measured in a fluorescence-based assay using a DNA intercalant, SYBR green. The fluorescence signal was proportional to the amount (mass) of DNA in the sample. The results confirmed a linear fit from 0.0665 to 1.17 µg/µL for gDNA, corresponding to 2.0 × 106 to 35.0 × 106 cells/PBMC sample. Intra-batch and inter-batch accuracy (%RE) was within ±15%, and precision (%CV) was <15%. Benchtop stability, freeze/thaw stability and long term storage stability of gDNA in QC sample matrix, PBMC pellets samples, and pellet debris samples, respectively, as well as dilution linearity had been established. Consistency between hemocytometry cell counting method and gDNA-based counting method was established. 6 out of 6 evaluated PBMC lots had hemocytometry cell counts that were within ±20% of the cell counts determined by the gDNA method. This method was used in conjunction with a validated LC-MS/MS method to determine the level of tenofovir diphosphate (TFV-DP), the active intracellular metabolite of the prodrugs tenofovir alafenamide (TAF) and tenofovir disoproxil fumarate (TDF), measured in PBMCs in clinical trials of TAF or TDF-containing fixed dose combinations.

Genome-wide TOP2A DNA cleavage is biased toward translocated and highly transcribed loci.

Type II topoisomerases orchestrate proper DNA topology, and they are the targets of anti-cancer drugs that cause treatment-related leukemias with balanced translocations. Here, we develop a high-throughput sequencing technology to define TOP2 cleavage sites at single-base precision, and use the technology to characterize TOP2A cleavage genome-wide in the human K562 leukemia cell line. We find that TOP2A cleavage has functionally conserved local sequence preferences, occurs in cleavage cluster regions (CCRs), and is enriched in introns and lincRNA loci. TOP2A CCRs are biased toward the distal regions of gene bodies, and TOP2 poisons cause a proximal shift in their distribution. We find high TOP2A cleavage levels in genes involved in translocations in TOP2 poison-related leukemia. In addition, we find that a large proportion of genes involved in oncogenic translocations overall contain TOP2A CCRs. The TOP2A cleavage of coding and lincRNA genes is independently associated with both length and transcript abundance. Comparisons to ENCODE data reveal distinct TOP2A CCR clusters that overlap with marks of transcription, open chromatin, and enhancers. Our findings implicate TOP2A cleavage as a broad DNA damage mechanism in oncogenic translocations as well as a functional role of TOP2A cleavage in regulating transcription elongation and gene activation.

Prospective tracing of MLL-FRYL clone with low MEIS1 expression from emergence during neuroblastoma treatment to diagnosis of myelodysplastic syndrome.

We prospectively observed a child exposed to intensive multimodality therapy for metastatic neuroblastoma from emergence of a MLL translocation to disease diagnosis. The t(4;11)(p12;q23) was detected in the marrow 17 months after starting treatment following topoisomerase II poisons, alkylating agents, local radiation, hematopoietic stem cell transplantation, anti-GD2 monoclonal antibody with granulocyte macrophage-colony-stimulating factor, and a high cumulative dose of oral etoposide. Reciprocal genomic breakpoint junctions and fusion transcripts joined MLL with FRYL, the Drosophila melanogaster protein homologue of which regulates cell fate. Etoposide metabolites induced topoisomerase II cleavage complexes that could form both breakpoint junctions. Cells harboring the translocation replaced the marrow without clinical evidence of leukemia and differentiation appeared unaffected for 37 months. Subsequent bilineage dysplasia and increased blasts in addition to the translocation fulfilled criteria for MDS. The MEIS1 target gene of typical MLL fusion oncoproteins was underexpressed before and at MDS diagnosis. These results are consistent with repair of topoisomerase II cleavage from etoposide metabolites as the translocation mechanism, whereas other agents in the regimen may have contributed to progression of the clone with the translocation to MDS. MLL-FRYL did not increase MEIS1 expression, conferred a proliferative advantage without altering differentiation, and had protracted latency to disease.

Topoisomerase II and the etiology of chromosomal translocations.

Acute leukemias with balanced chromosomal translocations, protean morphologic and immunophenotypic presentations but generally shorter latency and absence of myelodysplasia are recognized as a complication of anti-cancer drugs that behave as topoisomerase II poisons. Translocations affecting the breakpoint cluster region of the MLL gene at chromosome band 11q23 are the most common molecular genetic aberrations in leukemias associated with the topoisomerase II poisons. These agents perturb the cleavage-religation equilibrium of topoisomerase II and increase cleavage complexes. One model suggests that this damages the DNA directly and leads to chromosomal breakage, which may result in untoward DNA recombination in the form of translocations. This review will summarize the evidence for topoisomerase II involvement in the genesis of translocations and extension of the model to acute leukemia in infants characterized by similar MLL translocations.