More detailed characterization of some of the HL60 karyotypic features by fluorescence in situ hybridization

Pisosterol induces interphase arrest in HL60 cells with c-MYC amplification

The leukaemia cell line HL60 is widely used in studies of the cell cycle, apoptosis and adhesion mechanisms in cancer cells. One marked characteristic of HL60 cells is the c-MYC proto-oncogene amplification, resulting in the formation of homogeneously staining regions (HSRs) at 8p24. We conducted a fluorescence in situ hybridization study in an HL60 cell line, using a locus-specific probe for c-MYC, before and after treatment with pisosterol (at 0.5, 1.0 and 1.8 microg/mL), a triterpene isolated from the fungus Pisolithus tinctorius. Before treatment, 87.5% of the cells showed HSRs. After treatment, no effects were detected at lower concentrations of pisosterol (0.5 and 1.0 microg/mL). However, at 1.8 microg/mL only 15% of the cells presented HSRs, and 39.5% presented few fluorescent signals (3 or 4 alleles), suggesting that pisosterol probably blocks the cells with HSRs at interphase. This result is particularly interesting because cells that do not show a high degree of c-MYC gene amplification have a less aggressive and invasive behaviour and are easy targets for chemotherapy. Therefore, further studies are needed to examine the use of pisosterol in combination with conventional anti-cancer therapy.

Apoptosis induction by (+)alpha-tocopheryl succinate in the absence or presence of all-trans retinoic acid and arsenic trioxide in NB4, NB4-R2 and primary APL cells

We analyzed the effect of (+)alpha-tocopheryl succinate (alpha-TOS) alone or associated with arsenic trioxide (ATO) or all-trans retinoid acid (ATRA) in acute promyelocytic leukemia (APL). alpha-TOS-induced apoptosis in APL clinical samples and in ATRA-sensitive (NB4) and ATRA-resistant (NB4-R2) APL cell lines. The effective dose 50% (ED-50) was calculated to be 71 and 58muM, for NB4 and NB4-R2, respectively. alpha-TOS neither induced nor modified ATRA-induced differentiation of APL cells, and did not affect the proliferation and differentiation of normal CD34(+) hematopoietic progenitors in methylcellulose assays. alpha-TOS exerted a moderate antagonistic effect to ATO-induced apoptosis when treatment was done simultaneously but when alpha-TOS was added 24h after ATO, an additive effect was observed. Our results support the concept of alpha-TOS as an anti-leukemic compound which spares normal hematopoiesis.

Glycolytic metabolism confers resistance to combined all-trans retinoic acid and arsenic trioxide-induced apoptosis in HL60rho0 cells

Glycolytic cancers are resistant to many forms of chemotherapy and some respond poorly to differentiation therapies. Here, we investigate the effects of exposure to all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) on differentiation and cell survival in the human leukemia cell line, HL60 and its mitochondrial gene knockout mutant, HL60rho0. Glycolytic HL60rho0 cells exposed to single and combined treatments expressed less CD15, in most cases, but produced a stronger respiratory burst than parental HL60 cells. HL60rho0 cells were also significantly more resistant to apoptosis after combined ATO+ATRA treatment compared with HL60 cells, and this was associated with failure to upregulate Fas expression.

High-resolution genomic profiling of chromosomal aberrations using Infinium whole-genome genotyping

Array-CGH is a powerful tool for the detection of chromosomal aberrations. The introduction of high-density SNP genotyping technology to genomic profiling, termed SNP-CGH, represents a further advance, since simultaneous measurement of both signal intensity variations and changes in allelic composition makes it possible to detect both copy number changes and copy-neutral loss-of-heterozygosity (LOH) events. We demonstrate the utility of SNP-CGH with two Infinium whole-genome genotyping BeadChips, assaying 109,000 and 317,000 SNP loci, to detect chromosomal aberrations in samples bearing constitutional aberrations as well tumor samples at sub-100 kb effective resolution. Detected aberrations include homozygous deletions, hemizygous deletions, copy-neutral LOH, duplications, and amplifications. The statistical ability to detect common aberrations was modeled by analysis of an X chromosome titration model system, and sensitivity was modeled by titration of gDNA from a tumor cell with that of its paired normal cell line. Analysis was facilitated by using a genome browser that plots log ratios of normalized intensities and allelic ratios along the chromosomes. We developed two modes of SNP-CGH analysis, a single sample and a paired sample mode. The single sample mode computes log intensity ratios and allelic ratios by referencing to canonical genotype clusters generated from approximately 120 reference samples, whereas the paired sample mode uses a paired normal reference sample from the same individual. Finally, the two analysis modes are compared and contrasted for their utility in analyzing different types of input gDNA: low input amounts, fragmented gDNA, and Phi29 whole-genome pre-amplified DNA.

Mitochondrial gene knockout HL60rho0 cells show preferential differentiation into monocytes/macrophages

This study compares the differentiation potential of mitochondrial gene knockout (rho0) and parental HL60 cells in response to 1.25% dimethylsulfoxide (DMSO) and 10nM phorbol myristate acetate (PMA). Compared to HL60 cells, undifferentiated HL60rho0 cells showed partial monocyte/macrophage differentiation, with increased CD11c and CD14 expression, decreased CD71 expression, and weak non-specific esterase staining. Differentiation along the monocyte/macrophage pathway (PMA) was more pronounced in HL60rho0 than parental HL60 cells with increased CD11c and CD14 expression and stronger non-specific esterase staining. DMSO-exposure resulted in a poorly differentiated nuclear morphology, small respiratory burst and marginal up-regulation of CD15 expression in HL60rho0 cells.

Distinct mechanisms lead to HPRT gene mutations in leukemic cells

Leukemias are considered malignant clonal disorders arising from the accumulation of mutations in hematopoietic cells; the majority of these mutations are thought to be acquired somatically. Measurement of mutation frequency (Mf) at the hypoxanthine phosphoribosyltransferase (HPRT) locus has been developed as a method for estimating genomic instability. We investigated the Mf in 16 leukemic cell lines to determine whether these cell lines showed evidence of genomic instability. Although some leukemic cell lines had markedly elevated Mfs, the Mfs at the HPRT locus in leukemic cell lines were not always higher than those of B-lymphoblastoid cell lines and T lymphocytes from normal individuals. We were able to identify the HPRT mutation for 159 of 160 individual HPRT mutants. The HPRT mutations were characterized at a molecular level and classified as either gross chromosomal rearrangements (GCRs) or point mutations, such as single-nucleotide substitutions, insertions, or deletions. With rare exceptions, individual leukemic cell lines showed either point mutations or GCR, but not both. Of note, all the cell lines that primarily showed point mutations are known to be defective in mismatch repair machinery.

The diphtheria toxin/urokinase fusion protein (DTAT) is selectively toxic to CD87 expressing leukemic cells

Diphtheria fusion proteins are a novel class of agents for the treatment of chemotherapy resistant acute myelogenous leukemia (AML). We prepared diphtheria toxin/urokinase fusion protein (DTAT) composed of the amino terminal fragment of the urokinase-type plasminogen activator (uPA) fused to the catalytic and translocation domains of diphtheria toxin (DT) and assessed its activity on leukemic cell lines. The number of uPA receptors (uPAR or CD87) was measured using a phycoerythrin conjugated monoclonal antibody to CD87 and flow cytometry. Seven of 23 cell lines (30%) showed CD87 expression (> or =5000 receptors/cell). DTAT cytotoxicity (IC(50)< or =30pM) was observed in all seven of these samples and none of the 16 samples with low or absent CD87 expression. There was a significant correlation between DTAT sensitivity and CD87 density (P=0.0007). These results show that specific CD87 binding is one factor important in the sensitivity of patient's leukemic blasts to DTAT and demonstrate for the first time that the CD87/uPAR can be used as a target for fusion protein therapy of AML.

V(D)J recombination activity in human hematopoietic cells: correlation with developmental stage and genome stability

V(D)J recombinase activity was measured in an array of human cell lines derived from hematopoietic malignancies representing various lineages and developmental stages. The level of recombinase activity was found to vary over a 2000-fold range between different cell lines. Several myeloid cell lines were positive for V(D)J recombinase activity, providing additional insight into the relationship between myeloid and lymphoid differentiation. Despite high levels of V(D)J recombination in two human acute lymphoblastic leukemia cell lines, the cytogenetic karyotype has remained essentially constant over several years of continuous cell culture. Silencing of recombination of chromosomal and minichromosomal targets has been strongly correlated with the replication of CpG methylated DNA in murine cells. Here, in human cells, we show that human minichromosomes bearing V(D)J recombination signals are protected well over 100-fold from recombination if they are CpG methylated, providing a rational basis for the karyotypic stability in cells with high levels of V(D)J recombination activity.