Blaine W. Robinson

Gene expression profiles predictive of outcome and age in infant acute lymphoblastic leukemia: a Children's Oncology Group study

Gene expression profiling was performed on 97 cases of infant ALL from Childrens Oncology Group Trial P9407. Statistical modeling of an outcome predictor revealed 3 genes highly predictive of event-free survival (EFS), beyond age and MLL status: FLT3, IRX2, and TACC2. Low FLT3 expression was found in a group of infants with excellent outcome (n = 11; 5-year EFS of 100%), whereas differential expression of IRX2 and TACC2 partitioned the remaining infants into 2 groups with significantly different survivals (5-year EFS of 16% vs 64%; P < .001). When infants with MLL-AFF1 were analyzed separately, a 7-gene classifier was developed that split them into 2 distinct groups with significantly different outcomes (5-year EFS of 20% vs 65%; P < .001). In this classifier, elevated expression of NEGR1 was associated with better EFS, whereas IRX2, EPS8, and TPD52 expression were correlated with worse outcome. This classifier also predicted EFS in an independent infant ALL cohort from the Interfant-99 trial. When evaluating expression profiles as a continuous variable relative to patient age, we further identified striking differences in profiles in infants less than or equal to 90 days of age and those more than 90 days of age. These age-related patterns suggest different mechanisms of leukemogenesis and may underlie the differential outcomes historically seen in these age groups.

Mismatched nucleotides as the lesions responsible for radiosensitization with gemcitabine: a new paradigm for antimetabolite radiosensitizers

Radiation sensitization by 2′,2′-difluoro-2′-deoxycytidine (dFdCyd) has correlated with dATP depletion [dFdCDP-mediated inhibition of ribonucleotide reductase (RR)] and S-phase accumulation. We hypothesized that radiosensitization by dFdCyd is due to nucleotide misincorporations in the presence of deoxynucleotide triphosphate pool imbalances, which, if not repaired, augments cell death following irradiation. The ability of dFdCyd to produce misincorporations was measured as pSP189 plasmid mutations in hMLH1-deficient [mismatch repair (MMR) deficient] and hMLH1-expressing (MMR proficient) HCT116 cells. Only MMR-deficient cells showed a significant increase in nucleotide misincorporations (2- to 3-fold increase; P ≤ 0.01) after radiosensitizing concentrations of dFdCyd ± 5 Gy radiation, which persisted for at least 96 h. dFdCyd (10 nmol/L) did not radiosensitize MMR-proficient HCT116 or A549 cells, but following small interfering RNA–mediated suppression of hMLH1, this concentration produced excellent radiosensitization (radiation enhancement ratios = 1.6 ± 0.1 and 1.5 ± 0.1, respectively; P < 0.05) and a 2.5-fold increase in mutation frequency in A549 cells. Cytosine arabinoside (1-β-d-arabinofuranosylcytosine), which can be incorporated into DNA but does not inhibit RR, failed to radiosensitize MMR-deficient cells or increase mutation frequency in the MMR-deficient and MMR-proficient cells. However, the RR inhibitor hydroxyurea radiosensitized MMR-deficient cells and increased nucleotide misincorporations (≥5-fold increase; P < 0.05), thus further implicating the inhibition of RR as the mechanism underlying radiosensitization by dFdCyd. These data showed that the presence and persistence of mismatched nucleotides is integral to radiosensitization by dFdCyd and suggest a role for hMLH1 deficiency in eliciting the radiosensitizing effect. [Mol Cancer Ther 2007;6(6):1858–68]

Abundant anti-apoptotic BCL-2 is a molecular target in leukaemias with t(4;11) translocation

Chemotherapy resistance from imbalanced apoptosis regulation may contribute to poor outcome in leukaemias with t(4;11). Anti‐apoptotic BCL‐2 expression and target modulation were characterized in cell lines with t(4;11) and BCL‐2 expression was examined in MLL and non‐MLL infant/paediatric leukaemia cases by Western blot analysis and/or real‐time polymerase chain reaction. Cytotoxicity of Genasense™ (Oblimersen Sodium, G3139) alone or combined with cytotoxic drugs was assessed by MTT [(3‐4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide] assays of the cell lines, applying pharmacostatistical response surface modelling of drug interactions. Apoptosis and cell cycle were evaluated by flow cytometry in RS4:11 cells. Primary leukaemias and cell lines with t(4;11) expressed abundant BCL2 mRNA and protein. Variable, sometimes substantial BCL2 mRNA was detected in other leukaemia subtypes. G3139 reduced BCL2 mRNA and protein in RS4:11 cells. The most sensitive cell line to single‐agent G3139 was RS4:11. Low G3139 concentrations sensitized RS4:11 and MV4‐11 cells to select anti‐leukaemia cytotoxic drugs. In RS4:11 cells, combining G3139 with doxorubicin (ADR) increased active caspase 3 and TUNEL staining compared to ADR alone, indicating greater apoptosis, and G3139 increased S‐phase progression. The abundant BCL‐2 affords a molecular target in leukaemias with t(4;11). G3139 exhibits preclinical activity and synergy with select cytotoxic agents in RS4:11 and MV4‐11 cells, and these effects occur through apoptosis.

Intensified chemotherapy without SCT in infant ALL: Results from COG P9407 (Cohort 3)

Infants with acute lymphoblastic leukemia (ALL) present with aggressive disease and a poor prognosis. Early relapse within 6–9 months of diagnosis is common. Approximately 75% of infants have MLL‐rearranged (MLL‐R) ALL with event free survival (EFS) ranging from 20% to 30%. Childrens Oncology Group (COG) P9407 used shortened (46 weeks), intensified therapy to address early relapse and poor EFS.

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.

BglII‐based panhandle and reverse panhandle PCR approaches increase capability for cloning der(II) and der(other) genomic breakpoint junctions of MLL translocations

Panhandle PCR techniques to amplify known sequence flanked by unknown sequence have been useful for MLL genomic breakpoint junctions and fusion transcripts because MLL has a large number of partner genes. However, genomic panhandle PCR approaches are impeded when the restriction fragment that contains the breakpoint junction is too large to amplify. We devised new panhandle PCR approaches for MLL genomic breakpoint junctions that create the template from BglII restriction fragments by attaching MLL sequence to a BglII site in the partner gene. This leads to the annealing of MLL and its complement in the handle and creates an intrastrand loop containing the breakpoint junction sequence for amplification with primers all from MLL. BglII panhandle PCR for der(11) breakpoint junctions was accomplished by ligating a phosphorylated oligonucleotide containing a BglII overhang and sequence complementary to MLL exon 7 to the 3′ ends of BglII digested DNA, and forming the template from the sense strand of DNA. In BglII reverse panhandle PCR for der(other) breakpoint junctions, a phosphorylated oligonucleotide containing a BglII overhang and the complement of antisense sequence in MLL exon 10 was ligated to the 3′ ends of BglII digested DNA, and the template was formed from the antisense strand of DNA. These approaches amplified 5′‐MLL‐MLLT4‐3′ and 5′‐AFF1‐MLL‐3′ breakpoint junctions. The former is significant because few t(6;11) genomic breakpoint junctions have been sequenced. BglII panhandle PCR approaches increase the possibilities for cloning MLL genomic breakpoint junctions where there is heterogeneity in partner genes and breakpoint locations.

mll ortholog containing functional domains of human MLL is expressed throughout the zebrafish lifespan and in haematopoietic tissues

Infant leukaemia is an embryonal disease in which the underlying MLL translocations initiate in utero. Zebrafish offer unique potential to understand how MLL impacts haematopoiesis from the earliest embryonic timepoints and how translocations cause leukaemia as an embryonal process. In this study, a zebrafish mll cDNA syntenic to human MLL spanning the 5′ to 3′ UTRs, was cloned from embryos, and mll expression was characterized over the zebrafish lifespan. The protein encoded by the 35‐exon ORF exhibited 46·4% overall identity to human MLL and 68–100% conservation in functional domains (AT‐hooks, SNL, CXXC, PHD, bromodomain, FYRN, taspase1 sites, FYRC, SET). Maternally supplied transcripts were detected at 0–2 hpf. Strong ubiquitous early zygotic expression progressed to a cephalo‐caudal gradient during later embryogenesis. mll was expressed in the intermediate cell mass (ICM) where primitive erythrocytes are produced and in the kidney where definitive haematopoiesis occurs in adults. mll exhibits high cross species conservation, is developmentally regulated in haematopoietic and other tissues and is expressed from the earliest embryonic timepoints throughout the zebrafish lifespan. Haematopoietic tissue expression validates using zebrafish for MLL haematopoiesis and leukaemia models.

Unique Familial MLL(KMT2A)-Rearranged Precursor B-Cell Infant Acute Lymphoblastic Leukemia in Non-twin Siblings

Infant acute lymphoblastic leukemia (ALL) has never occurred in families except for the ∼100% concordant cases in monozygous twins attributed to twin‐to‐twin metastases. We report the first kindred with infant ALL in non‐twin siblings. The siblings were diagnosed with MLL‐rearranged (MLL‐R) ALL 26 months apart. The second affected sibling had an unaffected dichorionic monozygous co‐twin. Both had fatal outcomes.

Intensified chemotherapy without SCT in infant ALL

Infants with acute lymphoblastic leukemia (ALL) present with aggressive disease and a poor prognosis. Early relapse within 6–9 months of diagnosis is common. Approximately 75% of infants have MLL‐rearranged (MLL‐R) ALL with event free survival (EFS) ranging from 20% to 30%. Childrens Oncology Group (COG) P9407 used shortened (46 weeks), intensified therapy to address early relapse and poor EFS.

Intensified chemotherapy without SCT in infant ALL: Results from COG P9407 (Cohort 3): Intensified Therapy Without Sct in Infant All

Infants with acute lymphoblastic leukemia (ALL) present with aggressive disease and a poor prognosis. Early relapse within 6–9 months of diagnosis is common. Approximately 75% of infants have MLL‐rearranged (MLL‐R) ALL with event free survival (EFS) ranging from 20% to 30%. Childrens Oncology Group (COG) P9407 used shortened (46 weeks), intensified therapy to address early relapse and poor EFS.