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Biomedical subjects

R A Wells

Publications and source records attributed to R A Wells.

At least 19 recordsLinked to original sources
PubMed2005

Treatment of elderly patients with acute lymphoblastic leukemia--evidence for a benefit of imatinib in BCR-ABL positive patients.

All patients with acute lymphoblastic leukemia (ALL) over age 60 years seen at Princess Margaret Hospital over an 11-year period were analysed retrospectively. Of 53 patients, 45 received multiagent induction chemotherapy using a variety of regimens. There were 13 BCR-ABL positive patients, 9 of who received imatinib mesylate, either during induction or post-remission therapy. The overall complete remission (CR) rate of all 45-induction patients was 56%, with a 27% induction-related mortality rate. The CR rate was not influenced by induction regimen, age, initial WBC, LDH or BCR-ABL status. The median overall survival of the induction patients was 9 months, while the median progression-free survival (PFS) of the patients achieving CR was 10 months. The estimated overall survival (OS) at 3 years was 18.4% (95% CI: 9.8-34.3%). Age and initial WBC did not significantly predict for OS when evaluating the entire group of induction patients. However, there was a strong trend for BCR-ABL status to favorably predict for PFS, and for OS when only patients treated after July 2000 (when imatinib became available) were evaluated. The results indicate that ALL remains a poor prognosis disease in elderly patients, and that aggressive induction regimens designed for younger patients are very toxic for these patients. These data suggest that BCR-ABL+ ALL is becoming a relatively more favorable prognosis disease in the elderly, likely due to the influence of imatinib therapy. Further regimens should explore the use of less aggressive regimens in elderly patients and should evaluate the optimal way of combining imatinib with conventional agents in BCR-ABL+ patients.

Aged↗
PubMed2005

Assessment of the downstream portion of the mitochondrial pathway of caspase activation in patients with acute myeloid leukemia.

Most chemotherapeutic agents used in the treatment of acute myeloid leukemia (AML) induce apoptosis by triggering the mitochondrial pathway of caspase activation. To investigate the downstream portion of the mitochondrial pathway of caspase activation in patients with AML, cytosolic lysates were stimulated with cytochrome c and dATP and hydrolysis of Ac-DEVD-AFC by effector caspases was measured. Defects in the distal mitochondrial pathway were more common in samples from patients with AML that relapsed rapidly after induction chemotherapy compared to samples from treatment naïve patients. The incidence of blocked pathways did not differ based on response to induction chemotherapy, as even nonresponders generally had an intact pathway. When the distal mitochondrial pathway was blocked, defects were usually at the level of the effector caspases. Thus, functional defects in the distal portion of the mitochondrial pathway of caspase activation may help explain the nature of response and relapse after treatment.

Adenosine Triphosphate↗
PubMed2004

The role of allogeneic bone marrow transplantation in adult patients below the age of 55 years with acute lymphoblastic leukemia in first complete remission: a donor vs no donor comparison.

The role of allogeneic bone marrow transplantation (alloBMT) in adults with acute lymphoblastic leukemia (ALL) in first complete remission (CR1) remains controversial. At our institution, the policy is to offer alloBMT to ALL patients in CR1 up to the age of 55 years if a related donor is available. In addition, unrelated donor transplants are offered to patients with Philadelphia (Ph+) ALL. We report the results on 92 patients with ALL treated according to this policy from September 1992 to October 2001. Of the 87 patients achieving CR1, the comparison of patients with (n=48) or without donors (n=39) was done using an intention-to-treat approach. Of the 48 patients with donors (39 related and nine unrelated), 35 (73%) received alloBMT in CR1. No significant difference in 3-year event-free survival (EFS) (40 vs 39%, P=0.74) or overall survival (OS) (46 vs 58%, P=0.41) was seen in 'donor' vs 'no-donor' groups. For Ph+ patients, 3-year EFS and OS in 'donor' group were 46 and 57%, respectively, none of the patients in 'no-donor' group survived beyond 3 years. With our treatment strategy, 3-year OS of Ph+ patients was equivalent to Ph-negative (Ph-) patients (51 vs 52%, P=0.77). In conclusion, our data show that the policy of performing alloBMT if a sibling donor is available has not resulted in better outcome in Ph- patients.

Adolescent↗
PubMed1999

Deregulation of NPM and PLZF in a variant t(5;17) case of acute promyelocytic leukemia.

Greater than 95% of acute promyelocytic leukemia (APL) cases are associated with the expression of PML-RARalpha. This chimeric protein has been strongly implicated in APL pathogenesis because of its interactions with growth suppressors (PML), retinoid signaling molecules (RXRalpha), and nuclear hormone transcriptional co-repressors (N-CoR and SMRT). A small number of variant APL translocations have also been shown to involve rearrangements that fuse RARalpha to partner genes other than PML, namely PLZF, NPM, and NuMA. We describe the molecular characterization of a t(5;17)(q35;q21) variant translocation involving the NPM gene, identified in a pediatric case of APL. RT-PCR, cloning, and sequence studies identified NPM as the RARalpha partner on chromosome 5, and both NPM-RARalpha and RARalpha-NPM fusion mRNAs were expressed in this patient. We further explored the effects of the NPM-RARalpha chimeric protein on the subcellular localization of PML, RXRalpha, NPM, and PLZF using immunofluorescent confocal microscopy. While PML remained localized to its normal 10-20 nuclear bodies, NPM nucleolar localization was disrupted and PLZF expression was upregulated in a microspeckled pattern in patient leukemic bone marrow cells. We also observed nuclear co-localization of NPM, RXRalpha, and NPM-RARalpha in these cells. Our data support the hypothesis that while deregulation of both the retinoid signaling pathway and RARalpha partner proteins are molecular consequences of APL translocations, APL pathogenesis is not dependent on disruption of PML nuclear bodies.

Cell Nucleolus↗
PubMed1997

Fusion of retinoic acid receptor alpha to NuMA, the nuclear mitotic apparatus protein, by a variant translocation in acute promyelocytic leukaemia.

Acute promyelocytic leukaemia (APL) is uniquely associated with chromosomal translocations that disrupt the gene encoding the retinoic acid receptor, RARA. In more than 99% of cases, this disruption results in the formation of a PML-RARA gene fusion. Two rare variants of APL have been described, in which RARA is fused to one of two other genes, PLZF and NPM. Although RARA dysregulation is evidently important in APL, the role of the various fusion partners remains unclear. We have characterized a fourth APL gene fusion, which links exons encoding the retinoic acid and DNA-binding domains of RARA to 5' exons of NuMA, a gene that encodes the nuclear mitotic apparatus protein. The NuMA-RARA fusion protein exists in sheet-like nuclear aggregates with which normal NuMA partly co-localizes. In contrast to t(15;17) APL, the intracellular distribution of PML is normal in these cells. Our results suggest that interference with retinoid signalling, and not disruption of PML organization, is essential to the APL phenotype and implicates for the first time an element of the mitotic apparatus in the molecular pathogenesis of human malignancy.

Amino Acid Sequence↗
PubMed1996

A new variant translocation in acute promyelocytic leukaemia: molecular characterization and clinical correlation.

Translocation t(15;17)(q22;q21) is an acquired clonal cytogenetic change present in almost all cases of acute promelocytic leukemia (APL). The molecular genetic basis of the translocation supports its integral role in pathogenesis. We describe a patient with APL in whom the leukaemic clone was characterized by a true variant of the classical t(15;17). The patient whose disease had numerous atypical clinical features, had t(11;17)(q13;121). The chromosome 17 breakpoint was localized to intron 2 of RARA by Southern blotting, and there was no evidence at the molecular level for rearrangement at PML locus. These data, along with previous reports of rare variant translocations in APL, indicate that while dysregulation of RARA by gene fusion may be essential for the APL phenotype, the particular fusion partner may determine clinicopathological aspects, including presentation, response to treatment with all-trans retinoic acid (ATRA), and prognosis. This heterogeneity suggests that the variant fusion partners of RARA in APL encode factors with properties both common to and distinct from those of PML. Investigation of these factors promises to shed light on the complex development pathways involved in the regulation of haematopoiesis.

Bone Marrow↗
PubMed1993

Chromosomal localization and regulation of the longevity determinant genes in a selected strain of Drosophila melanogaster.

A controlled chromosome substitution experiment was performed on a strain (NDC-L) selected for long life to determine if the genes responsible for the extended-longevity phenotype could be localized to any particular chromosome(s). All 27 different possible combinations of the three major chromosomes of Drosophila melanogaster were constructed and longevities were determined on 3875 individual animals of both sexes and analysed. The results are statistically significant and demonstrate that mean longevity is specified primarily by recessive genes on the third chromosome (c3). The extended longevity phenotype (ELP) is only expressed in those lines which are homozygous for the NDC-L type c3. Loci on the first (c1) and second (c2) chromosomes interact, both positively (c1) and negatively (c2), respectively, such that c1 represses c2 which in turn represses c3. The ELP is fully expressed in the mutual presence and mutual absence of c1 and c2. The significance of these results is discussed in the context of broader categories of molecular genetic mechanisms suggested previously to be involved in the modulation of longevity in Drosophila.

Animals↗
PubMed1993

A family of cation ATPase-like molecules from Plasmodium falciparum.

We report the nucleotide and derived amino acid sequence of the ATPase 1 gene from Plasmodium falciparum. The amino acid sequence shares homology with the family of "P"-type cation translocating ATPases in conserved regions important for nucleotide binding, conformational change, or phosphorylation. The gene, which is present on chromosome 5, has a product longer than any other reported for a P-type ATPase. Interstrain analysis from 12 parasite isolates by the polymerase chain reaction reveals that a 330-bp nucleotide sequence encoding three cytoplasmic regions conserved in cation ATPases (regions a-c) is of constant length. By contrast, another 360-bp sequence which is one of four regions we refer to as "inserts" contains arrays of tandem repeats which show length variation between different parasite isolates. Polymorphism results from differences in the number and types of repeat motif contained in this insert. Inserts are divergent in sequence from other P-type ATPases and share features in common with many malarial antigens. Studies using RNA from the erythrocytic stages of the malarial life cycle suggest that ATPase 1 (including the sequence which encodes tandem repeats) is expressed at the large ring stage of development. Immunolocalization has identified ATPase 1 to be in the region of the parasite plasma membrane and pigment body. These findings suggest a possible model for the genesis of malarial antigens.

Adenosine Triphosphatases↗
PubMed1992

FRA2B is distinct from inverted telomere repeat arrays at 2q13.

Human chromosome 2 was formed by a telomere-to-telomere fusion of two ancestral ape chromosomes. The fusion point is localized in chromosomal band 2q13, which also contains the rare, folate-sensitive fragile site FRA2B. It has been hypothesized that this fragile site may be related to the presence of interstitial telomeric and subtelomeric sequences, which have come to lie in an inverted repeat arrangement as a result of the fusion event. Fluorescence in situ hybridization of a genomic cosmid c8.1, which spans the fusion point, was carried out on metaphase spreads of an individual who expressed the fragile site at 2q13. We show that the fusion point maps distal to this fragile site. Therefore, we conclude that the inverted arrays of telomeric and subtelomeric sequences found at this fusion point are unlikely to correspond to the rare fragile site at 2q13.

Base Sequence↗
PubMed1992

Multiple variants in subtelomeric regions of normal karyotypes.

We describe a human genomic cosmid clone, 56.1.1, that contains subtelomeric sequences present on multiple human chromosomes. In particular, using fluorescence in situ hybridization, we have identified 16 sites of hybridization on 12 chromosomes. In a sample of 8 unrelated individuals, 10 of these sites showed interindividual variation. Co-hybridization with other polymorphic probes allowed us to demonstrate cytologically heterozygosity at three sites in six individuals. The chromosomal distribution of hybridization sites in a family strongly suggests that these variants are inherited in a Mendelian fashion. These data show that subtelomeric repeats are a rich source of genetic variability. Possible mechanisms of generation of such variants are discussed.

Chromosomes, Human↗
PubMed1991

Origin of human chromosome 2: an ancestral telomere-telomere fusion.

We have identified two allelic genomic cosmids from human chromosome 2, c8.1 and c29B, each containing two inverted arrays of the vertebrate telomeric repeat in a head-to-head arrangement, 5'(TTAGGG)n-(CCCTAA)m3'. Sequences flanking this telomeric repeat are characteristic of present-day human pretelomeres. BAL-31 nuclease experiments with yeast artificial chromosome clones of human telomeres and fluorescence in situ hybridization reveal that sequences flanking these inverted repeats hybridize both to band 2q13 and to different, but overlapping, subsets of human chromosome ends. We conclude that the locus cloned in cosmids c8.1 and c29B is the relic of an ancient telomere-telomere fusion and marks the point at which two ancestral ape chromosomes fused to give rise to human chromosome 2.

Base Sequence↗
PubMed1990

Genetic alteration of normal aging processes is responsible for extended longevity in Drosophila.

The first step in a genetic analysis of aging is to identify and characterize the genetic mutants and their controls that will be used. Such mutants or strains are initially identified by their effect on the life span. Yet many genetic interventions are known to have some effect on the life span without necessarily affecting the aging process. It is therefore necessary to prove that one is actually dealing with an aging mutant before one draws strong inferences from the data. Casarett's rules provide an operational test for doing so, relying as they do on the comparison of aging bio-markers in the experimental and reference strains. We show that our previously described genetically based long-lived NDC-L strain and its normal-lived NDC-R control strain differ only in the chronological age of expression of two behavioral and three physiological functional age biomarkers. They do not differ in the sequence or the physiological age of expression of these biomarkers. These two strains comply with the Casarett rules and thereby comprise a valid tool with which to conduct a comparative genetic analysis of aging. The implications of the available data are discussed, including the possibility that aging in these strains of Drosophila melanogaster may be the result of a multiphasic developmental process.

Aging↗
PubMed1990

Telomere-related sequences at interstitial sites in the human genome.

The ends (telomeres) of eukaryotic chromosomes are protected from degradation and from loss during DNA replication by buffers of simple tandem repetitive sequence. The nucleotide sequence of these telomeric arrays is fundamental to telomere function as a site for protein and ribonucleoprotein binding and varies only slightly in a wide range of organisms. We present evidence that arrays of this human telomeric sequence, TTAGGG, are present not only at the ends of human chromosomes but also at numerous interstitial sites. These interstitial loci share nucleotide sequence similarity outside the repetitive array, suggesting that they are related functionally or have evolved from a common progenitor locus.

Base Sequence↗
PubMed1989

Hypervariable minisatellites: recombinators or innocent bystanders?

It has become apparent in recent years that unexpectedly large numbers of minisatellites exist within the eukaryotic genome. Their use in genetics is well known, but as with any new class of sequence, there is also much speculation about their involvement in a range of biological processes. How much is known of their biology?

Base Sequence↗
PubMed1989

Simultaneous genetic mapping of multiple human minisatellite sequences using DNA fingerprinting.

We have used several DNA probes which simultaneously recognize multiple loci to follow the segregation of a large number of minisatellite loci through two large reference pedigrees. The segregation data were analyzed for linkage to previously characterized marker loci using RFLP mapping data for these pedigrees from a previous study and from the Centre d'Etude du Polymorphisme Humain data bank. In this way we have mapped 31 separate minisatellite alleles of a total of 146 studied. The results of these analyses suggest that the distribution of minisatellites in the human genome is skewed toward telomeres and is highly clustered in character. A group of at least five separate minisatellites was found at 7 qter, and smaller clusters are present in several other regions. We detected a smaller than expected number of linkages, perhaps because of the clustering of minisatellite loci. The 7qter minisatellite cluster is in a region of excess male meiotic recombination, and in this respect is similar to minisatellite clusters at 16pter and in the X-Y pseudoautosomal region.

Alleles↗