Biomedical subjects

S Grant

Publications and source records attributed to S Grant.

At least 19 recordsLinked to original sources

PubMed1992

Granulocyte-macrophage colony-stimulating factor/interleukin-3 fusion protein (pIXY 321) enhances high-dose Ara-C-induced programmed cell death or apoptosis in human myeloid leukemia cells.

High dose Ara-C (HIDAC) induces programmed cell death (PCD) or apoptosis in vitro in human myeloid leukemia cells, which correlates with the inhibition of their clonogenic survival. Hematopoietic growth factors (HGFs) granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) have been demonstrated to enhance the metabolism and cytotoxic effects of HIDAC against leukemic progenitor cells. We examined the effect of pIXY 321 (a GM-CSF/IL-3 fusion protein) on HIDAC-induced PCD and related gene expressions as well as HIDAC-mediated colony growth inhibition of human myeloid leukemia cells. Unlike the previously described effects of HGFs on normal bone marrow progenitor cells, exposure to pIXY 321 alone for up to 24 hours did not suppress PCD in HL-60 or KG-1 cells. However, exposure to pIXY 321 for 20 hours followed by a combined treatment with Ara-C plus pIXY 321 for 4 or 24 hours versus treatment with Ara-C alone significantly enhanced the oligonucleosomal DNA fragmentation characteristic of PCD. This was temporally associated with a marked induction of c-jun expression and a significant decrease in BCL-2. In addition, the treatment with pIXY 321 plus HIDAC versus HIDAC alone produced a significantly greater inhibition of HL-60 colony growth. These findings highlight an additional mechanism of HIDAC-induced leukemic cell death that is augmented by cotreatment with pIXY 321 and may contribute toward an improved antileukemic activity of HIDAC.

Actins↗

PubMed1992

Bryostatin 1 modulates the proliferation and lineage commitment of human myeloid progenitor cells exposed to recombinant interleukin-3 and recombinant granulocyte-macrophage colony-stimulating factor.

The activity of protein kinase C (PK-C) has been implicated in the regulation of the growth and differentiation of both normal and neoplastic hematopoietic cells. We have examined the effects of the PK-C-activating agents phorbol 12,13-dibutyrate (PDBu), mezerein, and bryostatin 1 on the proliferation and lineage commitment of CD34+ human myeloid progenitor cells stimulated by recombinant interleukin-3 (rIL-3) and/or recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF). Although each of the PK-C activators administered alone induced no colony formation, coadministration of these agents with plateau concentrations of each cytokine (eg, 50 ng/mL) increased the number of day 14 granulocyte-macrophage colony-forming units by 100% to 150%. The number of pure and mixed neutrophil and macrophage colonies was substantially enhanced in the presence of PK-C activators, whereas the percentage and, in most cases, the absolute number of eosinophilic colonies was significantly reduced. The inhibition of eosinophilic colony formation was not overcome by the addition of rIL-5. Although addition of bryostatin 1 24 hours before rIL-3 abrogated the increase in total colony formation observed with simultaneous administration of factors, the inhibition of eosinophilic colonies and the increase in neutrophil/macrophage colonies persisted under these conditions. The addition of bryostatin 1 for up to 144 hours after rIL-3 continued to potentiate total colony formation, whereas the inhibition of eosinophilic commitment was lost after 120 hours. Together, these results suggest that pharmacologic interventions at the level of PK-C may regulate both the proliferation as well as the lineage commitment of human hematopoietic progenitors exposed to rGM-CSF and rIL-3.

Bryostatins↗

PubMed1992

Potentiation of the activity of 1-beta-D-arabinofuranosylcytosine by the protein kinase C activator bryostatin 1 in HL-60 cells: association with enhanced fragmentation of mature DNA.

We have examined the interaction between 1-beta-D-arabinofuranosylcytosine (ara-C) and the macrocyclic lactone protein kinase C activator bryostatin 1 in the human promyelocytic leukemia cell line HL-60. Preexposure of cells to 10 nM bryostatin 1 for 24 h, followed by an additional 24-h incubation with 10 microM ara-C, resulted in greater than additive inhibitory effects toward clonogenic HL-60 cells. In a series of alkaline elution assays, cells preincubated with bryostatin 1 and prelabeled with [3H]thymidine exhibited a significant increase in DNA fragmentation following exposure to ara-C in comparison to cells exposed to ara-C alone. This increase in DNA damage was apparent at both neutral and alkaline pH and was not protein associated. In contrast, studies using cells pulse-labeled with [3H]thymidine immediately before analysis suggested that bryostatin 1 pretreatment did not increase the ability of ara-C to interfere with DNA replicative intermediates. Additional studies demonstrated that the increase in DNA fragmentation induced by bryostatin 1 and ara-C preceded both loss of cell membrane integrity (as determined by trypan blue exclusion) as well as depletion of intracellular ATP and NAD pools. Furthermore, the enhanced inhibitory effects of bryostatin 1 and ara-C toward clonogenic HL-60 cells did not appear to result from the induction of cellular differentiation. Finally, agarose gel electrophoresis of DNA obtained from cells exposed to both bryostatin 1 and ara-C revealed a pattern of integer multiples of 180- to 200-base pair fragments commonly associated with endonucleolytic cleavage; the extent of this fragmentation was considerably greater than that observed in cells exposed to ara-C alone. Taken together, these findings suggest that exposure of HL-60 cells to bryostatin 1 renders them more susceptible to ara-C-related DNA damage and that this phenomenon contributes to the cytotoxic effects of this drug combination. They also raise the possibility that bryostatin 1, perhaps through modulation of intracellular signaling events in leukemic cells, has the capacity to potentiate ara-C-related apoptosis or programmed cell death.

Adenosine Triphosphate↗

PubMed1992

A topographic representation of auditory space in the external nucleus of the inferior colliculus of the guinea-pig.

The possibility that the external nucleus of the inferior colliculus (ICX) of the pigmented guinea-pig contains a map of auditory space has been investigated. Auditory stimuli consisted of broad-band sound delivered under free-field anechoic conditions from a range of positions around the animal's azimuthal axis. The responses of clusters of neurons in the ICX to threshold and to near-threshold stimuli displayed sharp spatial tuning. The responses recorded from rostral ICX revealed a preference for auditory stimuli in the anterior field while more caudal neurons preferentially responded to sounds presented in the posterior field. Neurons at intermediate points, along the rostro-caudal axis of the nucleus, displayed preferences for sound stimuli in appropriately intermediate field positions along the contralateral azimuthal axis. At higher stimulus intensities the spatial tuning of the responses decreased, but the optimal direction of preference was usually retained. The contribution of binaural processing to auditory spatial tuning was evident, since unilateral cochlea ablation destroyed the spatial tuning at higher stimulus intensities. The results presented provide the first evidence that a topographically ordered representation of the contralateral auditory azimuth is present in the ICX of a mammal.

Acoustic Stimulation↗

PubMed1992

Industrial blood lead levels in the South Island during 1988 and 1989: trends and follow up patterns.

AIMS: to assess trends in industrial lead exposure and the monitoring programmes in the South Island of New Zealand. METHODS: during the period 1 January 1988 to 31 December 1989, industrial lead exposure was analysed in 1425 workers in at risk occupations and the efficiency of retesting programmes was determined. RESULTS: forty-four percent of these workers had red cell lead levels above 1.9 mumol/L, the top of the reference range for an unexposed population, and 71 individuals had levels exceeding the recommended action limits (males greater than 5.0 mumol/L, and females greater than 3.8 mumol/L). Although most occupational groups showed a small decline in mean red cell lead levels, the pattern of exposure was similar to previous reports. On average, only 43% of exposed workers were retested within the recommended period and 32% of these workers were not retested within 2 years of having a raised blood lead level. CONCLUSIONS: retesting was inefficient but was most reliable when industrial health nurses were employed for monitoring. Not all lead poisoning comes from the traditional lead based industries and significant decreases were found in workers whose primary exposure is to lead from petrol.

Aftercare↗

PubMed1992

The mosaic of alpha cells in the cat retina is not dependent on axon terminal interactions during development.

Alpha ganglion cells in the cat retina are distributed in a regular array. It has been proposed that the development of this mosaic pattern is achieved by class-specific interactions between the dendrites and/or axon terminals of neighbouring alpha cells, but the relative contributions that are made by each of these factors to the regularity of the mosaic remain unclear. An opportunity to address this question is provided by a comparative study of the distribution of alpha cells across the nasotemporal division of normally pigmented and Siamese cat retinae. In this strip of retina the alpha cell population divides its axon terminals between the two sides of the brain. Hence, the potential for interactions between axon terminals of alpha cells whose somata are adjacent within this region of the retina is undermined. This situation is exacerbated in Siamese cats because they have a congenital abnormality in this region, which results in an abnormally wide nasotemporal division. In this study the regularity of the alpha cell mosaic has been analysed at a wide range of eccentricities, including the nasotemporal division. In normally pigmented cats the nasotemporal division was visualised directly following unilateral horseradish peroxidase injections into the thalamus. In Siamese cats, the location of the abnormally wide nasotemporal division was inferred from electrophysiological recordings undertaken in their striate cortices. In both strains of cat the regularity of the alpha cell mosaic was shown to be largely independent of their density or retinal location. Furthermore, in the normals, the separate mosaics for ipsilaterally or contralaterally projecting alpha cells within the nasotemporal division were found to be no more or less regular than that for the combined population. This finding implies that there is no disturbance in their order across the discontinuity formed by their separate chiasmatic routes. Similar results were obtained from within the abnormal nasotemporal division of the Siamese cat. It is concluded that terminal interactions play an insignificant role in the formation of the adult alpha cell mosaic, the regularity of which is probably established by class-specific intraretinal interactions.

Animals↗

PubMed1992

Changing patterns of binocular visual connections in the intertectal system during development of the frog, Xenopus laevis. III. Modifications following early eye rotation.

In the frog, Xenopus laevis, a system of intertectal connections underlies the visual projection from an eye to its ipsilateral tectal lobe and is involved in the topographic representation of binocular visual space. Rotation of one eye in early life may be followed by a radical rearrangement of the connections in this system. The modified pattern which later emerges is that which keeps the visual projection through the ipsilateral eye in topographic registration with the direct visual projection from the contralateral eye to the same tectal lobe. This plasticity requires visual experience. In this paper we describe the time-course and sequence of events by which this plasticity is effected. Following rotation of one eye in larval animals or in animals undergoing metamorphic climax, the earliest evidence of intertectal modification was found 3-4 weeks after metamorphosis. With increasing intervals after metamorphosis an increasing proportion of animals displayed modified intertectal systems. At intermediate intervals many animals showed partial modifications, which were interpreted as transitional stages in the modification process. Analysis of these transitional stages indicated that the sequence of events involved in the elaboration of a modified intertectal system following the experimental alteration of eye alignment exhibits features in common with rearrangements of the system that occur during normal development in response to growth-related alterations in eye alignment.

Animals↗

PubMed1992

Plasticity of binocular visual connections in the frog, Xenopus laevis: reversibility of effects of early visual deprivation.

In frogs, each lobe of the midbrain optic tectum receives two spatially aligned maps of binocular visual space, one through each eye. The map from the contralateral eye is the product of direct retinal input to the tectum, while that from the ipsilateral eye is mediated by a commissural system of connections that relays binocular visual information from one tectal lobe to the other. In Xenopus laevis, dark-reared from early life, the visuotectal map through the ipsilateral eye exhibits significant signs of disorder indicating that the normal development of the underlying "intertectal" system involves experience-dependent processes. Here we investigate the potential of this system for recovery from such deprivation-induced disruption. Three groups of animals were first dark-reared from embryonic stages until 3 months, 12 months or 2 years after metamorphosis. These short-, medium- and long-term periods of visual deprivation are associated with a progressive disturbance of the intertectal system (Grant and Keating 1989b). The animals then experienced 12-18 months in a normal visual environment, before an electrophysiological mapping experiment was carried out to reveal the status of their intertectal system. Quantitative analyses of the visuotopic order in the ipsilateral visuotectal map and of its spatial alignment with the map derived from the contralateral eye revealed that these features were completely normal in all 3 experimental groups. It is concluded that defects present in the intertectal system of dark-reared Xenopus can be repaired by subsequent visual experience, and that the reparative capacity is not limited either by the animal's age or by the existing degree of prior disruption.

Animals↗

PubMed1992

Topographic organization, number, and laminar distribution of callosal cells connecting visual cortical areas 17 and 18 of normally pigmented and Siamese cats.

The callosal connections between visual cortical areas 17 and 18 in adult normally pigmented and "Boston" Siamese cats were studied using degeneration methods, and by transport of WGA-HRP combined with electrophysiological mapping. In normal cats, over 90% of callosal neurons were located in the supragranular layers. The supragranular callosal cell zone spanned the area 17/18 border and extended, on average, some 2-3 mm into both areas to occupy a territory which was roughly co-extensive with the distribution of callosal terminations in these areas. The region of the visual field adjoining the vertical meridian that was represented by neurons in the supragranular callosal cell zone was shown to increase systematically with decreasing visual elevation. Thus, close to the area centralis, receptive-field centers recorded from within this zone extended only up to 5 deg into the contralateral hemifield but at elevations of -10 deg and -40 deg they extended as far as 8 deg and 14 deg, respectively, into this hemifield. This suggests an element of visual non-correspondence in the callosal pathway between these cortical areas, which may be an essential substrate for "coarse" stereopsis at the visual midline. In the Siamese cats, the callosal cell and termination zones in areas 17 and 18 were expanded in width compared to the normal animals, but the major components were less robust. The area 17/18 border was often devoid of callosal axons and, in particular, the number of supragranular layer neurons participating in the pathway were drastically reduced, to only about 25% of those found in the normally pigmented adults. The callosal zones contained representations of the contralateral and ipsilateral hemifields that were roughly mirror-symmetric about the vertical meridian, and both hemifield representations increased with decreasing visual elevation. The extent and severity of the anomalies observed were similar across individual cats, regardless of whether a strabismus was also present. The callosal pathway between these visual cortical areas in the Siamese cat has been considered "silent," since nearly all neurons within its territory are activated only by the contralateral eye. The paucity of supragranular pyramidal neurons involved in the pathway may explain this silence.

Albinism↗

PubMed1992

Effects of bryostatin 1 and rGM-CSF on the metabolism of 1-beta-D-arabinofuranosylcytosine in human leukaemic myeloblasts.

The effects of the protein kinase C activator bryostatin 1, either with or without recombinant granulocyte-macrophage colony stimulating factor (rGM-CSF) were examined with respect to the in vitro metabolism of ara-C in leukaemic myeloblasts obtained from 10 patients with acute myelogenous leukaemia (AML). Coincubation of cells with 12.5 x 10(-9) M bryostatin 1 and 10(-5) M ara-C for 4 h resulted in a significant increase in ara-CTP formation (compared to controls) in 6/10 specimens (mean increase 106%; range 38-255%), and no change in the remainder. In contrast, coincubation of cells with 1.25 ng/ml rGM-CSF resulted in a significant increase in only one specimen, and decreases in two. Bryostatin 1 also significantly increased ara-C DNA incorporation in 6/9 evaluable samples, including two which did not display an increase in ara-CTP formation. Coincubation of cells with both bryostatin 1 and rGM-CSF did not lead to a further increase in ara-CTP formation or ara-C DNA incorporation compared to values obtained with either agent alone. Finally, exposure of blasts to bryostatin 1 for 24 h before ara-C led to an increase in ara-CTP formation in 3/8 additional specimens, and a decrease in one sample displaying evidence of bryostatin 1-induced macrophage differentiation. Incubation of cells with both rGM-CSF and bryostatin 1 for this period resulted in ara-CTP levels equivalent to those obtained with bryostatin 1 alone. These studies indicate that while bryostatin 1 exerts a heterogeneous effect on ara-C metabolism in leukaemic myeloblasts, it is capable of potentiating ara-C phosphorylation in a subset of patient samples, including some that do not exhibit an increase in response to rGM-CSF. They also raise the possibility that bryostatin 1-induced potentiation of ara-C metabolism in some leukaemic cells may contribute, at least in part, to the antileukaemic efficacy of this drug combination.

Antineoplastic Agents↗

PubMed1992

The effects of a university fitness programme on health-related variables in previously sedentary males.

This study reports on the effects of a 10-week university fitness programme on health-related fitness variables. Twenty-one male exercisers, aged 37.0(10.3) years (mean(s.d.); range 21-58), and 22 male controls, aged 38.6(7.9) years (mean(s.d.); range 17-54), volunteered to take part. Two sample t-tests and 95% confidence intervals were used to determine if the exercise group demonstrated a greater average improvement than the control group and the average improvement in both groups separately. The exercise group showed a greater average improvement over the controls from Test 1 (before fitness programme) to Test 2 (after) in the following: steady-state heart rate (beats min-1) 95% confidence intervals (-7.8, -16.2); predicted VO2max (ml kg-1 min-1): 95% confidence intervals (3.2, 6.6); sit-ups (repetitions): 95% confidence intervals (3.1, 7.0); flexibility (cm): 95% confidence intervals (3.3, 6.9). There was no significant difference between the exercise group and control group in body weight, percentage body fat, blood pressure, total plasma cholesterol, high-density lipoprotein and triglycerides. The exercise programme improved aerobic fitness, local muscular endurance and flexibility. However, the increase in aerobic fitness did not coincide with beneficial changes in the coronary risk profile.

Adolescent↗

PubMed1992

Altered expression of cell cycle related genes including c-myb in a subclone of HL-60 that exhibits reversible differentiation.

A differentiation resistant subclone of HL-60, DMSOr, was removed from the selective pressure of dimethyl sulfoxide and characterized with a new stable phenotype of reversible differentiation. DMSOr cells, when treated with 1.25% dimethyl sulfoxide, differentiated in a manner similar to the parental HL-60 with respect to morphological changes, increase in superoxide production, and withdrawal from cell cycle. Upon removal of the dimethyl sulfoxide at points normally associated with commitment to terminal differentiation, DMSOr reverted to the immature phenotype. This demonstrates an uncoupling of the morphological, functional, and antiproliferative effects of differentiation from commitment to terminal differentiation. Associated with the reversible phenotype of DMSOr was an altered expression of the c-myb oncogene. In HL-60, c-myb expression was down-regulated by 72 h and completely diminished by 144 h. Northern blot analysis of DMSOr demonstrated greater levels of expression of c-myb at 72 and 144 h. Similar results were shown with histone H4, cdc2 kinase, and, to a lesser extent, ornithine decarboxylase. The c-myb related gene B-myb did not show altered regulation during differentiation. The results suggest that altered expression of genes that control cell cycle may be critical for the reversible phenotype of DMSOr.

Base Sequence↗

PubMed1992

Effect of bryostatin 1 on the in vitro radioprotective capacity of recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) toward committed human myeloid progenitor cells (CFU-GM).

We have examined the effect of the macrocyclic lactone protein kinase C (PK-C) activator bryostatin 1 on the in vitro radioprotective capacity of recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) toward normal committed myeloid progenitor cells (day-14 granulocyte-macrophage colony-forming units [CFU-GM]). Preincubation of T-cell- and adherent cell-depleted bone marrow mononuclear cells with 12.5 nM bryostatin 1 and either 1.25 or 50 ng/ml rGM-CSF for 24 h resulted in an 18%-30% survival at 4-5 Gy, whereas cells exposed to rGM-CSF alone gave rise to no detectable colonies at radiation doses greater than 2.5 Gy. Coadministration of bryostatin 1 also led to a threefold increase in Do values for both rGM-CSF concentrations. A similar enhancement of radioprotective effects was observed with the tumor-promoting phorbol ester phorbol dibutyrate. Exposure of cells to both bryostatin 1 and rGM-CSF immediately following irradiation also resulted in enhanced progenitor cell survival when compared to rGM-CSF alone, but radioprotective effects were less than those observed when cells were preincubated with these factors. Cells preconditioned with bryostatin 1 and rGM-CSF prior to exposure to 2 or 4 Gy gave rise to significantly more colonies when radiation was administered as a 4-h divided dose, suggesting that bryostatin 1 may act by potentiating rGM-CSF-induced repair of sublethal radiation damage. Finally, pre-exposure of enriched progenitor cells (CD34+) to bryostatin 1 and rGM-CSF resulted in radioprotective effects that were less than those observed for partially purified populations with respect to the total population of surviving myeloid colonies. However, CD34+ cells preincubated with bryostatin 1 and rGM-CSF prior to irradiation exhibited a significant increase in both the percentage and absolute number of neutrophilic and macrophage colonies, and a reduction in eosinophilic colonies, compared to cells exposed to rGM-CSF alone. These studies suggest that bryostatin 1 (and possibly other PK-C activators) potentiates the in vitro radioprotective effects of rGM-CSF and may also regulate the lineage specificity of this response.

Antigens, CD↗

PubMed1992

Effect of a combined exposure to cytosine arabinoside, bryostatin 1, and recombinant granulocyte-macrophage colony-stimulating factor on the clonogenic growth in vitro of normal and leukemic human hematopoietic progenitor cells.

We have examined the effect of a combined 24 h exposure to cytosine arabinoside (ara-C) and the protein kinase C activator bryostatin 1, either alone or in conjunction with recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF), on the clonogenic growth of 14 primary samples from acute myelogenous leukemia (AML) patients, as well as normal human committed and early hematopoietic progenitors. Incubation of blasts with 1 microM ara-C and 12.5 nM bryostatin 1(+/- 1.25 ng/ml rGM-CSF) resulted in a heterogeneous pattern of inhibitory effects toward primary leukemic colonies, ranging from 32-98%, and subadditive to synergistic drug interactions. However, exposure of blasts to ara-C and bryostatin 1, either with or without rGM-CSF, eliminated leukemic cell self-renewal in 80-93% of samples, and very substantially reduced growth in the remainder. Exposure of normal human bone marrow mononuclear cells to identical concentrations of ara-C and byostatin 1 permitted the survival of 23% of committed myeloid progenitors (granulocyte-macrophage colony-forming units), and greater than 50% when rGM-CSF was included. Finally, exposure of bone marrow populations highly enriched for progenitor cells (CD34+, DR-, CD71-) to ara-C and bryostatin 1 +/- rGM-CSF for 24 h led to minimal reductions (e.g. 10-15%) in the survival of early hematopoietic progenitors (high proliferative potential colony-forming cells). Together, these findings indicate that combined exposure in vitro to ara-C and bryostatin 1, both with and without rGM-CSF, effectively inhibits the growth of leukemic cells with self-renewal capacity, while sparing a significant fraction of normal committed and primitive hematopoietic progenitors.

Adult↗

PubMed1991

c-kit expression by CD34+ bone marrow progenitors and inhibition of response to recombinant human interleukin-3 following exposure to c-kit antisense oligonucleotides.

The c-kit proto-oncogene encodes a receptor having tyrosine-specific kinase activity and has been mapped to chromosome 4 in the human and chromosome 5 in the mouse, at the dominant white spotting locus (W). Mutations at the W locus affect various aspects of murine hematopoiesis. The c-kit proto-oncogene has been shown to be expressed by leukemic myeloblasts, but not by normal unseparated human bone marrow cells. The role of this oncogene in differentiation and proliferation of human hematopoietic progenitors is presently undefined. To determine c-kit expression by normal hematopoietic progenitors, CD34+ cells were isolated from disease-free human bone marrow, and RNA-based polymerase chain reaction (PCR) techniques were used to assess expression. By this method, we have demonstrated c-kit expression by CD34+ bone marrow progenitors. To address the functional requirement for c-kit expression in normal human hematopoiesis, CD34+ cells were incubated in the presence of sense, antisense, or missense oligonucleotides to c-kit, and subsequently cultured in the presence of either recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) or recombinant human interleukin-3 (rhIL-3). Exposure of CD34+ cells to c-kit antisense oligonucleotides significantly inhibited colony-forming ability of cells cultured in the presence of rhIL-3, but had no effect on colony formation of cells cultured in rhGM-CSF. Together, these data suggest a possible role for c-kit in hematopoietic proliferation and differentiation that may be linked to some, but not all, stimulatory factors.

Antigens, CD↗

PubMed1991

Effects of thymidine and hydroxyurea on the metabolism and cytotoxicity of 1-B-D arabinofuranosylcytosine in highly resistant human leukemia cells.

We have examined the effect of the ribonucleotide reductase inhibitors thymidine (dThd) and hydroxyurea (HU) on the metabolism and cytotoxicity of high concentrations (10 to 100 mumol/L) of cytosine arabinoside (Ara-C) in a deoxycytidine kinase-deficient, highly Ara-C-resistant human promyelocytic leukemic cell subline (HL-60/Ara-C). Administration of dThd or HU (0.5 to 3 mmol/L) in conjunction with high concentrations of Ara-C either sequentially or simultaneously lead to enhanced (and in some cases a supra-additive) inhibition of HL-60/Ara-C suspension culture growth and soft agar colony formation. In addition, exposure of cells to 0.5 mmol/L dThd or HU for 48 hours significantly increased the percentage of HL-60/Ara-C in S-phase. In contrast to previous studies involving low-dose Ara-C administration, we were unable to detect dThd- or HU-mediated increments in Ara-CTP formation in HL-60/Ara-C cells treated with high-dose Ara-C despite reductions in intracellular dCTP pools as great as 65%. However, dThd or HU did increase Ara-C incorporation into newly synthesized DNA. These studies show that administration of dThd or HU in conjunction with high concentrations of Ara-C results in an enhanced antiproliferative effect of Ara-C against Ara-C-resistant leukemic cells deficient in deoxycytidine kinase.

Arabinofuranosylcytosine Triphosphate↗

PubMed1991

Treatment with interleukin-3 plus granulocyte-macrophage colony-stimulating factors improves the selectivity of Ara-C in vitro against acute myeloid leukemia blasts.

Hematopoietic growth factors (HGFs) interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) individually have been shown to increase the percentage of acute myeloid leukemia (AML) blasts in S phase and enhance the cytotoxic effects of Ara-C against these blasts in culture. We compared in vitro the effects of a combined treatment with GM-CSF (10 ng/mL) plus IL-3 (10 ng/mL) on the metabolism and cytotoxicity of Ara-C in normal bone marrow mononuclear cells (NBMMC) and AML blasts. NBMMC from six healthy volunteers and AML blasts from 10 patients were incubated for 20 hours with or without IL-3 plus GM-CSF, followed by a concurrent treatment with Ara-C for 4 additional hours. Exposure to the HGFs and Ara-C produced significantly higher intracellular Ara-CTP levels as well as higher Ara-CTP/dCTP pool ratios in AML blasts as compared with NBMMC. Treatment with HGFs resulted in [3H] Ara-C DNA incorporation that was significantly higher in AML blasts versus NBMMC. This selective improvement of Ara-C metabolism in AML blasts was associated with an enhanced Ara-C-mediated leukemia colony-forming unit (CFU) growth inhibition. In contrast, exposure to HGFs resulted in an improved colony growth of normal CFU granulocyte-monocyte and CFU-granulocyte, erythroid, monocyte, megakaryocyte. These in vitro studies indicate that a combined treatment with IL-3 plus GM-CSF may improve the selectivity of Ara-C against AML blasts.

Acute Disease↗

PubMed1991

Exercise.

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Coronary Disease↗