Exactly Solvable System of One-Dimensional Trapped Bosons with Short- and Long-Range Interactions

We introduce a model of trapped bosons with contact interactions as well as Coulomb repulsion or gravitational attraction in one spatial dimension. We find the exact ground-state energy and many-body wave function. The density profile and the pair-correlation function are sampled using Monte Carlo method and show a rich variety of regimes with crossovers between them. Strong attraction leads to a trapped McGuire quantum soliton. Weak repulsion results in an incompressible Laughlin-like fluid with flat density, well reproduced by a Gross-Pitaevskii equation with long-range interactions. Stronger repulsion induces Friedel oscillations and the eventual formation of a Wigner crystal.

Dirac Equation in (1+1)-Dimensional Curved Spacetime and the Multiphoton Quantum Rabi Model

We introduce an exact mapping between the Dirac equation in (1+1)-dimensional curved spacetime (DCS) and a multiphoton quantum Rabi model (QRM). A background of a (1+1)-dimensional black hole requires a QRM with one- and two-photon terms that can be implemented in a trapped ion for the quantum simulation of Dirac particles in curved spacetime. We illustrate our proposal with a numerical analysis of the free fall of a Dirac particle into a (1+1)-dimensional black hole, and find that the Zitterbewegung effect, measurable via the oscillatory trajectory of the Dirac particle, persists in the presence of gravity. From the duality between the squeezing term in the multiphoton QRM and the metric coupling in the DCS, we show that gravity generates squeezing of the Dirac particle wave function.

Dynamical tunneling versus fast diffusion for a non-convex Hamiltonian

This paper attempts to resolve the issue of the nature of the 0.01-0.1 cm(-1) peak splittings observed in high-resolution IR spectra of polyatomic molecules. One hypothesis is that these splittings are caused by dynamical tunneling, a quantum-mechanical phenomenon whereby energy flows between two disconnected regions of phase-space across dynamical barriers. However, a competing classical mechanism for energy flow is Arnol'd diffusion, which connects different regions of phase-space by a resonance network known as the Arnol'd web. The speed of diffusion is bounded by the Nekhoroshev theorem, which guarantees stability on exponentially long time scales if the Hamiltonian is steep. Here we consider a non-convex Hamiltonian that contains the characteristics of a molecular Hamiltonian, but does not satisfy the Nekhoroshev theorem. The diffusion along the Arnol'd web is expected to be fast for a non-convex Hamiltonian. While fast diffusion is an unlikely competitor for longtime energy flow in molecules, we show how dynamical tunneling dominates compared to fast diffusion in the nearly integrable regime for a non-convex Hamiltonian, as well as present a new kind of dynamical tunneling.

Induction of apoptosis in peripheral blood lymphocytes following treatment in vitro with hydroxychloroquine

OBJECTIVE

Defective regulation of apoptosis may be central to the development of autoimmune disorders. This study investigated the possibility that the antirheumatic effect of hydroxycholoroquine (HCQ) may be achieved by up-regulation of apoptosis.

METHODS

Peripheral blood lymphocytes collected from normal controls and patients with systemic lupus erythematosus (SLE) were cultured in the presence or absence of a range of concentrations of HCQ. Cells undergoing apoptosis were identified by several standard methods, including morphologic changes, DNA fragmentation, and flow cytometry. For some experiments, lymphocytes were simultaneously stained with antibodies to T cell surface markers and with propidium iodide for dual-stain flow cytometric studies.

RESULTS

HCQ was able to induce apoptosis in peripheral blood lymphocytes in a dose- and time-dependent manner. HCQ induced these changes in all T cell subpopulations studied. There was no significant difference between the controls and patients with SLE in terms of the percentage of apoptotic cells detected following treatment with HCQ.

CONCLUSION

The present study demonstrated that HCQ induces apoptosis in peripheral blood lymphocytes, which leads to the speculation that HCQ may exert its antirheumatic effect through this mechanism.

Endo-exonuclease of human leukaemic cells: evidence for a role in apoptosis

Inactive forms of endo-exonuclease, activated in vitro by treatment with trypsin, have been identified in human leukaemic CEM and MOLT-4 cells. They comprise over 95% of the total single-strand DNase activity in nuclei and are mainly bound to chromatin and the nuclear matrix. The activated enzyme had Mg2+(Mn2+)-dependent, Ca(2+)-stimulated activities with single- and double-strand DNAs and RNA (polyriboadenylic acid) and other properties characteristic of endo-exonucleases previously described. At least twice as much inactive endo-exonuclease has also been localised in extranuclear compartments of CEM and MOLT-4 cells, 85% bound to the membranes of the endoplasmic reticulum and 15% free in the cytosol. The soluble cytosolic trypsin-activatable endo-exonuclease was immunoprecipitated by antibodies raised independently to both Neurospora and monkey CV-1 cell endo-exonucleases. The free and bound enzymes of both nuclear and extranuclear compartments also cross-reacted on immunoblots with the antibody raised to Neurospora endo-exonuclease to reveal multiple polypeptides ranging in size from 18 to 145 kDa, many of which exhibited activity on DNA gels. The major species bound to the chromatin/matrix were in the 55–63 kDa range. Limited proteolysis of the large polypeptides to those of 18 to 46 kDa accompanied spontaneous chromatin DNA fragmentation to form DNA “ladders' in an isolated nuclei/cytosol system. When the leukaemic cells were treated in culture with either etoposide or podophyllotoxin to induce apoptosis, the largest polypeptides disappeared and smaller endo-exonuclease-related polypeptides of 18 to 46 kDa were detected in the nuclear extracts. The appearance of these polypeptides also correlated with extensive chromatin DNA fragmentation. In addition, there were correlations between the depletion of the major 55–63 kDa species bound to the membranes of the endoplasmic reticulum, depletion of the extranuclear trypsin-activatable activity and the onset and extent of chromatin DNA fragmentation in both cell lines. The extranuclear 55–63 kDa species may be precursors of the chromatin/matrix bound endo-exonuclease. The results indicate that endo-exonuclease plays a role in chromatin DNA degradation in mammalian cells during apoptosis.

Increased tubulin acetylation accompanies reversion to stable ploidy in vincristine-resistant CCRF-CEM cells

The T-cell leukemia line CCRF-CEM is unstable with respect to ploidy, whereas a vincristine-resistant subline, CEM/VCR R, maintains a stable pseudodiploid karyotype. Ploidy change in the parental cells requires the involvement of two cell cycle lesions. The first, in mitosis, prevents cell division after S-phase. The second, in G1, allows a cell with 4N DNA content to re-enter S-phase. We examined differences in expression of tubulin, a major component of the mitotic spindle and the cellular target for vincristine, between the two cell lines. Levels of the beta III isotype were decreased and levels of acetylated alpha-tubulin, a marker for microtubule stability, were increased in the CEM/VCR R cells relative to the parental line, which suggests that the CEM/VCR R cells have a more stable mitotic spindle. Both cell lines exhibit some level of constitutive expression of p53 and c-myc. Constitutive expression of and mutant p53 would contribute to the failure of these cells to recognise G1 checkpoints. Therefore, G1 checkpoint failure and the intrinsically less stable mitotic spindle in the CCRF-CEM cells may contribute to the observed ploidy instability. Conversely, the presence of markers of microtubule stability in the CEM/VCR R cells would predispose them to maintain their ploidy.

Resistance to apoptotic cell death in a drug resistant T cell leukaemia cell line

In this study, we investigated the responses of the T cell leukaemia cell line, CCRF-CEM, and a vincristine-resistant subline, CEM/VCR R, to the induction of cell death by serum withdrawal. This treatment was used to overcome any contribution of P-glycoprotein-mediated drug resistance to the responses of the CEM/VCR R cells. Following serum withdrawal both cell lines exhibited typical apoptotic responses including morphological changes and nucleosomal cleavage of the DNA. However, using several different assays for cell death the CEM/VCR R cell line was shown to undergo apoptosis at a slower rate than the parental CCRF-CEM cell line. Expression of c-Myc, Bcl-2 and p53 was found to be similar in both cell lines, discounting involvement of these proteins in the observed difference in apoptotic response. Given our previous finding that reorganisation of tubulin is involved in apoptosis, we examined the expression of alpha-, beta- and acetylated alpha-tubulin in the parental and resistant lines. The CEM/VCR R cell line had altered tubulin expression when compared to that of the CCRF/CEM line. Transnuclear microtubule networks were observed in log phase CEM/VCR R cells. In addition, increased expression of the acetylated form of the alpha-tubulin isotype suggested that a more stable microtubule network was present in the CEM/VCR R cells. These findings imply that the drug-resistance phenotype in the CEM/VCR R cells may involve the suppression of apoptosis, and that the development of an altered microtubule network may contribute to this suppression.

Tubulin alterations in taxol-induced apoptosis parallel those observed with other drugs

We have described previously that during apoptosis cellular tubulin is reorganized into visible tubulin structures that correlate with apoptotic morphology. Such changes have been observed in human leukaemic cells treated with a variety of cytotoxic agents. These structures are unlike those seen in untreated non-mitotic or mitotic cells. As taxol is known to act by enhancing the polymerization of tubulin in the initiation and extension of microtubules (MTs), and has been shown to induce and stabilize the formation of tubulin structures in a variety of cells, we examined the involvement of tubulin in apoptosis induced by taxol. Apoptosis was induced in a human T-cell leukaemic line, CCRF-CEM, following treatment with 10 nM taxol. The morphological features typical of apoptosis were apparent in taxol-treated cells after drug addition. Immunocytochemical analysis using a monoclonal antibody to beta-tubulin indicated that taxol induced visible tubulin polymerization. DNA fragmentation was detected at 10 hr post-treatment. Flow cytometric analysis of taxol-treated cells showed a time-dependent accumulation of cells in G2/M phase with the appearance of a hypodiploid peak coincident with the detection of DNA fragmentation. Microtubule structures observed following taxol treatment were of three types. At the time of DNA fragmentation, 50% of the cells displayed tubulin structures associated with apoptotic morphology similar to those seen in apoptosis induced by treatment with methotrexate (10(-8) M) or etoposide (17 microM). Twenty percent of the cells were arrested in mitosis at this time. These cells contained either multiple asters or disordered mitotic spindles, and did not display apoptotic morphology. The remaining cells, while normal in morphology, had extensive tubulin polymerization in the cytoplasm and around the nucleus. We examined the time-course of tubulin mRNA expression in apoptosis induced by taxol, methotrexate and etoposide. The level of tubulin mRNA displayed a transient increase after treatment, and prior to the onset of DNA fragmentation with each of the three drugs. These results suggest that during apoptosis taxol induces tubulin changes that display characteristics similar to those observed during apoptosis following treatment with drugs that do not interact directly with tubulin.

Polymerization of tubulin in apoptotic cells is not cell cycle dependent

Prominent, specific tubulin structures were identified in human leukemic cells undergoing apoptosis following treatment with cytotoxic drugs. In order to determine whether tubulin reorganization was dependent upon the stage of the cell cycle at which apoptosis was induced, the human leukemic T-cell line CCRF-CEM was treated with cytotoxic doses of drugs known to arrest cells at different stages of the cell cycle. Apoptosis was confirmed by the detection of characteristic single and multiple nucleosome-sized fragments by agarose gel electrophoresis of isolated DNA. Cells were treated with vincristine, methotrexate, and dexamethasone, which have been shown to induce cell cycle arrest at G2-M, S-phase, and G1, respectively. Treated and untreated cells were analyzed by immunocytochemistry for beta-tubulin or Ki-67 antigen (to confirm cell cycle phase) and scored for apoptotic morphology. Dual staining for cellular tubulin and DNA content, measured by flow cytometry, was used to confirm the stage at which the cycling cells arrested. Increased total cellular tubulin immunofluorescence was observed in treated compared to untreated cells. Our results indicate that CCRF-CEM cells undergo apoptosis (identified morphologically) at all stages of the cell cycle except mitosis. We conclude that the reorganization of cellular tubulin that we have observed in apoptotic cells is independent of the tubulin involvement in cell division and thus may be an integral part of the apoptotic process.

Establishment of an in vitro model for cisplatin resistance in human neuroblastoma cell lines

Two unique cisplatin-resistant neuroblastoma (NB) cell lines have been derived from the established lines IMR-32 and SK-N-SH by treatment with escalating doses of cisplatin. IMR/CP.20 was 6.6-fold and SK/CP.15 was 3.8-fold more resistant to the cytotoxic effects of cisplatin than the parent lines. The parent SK-N-SH cells were 16.6-fold more resistant to the effects of cisplatin than IMR-32 cells. The cisplatin-resistant cell lines demonstrated alterations to their morphology, but there was no change in the cell growth characteristics of the resistant compared to the sensitive lines. Cytogenetic analysis revealed that clonal selection of parental subclones had occurred with additional chromosomal changes in both resistant lines. Both IMR/CP.20 and SK/CP.15 lines were cross-resistant to aphidicolin and to L-phenylalanine mustard. The IMR/CP.20 line was 7.3-fold more resistant to mitomycin C than the parent line. Neither cisplatin-resistant NB line was cross-resistant to 5-fluorouracil, etoposide or doxorubicin. All NB lines had low levels of DNA repair compared to HeLa or CHO-K1 cells. However, the IMR/CP.20 cell line showed a significantly higher ability to effect DNA repair than the parent IMR-32 line, indicating that the increased resistance to cisplatin observed in this line may, in part, be due to an enhanced DNA repair capacity.

Heterotransplantation of early B-lineage acute lymphoblastic leukemia using a solubilized attachment matrix (Matrigel)

Maintenance of long term culture and conventional xenografting of early B-lineage acute lymphoblastic leukemia cells is most difficult. Matrigel, a solubilized attachment matrix shown to aid growth of anchorage dependent solid tumors, was studied in heterotransplantation. Material for xenografting was derived from 5 patient bone marrow aspirates and 5 cell lines previously established and maintained by intraocular inoculation in nude mice. Specimens were injected by 3 methods: intraocular (n = 397); s.c. in medium (n = 78); and s.c. in medium supplemented by Matrigel (n = 69). With intraocular injection, 6 of 10 cell sources grew with respective ingraftment rates of 29-76%. Using the conventional s.c. method, no tumors resulted. The addition of Matrigel produced s.c. ingraftment from 8 of 10 cell sources (ingraftment rate, 50-100%). Immunophenotype, histopathology, and karyotype of the cells derived after Matrigel dependent ingraftment correlated with the cells of origin. It is concluded that Matrigel enables establishment and maintenance of early B-lineage acute lymphoblastic leukemia cell growth in a s.c. xenograft model.

Karyotypic analysis of CCRF-CEM and drug-resistant cell lines with stable and unstable ploidy

Karyotypic studies were performed on methotrexate (MTX)- and vincristine (VCR)-resistant cell lines derived from the human T-cell leukemia CCRF-CEM cell line. We noted karyotypic selection and additional chromosome change associated with acquisition of drug-resistance. Furthermore, we observed that both the parental and MTX-resistant sublines, CEM/MTX R1-3, had a tendency to ploidy change. Karyotypic studies of malignant cells have shown that polyploidy is frequently a consequence of a single sporadic event, followed by growth and selection of the polyploid clone [1]. In this study, however, various karyotypic clones were identified with near- and pseudotetraploid karyotypes that appeared to be derived from different near- and pseudodiploid sidelines. Polyploidy was invariably associated with loss of at least two of the four chromosomes 8 whether the pseudodiploid sideline from which it was derived carried one or both chromosomes 8. In contrast, neither polyploid clones nor loss of chromosome 8 was noted in the CEM/VCR R cells.

Phenotypic and cytogenetic analysis of atypical multidrug resistance in human leukaemic cells selected with methotrexate at high concentration

A series of CCRF-CEM sublines selected for extreme resistance to methotrexate has been shown previously to exhibit cross resistance to a number of agents belonging to the multidrug resistance phenotype. The mechanism(s) underlying resistance to vincristine, vinblastine and actinomycin D in the most resistant subline (CEM/MTX R3) has now been investigated. Efflux of [3H]vincristine was more rapid in CEM/MTX R3 than in either CCRF-CEM cells or a methotrexate-resistant subline not refractory to Vinca alkaloids. In addition, verapamil completely reversed resistance to vincristine, vinblastine and actinomycin D in the CEM/MTX R3 cells. While these results are suggestive of P-glycoprotein-mediated multidrug resistance, Northern analysis revealed no detectable expression of the mdr 1/gene in CEM/MTX R3 cells. Likewise, karyotypic analysis of the resistant subline, while revealing certain clonal abnormalities, provided no evidence of alteration in the mdr 1/gene locus on chromosome 7. The data suggest therefore the operation, in these cells, of a novel mechanism of resistance.

Cytogenetic basis of acute myeloid leukemia

The chromosomes of 12 adult patients with acute leukemia were analyzed by conventional means and by Giemsa and centromeric banding techniques. Acute myeloblastic leukemia was diagnosed in 7, acute myelomonocytic leukemia in 2, and acute undifferentiated leukemia in 3. Bone marrow was aspirated from patients when in relapse or remission, and both euploid and aneuploid cells were examined. All patients showed trisomy no. 9 and many showed additional numerical or structural changes in some or all their cells. These changes included monosomy no. 21 and/or monosomy no. 8. The proportion of trisomy no. 9 cells was 30-50% in patients in full remission and up to 100% in patients in relapse; thus trisomy no. 9 might be an important marker of leukemic cells. A mechanism was proposed to explain the induction and selection of the trisomy no. 9 karotype.

Letter: Consistent chromosome abnormalities in acute leukaemia

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