Preferences about Future Alzheimer's Disease Treatments Elicited through an Online Survey Using the Threshold Technique.

BACKGROUND: Treatments aiming at slowing down the progression of Alzheimer's disease (AD) may soon become available. However, information about the risks that people are willing to accept in order to delay the progression of the disease is limited. OBJECTIVE: To determine the trade-offs that individuals are willing to make between the benefits and risks of hypothetical treatments for AD, and the extent to which these trade-offs depend on individuals' characteristics and beliefs about medicines. DESIGN: Online, cross-sectional survey study. SETTING: Population in the UK. Public link to the survey available at the websites of Alzheimer's Research UK and Join Dementia Research. PARTICIPANTS: Everyone self-reported ≥18 years old was eligible to participate. A total of 4384 people entered the survey and 3658 completed it. MEASUREMENTS: The maximum acceptable risks (MARs) of participants for moderate and severe adverse events in exchange for a 2-year delay in disease progression. The risks were expressed on ordinal scales, from <10% to ≥50%, above a pre-existing risk of 30% for moderate adverse events and 10% for severe adverse events. We obtained the population median MARs using log-normal survival models and quantified the effects of individuals' characteristics and beliefs about medicines in terms of acceleration factors. RESULTS: For the moderate adverse events, 26% of the participants had a MAR ≥50%, followed by 25% of the participants with a MAR of 10 to <20%, giving an estimated median MAR of 25.4% (95% confidence interval [CI] 24.5 to 26.3). For the severe adverse events, 43% of the participants had a MAR <10%, followed by 25% of the participants with a MAR of 10 to <20%, resulting in an estimated median MAR of 12.1% (95%CI 11.6 to 12.5). Factors that were associated with the individuals' MARs for one or both adverse events were age, gender, educational level, living alone, and beliefs about medicines. Whether or not individuals were living with memory problems or had experience as a caregiver had no effect on the MARs for any of the adverse events. CONCLUSION: Trade-offs between benefits and risks of AD treatments are heterogeneous and influenced by individuals' characteristics and beliefs about medicines. This heterogeneity should be acknowledged during the medicinal product decision-making in order to fulfil the needs of the various subpopulations.

Intestinal crypt properties fit a model that incorporates replicative ageing and deep and proximate stem cells.

A model of intestinal crypt organization is suggested based on the assumption that stem cells have a finite replicative life span. The model assumes the existence in a crypt of a quiescent ('deep') stem cell and a few more actively cycling ('proximate') stem cells. Monte Carlo computer simulation of published intestinal crypt mutagenesis data is used to test the model. The results of the simulation indicate that stabilization of the crypt mutant phenotype following treatment with external mutagen is consistent with a stem cell replicative life span of about 40 divisions for mouse colon and 90-100 divisions for mouse small intestine, corresponding to a deep stem cell cycle time of about 3.9 and 8.5 weeks for colon and small intestine, respectively. Simulation of the data obtained for human colorectal crypts suggests that the proximate stem cell cycle time is about 80 h, assuming a replicative life span of 50-150 divisions, and that the deep stem cell divides approximately every 30 weeks.

An enteroendocrine cell-based model for a quiescent intestinal stem cell niche.

We have shown that the kinetics of conversion of intestinal crypt cell populations to a partially or wholly mutant phenotype are consistent with a model in which each crypt contains an infrequently dividing 'deep' stem cell that is the progenitor of several more frequently dividing 'proximate' stem cells. An assumption of our model is that each deep stem cell exists in a growth inhibitory niche. We have used information from the literature to develop a model for a quiescent intestinal stem cell niche. This niche is postulated to be primarily defined by an enteroendocrine cell type that maintains stem cell quiescence by secretion of growth inhibitory peptides such as somatostatin and guanylin/uroguanylin. Consistent with this model, there is evidence that the proteins postulated as defining a growth-inhibitory stem cell niche can act as intestinal tumour suppressors. Confirmation that a growth-inhibitory niche does exist would have important implications for our understanding of intestinal homeostasis and tumorigenesis.

Explaining differences in sensitivity to killing by ionizing radiation between human lymphoid cell lines.

We surveyed five human hematopoietic cell lines (HSB-2, MOLT-4, Reh, CEM, and HL-60) to determine whether any simple correlates with sensitivity to killing by gamma-irradiation might be revealed. The clonogenic survival gamma-ray dose-response curves for these cell lines cover a wide range of sensitivities. Consistent with previous results for murine hematopoietic cell lines, there was a clear correlation between the rapidity with which irradiation induced apoptosis and clonogenic radiosensitivity of a cell line, although the relationship between timing of apoptosis and radiosensitivity differed between human and murine cell lines. Flow cytometric determination of cell cycle distribution after irradiation showed that differences between human hematopoietic cell lines, in the rate of induction of apoptosis, were generally related to the functioning of cell cycle checkpoints. Whereas the rapidly dying and radiosensitive HSB-2 cell line underwent apoptosis from different points in the cell cycle, the more slowly dying cell lines showed a variety of cell cycle arrest profiles and initiated apoptosis after accumulation of cells in the G2 phase. The lag-phase between arrest in G2 and induction of apoptosis was comparable for MOLT-4, Reh, and CEM; however, HL-60 cells showed a markedly longer G2 arrest that correlated with their greater radioresistance. The results suggest that the total length of time available for DNA damage repair (irrespective of whether this time accrues as blockage in G1, S, or G2), prior to potential activation of apoptosis, is a critical determinant of radiosensitivity in human hematopoietic cell lines. Comparison of the p53 status of these cell lines suggested that mutations in the TP53 gene are contributing to the delay of induction of apoptosis seen in the more radioresistant cell lines. The sensitivity of MOLT-4 and HL-60 cells to killing by DNA-associated 125I decays was determined and was found to correlate with the relative sensitivity of these lines to gamma-irradiation. The highly localized deposition of energy by 125I decays argues that DNA damage is a potent initiator of apoptosis in these cell lines. The results presented suggest that differences in the radiosensitivity of the cell lines examined reflect differences in the rapidity of induction of apoptosis and that radiation-induced cell death in hematopoietic cells can be explained as a response to DNA damage.

Effects of hydroxyurea on DNA synthesis in mouse L-cells.

The effect of the anti-metabolite hydroxyurea on DNA synthesis in mouse L-cells has been examined. It was shown previously that when DNA synthesis was diminished to very low levels by treatment with the drug there was preferential incorporation of added [3H]dThd into low molecular weight fragments (Martin, R.F., Radford, I. And Pardee, M. (1977) Biochem. Biophys. Res. Commun. 74, 9-15). On the basis of several criteria it is concluded here that these fragments are a product of semi-conservative nuclear DNA replication. The preferential labelling of DNA fragments, but not their size, is shown to be dependent on the hydroxyurea concentration used. These DNA fragments are also shown, by comparison with normal DNA replication intermediates, to comprise a heterogeneous population of 'larger-than-normal' fragments. Different models to account for these findings are considered and it is concluded that the results are compatible with a loss of coordination of DNA synthesis following drug treatment.

Inhibition of DNA synthesis and cell death.

The association between DNA synthesis inhibition and cell death in mouse L-cells was investigated using the drug hydroxyurea. This drug produces a preferential labelling of low molecular weight DNA and dose-response studies revealed a correlation between this effect and cytoxicity. Investigation of the reassociation kinetics of DNA labelled during hydroxyurea inhibition showed an over-replication of middle repetitive sequences, but the concentration dependence of this effect was quite different to that of cytotoxicity.

Abnormalities of the short arm of chromosome 12 in T cell prolymphocytic leukemia.

Abnormalities of the short arm of chromosome 12 are nonrandom events in T cell prolymphocytic leukemia (T-PLL). Fluorescence in situ hybridization (FISH) studies were performed in three patients with T-PLL and one patient with T cell peripheral lymphoma and rearrangement of 12p. Whereas the rearrangements of 12p were different in the four patients, a breakpoint centromeric to the ETV6 gene was present in the three T-PLL patients. In addition, loss of heterozygosity for a chromosomal segment telomeric to ETV6 with loss of the RAD52 locus was also shown by FISH studies. In contrast, the breakpoint was telomeric to ETV6 in the patient with peripheral lymphoma.

Fluorescence in situ hybridization analysis of chromosome 1 abnormalities in hematopoietic disorders: rearrangements of DNA satellite II and new recurrent translocations.

Using fluorescence in situ hybridization analysis, breakpoints involving the long arm of chromosome 1 (1q) were localized in 36 patients with various hematopoietic disorders and rearrangements of the proximal part of 1q, as ascertained with banding techniques. The breakpoint was localized within the satellite II (sat II) domain in 14 patients with various abnormalities, between the sat II domain and the BCL9 locus in eight, between the BCL9 and ARNT loci in two, between sat II and ARNT in two others, and distal to ARNT in seven. A dicentric chromosome 1 was present in two patients. A high incidence of heterochromatin heteromorphism of chromosome 1 was present in this series. Two recurrent translocations were identified, t(1;2)(q12;q37) in three patients suffering from three different acute leukemia subtypes, and t(1;16)(q12;q24) in two patients with different diseases. Two patients had jumping translocations. Most of the rearrangements of 1q were secondary abnormalities, included in complex karyotypes. The roles of methylation, interactions with the proteins interfering with heterochromatin and possible gene silencing due to heterochromatin rearrangements are discussed.

t(5;14)/HOX11L2-positive T-cell acute lymphoblastic leukemia. A collaborative study of the Groupe Français de Cytogénétique Hématologique (GFCH).

To accurately estimate the incidence of HOX11L2 expression, and determine the associated cytogenetic features, in T-cell acute lymphoblastic leukemia (T-ALL), the Groupe Français de Cytogénétique Hématologique (GFCH) carried out a retrospective study of both childhood and adult patients. In total, 364 patients were included (211 children

Gd-Tex Pharmacyclics Inc.

Pharmacyclics is developing Gd-Tex (gadolinium texaphyrin) as a radiosensitizer for the potential treatment of various cancers including brain metastases and primary brain tumors, pancreatic tumors, lung tumors and pediatric cancers [196711], [348919]. The compound entered phase III pivotal trials for brain metastases in September 1998 [323929]. Phase I clinical trials for the treatment of primary brain tumors and pancreatic cancer have been initiated while several trials in other cancer types are in the planning stages [367716]. In September 1998, Pharmacyclics announced the initiation of a pivotal phase III trial for the treatment of patients with brain metastases. This multicenter trial originally included 30 sites in the US, Canada and Europe, and was expected to enroll 425 patients. The FDA agreed that this trial qualified for Fast Track review if efficacy end-points are met [301265]. By October 2000, nearly all 450 patients in 50 sites had been completed [375959], [387023]. In September 2000, Pharmacyclics and the National Cancer Institute (NCI) initiated two phase I trials of Gd-Tex. The first was to determine the safety of two different dosing regimens of the drug during preoperative radiotherapy after induction chemotherapy in patients with stage IIA non-small cell lung cancer (NSCLC). The second would examine the use of Gd-Tex in combination with stereotactic Gamma Knife radiosurgery in patients with primary brain tumors known as glioblastoma multiforme [381561]. A phase Ib/II trial, for brain metastases, was conducted in America and France, and involved over 100 patients. At the ASCO 1998 meeting, interim tumor response data were presented for 37 patients. The overall tumor response rate (complete plus partial response rate) was 73%. Furthermore, MRI scanning confirmed that Gd-Tex accumulated selectively in tumors [287459]. Full results were announced in October 1998 at the American Society of Therapeutic Radiology and Oncology. Following ten daily injections followed by whole brain radiation, 77.7% of patients demonstrated a tumor response defined as greater than 50% reduction in tumor volume. Gd-Tex was well tolerated, and liver enzyme elevation was the dose-limiting effect, which was reversible. Death due to tumor progression was seen in 15% of the Gd-Tex group as opposed to 35% in the control group [302872]. In November 1999, Pharmacyclics commenced a phase I trial of Gd-Tex injection, sponsored by the NCI, for treating children with intrinsic pontine glioma. The goals of the phase I dose-ranging study were to determine the Gd-Tex dose and administration schedule that can be safely administered with radiation and to evaluate the localization of Gd-Tex in affected tumors using MRI [348035]. In March 1997 the Decision Network of the NCI voted to sponsor additional clinical indications including adult and pediatric brain tumors, as well as cancers involving the lung, head & neck, pancreas and prostrate. Two phase I trials of Gd-Tex for the treatment of primary brain tumors commenced in August 1998 under a CRADA with the NCI [237538], [295592], [348919]. Pharmacyclics is collaborating with the NCI under a CRADA in phase I trials in primary brain tumors and pancreatic tumors [323929], [323952], [346596]. Analysts expected a filing to occur by the end of 1999 or early 2000, with sales in 2001 [303186].

Computerized video time-lapse microscopy studies of ionizing radiation-induced rapid-interphase and mitosis-related apoptosis in lymphoid cells.

Computerized video time-lapse (CVTL) microscopy of X-irradiated cultures of cells of the murine lymphoma cell lines ST4 and L5178Y-S and the human lymphoid cell line MOLT-4 demonstrated that these cells exhibit a wide disparity in the timing of induction and execution of radiation-induced cell death that included rapid-interphase apoptosis, delayed apoptosis, and postmitotic apoptosis. ST4 cells that received 2.5 or 4 Gy of X radiation underwent rapid-interphase apoptosis within 2 h. Apoptosis commenced with a 10-20-min burst of membrane blebbing followed by swelling for 2-4 h and cell collapse. No apoptotic bodies were formed. After a dose of 1 Gy, approximately 90% of ST4 cells died by rapid-interphase apoptosis, while the remainder completed several rounds of cell division prior to cell death. Postmitotic death of ST4 cells occurred with the same morphological sequence of events as during rapid-interphase apoptosis induced by doses of 1-4 Gy. In contrast, L5178Y-S and MOLT-4 cells that received 4 Gy underwent apoptosis more slowly, with a complex series of events occurring over 30-60 h. Only 3% of L5178Y-S cells and 24% of MOLT-4 cells underwent apoptosis without attempting cell division. The cells became abnormally large during a long G(2)-phase delay, and then most of the cells (76-97%) attempted to divide for the first or second time at approximately 18-30 h postirradiation. However, either mitosis failed or division was aberrant; i.e., the large cells divided into three or four fragments which eventually fused together. This process was followed by several rounds of complex and unpredictable membrane blebbing, gross distortions of shape, fragmentation-refusion events, and formation of apoptotic bodies, after which the cells collapsed at 36-60 h postirradiation.

The dose-response for low-LET radiation-induced DNA double-strand breakage: methods of measurement and implications for radiation action models.

There is considerable controversy over the form of the dose-response for DNA double-strand breakage (dsb) induction in mammalian cells by low-LET type radiation. This controversy centres on the techniques used for measuring DNA dsb. The applications and shortcomings of the four major techniques for estimating DNA size--sedimentation, viscoelastometry, electrophoresis, and non-denaturing filter elution--are examined. In particular, the criticisms of the results obtained using the non-denaturing filter elution technique, which have suggested that the DNA dsb dose-response is non-linear, are discussed. It is concluded that these results may require a re-evaluation of the basic assumptions of many radiation action models.

Chromosomal rearrangement as the basis for human tumourigenesis.

PURPOSE: To develop a model for the initiation of human tumourigenesis that is consistent with various observations that are difficult to reconcile with current models. CONCLUSIONS: A novel model of tumourigenesis was developed that includes three basic postulates: (1) tumourigenesis is initiated by recombinogenic DNA lesions, (2) potentially recombinogenic DNA lesions in transcribed regions of the genome can be converted into chromosomal rearrangements and (3) chromosomal rearrangements alone are insufficient for tumourigenesis but can initiate a mutator/recombinator phenotype.

p53 status, DNA double-strand break repair proficiency, and radiation response of mouse lymphoid and myeloid cell lines.

The p53 status of a panel of 10 mouse lymphoid or myeloid cell lines was determined by immunoprecipitation with mutant- and wild-type-specific antibodies and was compared with the radiation response of the lines. The more rapidly dying cell lines all contained p53 displaying the wild-type epitope. By contrast, four of six more slowly dying cell lines contained either no or mutant p53 protein. It was of interest that radiation-induced apoptosis occurred, albeit at a considerable time after irradiation, in cells ostensibly lacking p53 protein. DNA double-strand break (dsb) repair was examined in both a rapidly and more slowly dying cell line. The rapidly dying cell line was capable of DNA dsb rejoining, however this repair was interrupted by postirradiation DNA degradation.

Radiation response of mouse lymphoid and myeloid cell lines. Part I. Sensitivity to killing by ionizing radiation, rate of loss of viability, and cell type of origin.

The sensitivity of 10 mouse lymphoid or myeloid cell lines to gamma-ray- and DNA-associated 125I-decay-induced clonogenic cell killing have been compared with their rate of loss of viability (membrane integrity) and with their putative cell type of origin. The pseudodiploid haematopoietic cell lines showed D0 values for 125I-induced DNA double-strand breakage (dsb) that ranged from 7.7 +/- 0.7 to 40.8 +/- 2.8 decays. These lines generally appeared to be more sensitive to killing by radiation-induced DNA dsb than are fibroblast-like cell lines. The increased sensitivity of haematopoietic cell lines to killing by DNA dsb may be related to their mode of death (apoptosis versus necrosis). Mode of cell death may thus be an important factor in determining the 'inherent radiosensitivity' of normal cells/tissues. Haematopoietic cell lines that undergo rapid interphase apoptotic death showed extreme sensitivity to DNA dsb. The latter cell lines were found to have derived from immature lymphoid cells, and it is speculated that their high radiosensitivity might reflect the action of a mechanism that normally eliminates cells containing illegitimate V(D)J recombinase-induced DNA dsb.

Phorbol esters can protect mouse pre-T cell lines from radiation-induced rapid interphase apoptosis.

Protein kinase C stimulators were found to increase the radioresistance of the mouse pre-T cell-derived line ST4. Increased resistance to gamma-ray-induced killing could be produced by addition of 10 nM phorbol 12-myristate 13-acetate (PMA) to ST4 cultures either immediately before or up to 2 h after irradiation. Following PMA treatment, ST4 changed from a cell line that underwent rapid interphase apoptosis (i.e. DNA degradation and morphology characteristic of apoptosis were evident 2-3 h after irradiation) to a line that continued to cycle after irradiation and began to die by apoptosis after completing mitosis. Associated with these PMA-induced changes, the D0 of ST4 cells increased from 7.7 +/- 0.7 to 18.8 +/- 2.7 125I decays. Another mouse pre-T cell-derived line, ST1, which is susceptible to radiation-induced rapid interphase apoptosis, also showed radioprotection after PMA treatment. In contrast, PMA increased the radiosensitivity of the pre-T cell-derived W7 line, which undergoes radiation-induced delayed interphase apoptosis (i.e. death following blockage in G2 phase). PMA had no effect on the radiosensitivity of a pre-B cell-derived line, A8, which undergoes rapid interphase apoptosis, and on a pre-T cell-derived line, W22, which undergoes apoptosis after mitosis. These results suggest that the radiomodifying ability of PMA treatment is dependent upon the cell death pathway induced by irradiation and upon the cell lineage.

DNA lesion complexity and induction of apoptosis by ionizing radiation.

PURPOSE: To determine whether murine lymphoid cell lines can discriminate between high- and low-LET (linear energy transfer) radiation-induced DNA lesions. MATERIALS AND METHODS: Sensitivity to killing by DNA-incorporated 3H and 125I decays, accumulated during storage in the gas phase of a liquid nitrogen tank, was determined by clonogenic survival assay. RESULTS: Induction of a lethal event in the STRij-4-2.2, WEHI-22.1, and L5178Y-R cell lines required approximately 30 times more 3H than 125I decays. Hence, the same ratio of 3H to 125I decays was found irrespective of whether the cell lines contained mutant or wild-type p53 and irrespective of whether they underwent rapid interphase or mitosis-related apoptosis after irradiation. The 18-81 cell line differed in showing a ratio of around 21 and it is argued that this may be a consequence of v-ABL over-expression. The assumption that DNA-incorporated 3H and 125I decays are low- and high-LET-like events respectively was confirmed by the similar sensitivity of L5178Y-R and -S cells to killing by 125I decays in contrast with their difference in sensitivity to 3H decays. CONCLUSIONS: The difference in lethal effectiveness between DNA-incorporated 3H and 125I decays can be explained by the hypothesis that simple DSB (double-strand breaks) are non-lethal and that cell killing is attributable to complex DSB. The low-LET radiation-specific sensitization of L5178Y-S cells may reflect defective repair of a DNA lesion class (presumably simple DSB) that is differentially induced by high- and low-LET radiation and is non-lethal to cells with normal repair capacity.

Model for the initiation of ionizing radiation-induced apoptosis in lymphoid cells by complex DNA double-strand breaks.

PURPOSE: To present a model for the molecular events that lead to the induction of apoptosis in irradiated lymphoid cells based on the assumption that the process is triggered by complex DNA double-strand breaks (DSB). OUTLINE OF THE MODEL: * Cellular DNA repair mechanisms have difficulty rejoining complex DSB because of the nature of the end groups on such breaks. * Association between p53 and DNA topoisomerase I (topo I) can occur at complex DSB in open regions of the genome and the enzymic activity of such associations is not suppressed by polyADP-ribosylation. * Binding of p53 and topo I at a complex DSB results in the transient trapping of a DNA-topo I cleavage complex. * Transiently trapped DNA-topo I cleavage complexes at complex DSB are reversed following association with topo I bound elsewhere in the genome, thus initiating a misrejoining event. * Topo I-mediated DNA misrejoining creates a structure that activates p53. Initiation of rapid interphase apoptosis requires that the inducing signal from activated p53 exceeds a threshold level. * Initiation of rapid interphase apoptosis is regulated by poly(ADP-ribose) polymerase.

Lysis solution composition and non-linear dose-response to ionizing radiation in the non-denaturing DNA filter elution technique.

The suggestion by Okayasu and Iliakis (1989) that the non-linear dose-response curve, obtained with the non-denaturing filter elution technique for mammalian cells exposed to low-LET radiation, is the result of a technical artefact, was not confirmed.

Mouse lymphoma cells that undergo interphase death show markedly increased sensitivity to radiation-induced DNA double-strand breakage as compared with cells that undergo mitotic death.

The relationship between radiation-induced DNA double-strand breakage (dsb) and reproductive death (clonogenicity) for two mouse lymphoma cell lines was compared with that for the fibroblast-like hamster cell line V79. One of the lymphoma lines (STRij-4-2.2), which undergoes rapid disintegration following cytotoxic insult, showed extreme sensitivity to gamma-ray or DNA-associated 125I decay-induced DNA dsb (7 +/- 1 125I decays per clonogenic lethal event). Surprisingly, the other lymphoma line (WEHI-22.1), which does not undergo rapid disintegration, was also much more sensitive to DNA dsb than were V79 cells (17 +/- 1 versus 61 +/- 2 125I decays per clonogenic lethal event). Ultrastructure, DNA degradation, and flow cytometric cell cycle data suggested that both lymphoma cell lines may undergo interphase death, but that the induction of this process in WEHI-22.1 may depend upon blockage in the G2 phase. It is concluded that there are marked differences between the radiation responses of lymphoma and fibroblast lines, that there may be different forms of radiation-induced interphase death, and that the low number of DNA dsb required to produce a clonogenic lethal event in cells undergoing interphase death could explain the radiosensitivity of organs such as ovary, testis and thymus.