Expression of the p210BCR-ABL oncoprotein drives centrosomal hypertrophy and clonal evolution in human U937 cells.

Centrosomes play fundamental roles in mitotic spindle organization, chromosome segregation and maintenance of genetic stability. Recently, we have shown that centrosome aberrations occur early in chronic myeloid leukemia (CML) and are induced by imatinib in normal fibroblasts in vitro. To investigate the influence of BCR-ABL on centrosomes, we performed long-term in vitro experiments employing the conditionally p210BCR-ABL-expressing (tetracycline-inducible promoter) human monocytic cell line U937p210BCR-ABL/c6 as a model of CML chronic phase. Centrosome hypertrophy was detectable after 4 weeks of transgene expression onset, increasing up to a rate of 25.7% aberrant cells within 13 weeks of propagation. This concurred with clonal expansion of aneuploid cells displaying a hyperdiploid phenotype with 57 chromosomes. Partial reversibility of centrosome aberrations (26-8%) was achieved under prolonged propagation (14 weeks) after abortion of induction and bcr-abl silencing using small interfering RNA. Therapeutic doses of imatinib did not revert the aberrant phenotype, but counteracted the observed reverting effect of bcr-abl gene expression switch off. Suggesting a mechanistic model that features distinct abl-related tyrosine kinase activity levels as essential determinants of centrosomal integrity, this is the first report mechanistically linking p210BCR-ABL oncoprotein activity to centrosomal hypertrophy.

Gene expression profiling of CD34+ cells identifies a molecular signature of chronic myeloid leukemia blast crisis.

Despite recent success in the treatment of early-stage disease, blastic phase (BP) of chronic myeloid leukemia (CML) that is characterized by rapid expansion of therapy-refractory and differentiation-arrested blasts, remains a therapeutic challenge. The development of resistance upon continuous administration of imatinib mesylate is associated with poor prognosis pointing to the need for alternative therapeutic strategies and a better understanding of the molecular mechanisms underlying disease progression. To identify transcriptional signatures that may explain pathological characteristics and aggressive behavior of BP blasts, we performed comparative gene expression profiling on CD34+ Ph+ cells purified from patients with untreated newly diagnosed chronic phase CML (CP, n=11) and from patients in BP (n=9) using Affymetrix oligonucleotide arrays. Supervised microarray data analysis revealed 114 differentially expressed genes (P<10(-4)), 34 genes displaying more than two-fold transcriptional changes when comparing CP and BP groups. While 24 of these genes were downregulated, 10 genes, especially suppressor of cytokine signalling 2 (SOCS2), CAMPATH-1 antigen (CD52), and four human leukocyte antigen-related genes were strongly overexpressed in BP. Expression of selected genes was validated by real-time-polymerase chain reaction and flow cytometry. Our data suggest the existence of a common gene expression profile of CML-BP and provide new insight into the molecular phenotype of blasts associated with disease progression and high malignancy.

Centrosome aberrations in chronic myeloid leukemia correlate with stage of disease and chromosomal instability.

Centrosome abnormalities are hallmarks of various cancers and have been implicated in chromosome missegregation, chromosomal instability, and aneuploidy. Since genetic instability is a common feature in chronic myeloid leukemia (CML), we sought to investigate whether centrosome aberrations occur and correlate with disease stage and cytogenetic findings in CML. We examined 34 CML samples including CD 34+Ph+cells of 18 newly diagnosed patients (chronic phase (CP)) and 16 blast crisis (BC) specimens by using a centrosome-specific antibody to pericentrin. All CP and BC samples displayed centrosome alterations as compared with corresponding CD 34+control cells. Centrosome abnormalities were detected in 29.1+/-5.9% of CP blasts and in 54.3+/-4.8% of BC blasts, but in only 2.4+/-1.1% of controls (P<0.0001). Additional karyotypic alterations to the t(9;22) translocation were found in only 1/18 CML-CP patients. In contrast, 11/16 (73%) CML-BC patients displayed additional karyotype alterations in 48.7% of analyzed cells, correlating with an abnormal centrosome status (P=0.0005). Our results indicate that centrosome defects are a common and early detectable feature in CML that may contribute to acquisition of chromosomal aberrations and aneuploidy. They may be considered as the driving force of disease progression and could serve as future prognostic markers.

Induction of centrosome and chromosome aberrations by imatinib in vitro.

Imatinib (STI571, Gleevec/Glivec) is a potent selective tyrosine kinase inhibitor and is used successfully in the treatment of chronic myeloid leukemia (CML). While karyotype alterations, in addition to the Philadelphia chromosome, are a common phenomenon of progressing CML, the observation of BCR-ABL-negative leukemic clones with distinct aberrant karyotypes under an imatinib regimen is not yet understood. Here we test the hypothesis that such tumor clones may be induced de novo from normal cells by imatinib. In vitro experiments with varying drug concentrations (5-20 microM) were performed on normal human dermal fibroblasts (NHDF), Chinese hamster embryonal and Indian muntjak fibroblasts. After 3 weeks of treatment, analysis of cell cultures by centrosome immunostaining and conventional cytogenetics revealed that imatinib induced centrosome and chromosome aberrations in all cultures in a significant dose-dependent and species-independent manner. Moreover, the results of NHDF long-term culture experiments demonstrated that aberrant phenotypes, emerging under imatinib treatment for 12 weeks, were not reversible after prolonged propagation omitting the drug. These observations suggest a causative role of imatinib in the origin of centrosome and karyotype aberrations (genetic instability) and thus may explain the emergence of clonal chromosomal abnormalities in BCR-ABL-negative progenitor cells under imatinib therapy.

A concept for pharmacokinetic-pharmacodynamic dosage adjustment in renal impairment: the case of aminoglycosides.

BACKGROUND: For patients with impaired renal function, dosage adjustment is necessary for many drugs. Adjustment with respect only to pharmacokinetic parameters may be insufficient. OBJECTIVE: To apply the theory of pharmacokinetics and pharmacodynamics to derive a mathematical model that links the concentration-time course and the clinical response by means of the pharmacokinetic-pharmacodynamic parameter 'area under the effect-time curve' (AUETC), and to use this analysis and clinical data for aminoglycosides to calculate dosage adjustments in renal impairment. METHODS: Model parameters were estimated for the antimicrobial and nephrotoxic effects of aminoglycosides on the basis of data from the literature. Effect parameters were calculated for various degrees of impaired renal function. RESULTS: Use of the model parameters gave a high correlation between the predicted and the observed (literature) values for antimicrobial efficacy and nephrotoxicity. When calculating dosage adjustments in renal impairment, it was possible to hold only one effect (antimicrobial or nephrotoxic) constant by dosage adjustment, whereas the other changed unfavourably. This was explained by differences between the pharmacodynamic parameters for each effect. For high antimicrobial efficacy, a target peak concentration of 9 mg/L (for gentamicin) should be obtained every 48 hours in advanced renal impairment. For low nephrotoxicity, the peak concentration should not exceed 3 mg/L. CONCLUSIONS: The parameter AUETC could be a useful pharmacokinetic-pharmacodynamic surrogate marker for dosage adjustment in renal impairment. Using the AUETC method, the beneficial effect can be balanced against the adverse effect.

Nonparametric meta-analysis of published data on kidney-function dependence of pharmacokinetic parameters for the aminoglycoside netilmicin.

The distribution and elimination of various drugs depend on kidney function. This dependence is published either as a linear regression equation or as the discrete extreme values for normal kidney function and anuria. A meta-analysis of the published pharmacokinetic data is required to build up a knowledge-based computer system for dosage adjustment in renal failure. A sample comparison of 4 statistical methods for meta-analysis was performed by applying them to 13 publications about the aminoglycoside netilmicin. Parametric meta-analytical methods I and II are based on regression equations alone (Z-transformation, maximum likelihood) and yield unreliable data, especially with regard to extreme values for anuria. The parametric meta-analytical method III is based on means of extreme values (standard 2-stage approach) and does not permit a decision as to whether linear interpolation of a parameter (e.g. volume of distribution) can be used for all degrees of renal insufficiency. In contrast, the nonparametric median (meta-analytical method IV) is based on the extreme values calculated from regression equations and empirical extreme values combined into 1 group of data on normal kidney function and another on anuria. For netilmicin, the meta-analytical median with the 95% confidence interval (95% CI) yields a significant increase in the dominant elimination half-life from 2h (95% CI 1.9h, 2.6h) in patients with normal kidney function to 45h (95% CI 41h, 301h) in those with anuria (p = 0.001). For a normal bodyweight of 65kg, the volume of distribution also increases significantly from 13L (95% CI 9L, 15L) to 20L (95% CI 14L, 21L) in patients with anuria (p = 0.04). Thus, drug dosage adjustment according to therapeutic peak and trough concentrations requires knowledge of the distribution and elimination parameters, since they can both be independently altered in renal failure. We conclude that the most robust meta-analysis of these alterations is achieved with the nonparametric median of extreme values.

Adjusting for the partial volume effect in cortical bone analyses of pQCT images.

Quantitative analyses of computed tomography images are prone to errors due to the partial volume effect which affects objects (e.g., bones) that have a different size or are assessed with different resolution. We have developed a set of equations suitable for both modeling the partial volume effect in cortical bone and for performing the corresponding adjustment. Seven hollow cylinders and 2 cuboid phantoms were made out of Al with 1% Si. The specimens were scanned with a pQCT machine (XCT2002, Stratec Medizintechnik, Pforzheim, Germany) and analyzed with the integrated software, version 5.50. Measurements were performed at different resolutions (voxel size=0.20 to 0.75 mm), both in air and in Ringer solution, and analyses were performed at different detection thresholds. Applying the correcting equations set we could reduce the errors in cortical density by about 80%. The cortical area was assessed with a negligible error at a threshold (theta0) that is equivalent to the mean of the cortical bone density and of the background density. On choosing theta0 as the detection threshold the error in density was lowered to less than 2%. We propose to assess cortical area and cortical density in several steps, first assessing the area and density thereafter. Applying this method should be beneficial whenever "true world" values are required, or objects of different size are compared.

Aminoglycoside pharmacokinetics and -dynamics: a nonlinear approach.

A model which correctly describes the pharmacokinetic-pharmacodynamic relationship is necessary to perform a rational pharmacotherapy. This model could predict the effects under variable conditions. The prediction will provide a basis for adapting therapy to individuals. A nonlinear model should be most appropriate for describing drug effects. A new model, containing nonlinear pharmacokinetics and pharmacodynamics, is presented to describe effects of aminoglycosides on bacterial growth and accumulation in kidney tissue.

PK-PD curve-fitting problems with the Hill equation? Try one of the 1-exp functions derived from Hodgkin, Douglas or Gompertz.

UNLABELLED: Non-linear phenomena are observed with enzyme kinetics, protein binding, pharmacokinetics or pharmacodynamics. The Hill equation, the Michaelis-Menten equation extended by a power coefficient, is traditionally used for sigmoid curve fitting. Sigmoid saturation phenomena can also be described by exponential functions (1-exp), extended by a power coefficient such as those derived by Hodgkin, Douglas or Gompertz. Comparing the 4 equations, the sigmoid 1-exp function in the form of Hodgkin and Huxley comes closest to the principle of simplicity and succinctness with regard to definition, slope and flexibility of the inflection point. To compare the applicability, a standardized sample of 250 curves was generated by each I of the 4 equations and mutually fitted with the remaining 3. The Hill equation gives the closest fit with the data generated by the other functions. The Douglas variant exhibits the highest rate of convergence. The Gompertz function provides the basic feature of a baseline effect. CONCLUSION: The sigmoid functions investigated (Hill, Hodgkin, Douglas, Gompertz) have differing characteristics and can be used interchangeably for solving specific problems in non-linear modeling.

Relationship between pharmacokinetic half-life and pharmacodynamic half-life in effect-time modeling.

A pharmacodynamic parameter relating time-dependent changes of the effect with time-dependent changes of concentrations has yet to be developed. In pharmacokinetics, half-lives (T1/2kin) are used to describe the relation between concentration (C) and time (t). In pharmacodynamics, often the sigmoid Emax model and the Hill equation are used (E = Emax CH/(EC50H + CH)) to describe the relation between effect (E) and concentration (C). To describe the correlation between effect (E) and time (t), a pharmacodynamic half-life (T1/2dyn) could be estimated if the use of the term half-life is not restricted only to log-linear first order processes. To bisect the drug effect a variable time (t1-2 = t2-t1) will be required for this nonlinear process. The bisection of the effect (E2 = 1/2 E1) is associated with a decrease in concentrations (C2 = C1 exp(-0.693 t1-2/T1/2kin)). A mathematical relationship can be derived between pharmacodynamic half-life (T1/2dyn = t1-2) and pharmacokinetic half-life (T1/2dyn = T1/2kin (ln (1 + ln(a)/ln(2))/H ) with (a = (EC50H + C1H)/(EC50H + C2H)). For concentrations in the range of the EC50 value with the Hill coefficient (H = 1), the pharmacodynamic half-life will be 1.6-2.0 times the kinetic half-life (T1/2dyn < or = 2.0 T1/2kin). For high concentrations (C1 > EC50), the dynamic half-life will grow much longer than the kinetic half-life, consequently the effect of a drug will not increase but it will last longer. The pharmacodynamic half-life turns out to be a specific estimate for the effect time relation, being a concentration-dependent function of the kinetic half-life.

Structured data entry for reliable acquisition of pharmacokinetic data.

A pharmacokinetic database was constructed that is as free of errors as possible. Pharmacokinetic parameters were derived from the literature using a text-processing system and a database system. A random data sample from each system was compared with the original literature. The estimated error frequencies using statistical methods differed significantly between the two systems. The estimated error frequency in the text-processing system was 7.2%, that in the database system 2.7%. Compared with the original values in the literature, the estimated probability of error for identical pharmacokinetic parameters recorded in both systems is 2.4% and is not significantly different from the error frequency in the database. Parallel data entry with a text-processing system and a database system is, therefore, not significantly better than structured data entry for reducing the error frequency.

Vancomycin dosing in haemodialysis patients and Bayesian estimate of individual pharmacokinetic parameters.

A dose reduction of vancomycin to 1000 mg once a week usually is recommended for haemodialysis patients. Our modified dosing schedule consists of a loading dose of 1000 mg and a maintenance dose of 500 mg administered 3 times a week after haemodialysis. Different vancomycin regimens were retrospectively evaluated by therapeutic drug monitoring and bayesian parameter estimates in 39 dialysis patients. The mean (+/- SD) trough level in 7 patients receiving only the conventional dosage regimen was significantly lower than in 17 patients strictly treated by the modified schedule (7 +/- 4 versus 17 +/- 8 mg/L; p = 0.001). The corresponding peaks were low in both groups and no different (23 +/- 10 versus 27 +/- 12 mg/L). The one week average vancomycin clearance was significantly lower in the conventional dosage group compared to the modified dosage group (6 +/- 3 versus 10 +/- 3 ml/min; p = 0.001). High-flux dialysers were not used in the conventional dosage group but for 30 percent of the procedures in the modified dosage group, where the vancomycin one week average elimination half-life was 66 hours (+/- 18) and the volume of distribution 50 litres (+/- 5). As compared to the bayesian programme, NONMEM calculated comparable pharmacokinetic parameters but could be applied only in 5 cases with a sufficient number of concentration measurements. Ototoxicity occurred in 1 patient, whereas vancomycin treatment was judged as ineffective against infection in 5 of the 39 patients. Their troughs were below 15 mg/L.(ABSTRACT TRUNCATED AT 250 WORDS)

Standardized structure and modular design of a pharmacokinetic database.

BACKGROUND: The accumulated knowledge on drugs can be used for an individual drug dosage adjustment if it is placed at our disposal in an informatically structured form. THEORY AND METHODS: We have started building up a pharmacokinetic database aimed at adjusting drug dosages, in exemplary form, to patients with renal impairment. Parameters needed for the three dosage adjustment rules (Dettli, Kunin, Holford) and the most general concept of pharmacokinetics constituted the theoretical basis. TWO PROCESSES PERTAIN TO ALL DRUGS: Distribution and elimination. Total drug clearance and at least two parameters representing distribution and elimination processes are closely interdependent in mathematical terms (clearance = volume of distribution*rate of elimination). This relation yields the unifying concept that serves as a prerequisite for a structured recording of 30 assigned pharmacokinetic and pharmacodynamic parameters within an informatic database. SOLUTIONS AND RESULTS: The information is retrieved and referenced from 2383 original publications by means of a standardized input module. The complete database at present contains 15,397 records for 1573 drugs. A programmed meta-analytic algorithm is used to calculate the statistical measures for the central value and variance--as available--from the pooled values of primary records. The statistically standardized parameters are extracted for 6601 pharmacokinetic parameters, and placed at the users disposal with the output module. PRACTICAL UTILITY: Following meta-analysis, published pharmacokinetics can be used as statistical estimates of population parameters. The statistical estimates with variances permit an individual drug dosage adjustment by applying the Bayesian approach or neural networks.

Nonlinear kinetics and the 1-exp function in nephropharmacology.

The basic law in nephropharmacology states that pharmacokinetic parameters depend linearly on renal function. Few exceptions to linear dependence have been reported, e.g. substances with saturable tubular reabsorption or secretion. A further example is cyclosporin, which was found to be eliminated according to log-concave nonlinear kinetics in 3 patients with hepatotoxicity after kidney transplantation. The nonlinear cyclosporin kinetics were computer-fitted to the integrated forms of the 1-exp function and the Michaelis-Menten equation by nonlinear regression analysis. The same maximal velocity (Vmax = 23 ng ml-1 h-1) and Michaelis constant (Km = 686 ng ml-1) were calculated for cyclosporin when applying either the 1-exp function or the Michaelis-Menten equation. The nonlinear elimination of cyclosporin, however, was described even more closely by the 1-exp function than by the Michaelis-Menten equation.

Intubation complications in the critically ill child.

The acutely ill child requiring intubation is at risk for complications at three crucial points: during the intubation procedure, in the first few hours or days after intubation, and during long-term endotracheal tube (ETT) placement. Consideration must be given to the anatomic and physiologic differences between children and adults that place children at risk for acute respiratory failure and that present difficulties in providing respiratory support. Each potential complication must be understood in terms of cause, assessment, prevention, and intervention. The method of securing the ETT can decrease tube displacement, trauma to the airway, and breakdown of the skin. Intra- and interhospital transport presents more considerations in maintaining ETT placement and physiologic stability of the patient. Prevention of intubation complications in children can reduce length of stay, decrease cost of care, minimize length of time for family separation, decrease potential disabilities and prevent death in the critically ill child who requires intubation.

Detecting microdamage in bone.

Fatigue-induced microdamage in bone contributes to stress and fragility fractures and acts as a stimulus for bone remodelling. Detecting such microdamage is difficult as pre-existing microdamage sustained in vivo must be differentiated from artefactual damage incurred during specimen preparation. This was addressed by bulk staining specimens in alcohol-soluble basic fuchsin dye, but cutting and grinding them in an aqueous medium. Nonetheless, some artefactual cracks are partially stained and careful observation under transmitted light, or epifluorescence microscopy, is required. Fuchsin lodges in cracks, but is not site-specific. Cracks are discontinuities in the calcium-rich bone matrix and chelating agents, which bind calcium, can selectively label them. Oxytetracycline, alizarin complexone, calcein, calcein blue and xylenol orange all selectively bind microcracks and, as they fluoresce at different wavelengths and colours, can be used in sequence to label microcrack growth. New agents that only fluoresce when involved in a chelate are currently being developed--fluorescent photoinduced electron transfer (PET) sensors. Such agents enable microdamage to be quantified and crack growth to be measured and are useful histological tools in providing data for modelling the material behaviour of bone. However, a non-invasive method is needed to measure microdamage in patients. Micro-CT is being studied and initial work with iodine dyes linked to a chelating group has shown some promise. In the long term, it is hoped that repeated measurements can be made at critical sites and microdamage accumulation monitored. Quantification of microdamage, together with bone mass measurements, will help in predicting and preventing bone fracture failure in patients with osteoporosis.