Differential response to cytotoxic therapy explains treatment dynamics of acute myeloid leukaemia patients: insights from a mathematical modelling approach

Disease response and durability of remission are very heterogeneous in patients with acute myeloid leukaemia (AML). There is increasing evidence that the individual risk of early relapse can be predicted based on the initial treatment response. However, it is unclear how such a correlation is linked to functional aspects of AML progression and treatment. We suggest a mathematical model in which leukaemia-initiating cells and normal/healthy haematopoietic stem and progenitor cells reversibly change between an active state characterized by proliferation and chemosensitivity and a quiescent state, in which the cells do not divide, but are also insensitive to chemotherapy. Applying this model to 275 molecular time courses of nucleophosmin 1-mutated patients, we conclude that the differential chemosensitivity of the leukaemia-initiating cells together with the cells' intrinsic proliferative capacity is sufficient to reproduce both, early relapse as well as long-lasting remission. We can, furthermore, show that the model parameters associated with individual chemosensitivity and proliferative advantage of the leukaemic cells are closely linked to the patients' time to relapse, while a reliable prediction based on early response only is not possible based on the currently available data. Although we demonstrate with our approach, that the complete response data is sufficient to quantify the aggressiveness of the disease, further investigations are necessary to study how an intensive early sampling strategy may prospectively improve risk assessment and help to optimize individual treatments.

TK inhibitor treatment disrupts growth hormone axis: clinical observations in children with CML and experimental data from a juvenile animal model

BACKGROUND

Long-term treatment of chronic myeloid leukemia (CML) with tyrosine kinase inhibitors (TKIs) exerts off-target effects on bone growth by either impaired growth hormone (GH) action or osseous modelling impairment.

METHODS

Body height and the GH-related parameters insulin-like growth factor 1 (IGF-1) and insulin-like growth factor-binding protein 3(IGFBP-3) were determined repetitively 3-monthly over 2 years in 21 pediatric CML-patients on standardized imatinib treatment. In an animal model 4-week-old male Wistar rats were exposed over 10 weeks to imatinib, dasatinib, or bosutinib at varying concentrations via the drinking water. Blood was collected at prepubertal age, pubertal age, and at adult age, respectively, and animals' serum levels of IGFBP-3 were measured.

RESULTS

Independent from treatment duration patients exhibited IGF-1 and IGFBP-3 levels almost exclusively in the very low range when compared to age-matched references. No clear pattern of rising or falling IGF-1 and IGFBP-3 levels was observed. In rats, compared to controls, serum IGFBP-3 was significantly lowered for all TKIs tested, at all concentrations applied, and at all ages under investigation.

CONCLUSION

Besides direct off-target effects on the growing skeleton, TKI treatment also results in lowered blood levels of IGF-1 and IGFBP-3.A juvenile rat model predicts this side effect for dasatinib and bosutinib. Thus, growth and GH- related parameters should be monitored regularly in pediatric patients with CML on TKIs.

Imaging, quantification and visualization of spatio-temporal patterning in mESC colonies under different culture conditions

MOTIVATION

Mouse embryonic stem cells (mESCs) have developed into a prime system to study the regulation of pluripotency in stable cell lines. It is well recognized that different, established protocols for the maintenance of mESC pluripotency support morphologically and functionally different cell cultures. However, it is unclear how characteristic properties of cell colonies develop over time and how they are re-established after cell passage depending on the culture conditions. Furthermore, it appears that cell colonies have an internal structure with respect to cell size, marker expression or biomechanical properties, which is not sufficiently understood. The analysis of these phenotypic properties is essential for a comprehensive understanding of mESC development and ultimately requires a bioinformatics approach to guarantee reproducibility and high-throughput data analysis.

RESULTS

We developed an automated image analysis and colony tracking framework to obtain an objective and reproducible quantification of structural properties of cell colonies as they evolve in space and time. In particular, we established a method that quantifies changes in colony shape and (internal) motion using fluid image registration and image segmentation. The methodology also allows to robustly track motion, splitting and merging of colonies over a sequence of images. Our results provide a first quantitative assessment of temporal mESC colony formation and estimates of structural differences between colony growth under different culture conditions. Furthermore, we provide a stream-based visualization of structural features of individual colonies over time for the whole experiment, facilitating visual comprehension of differences between experimental conditions. Thus, the presented method establishes the basis for the model-based analysis of mESC colony development. It can be easily extended to integrate further functional information using fluorescence signals and differentiation markers.

AVAILABILITY

The analysis tool is implemented C++ and Mathematica 8.0 (Wolfram Research Inc., Champaign, IL, USA). The tool is freely available from the authors. We will also provide the source code upon request.

CONTACT

nico.scherf@tu-dresden.de.

A novel view on stem cell development: analysing the shape of cellular genealogies

OBJECTIVES

The analysis of individual cell fates within a population of stem and progenitor cells is still a major experimental challenge in stem cell biology. However, new monitoring techniques, such as high-resolution time-lapse video microscopy, facilitate tracking and quantitative analysis of single cells and their progeny. Information on cellular development, divisional history and differentiation are naturally comprised into a pedigree-like structure, denoted as cellular genealogy. To extract reliable information concerning effecting variables and control mechanisms underlying cell fate decisions, it is necessary to analyse a large number of cellular genealogies.

MATERIALS AND METHODS

Here, we propose a set of statistical measures that are specifically tailored for the analysis of cellular genealogies. These measures address the degree and symmetry of cellular expansion, as well as occurrence and correlation of characteristic events such as cell death. Furthermore, we discuss two different methods for reconstruction of lineage fate decisions and show their impact on the interpretation of asymmetric developments. In order to illustrate these techniques, and to circumvent the present shortage of available experimental data, we obtain cellular genealogies from a single-cell-based mathematical model of haematopoietic stem cell organization.

RESULTS AND CONCLUSIONS

Based on statistical analysis of cellular genealogies, we conclude that effects of external variables, such as growth conditions, are imprinted in their topology. Moreover, we demonstrate that it is essential to analyse timing of cell fate-specific changes and of occurrence of cell death events in the divisional context in order to understand the mechanisms of lineage commitment.