HEMATOTHESIS

In search of novel working mechanisms of proteasome inhibitors in multiple myeloma

SUMMARY

Proteasome inhibitors (PIs) constitute one of the cornerstones of the treatment of multiple myeloma (MM), with bortezomib, carfilzomib and ixazomib being approved for clinical use. Due to the relatively recent introduction of PIs to clinical practice, many aspects of the pleiotropic effects of PIs still remain unexplored, particularly for the second-generation PIs carfilzomib and ixazomib. Since MM still remains incurable and many patients will eventually develop treatment-refractory disease, the search for validated biomarkers to predict treatment response is of great clinical importance. In the first aim of this project, we evaluated the effect of proteasome inhibitors on erythropoiesis. During the follow-up of MM patients treated with PIs in the first part of this project, we observed a consistent and highly significant increase in the reticulocyte count during treatment with carfilzomib-based regimens in patients with relapsed multiple myeloma. This observation was not made in a matched cohort of bortezomib-treated patients. In subsequent ex vivo experiments, we demonstrated that carfilzomib exposure significantly impaired terminal erythroid maturation, independent of erythroid commitment, expansion or differentiation. Our results therefore report the first pharmacologically induced delay in erythroid maturation as a mechanism for carfilzomib-induced reticulocytosis in patients with multiple myeloma. These findings might therefore lead to new therapeutic applications for carfilzomib in disorders of mature erythrocytes, such as sickle cell anaemia. In the second part of this project, we evaluated proteasome activity as a potential biomarker for PI drug sensitivity. For this purpose, we measured proteasome activity in primary myeloma cells, purified from the bone marrow of patients with MM. Baseline proteasome activity was not significantly different in myeloma cells derived from treatment-responsive or –refractory MM patients. The degree of proteasome inhibition by PIs was similar in both groups. As a result, the clinical applicability of proteasome activity as a biomarker for drug sensitivity in MM currently remains limited. Nevertheless, these data also suggest that drug sensitivity to PIs is in part proteasome-independent, indicating that our understanding of PI drug resistance should be further improved. In a follow-up project to the present thesis, we have designed several genome-wide screening experiments using CRISPR-Cas9 technology to gain novel insights in the mechanisms driving drug resistance to PIs in MM.

(BELG J HEMATOL 2020;11(3):133–5)

Erythropoiesis and iron metabolism after haematopoietic stem cell transplantation

After haematopoietic stem cell transplantation (HCT), many patients present anaemia, which can persist for months due to an inadequate erythropoietin production for the degree of the anaemia. In this thesis, we performed two randomised studies with erythropoiesis-stimulating agents therapy after allogeneic (including myeloablative and non-myeloablative conditioning) and autologous transplantation. We showed a great efficacy of this growth factor to ensure full erythroid reconstitution when initiated soon after engraftment and not immediately after the transplant. Furthermore, as iron parameters are quite disturbed following HCT, we sought to study iron metabolism after HCT (which has not been much investigated), integrating the role of hepcidin, the key regulator in iron metabolism. Hence, we demonstrated that hepcidin levels prior to and following autologous HCT were influenced by iron stores and changes in erythropoietic activity.

(BELG J HEMATOL 2019;10(2):89–95)

Impact of new treatment guidelines pertaining to the indication for allogeneic stem cell transplantation in intermediate-risk acute myeloid leukaemia at Ghent University Hospital: A retrospective analysis

SUMMARY

Since several years, it has become clear that intermediate-risk acute myeloid leukaemia patients in an acceptable clinical condition can benefit from allogeneic stem cell transplantation thanks to the improvement in relapse free survival. This study retrospectively analysed the outcome of all intermediate-risk acute myeloid leukaemia patients treated with intensive chemotherapy at the Ghent University Hospital between 01-01-2013 and 30-04-2017 in an effort to determine the impact of a new in-hospital treatment guideline adopted in April 2015. This guideline recommends all intermediate-risk acute myeloid leukaemia patients who are fit for intensive therapy to proceed to allogeneic stem cell transplantation in first complete remission. Unfortunately, we could not demonstrate an improvement in the relapse free survival after implementation of the treatment guideline. Nevertheless, exploratory analysis of the entire group suggests a survival benefit from allogeneic stem cell transplantation, with significantly improved relapse free survival and a trend towards a better overall survival.

(BELG J HEMATOL 2018;9(7):285–9)

Whole-body diffusion-weighted magnetic resonance imaging for staging and early treatment response assessment in malignant lymphoma

SUMMARY

Diffusion-weighted magnetic resonance imaging (DW/MRI) is a radiation-free functional imaging technique reflecting tissue cellularity by probing the diffusion of water molecules on a microstructural level. This can be assessed visually, but also quantified by calculating the apparent diffusion coefficient (ADC). Although established in many solid tumours and multiple myeloma, its role in disease assessment in malignant lymphoma has yet to be determined. Therefore, the main purpose of this work was twofold: exploring the performance of whole-body DW/MRI (WB-DW/MRI) in staging malignant lymphoma and assessing treatment response early during treatment with 18F-FDG-PET/CT in combination with bone marrow biopsy results serving as the gold standard. Regarding staging, we found that WB-DW/MRI is a feasible imaging technique. Visual image analysis sufficed to accurately detect extranodal disease, while adequate nodal characterisation required ADC calculations. Lymph node characterisation was further improved by using a more elaborate quantitative analysis based on ADC parameters derived from whole-lesion ADC histogram analysis next to the commonly used mean ADC. In the context of treatment response assessment, mean ADC changes between the baseline and interval scan performed after one cycle of (immuno)chemotherapy significantly correlated with progression-free-survival in patients with aggressive non-Hodgkin lymphoma (NHL). For Hodgkin lymphoma, taking into account the typical intralesional heterogeneity, an advanced 3-D texture analysis was performed, which demonstrated that ADC parameters associated with tumour heterogeneity (energy, local homogeneity, and entropy) were predictive of outcome in contrast to conventional ADC parameters.

(BELG J HEMATOL 2018;9(6):242–4)

A nursing intervention that reduces symptom burden during chemotherapy

SUMMARY

The aim of this dissertation was to develop and evaluate a nursing intervention that reduces symptom burden during chemotherapy. We developed an intervention that uses motivational interviewing to support self-efficacy and to improve symptom self-management. In a quasi-experimental study in adult patients treated with chemotherapy, the intervention significantly reduced overall symptom distress and symptom severity at all three time points in the study (three, six and twelve weeks after the start of the treatment).

(BELG J HEMATOL 2018;9(5):192–4)

Is it possible to predict who may never need treatment for B-CLL?

SUMMARY

Chronic lymphocytic leukaemia has a very heterogeneous disease evolution. Prognostic factors of B-CLL overall survival have been extensively studied. However, much less is known about prognostic factors that can identify patients who will never develop an indication for treatment, at the time of their initial diagnosis. In this study we give an overview of variables that have a predictive value for treatment free survival. Subsequently, we try to develop a novel prognostic index, to address the question ‘who will never need treatment for B-CLL?’.

(BELG J HEMATOL 2018;9(3):124–9)

The impact of chemotherapy on the host microbiota in the context of oral and gastrointestinal mucositis

SUMMARY

In this PhD thesis, we investigated the impact of chemotherapy on the microbiota in the context of mucositis by using different experimental set-ups. Using bacterial monocultures, we showed that exposure to 5-fluorouracil at physiologically relevant concentrations differentially impacts oral microorganisms. Despite this difference in microbial sensitivity to 5-fluorouracil in pure cultures, we showed that the impact of 5-fluorouracil, as well as irinotecan, towards highly diverse gastrointestinal microbial populations is only marginal. These findings were generated with two different model systems that exclude host cells and this led us to conclude that the host is crucial in the establishment of chemotherapy-induced shifts in microbial composition and functionality. The next step in our research entailed the use of an in vitro wound healing model, where we demonstrated that the presence of microbiota negatively impacts the wound healing capacity of damaged oral epithelial cells. This indicates that microbial presence can delay the recovery from mucositis. Yet, we also found that microbial composition, which is for instance disturbed in patients receiving cancer therapy, is an additional determinant of aggravated wound healing. We further substantiated this conclusion with an in vivo longitudinal monitoring study of paediatric patients treated for haematological malignancies. While shifts in the oral microbial community during and following chemotherapy were mostly patient-specific, clear associations were made with the use of systemic antibiotics and antibacterial mouth rinses, which create microbial dysbiosis. In view of these findings we propose that the preventive use of antimicrobials needs careful consideration given the profound impact on the microbiome and subsequent consequence for the host.

(BELG J HEMATOL 2018;9(2):68–70.)