(I) DNA damage response
The DNA damage response axis plays a crucial role in chemoresistance in CLL, as indicated by the prognostic impact of deletions of 17p (locus of TP53) and 11q (locus of ATM). These deletions coincide with mutations in the remaining allele, although frequency, especially for ATM varies. Functional read-outs of the p53 axis are expected to add clinical relevant information on the actual DNA damage response. Currently, different p53 function analyses are being developed. These assays are either based on measurement of (i) RNA expression levels of a single gene (RT-PCRp21) or gene sets (RT-MLPA, currently further developed by us), or protein expression levels (FACSp53-p21) after DNA damage by irradiation or etoposide/nutlin exposition or (ii) gene expression levels at base-line (RT-PCR miR34a). Although all tests relate to p53 function, they provide different information regarding expected responses towards therapy. P53 function assays are of promise in predicting sensitivity to chemotherapeutic agents provided that robustness and clinical applicability is thoroughly studied. In 2011 I started a pilot project within the framework of the European Research initiative on CLL (ERIC) to
perform detailed side-by-side analysis of available p53 functional assays in 5 different countries (UK, the Netherlands, Germany, Austria, France, and Czech Republic). This unique collaborative approach will continue the following years and will include (mechanistic) analysis of novel described genetic aberrations in the DNA damage pathway.
(II) Signaling and cross-talk with the microenvironment
In the pathobiology of chronic lymphocytic leukemia (CLL), the tumor microenvironment plays a pivotal role by providing stimuli for survival and proliferation. However, the relevant interactions are still ill-defined and not targeted by current "conventional" treatments. This may explain why, despite major therapeutic advances, B-cell malignancies like CLL still remain incurable. For targeted therapy to succeed, better understanding of the interactions between leukemic cells and their microenvironment is critical. A variety of external signals has been suggested to influence survival of CLL cells, including B cell receptor (BCR) activation, interleukins/chemokines and cellular contact. Yet, these assumptions are predominantly based on in vitro model systems. In the first comparative survey between lymph node (LN) proliferation centers and blood derived CLL cells, we observed striking differences in Bcl-2 family members which correlated with sensitivity to standard chemotherapeutics. Our recent preliminary in vitro data indicate that besides tonic B-cell receptor (BCR) triggering, TNF-receptor family mediated signaling could account for the observed changes. We have also found that
besides receptor/ligand interactions, activation of specific kinases by these stimuli hold high promise for targeted intervention. TNF-receptor family ligands CD40L, BAFF and APRIL, purportedly expressed by activated T cells and/or Nurse-like cells in CLL LN, enhance survival at least partly by NF-κB signaling. No study has yet attempted to directly compare CD40L, BAFF and APRIL and the NF-κB signaling involved for their impact on CLL survival and drug sensitivity. In fact, compelling evidence of expression of these ligands in CLL derived LN tissue is lacking. Moreover, no study has yet attempted to dissect pro-survival effects of T cells versus NLC, in relation to TNF(R) and kinase signaling.
In order to turn these concepts into targeted clinical approaches, this program aims to fill the following gaps in knowledge: 1. which signals predominate within the CLL microenvironment to provide chemoresistance and proliferation, 2. what molecular and functional events occur following distinct TNF-receptor family member mediated signaling. 3. Which intracellular signaling pathways hold most promise for therapeutic intervention with emphasis on kinase (family) activation. In order to gather meaningful and clinical relevant results these questions will be addressed by integrated study of LN CLL biopsy specimens, in vitro model systems and in vivo mouse models.
In addition, impact of novel drugs targeting the microenvironment will be addressed by phase 1, 2 and 3 clinical studies in CLL patients of which I am the principal investigator:
- Hovon 109: Lenalidomide in addition to chlorambucil and rituximab for first-line elderly patients; phase 1/2
- Hovon 121: Lenalidomide maintenance following induction treatment in Young/fit patients; phase 3
- Hovon 122: Ofatumumab and CAL101 followed by allo-SCT in refractory patients; phase 2
- LLPC: GS9820 (PI3-kinase inhibitor) for relapsed and refractory CLL and (non-) Hodgkin lymphoma; phase 1
Effective start/end date01/06/2012 → …

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