High-throughput screen for novel apoptosis-inducing substances for CLL

Even though most CLL patients respond to currently available chemo- or immunotherapies with a profound reduction in tumor burden, relapse of disease and subsequent resistance to therapy is frequent and often associated with clonal evolution of CLL cells. This is mainly due to the fact that quiescent CLL cells within the peripheral blood are effectively eliminated, but malignant cells within protective microenvironments like in the lymph nodes or bone marrow are less effectively targeted by the therapeutics. Therefore, novel drug screening approaches using CLL coculture systems that mimic the protective in vivo microenvironment are necessary to identify substances that are able to overcome this protection. The CLL/stroma coculture models we have established are very well suited for such testing. As they allow for a simultaneous monitoring of effects on CLL cells and stromal cells, general cytotoxic substances can be excluded.
Fungal extracts have been shown to be an important source for biologically active agents, which can be of therapeutic use. In cooperation with Prof. Thomas Larsen we are screening for novel potential drugs for CLL by using an extensive extract library from the IBT Culture Collection of Fungi (Technical University of Denmark) in a high-throughput coculture set-up of primary CLL cells. Chaetoglobosin A was identified as the active compound of one of the most promising hits of this screen. Functional studies revealed that this substance induces apoptosis preferentially in CLL cells, most likely by impacting on cytoskeleton-dependent signalling pathways (see Knudsen et al., 2013). We are in the process of testing the efficacy of Chaetoglobosin A in a murine animal model for CLL, the Eµ-TCL1 transgenic mice, as well as in xenotransplants of human CLL cells in immunodeficient mice (see CLL mouse models).
In addition, further identification and characterization of active substances within fungal extracts that showed CLL-specific cytotoxic activities are ongoing.

The IBT fungal culture collection was used to screen for novel potential drugs for CLL. Thereby, Chaetoglobosin A (ChA) was identified as the active compound within Penicillium aquamarinium extracts, and confirmed to have preferential cytotoxic activity for CLL cells compared to healthy donor lymphocytes (HD). Results of functional studies suggest that Chaetoglobosin A disrupts pro-survival signalling and migration of CLL cells by inhibiting actin filament formation.