Eric Si1,2, Peter Czabotar1,2, Seong Lin Khaw1,2,4, Andrew W Roberts1,2,3, David CS Huang1,2, Ian Majewski1,2,
The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
1The Walter and Eliza Hall Institute of Medical Research, Parkville, Australia.
2Department of Medical Biology, University of Melbourne, Melbourne, Australia.
3Department of Clinical Haematology and Bone Marrow Transplantation, The Royal Melbourne Hospital, Parkville, Australia.
4 Royal Children’s Hospital, Parkville, Australia.
A detailed functional assessment of mutations in BCL2 that could undermine therapeutic targeting with Venetoclax.
Venetoclax (ABT-199), a potent and selective inhibitor of BCL2, is a promising new therapeutic for the treatment of Chronic Lymphocytic Leukemia (CLL). ABT-199 was generated through structure-guided chemical modification of its predecessor, ABT-263 (navitoclax), resulting in specific and high affinity binding to BCL2.
A key question is whether Venetoclax resistance emerges as a result of mutations in BCL2 that alter the drug-binding site. Recently Fresquet et al. (2014) demonstrated that binding site mutations contribute to ABT-199 resistance in a mouse model of mantle cell lymphoma. However, because binding site mutations have not yet been observed in CLL patients treated with ABT-199 (unpublished data), it remained unclear whether these mutant forms of BCL2 were functional and were sufficient to confer resistance.
To address this question, we exploited the CRISPR/Cas9 technology to generate cell lines that only express wild-type or mutant forms of BCL2. In killing assays, we were able to demonstrate that the mutant form is fully functional but unlike the wild-type protein, its activity was unaffected by ABT-199. As this mutation has not, to date, been detected in patients with clinical resistance, our study leaves open the question as to how CLL cells become resistant to ABT-199.