Poster Presentation 31st Lorne Cancer Conference 2019

Acquisition of the Recurrent Gly101Val Mutation in BCL2 Confers Resistance to Venetoclax in Patients with Progressive Chronic Lymphocytic Leukemia (#191)

Jianan Gong 1 2 , Piers Blombery 3 4 5 , Mary Ann Anderson 1 2 4 , Rachel Thijssen 1 2 , Richard W. Birkinshaw 1 2 , Charis E. Teh 1 2 , Tamia Nguyen 3 5 , Zhen Xu 1 2 , Christoffer Flensburg 1 2 , Thomas E. Lew 2 , Ian J. Majewski 1 2 , Daniel H.D. Gray 1 2 , David A. Westerman 3 4 5 , Constantine S. Tam 4 5 , John F. Seymour 4 5 , Peter E. Czabotar 1 2 , David C.S. Huang 1 2 , Andrew W. Roberts 1 2 4 6
  1. Department of Medical Biology, University of Melbourne, Melbourne
  2. Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia
  3. Department of Pathology, Peter MacCallum Cancer Centre, Melbourne, VIC, Australia
  4. Department of Clinical Haematology and Bone Marrow Transplantation, The Royal Melbourne Hospital, Melbourne
  5. Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, VIC, Australia
  6. Centre for Cancer Research, University of Melbourne, Melbourne, VIC, Melbourne

The BCL2 inhibitor, venetoclax, induces marked disease remission in previously treated chronic lymphocytic leukemia (CLL) patients. However, leukemia recurs in most patients during treatment. The molecular mechanisms that mediate clinical resistance to venetoclax are largely unknown.

To investigate the underlying mechanisms, we analyzed paired pre-venetoclax and progression samples from 15 patients with CLL progression enrolled on venetoclax clinical trials. A novel Gly101Val mutation in BCL2 was identified in seven patients at progression, but not at study entry. Our survey in samples from patients who had not received venetoclax and also public databases further confirmed that this mutation only occurs in the setting of CLL-type progression on venetoclax treatment. We therefore hypothesized that Gly101Val contributes to venetoclax resistance. As expected, CLL cells collected from patients at progression were much less sensitive to venetoclax compared to their paired pre-treatment samples.  Moreover, overexpression of the mutant in two human B-lineage cell lines marked reduced their sensitivity to venetoclax and also provided a selective growth advantage over wild-type cells during continuous exposure to sub-lethal concentrations of drug.

We next investigated how Gly101Val confers venetoclax resistance. Although the available structures indicated that venetoclax does not directly contact Gly101, our biochemical and cellular assays showed that venetoclax has markedly decreased binding to Gly101Val compared to wild-type BCL2, which thereby compromised its ability to displace pro-apoptotic proteins such as BAX and BIM, and consequently, the induction of apoptosis. These results suggested that the binding groove is malleable such that this mutation indirectly impacts upon the binding groove to impair venetoclax binding.

In conclusion, we identified and functionally characterized a novel recurrent Gly101Val BCL2 mutation emerging in a cohort of patients with CLL-type progressions on venetoclax treatment. Gly101Val markedly reduces the affinity of venetoclax for BCL2 and confers acquired resistance in vitro and in patients. This mutation provides new insights into the pathobiology of venetoclax resistance and provides a potential biomarker of impending clinical relapse.

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  2. Roberts AW, Davids MS, Pagel JM, Kahl BS, Puvvada SD, Gerecitano JF, et al. Targeting BCL2 with Venetoclax in Relapsed Chronic Lymphocytic Leukemia. N Engl J Med 2016;374(4):311-22.