Flash Talk and Poster Presentation 35th Lorne Cancer Conference 2023

Determining the essential functions of distinct pro-survival BCL-2 family members by using gene-swap mice (#9)

Kerstin Brinkmann 1 2 , Andrew J Kueh 1 2 , Annli Tee 1 2 , Tim Thomas 1 2 , Anne K Voss 1 2 , Marco Herold 1 2 , Andreas Strasser 1 2
  1. Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
  2. Department of Medical Biology, University of Melbourne, Melbourne

The pro-survival Bcl-2 protein family member MCL1 is amplified in >10% of human cancers1. MCL-1-inhibitors have recently entered clinical trials. However, despite very promising findings from pre-clinical studies, concerning on-target side effects were observed (e.g cardiotoxicity)1. In contrast the BCL-2 inhibitor Venetoclax/ABT199 is well-tolerated and many patients have been already successfully treated with this drug. To allow the safe application of MCL-1 inhibitors, and thereby provide benefits for a huge number of cancer patients, a more detailed understanding of the overlapping and distinct functions of the pro-survival Bcl-2 family members is urgently needed.

In contrast to the other pro-survival Bcl-2 family proteins MCL-1 is essential for embryogenesis, haematopoiesis as well as adult tissue homeostasis2. It remains unclear what characteristics of MCL-1 make it so unique. Notably, a non-apoptotic function of MCL-1 in mitochondrial energy production was proposed. Our study aims to clarify whether a non-apoptotic function of MCL-1 exists and may contribute to the observed on-target toxicities of MCL-1-inhibitors in clinical trials.

HYPOTHESIS: If MCL-1 has unique non-apoptotic functions, the consequences of its loss cannot be rescued by any other pro-survival Bcl-2 family member

To test our hypothesis, we generated “pro-survival gene-swap” mice by replacing the coding region for MCL-1 with a tagged version of another pro-survival protein (Mcl-1Bcl-xL, Mcl‑1Bcl‑2, Mcl-1A1) using CRIPR/Cas9 gene editing.

In contrast to Mcl-1-/- embryos (lethal~E3.5) viable Mcl-1Bcl-xL/Bcl-xL and Mcl-1Bcl-2/Bcl-2 embryos are found until ~E12.5 but show severe defects later during embryogenesis (imbred C57/B6). On a “robust” mixed genetic background Mcl-1Bcl-xL/Bcl-xL mice are born but succumb early postnatally due to severe liver damage that might result from impaired mitochondrial energy production. Hematopoietic chimeras generated by transplanting E12.5 fetal livers from Mcl-1Bcl-xL/Bcl-xL and Mcl-1Bcl-2/Bcl-2 embryos into wt mice had no defects in hematopoiesis. However, Mcl-1Bcl-2/Bcl-2 chimeras develop a BCL-2-driven SLE-like autoimmune disease.

Our results demonstrate that a unique non-apoptotic function of MCl-1 is not essential for early embryogenesis nor haematopoiesis. However, a unique non-apoptotic function of MCL-1 may be required for later stages of embryogenesis and the survival of cells that highly depend on mitochondrial energy production (e.g liver).

  1. Kelly, G. L. & Strasser, A. Toward Targeting Antiapoptotic MCL-1 for Cancer Therapy. Annual Review of Cancer Biology 4, 299-313, doi:10.1146/annurev-cancerbio-030419-033510 (2020).
  2. Brinkmann, K., Ng, A. P., de Graaf, C. A. & Strasser, A. What can we learn from mice lacking pro-survival BCL-2 proteins to advance BH3 mimetic drugs for cancer therapy? Cell Death Differ, doi:10.1038/s41418-022-00987-0 (2022)