We used BH3 profiling, a functional assay that measures “cell priming,” defined as the cell readiness to undergo apoptosis, and to identify anti-apoptotic proteins essential for tumor cell survival. We found that ChRCC-derived cell lines are generally unprimed for apoptosis and exhibit a consistent dependency on BCL-xL, a key member of the anti-apoptotic BCL-2 family of proteins. Consistent with this finding, analysis of The Cancer Genome Atlas (TCGA) revealed that ChRCC has the second-highest expression of BCL2L1 (gene encoding BCL-xL) among all tumor subtypes in TCGA, with a fourfold upregulation in ChRCC compared to normal kidney.
Genetic knockdown of BCL2L1 induced apoptotic cell death and upregulation of MCL-1, another anti-apoptotic protein in ChRCC-derived cells, supporting a compensatory mechanism that maintains tumor cell survival. Combined pharmacologic inhibition of BCL-xL and MCL-1 produced synergistic death of up to 80% of the ChRCC cells. DT2216 is a proteolysis-targeting chimera (PROTAC) that selectively degrades BCL-xL with minimal platelet toxicity. DT2216 effectively induced apoptotic markers and reduced the viability of ChRCC-derived cell lines, highlighting its therapeutic promise in ChRCC.
Given the known hypersensitivity of ChRCC to ferroptosis, we next explored whether promoting apoptosis could further enhance ferroptotic cell death in ChRCC. Combining pharmacologic inhibitors of BCL-xL and MCL-1 with IKE or RSL3, two ferroptosis inducers, markedly increased cell death, revealing potential crosstalk between apoptosis and ferroptosis.
To our knowledge, this is the first study to explore apoptotic dependencies in ChRCC. We found that inhibition of BCL-xL induces cell death in ChRCC, and that concurrent inhibition of MCL-1 enhances this effect synergistically. This work provides preclinical insight into the activity of BCL-xL–targeting PROTACs, including DT2216, which is currently in Phase I clinical trials for solid tumors. While our results are encouraging, these findings need to be confirmed in in vivo models of ChRCC to assess the efficacy of BCL-xL–targeting strategies, alone and in combination with MCL-1 inhibition or ferroptosis induction. Future research should aim to identify the mechanisms underlying the crosstalk between apoptosis and ferroptosis in ChRCC, including any common upstream pathways, which could uncover additional therapeutic vulnerabilities.
Together, our findings reveal a targetable dependency on BCL-xL in ChRCC, underscoring the translational potential of BCL-xL targeting PROTACs, and identify potential combination approaches targeting both apoptosis and ferroptosis.
Written by: Nadine Mahmoud,1 Xingping Qin,2,3,4 Wafaa Bzeih,1 Damir Khabibullin,1 Michel Alchoueiry,1 Steven Safi,1 Joelle Chami,1 Tiegang Han,1 Samer Salem,1 Carmen Priolo,1 Abhishek A. Chakraborty,5 Kristopher A. Sarosiek,2,3,4,6 Elizabeth P. Henske,1
- Pulmonary and Critical Care Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
- Laboratory of Systems Pharmacology, Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA, USA.
- Molecular and Integrative Physiological Sciences Program, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
- Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, USA.
- Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA, USA.