2. Nadine Mahmoud, MD

Chromophobe renal cell carcinoma (ChRCC) is the second most common form of non-clear cell RCC. Effective treatment options for metastatic disease are limited, with a median survival of about 2 years. We performed BH3 profiling, a functional assay of susceptibility to apoptosis, in four ChRCC cell lines, revealing dependency on two anti-apoptotic proteins: BCL-xL and MCL-1. Analysis of The Cancer Genome Atlas (TCGA) ChRCC dataset showed that BCL-xL is upregulated by approximately 1.5-fold compared to matched normal kidney. Notably, BCL-xL expression in ChRCC is the second highest among all cancer types in TCGA.
Dual inhibition with selective inhibitors – A-1331852 (targeting BCL-xL) and S-63845 (targeting MCL-1) – resulted in a synergistic reduction in cell viability compared to single-agent treatments, with combination treatment leading to a 12-fold increase in cell death. Supporting these findings, siRNA knockdown of MCL-1 enhanced sensitivity to BCL-xL inhibition, whereas knockdown of BCL-xL alone induced a cytostatic effect (p < 0.0001). Additionally, cells with MCL-1 knockdown showed a marked reduction in viability compared to control siRNA-treated cells at each tested concentration of A-133 (p < 0.0001). Apoptosis was confirmed through increased levels of cleaved PARP and cleaved caspase 3 proteins. Previous work in our lab demonstrated that ChRCC cells are hypersensitive to ferroptosis, an iron-dependent form of non-apoptotic cell death. Treatment with BCL-xL and MCL-1 inhibitors further sensitized ChRCC cells to ferroptosis induced by erastin, which inhibits cysteine uptake, or RSL3, which inhibits GPX4, suggesting a link between ferroptosis and apoptosis in this context. Our results identify a critical role of BCL-xL in ChRCC and indicate that BCL-xL inhibition induces a compensatory dependency on MCL-1. In addition, our data indicate that combining BCL-xL and MCL-1 inhibitors sensitizes to ferroptosis induction in ChRCC.