Nephrotoxicity of the BRAF-kinase inhibitor Vemurafenib is driven by off-target Ferrochelatase inhibition

Abstract

A multitude of disease and therapy related factors drive the frequent development of renal disorders in cancer patients. Along with chemotherapy, the newer targeted therapeutics can also cause renal dysfunction through on and off-target mechanisms. Interestingly, among the small-molecule inhibitors approved for the treatment of cancers that harbor BRAF-kinase activating mutations, vemurafenib can trigger tubular damage and acute kidney injury (AKI). To investigate the underlying mechanisms, here, we have developed cell culture and mouse models of vemurafenib nephrotoxicity. Our studies show that at clinically relevant concentrations vemurafenib induces cell-death in transformed and primary murine and human renal tubular epithelial cells (RTEC). In mice, two weeks of daily vemurafenib treatment causes moderate AKI with histopathological characteristics of RTEC injury. Importantly, RTEC-specific BRAF gene deletion did not influence renal function under normal conditions or alter the severity of vemurafenib-associated renal impairment. Instead, we found that inhibition of ferrochelatase (FECH), an enzyme involved in heme biosynthesis contributes to vemurafenib nephrotoxicity. FECH overexpression protected RTECs and conversely FECH knockdown increased the sensitivity to vemurafenib nephrotoxicity. Collectively, these studies suggest that vemurafenib-associated RTEC dysfunction and nephrotoxicity is BRAF-independent and caused in part by off-target FECH inhibition.Translational StatementBRAF is the most frequently mutated protein kinase and a critical oncogenic driver in human cancers. In melanoma and other cancers with BRAF activating mutations, BRAF targeted small-molecule therapeutics such as vemurafenib, and dabrafenib have shown remarkable clinical benefits. However, recent clinical studies have shown that a significant number of patients that receive vemurafenib develop AKI through mechanisms that remain unknown. The present study describes the development of novel experimental models of vemurafenib nephrotoxicity and reveals the underlying off-target mechanisms that contribute to renal injury.

Drug Target Identification in Tissues by Thermal Proteome Profiling

“…The major limitation of this approach is that it restricts itself to kinase targets. However, kinases constitute 10% of the currently targeted proteome (23), and due to the use of several unselective kinase inhibitors, it has been possible to confirm that ferrochelatase is a common off-target of kinase inhibitors (24,25), which appears to drive their toxicity (26). This strategy is also expandable to other target classes such as histone deacetylases (HDACs) (27) or poly (ADP-ribose) polymerases (28).…”

“…It has also led to the identification of ferrochelatase (FECH) as an off-target of kinase inhibitors, such as staurosporine or vemurafenib, and of phenylalanine hydroxylase as an off-target of the HDAC inhibitor panobinostat. The inhibition of these proteins is likely to contribute to adverse reactions upon administration of these drugs, including nephrotoxicity of kinase inhibitors (26) or hypothyroidism-like symptoms of panobinostat.…”