Chemical Proteomics Reveals Ferrochelatase as a Common Off-target of Kinase Inhibitors

ABSTRACT: Protein kinases are key components in signal transduction pathways and are established drug targets in oncology. Consequently, small molecule kinase inhibitors are on the rise but often show a rather broad target spectrum, potentially leading to toxic side effects. As a result, a broad assessment of the target space is desirable for proper interpretation of observed biological effects. The enzyme Ferrochelatase (FECH), which catalyzes the conversion of protoporphyrin IX into heme, was recently found to be an off-target of the BRAF inhibitor Vemurafenib potentially explaining the often severe phototoxicity associated with this drug in melanoma patients. However, the extent to which kinase inhibitors bind to FECH in general is currently unclear. Here, we used a chemical proteomics approach based on the kinobead technology to profile 226 clinical kinase inhibitors for their potential to bind FECH. Surprisingly, low or sub-micromolar FECH binding was detected for 29 (13%) of all compounds tested and isothermal dose response measurements confirmed drug binding to FECH in cells. We also show that Vemurafenib, Linsitinib, Neratinib and MK-2461 reduce heme levels in K562 cells, verifying that drug binding leads to loss of FECH activity. Further experiments identified the protoporphyrin pocket in FECH as one major binding site for small molecule inhibitors. Since genetic loss of FECH function leads to photosensitivity in humans, we suggest that FECH inhibition by kinase inhibitors is the molecular mechanism triggering photosensitivity in patients and should therefore be part of the pre-clinical tox package for kinase inhibitors.

INSTRUMENT(S): LTQ Orbitrap Elite

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Susan Klaeger  

LAB HEAD: Bernhard Kuster

PROVIDER: PXD003373 | Pride | 2017-03-22

REPOSITORIES: Pride