A chemical and phosphoproteomic characterization of dasatinib action in lung cancer

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Abstract
Determining relevant targets of promiscuous kinase inhibitors has proven difficult. A combination of two mass spectrometry–based proteomic approaches, RNAi depletion and rescue studies with drug-resistant mutants now reveal that SRC, FYN and EGFR are functionally important targets of dasatinib in lung cancer cells. We describe a strategy for comprehending signaling pathways that are active in lung cancer cells and that are targeted by dasatinib using chemical proteomics to identify direct interacting proteins combined with immunoaffinity purification of tyrosine-phosphorylated peptides corresponding to activated tyrosine kinases. We identified nearly 40 different kinase targets of dasatinib. These include SRC-family kinase (SFK) members (LYN, SRC, FYN, LCK and YES), nonreceptor tyrosine kinases (FRK, BRK and ACK) and receptor tyrosine kinases (Ephrin receptors, DDR1 and EGFR). Using quantitative phosphoproteomics, we identified peptides corresponding to autophosphorylation sites of these tyrosine kinases that are inhibited in a concentration-dependent manner by dasatinib. Using drug-resistant gatekeeper mutants, we show that SFKs (particularly SRC and FYN), as well as EGFR, are relevant targets for dasatinib action. The combined mass spectrometry–based approach described here provides a system-level view of dasatinib action in cancer cells and suggests both functional targets and a rationale for combinatorial therapeutic strategies.