Systematic analysis uncovers SYK dependency in NF1LoF melanoma cells

The loss of function (LoF) of NF1 is the third most frequent mutation that drives hyperactivated RAS and tumor growth in >10% of melanomas. NF1LoF melanoma cells, however, do not show consistent sensitivity to individual MEK, ERK, or PI3K/mTOR inhibitors. Here, we perform a targeted kinase inhibitor screen and identify a tool compound, named MTX-216, to be highly effective in blocking NF1LoF melanoma cells. Single-cell analysis links drug-induced cytotoxicity to effective co-suppression of proliferation marker Ki-67 and the ribosomal S6 phosphorylation, an integrator of multiple RAS-mediated signaling pathways. Using a combination of kinome selectivity assay, transcriptomic analysis, and genetic experiments, we find the anti-tumor efficacy of MTX-216 to be dependent on its ability to inhibit not only PI3K (its nominal target) but also SYK, and suppression of a group of genes that regulate mitochondrial electron transport chain and whose expression is associated with poor survival in NF1LoF melanoma patients. Furthermore, combinations of inhibitors targeting either MEK or PI3K/mTOR with an independent SYK kinase inhibitor or SYK knockdown show favorable effects. These studies provide a path to exploit SYK dependency to selectively block NF1LoF melanoma cells. Statement of significanceNF1LoF melanomas represent a subtype with hyperactivated RAS signaling, for which currently no targeted therapies are clinically available. Our systems pharmacology studies identify SYK as a new vulnerability in NF1LoF melanoma cells.