Acute Myeloid Leukemia (AML) is the most common and aggressive form of acute leukemia, with a 5-year survival rate of just 24%. Over a third of all AML patients harbour activating mutations in kinases, such as the receptor tyrosine kinase KIT. KIT mutations are associated with poor clinical outcomes and lower remission rates in response to standard-of-care chemotherapy. A better characterisation of KIT signalling is required to identify improved therapeutic targets.
Phosphoproteomic profiling was performed on isogenic FDC-P1 mouse myeloid progenitor cell lines transduced with oncogenic mutant KIT (V560G, D816V), or vector control. The expression of mutant KIT was associated with increased KIT phosphorylation, consistent with activation of KIT. This was coupled with increased phosphorylation of KIT downstream signalling proteins including ERK, transcription factor Jun-b, and apoptosis regulator Bad, suggestive of increased pro-survival signalling.
Novel KIT signalling proteins were also identified, including increased phosphorylation of the DNA double strand break repair kinase, DNA-PK; suggesting activation of DNA-PK in KIT mutant cells. Accordingly, proliferation assays revealed that KIT mutant cells were more sensitive to DNA-PK inhibitor treatment, compared to empty vector controls. DNA-PK inhibition combined with inhibition of KIT signalling led to synergistic cell death. Phosphoproteomic analysis of KIT-mutant D816V cells revealed that KIT inhibitor treatment reduced KIT and ERK phosphorylation, while DNA-PK inhibitor treatment reduced mTOR and Bad phosphorylation. Combined KIT and DNA-PK inhibitor treatment reduced both ERK/MAPK and AKT/mTOR activity, suggesting a combinatorial approach is required for efficient inhibition of mutant KIT signalling. This study provides insight into the oncogenic pathways regulated by KIT and DNA-PK, and demonstrates that DNA-PK is a promising therapeutic target for KIT mutant cancers.