The Epigenetic Mechanism Study Of The Drug Resistance Of BRAF^V600E Mutant Tumor

BRAF is one of the most commonly mutated kinases and oncogenes in solid malignancies(approximately 7-9%).All mutations in B-Raf cluster within the kinase domain,with a single substitution(V600E)accounting for?80%of the mutations observed.Inhibitors of BRAF(BRAFi)have shown high survival rates in patients with melanoma that express mutations encoding BRAF proteins mutant at Va1600.Unfortunately,the treatment is limited by the development of primary resistance or acquired resistance.Several mechanisms have been reported,mostly involving reactivation of the Ras/Raf/MEK/MAPK pathway or the PI3K/AKT/mTOR pathway.However,a portion of BRAFi-resistant melanomas are not driven by any of these known resistance mechanisms.The importance of an apparent regulator of histone or histone modification in melanoma has just been elucidated,providing new opportunities to address clinical treatment resistance.We found that BRAFi-resistant tumor cells were more sensitive to MI-3,a small molecule inhibitor targeted H3K4me3,by examining the sensitivity of before and after acquired resistance of BRAFi to epigenetic compound libraries.We differentiate different types of tumor cells into two classes:BRAFi-sensitive,BRAFi endogenous resistance,according to the different sensitivity of BRAFV600E mutant tumor cells to dabrafenib.In the BRAFi-sensitive cells,BRAFi inhibited the RAF-ERK pathway,the positive histone H3K4me3 which mediated by methyltransferase menin-MLL complex was significantly inhibited,whereas in BRAFi endogenous resistant cells BRAFi can not mediate the inhibition of RAF-ERK pathway,and thus can not inhibit the expression of menin-MLL complex.BRAFi did not inhibit the RAF-ERK pathway,resulting in loss of inhibition of the menin-MLL complex.Menin-MLL complex was administered by regulating DUSP6,SPRY4.We found that MI-3 could re-inhibit the activation of ERK1/2 in BRAFi-resistant cells,and MI-3 combined with BRAFi dabrafenib can significantly inhibit the phosphorylation of ERK permanently and the activity of tumor cells as well as the clony ability.Our results suggest that H3K4me3 is involved in the regulation of BRAFi resistance,and MI-3,a targeted H3K4me3 inhibitor can be used as a sensitizer for BRAFi to improve the treatment of BRAF mutant tumors.