[Chidamide Combined with (+) -JQ-1 to Kill MLL-Rearrangement Acute Myeloid Leukemia Cells by Disrupting the DNA Damage Response Pathway].

Objective: To investigate the mechanism of DNA damage and repair in MLL -rearranged acute myeloid leukemia（ MLL-r AML）cells by the combination of Chidamide and the BRD4 inhibitor(+)-JQ-1.

Methods: MLL-r AML cell lines Molm-13, MV4-11 and non- MLL-r AML cell line Kasumi were divided into control group（contr）, Chidamide group（chida）, (+)-JQ-1 group and Combination group（combi）, respectively. Cell viability of Molm-13 was measured by CCK-8 to determine optimal the concentrations of Chidamide and(+)-JQ-1. The cell cycle was detected by flow cytometry, and apoptosis-related factors Bcl-2, Bax and caspase-3 were detected by Western blot. DNA damage marker γH2AX was detected by immunofluorescence. The protein expressions of DNA damage factor γH2AX, DNA damage checkpoint kinases p-ATR, p-CHK1, p-ATM, p-CHK2 and DNA damage repair factors Rad51 and 53BP1 were detected by Western blot. The expression of DNA damage repair factors Rad51 and 53BP1 mRNA was detected by qRT-PCR.

Results: Under the treatment of Chidamide (300 nmol/L) and (+)-JQ-1 (400 nmol/L), the proportion of G₁ phase cells in MLL-r AML cell lines Molm-13 and MV4-11 was increased in combination group compared with control group. In non- MLL-r AML cell line Kasumi, compared with control group, the proportion of G₁ phase cells in combination group was increased (P < 0.05). In Molm-13 and MV4-11 cell lines, compared with control group, the expression level of DNA damage marker γH2AX in combination group was increased (P < 0.05). The expression levels of DNA damage checkpoint and damage repair factors p-ATR, p-CHK1, p-ATM, p-CHK2, Rad51, 53BP1 were decreased (P < 0.05). In Kasumi cell line, compared with control group, there was no significant change in the expression of some of the above factors in combination group (P >0.05), but the expression trend of some factors was opposite. In MLL-r AML cell lines Molm-13 and MV4-11, compared with control group, the expression levels of Bax and caspase-3 protein were increased in combination group, while the expression levels of Bcl-2 protein were decreased (P < 0.05). In non- MLL-r AML cell line Kasumi, there was no significant change in apoptotic factor protein expression in combination group compared with control group (P >0.05).

Conclusion: Chidamide combined with (+)-JQ-1 can inhibit the proliferation of MLL-r AML cells, inhibit the initiation of protective self-repair of these leukemia cells by inhibiting the DNA damage response pathway, and ultimately increase the apoptosis of these cells, but non- MLL-r AML cells have no similar results.