PALB2 deficiency may sensitize H3K27M-mutant pediatric HGG cells to BMN673/talazoparib

Xiaowen Guan^1,2*Xinke Xu³Xiaolan Mo³Houliang Deng³

• ¹Zhengzhou University, Zhengzhou, China
• ²School of Life Sciences, Zhengzhou University, Zhengzhou, Henan Province, China
• ³Department of Neurosurgery, Guangzhou Women and Children's Medical Center, Guangzhou Medical University, Guangzhou, China

Pediatric high-grade glioma (pHGG) with the histone H3 Lys27Met substitution (H3K27M) is a devastating disease with a high mortality rate in children and adolescents (from birth to 19 years of age). No effective treatments have been developed for this tumor type. Thus, a better understanding of the underlying complex mechanisms and identify more potential drugs targeting H3K27M-mutant pHGG are urgently needed. In the current study, we established pHGG cell models harboring H3K27M by transfecting two pHGG cell lines, SF188 and Res259, with the H3K27M mutant and H3 wild-type (WT) plasmids and then performed drugs screening.Notably, BMN673 (talazoparib) was identified as a synthetic lethal hit in the H3K27Mmutant SF188 cell model. However, BMN673 did not affect the constructed H3K27Mmutant Res259 cells. Moreover, using an EJ5 reporter assay, we showed that the H3K27M mutation induced an aberrant increase in nonhomologous end joining (NHEJ) activity. The Western blotting results revealed that BMN673 treatment increased the protein levels of the DNA damage markers γ-H2AX and PLK1. In addition, we found that BMN673 treatment can drive cell cycle arrest and PARP1 trapping in H3K27Mmutant SF188 cells. Specifically, by combining whole-exome sequencing and CRISPR/Cas9 genome editing, H3K27M-mutant Res259 cells and H3K27M-WT Res259 cells with stable ARID1A, P53 or PALB2 deficiency were successfully established, and the results of a series of viability assays revealed that the H3K27M mutation combined with PALB2 deficiency sensitized H3K27M-mutant Res259 cells to BMN673. Overall, our results may provide some reference value for further study of the effects of BMN673 and PALB2 deficiency in the treatment of H3K27M-mutant pHGG.