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

## TL;DR

This study explores how a drug called BMN673 may be more effective against a specific type of childhood brain tumor when combined with a genetic deficiency in PALB2.

## Contribution

The study identifies a potential synthetic lethal interaction between BMN673 and PALB2 deficiency in H3K27M-mutant pediatric high-grade glioma cells.

## Key findings

- BMN673 was effective in H3K27M-mutant SF188 cells but not in H3K27M-mutant Res259 cells.
- PALB2 deficiency, but not ARID1A or P53 deficiency, sensitized H3K27M-mutant Res259 cells to BMN673.
- BMN673 treatment increased DNA damage markers and induced cell cycle arrest in H3K27M-mutant SF188 cells.

## Abstract

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. Then we employed an EJ5 reporter assay to measure nonhomologous end joining (NHEJ) activity. Western blotting was used to analyze DNA damage markers (γ-H2AX and PLK1), and cell cycle progression was assessed. Additionally, we utilized whole-exome sequencing and CRISPR/Cas9 genome editing to generate Res259 cell lines with stable deficiencies in ARID1A, P53, or PALB2, followed by viability assays to evaluate drug sensitivity.

Notably, BMN673 (talazoparib) was identified as a synthetic lethal hit in the H3K27M-mutant SF188 cell model. However, BMN673 did not affect the constructed H3K27M-mutant Res259 cells. Moreover, we showed that the H3K27M mutation induced an aberrant increase in NHEJ activity. Furthermore, BMN673 treatment increased the protein levels of γ-H2AX and PLK1, induced cell cycle arrest, and promoted PARP1 trapping in H3K27M-mutant SF188 cells. In addition, the results of a series of viability assays revealed that the H3K27M mutation combined with PALB2 deficiency sensitized H3K27M-mutant Res259 cells to BMN673. However, deficiencies in ARID1A or P53 did not produce similar effects.

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.