21P - Implications of KMT2C knockdown for DNA damage repair in breast cancer

Background

Pathogenic mutations in the epigenetic modulator histone-lysine N-methyltransferase 2C (KMT2C) occur in up to 1 in every 6 breast cancers and KMT2C likely functions as a tumour suppressor. Despite this high frequency, therapeutic implications of deleterious KMT2C mutations are poorly understood and detailed pre-clinical work is still needed. DNA damage repair pathways may be affected by KMT2C mutations according to published preclinical data. The aim of this study is to identify the effects of KMT2C knockdown in vitro in breast cancer cells as a basis for identifying potential synthetic lethality drug targets.

Methods

MCF-7 (ER+ breast cancer) cells were cultured and 500,000 cells per well were plated on 6-well plates. KMT2C siRNA was transfected via Lipofectamine as per protocol in three wells, with universal control siRNA in three wells. Total RNA was extracted and sent for sequencing. RNA expression was quantified by RT-qPCR.

Results

RNA-seq confirmed reduction in expression of KMT2C in KMT2C siRNA-treated cells vs controls. RT-qPCR showed a reduction in expression of DNA damage repair genes including BRCA1 (RQ = 0.36), BRCA2 (RQ = 0.37), RAD51 (RQ = 0.36), RAD54L (RQ = 0.28) and POLD3 (RQ = 0.47).

Conclusions

KMT2C loss-of-function in breast cancer may impact DNA damage response pathways including homologous recombination and therefore be implicated in response to established treatments such as PARP-inhibitors. Further study including mapping of co-dependencies by whole genome siRNA screens in KMT2C-mutant breast cancer cells to identify synthetic lethality targets, as well as cell toxicity assays, are being performed in light of these results.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Beaumont RCSI Cancer Centre.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.