Dual G9A and EZH2 inhibition stimulates an anti-tumour immune response in ovarian high-grade serous carcinoma. Dual G9A and EZH2 inhibition in ovarian high-grade serous carcinoma

Ovarian high-grade serous carcinoma (HGSC) prognosis is directly linked to the presence of intratumoral lymphocytes. However, cancer immunotherapy has yet to achieve meaningful survival benefit in patients with HGSC. Epigenetic silencing of immunostimulatory genes is implicated in immune evasion in HGSC and re-expression of these genes could promote tumour immune clearance. We discovered that simultaneous inhibition of the histone methyltransferases G9A and EZH2 activates the CXCL10-CXCR3 axis and increases homing of intratumoral effector lymphocytes and NK cells whilst suppressing the tumour-promoting FoxP3+ CD4 T cells. The dual G9A/EZH2 inhibitor HKMTI-1-005 induces chromatin changes that result in the transcriptional activation of immunostimulatory gene networks, including the re-expression of elements of the ERV-K endogenous retroviral family. Importantly, treatment with HKMTI-1-005 improves the survival of mice bearing Trp53-/- null ID8 ovarian tumours and results in tumour burden reduction.These results indicate that inhibiting G9A/EZH2 in OC alters the immune microenvironment and reduces tumour growth and therefore positions dual inhibition of G9A/EZH2 as a strategy for clinical development.