Heme oxygenase-1 expressing omental macrophages as a therapeutic target in ovarian high grade serous carcinoma

Abstract

AbstractOvarian high grade serous carcinoma (HGSC) remains a disease of poor prognosis that is unresponsive to current immune checkpoint inhibitors. Although PI3K pathway alterations are common in HGSC, attempts to target this pathway have been unsuccessful. We hypothesised aberrant PI3K pathway activation may alter the HGSC immune microenvironment and present a novel targeting strategy. We used both murine models and HGSC patient samples to study the impact of loss ofPten, a negative regulator of PI3K pathway signalling. We identified populations of resident macrophages specifically inPtennull omental tumours. These macrophages derive from peritoneal fluid macrophages and have a unique gene expression programme, marked by high levels ofHMOX1expression, the gene for the enzyme heme oxygenase-1. Targeting resident peritoneal macrophages prevents appearance of HMOX1himacrophages and in doing so reduces tumour growth. Furthermore, direct inhibition of HMOX1 extends survivalin vivo. HMOX1himacrophages with corresponding gene expression programmes are also identified in human HGSC tumours and their presence correlates with activated tumoural PI3K pathway/mTOR signalling and poor overall survival in HGSC patients. In contrast, tumours with low number of HMOX1himacrophages are marked by increased adaptive immune response gene expression. Our data suggest that HMOX1himacrophages represent a potential therapeutic target and biomarker for poor prognosis HGSC.