Immune cell-mediated de novo steroid biosynthesis in the tumour microenvironment dysregulates anti-tumour immunity

BACKGROUND Established tumours often foster an immunosuppressive microenvironment.

Therefore, the major challenge in developing cancer-immunotherapy is to discover the anti-tumour immunosuppressive mechanisms and target those to reinstate anti-tumour immunity. Steroidogenesis is a metabolic process by which cholesterol is converted to steroids. Cyp11a1 catalyses the first and rate-limiting step of the pathway.

I have shown that T cell-mediated steroidogenesis in the tumour dysregulates cancer immunity, and genetic deletion of Cyp11a1 stimulates anti-tumour immunity. Many human tumour types are predicted to be steroidogenic.

Therefore, the current proposal aims to investigate this novel facet of immunometabolism in regulating cancer immunity, both in human and mice, and discover new and specific targets for cancer therapy.

AIMS AND METHODS Aim-1 Determine the mechanism of establishment of a steroidogenic and steroid-responsive tumour microenvironment In human tumours, we will assess CYP11A1 expression by immunohistochemistry and gene expression analysis; characterise de novo steroidogenic immune cells using flow cytometry, immunohistochemistry and confocal microscopy; profile and quantify steroids by liquid chromatography-tandem mass spectrometry and correlate steroidogenesis with the T cell dysfunction.

We will characterise and demonstrate the signalling cues that induce immune cell steroidogenesis by using Cyp11a1-reporter mice. We will show how pregnenolone is converted to glucocorticoids.

Aim-2 Determine the mechanisms of immune cell steroidogenesis-mediated anti-tumour immunosuppression in syngeneic melanoma and breast cancer model.

We will delete Cyp11a1 in T cells by crossing Cyp11a1-floxed and T cell-specific Cre-expressing mice, then assess the impact whether the dysfunctional state of immune cells can be reversed.

We will analyse the steroid-responder cells to determine how steroids exert suppressive effect in the tumour microenvironment.

In particular, using cell type-specific glucocorticoids receptor knockout mice, we will investigate how intratumoural steroids increase the number and potency of regulatory T cells and decrease the number functional cytotoxic T-cells.

Aim-3 Dissect the regulatory mechanisms of steroidogenesis process in immune cells and how it is different from that in classic glandular steroidogenic tissues to identify new and specific targets for cancer immunotherapy We will investigate whether the Cyp11a1 expression, cholesterol import into the mitochondria and the rate of steroidogenesis are differentially regulated in immune cells.

We will investigate whether these steps can be targeted by using pharmacological inhibitors of steroidogenesis. HOW THE RESULTS OF THIS RESEARCH WILL BE USED?

This study will uncover the mechanisms of immune cell-mediated steroidogenesis and how that dysregulate anti-tumour immunity. The study will identify the new and specific target(s) for cancer immunotherapy.