Molecular dissection of macrophage-tumour cell interactions to identify novel treatment strategies for pancreatic cancer
Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive forms of adult tumours with a median survival time of twelve months. PDAC is highly resistant to conventional therapy which includes surgical resection of the tumour, radiation treatment and chemotherapy. PDAC cells are highly motile and invasive resulting in infiltrative PDAC with poorly defined borders. PDAC tumours are heavily infiltrated with fibroblasts and subpopulations of immune suppressive cells, macrophages, which we demonstrate to stimulate PDAC cell invasion. Our data reveals the dichotomy of phenotypes epithelial and mesenchymal PDAC cells exhibit in 3D culture and the role of macrophages in coercing PDAC cells to acquire invasive characteristics. This interaction was found to be dependent on CCR1 which is expressed on all tumours and infiltrating macrophages. Blockade of the CCR1 using small molecule inhibitors, such as BX-471, can inhibit macrophage-stimulated PDAC invasion in vitro and in vivo. A variety of chemokines are upregulated in the PDAC tumour microenvironment and facilitate cross-talk between macrophages and PDAC cells eliciting a chemotactic response. We demonstrate that the chemotactic ligand family, CCLs, are similarly upregulated in PDAC tumours. We postulate that inhibition of CCLs associated receptors, specifically CCR1, might also inhibit PDAC invasion, thus, a CCR1 antagonist could prove efficacious for blockade of macrophage-induced PDAC invasion in vitro. Many potent CCR1 antagonists have been described in the literature. We chose three of these compounds with two distinct structural cores, all with reported IC50’s of less than 200 nM for inhibition of CCR1 binding of CCL3/CCL9. We examined the ability of these antagonists to block macrophage-stimulated PDAC invasion using an in vitro co-culture invasion assay. Deploying a multi-omics approach, we also show that expression of chemokines and chemokine receptor genes is greatly altered in PDAC following prolonged co-culture with macrophages. Understanding the pattern of tumour-associated macrophage chemokine secretion in PDAC may present novel targets for therapeutic intervention and enhance immunotherapy. Preliminary in vivo results incorporating CCR1 inhibition suggest that targeting CCR1 therapeutically can result in changes in the tissue architecture of PDAC tumours. A triple therapy arm consisting of an antagonist of CCR1 with gemcitabine and anti-PD-1 aims to, first, block the communication between tumour cells and macrophages. A regimen of gemcitabine will act to provide systemic and direct tumour kill with the addition of anti-PD-1 boosting the activity of immune cells by stopping this checkpoint molecule from switching off infiltrating cytotoxic T cells at the tumour site.