Identifying mechanisms of macrophage-mediated metastasis and treatment resistance in pancreatic cancer

Abstract

Background: Pancreatic ductal adenocarcinoma (PDAC) is a lethal, incurable disease and desmoplasia is one of its fundamental characteristics. Though a significant body of literature has been published regarding the disease, mechanisms for PDAC progression, invasion and metastasis still remain unclear. Stromal elements have been demonstrated to serve both pro-and anti-tumoural functions. Macrophages, one of the most abundant immune cell populations in the tumour microenvironment (TME), are a major component of the immune infiltrate in PDAC. Methods: Employing a multi-omics approach, PDAC cell lines and primary macrophages were CTAP (cell-type specific labelling using amino acid precursors)-labelled and admixed together for a prolonged period of time. To identify cell-of-origin of novel RNA and proteins, these mixed co-cultures were FACS sorted for downstream RNAsequencing analysis or harvested in bulk for downstream Tandem mass tag (TMT)-proteome and secretome analysis. Results: Here, we provide new insight into the dichotomous relationship between epithelial and mesenchymal phenotypes of PDAC cells in 3D culture. We report the ability of PDAC mesenchymal cells to form vascular mimicry-like structures in a 3D in vitro assay of invasion. Additionally, we demonstrate that macrophages have the ability to impart a pro-invasive phenotype to PDAC cells when co-cultured in 3D, regardless of EMT status. Preliminary integration of cell culture transcriptomes with CTAP-TMT proteomes and secretomes implicates several key epithelial-and macrophage-derived signalling molecules as principal instructing signals for mediating the observed proinvasive phenotype. Conclusion: Blockade of these signalling molecules or their receptors disrupted the crosstalk between PDAC cells and macrophages within the TME and impaired the ability of macrophages to induce a pro-invasive phenotype to PDAC cells.