Peritoneal carcinomatosis (PC) is a form of secondary metastasis that arises from several intra-abdominal malignancies [1]. Typically, ascites in these patients develops as a late manifestation of advanced cancer and was conventionally regarded as a byproduct of the debilitating condition. Numerous recent studies have demonstrated that ascites is biologically active and forms a critical component of the tumour microenvironment [2,3]. However, little is known about the underlying molecular mechanism of how ascites activates cancer cells.
In our recent study, published in Cell Reports Medicine on 15 February 2022, our team described a new approach of inhibiting PAI-1, a key ligand in ascites which cancer cells are reliant on, as a form of potential therapy in patients with PC [4]. Combining data from functional experiments with transcriptomic profiling of ascites-treated PC cell lines, we found that STAT3 is one of the key upregulated pathways. Key putative activators of STAT3 signaling were identified via multi-omics and integrative analysis using publicly available datasets. Among the 14 shortlisted putative markers that could predict survival in patients in at least three types of cancer origins, our cytokine profiling data of an NCCS internal cohort showed concordant results that PAI-1 is highly abundant in ascites of colorectal PC, highlighting the importance of PAI-1 in this disease context.
Figure 1. Overall workflow of deciphering key secretors of PAI-1 in ascites of PC.
Deciphering the cell type responsible for PAI-1 secretion into ascites in peritoneal carcinomatosis
PAI-1 is an extensively-studied protein that plays a critical role in fibrinolysis and the coagulation cascade. To demonstrate that PAI-1 is not a byproduct but an actively secreted ligand within ascites, we conducted single-cell RNAseq profiling to determine the primary source of PAI-1 within ascites. To this end, we worked closely with expert scientists from the Cancer Discovery Hub (CDH) on the single-cell RNA-seq as well as data analysis. This collaboration enabled our team to obtain robust single cell transcriptomic data that provided critical insights for our flagship project.
Single-cell RNA-seq libraries were curated from peritoneal tissue samples and ascites derived from 2 individual patients (colorectal and ovarian origins) with PC. The overall workflow is shown in Figure 1. Our data showed that PAI-1 is largely secreted by fibroblasts and not by other cell types. Furthermore, this was observed in the data derived from both patients of different histological subtypes. We further validated this finding in an in-vitro setting where we studied the PAI-1 levels in conditioned media derived from various cell lines. We found that PAI-1 levels were low in the conditioned media obtained from colorectal PC cell lines (SNU-C1 and Colo-205). On the other hand, as compared to normal colonic fibroblasts (CCD-19Co), PAI-1 was significantly enriched in conditioned media obtained from normal mesothelial cells (HM-3/TERT and LP9/TERT) and colorectal tumor cancer-associated fibroblasts (CAF05) (p < 0.001). Taken together, the findings from both assays allude that the two cell types primarily responsible for secreting PAI-1 into PC ascites are fibroblasts and mesothelial cells, leading us to the proposed mechanism of paracrine addiction.
References
Coccolini F. Peritoneal carcinomatosis. WJG. 2013;19(41):6979.
Lane D, Matte I, Rancourt C, Piché A. Prognostic significance of IL-6 and IL-8 ascites levels in ovarian cancer patients. BMC Cancer. 2011 May 30;11:210.
Matte I, Lane D, Laplante C, Rancourt C, Piché A. Profiling of cytokines in human epithelial ovarian cancer ascites. Am J Cancer Res. 2012 Aug 20;2(5):566–80.
Hendrikson J, Liu Y, Ng WH, et al. Ligand-mediated PAI-1 inhibition in a mouse model of peritoneal carcinomatosis. Cell Reports Medicine. 2022 Feb;3(2):100526.
Ms Qiu Xuan
Research Officer, Laboratory of Applied Human Genetics
National Cancer Centre Singapore
Dr Liu Ying
Research Fellow, Laboratory of Applied Human Genetics
National Cancer Centre Singapore
Dr Johnny Ong
Principal Investigator, Laboratory of Applied Human Genetics
National Cancer Centre Singapore