Ovarian cancer cells direct monocyte differentiation through a non-canonical pathway

Abstract

Background Alternatively-activated macrophages (AAMs), an anti-inflammatory macrophage subpopulation, have been implicated in the progression of high grade serous ovarian carcinoma (HGSOC). Increased levels of AAMs are correlated with poor HGSOC survival rates, and AAMs increase the attachment and spread of HGSOC cells in vitro. However, the mechanism by which monocytes in the HGSOC tumor microenvironment are differentiated and polarized to AAMs remains unknown. Methods Using an in vitro co-culture device, we cultured naïve, primary human monocytes with a panel of five HGSOC cell lines over the course of 7 days. An empirical Bayesian statistical method, EBSeq, was used to couple RNA-seq with observed monocyte-derived cell phenotype to explore which HGSOC-derived soluble factors supported differentiation to CD68+ macrophages and subsequent polarization towards CD163+ AAMs. Pathways of interest were interrogated using small molecule inhibitors, neutralizing antibodies, and CRISPR knockout cell lines. Results HGSOC cell lines displayed a wide range of abilities to generate AAMs from naïve monocytes. Much of this variation appeared to result from differential ability to generate CD68+ macrophages, as most CD68+ cells were also CD163+. Differences in tumor cell potential to generate macrophages was not due to a MCSF-dependent mechanism, nor variance in established pro-AAM factors. TGFα was implicated as a potential signaling molecule produced by tumor cells that could induce macrophage differentiation, which was validated using a CRISPR knockout of TGFA in the OVCAR5 cell line. Conclusions HGSOC production of TGFα drives monocytes to differentiate into macrophages, representing a central arm of the mechanism by which AAMs are generated in the tumor microenvironment.

Human fallopian tube single-cell analysis reveals monocytic transcriptional and interaction changes in high-grade serous ovarian cancers

“…We suspect that early changes in tumor development may differentiate monocytes in a tissue-specific manner. Others have shown that the co-culture of PBMC-derived monocytes with ovarian cancer cell lines was sufficient for alternative macrophage development through TGF-alpha (Fogg et al 2020). We hypothesize that the macrophage-to-monocyte ratio could be an indicator of HGSC progression.…”

Fallopian tube single cell analysis reveals myeloid cell alterations in high-grade serous ovarian cancer

“…Others have shown that the co-culture of peripheral blood mononuclear cells (PBMC) derived monocytes with ovarian cancer cell lines was sufficient for alternative macrophage development through TGF-alpha. 55 We hypothesize that the macrophage-to-monocyte ratio could be an indicator of HGSC progression. This concept was recently applied within a melanoma and renal cell carcinoma context, 34 showing that the macrophage-to-monocyte ratio positively correlated with tumor Treg infiltration.…”

Monocytes in Tumorigenesis and Tumor Immunotherapy

“…Interestingly, several mechanisms have been elucidated that tumor-derived factors trigger monocyte differentiation into M2-like macrophages. In high-grade serous ovarian carcinoma (HGSOC), a high level of transforming growth factor alpha (TGFα) was directly related to the modulation of differentiation of monocytes into M2-like macrophages and, thereby, tumor transformation [ 21 ]. Hyaluronic acid (HA), a common component found in various tumor-associated extracellular matrices (ECM) [ 22 ], was found to contribute to the development of pro-tumor, immunosuppressive M2-like monocytes/macrophages.…”