Perioperative escape from dormancy of spontaneous micro-metastases: A role for malignant secretion of IL-6, IL-8, and VEGF, through adrenergic and prostaglandin signaling.

We recently showed that a minimally-invasive removal of MDA-MB-231HM primary tumors (PTs) and elimination of their secreted factors (including IL-6, IL-8, VEGF, EGF, PDGF-aa, MIF, SerpinE1, and M-CSF), caused regression of spontaneous micro-metastases into a non-growing dormant state. To explore the underlying mechanisms and potential clinical ramifications of this phenomenon, we herein used the MDA-MB-231HM human breast cancer cell-line, in-vitro, and in vivo following orthotopic implantation in immune-deficient BALB/C nu/nu mice. Employing bioluminescence imaging, we found that adding laparotomy to minimally-invasive removal of the PT caused an outbreak of micro-metastases. However, perioperative ß-adrenergic and COX-2 inhibition, using propranolol + etodolac, maintained metastatic dormancy following laparotomy. In-vitro, ß-adrenergic agonists (epinephrine or metaproterenol) and prostaglandin-E2 markedly increased MDA-MB-231HM secretion of the pro-metastatic factors IL-6, IL-8, and VEGF, whereas cortisol reduced their secretion, effects that were maintained even 12 h after the washout of these agonists. In-vivo, laparotomy elevated IL-6 and IL-8 levels in both plasma and ex-vivo PT spontaneous secretion, whereas perioperative propranolol + etodolac administration blocked these effects. Similar trends were evident for EGF and MIF. Promoter-based bioinformatics analyses of excised PT transcriptomes implicated elevated NF-kB activity and reduced IRF1 activity in the gene regulatory effects of laparotomy, and these effects were inhibited by pre-surgical propranolol + etodolac. Taken together, our findings suggest a novel mechanism of post-operative metastatic outbreak, where surgery-induced adrenergic and prostanoid signaling increase the secretion of pro-metastatic factors, including IL-6, IL-8, and VEGF, from PT and possibly residual malignant tissue, and thereby prevent residual disease from entering dormancy.

Tumour-derived Extracellular Vesicle and Particle Reprogramming of Interstitial Macrophages in the Lung Pre-Metastatic Niche Enhances Vascular Permeability and Metastatic Potential.

Extracellular vesicles and particles (EVPs) are pivotal mediators of pre-metastatic niche formation and cancer progression, including induction of vascular permeability, which facilitates tumor cell extravasation and metastasis. However, the mechanisms through which EVPs exert this effect remain poorly understood. Here, we elucidate a novel mechanism by which tumor EVPs enhance endothelial cell permeability, tumor extravasation, and lung metastasis to different degrees, depending on tumor type. Strikingly, vascular leakiness is observed within 48h following tumor implantation and as early as one hour following intravenous injection of tumour-derived EVPs in naïve mice. Surprisingly, rather than acting directly on endothelial cells, EVPs first activate interstitial macrophages (IMs) leading to activation of JAK/STAT signaling and IL-6 secretion in IMs which subsequently promote endothelial permeability. Depletion of IMs significantly reduces tumour-derived EVP-dependent vascular leakiness and metastatic potential. Tumour EVPs that strongly induce vascular leakiness express high levels of ITGα5, and ITGα5 ablation impairs IM activation, cytokine secretion, and subsequently vascular permeability and metastasis. Importantly, IL-6 expression is elevated in IMs from non-involved tumor-adjacent lung tissue compared to distal lung tissue in lung cancer patients, highlight the clinical relevance of our discovery. Our findings identify a key role for IM activation as an initiating step in tumor type-specific EVP-driven vascular permeability and metastasis, offering promising targets for therapeutic intervention.