<p>PDF file - 643KB, Figure S1: Reactivation of Slit2 expression in Panc1 cells by 5-AZA-dC suggests silencing of Slit2 gene due to promoter hypermethylation. Figure S2: Slit2 inhibits directed migration of pancreatic tumor cells. Figure S3: Re-expression of Slit2 does not affect random migration of MiaPaCaTR-Slit2 Cells. Figure S4: Doxycycline treatment results in induction of Slit2 protein in MiaPaCaTR-Slit2 tumors in vivo. Figure S5: Inducible re-expression of Slit2 inhibits invasion, metastasis and angiogenesis in size-matched orthotopic pancreatic tumors. Figure S6: Stable knock down of Robo1 in pancreatic tumor cells promotes metastasis, but does not affect angiogenesis of orthotopic pancreatic tumors. Figure S7: Functional inhibition of Slit2 via Robo1-Fc stimulates angiogenesis in DANGRobo1-KD tumors subjected to Robo1 receptor knock down. Figure S8: Forced expression of Slit2 inhibits metastasis and invasion in the orthotopic Panc02 syngeneic tumor model. Figure S9: Time-lapse microscopy reveals directional navigation of tumor cells along Neuritis.</p>
<div>Abstract<p>Metastases largely rely on hematogenous dissemination of tumor cells via the vascular system and significantly limit prognosis of patients with solid tumors. To colonize distant sites, circulating tumor cells must destabilize the endothelial barrier and transmigrate across the vessel wall. Here we performed a high-content screen to identify drugs that block tumor cell extravasation by testing 3,520 compounds on a transendothelial invasion coculture assay. Hits were further characterized and validated using a series of <i>in vitro</i> assays, a zebrafish model enabling three-dimensional (3D) visualization of tumor cell extravasation, and mouse models of lung metastasis. The initial screen advanced 38 compounds as potential hits, of which, four compounds enhanced endothelial barrier stability while concurrently suppressing tumor cell motility. Two compounds niclosamide and forskolin significantly reduced tumor cell extravasation in zebrafish, and niclosamide drastically impaired metastasis in mice. Because niclosamide had not previously been linked with effects on barrier function, single-cell RNA sequencing uncovered mechanistic effects of the drug on both tumor and endothelial cells. Importantly, niclosamide affected homotypic and heterotypic signaling critical to intercellular junctions, cell–matrix interactions, and cytoskeletal regulation. Proteomic analysis indicated that niclosamide-treated mice also showed reduced levels of kininogen, the precursor to the permeability mediator bradykinin. Our findings designate niclosamide as an effective drug that restricts tumor cell extravasation through modulation of signaling pathways, chemokines, and tumor–endothelial cell interactions.</p>Significance:<p>A high-content screen identified niclosamide as an effective drug that restricts tumor cell extravasation by enhancing endothelial barrier stability through modulation of molecular signaling, chemokines, and tumor–endothelial cell interactions.</p></div>
Pancreatic ductal adenocarcinoma (PDAC) metastasizes by neural, vascular, and local invasion routes, which limit patient survival. In nerves and vessels, SLIT2 and its ROBO receptors constitute repellent guidance cues that also direct epithelial branching. Thus, the SLIT2-ROBO system may represent a key pinch point to regulate PDAC spread. In this study, we examined the hypothesis that escaping from repellent SLIT2-ROBO signaling is essential to enable PDAC cells to appropriate their local stromal infrastructure for dissemination. Through immunohistochemical analysis, we detected SLIT2 receptors ROBO1 and ROBO4 on epithelia, nerves, and vessels in healthy pancreas and PDAC specimens, respectively. SLIT2 mRNA expression was reduced in PDAC compared with nontransformed pancreatic tissues and cell lines, suggesting a reduction in SLIT2-ROBO pathway activity in PDAC. In support of this interpretation, restoring the SLIT2 expression in SLIT2-deficient PDAC cells inhibited their bidirectional chemoattraction with neural cells, and more specifically, impaired unidirectional PDAC cell navigation along outgrowing neurites in models of neural invasion. Restoring autocrine/paracrine SLIT2 signaling was also sufficient to inhibit the directed motility of PDAC cells, but not their random movement. Conversely, RNA interference-mediated silencing of ROBO1 stimulated the motility of SLIT2-competent PDAC cells. Furthermore, culture supernatants from SLIT2-competent PDAC cells impaired migration of endothelial cells (human umbilical vein endothelial cells), whereas an N-terminal SLIT2 cleavage fragment stimulated such migration. In vivo investigations of pancreatic tumors with restored SLIT2 expression demonstrated reduced invasion, metastasis, and vascularization, with opposing effects produced by ROBO1 silencing in tumor cells or sequestration of endogenous SLIT2. Analysis of clinical specimens of PDAC showed that those with low SLIT2 mRNA expression exhibited a higher incidence and a higher fraction of tumor-infiltrated lymph nodes. Taken together, our findings argue that disrupting SLIT2-ROBO signaling in PDAC may enhance metastasis and predispose PDAC cells to neural invasion.
Einleitung: Slit2 und seine Robo-Rezeptoren sind axon guidance Faktoren mit repulsiver Wirkung auf die Navigation von Nerven und Gefäßen. Aufgrund der neuronalen Differenzierung von NETs könnte somit das Slit2-Robo axon guidance Liganden-Rezeptor System eine entsprechend konservierte Funktion bei der Regulation der Motilität und der Interaktion von Tumorzellen mit Kompartimenten des Tumormikromilieus spielen.
Placental growth factor (PlGF), a VEGF-homolog implicated in tumor angiogenesis and adaptation to antiangiogenic therapy, is emerging as candidate target in malignancies. Here, we addressed the expression, function, and prognostic value of PlGF in neuroendocrine tumors (NETs). PlGF was determined in NET patients' sera collected retrospectively ( n =88) and prospectively ( n =87) using Roche-Elecsys and correlated with clinicopathological data. Tumoral PlGF was evaluated by immunohistochemistry, effects of PlGF on proliferation and migration in vitro were assessed using different NET cell lines and effects on tumor growth in vivo in orthotopic xenografts. Circulating and tumoral PlGF was elevated in patients with pancreatic NETs (pNETs) compared with control sera and respective healthy tissue. De novo PlGF expression occurred primarily in the tumor stroma, suggesting paracrine stimulatory circuits. Indeed, PlGF enhanced NET proliferation and migration in vitro and, conversely, neutralizing antibodies to PlGF reduced tumor growth in vivo . Elevated circulating PlGF levels in NET patients correlated with advanced tumor grading and were associated with reduced tumor-related survival in pNETs. Subsequent determinations confirmed and extended our observation of elevated PlGF levels in a prospective cohort of grade 1 and grade 2 pNETs ( n =30) and intestinal NETs ( n =57). In low-grade pNETs, normal circulating PlGF levels were associated with better survival. In intestinal NETs, circulating PlGF above median emerged as an independent prognostic factor for shorter time-to-progression in multivariate analyses. These data assign to PlGF a novel function in the pathobiology of NETs and propose PlGF as a prognostic parameter and therapeutic target.
