Reprogrammed Schwann Cells Organize into Dynamic Tracks that Promote Pancreatic Cancer Invasion

Pancreatic Tumor-Derived Extracellular Vesicles Stimulate Schwann Cell Phenotype Indicative of Perineural Invasion via IL-8 Signaling

Pancreatic cancer remains a pre-eminent cause of cancer-related deaths with late-stage diagnoses leading to an 11% five-year survival rate. Moreover, perineural invasion (PNI), in which cancer cells migrate into adjacent nerves, occurs in an overwhelming majority of patients, further enhancing tumor metastasis. PNI has only recently been recognized as a key contributor to cancer progression; thus, there are insufficient treatment options for the disease. Attention has been focused on glial Schwann cells (SC) for their mediation of pancreatic PNI. Under stress, SCs dedifferentiate from their mature state to facilitate the repair of peripheral nerves; however, this signaling can also re-direct cancer cells to accelerate PNI. Limited research has explored the mechanism that causes this shift in SC phenotype in cancer. Tumor-derived extracellular vesicles (TEV) have been implicated in other avenues of cancer development, such as pre-metastatic niche formation in secondary locations, yet how TEVs contribute to PNI has not been fully explored. In this study, we highlight TEVs as initiators of SC activation into a PNI-associated phenotype. Proteomic and pathway assessments of TEVs revealed an elevation in interleukin-8 (IL-8) signaling and nuclear factor kappa B (NFκB) over healthy cell-derived EVs. TEV-treated SCs exhibited higher levels of activation markers, which were successfully neutralized with IL-8 inhibition. Additionally, TEVs increased NFκB subunit p65 nuclear translocation, which may lead to increased secretion of cytokines and proteases indicative of SC activation and PNI. These findings present a novel mechanism that may be targeted for the treatment of pancreatic cancer PNI.

Statement of Significance

Identifying pancreatic tumor extracellular vesicles as key players in Schwann cell activation and perineural invasion by way of IL-8 will educate for more specialized and effective targets for an under-valued disease.

Rapid cancer cell perineural invasion utilizes amoeboid migration

The invasion of nerves by cancer cells, or perineural invasion (PNI), is potentiated by the nerve microenvironment and is associated with adverse clinical outcomes. However, the cancer cell characteristics that enable PNI are poorly defined. Here, we generated cell lines enriched for a rapid neuroinvasive phenotype by serially passaging pancreatic cancer cells in a murine sciatic nerve model of PNI. Cancer cells isolated from the leading edge of nerve invasion showed a progressively increasing nerve invasion velocity with higher passage number. Transcriptome analysis revealed an upregulation of proteins involving the plasma membrane, cell leading edge, and cell movement in the leading neuroinvasive cells. Leading cells progressively became round and blebbed, lost focal adhesions and filipodia, and transitioned from a mesenchymal to amoeboid phenotype. Leading cells acquired an increased ability to migrate through microchannel constrictions and associated more with dorsal root ganglia than nonleading cells. ROCK inhibition reverted leading cells from an amoeboid to mesenchymal phenotype, reduced migration through microchannel constrictions, reduced neurite association, and reduced PNI in a murine sciatic nerve model. Cancer cells with rapid PNI exhibit an amoeboid phenotype, highlighting the plasticity of cancer migration mode in enabling rapid nerve invasion.

Pancreatic Ductal Adenocarcinoma Induces Neural Injury that Promotes a Transcriptomic and Functional Repair Signature by Peripheral Neuroglia

Perineural invasion (PNI) is the phenomenon whereby cancer cells invade the space surrounding nerves. PNI occurs frequently in epithelial malignancies, but is especially characteristic of pancreatic ductal adenocarcinoma (PDAC). The presence of PNI portends an increased incidence of local recurrence, metastasis and poorer overall survival. While interactions between tumor cells and nerves have been investigated, the etiology and initiating cues for PNI development is not well understood. Here, we used digital spatial profiling to reveal changes in the transcriptome and to allow for a functional analysis of neural-supportive cell types present within the tumor-nerve microenvironment of PDAC during PNI. We found that hypertrophic tumor-associated nerves within PDAC express transcriptomic signals of nerve damage including programmed cell death, Schwann cell proliferation signaling pathways, as well as macrophage clearance of apoptotic cell debris by phagocytosis. Moreover, we identified that neural hypertrophic regions have increased local neuroglial cell proliferation which was tracked using EdU tumor labeling in KPC mice. This study reveals a common gene expression pattern that characterizes solid tumor-induced damage to local nerves. These data provide new insights into the pathobiology of the tumor-nerve microenvironment during PDAC as well as other gastrointestinal cancers.

Melanoma-associated repair-like Schwann cells suppress anti-tumor T-cells via 12/15-LOX/COX2-associated eicosanoid production

Peripheral glia, specifically the Schwann cells (SCs), have been implicated in the formation of the tumor microenvironment (TME) and in cancer progression. However, in vivo and ex vivo analyses of how cancers reprogram SC functions in different organs of tumor-bearing mice are lacking. We generated Plp1-CreERT/tdTomato mice which harbor fluorescently labeled myelinated and non-myelin forming SCs. We show that this model enables the isolation of the SCs with high purity from the skin and multiple other organs. We used this model to study phenotypic and functional reprogramming of the SCs in the skin adjacent to melanoma tumors. Transcriptomic analyses of the peritumoral skin SCs versus skin SCs from tumor-free mice revealed that the former existed in a repair-like state typically activated during nerve and tissue injury. Peritumoral skin SCs also downregulated pro-inflammatory genes and pathways related to protective anti-tumor responses. In vivo and ex vivo functional assays confirmed immunosuppressive activities of the peritumoral skin SCs. Specifically, melanoma-reprogrammed SCs upregulated 12/15-lipoxygenase (12/15-LOX) and cyclooxygenase (COX)-2, and increased production of anti-inflammatory polyunsaturated fatty acid (PUFA) metabolites prostaglandin E2 (PGE2) and lipoxins A4/B4. Inhibition of 12/15-LOX or COX2 in SCs, or EP4 receptor on lymphocytes reversed SC-dependent suppression of anti-tumor T-cell activation. Therefore, SCs within the skin adjacent to melanoma tumors demonstrate functional switching to repair-like immunosuppressive cells with dysregulated lipid oxidation. Our study suggests the involvement of the melanoma-associated repair-like peritumoral SCs in the modulation of locoregional and systemic anti-tumor immune responses.

Cancer hallmarks intersect with neuroscience in the tumor microenvironment

The mechanisms underlying the multistep process of tumorigenesis can be distilled into a logical framework involving the acquisition of functional capabilities, the so-called hallmarks of cancer, which are collectively envisaged to be necessary for malignancy. These capabilities, embodied both in transformed cancer cells as well as in the heterotypic accessory cells that together constitute the tumor microenvironment (TME), are conveyed by certain abnormal characteristics of the cancerous phenotype. This perspective discusses the link between the nervous system and the induction of hallmark capabilities, revealing neurons and neuronal projections (axons) as hallmark-inducing constituents of the TME. We also discuss the autocrine and paracrine neuronal regulatory circuits aberrantly activated in cancer cells that may constitute a distinctive "enabling" characteristic contributing to the manifestation of hallmark functions and consequent cancer pathogenesis.

Important Cells and Factors from Tumor Microenvironment Participated in Perineural Invasion

Perineural invasion (PNI) as the fourth way for solid tumors metastasis and invasion has attracted a lot of attention, recent research reported a new point that PNI starts to include axon growth and possible nerve "invasion" to tumors as the component. More and more tumor-nerve crosstalk has been explored to explain the internal mechanism for tumor microenvironment (TME) of some types of tumors tends to observe nerve infiltration. As is well known, the interaction of tumor cells, peripheral blood vessels, extracellular matrix, other non-malignant cells, and signal molecules in TME plays a key role in the occurrence, development, and metastasis of cancer, as to the occurrence and development of PNI. We aim to summarize the current theories on the molecular mediators and pathogenesis of PNI, add the latest scientific research progress, and explore the use of single-cell spatial transcriptomics in this invasion way. A better understanding of PNI may help to understand tumor metastasis and recurrence and will be beneficial for improving staging strategies, new treatment methods, and even paradigm shifts in our treatment of patients.

Neuroepithelial Interactions in Cancer

Nerves not only regulate the homeostasis and energetic metabolism of normal epithelial cells but also are critical for cancer, as cancer recapitulates the biology of neural regulation of epithelial tissues. Cancer cells rarely develop in denervated organs, and denervation affects tumorigenesis, in vivo and in humans. Axonogenesis occurs to supply the new malignant epithelial growth with nerves. Neurogenesis happens later, first in ganglia around organs or the spinal column and subsequently through recruitment of neuroblasts from the central nervous system. The hallmark of this stage is regulation of homeostasis and energetic metabolism. Perineural invasion is the most efficient interaction between cancer cells and nerves. The hallmark of this stage is increased proliferation and decreased apoptosis. Finally, carcinoma cells transdifferentiate into a neuronal profile in search of neural independence. The latter is the last stage in neuroepithelial interactions. Treatments for cancer must address the biology of neural regulation of cancer.

Schwann cell functions in peripheral nerve development and repair

The glial cell of the peripheral nervous system (PNS), the Schwann cell (SC), counts among the most multifaceted cells of the body. During development, SCs secure neuronal survival and participate in axonal path finding. Simultaneously, they orchestrate the architectural set up of the developing nerves, including the blood vessels and the endo-, peri- and epineurial layers. Perinatally, in rodents, SCs radially sort and subsequently myelinate individual axons larger than 1 μm in diameter, while small calibre axons become organised in non-myelinating Remak bundles. SCs have a vital role in maintaining axonal health throughout life and several specialized SC types perform essential functions at specific locations, such as terminal SC at the neuromuscular junction (NMJ) or SC within cutaneous sensory end organs. In addition, neural crest derived satellite glia maintain a tight communication with the soma of sensory, sympathetic, and parasympathetic neurons and neural crest derivatives are furthermore an indispensable part of the enteric nervous system. The remarkable plasticity of SCs becomes evident in the context of a nerve injury, where SC transdifferentiate into intriguing repair cells, which orchestrate a regenerative response that promotes nerve repair. Indeed, the multiple adaptations of SCs are captivating, but remain often ill-resolved on the molecular level. Here, we summarize and discuss the knowns and unknowns of the vast array of functions that this single cell type can cover in peripheral nervous system development, maintenance, and repair.