In Vitro Modeling of Cancerous Neural Invasion: The Dorsal Root Ganglion Model

Development of an in vivo murine model of perineural invasion and spread of cutaneous squamous cell carcinoma of the head and neck

Introduction

Cutaneous squamous cell carcinoma of the head and neck (cSCCHN) can metastasize by invading nerves and spread toward the central nervous system. This metastatic process is called perineural invasion (PNI) and spread (PNS). An in vivo sciatic nerve mouse model is used for cSCCHN PNI/PNS. Here we describe a complementary whisker pad model which allows for molecular studies investigating drivers of PNI/PNS in the head and neck environment.

Methods

A431 cells were injected into the whisker pads of BALB/c Foxn1nu and NSG-A2 mice. Tumor progression was monitored by bioluminescence imaging and primary tumor resection was performed. PNI was detected by H&E and IHC. Tumor growth and PNI were assessed with inducible ablation of LOXL2.

Results

The rate of PNI development in mice was 10%-28.6%. Tumors exhibited PNI/PNS reminiscent of the morphology seen in the human disease. Our model's utility was demonstrated with inducible ablation of LOXL2 reducing primary tumor growth and PNI.

Discussion

This model consists in a feasible way to test molecular characteristics and potential therapies, offers to close a gap in the described in vivo methods for PNI/PNS of cSCCHN and has uses in concert with the established sciatic nerve model.

Tumour microenvironment 3D-modelling: simplicity to complexity and back again

Tumours are surrounded by a host of noncancerous cells that fulfil both supportive and suppressive roles within the tumour microenvironment (TME). The drive to understand the biology behind each of these components has led to a rapid expansion in the number and use of 3D in vitro models, as researchers find ways to incorporate multiple cell types into physiomimetic configurations. The use and increasing complexity of these models does however demand many considerations. In this review we discuss approaches adopted to recapitulate complex tumour biology in tractable 3D models. We consider how these cell types can be sourced and combined and examine methods for the deconvolution of complex multicellular models into manageable and informative outputs.

Nerve input to tumours: Pathophysiological consequences of a dynamic relationship

It is well known that tumours arising in different organs are innervated and that 'perineural invasion' (cancer cells escaping from the tumour by following the nerve trunk) is a negative prognostic factor. More surprisingly, increasing evidence suggests that the nerves can provide active inputs to tumours and there is two-way communication between nerves and cancer cells within the tumour microenvironment. Cells of the immune system also interact with the nerves and cancer cells. Thus, the nerve connections can exert significant control over cancer progression and modulating these (physically or chemically) can affect significantly the cancer process. Nerve inputs to tumours are derived mainly from the sympathetic (adrenergic) and the parasympathetic (cholinergic) systems, which are interactive. An important component of the latter is the vagus nerve, the largest of the cranial nerves. Here, we present a two-part review of the nerve inputs to tumours and their effects on tumorigenesis. First, we review briefly some relevant general issues including ultrastructural aspects, stemness, interactions between neurones and primary tumours, and communication between neurones and metastasizing tumour cells. Ultrastructural characteristics include synaptic vesicles, tumour microtubes and gap junctions enabling formation of cellular networks. Second, we evaluate the pathophysiology of the nerve input to five major carcinomas: cancers of prostate, stomach, colon, lung and pancreas. For each cancer, we present (i) the nerve inputs normally present in the cancer organ and (ii) how these interact and influence the cancer process. The best clinical evidence for the role of nerves in promoting tumorigenesis comes from prostate cancer patients where metastatic progression has been shown to be suppressed significantly in cases of spinal cord injury. The balance of the sympathetic and parasympathetic contributions to early versus late tumorigenesis varies amongst the different cancers. Different branches of the vagus provide functional inputs to several of the carcinomas and, in two-way interaction with the sympathetic nervous system, affect different stages of the cancer process. Overall, the impact of the vagus nerve can be 'direct' or 'indirect'. Directly, the effect of the vagus is primarily to promote tumorigenesis and this is mediated through cholinergic receptor mechanisms. Indirectly, pro- and anti-tumour effects can occur by stimulation or inhibition of the sympathetic nervous system, respectively. Less well understood are the 'indirect' anti-tumour effect of the vagus nerve via immunomodulation/inflammation, and the role of sensory innervation. A frequent occurrence in the nerve-tumour interactions is the presence of positive feedback driven by agents like nerve growth factor. We conclude that the nerve inputs to tumours can actively and dynamically impact upon cancer progression and are open to clinical exploitation.

M3 muscarinic acetylcholine receptors regulate epithelial-mesenchymal transition, perineural invasion, and migration/metastasis in cholangiocarcinoma through the AKT pathway

Background

Cholangiocarcinoma is a highly malignant tumor type that is not sensitive to radiotherapy or chemotherapy due to aggressive perineural invasion and metastasis. Unfortunately, the mechanisms underlying these processes and the signaling factors involved are largely unknown. In this study, we analyzed the role of M3 muscarinic acetylcholine receptors (M3-mAChR) in cell migration, perineural invasion, and metastasis during cholangiocarcinoma.

Methods

We assessed 60 human cholangiocarcinoma tissue samples and 30 normal biliary tissues. Immunohistochemical staining was used to detect M3-mAChR expression and the relationship between expression and clinical prognosis was evaluated. The biological functions of M3-mAChR in cholangiocarcinoma cell migration, perineural invasion, and epithelial–mesenchymal transition (EMT) were investigated using the human cholangiocarcinoma cell lines FRH0201 and RBE in conjunction with various techniques, including agonist/antagonist treatment, RNA interference, M3-mAChR overexpression, dorsal root ganglion co-culturing, immunohistochemistry, western blotting, etc.

Results

M3-mAChR were highly expressed in cholangiocarcinoma tissue and expression was closely related to differentiation and lymphatic metastasis, affecting patient survival. Treatment with the M3-mAChR agonist pilocarpine and M3-mAChR overexpression significantly promoted migration and perineural invasion, while the M3-mAChR antagonist atropine blocked these effects. Similarly, M3-mAChR knock-down also weakened cell migration and perineural invasion. The expression of phosphatase and tensin homolog, AKT, E-cadherin, vimentin, and Snail, which are components of the phosphatidylinositol 3-kinase/AKT signaling pathway and EMT, were altered by pilocarpine, and these effects were again blocked by atropine. Notably, AKT knock-down decreased M3-mAChR expression and reversed the downstream effects of this receptor.

Conclusions

M3-mAChR are involved in tumor cell migration, perineural invasion, and EMT during cholangiocarcinoma, and these effects are modulated via the AKT signaling pathway.

A Model for Perineural Invasion in Head and Neck Squamous Cell Carcinoma

Perineural invasion (PNI) is found in approximately 40% of head and neck squamous cell carcinomas (HNSCC). Despite multimodal treatment with surgery, radiation, and chemotherapy, locoregional recurrences and distant metastases occur at higher rates, and overall survival is decreased by 40% compared to HNSCC without PNI. In vitro studies of the pathways involved in HNSCC PNI have historically been challenging given the lack of a consistent, reproducible assay. Described here is the adaptation of the dorsal root ganglion (DRG) assay for the examination of PNI in HNSCC. In this model, DRG are harvested from the spinal column of a sacrificed nude mouse and placed within a semisolid matrix. Over the subsequent days, neurites are generated and grow in a radial pattern from the cell bodies of the DRG. HNSCC cell lines are then placed peripherally around the matrix and invade preferentially along the neurites toward the DRG. This method allows for rapid evaluation of multiple treatment conditions, with very high assay success rates and reproducibility.