An In Vivo Murine Sciatic Nerve Model of Perineural Invasion

Summary

We describe an in vivo murine model of perineural invasion by injecting syngeneic pancreatic cancer cells into the sciatic nerve. The model allows for quantification of the extent of nerve invasion, and supports investigation of the cellular and molecular mechanisms of perineural invasion.

Abstract

Cancer cells invade nerves through a process termed perineural invasion (PNI), in which cancer cells proliferate and migrate in the nerve microenvironment. This type of invasion is exhibited by a variety of cancer types, and very frequently is found in pancreatic cancer. The microscopic size of nerve fibers within mouse pancreas renders the study of PNI difficult in orthotopic murine models. Here, we describe a heterotopic in vivo model of PNI, where we inject syngeneic pancreatic cancer cell line Panc02-H7 into the murine sciatic nerve. In this model, sciatic nerves of anesthetized mice are exposed and injected with cancer cells. The cancer cells invade in the nerves proximally toward the spinal cord from the point of injection. The invaded sciatic nerves are then extracted and processed with OCT for frozen sectioning. H&E and immunofluorescence staining of these sections allow quantification of both the degree of invasion and changes in protein expression. This model can be applied to a variety of studies on PNI given its versatility. Using mice with different genetic modifications and/or different types of cancer cells allows for investigation of the cellular and molecular mechanisms of PNI and for different cancer types. Furthermore, the effects of therapeutic agents on nerve invasion can be studied by applying treatment to these mice.

Introduction

Nerves form a specific tumor microenvironment that stimulates cancer growth and migration^1,2,3. Perineural invasion (PNI) is the process through which cancer cells invade in and around the nerves. It may be considered as a unique route of metastasis since cancer invasion extends away from the sites of origin along nerves. PNI is found in several cancer types including pancreatic, prostate, head & neck, salivary, cervical, and colorectal cancers with an incidence ranging from 22% to 100%^1,2. PNI is associated with ....

Protocol

All of the procedures with animal subjects were approved by the Institutional Animal Care and Use Committee at Memorial Sloan Kettering Cancer Center.

1. Preparation of the Cancer Cells

1. Harvest sub-confluent Panc02-H7 cells with 0.25% trypsin for 5 min at 37 °C. Collect the cells in a 15 mL centrifuge tube.
   NOTE: The cells are grown in T-225 flask, which contains about 12 x 10⁶ cells per flask at 80% confluency and 4 mL trypsin/ flask is used.
2. Centrifuge the cells at x 900 g at 4°C for 5 min. Wash the cells by resuspending the cell pellet in 1 mL of PBS (by pipetting up and down twice), and ....

Results

This method describes the surgical implantation of pancreatic cancer cells into the murine sciatic nerve to create an in vivo model of quantifiable nerve invasion. Figure 1 illustrates the anatomical location of the sciatic nerve and the site of injection. Figure 2 shows the two sciatic nerves of a nude mouse. A PBS injected nerve (left) may be compared to a nerve injected with MiaPaCa-2 cancer cells (right). The nerve i.......

Discussion

In this protocol we describe an in vivo murine model of perineural invasion that allows for the quantification of sciatic nerve invasion by pancreatic cancer cells. This model enables the study of molecular mechanisms of nerve invasion. Successful experiments using this technique require a careful approach to three critical steps in the process: 1) the injection of cancer cells (steps 2.7, 2.8), 2) the extraction of invaded nerves (step 3.4), and 3) processing of harvested nerves (step 4.1).

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Mouse			Number and age variable depending on experimental needs
Cell culture media (PBS, Trypsin, and DMEM+10% FBS)	Any		Steps 1.1, 1.2, 1.3.
Conical centrifuge tube, 50 mL	Falcon	352098	Step 1.1
Microcentrifuge tube 1.5 mL	Axygen	MCT-150-C-S	Step 1.2
Electric razor	WAHL	9962	Step 2.1. Can be substituted with commercial hair removal agent
Isoflurane, 250 mL	Baxter	1001936060	Step 2.2
Hypoallergenic surgical tape	3M Blenderm	70200419342	Step 2.3
Betadine Swapsticks	PDI	SKU 41350	Step 2.4
Webcol Alcohol Preps	Covidien	5110	Step 2.4
Sterile surgical tools (scissors and forceps)			Steps 2.4, 2.5, 3.3, 3.4, 3.5
10 μL Hamilton syringe	Hamilton	80308	Steps 2.7, 2.8
Steel Micro spatula	Fisher Scientific	S50823	Step 2.7
Dissecting microscope			Step 2.7
Bupivacine, 1 g	Enzo Life Sciences	BML-NA139-0001	Step 2.9. Reconstitute to 0.5%
5-0 Nylon suture	Ethicon	698H	Step 2.9
Tissue-Tek O.C.T. Compound	VWR	25608-930	Step 4.1
Tissue-Tek Cryomold Molds	VWR	25608-916	Step 4.1