Handling of the Cotton Rat in Studies for the Pre-clinical Evaluation of Oncolytic Viruses

Summary

Cotton rats are extremely excitable and have a strong flight-or-fight response. A handling method optimized to reduce the stress of the animals is described which will make cotton rats more accessible as a preclinical model.

Abstract

Oncolytic viruses are a novel anticancer therapy with the ability to target tumor cells, while leaving healthy cells intact. For this strategy to be successful, recent studies have shown that involvement of the host immune system is essential. Therefore, oncolytic virotherapy should be evaluated within the context of an immunocompetent model. Furthermore, the study of antitumor therapies in tolerized animal models may better recapitulate results seen in clinical trials. Cotton rats, commonly used to study respiratory viruses, are an attractive model to study oncolytic virotherapy as syngeneic models of mammary carcinoma and osteosarcoma are well established. However, there is a lack of published information on the proper handling procedure for these highly excitable rodents. The handling and capture approach outlined minimizes animal stress to facilitate experimentation. This technique hinges upon the ability of the researcher to keep calm during handling and perform procedures in a timely fashion. Finally, we describe how to prepare cotton rat mammary tumor cells for consistent subcutaneous tumor formation, and how to perform intratumoral and intraperitoneal injections. These methods can be applied to a wide range of studies furthering the development of the cotton rat as a relevant pre-clinical model to study antitumor therapy.

Introduction

Oncolytic viruses (OV) selectively replicate in tumor cells by exploiting biochemical differences between normal and tumor cells ^1,2. There are two types of OVs: those that do not require a mutation to achieve selective oncolysis, referred to as naturally occurring wild-type viruses and those which must be engineered to achieve selective oncolysis. The collection of mutations within a given tumor type determines the nature of the selective growth advantage over normal cells for an OV ². The safety and benefit of using OVs has been demonstrated in clinical trials ^3-7. Despite advancements in the field of oncolytic virotherapy there exis....

Protocol

NOTE: The protocols used have been approved by our institutional Animal Research Ethics Board at McMaster University according to Canadian Council on Animal Care guidelines. Experiments were performed at the McMaster University Central Animal Facility.

1. Culturing LCRT Cells

1. Culture LCRT cells in Dulbecco’s modified Eagle’s medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 2 mM L-glutamine, 100 U/ml penicillin and 100 µg/ml streptomycin. Maintain cells in T-150 tissue culture flasks at 37 °C and 5% CO₂. Passage cells when they form a 90% confluent monolayer (every 2-3 days, <....

Results

Due to the extremely excitable nature of cotton rats, being familiar with and utilizing procedures optimized to reduce the stress of the animals will ease in their use as a pre-clinical animal model. Use of proper handling techniques will also minimize risk to the researcher.

When using cotton rats it is imperative to stay calm. The rats are highly excitable and will attempt to escape their cage. Use of an enrichment tube and nestlets will minimize escape attempts. Figure 2 sh.......

Discussion

Cotton rats are highly excitable and have a strong flight response. Therefore, special care should be taken to minimize any undue stress on the animal. The cage setup described will allow for safe and easy capture of the animals, with the placement of the enrichment tube being of the utmost importance. When setting up cages, ensure that the enrichment tubes meet the size and shape requirements, and are placed in proper orientation in the cage. It is also important to ensure that any technicians who might be aiding in ani.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Dulbecco’s modified Eagle’s medium	Gibco	11965-092	May use any brand
1X Phosphate Buffered Saline			Can prepare in lab, filter to sterilize
200 mM L-glutamine	Gibco	25030164	May use any brand
100x Antibiotic-Antimycotic	Gibco	15240-062	May use any brand
Fetal bovine serum	Quality Biological Inc.	110-001-101HI	May use any brand
T-150cm2 tissue culture flask	Fisher Scientific	14-826-80	May use any brand
1X TypLE Express	Life Technologies	12604-013
12-well cell culture plate, flat bottom	Fisher Scientific	08-772-29	May use any brand, must be tissue culture treated
alamarBlue	Life Technologies	DAL1025	May use an alternative reagent for determination of cell viability
8640 Teklad 22/5 Rodent diet	Harlan	8640
1/8” corncob rodent bedding	Harlan	7092
Nestlets	Ancare	-	Made of pulped virgin cotton fiber, dust-free and autoclavable
50 mL Conical tubes	Fisher Scientific	14-432-22	May use any brand, must be sterile
Isoflurane USP, 99.9 %, inhalation anesthetic	Pharmaceutical Partners of Canada Inc.	M60302
70% Ethanol			Can prepare in lab
10 % Neutral Buffered Formalin	Sigma-Aldrich	HT501128	May use any brand
NAPCO NapFlow 1200 Class II A/B3 Biosafety Microbiological Safety Cabinet (cell culture hood)	NAPCO	Model used not currently available	May use any brand
Thermo Fisher Scientific Precision Heated Water Bath	Fisher Scientific	Model used not currently available	May use any brand
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Reichert Bright-line Hemacytometer	Sigma-Aldrich	Z359629	May use any brand
Typhoon Trio BioAnalyzer	GE Healthcare Life Sciences	Model used not currently available	May use any fluorescence plate reader
Tecan Safire2 Multi-detection Microplate Reader	Tecan	Model used not currently available	May use any fluorescence plate reader
Allegra 6R benchtop centrifuge	Beckman Coulter	366816	May use any brand
Table Top Anaesthesia machine	VetEquip	Model used not currently available	May use any brand, must be portable
Wahl Peanut Mini Clippers	Wahl		May use any brand of small clippers
Insulin syringes 29 G x 1/2', 0.3 mL	BD	329464	May use any brand. Insulin syringes are recommended as they make injections easier through the rat’s tough skin.
Cotton swabs	MedPro	018-425	May use any brand
Sharp-Pointed Dissecting Scissors	Fisher Scientific	8940	May use any brand
Dissecting Tissue Forceps	Fisher Scientific	13-812-41	May use any brand