The Colon-26 Carcinoma Tumor-bearing Mouse as a Model for the Study of Cancer Cachexia

Summary

Mice bearing the Colon-26 (C26) carcinoma represent a classical model of cancer cachexia. Progressive muscle wasting occurs in association with tumor growth, over-expression of muscle-specific ubiquitin ligases, and reductions in muscle cross-sectional area. Fat loss is also observed. Cachexia is studied in a time-dependent manner with increasing severity of wasting.

Abstract

Cancer cachexia is the progressive loss of skeletal muscle mass and adipose tissue, negative nitrogen balance, anorexia, fatigue, inflammation, and activation of lipolysis and proteolysis systems. Cancer patients with cachexia benefit less from anti-neoplastic therapies and show increased mortality¹. Several animal models have been established in order to investigate the molecular causes responsible for body and muscle wasting as a result of tumor growth. Here, we describe methodologies pertaining to a well-characterized model of cancer cachexia: mice bearing the C26 carcinoma^2-4. Although this model is heavily used in cachexia research, different approaches make reproducibility a potential issue. The growth of the C26 tumor causes a marked and progressive loss of body and skeletal muscle mass, accompanied by reduced muscle cross-sectional area and muscle strength^3-5. Adipose tissue is also lost. Wasting is coincident with elevated circulating levels of pro-inflammatory cytokines, particularly Interleukin-6 (IL-6)³, which is directly, although not entirely, responsible for C26 cachexia. It is well-accepted that a primary mechanism by which the C26 tumor induces muscle tissue depletion is the activation of skeletal muscle proteolytic systems. Thus, expression of muscle-specific ubiquitin ligases, such as atrogin-1/MAFbx and MuRF-1, represent an accepted method for the evaluation of the ongoing muscle catabolism². Here, we present how to execute this model in a reproducible manner and how to excise several tissues and organs (the liver, spleen, and heart), as well as fat and skeletal muscles (the gastrocnemius, tibialis anterior, and quadriceps). We also provide useful protocols that describe how to perform muscle freezing, sectioning, and fiber size quantification.

Introduction

Muscle wasting is a serious complication of various clinical conditions such as cancer, sepsis, liver, cirrhosis, heart and kidney failure, chronic obstructive pulmonary disease, and AIDS. In particular, muscle wasting is evident in at least 50% of patients with cancer¹. Loss of skeletal muscle in cancer results from increased protein degradation due to the over-activation of the skeletal muscle proteolytic systems and/or from decreased protein synthesis⁶. Lipolysis is also evident, leading to the depletion of adipose tissue. Clinically, cachexia is associated with reduced quality and length of life and is estimated to be the cause of death in 20 – 30% of cancer patients⁷. Use of experimental models that resemble the human disease as closely as possible would be beneficial. An optimal animal model is characterized by high reproducibility, as well as by limited interference from different therapies and the unpredictable factors of diet, sex, and genetic background that are usually associated with the clinical condition⁸. So far, cancer cachexia has been studied mainly in animal models characterized by transplantation of cancer cells or injection of carcinogens, although a new method is to use genetically modified mice susceptible to the development of cancer.

Mice bearing the C26 carcinoma (also referred to as colon-26 and adenocarcinoma) represent a well-characterized and extensively used model of cancer cachexia^2,5. The growth of the C26 tumor results in body and muscle weight loss, mainly through enhanced fat and protein catabolism⁹. Generally, a 10% tumor weight versus total body weight is associated with a reduction of 20-25% in skeletal muscle weight and a greater depletion of fat^3,10. Hepatomegaly and splenomegaly are also observed with tumor growth, along with the activation of the acute phase response and the elevation of pro-inflammatory cytokine levels^3,11. Among these, it is well known that IL-6 plays a pivotal role in mediating muscle wasting in the C26 model, even though this cytokine is probably not the only inducer of cachexia¹². Elevated IL-6 causes muscle atrophy through activation of the JAK/STAT3 pathway, and inhibiting this transcription factor can prevent muscle wasting^3,4.

During C26-induced muscle wasting, as in many conditions of muscle atrophy, muscle mass is lost largely through reductions in muscle protein content across muscle fibers, not through cell death or loss of fibers¹³. In C26 cachexia, a shift towards smaller cross-sectional areas is observed in both glycolytic and oxidative fibers². This is also consistent with reduced muscle strength⁵. Many groups worldwide have taken advantage of the C26 model in order to discover new mediators of muscle wasting or clinically relevant drugs for cancer cachexia. However, many different procedures for the use of this model have been reported, raising concerns about the consistency of the obtained data and posing barriers to reproducibility in different experimental conditions. Here we report a typical use of this model for the study of cancer cachexia that yields standardized and reproducible data.

Protocol

Ethics Statement: All studies described were approved by the Institutional Animal Care and Use Committees of the Thomas Jefferson University and Indiana University School of Medicine. 1. C26 Cell Growth and Preparation Obtain C26 colorectal cancer cells (Ohio State University Medical Center (OSUMC)) and prepare complete growth medium (i.e., high-glucose Dulbecco's Modified Eagle's Medium (DMEM) containing 10% Fetal Bovine Serum (FBS), 1 mM sodium pyruvate, 1% gluta…

Representative Results

C26 tumor growth kinetics show a lag phase for the first 7 – 8 d after injection, followed by exponential cell growth (4 – 5 d). The tumor mass eventually reaches ~10% of the body weight (about 2 g; Figure 1A-B). During the first phase, the tumor can be located by palpation only and appears as a small protrusion of the skin. In the second phase, the tumor is observed as a mass under the skin. Rarely, the tumor becomes ulcerated, resulting in an open wound…

Discussion

Especially in its latest stages, colorectal cancer is associated with the development of cachexia, which is responsible for poorer outcomes and reductions in patient quality of life. Many studies have focused on the treatment of conditions secondary to cancer; however, despite many efforts in this direction, there is still no approved therapy for cancer cachexia²¹. Thus, it is imperative that animal models resemble the human pathology as closely as possible in order to maximize the translation of findings.

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Materials

Cell culture Flasks	Falcon – Becton Dickinson	35-5001
DMEM	Cellgro	10-017-CV
FBS	Gibco	26140
Streptomycin-Penicillin	Cellgro	30-002-CI
CD2F1 mice	Harlan	060
Anesthesia apparatus	EZ-Anesthesia	EZ-7000
2-Methyl Butane	Sigma-Aldrich	M32631
OCT	Tissue-Tek	4583
Cryostat	Leica	CM1850
Cork disks	Electron Microscopy Sciences	63305
Superfrost plus glass slides	VWR	48311-703
Anti-Laminin Rabbit polyclonal antibody	Sigma-Aldrich	L9393
Anti-Dystrophin Mouse Monoclonal antibody	Vector Laboratories	VP-D508
Alexa Flour 594 anti-mouse IgG	Life Technologies	A11062
Alexa Flour 594 anti-rabbit IgG	Life Technologies	A21211
Hematoxylin	Sigma-Aldrich	GHS216
Eosin	Sigma-Aldrich	HT110332
Xylene	Acros Organics	422680025
Cytoseal-XYL	Thermo	8312-4
Microscope	Zeiss	Observer.Z1
Bamboo Tablet	Wacom	CTH-661
Prism 7.0 for Mac OS X	GraphPad Software, Inc.
Excel for Mac 2011	Microsoft Corp.
Image J	US National Institutes of Health	IJ1.46	http://rsbweb.nih.gov/ij/download.html
Microtainer	BD	365873