**1. Introduction**

Cancer research requires a significant amount of in vitro and in vivo preclinical studies. In vitro cancer cell line cultures are routinely used as the first step for evaluating potential efficacy for cancer drugs and therefore determine the "stop/go" decision for drug development,

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

followed by animal and finally human trials [1]. However, only about 5% of anticancer drugs finally get approved for clinical use due to lack of clinical efficacy or intolerable toxicity [1, 2].

**2. Model review**

mation environment [7].

inflammation and wound-healing" [6].

1953: The air pouch model was described by Selye for the study of the mechanism of action of hydrocortisone. Selye termed his model the granuloma pouch model and described it as a "procedure designed to permit the objective, quantitative analysis of factors regulating

Air Pouch Model: An Alternative Method for Cancer Drug Discovery

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1954: Kleinfeld and Habif evaluated the anti-inflammatory effect of trypsin and chymotrypsin inside a granuloma pouch. According to the authors, this method provides a standardized and reproducible inflammatory lesion. They evaluated the volume of the exudate and the weight of the pouches. The authors concluded that parenteral administration of trypsin and chymotrypsin does not affect the formation of granulation tissue in a chronic sterile inflam-

1956: Hewitt observed that the number of viable cancer cells needed to induce tumors in half of an experimental group of adult mice was 1641 and in newborn mice was 10. He hypothesized that tumorigenesis could be affected by the dispersion of cancer cells and by the vascularity of the injection site. To test this hypothesis, he injected tumor cells into subcutaneous tissue and into an air pouch, and to evaluate the vascularity effect, he induced hyperemia in air pouches with a formic acid solution. Hewitt concluded that neither cancer cell dispersion nor vascularity affected the capacity of cancer cells to induce a tumor. He also suggested the

1957: Selye wrote another article this time addressing the question: is inflammation good or bad for cancer development? He induced two air pouches on the back of the same animal, administered croton oil into one of the pouches to establish an inflammatory environment, inoculated cancer cells into both pouches, and evaluated which tumor developed faster. The

1957: A scientific report stated that the air pouch model presented several advantages over other methods for the study of inflammation. According to Robert and Nezamis, the granuloma pouch technique is simple and yields uniform results, and it is quantifiable because the degree of inflammation is reported in grams of the tissue, thickness of the pouch membrane, or volume of exudate. There is no systemic response, and furthermore they recommend this technique as a screening test for unknown compounds because minimal amounts of sub-

1957: Based on the observation that two concomitant tumors in the same animal inhibited or promoted their development, Hans Richer inoculated nonviable sarcoma cells and viable Walker tumor cells into a mouse air pouch, to determine if the growth inhibition between tumors was due to nutrient competition. The air pouch model was used in this study because, according to the author, it is an ideal method to test a localized effect. He concluded that nonviable sarcoma cells delayed tumor growth when injected previously or concomitantly

use of the air pouch technique for further tumor transplantation studies [8].

results showed that inflammation can promote tumor development [9].

stance can be tested with high sensitivity in a short period of time [10].

with the viable Walker tumor [11].

In vitro approach contribution for biotechnological development is undeniable; however, cell lines are maintained in nonphysiological conditions that do not resemble body temperature, electrolyte concentration, extracellular matrix contact, cell density, and heterogeneity. Culture conditions also implicate sudden changes such as media exchange and nutrient depletion. Furthermore, rapid cell growth is desirable and induced, driving cell subpopulations not to differentiate. All of these factors alter cell signaling and favor specific subpopulations of cells that adapt to these artificial conditions and loose some of their original characteristics [3].

To optimize cancer drug screening, it is necessary to include the biological and genetic components that influence cancer treatment outcome. Therefore, to study the cancer cell in vivo, it is essential to understand how to prevent the establishment, growth, progression, and metastasis of cancers and how to modulate the tumor microenvironment (TME) for therapeutic gain [4].

Mouse models have been used to assess toxicology and efficacy of anticancer drugs, as well as for the study of tumor induction (establishment), progression, and metastasis; these traditional mouse models have been successfully used to identify cytotoxic drugs that are still the main anticancer treatment in therapy today [4, 5].

In this chapter, we discuss about the benefits of a tumor model in which tumors can grow inside an air pouch created in the dorsal part of the mouse (**Figure 1**). The air pouch cancer model serves as the local microenvironment, which can be modulated to study establishment, progression, and metastasis as well as the efficacy of therapeutic agents.

**Figure 1.** Mouse air pouch model for the study of cancer scheme. The general methodology to induce the air pouch model for the study of cancer and its advantages is depicted. Briefly, 5 milliliters of sterile air is injected into the shaved back of a mouse; after 3 days the pouch is reinflated with 5 milliliters of sterile air. After 3 days tumor cells are inoculated and allowed to grow prior to drug administration.
