Background

Prostate cancer is a leading cause of cancer death in men due to a subset of cancers that metastasize. The genetic and molecular factors that drive local tumor development and progression to metastatic disease, however, remain incompletely understood. Both genetically engineered mouse (GEM) models and xenograft models of prostate cancer have contributed to our understanding of the genetics of prostate cancer (Ittmann et al., 2013; Park et al., 2010). Genetic manipulation, either by prostate specific transgenic overexpression such as in Hi-Myc mice (Ellwood-Yen et al., 2003) or by prostate specific deletion such as in Pten^-/- mice (Wang et al., 2003), is advantageous because it models tumor development and progression in the organ microenvironment in an immune competent mouse. Development of metastatic prostate cancer is variable among these GEM models, with a low frequency in some such as the Pten^-/- model (Wang et al., 2003), and a higher frequency in other models such as TRAMP (transgenic adenocarcinoma mouse prostate) (Greenberg et al., 1995) and Hi-Myc/Pten^-/- (Hubbard et al., 2016). Despite their great utility for prostate cancer research, it is difficult, time-consuming, and costly to further genetically manipulate GEM models. To overcome some of these limitations, researchers have relied on both subcutaneous and orthotopic xenografts of human cell lines. Cell lines can be genetically manipulated in vitro in a variety of ways. While subcutaneous xenografts are advantageous due to their ease of injection and monitoring, orthotopic xenografts better recapitulate the local tumor microenvironment which may affect sensitivity to drugs (Wilmanns et al., 1992; Kuo et al., 1993), methylation patterns (Fleming et al., 2010), growth rate (Fleming et al., 2010), and ultimately predictions for clinical response (Killion et al., 1998; Hoffman, 1999). In addition, some human prostate cancer cell line models metastasize from xenografts implanted orthotopically. A limitation of all xenograft models is that they require immunocompromised mice making it difficult to model tumor progression in an intact immune system. The Myc-CaP cell line (Watson et al., 2005) allows for engraftment either subcutaneously or orthotopically in immune competent syngeneic (FVB/N) mice (Watson et al., 2005; Hurley et al., 2015). Myc-CaP was derived from a prostate carcinoma from a Hi-Myc mouse (Watson et al., 2005). When engrafted orthotopically, Myc-CaP cells metastasize to abdominal lymph nodes, liver, and lung (Hurley et al., 2015). Additionally, Myc-CaP is amenable to in vitro manipulation of gene expression (Hurley et al., 2015). Thus, Myc-CaP can be used as an easily manipulable model for both tumor growth in the prostate and metastatic growth in mice with an intact immune system. Herein, we describe the methods for orthotopic engraftment of Myc-CaP cells into the mouse anterior prostate.