Basic and Translational Science Potential Establishment of Lung Metastatic Xenograft Model of Androgen Receptor-positive and Androgen- independent Prostate Cancer (C4-2B) Fukashi Yamamichi, Takayuki Matsuoka, Katsumi Shigemura, Masato Kawabata, Toshiro Shirakawa, and Masato Fujisawa OBJECTIVE To establish a mouse xenograft model of metastatic prostate cancer (PCa) and investigate the relationship between metastasis and circulating tumor cells. METHODS Flow cytometry (FACS) was used to detect suitable PCa cells and markers for detecting circulating tumor cells in vivo. We orthotopically injected androgen receptor-positive and androgen-independent C4-2B PCa cells into 12 severe combined immunodeficiency (SCID) mouse prostates, including 1 vehicle control. We measured the serum prostate-specific antigen levels biweekly after tumor inoculation. Circulating tumor cells (CTCs) were measured quali- tatively by fluorescent microscopy immediately after the mice were sacrificed. The mouse prostates and lungs were examined for tumor formation using immunohistochemistry because we found no apparent metastasis, except in the lung. RESULTS FACS analyses in vitro identified the marker, prostate-specific membrane antigen, and C4-2B cells to be appropriate for additional in vivo study. We confirmed that the serum prostate-specific antigen increase was dependent on time and prostate tumor weight in mice. Of the 11 mice, 6 could be used as the mouse PCa xenograft model. Fluorescent microscopy detected CTCs in the peripheral blood in 5 of the 6 mice constituting the PCa model. Human prostate-specific antigen expression was detected by immunohistochemistry in the prostates of all the mice and in the lung of 2 of the 6 mice, suggesting 2 mice with lung metastasis. CONCLUSION We have shown the potential establishment of a mouse lung metastatic xenograft model of androgen receptor-positive and androgen-independent C4-2B PCa tumor. However, the present model requires improvement to be a more reproducible, accurate and complete experimental model. Additional study is necessary to verify the relationship between metastasis and CTCs. UROLOGY 80: 951.e1–951.e7, 2012. © 2012 Elsevier Inc. T umor metastasis, including that with prostate cancer (PCa), is a multistep process. Dissemina- tion from the primary tumor into the blood cir- culation is one of the essential steps in the spread of the disease. Several xenograft models of distant metastasis have been proposed, 1,2 with distant metastases predomi- nantly observed in the orthotopic xenograft inoculation model. 3 Xenograft metastasis models recapitulating the clinical features of human PCa are critically lacking. The establishment of a novel in vivo metastasis model is vital for research into the mechanisms of metastasis and could have clinical implications for the early detection of PCa metastasis. Circulating tumor cells (CTCs) are an extremely rare population disseminated from a primary solid carcinoma into the circulation. Quantitative reverse transcriptase polymerase chain reaction was more effective than con- ventional reverse transcriptase polymerase chain reaction in a breast cancer CTC study. 4 However, the purpose of this study was to investigate qualitative CTCs using fluorescent microscopy which had a character of the small number of CTCs lost with high sensitivity and specificity without an enrichment procedure. 5,6 The development of an animal model for testing will help develop techniques for the detection, diagnosis, and Financial Disclosure: The authors declare that they have no relevant financial interests. From the Department of Urology, Hyogo Prefectural Tsukaguchi Hospital, Amaga- saki, Japan; Department of Urology, Kobe University Graduate School of Medicine, Kobe, Japan; Division of Infectious Disease Control, Infectious Disease Center, Kobe University Graduate School of Medicine, Kobe, Japan; and Division of Infectious Disease, Department of International Health, Kobe University Graduate School of Health Science, Kobe, Japan Reprint requests: Katsumi Shigemura, M.D., Ph.D., Division of Urology, Depart- ment of Surgery, Kobe University Graduate School of Medicine, 7-5-1, Kusunoki-cho, Chuo-ku, Kobe, Japan. E-mail: yutoshunta@hotmail.co.jp Submitted: August 23, 2011, accepted (with revisions): June 12, 2012 © 2012 Elsevier Inc. 0090-4295/12/$36.00 951.e1 All Rights Reserved http://dx.doi.org/10.1016/j.urology.2012.06.023