[Biological behavior of prostate cancer cells in 3D culture systems]

Prostate cancer is the most common non-cutaneous malignant neoplasm in men in Western countries. In Japan, the number of afflicted men has been increasing although it is still low compared with Western countries. One of the most important problems in prostate cancer patients is treatment for hormone-refractory prostate cancer (HRPC). Although docetaxel is considered as a first-line chemotherapeutic option in patients with HRPC in the USA, it is still necessary to search and develop new drugs. Spheroid culture models have an invaluable role in tumor biology or drug screening. Characteristics of cancer cells in three-dimensional (3D) culture, especially spheroid culture, differ dramatically from those in two-dimensional (2D) culture. Spheroid culture models appear to be an ideal tool, however, their models have not been incorporated in drug screening. In this article, we demonstrate characterization of prostate cancer spheroids including chemo-resistance compared with 2D culture and xenograft models. Prostate cancer cells except PC-3 formed E-cadherin-mediated spheroids. An immunocytochemical analysis of the spheroids revealed that cells showing Ki-67 were localized in the peripheral layer and the intermediate zone cells showed p27 and poly (ADP-ribose) polymerase-1 (PARP-1), suggesting quiescent cell character. Prostate cancer cells acquired resistance to most agents when grown as spheroids, but not to all of the anticancer agents tested. This article also attempts to provide up-to-date information about spheroids, especially quiescent cells as therapeutic targets and the involvement of genetics and epigenetics in forming spheroids.