Value of Xenografts in the Investigation of Prostatic Function: Preliminary Communication

Mouse Models in Prostate Cancer Translational Research: From Xenograft to PDX

Despite the advancement of clinical and preclinical research on PCa, which resulted in the last five years in a decrement of disease incidence by 3-4%, it remains the most frequent cancer in men and the second for mortality rate. Based on this evidence we present a brief dissertation on numerous preclinical models, comparing their advantages and disadvantages; among this we report the PDX mouse models that show greater fidelity to the disease, in terms of histopathologic features of implanted tumor, gene and miRNA expression, and metastatic pattern, well describing all tumor progression stages; this characteristic encourages the translation of preclinical results. These models become particularly useful in meeting the need of new treatments identification that eradicate PCa bone metastases growing, clarifying pathway of angiogenesis, identifying castration-resistant stem-like cells, and studying the antiandrogen therapies. Also of considerable interest are the studies of 3D cell cultures derived from PDX, which have the ability to maintain PDX cell viability with continued native androgen receptor expression, also showing a differential sensitivity to drugs. 3D PDX PCa may represent a diagnostic platform for the rapid assessment of drugs and push personalized medicine. Today the development of preclinical models in vitro and in vivo is necessary in order to obtain increasingly reliable answers before reaching phase III of the drug discovery.

Serially heterotransplanted human prostate tumours as an experimental model

* Introduction * Serially heterotransplanted human tumours in immunosuppressed mice: similarity to the tumour of origin - Cytological and histological analysis - Karyotype - Marker expression - Other PC markers - Tumour cell proliferation and frequency of mitosis - Vasculature - Stromal compartment - Heterotransplant hormone dependency - Androgen dependent - Partially androgen dependent - Androgen independent - Metastases * Conclusions Preclinical research on prostate cancer (PC) therapies uses several models to represent the human disease accurately. A common model uses patient prostate tumour biopsies to develop a cell line by serially passaging and subsequent implantation, in immunodeficient mice. An alternative model is direct implantation of patient prostate tumour biopsies into immunodeficient mice, followed by serial passage in vivo. The purpose of this review is to compile data from the more than 30 years of human PC serial heterotransplantation research. Serially heterotransplanted tumours are characterized by evaluating the histopathology of the resulting heterotransplants, including cellular differentiation, karyotype, marker expression, hormone sensitivity, cellular proliferation, metastatic potential and stromal and vascular components. These data are compared with the initial patient tumour specimen and, depending on available information, the patient's clinical outcome was compared with the heterotransplanted tumour. The heterotansplant model is a more accurate preclinical model than older generation serially passaged or genetic models to investigate current and newly developed androgen-deprivation agents, antitumour compounds, anti-angiogenic drugs and positron emission tomography radiotracers, as well as new therapeutic regimens for the treatment of PC.

Human prostate cancer heterotransplants: a review on this experimental model

A common model used for preclinical research was in vitro human tumor cell culture. An alternative model was the direct implantation of a unique patient's tumor biopsy specimens into immunodeficient host mice. Published data from PubMed (http://www.ncbi.nlm.nih.gov) and Current Contents Connect databases (http://thomsonreuters.com/products_services/science/science_products/a-z/current_contents_connect) were reviewed. Prostate cancer (PCa) heterotransplantation was evaluated using histopathology, morphology, cell differentiation, DNA content, tumor marker expression, metastases, tumor kinetics, tumor take rate and tumor vasculature in the first tumor heterotransplant. The heterotransplanted tumor retained the biological properties of the original tumor, such as morphology, degree of differentiation, pathology, secretory activity, expression of tumor markers and human vasculature. Human PCa heterotransplants have considerable experimental advantages over cell culture following xenotransplantation.

Biological effects of hormonal treatment regimens on a transplantable human prostatic tumor line (PC-82)

The effects of hormonal manipulation on the growth of a transplantable human prostatic carcinoma line (PC-82) were studied. The histological pattern of the PC-82 tumor, which still closely resembles the original tumor material, and the tumor growth rate did not change during the subsequent mouse passages. Growth of PC-82 tumor tissue on female and castrated male mice did not occur. Castration of tumor-bearing mice resulted in a cessation of tumor growth, after which the tumor volume decreased 50 +/- 27 per cent within 6 weeks after castration. Hormone-independent regrowth of the tumor tissue was not observed after long-term withdrawal of androgens. After a period of 10 weeks following tumor growth arrest, administration of testosterone almost directly resulted in regrowth of the tumor. Hormones, testosterone and estradiol, were administered by silastic implants. Intact male nude mice were shown to have highly fluctuating levels of testosterone. Implantation with testosterone resulted in constant levels of circulating testosterone, which could be maintained for at least 10 weeks, while the mean concentration of plasma testosterone was not different from that in control male mice. The doubling time of tumors grown on testosterone-substituted intact female and intact and castrated male mice was significantly shorter than that of tumors grown on intact male mice. Histologically the tumors grown on androgen-substituted mice were similar to those grown on untreated mice; the mitotic index, however, was much higher in the testosterone treated animals. Implantation of intact male mice with estradiol suppressed plasma testosterone to a mean level of 1 ng. per ml. and prevented the growth of PC-82 tumor tissue almost completely. Treatment of tumor-bearing mice with an estradiol implant following androgen withdrawal did not result in a further decrease of the tumor volume compared to the mice without additional estradiol implantation.