Animal models for prostate cancer

Mouse models of prostate cancer

The development and optimization of high-throughput screening methods has identified a multitude of genetic changes associated with human disease. The use of immunodeficient and genetically engineered mouse models that mimic the human disease has been crucial in validating the importance of these genetic pathways in prostate cancer. These models provide a platform for finding novel therapies to treat human patients afflicted with prostate cancer as well as those who have debilitating bone metastases. In this paper, we focus on the historical development and phenotypic descriptions of mouse models used to study prostate cancer. We also comment on how closely each model recapitulates human prostate cancer.

Histological findings in the rat prostate cancer model during treatment with a luteinizing hormone-releasing hormone agonist and novantrone

Morphological changes produced by the treatment with the D-tryptophan-6 analog of luteinizing hormone-releasing hormone (D-Trp-6-LH-RH) and mitoxantrone (novantrone) were studied in the Dunning R3327H rat prostate cancer model. Microcapsules of D-Trp-6-LH-RH, calculated to release a controlled dose of 25 micrograms/day, were injected intramuscularly once a month. Novantrone (0.25 mg/kg body weight) was injected intravenously once every 3 weeks. The pathology of tumors was studied in two experiments. In the first experiment, the treatment was started 135 days after tumor transplantation, and the therapy was continued for 105 days. In the second experiment, the treatment was initiated 45 days after tumor transplantation, and was carried on for 70 days. The rats were divided into four groups: 1) untreated control, 2) microcapsule-injected, 3) novantrone-injected, and 4) combination of microcapsules and novantrone-injected. In both experiments, similar results were obtained, which included significant reduction in the tumor volume and weight, a very striking decrease in the number of epithelial tumoral cells with atrophy of the glandular epithelium, and an increase in the stromal connective tissue. All these changes were more prominent in the group treated with the combination of microcapsules and novantrone than in the groups treated with microcapsules or novantrone alone. Pathological results support the view that combined therapy may be more efficacious than the treatment with single agents.

Autochthonous prostate adenocarcinomas in Lobund-Wistar rats: a model system

An experimental model system for autochthonous prostate adenocarcinoma (PA) has been developed in Lobund-Wistar (L-W) rats. Large primary PAs were induced in 31 of 40 (77.5%) L-W rats within an average of 10.7 months after a single dose of methylnitrosourea (MNU) and subcutaneous implants of testosterone. Metastatic tumors had developed in over 60% of the tumor-bearing rats. In addition, localized in situ PAs had developed in 5 of the 40 test rats. At 14 months 50 untreated L-W rats were free of demonstrable PAs. Two of 20 (10%) L-W rats developed PA at 14 months after inoculation of MNU alone. Six of 42 (14%) L-W rats developed PAs within 14 months after s.c. administration of testosterone implants. Thus, testosterone acted as a tumor promoter of PA for cells that had been initiated by MNU. The manifestations of the PAs in the L-W rats resembled many aspects of the counterpart disease in man.

Metastatic spread of the PAIII prostatic adenocarcinoma after implantation in the tail of the rat

The spontaneous metastatic spread of a suspension of PAIII prostatic adenocarcinoma cells from the tail site of implantation was analyzed over a period of 5 weeks in male Lobund-Wistar (LW) rats. Following subcutaneous injection of the PAIII cells, the tumor metastasized through the primary lymphatic drainage. PAIII microfoci were evident in the gluteal and iliac lymph nodes prior to colonization of the lungs. Growth of the primary tumor was evidenced by significant weight differences of the tails of PAIII-bearing and control rats 1 week after tumor implantation. Time-dependent sequential spread of the adenocarcinoma was quantitated. Significant differences were noted between PAIII-bearing and control animals with respect to the gluteal lymph node weights (+2 weeks), iliac lymph node weights (+3 weeks), dry lung weights, and lung colony numbers (+4 weeks) after tumor implantation. During the course of these studies, the whole blood prothrombin, activated partial thromboplastin, and recalcification times for the PAIII-bearing animals were similar to those of the control group. These findings indicate that there were no gross changes in systemic blood coagulation accompanying the metastasis of PAIII cells from the primary tumor. The tumor in LW rats produced a consistent pattern of growth and metastasis that is suitable for quantitation. The PAIII prostatic adenocarcinoma is a sensitive and reproducible system that may be useful to evaluate potential antimetastatic and cytotoxic agents for the treatment of hormone-insensitive prostatic cancer.

The relationship of natural killer cells to metastasis of a transplantable prostate adenocarcinoma

Natural killer (NK) cells have been proposed to play a significant role in the inhibition of metastasis. The prostate adenocarcinoma (PA-11) in the Lobund-Wistar (L-W) rat provides a unique model of spontaneous metastasis in which to study NK response. Cultured PA-11 tumor cells were shown to be resistant to NK lysis in vitro, and enhancement or inhibition of NK reactivity in vivo using drugs or antiserum did not change the rate or extent of metastasis evident at autopsy. Exposure to PA-11 tumor cells, supernatants from cultured tumor cells, or sera from rats with advanced PA-11 in vitro did not result in inhibition of NK activity. Exposure to PA-11 tumor cells in vivo also did not cause suppression of NK activity. These data indicate that, in the PA-11/L-W system, metastasis is independent of NK activity.

Animal models and treatment of prostate cancer

Model systems for prostate cancer in rats have been developed and used for investigations on tumor biology and therapy. The "Pollard tumors" provide a combination of in vitro and in vivo attributes by which investigations can be directed at local tumor development and spontaneous metastasis. The evolution and early applications of this model system are reviewed, and the therapeutic benefits of delayed release of cyclophosphamide are presented.