A novel model of bone-metastatic prostate cancer in immunocompetent mice.

BACKGROUND: Bone metastasis is a frequent and catastrophic consequence of prostate cancer for which only palliative treatment is available. Animal models of bone metastatic prostate cancer are necessary for understanding disease mechanisms but few models exist. METHODS: We have used the murine prostate carcinoma cell line RM1 to generate a bone metastatic model of prostate cancer. Repeated intracardiac injection of RM1 cells followed by isolation of cells from bone tumors has yielded a cell line with strong bone-metastatic potential, RM1 bone metastatic (BM). RESULTS: This cell line metastasizes to multiple bony sites in over 95% of injected C57BL/6 mice and is far less tropic to soft tissues. Bone tumors produced by the RM1(BM) cell line show no preference for particular skeletal sites as most bones are affected. Histology, and micro-computed tomography show that RM1(BM) cells form osteolytic tumors, but with evidence of osteoblastic changes. In vitro the RM1 cells express E-cadherin but not vimentin, do not form colonies in soft agar, are non-invasive but are more motile than the parent cell line. CONCLUSIONS: This model provides a novel means for identifying cellular and molecular mechanisms that contribute to bone metastasis and allow for preclinical testing of therapies to prevent and treat tumor metastasis to bone. Finally as the syngeneic tumor cells are injected into immunocompetent mice, this model will provide a means to study interactions between the immune system, tumors and bone, and therapies that target such interactions.

Combination of cytosine deaminase with uracil phosphoribosyl transferase leads to local and distant bystander effects against RM1 prostate cancer in mice.

BACKGROUND: We aimed to evaluate the efficacy of gene-directed enzyme-prodrug therapy (GDEPT) using cytosine deaminase in combination with uracil phosphoribosyl transferase (CDUPRT) against intraprostatic mouse androgen-refractory prostate (RM1) tumors in immunocompetent mice. The product of the fusion gene, CDUPRT, converts the prodrug, 5-fluorocytosine (5FC), into 5-fluorouracil (5FU) and other cytotoxic metabolites that kill both CDUPRT-expressing and surrounding cells, via a 'bystander effect'. METHODS: Stably transformed andogen-independent mouse prostate cancer (PC) cells, RM1-CDUPRT, -GFP or GFP/LacZ cells were used. To assess the local bystander effects of CDUPRT-GDEPT, immunocompetent C57BL/6 mice implanted with cell mixtures of RM1-GFP/CDUPRT and RM1-GFP cells in different proportions intraprostatically were treated with 5FC. Pseudo-metastases in the lungs were established by a tail vein injection of untransfected RM1 cells. At necropsy, prostate weight/volume and lung colony counts were assessed. Tumors, lymph nodes, spleens and lungs were frozen or fixed for immunohistochemistry. RESULTS: CDUPRT expression in RM1-GFP/CDUPRT cells or tumors was confirmed by enzymic conversion of 5FC into 5FU, using HPLC. Treatment of mice bearing intraprostatic RM1-GFP/CDUPRT tumors with 5FC resulted in complete regression of the tumors. A 'local bystander effect' was seen, even though only 20% of the cells expressed CDUPRT. More importantly a significant reduction in pseudo-metastases of RM1 cells in lungs indicated a 'distant bystander effect'. Immunohistochemical evaluation of the treated tumors showed increased necrosis and apoptosis, with decreased tumor vascularity. There was also a significant increase in tumour-infiltration by macrophages, CD4+ T and natural killer cells. CONCLUSIONS: We conclude that CDUPRT-GDEPT significantly suppressed the aggressive growth of RM1 prostate tumors and lung pseudo-metastases via immune mechanisms involving necrosis and apoptosis.