New bone formation in nude mouse calvaria induced by canine prostate tissue

Three-dimensional cancer-bone metastasis model using ex-vivo co-cultures of live calvarial bones and cancer cells

One of the major limitations of studying cancer-bone metastasis has been the lack of an appropriate ex-vivo model which can be used under defined conditions that simulates closely the in vivo live bone microenvironment in response to cancer-bone interactions. We have developed and utilized a three-dimensional (3D) cancer-bone metastasis model using free-floating live mouse calvarial bone organs in the presence of cancer cells in a roller tube system. In such co-cultures under hypoxia and a specifically defined bone remodeling stage, viz., resorption system, cancer cells showed a remarkable affinity and specificity for the "endosteal side" of the bone where they colonize and proliferate. This was concurrent with differentiation of resident stem/progenitor cells to osteoclasts and bone resorption. In contrast, under bone formation conditions this model revealed different pathophysiology where the breast cancer cells continued to induce osteoclastic bone resorption whereas prostate cancer cells led to osteoblastic bone formation. The current 3D model was used to demonstrate its application to studies involving chemical and biochemical perturbations in the absence and presence of cancer cells and cellular responses. We describe proof-of-principle with examples of the broad versatility and multi-faceted application of this model that adds another dimension to the ongoing studies in the cancer-bone metastasis arena.

Intraosseous injection of RM1 murine prostate cancer cells promotes rapid osteolysis and periosteal bone deposition

The molecular mechanisms associated with prostate cancer (PCa) progression within bone remain a topic of intense investigation. With the availability of transgenic mouse strains, a model of PCa for use in immune competent/transgenic mice would be highly beneficial. This study was designed to explore the utility of RM1 mouse PCa cells in investigations of tumor:bone interactions. The efficacies of several implantation techniques were examined for reliably producing intra-bone RM1 tumor growth and bone lesion formation in immune competent mice. Longitudinal monitoring of bone remodeling and lesion phenotypes was conducted by microcomputed tomography (muCT) and histological analyses. Our results indicate that direct intrabone injections of RM1 cells are necessary for tumor growth within bone and direct implantation promotes the rapid development of osteolytic bone lesions with periosteal bone deposition post-cortical breach. In vitro, RM1 cells promote the proliferation of osteoblast (MC3T3-E1) and osteoclast (Raw264.7) progenitors in a dose dependent manner. Conditioned culture media from RM1 cells appears to promote earlier expression of genes/proteins associated with osteoblastic differentiation. While clearly stimulating osteoclast function in vivo, RM1 cells had little effect on differentiation and tartate resistant acid phosphatase (TRAP) expression by Raw264.7 cells. These data, coupled with in vivo muCT images, indicate the ability of RM1 cells to induce mixed, yet predominentally osteolytic, responses in bone and illustrate the potential of RM1 cells as a model of investigating prostate tumor:stroma interactions in immune competent/transgenic mice on a C57BL/6 background.

Effects of transforming growth factor-beta1 on parathyroid hormone-related protein mRNA expression and protein secretion in canine prostate epithelial, stromal, and carcinoma cells

BACKGROUND

Bone metastases of prostate carcinoma are associated with osteoblastic metastases. Tumor-derived factors, such as parathyroid hormone-related protein (PTHrP), may promote the development of osteoblastic metastases. We examined the effect of transforming growth factor-beta1 (TGF beta 1) on PTHrP mRNA expression and PTHrP secretion in normal canine prostate epithelial cells (PEC) and stromal cells (PSC), and in canine prostate carcinoma cells (PCC).

METHODS

Primary cultures of PEC, PSC, and PCC were produced. The effect of TGF beta 1 on PTHrP mRNA expression was measured by Northern blot, and secretion of PTHrP into culture medium was measured by immunoradiometric assay (IRMA). Degradation of recombinant-human PTHrP (rhPTHrP) (1-84) inoculated in prostate cell cultures was measured over 24 hr. Arginine esterase (AE) activity in tissue and conditioned medium was also measured.

RESULTS

TGF beta 1 increased PTHrP mRNA expression in a time- and dose-dependent manner in PEC and in PCC. TGF beta 1 decreased PTHrP mRNA in PSC. TGF beta 1 significantly increased PTHrP secretion (P < or = 0.05) into PEC but not PSC conditioned medium. rhPTHrP was significantly (P < or = 0.05) degraded in PEC conditioned medium as compared to PSC conditioned medium. AE activity was present in prostate and prostate carcinoma tissue, but not in conditioned medium from PEC or PSC.

CONCLUSIONS

TGF beta 1 increased PTHrP mRNA expression in canine PEC and PCC, and decreased expression in PSC. This regulatory pathway may be important in the pathogenesis of osteoblastic metastases.