Osteosclerotic prostate cancer metastasis to murine bone are enhanced with increased bone formation

Abstract

Spontaneous development of osteoblastic lesions of prostate cancer (PCa) in mice is modeled by orthotopic (intraprostatic) deposition of neoplastic cells followed by an extremely long latency associated with low incidence of spontaneous bone metastasis. Intracardial injection results in overt bone metastases only with osteoclastic PCa cells (i.e., PC-3). Herein, we report that androgen independent osteoblastic PCa cells readily colonize bone when in a high remodeling state. SCID/Beige mice were subjected to periods of intermittent human parathyroid hormone 1-34 (hPTH) exposure, followed by an intracardiac infusion of osteoblastic C4-2 PCa cells. At the time of PCa infusion, analysis of bone turnover markers from mice treated with hPTH revealed significant increases in osteocalcin (55.06 +/- 7.5 vs. 74.01 +/- 18.5 ng/ml) and TRAcP-5b (3.3 +/- 0.6 vs. 4.81 +/- 0.8 U/l), but no change in type I collagen C-terminal teleopeptide levels relative to control mice. Analysis of femoral cancellous bone architecture revealed significant increases in bone mineral density, trabecular thickness (0.056 +/- 0.002 vs. 0.062 +/- 0.001 mm) and porosity, but significant decreases in connectivity density and trabecular number in hPTH treated mice relative to controls. By 8 weeks post-infusion, 70% of mice pre-treated with hPTH demonstrated detectable serum prostate specific antigen (PSAs) ranging between 2 and 18.8 ng/ml. Immuno-histochemical labeling of femurs for PSA and pan-Cytokeratin revealed the presence of significant tumor cell nests in marrow and trabecular spaces. These results suggest that: (1) local bone physiology is an important factor for developing osteoblastic/sclerotic PCa bone metastases in murine hosts; (2) the establishment of osteosclerotic PCa bone metastases in mice is enhanced by alterations that drive bone formation.

Short-term intermittent PTH 1-34 administration enhances bone formation in SCID/Beige mice

“…This discrepancy may be attributed to the lower dose of PTH 1-34 and/ or the timing of end stage analysis of bone turnover markers employed in this study. Elevations in bone resorptive parameters (osteoclast number and activity) have been reported when PTH 1-34 is administered intermittently, at doses of 40 µg/kg and higher, over a time course similar to the present investigation [12,19,26]. Herein the highest dose of PTH 1-34 administered was 2-4 times less than those typically administered; a dose that may be insufficient to increase osteoclast number or activity.…”

“…Indeed, morphologic changes in osteoclasts and elevations in serum calcium and collagen cross links have been reported to occur within minutes following a single PTH injection, and return to baseline following PTH 1-34 clearance [35][36][37]. While levels of calcium and collagen cross links in circulation may return to baseline following PTH clearance, our previous report [26] suggests elevations in serum TRACP 5b are detectable at least 2 days following the last PTH injection.…”

“…Finally, since independent markers of bone formation were enhanced, but markers of bone resorption were unchanged, three weeks of intermittent PTH 1-34, administered at 20 µg/kg, enhances bone formation in SCID/Beige mice primarily by enhancing the number and activity of osteoblasts but not osteoclasts. SCID/Beige mice were chosen for study because our laboratory currently employs this animal model in studies regarding the role of bone turnover in the colonization and establishment of human prostate cancer in bone [26]. SCID/Beige mice demonstrate great effi- [12,17].…”

“…PTH 1-34 was reconstituted in 10 mM acetic acid/ sterile phosphate buffered saline (PBS) solution and stored at -80°C at a concentration of 400 μg/mL in silconized tubes [12,26]. For injections, the stock solution was diluted to 50 μg/mL and then further diluted to 4 μg/mL, 2 μg/mL, and 1 μg/mL solutions for administration, control animals were injected with equivalent volumes of acetic acid diluted in PBS.…”

“…Therein, we observed that short term intermittent PTH 1-34 administration (40 µg/kg) enhanced bone formative as well as resorptive indices (serum mTRACP 5b levels) [26]. We wondered if a lower dose of PTH 1-34 could enhance bone formation without elevating bone resorption.…”