This study describes the first known model of bone cancer pain in the rat. Sprague-Dawley rats receiving intra-tibial injections of syngeneic MRMT-1 rat mammary gland carcinoma cells developed behavioural signs indicative of pain, including: mechanical allodynia, difference of weight bearing between hind paws and mechanical hyperalgesia. The development of the bone tumour and structural damage to the bone was monitored by radiological analysis, quantitative measurement of mineral content and histology. Intra-tibial injections of 3 x 10(3) or 3 x 10(4) syngeneic MRMT-1 cells produced a rapidly expanding tumour within the boundaries of the tibia, causing severe remodelling of the bone. Radiographs showed extensive damage to the cortical bone and the trabeculae by day 10-14 after inoculation of 3 x 10(3) MRMT-1 cells, and by day 20, the damage was threatening the integrity of the tibial bone. While both mineral content and mineral density decreased significantly in the cancerous bone, osteoclast numbers in the peritumoural compact bone remained unchanged. However, tartarate-resistant acid phosphatase staining revealed a large number of polykariotic cells, resembling those of osteoclasts within the tumour. No tumour growth was observed after the injection of heat-killed MRMT-1 cells. Intra-tibial injections of 3 x 10(3) or 3 x 10(4) MRMT-1 cells, heat-killed cells or vehicle did not show changes in body weight and core temperature over 19-20 days. The general activity of animals after injection with live or heat-killed MRMT-1 cells was higher than that of the control group, however, the activity of the MRMT-1 treated group declined during the progress of the disease. Rats receiving intra-tibial injections of MRMT-1 cells displayed the gradual development of mechanical allodynia and mechanical hyperalgesia/reduced weight bearing on the affected limb, beginning on day 12-14 or 10-12 following injection of 3 x 10(3) or 3 x 10(4) cells, respectively. These symptoms were not observed in rats receiving heat-killed cells or vehicle. Behavioural data suggest a reasonable time window for evaluation of anti-nociceptive agents between day 14 and 20 after cancer cell inoculation in this model. Acute treatment with morphine (1-3mg/kg, subcutanously (s.c.)) produced a dose-dependent reduction in the response frequency of hind paw withdrawal to von Frey filament stimulation 17 or 19 days following intra-tibial injections of 3 x 10(3) MRMT-1 cells. A significant reduction in the difference in hind limb weight bearing was also observed. Acute treatment with celebrex (10-30 mg/kg, s.c.) did not affect mechanical allodynia or difference in weight bearing in rats 20 days following treatment with 3 x 10(3) MRMT-1 cells. Although the pathophysiology of cancer pain is largely unknown, significant enhancement of glial fibrillary acidic protein (GFAP) staining in the corresponding segments of the ipsilateral spinal cord highlights the possible involvement of astrocytes. In summary, the induction of bone cancer in the rat by the syngeneic MRM...

Bisphosphonates (BPs) are pyrophosphate analogues in which the oxygen in P-O-P has been replaced by a carbon, resulting in a metabolically stable P-C-P structure. Pamidronate (1b, Novartis), a second-generation BP, was the starting point for extensive SAR studies. Small changes of the structure of pamidronate lead to marked improvements of the inhibition of osteoclastic resorption potency. Alendronate (1c, MSD), with an extra methylene group in the N-alkyl chain, and olpadronate (1h, Gador), the N,N-dimethyl analogue, are about 10 times more potent than pamidronate. Extending one of the N-methyl groups of olpadronate to a pentyl substituent leads to ibandronate (1k, Roche, Boehringer-Mannheim), which is the most potent close analogue of pamidronate. Even slightly better antiresorptive potency is achieved with derivatives having a phenyl group linked via a short aliphatic tether of three to four atoms to nitrogen, the second substituent being preferentially a methyl group (e.g., 4g, 4j, 5d, or 5r). The most potent BPs are found in the series containing a heteroaromatic moiety (with at least one nitrogen atom), which is linked via a single methylene group to the geminal bisphosphonate unit. Zoledronic acid (6i), the most potent derivative, has an ED(50) of 0.07 mg/kg in the TPTX in vivo assay after sc administration. It not only shows by far the highest therapeutic ratio when comparing resorption inhibition with undesired inhibition of bone mineralization but also exhibits superior renal tolerability. Zoledronic acid (6i) has thus been selected for clinical development under the registered trade name Zometa. The results of the clinical trials indicate that low doses are both efficacious and safe for the treatment of tumor-induced hypercalcemia, Paget's disease of bone, osteolytic metastases, and postmenopausal osteoporosis.

The gp130-dependent cytokines, which signal through at least two intracellular pathways, regulate osteoclast and osteoblast formation. To define their roles in regulating bone mass, we analyzed mice in which gp130 signaling via either the signal transducer and activator of transcription (STAT) 1/3 (gp130 ∆STAT/∆STAT ) or SHP2/ras/MAPK (gp130 Y757F/Y757F ) pathway was attenuated. In gp130 ∆STAT/∆STAT mice, trabecular bone volume (BV/TV) and turnover were normal, but bone length was reduced by premature growth plate closure, indicating an essential role for gp130-STAT1/3 signaling in chondrocyte differentiation. In contrast, while bone size was normal in gp130 Y757F/Y757F mice, BV/TV was reduced due to high bone turnover, indicated by high osteoclast surface/bone surface (OcS/BS) and osteoblast surface/bone surface (ObS/BS). Furthermore, generation of functional osteoclasts from bone marrow of gp130 Y757F/Y757F mice was elevated, revealing that while gp130 family cytokines stimulate osteoclastogenesis through the osteoblast lineage, gp130, via SHP2/Ras/MAPK, inhibits osteoclastogenesis in a cell lineage-autonomous manner. Genetic ablation of IL-6 in gp130 Y757F/Y757F mice exacerbated this osteopenia by reducing ObS/BS without affecting OcS/BS. Thus, while IL-6 is critical for high bone formation in gp130 Y757F/Y757F mice, it is not involved in the increased osteoclastogenesis. In conclusion, gp130 is essential for normal bone growth and trabecular bone mass, with balanced regulation depending on selective activation of STAT1/3 and SHP2/ras/MAPK, respectively. Furthermore, the latter pathway can directly inhibit osteoclastogenesis in vivo.

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Objective. To study the effect of zoledronic acid (ZA) on synovial inflammation, structural joint damage, and bone metabolism in rats during the effector phase of collagen-induced arthritis (CIA).Methods. CIA was induced in female dark agouti rats. At the clinical onset of CIA, rats were assigned to treatment with vehicle or single subcutaneous doses of ZA (1.0, 10, 50, or 100 g/kg). Clinical signs in all 4 paws were scored on a daily basis. After 2 weeks, the joints in the hind paws were assessed using plain radiographs, microfocal computed tomography (micro-CT), histologic scoring, and histomorphometry, and the serum levels of type I collagen crosslinks were measured by enzyme-linked immunosorbent assay.Results. Although ZA mildly exacerbated synovitis, it effectively suppressed structural joint damage. At doses of >10 g/kg, ZA significantly reduced radiographic bone erosions, Larsen scores, and juxtaarticular trabecular bone loss as quantified by micro-CT. ZA prevented increased type I collagen (bone) breakdown in CIA and diminished histologic scores of focal bone erosion by up to 80%. Increases in the percentage of eroded surface, osteoclast surface, and osteoclast numbers associated with CIA were prevented by ZA, even though synovitis scores were unchanged.Conclusion. Single doses (>10 g/kg) of ZA strikingly reduced focal bone erosions and juxtaarticular trabecular bone loss, although synovitis was mildly exacerbated. Targeting osteoclasts with ZA may therefore be an effective strategy for preventing structural joint damage in rheumatoid arthritis.