Characterization of bone resorption in novel in vitro and in vivo models of oral squamous cell carcinoma.

Oral squamous cell carcinoma (OSCC) is the most commonly diagnosed oral malignancy in humans and cats and frequently invades bone. The objective of this study was to determine if feline OSCC serves as a relevant model of human OSCC in terms of osteolytic behavior and expression of bone resorption agonists. Novel feline OSCC cell lines (SCCF2 and SCCF3) were derived from spontaneous carcinomas. Gene expression and osteolytic behavior were compared to an established feline OSCC cell line (SCCF1) and three human OSCC cell lines (UMSCC-12, A253 and SCC25). Interaction of OSCC with bone and murine pre-osteoblasts (MC3T3) was investigated using in vitro co-culture techniques. In vivo bioluminescent imaging, Faxitron radiography and microscopy were used to measure xenograft growth and bone invasion in nude mice. Human and feline OSCC expressing the highest levels of parathyroid hormone-related protein (PTHrP) were associated with in vitro and in vivo bone resorption and osteoclastogenesis. MC3T3 cells had increased receptor activator of nuclear factor κB ligand (RANKL) expression and reduced osteoprotegerin (OPG) expression in conditioned medium from bone-invasive SCCF2 cells compared to minimally bone invasive SCCF3 cells, which was partially reversed with a neutralizing anti-PTHrP antibody. Human and feline OSCC cells cultured in bone-conditioned medium had increased PTHrP secretion and proliferation. Feline OSCC-induced bone resorption was associated with tumor cell secretion of PTHrP and with increased RANKL:OPG expression ratio in mouse preosteoblasts. Bone-CM increased OSCC proliferation and secretion of PTHrP. The preclinical models of feline OSCC recapitulated the bone-invasive phenotype characteristic of spontaneous OSCC and will be useful to future preclinical and mechanistic studies of bone invasive behavior.

Effect of zoledronic acid and amputation on bone invasion and lung metastasis of canine osteosarcoma in nude mice.

Osteosarcoma (OSA) is an aggressive, highly metastatic and lytic primary bone neoplasm commonly affecting the appendicular skeleton of dogs and children. Current treatment options include amputation of the afflicted limb, limb-sparing procedures, or palliative radiation with or without adjunct chemotherapy. Therapies that inhibit bone resorption, such as the bisphosphonates, may be an effective palliative therapy by limiting the local progression of OSA in those patients that are not viable candidates for amputation. We have developed a mouse model of canine skeletal OSA following intratibial inoculation of OSCA40 cells that spontaneously metastasized to the lungs. We demonstrated that therapy with a nitrogen-containing bisphosphonate, zoledronic acid (Zol), reduced OSA-induced bone lysis; however, Zol monotherapy or in combination with amputation was not effective at inhibiting pulmonary metastasis. While not reaching statistical significance, amputation of the tumor-bearing limb reduced the average incidence of lung metastases; however, this effect was nullified when Zol was added to the treatment protocol. In untreated mice, the magnitude of proximal tibial lysis was significantly correlated with the incidence of metastasis. The data support amputation alone for the management of appendicular OSA rather than combining amputation with Zol. However, in patients that are not viable candidates for amputation, Zol may be a useful palliative therapy for OSA by reducing the magnitude of lysis and therefore bone pain, despite the risk of increased pulmonary metastasis.

Zoledronic acid reduces bone loss and tumor growth in an orthotopic xenograft model of osteolytic oral squamous cell carcinoma.

Squamous cell carcinoma (SCC) is the most common form of oral cancer. Destruction and invasion of mandibular and maxillary bone frequently occurs and contributes to morbidity and mortality. We hypothesized that the bisphosphonate drug zoledronic acid (ZOL) would inhibit tumor-induced osteolysis and reduce tumor growth and invasion in a murine xenograft model of bone-invasive oral SCC (OSCC) derived from an osteolytic feline OSCC. Luciferase-expressing OSCC cells (SCCF2Luc) were injected into the perimaxillary subgingiva of nude mice, which were then treated with 100 µg/kg ZOL or vehicle. ZOL treatment reduced tumor growth and prevented loss of bone volume and surface area but had no effect on tumor invasion. Effects on bone were associated with reduced osteolysis and increased periosteal new bone formation. ZOL-mediated inhibition of tumor-induced osteolysis was characterized by reduced numbers of tartrate-resistant acid phosphatase-positive osteoclasts at the tumor-bone interface, where it was associated with osteoclast vacuolar degeneration. The ratio of eroded to total bone surface was not affected by treatment, arguing that ZOL-mediated inhibition of osteolysis was independent of effects on osteoclast activation or initiation of bone resorption. In summary, our results establish that ZOL can reduce OSCC-induced osteolysis and may be valuable as an adjuvant therapy in OSCC to preserve mandibular and maxillary bone volume and function.