Wessel P. Dirksen

Osteolytic bone resorption in adult T-cell leukemia/lymphoma.

Adult T-cell leukemia/lymphoma (ATLL) is caused by human T lymphotropic virus type 1 (HTLV-1). Patients with ATLL frequently develop humoral hypercalcemia of malignancy (HHM) resulting from increased osteoclastic bone resorption. Our goal was to investigate the mechanisms of ATLL-induced osteoclastic bone resorption. Murine calvaria co-cultured with HTLV-1-infected cells directly or conditioned media from cell cultures had increased osteoclast activity that was dependent on RANKL, indicating that factors secreted from ATLL cells had a stimulatory effect on bone resorption. Factors released from resorbing bone stimulated proliferation of HTLV-1-infected T-cells. Parathyroid hormone-related protein (PTHrP) and macrophage inflammatory protein-1α (MIP-1α), both osteoclast stimulators, were expressed in HTLV-1-infected T-cell lines. Interestingly, when HTLV-1-infected T-cells were co-cultured with pre-osteoblasts, the expression of osteoprotegerin (OPG), an osteoclast inhibitory factor, was significantly down-regulated in the pre-osteoblasts. When OPG was added into the ex vivo osteoclastogenesis assay induced by HTLV-1-infected T-cells, osteoclastogenesis was strongly inhibited. In addition, HTLV-1-infected T-cells inhibited expression of early osteoblast genes and induced late genes. These regulators will serve as future therapeutic targets for the treatments of HHM in ATLL.

Interferon-γ Targets Cancer Cells and Osteoclasts to Prevent Tumor-associated Bone Loss and Bone Metastases

Interferon-γ (IFN-γ) has been shown to enhance anti-tumor immunity and inhibit the formation of bone-resorbing osteoclasts. We evaluated the role of IFN-γ in bone metastases, tumor-associated bone destruction, and hypercalcemia in human T cell lymphotrophic virus type 1-Tax transgenic mice. Compared with Tax+IFN-γ+/+ mice, Tax+IFN-γ-/- mice developed increased osteolytic bone lesions and soft tissue tumors, as well as increased osteoclast formation and activity. In vivo administration of IFN-γ to tumor-bearing Tax+IFN-γ-/- mice prevented new tumor development and resulted in decreased bromodeoxyuridine uptake by established tumors. In vitro, IFN-γ directly decreased the viability of Tax+ tumor cells through inhibition of proliferation, suppression of ERK phosphorylation, and induction of apoptosis and caspase 3 cleavage. IFN-γ also inhibited macrophage colonystimulating factor-mediated proliferation and survival of osteoclast progenitors in vitro. Administration of IFN-γ to C57BL/6 mice decreased Tax+ tumor growth and prevented tumor-associated bone loss and hypercalcemia. In contrast, IFN-γ treatment failed to protect IFN-γR1-/- mice from Tax+ tumor-induced skeletal complications, despite decreasing tumor growth. These data demonstrate that IFN-γ suppressed tumor-induced bone loss and hypercalcemia in Tax+ mice by inhibiting both Tax+ tumor cell growth and host-induced osteolysis. These data suggest a protective role for IFN-γ in patients with bone metastases and hypercalcemia of malignancy.

CD147 and Cyclooxygenase Expression in Feline Oral Squamous Cell Carcinoma

Feline oral squamous cell carcinoma (OSCC) is a highly invasive form of cancer in cats. In human OSCC, cluster of differentiation 147 (CD147) contributes to inflammation and tumor invasiveness. CD147 is a potential therapeutic target, but the expression of CD147 in feline OSCC has not been examined. Immunohistochemistry was used to determine if cyclooxygenase 2 (COX-2) and CD147 expression in feline OSCC biopsies was coordinated. Tumor cells were more likely to express COX-2 (22/43 cases or 51%) compared to stroma (8/43 or 19%) and adjacent oral epithelium (9/31 cases or 29%) (p < 0.05). CD147 was also more likely to occur in tumor cells compared to stroma and adjacent mucosa, with 21/43 (49%) of cases having >50% tumor cells with mild or moderate CD147 expression, compared to 9/28 (32%) in adjacent epithelium and only 5/43 (12%) in adjacent stroma (p < 0.05). In feline OSCC cell lines (SCCF1, SCCF2, and SCCF3), CD147 gene expression was more consistently expressed compared to COX-2, which was 60-fold higher in SCCF2 cells compared to SCCF1 cells (p < 0.05). CD147 expression did not correlate with COX-2 expression and prostaglandin E2 (PGE2) secretion, indicating that they may be independently regulated. CD147 potentially represents a novel therapeutic target for the treatment of feline OSCC and further study of CD147 is warranted.

Mechanisms of Humoral Hypercalcemia of Malignancy in Leukemia/Lymphoma

Hypercalcemia is one of the most common paraneoplastic syndromes. The incidence of hypercalcemia is 50-90% in adult T-cell leukemia/lymphoma (ATLL), 27-35% in lung cancer, 25-30% in breast cancer, 7-30% in multiple myeloma, and less than 10% in other types of cancer patients (Mundy & Martin, 1982; Roodman, 1997). Patients with severe hypercalcemia (>12 mg/dL; > 6.0 mM) usually develop neuromuscular, gastrointestinal and renal symptoms including lethargy, depression, anorexia, nausea, vomiting, polyuria and polydipsia. Patients with serum calcium concentrations >15 mg/dL (7.6 mM) can develop renal failure or cardiovascular abnormalities with arrhythmias and coma (Mundy & Martin, 1982). Depending on the sources of the stimulating factors, hypercalcemia in cancer can be divided into 3 types: (1) humoral hypercalcemia of malignancy (HHM) in which humoral factors secreted by tumor cells directly or indirectly affect cells in the target organs including bone, kidney and intestine that regulate calcium homeostasis; (2) local osteolytic hypercalcemia in which factors secreted by either primary or metastatic tumor cells locally in the bone microenvironment stimulate osteoclastic bone resorption; and (3) primary hyperparathyroidism that coexists with the malignancy (Stewart, 2005). This review will focus on HHM, although some types of cancers may induce both HHM and local osteolytic hypercalcemia, since several factors can function both systemically and locally.