HTLV-1 Tax transgenic mice develop spontaneous osteolytic bone metastases prevented by osteoclast inhibition

Abstract

One in 20 carriers of human T-cell leukemia virus type 1 (HTLV-1) will develop adult T-cell leukemia/lymphoma (ATL), a disease frequently associated with hypercalcemia, bone destruction, and a fatal course refractory to current therapies. Overexpression of the HTLV-1-encoded Tax oncoprotein under the human granzyme B promoter causes large granular lymphocytic leukemia/lymphomas in mice. We found that Tax ؉ mice spontaneously developed hypercalcemia, highfrequency osteolytic bone metastases, and enhanced osteoclast activity. We evaluated Tax tumors for the production of osteoclast-activating factors. Purification of Tax ؉ tumor cells and nonmalignant tumor-infiltrating lymphocytes demonstrated that each of these populations expressed transcripts for distinct osteoclastactivating factors. We then evaluated the effect of osteoclast inhibition on tumor formation. Mice doubly transgenic for Tax and the osteoclast inhibitory factor, osteoprotegerin, were protected from osteolytic bone disease and developed fewer soft-tissue tumors. Likewise, osteoclast inhibition with bone-targeted zoledronic acid protected Tax IntroductionAdult T-cell leukemia/lymphoma (ATL) is an aggressive lymphoproliferative malignancy of helper T lymphocytes and is associated with hypercalcemia and osteolytic bone lesions. 1 Human T-cell leukemia virus type 1 (HTLV-1), the first pathogenic retrovirus discovered in humans, is the etiologic agent of tropical spastic paraparesis myelopathy and ATL. 2,3 It is estimated that 10 to 20 million people worldwide are infected with HTLV-1. Infection with HTLV-1 in infancy is a major risk factor for the development of leukemia. 4 Approximately 1 in 20 people infected with HTLV-1 develop ATL at 20 to 60 years of age, indicating a long latency for this disease. The viral regulatory protein, Tax, has been implicated in the pathogenesis of ATL. [5][6][7] Tax is a transcriptional activator that can transactivate several viral and cellular genes encoding proteins such as interleukins 6 and 1 (IL-6 and IL-1), tumor necrosis factor ␣ (TNF␣), transforming growth factor-␤ (TGF␤), and parathyroid hormone-related peptide (PTHrP). 8,9 Tax is an oncoprotein with a capacity to transform cells, inhibit p53, and induce tumor formation in several transgenic mouse models using different tissuespecific promoters driving Tax expression. [10][11][12][13][14][15] Tax expression in mice under the HTLV-1 long terminal repeat or the metallothionein promoter did not produce leukemia; however, increased osteoclast resorption was noted. [15][16][17] Only the Tax transgenic mice under the regulation of the human granzyme B promoter (expressed in activated T and natural killer [NK] cells) develop lymphoproliferative disease (leukemia, lymphomas, splenomegaly) similar to ATL.Tax ϩ mice predominantly develop the large granular leukemia/ lymphoma (LGL) phenotype rather than the CD4 ϩ lymphoma/ leukemia most commonly seen in ATL. 18 Furthermore, Tax ϩ mice have been used to define cooperating genes critical to lymphoproliferative disease dev...

Anticancer mechanisms of doxorubicin and zoledronic acid in breast cancer tumor growth in bone

“…However, the concentrations of bisphosphonates used in these studies range from 5 to 20 μmol/L for up to 72 hours, compared with the 2 μmol/L circulating plasma concentration detectable in breast cancer patients for 1 to 2 hours following the standard 4-mg infusion of zoledronic acid (17). Antitumor effects of bisphosphonates have also been reported in in vivo model systems that mimic tumorinduced bone disease from a variety of cancer types including breast (18,19), prostate (20), leukemia (21), and multiple myeloma (22). These studies also used high doses and frequent administration of zoledronic acid (from 120 μg/kg 2× per week to 120 μg/kg daily), whereas a clinically relevant dose of zoledronic acid (100 μg/kg 1× per month) was reported not to exert anticancer effects in a model of breast cancer bone metastases (23).…”

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

“…OC numbers, OC perimeter, bone marrow space, and bone erosion were measured according to a standard protocol as described previously, using ImagePro Plus, version 5.0 software (Media Cybernetics, Bethesda) (19). Peripheral soft tumor, visceral metastatic tumor, and mouse bone samples were processed as described previously (17). For in vivo BrdUrd labeling, 200 l of 1 mg/ml BrdUrd (Pharmingen) dissolved in phosphate-buffered saline was injected intraperitoneally into mice 24 h before mice necropsy.…”

“…RT-PCR was performed using an Invitrogen kit as described previously (17). Primers specific for mouse IFN-␥ receptor were synthesized by IDT, and the sequences are as follows: mouse IFN-␥ receptor forward, 5Ј-CAAATACCAGGATAACTACTG-3Ј, and mouse IFN-␥ receptor reverse, 5Ј-CGAAAGACGTCTG-TATCCCTC-3Ј.…”

“…We evaluated the effects of IFN-␥ in HTLV-1-Tax transgenic mice that develop osteolytic bone tumors and hypercalcemia (16,17). Previously, it was shown that HTLV-1-Tax…”

“…Interestingly, IFN-␥ has been used to treat infantile osteopetrosis in which patients suffered from high bone mass secondary to osteoclast dysfunction or osteoblast hyperactivity, but the mechanism of action may be through modulation of the host immune system rather than direct effects on bone cells (13-15). However, the role of IFN-␥ in the treatment of osteolytic bone metastases has not been elucidated.We evaluated the effects of IFN-␥ in HTLV-1-Tax transgenic mice that develop osteolytic bone tumors and hypercalcemia (16,17). Previously, it was shown that HTLV-1-Tax…”