Low-intensity continuous ultrasound triggers effective bisphosphonate anticancer activity in breast cancer.

Ultrasound (US) is a non-ionizing pressure wave that can produce mechanical and thermal effects. Bisphosphonates have demonstrated clinical utility in bone metastases treatment. Preclinical studies suggest that bisphosphonates have anticancer activity. However, bisphosphonates exhibit a high affinity for bone mineral, which reduces their bioavailability for tumor cells. Ultrasound has been shown to be effective for drug delivery but in interaction with gas bubbles or encapsulated drugs. We examined the effects of a clinically relevant dose of bisphosphonate zoledronate (ZOL) in combination with US. In a bone metastasis model, mice treated with ZOL+US had osteolytic lesions that were 58% smaller than those of ZOL-treated animals as well as a reduced skeletal tumor burden. In a model of primary tumors, ZOL+US treatment reduced by 42% the tumor volume, compared with ZOL-treated animals. Using a fluorescent bisphosphonate, we demonstrated that US forced the release of bisphosphonate from the bone surface, enabling a continuous impregnation of the bone marrow. Additionally, US forced the penetration of ZOL within tumors, as demonstrated by the intratumoral accumulation of unprenylated Rap1A, a surrogate marker of ZOL antitumor activity. Our findings made US a promising modality to trigger bisphosphonate anticancer activity in bone metastases and in primary tumors.

Bisphosphonates' antitumor activity: an unravelled side of a multifaceted drug class.

Bisphosphonates, especially nitrogen-containing bisphosphonates (N-BPs), are widely used to preserve and improve bone health in patients with cancer because they inhibit osteoclast-mediated bone resorption. In addition to their effects on bone, preclinical evidence strongly suggests that N-BPs exert anticancer activity without the involvement of osteoclasts by interacting with macrophages, endothelial cells and tumor cells, and by stimulating the cytotoxicity of γδ T cells, a subset of human T cells. This review examines the current insights and fronts of ongoing preclinical research on N-BPs' antitumor activity.

Bisphosphonates in preclinical bone oncology.

Bisphosphonates, especially nitrogen-containing bisphosphonates, are widely used to block bone destruction in cancer patients with bone metastasis because they are effective inhibitors of osteoclast-mediated bone resorption. In addition to their antiresorptive effects, preclinical evidence strongly suggests that nitrogen-containing bisphosphonates exert direct and indirect anticancer activities through inhibition of tumor cell functions, enhancement of the cytotoxic activity of chemotherapy agents, inhibition of tumor angiogenesis, and stimulation of antitumor immune reactions. This review examines the current evidence and provides insights into ongoing preclinical research on anticancer activities of these bisphosphonates in animal models of tumorigenesis and metastasis.

The molecular basis of bisphosphonate activity: a preclinical perspective.

Bisphosphonates are widely used to preserve and improve bone health in patients with cancer. Emerging evidence suggests that in addition to their effects on bone health, bisphosphonates may have anticancer activity. Some of the activity associated with bisphosphonates is observed in non-osteoclast cells; therefore, the bioavailability of bisphosphonates is briefly discussed. Structure-function correlations and the molecular and cellular mechanisms that underlie bisphosphonate activity are also examined. In addition to a detailed discussion of the molecular interaction between nitrogen-containing bisphosphonates and farnesyl pyrophosphate synthase and the formation of cytotoxic triphosphoric acid 1-adenosin-5'-yl ester 3-(3-methylbut-3-enyl) ester (ApppI), the effects of bisphosphonates on the transforming growth factor-beta (TGF)-beta pathway, the receptor activator of nuclear factor-kappaB (NFkappaB) ligand (RANKL)/osteoprotegerin (OPG) axis, and novel molecular targets are reviewed. Finally, a basis for the observed preclinical and clinical activity of bisphosphonates, including effects on apoptosis, cell proliferation, cell invasion, modulation of immune function, and suppression of tumor-mediated angiogenesis, is provided.

Metastasis and bone loss: advancing treatment and prevention.

Tumor metastasis to the skeleton affects over 400,000 individuals in the United States annually, more than any other site of metastasis, including significant proportions of patients with breast, prostate, lung and other solid tumors. Research on the bone microenvironment and its role in metastasis suggests a complex role in tumor growth. Parallel preclinical and clinical investigations into the role of adjuvant bone-targeted agents in preventing metastasis and avoiding cancer therapy-induced bone loss have recently reported exciting and intriguing results. A multidisciplinary consensus conference convened to review recent progress in basic and clinical research, assess gaps in current knowledge and prioritize recommendations to advance research over the next 5 years. The program addressed three topics: advancing understanding of metastasis prevention in the context of bone pathophysiology; developing therapeutic approaches to prevent metastasis and defining strategies to prevent cancer therapy-induced bone loss. Several priorities were identified: (1) further investigate the effects of bone-targeted therapies on tumor and immune cell interactions within the bone microenvironment; (2) utilize and further develop preclinical models to study combination therapies; (3) conduct clinical studies of bone-targeted therapies with radiation and chemotherapy across a range of solid tumors; (4) develop biomarkers to identify patients most likely to benefit from bone-targeted therapies; (5) educate physicians on bone loss and fracture risk; (6) define optimal endpoints and new measures of efficacy for future clinical trials; and (7) define the optimum type, dose and schedule of adjuvant bone-targeted therapy.

Antitumor effects of clinical dosing regimens of bisphosphonates in experimental breast cancer bone metastasis.

BACKGROUND: Bisphosphonates exhibit direct antitumor activity in animal models, but only at high doses that are incompatible with the clinical dosing regimens approved for the treatment of cancer patients with skeletal metastases. We compared the antitumor effects of clinical dosing regimens of the bisphosphonates zoledronic acid and clodronate in a mouse model of bone metastasis. METHODS: Mice (n = 6-10 per group) were treated with zoledronic acid, clodronate, or vehicle starting before (preventive protocols) or after (treatment protocols) intravenous injection with human B02/GFP.2 breast cancer cells, which express green fluorescent protein (GFP) and luciferase and metastasize to bone. Zoledronic acid was given as daily, weekly, or single doses at a cumulative dose of 98-100 microg/kg body weight, equivalent to the 4-mg intravenous dose given to patients. Clodronate was given as a daily dose (530 microg/kg/day), equivalent to the daily 1600-mg oral clinical dose given to patients. Bone destruction was measured by radiography, x-ray absorptiometry or tomography, and histomorphometry (as the ratio of bone volume to tissue volume). Skeletal tumor burden was measured by histomorphometry (as the ratio of tumor burden to soft tissue volume [TB/STV]) and luciferase activity. All statistical tests were two-sided. RESULTS: In treatment protocols, daily clodronate was less effective at decreasing the TB/STV ratio than daily (53% versus 87%, difference = 34%, 95% confidence interval [CI] = 16% to 44%, P < .001) or weekly (53% versus 90%, difference = 37%, 95% CI = 19% to 46%, P < .001) zoledronic acid-dosing regimens. Compared with vehicle, a single dose of zoledronic acid decreased tumor burden by only 16% (95% CI = 9% to 22%, P < .001). In preventive protocols, daily clodronate and daily or weekly zoledronic acid decreased the TB/STV ratio by 49% (95% CI = 40% to 57%, P = .006), 83% (95% CI = 68% to 98%, P < .001), and 66% (95% CI = 47% to 84%, P < .001), respectively, compared with vehicle, whereas a single dose of zoledronic acid decreased tumor burden by only 13% (95% CI = -2% to 28%, P = .84). Mice treated with a daily preventive regimen of clodronate or with a daily or weekly preventive regimen of zoledronic acid showed a decreased B02/GFP.2 cell tumor burden compared with vehicle, whereas a single preventive dose of zoledronic acid had no effect. CONCLUSION: Daily or repeated intermittent therapy with clinical doses of bisphosphonates inhibits skeletal tumor growth in a mouse model.

The antitumor potential of bisphosphonates.

Bisphosphonates are primarily known for their ability to inhibit osteoclast-mediated bone resorption and to slow the release of calcium and other bone minerals into the blood stream. However, recent preclinical research has shown that bisphosphonates also exhibit potent antitumor activity. Bisphosphonates reduce proliferation and induce apoptosis of tumor cell lines, and they inhibit tumor cell adhesion and invasion of the extracellular matrix in vitro. In addition, bisphosphonates have been shown to reduce skeletal tumor burden in a variety of animal models. This may reflect either direct antitumor effects or indirect effects via osteoclast inhibition and alteration of the bone microenvironment. The complex mechanisms by which bisphosphonates inhibit bone resorption and interfere with tumor growth and metastasis to bone are beginning to be understood. Research is ongoing to fully elucidate these biochemical mechanisms, and well-designed clinical trials are planned to investigate the antitumor potential of modern nitrogen-containing bisphosphonates in the clinical setting.