A Bisphosphonate With a Low Hydroxyapatite Binding Affinity Prevents Bone Loss in Mice After Ovariectomy and Reverses Rapidly With Treatment Cessation

Bisphosphonates (BPs) are a mainstay of osteoporosis treatment; however, concerns about bone health based on oversuppression of remodeling remain. Long-term bone remodeling suppression adversely affects bone material properties with microdamage accumulation and reduced fracture toughness in animals and increases in matrix mineralization and atypical femur fractures in patients. Although a “drug holiday” from BPs to restore remodeling and improve bone quality seems reasonable, clinical BPs have long functional half-lives because of their high hydroxyapatite (HAP) binding affinities. This places a practical limit on the reversibility and effectiveness of a drug holiday. BPs with low HAP affinity and strong osteoclast inhibition potentially offer an alternative approach; their antiresorptive effect should reverse rapidly when dosing is discontinued. This study tested this concept using NE-58025, a BP with low HAP affinity and moderate osteoclast inhibition potential. Young adult female C57Bl/6 mice were ovariectomized (OVX) and treated with NE-58025, risedronate, or PBS vehicle for 3 months to test effectiveness in preventing long-term bone loss. Bone microarchitecture, histomorphometry, and whole-bone mechanical properties were assessed. To test reversibility, OVX mice were similarly treated for 3 months, treatment was stopped, and bone was assessed up to 3 months post-treatment. NE-58025 and RIS inhibited long-term OVX-induced bone loss, but NE-58025 antiresorptive effects were more pronounced. Withdrawing NE-58025 treatment led to the rapid onset of trabecular resorption with a 200% increase in osteoclast surface and bone loss within 1 month. Cessation of risedronate treatment did not lead to increases in resorption indices or bone loss. These results show that NE-58025 prevents OVX-induced bone loss, and its effects reverse quickly following cessation treatment in vivo. Low-HAP affinity BPs may have use as reversible, antiresorptive agents with a rapid on/off profile, which may be useful for maintaining bone health with long-term BP treatment

Fluorescent Risedronate Analogues Reveal Bisphosphonate Uptake by Bone Marrow Monocytes and Localization Around Osteocytes In Vivo

Bisphosphonates are effective antiresorptive agents owing to their bone-targeting property and ability to inhibit osteoclasts. It remains unclear, however, whether any non-osteoclast cells are directly affected by these drugs in vivo. Two fluorescent risedronate analogues, carboxyfluorescein-labeled risedronate (FAM-RIS) and Alexa Fluor 647–labeled risedronate (AF647-RIS), were used to address this question. Twenty-four hours after injection into 3-month-old mice, fluorescent risedronate analogues were bound to bone surfaces. More detailed analysis revealed labeling of vascular channel walls within cortical bone. Furthermore, fluorescent risedronate analogues were present in osteocytic lacunae in close proximity to vascular channels and localized to the lacunae of newly embedded osteocytes close to the bone surface. Following injection into newborn rabbits, intracellular uptake of fluorescently labeled risedronate was detected in osteoclasts, and the active analogue FAM-RIS caused accumulation of unprenylated Rap1A in these cells. In addition, CD14high bone marrow monocytes showed relatively high levels of uptake of fluorescently labeled risedronate, which correlated with selective accumulation of unprenylated Rap1A in CD14+ cells, as well as osteoclasts, following treatment with risedronate in vivo. Similar results were obtained when either rabbit or human bone marrow cells were treated with fluorescent risedronate analogues in vitro. These findings suggest that the capacity of different cell types to endocytose bisphosphonate is a major determinant for the degree of cellular drug uptake in vitro as well as in vivo. In conclusion, this study shows that in addition to bone-resorbing osteoclasts, bisphosphonates may exert direct effects on bone marrow monocytes in vivo. © 2010 American Society for Bone and Mineral Researc

History of risedronate

Herein we review the discovery, development, commercial history and legacy of risedronate or NE-58095, a potent N-containing bisphosphonate developed by scientists at the Cincinnati Miami Valley Laboratories and the Norwich Eaton Laboratories of Procter and Gamble. It is characterized by a hydroxyl substituent (R1) and a pyridyl-methylene substituent (R2) at the carbon bridging two phosphonate moieties. It was shown to have greater potency than alendronate in cell-based systems while binding affinity to bone matrix was lower than alendronate, accounting for the relatively rapid offset of bone turnover inhibition when therapy is discontinued. Risedronate was shown to significantly reduce serum alkaline phosphatase and clinical features in patients with Paget's disease and was approved for this indication, at a dose of 30 mg daily for 2 months, in 1998. Formal dose response testing for treatment of osteoporosis was not performed. In large Phase 3 studies, 5 mg risedronate daily increased bone mineral density more than did the 2.5 mg dose. As a result, the 2.5 mg dose was dropped from most of the Phase 3 studies after 12 months. The 5 mg daily dose was approved for treating and preventing postmenopausal osteoporosis and glucocorticoid-induced osteoporosis in 2000. The drug was subsequently approved for treating men with osteoporosis. Following the leads of other companies, weekly and monthly preparations were developed and approved, based on non-inferiority BMD studies vs the 5 mg daily oral dose as was a unique dosing regimen of 75 mg given on 2 consecutive days each month. Finally, to overcome the effect of food on limiting the already poor gastrointestinal absorption of the drug, a once-weekly oral preparation containing the chelating agent EDTA and with an enteric coating delaying dissolution until the tablet was in the small intestine was approved in 2010 to be administered after breakfast. The Alliance for Better Bone Health, a collaboration between Procter & Gamble Pharmaceuticals and sanofi-aventis U.S. was formed to market risedronate as Actonel® and, subsequently, Actonel-EC® or Atelvia®. These drugs are still marketed by sanofi-aventis in some countries. The sale of the pharmaceutical division of Procter & Gamble to Warner Chilcott (US) was based, in large part, on the perceived value and marketability of the risedronate drugs. When marketing targets of Warner-Chilcott were not met, the rights of risedronate were sold to Allergan USA, Inc. which never actively promoted the drug. Generic forms of risedronate were introduced into the United States in 2015 but are rarely used, although several generic forms are actively marketed in other countries

How Do Bisphosphonates Inhibit Bone Metastasis In Vivo?1

Bisphosphonates are potent inhibitors of osteoclast-mediated bone resorption and have demonstrated clinical utility in the treatment of patients with osteolytic bone metastases. They also exhibit direct antitumor activity in vitro and can reduce skeletal tumor burden and inhibit the formation of bone metastases in vivo. However, whether such effects are caused by a direct action of bisphosphonates on tumor cells or indirectly through inhibition of bone resorption remains unclear. To address this question, we used here a structural analog of the bisphosphonate risedronate, NE-58051, which has a bone mineral affinity similar to that of risedronate, but a 3000-fold lower bone antiresorptive activity. In vitro, risedronate and NE-58051 inhibited proliferation of breast cancer and melanoma cell lines. In vivo, risedronate and NE-58051 did not inhibit the growth of subcutaneous B02 breast tumor xenografts or the formation of B16F10 melanoma lung metastasis. In contrast to NE-58051, risedronate did inhibit B02 breast cancer bone metastasis formation by reducing both bone destruction and skeletal tumor burden, indicating that the antitumor effect of bisphosphonates is achieved mainly through inhibition of osteoclast-mediated bone resorption

Synthesis of a Bone-Targeted Bortezomib with In Vivo Anti-Myeloma Effects in Mice

Multiple myeloma (MM) is the most common cancer affecting the bone and bone marrow and remains incurable for most patients; novel therapies are therefore needed. Bortezomib (Btz) is an FDA-approved drug for the treatment of patients with MM. However, its severe side effects require a dose reduction or the potential discontinuation of treatment. To overcome this limitation, we conjugated Btz to a bisphosphonate (BP) residue lacking anti-osteoclastic activity using a novel chemical linker and generated a new bone-targeted Btz-based (BP-Btz) proteasome inhibitor. We demonstrated that BP-Btz, but not Btz, bound to bone slices and inhibited the growth of MM cells in vitro. In a mouse model of MM, BP-Btz more effectively reduced tumor burden and bone loss with less systemic side effects than Btz. Thus, BP-Btz may represent a novel therapeutic approach to treat patients with MM