La(iii) biodistribution profiles from intravenous and oral dosing of two lanthanum complexes, La(dpp)3 and La(XT), and evaluation as treatments for bone resorption disorders

Trivalent lanthanum (La³⁺) has the potential to treat bone resorption disorders (such as osteoporosis) by eliciting a bone-building response in the cells which control skeletal remodelling. Because La³⁺ suffers from extremely poor intestinal absorption, specifically designed chelators are required in order that a biologically active form of lanthanum can be administered orally. Two such chelators, 1,2-dimethyl-3-hydroxy-4-pyridinone (Hdpp) and bis-{[bis(carboxymethyl)amino]methy}phosphinic acid (H₅XT), have previously been the subjects of extensive physical, in vitro, and in vivo testing as the tris- and mono-lanthanum(iii) complexes La(dpp)₃ and La(XT), respectively. In this manuscript, we expand upon those studies to include 4-week intravenous (IV) and oral La³⁺ biodistribution profiles, which show that the metal ion initially accumulates in the liver followed by preferential redistribution and retention by bone. Of the two compounds, La(XT) demonstrates the more favourable in vivo characteristics, therefore dose-dependent oral biodistribution studies were carried out with this complex. These show drug saturation above a dose of 100 mg kg^-1 day^-1, so liver histology was performed in order to assess any potential toxicity. Finally, we improve upon the physical characterization of La(dpp)₃ to include a single crystal X-ray structure, which exhibits an 8-coorindate La³⁺ centre with two bound water molecules, and a disordered exoclathrate-type hydrogen bonded network.

Angiogenesis in spontaneous tumors and implications for comparative tumor biology

Blood supply is essential for development and growth of tumors and angiogenesis is the fundamental process of new blood vessel formation from preexisting ones. Angiogenesis is a prognostic indicator for a variety of tumors, and it coincides with increased shedding of neoplastic cells into the circulation and metastasis. Several molecules such as cell surface receptors, growth factors, and enzymes are involved in this process. While antiangiogenic therapy for cancer has been proposed over 20 years ago, it has garnered much controversy in recent years within the scientific community. The complex relationships between the angiogenic signaling cascade and antiangiogenic substances have indicated the angiogenic pathway as a valid target for anticancer drug development and VEGF has become the primary antiangiogenic drug target. This review discusses the basic and clinical perspectives of angiogenesis highlighting the importance of comparative biology in understanding tumor angiogenesis and the integration of these model systems for future drug development.