A Novel Bone-targeted Magnetic Resonance Imaging Contrast Agent

Magnetic resonance imaging(MRI) plays a key role in clinical diagnosis. However, currently clinically applied MRI contrast agents have no tissue targeting, low relaxation rate and weak stability. Osteosarcoma morbidity is high, occupying 35% of total bone tumors. No bone-targeted MRI contrast agents are presented in clinics. In this study, a novel bone-targeted MRI contrast agent, Gd2-DTPA-bis(ALN), was designed and prepared. The in vitro/in vivo studies of it were performed. The clinically applied contrast agent, Gd-DTPA(Magnevist®) was as control.1) The design and synthesis of a novel bone-targeted MRI contrast agent. Through a multi-step chemical reaction, alendronate which can target to bone, has been connected to Magnevist®, a contrast agent used in clinic. We can get a novel bone-targeted contrast agent, Gd2-diethylenetriaminepentaacetate-bis(alendronate)(Gd2-DTPA-bis(ALN).2) The quantitative analysis of the new bone-targeted contrast agent. The novel bone-targeted contrast agent Gd2-DTPA-bis(ALN) had no double bond structure, no ultraviolet absorption. It is difficult to determinate its quantitative with spectrographic method currently. We used inductively coupled plasma mass spectrometer(ICP-MS) to determinate the content of Gd in drugs. The content of Gd is 23.8%. Then we can know the content of Gd2-DTPA-bis(ALN). This method is highly sensitivity, easy to operation and so on.3) The adsorption between new bone-targeted Contrast agent and hydroxyapatite. Hydroxyapatite is the main component of bone. Gd2-DTPA-bis(ALN) had higher adsorption rate about 39.925%. However, Gd-DTPA had no almost. New bone-targeted contrast agent can target to bone in vivo.4) Determination the relaxation rate of new bone-targeted contrast agent. Paramagnetic MRI contrast agent can increase the quality of magnetic resonance angiography. Experiments show that the relaxation rate of new bone-targeted contrast agent Gd2-DTPA-bis(ALN) is 3.806mmol-1.L.s-1. It is higher than Gd-DTPA, which is 2.718 mmol-1.L.s-1. The result proved that the MRI effect of Gd2-DTPA-bis(ALN) was higher than that of Gd-DTPA.5) Acute toxicity study on nude mice. Injection different dose of Gd2-DTPA-bis(ALN), we observed the toxicological effect. The median lethal dose(ID50) was 0.66 g/Kg, the zero lethal dose was 0.375mol/Kg,the 100% lethal was 3.0mol/Kg.6) Bone targeting study of the new bone-targeted contrast agent in osteosarcoma cells. Gd2-DTPA-bis(ALN) has bis(phosphonic acid), which can affine to osteoclasts and osteoclasts. Osteosarcoma UMR106 as model, we determined the effect of Gd2-DTPA-bis(ALN) and Gd-DTPA to osteosarcoma. When the concentration of Gd2-DTPA-bis(ALN) is low of 10-5mol/L, it is no effect on osteosarcoma. When is 10-3mol/L, it can promoted proliferation. However, Gd-DTPA had no this function.7) The studies of iconography of new bone-targeted contrast agents in osteosarcoma model. Through injecting the osteosarcoma UMR106 cells into proximal tibia and distal femur, we have established the osteosarcoma model in BALB/C mice. And we evaluated the model by X radial. Gd2-DTPA-bis(ALN) was major in the great vessels at 0-5 min, in osteosarcoma at 25-50 min, in liver and kidney at 75 min. However, Gd-DTPA was major in the great vessels at 0-5 min, in the whole body after 5 min. Gd2-DTPA-bis(ALN) showed higher MRI effect than Gd-DTPA. ICP-MS was used to determine Gd in vivo.The result above can provide that a novel bone-targeted contrast agent was prepared, which is bone-targeted, higher relaxation, stability and safe.