| The early diagnosis of malignant tumor becomes particularly important for it hasbeen increased steadily in recent years. Magnetic resonance imaging (MRI) is one ofthe most powerful clinical techniques with high spatial resolution and no ionizationradiation. Currently, various MRI contrast agents have low relaxation efficacy, shorthalf-life, poor specificity and high toxicity drawbacks. Therefore, the development ofa novel contrast agent is very necessary.The reported abroad said that the internal loading of US-tubes with aqueousGdCl3could greatly improve the effectiveness of its relaxation. Additionally, themulti-sites of SWCNTs could bind with drugs or molecular targets. All this resultssuggests a new way of constructing targeting antineoplastic drug delivery system forMRI contrast agents.Hyaluronic acid (HA) is a natural, linear, high molecular weightmucopolysaccharide with good biocompatibility and biodegradability. HA receptorhas been found on the surface of tumor cells recently. Therefore, sustained-releaseand tumor-targeting drug carriers with HA have been fabricated, because they canbind specifically to the HA receptor on the surface of tumor cells.In this research, a tumor-targeting carrier, HA-functionalized single-walledcarbon nanotubes (SWCNTs) was explored to deliver MRI contrast agents targetingto the tumor cells specifically. The Gd3+-ion loading may occur through the side-walldefects or end-of-tube openings by physical adsorption effects to construct targetingantineoplastic drug delivery system for Gd/HA-SWCNTs MRI contrast agents. Weconducted a comprehensive evaluation for this contrast agent by cellular uptakeexperiments, toxicity tests and MRI experiments. The results showed that Gd/HA-SWCNTs is an efficient, targeted, sustained-released and low toxicity magneticresonance contrast agent. The main contents are as follows:1. Construction of HA-SWCNTs vector and Gd/HA-SWCNTs targeted MRcontrast agent delivery system. SWCNTs was carboxylated by concentrated sulfuricacid and concentrated nitric acid to get SWCNT-COOH. HA then covalently attached to the SWCNT-COOH by the carrier arm of alkylene diamine，finally the Gd3+-ionloading may by physical adsorption effects to obtain targeting antineoplastic drugdelivery system for Gd/HA-SWCNTs MRI contrast agents. The covalent modificationof SWCNTs was tracking monitoring by TEM, UV-vis and FTIR. Then character ofthe covalent functionalization of HA-SWCNTs was detection of TGA. The drugloading and drug release character of Gd/HA-SWCNTs were evaluated, respectively.The results show that42.27%of HA has been successfully conjugatedwithSWCNTs-COOH; when the surfactant is10mg/ml of PC, ultrasound probes selectedfor30min, vector ratio of1:7, drug loading reached22.58%.2.Using the fluorescent microscope and flow cytometry method at differenttimes to tumor cells of the carrier system of the uptake condition. The fluorescentmicroscope results show that the signal of HA-SWCNTs group reached highlighted;the flow cytometry method results show the uptake of HA-SWCNTs group in MCF-7cellreached97.9%, and SWCNTs group has just reached87.4%.3.The safety evaluation of this MRI contrast agents was investigated in vitro andin vivo by SRB and HE staining. In vitro cytotoxicity study revealed thatHA-SWCNTs demonstrated almost no toxicity compared with free GdCl3at theconcentration of50μg/ml. Moreover, it demonstrated negligible systematic toxicitythrough the histopathological analysis, especially in liver and kidney.4.Using the chemical method for the determination of Gd/HA-SWCNTs of theuptake in tumor and targeted indexs. Determinate the imaging performance of thecontrast agent by small animal7.0T magnetic resonance imager. The results show thatthe absorption of Gd/HA-SWCNTs in tumor was high than other control groups, andits MRI imaging signal intensity higher and still have a signal at24h, these resultsillustrate the Gd/HA-SWCNTs contrast agent was not only tumor-targeted but alsocan persist in the body for a long time. |
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