Nano Controlled Release Systems And Its Application In Restenosis And Cancer Therapy

Cardiovascular diseases and cancer seriously threaten human health, and it is of positive significance to apply nanotechnology to treatment of these diseases.At present, percutaneous transluminal coronary angioplasty (PTCA) and stent implantation is one of the most effective treatment means for coronary atherosclerotic heart disease. However, the incidence of restenosis within6months after the operation is as high as30%to50%, becoming a main cause for the restricted long-term clinical efficacy and the increased medical expenses. Recent studies show that the difficult healing of blood vessel endothelium and the neointimal proliferation emphraxis arising from excess migration and proliferation of vascular smooth muscle cell are two main causes for the formation of restenosis. Prevention and treatment of restenosis using systematic administration is often restricted by systematic toxic and side effect as a result of overdose and such factors as low efficiency of drug distribution and metabolizing in blood vessel, resulting in hardly effective local concentration of drug in blood vessel and short lasting of effective local concentration of drug. Local administration can directly deliver the high concentration therapeutic agent to the target tissue, improving the efficiency of administration and avoiding the above-mentioned defects of systematic administration. Existing clinical tests have confirmed the good safety and feasibility of local administration, but the clinical efficacy is unsatisfactory, which is mainly caused by poor local retention of drug. Nanotechnology can be used in manufacturing pharmacy to improve infiltration and redistribution of drug in tissues and increase local retention of drug.Rapamycin (RPM) is a kind of macrolide antibiotic produced by means of fermentation of streptomyces hygro scopicus. In in-vitro experiments, this drug can inhibit VSMC migration and proliferation, in animal experiments and clinical tests it can reduce post-injury intimal proliferation and effectively lower the incidence of restenosis6months to1years after PTCA operation. It is one of the drugs with the greatest clinical application potential for prevention and treatment of restenosis at present. However, RPM also has such pharmacological defects as toxic effect, restricted absorption, poor hydrophilicity, restricted biological application by excipient and stability, sensitivity to pH and low treatment index. In Chapter Two of this paper, preparation of nanotechnology based RMP as anti-proliferation drug for vascular restenosis is explored.In Chapter Three, an innovative double-function concept brought forward based on the two main causes for vascular restenosis, that is difficult healing of endothelium and excess proliferation of vascular smooth muscle cell; the treatment effect of VEGF/paclitaxel double-function nanoparticle for vascular restenosis on rabbit saccule injury model is verified by saccule perfusion; nanotechnology based micropore double-function intravascular stent is prepared using ultrasonic spraying process, and finally the effect of such stent to inhibit vascular restenosis in experimental pig body is observed.Paclitaxel (PTX) is anti-proliferation drug with the widest application in clinic. It is diterpenes compound extracted from plants in Taxus Genus, Taxaceae Family. Being highly fat-soluble, it can induce and promote polymerization of tubulin, prevent depolymerization, stabilize tubulin, make cell rein in G2/M phase, and thus cause cell death. This drug is used for clinical treatment of cancer, but its formulation used clinically may easily cause anaphylactic reaction, so an ideal new drug form is in urgent need. In Chapter Four of this paper, such new drug form is explored, and its effect to inhibit breast cancer is verified on mouse mammary cancer model.The detailed contents of this study are as follows:1. RPM-PLGA NPs with a mean particle diameter of246.8nm and a mean drug load of19.42%were successfully prepared using ultrasonic emulsification&solvent volatilization method. Observed under scanning electron microscope, these NPs were spheres with smooth surface, and their in-vitro release was similar to a zero-order process, releasing75%drug by the end of Week2. Then,5mg/ml RPM-PLGA NPs were perfused into abdominal aorta cavity of New Zealand rabbit through dispatch perfusion balloon. After the administration7days, the drug concentration in local tissue was still as high as22.45±2.64μg/10mg dry weight, on the14th day after the administration the drug concentration in the tissue was4.64±0.77μg/10mg dry weight, and on the21st day after the administration no drug concentration was detected using HPLC method. A Chinese experimental minipig oversize saccule injury coronary artery model was successfully developed, and the coronary arteriongraphy on the30th day after the operation showed that:there was no significant difference among the control group perfused with physiological saline, the control group perfused with blank PLGA NPs and the group perfused with RPM, as indicated in vascular morphological indexes and coronary arteriongraphy; the degree of hemadostenosis in the group perfused with RMP-PLGA NPs (23.4±5.35%) was significantly lower than the physiological saline control group and the blank NPs control group (respectively46.07±18.33%and52.20±8.74%, P<0.01in both groups) and the group perfused with RMP (39.32±9.91%, P<0.05); the area of neointimal, the proliferation index and the NEELA/EELA ratio of the RMP-PLGA group on the30th day after coronary artery injury were significantly lower than the three control groups (P<0.05in all the three groups). Immunohistochemical staining results indicated that the RPM group had lower PCNA positive cell expression rate and MMP-2&TIMP-2protein positive expression volume than the physiological saline control group and the blank NPs control group, and the experimental group had significantly higher hybridization in situ p27mRNA level than the three control groups.2. VEGF/PTX double-function nanoparticles (VEGF/PTX NPs) were successfully prepared, with a mean particle diameter of78.82nm and mean Zeta electric potential measurement of-12.2. The PTX entrapment rate was92%, the PTX load was28.58%, the gene entrapment rate was98%, and the gene load was4.67%. After in-vivo perfusion into saccule of rabbit, the vascular restenosis in both the VEGF NPs group and the VEGF/PTX NPs groups was inhibited. Particularly, good healing was observed in VEGF NPs group. Immunohistochemical results indicated that the VEGF NPs group and the VEGF/PTX NPs groups had lower PCNA positive cell expression rate and MMP-2&TIMP-2protein positive expression volume than the physiological saline control group and the blank NPs control group. The double-function nanotechnology micropore stent used in experimental pig body effectively inhibited vascular restenosis, and lumen loss in the VEGF/PTX NPs group was as low as22.3%±8%, significantly better than the48%provided by the TAXUS(?) stent sold by Boston Scientific Corporation. This study provides a new thought and approach for prevention and treatment of cardiovascular restenosis, and may probably provide a new kind of genetical stent for clinical treatment of vascular restenosis.3. Paclitaxel nanoparticles (PTX NPs) with a mean particle diameter of233.74nm, entrapment efficiency is84.3%and PTX loading capacity is about19.58%, which means were successfully prepared, and was used to inhibit cancer growth in TA2mouse breast cancer pulmonary metastasis model. As shown in the two week injection observation, the cancer inhibition rate of the middle dose PTX NPs group was70.21%, that of the high dose PTX NPs group was84.16%, and that of the Taxol positive control group was48.96%, indicating a significant difference (P<0.001). Such rate of the low dose PTX NPs group was45.47%, which also had significant difference from the Taxol positive control group (P<0.001).