Development Of CEST MRI-guided Liposome-based Nanoparticle Drug Delivery Systems

BackgroundFunctionalized nanomedicine enables to offer numerous novel approaches for cancer therapy.However,the tumor microenvironment is highly heterogeneous.Individualized evaluation of the drug delivery efficiency within the tumor and optimization of nanomedicine treatment strategy remain unsolved problems.Theranostic nanomedicine not only can diagnose diseases non-invasively,but also monitor the image-guided drug delivery and biodistribution,in order to predict or improve the therapeutic efficiency.However,different image technologies have their own indications and limitations.So clinical translations of theranostic nano-probes still faces many bottlenecks.Chemical exchange saturation transfer(CEST)technology is a novel molecular image method based on chemical exchange and saturated signal without metal or chemical labeling.The diamagnetic CEST contrast agents demonstrate great potential for clinical translation owing to the advantages of good sensitivity and biocompatibility.PurposeHere,this study attempts to prepare two diamagnetic chemical exchange saturated transfer liposome nano-probes to explore the application of CEST MRguided iodixanol liposomes and iRGD-targeted metformin liposomes in tumor distribution and uptake.(1)To explore the feasibility to monitor the iodixanol liposomes by CT and CEST MR non-invasively and reveal the EPR-mediated passive targeted effect of iodixanol liposomes in xenografted CT26 colon cancer mouse model.(2)To explore the feasibility to monitor the iRGD targeted metformin liposomes by CEST MR non-invasively and reveal the improvement in drug delivery using iRGD-mediated active targeted effect of metformin liposomes in xenografted KPC mutant pancreatic cancer mouse model.Method(1)Characterize the CEST signal of free iodixanol in different experimental setting using 400MHz MR scanner;and characterize the bimodal CT/CEST MR density/signal of iodixanol liposomes prepared by hydration extrusion method.(2)Plot the UV/X-ray/CEST MR quantitative calibration curves and evaluate in vitro release kinetics of iodixanol liposomes by UV/X-ray/CEST MR.(3)Establish BALB/c mice bearing CT26 xenografted colon tumor model.CT scans at pre-injection,day 1,day 2 and day 3 post-injection and CEST MR at day 3 post-injection were performed in iodixanol liposomes and PBS liposomes groups without TGFa injection.CT and CEST MR scans were performed in iodixanol liposomes groups with TGFa injection on day 3 post-injection.Compare CT/CEST MR guided intratumor distribution of iodixanol liposomes.Finally,the tumors were taken out and stained after MR scan for fluorescence microscopy to validate the results of CT/CEST MR.(4)Characterize the CEST signal of free metformin in different experimental setting using 400MHz MR scanner;and characterize the CEST MR signal of metoformin liposomes prepared by hydration extrusion method.(5)Draw the UV/CEST quantitative calibration curve and evaluate in vitro release kinetics of metformin liposome by the UV/CEST MR.(6)Prepare iRGD targeted metformin liposomes.Establish KPC mutant C57/BL6J mice bearing xenografted pancreatic tumor model.CEST MR scan was performed to detect and compare the intratumor uptake of iRGD targeted and nontargeted metformin liposomes at pre-injection,3 hours and 15 hours post-injection.Finally,the tumors were taken out and stained after MR scan for fluorescence microscopy to validate the results of CEST MR.Results(1)Free iodixanol solution and iodixanol liposomes have the same CEST MTRasym signal characteristics.(2)UV results demonstrated that the release kinetics of iodixanol liposomes showed a biphasic release pattern with rapid release in first 12 hours and a plateau phase after 24 hours.The concentration and release rate of iodixanol liposomes quantified by CEST MR and X-rays were similar to UV measurements.(3)CT/CEST MR showed that iodixanol liposomes mainly accumulated at the edge of the tumor without TNFa injection and no density/signal changes were observed in the central region of the tumor.After TNFa injection,CT/CEST MRI showed iodixanol liposome entered the tumor central region and the CEST MR signal within whole tumors increased almost 40%.Fluorescence microscopy results showed that iodixanol liposome accumulated at tumor edge without TNFa injection and tumor center with TNFa injection,which were consistent with CT/CEST MR results.(4)Free metformin solution and metformin liposomes have the same CEST MTRsym signal characteristics.(5)UV results showed metformin liposomes released out rapidly within the first hour;The concentration and release rate of metformin liposomes quantified by CEST MRI were similar to UV measurements.(6)CEST MR showed that the MTRasym signal increased by about 2%at 1.8 ppm in the iRGD targeted group and the CEST MR signal within the tumor in the iRGD targeted group was higher than that in the non-targeted group after 15 h postinjection.Fluorescence microscopy showed more metformin liposomes were found within the tumor in the iRGD targeted group,which was consistent with CEST MR result.ConclusionIn this study,two diamagnetic CEST MR guided iodixanol liposome and metformin liposome probes were prepared.The bimodal CT/CEST MRI can be used to monitor the EPR effect mediated passive intratumor biodistribution of iodixanol liposomes in BALB/c mice bearing CT26 xenografted colon tumor model.CEST MRI can be used to monitor the drug delivery improvement of the iRGD-targeted metformin liposomes in KPC mutant C57/BL6J mice bearing xenografted pancreatic tumor model.Therefore,diamagnetic CEST MR image is a novel approach for image-guided drug delivery,which is expected to provide more accurate individualized information for tumor nanomedicine.