The Study Of Novel Doxorubicin Targeted Delivery System In Cancer Therapy

Cancer is one of the most lethal desease in the world.Anthracyclines such as doxorubicin(DOX)are leading chemotherapeutic agents with a broad spectrum of antitumor activity.DOX is widely used in many cancers,such as leukaemia,lymphoma,breast cancer,lung cancer and so on.However,cumulative DOX could cause slow loss of myofibrils and vacuolization of myocardial cells and,eventually,heart failure.The myocardial toxicity of DOX greatly limits its clinical application.For there are no other chemotherapeutic agents that could completely take place of anthracyclines recently,researchers are devoted to finding ways which could decrease the cardiac toxicity of anthracyclines.One of the most effective ways to decrease the cardiac toxicity of anthracyclines is to reduce their distribution in cardiac tissues by targeted delivery vehicles such as liposomes and polyplexes.In the first part of the paper,we developed a self-assembled,tumor microenvironment responsive delivery system for DOX.The core of the carrier was built upon the DOX/DNA intercalations,which were further combined with cationic gelatin(C-gel)to form the complex GDD.GDD was then packaged into a complex,namely HDD,based on the electrostatic interactions between the positively charged C-gel and negatively charged human serum albumin.The HSA molecules on the surface of the complex HDD effectively helped the particle evade the filtration of the body when injected into the circulation and then passive accumulation into the tumor sites via the enhanced permeability and retention effect(EPR effect).After entering the tumor tissue,where albumin is rapidly consumed,GDD was release from HDD and the C-gel was then digested by the tumor-specific matrix metalloproteinase(MMPs)to free DOX/DNA intercalations.DNases in the tissue could completely destroy the DNA molecules to release DOX into the microenvironments.After a series of in vitro optimization tests and the analysis of tumor responsive release ability,we evaluated the tissue distribution and toxicity of HDD,and then the anti-cancer capacity was studied in two animal models with cancer.The results are shown below.Firstly,the morphology measured by TEM demonstrated that HDD was a nanoparticle with diameter of about 80 nm.The zeta potential was-23 mV.Then enzymes mix which could digest the components of HDD and there specific inhibitors were used to examine the release capacity of HDD.The results showed that DOX could only be released in tumor,which reflected the tumor responsive drug release ability.The tissue distribution study demonstrated HDD could obviously prolong the circulation time of DOX,decrease its distribution in heart and increase its level in tumor.The distribution characteristic of HDD reduced the toxicities of DOX to heart,liver and other tissues.Then we examined the anti-tumor activity of HDD in two animal tumor models.HDD showed much higher anti-cancer capacity than free DOX.Theoretically,the dosage of anthracyclines could be reduced through increasing the sensitivity of tumor to anthracyclines,therefore decreasing the cardiotoxicity and increasing the safety of anthracyclines.So in the second part of the paper we improved our system by introducing a microRNA-miR-16 mimics to replace DNA.miR-16 has the pro-apoptotic bioactivity.Its use could increase the sensitivity of tumor to DOX.We also replaced gelatin with PEI which is a typical complex with ability of endosomal escape to guarantee miR-16 reaching cytosol.The core of the carrier was built upon the DOX/miR-16 intercalations,which were further combined with PEI to form the complex PMD(PEI+miR16+DOX).PMD was then packaged by human serum albumin to form HMD(HSA+PEI+miR16+DOX).The HSA molecules on the surface of the HMD effectively helped the particle evade the clearance by the mononuclear phagocytic system(MPS)when injected into the circulation and then passively accumulated into the tumor sites.After entering the tumor tissue,where albumin is rapidly consumed,PMD was release from HMD and entered the tumor cells.Then PEI could release miR-16/DOX to cytosol via endosomal escape.miR-16 was unwound by proteins such as Argonaute 2.Then the single strand of miR-16 was assembled into RISC complex to exert post-transcriptional regulation of Bcl-2.Meanwhile,DOX was release from the complex to exert its antitumor activity in nucleus.The results were shown below.HMD was a global particle with the diameter of 50 nm and the zeta potential was-18.43 mV.Ago 2 could unwind the miRNA duplex and release DOX,which can be inhibited by ATA,an Ago 2-loading inhibitor.Using the confocal microscope,we could see DOX in the nucleus increased gradually.The tissue distribution study showed HMD could decrease the concentration of DOX in heart and increase it in tumor.In HepG2 and SMMC-7721,the level of Bcl-2 protein was decreased after transfected with miR-16 precursor.Moreover,DOX could increase the transfection rate of miR-16 maybe via reducing the particle size.miR-16 could obviously increase the sensitivity of cells(HepG2 and SMMC-7721)to DOX.The anti-tumor study of HMD demonstrated the use of miR-16 could increase the anti-cancer ability of DOX,which could reduce the usage of DOX while achieving the same antitumor effect,and eventually alleviate cardiotoxicity.In summary,in this paper we developed a targeted delivery system for DOX which could response to the tumor physiological and pathological characteristics.And then we improved the all-round properties of this system by introducing a tumor suppressive microRNA.This targeted drug delivery system could effectively elevate the drug distribution in tumor and reduce it in heart,which decreased the cardiotoxicity and increased the safety and ani-tumor capacity obviously.This study was an innovative application of the natural characteristics of DOX and nucleotide combination with high efficiency.The use of microRNA as a part of the carrier and as an anti-tumor component is a great innovation of the study.At last,the materials used in the system are all bio-derived,with good biocompatibility,which give this system a sound transformation prospect.