Construction Of Supramolecular Systems Based On Nucleobases For Drug Delivery

Supramolecular chemistry has developed a wide range of very powerful procedures for creating ever more sophisticated molecules and materials with new functions.During the past two decades,supramolecular chemistry aiming at constructing highly complex and functional chemical systems based on noncovalent interactions has made great progress in a wide range of fields including molecular recognition,self-assembly,materials design and application.To date,a great progress has been achieved in synthesis and self-assembly of supramolecular systems.However,few research focus on the functionalization of supramolecular systems and their biomedical applications,especially for the supramolecular systems based on the hydrogen bonding interactions.Therefore,how to design and develop smart supramolecular systems with ease of preparation,tunable function and highly stimuli-responsive ability for biomedical applications based on reversible characteristics of noncovalent interactions,is still the frontier scientific issue in the field of supramolecular chemistry.In this dissertation,inspired by molecular recognition of nucleobases in DNA and RNA,a series of smart supramolecular systems based on nucleobase with diverse structures and functions have been successfully constructed by using suparmolecular strategies.Moreover,these supramolecular systems as functional biomaterials have been investigated through in vitro and in vivo experiments for a variety of biomedical applications including drug delivery and cancer therapy.This dissertation can be divided into five major sections,and the main research contents and conclusions are shown as follows:1.Supramolecular copolymer micelles based on the complementary multiple hydrogen bonds of nucleobases for drug deliveryStimuli-responsive micelles have gained widespread attention for programmable delivery systems in which the release of drugs can be readily controlled by exerting an appropriate stimulus.At present,most polymeric micelles are designed and prepared based on labile covalent bonds.Generally,these stimuli-responsive polymeric micelles based on covalent bonds exhibit slow release of drugs in the tumor microenvironment.However,for cancer therapy,it is often more desirable to accomplish rapid drug release after micelles arrive at the pathological sites,which may enhance the therapeutic efficacy as well as reduce probability of drug resistance in cells.Therefore,it is necessary to design and exploit novel polymeric micelles with rapid response to tumor microenvironment.In this work,novel supramolecular copolymer micelles with stimuli-responsive abilities were successfully prepared through the complementary multiple hydrogen bonds of nucleobases and then applied for rapid intracellular release of drugs.The supramolecular amphiphilic block copolymers were formed through multiple hydrogen bonding interactions between adenine-terminated poly(?-caprolactone)and uracil-terminated poly(ethylene glycol),which further self-assembled into supramolecular nanomicelles in aqueous solution.The supramolecular copolymer micelles were sufficiently stable in water but prone to fast aggregation in acidic condition due to the dynamic and sensitive nature of noncovalent interactions.As a hydrophobic anticancer model drug,doxorubicin was encapsulated into these supramolecular copolymer micelles.In vitro release studies demonstrated that the release of drug from micelles was significantly faster at mildly acid pH compared to physiological pH.In vitro cell evaluation showed that doxorubicin-loaded micelles had high anticancer efficacy against HeLa cancer cells.Hence,these supramolecular copolymer micelles based on the complementary multiple hydrogen bonds of nucleobases are very promising candidates for rapid controlled release of drugs.2.Supramolecular amphiphilic multiarm hyperbranched copolymers based on nucleobases for anticancer drug deliveryDespite their great potential for drug delivery,linear amphiphlic block copolymers and their assemblies as drug carriers still face some inevitable problems.Firstly,polymeric assemblies based on linear amphiphlic block copolymers are easy to disintegrate into unimers at concentrations below the critical micelle concentration when subjected to high dilution in the circulating blood,which may lead to serious side effects.Secondly,their drug loading content and efficiency are relatively low.Additionally,the linear polymers lack structural diversity,which could not satisfy the diversified demand for clinical applications.Therefore,it is still a great challenge to design intelligent polymeric nanocarriers.In this study,novel supramolecular amphiphilic multiarm hyperbranched copolymers were successfully constructed through the molecular recognition of nucleobases.These supramolecular hyperbranched polymers not only have similar properties to conventional covalent-linked multiarm hyperbranched copolymers,but also possess a dynamic and tunable nature.They self-assembled into pH-responsive micelles with low critical micelle concentration because of non-covalent connection and hyperbranched architecture.The size of the self-assembled micelles could be easily tailored by changing the ratio of hydrophobic core and hydrophilic arms.In vitro study showed that the supramolecular hyperbranched copolymer could encapsulate the anticancer drug doxorubicin and release them in a controlled manner,thus resulting in a significant reduction in the viability of tumor cells.3.Salt/pH dual-responsive supramolecular brush copolymer micelles for drug deliveryTo realize an efficient delivery of drugs,there are two basic requirements for the design of ‘‘smart'' polymeric drug carriers.Firstly,the polymer carrier should respond rapidly to intracellular stimulus and consequently release the drugs in the pathologic area.Secondly,a well-designed polymeric nanocarrier should have a high loading efficiency.Considering these two requirements,a new type of salt/pH dual-responsive micelles based on supramolecular amphiphilic brush copolymers was developed for the anticancer drug delivery owing to the fact that the tumor tissues show low pH and high salt concentration.Due to their compact architecture,they exhibited higher drug loading content and efficiency,thereby providing a sufficient concentration of drug in the tumor cells.They showed lower critical micelle concentration,which is beneficial for the stability of micelles.Supramolecular brush copolymers could self-assemble into smaller micelles,which could be rapidly localized intracellularly and subsequently provoked by the acidic pH and high salt concentration to release the drug,leading to higher anticancer efficacy with reduced side effects.The results showed that suparmolecular brush copolymer micelles were stable enough in a neutral environment(pH ? 7.4),whereas rapid disassembly was observed under the acidic environment with high salt concentration.Therefore,they could release the drug in response to the intracellular level of pH and salt concentration at tumor site and enhance the anticancer activity,which endows them as a promise candidate for delivering anticancer drugs.4.Preparation and anticancer activity evaluation of supramolecular nucleoside phospholipids and liposomesDespite of great advances of phospholipids and liposomes in clinical therapy,very limited success has been achieved in the preparation of smart phospholipids and controlled-release liposomes for in vivo drug delivery and clinical trials.It is of great significance to develop the responsive phospholipids and liposomes with high sensitivity and ease of chemical synthesis for in vivo drug delivery and clinical trials.Here we report a supramolecular approach to synthesize novel supramolecular nucleoside phospholipids,which could self-assemle into liposome-like bilayer structures with controlled size and property in aqueous solution,exhibiting fast stimuli-responsive ability due to the hydrogen bonding connection.Compared to traditional approaches,the present supramolecular synthesis greatly reduces the need of tedious chemical synthesis,including reducing the strict requirements for multistep chemical reactions,and the purification of the intermediates and the amount of waste generated.In vitro and in vivo evaluations demostrated the resulted supramolecular liposomes from nucleoside phospholipids could effectively transport drug into tumor tissue,rapidly enter tumor cells,and controllably release their payload in response to an intracellular acidic environment,thus resulting in a much higher antitumor activity than conventional liposomes.The present supramolecular nucleoside phospholipids represent an important evolution in comparison to conventional covalent-bonded phospholipid systems.5.Supramolecular amphiphilic drug-drug nanodelivery system for cancer therapyNanodrug delivery systems have demonstrated better therapeutic efficacy again tumor and fewer side effects over free drugs.However,almost all carriers have no therapeutic efficacy by themselves.Even worse,a lot of carriers show low drug loading capacity and may cause side-effects to kidneys and other organs in the course of degradation,metabolism,and excretion,such as high toxicity and serious inflammation.It can be imagined that if the anticancer drugs could self-assemle into nanoparticles by themselves without the help of nanovehicles,a promising drug self-delivery system integrating both the advantages of free drugs and nanocarriers could be expected.Here,we develop a new kind of supramolecular drug self-delivery system through the molecular recognition of base analog for cancer therapy.The hydrophobic anticancer drug raltitrexed and the hydrophilic anticancer drug clofarabine could self-assemble into stable nanoparticles through molecular recognition in aqueous solution,which promotes their cellular uptake and facilitates the accumulation of drugs in tumor tissues.After cellular internalization,the hydrogen bonding interaction between hydrophilic and hydrophobic drugs was broken to accecelarate the release of free clofarabine and reltitrexed,resulting in an excellent anticancer activity in vitro and in vivo.This supramolecular amphiphilic drug-drug nanodelivery system provides a new strategy for cancer therapy in clinic.