Recent advances in immunotherapeutic methods against cancer has shown great possibilities in the treatment of this obstinate disease. Among various treatment methodologies, some methods require site specific delivery of molecular cargo to maximize the therapeutic effect. Although delivering molecular cargo into target cells in programmed manner has been an important concern among researchers for few decades, it is not yet an easy problem in the field of nanomedicines. In the case of solid tumor, which is relatively well studied, an abnormal vasculature around the tissue let characteristic enhanced permeability and retention (EPR) effect to take place, which can accumulate the nanocarriers around target tissues. Unluckily, in the case of non-attached immune cells, we cannot expect the privilege of EPR effect mentioned above.
Thus we focused on making a delivery carrier that can home to the desired destination through affinity ligand at the surface of the nanoparticle. Active targeting ability is adopted by conjugating aptamers, an antibody-like DNA molecule, to our nanoparticle. To increase the efficiency of targeting, functional ligands are incorporated in special polymeric backbone, polyethylene glycol (PEG), in the form of polyrotaxane. Aptamers interlocked to the long polymer chain by supramolecular host-guest interaction have high degree of freedom along the linear axle. This gives the aptamer higher chance to meet the target protein wile contacting the cancer cell, and let neighboring ligand to migrate towards second membrane protein to form multimeric binding. In assistance of this novel strategy, our carrier system showed greater uptake compared to immobile control groups in vitro and even in in vivo fluidic bloodstream environment. Mobility of the ligand made almost 6-fold increase in uptake in our mouse bloodstream model mimicking the human acute lymphoblastic leukemia with CCRF-CEM cell line, which proved the efficacy of our polyrotaxane based polymeric nanocarrier in targeting floating cells in vivo.
As a model cargo, we utilized anticancer agent doxorubicin (DOX), which are widely used in various combination therapies. DOX molecules were intercalated into characteristic functional DNA sequence called ‘i-motif’ and its antisense counterpart, which responds to the intracellular acidic environment and forms quadruplex structure to release intercalated DOX. Cell cytotoxicity assays were carried out both in vitro and in vivo, which proved our assumption that only the stimuli responsive and actively targeted type of nanocarrier will successfully deliver the cargo to designated cells.
In summary, we developed a functional delivery carrier based on mechanically interlocked polymeric structure that enables the mobile targeting moiety, which enhances the active targeting efficiency even in in vivo fluidic bloodstream environment mimicking the human acute lymphoblastic leukemia. Additionally, we adopted acid-responsive system for programmed delivery of drug molecule specifically in site of our interest. The mobility of aptamer DNA greatly increased the adhesion of the carrier to target cells, as predicted. The enhanced therapeutic effect of this novel carrier was demonstrated both in vitro and in vivo to show the possibility of adopting the mobile ligand strategy in clinical problems.
Citation Format: Donghyun Jang, Won Jong Kim. Polyrotaxane based carrier system with mobile targeting ligands for enhanced active targeting in circulatory environment in vivo [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B139.
- ©2016 American Association for Cancer Research.