Title: Polylysine-based Effector Molecules and Clearing Agents for Pretargeting Systems in Therapy and Imaging - Increasing Avidity and Specific Activity and Providing Many Ways to Optimize In Vivo Distribution
Publisher: SPRINGER
Publication Year: 2014
JRC N°: JRC92711
ISSN: 1619-7070
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC92711
DOI: 10.1007/s00259-014-2901-9
Type: Articles in periodicals and books
Abstract: Aim Pretargeted radioimmunotherapy (PRIT) have great potential of improving conventional RIT. The labeled antibodies in RIT usually need several hours to find their target cells, which is far from optimal when using short‐lived radionuclides, e.g. 213Bi (t ½ = 45.6 min). The higher affinity and smaller size of the effector molecule used in PRIT compared with antibodies result in significantly faster tumor cell activity uptake. This increases radiation dose to tumor relative to normal tissue, thus expands the therapeutic window. The effector molecule can also penetrate larger tumors better and faster. This gives a more uniform activity distribution within the tumor, which can be crucial for therapeutic efficacy. In this study, a polylysine‐based effector molecule was produced. The polylysine enables attachment of several biotins (for binding to streptavidin‐conjugated antibodies) and several chelators to one molecule. This increases avidity to streptavidin, and elevates specific activity. The molecule is easily size‐ and charge‐modified, which provides opportunities to customize biodistribution, e.g. for lowering activity uptake in kidney. Other groups can also be attached to the polylysine for controlling biodistribution. Glucosylated and biotinylated polylysine as clearing agent for unbound antibody conjugates is under development, which is necessary for a maximal therapeutic window. Materials and Methods Polylysine‐based effector molecules were produced with 5 times molar excess of biotin and 5, 10 and 15 times molar excess of chelator (CHX‐A’’‐DTPA or p‐SCN‐Bn‐DOTA). The molecule was subsequently charge‐modified with succinic anhydride. Concentration and product purity were evaluated by FPLC. Composition and charge‐modification were analyzed using TNBSA, evaluating the degree of free amines after each reaction step. The molecules were labeled with 213Bi for use in α‐PRIT, with 68Ga for PET and with 111In for SPECT, and tested for avidin binding capacity. Results and Conclusions The effector molecules have on average 4 biotins and 3, 6 or 9 chelators attached. They have a maximal negative net charge, which is desirable for minimal renal activity uptake. FPLC analyses showed virtually no impurities. After purification of the labeled molecules, the decay‐corrected yield was 80.2 ± 2.4 %. Radiochemical purities of the different effector molecules were between 97.4 ± 0.6% and 99.6 ± 0.2%. Avidin binding capacity was 94.4 ± 0.9%. A specific activity of 7.61 × 1012 MBq/mol, or 1 labeled molecule in 20, was achieved with 213Bi. These results show great potential for the polylysine‐based molecules in preclinical trials, evaluating treatment and imaging of different types of cancer.
JRC Directorate:Nuclear Safety and Security

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