Dendritic polyglycerols as dual modal imaging agent for EGF-receptor mediated tumor targeting

Dendritic polymers represent a powerful, multifunctional nanoscalic platform for imaging and therapeutic applications. To overcome specific limitations in imaging, having multiple modalities on a single carrier molecule is preferred and also obviates the need to administer several compounds with different pharmacokinetics. In this regard, dendritic polyglycerols (dPG) are globular macromolecules with a narrow size distribution, high degree of branching and high end group functionalities. The great versatility of the dendritic polymers allows to fine tune physico-chemical parameters such as particle size, water solubility, surface charge, chemical functionalities, etc., that are relevant for the successful preparation of theranostic systems. Lower molecular weights (LMW) uncharged dPGs' (2-20kDa) however are known to show no/minimum uptake by the cells and thus represent ideal candidates for receptor mediated targeting. The present work here deals with the development of a dendritic polyglycerol derivative (10kDa,10% NH₂ groups) as a dual modal agent for epidermal growth factor receptor (EGFR) specific tumor targeting. In this respect, in a one pot reaction, simultaneously maleimido- bearing fluorescent labels (dye) and macrocyclic chelators for ⁶⁴Cu (PET tracer) were attached to thiol anchoring groups of the polymeric scaffold. For an EGFR specific targeting, a small camelid single-domain antibody (sdAb) representing a potential recognition agent for EGFR was attached via a PEG linker. Purification of the bioconjugates was achieved using size exclusion chromatography. ⁶⁴Cu radiolabeling was done under ambient temperature and physiological pH. Binding and uptake studies were performed using A431 and FaDu cell lines using ⁶⁴Cu-labeled bioconjugates. Confocal laser scanning microscopy was used to study the receptor mediated cellular uptake. The results obtained unveil the potential of dendritic polyglycerols as multimodal platforms for theranostic applications.