Rational design of novel fluorescent tagged glutamic acid dendrimers with different terminal groups and in-silico analysis of their properties

Dendrimers are hyperbranched polymers with a multifunctional architecture that can be tailored for the use in various biomedical applications. Peptide dendrimers are particularly relevant for drug delivery applications due to their versatility and safety profile. The overall lack of knowledge of their three-dimensional structure, conformational behaviour and structure activity relationships has slowed down their development. Fluorophores are often conjugated to dendrimers to study their interaction with biomolecules and provide information about their mechanism of action at the molecular level. However, these probes can change dendrimer surface properties and have a direct impact on their interactions with biomolecules and with lipid membranes. In this study, we have used computer aided molecular design and molecular dynamics simulations to identify optimal topology of a Poly(L-glutamic acid) (PG) backbone dendrimer that allows incorporation of fluorophores in the core with minimal availability for undesired interactions. Extensive all-atom molecular dynamic simulations with the CHARMM force field were carried out for different generations of PG dendrimers with the core modified with a fluorophore (nitrobenzoxadiazole, NBD and oregon-488, ORG) and various surface groups (glutamic acid, lysine and tryptophan). Analysis of structural and topological features of all designed dendrimers provided information about their size, shape, internal distribution and dynamic behaviour. We have found that four generations of a PG dendrimer are needed to ensure minimal exposure of a core-conjugated fluorophore to external environment and absence of undesired interactions regardless of the surface terminal groups. Our findings suggest that NBD PG G4 can provide a suitable scaffold to be used for biophysical studies of surface modified dendrimers to provide a deeper understanding of their intermolecular interactions, mechanisms of action and trafficking in a biological system.