Biophysical characterization of a riboflavin-conjugated dendrimer platform for targeted drug delivery

The present study describes the biophysical characterization of generation-five poly(amidoamine) (PAMAM) dendrimers conjugated with riboflavin (RF) as a cancer-targeting platform. Two new series of dendrimers were designed, each presenting the riboflavin ligand attached at a different site (isoalloxazine at N-3 and d-ribose at N-10) and at varying ligand valency. Isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC) were used to determine the binding activity for riboflavin binding protein (RfBP) in a cell-free solution. The ITC data shows dendrimer conjugates have K _D values of ≥465 nM on a riboflavin basis, an affinity ∼93-fold lower than that of free riboflavin. The N-3 series showed greater binding affinity in comparison with the N-10 series. Notably, the affinity is inversely correlated with ligand valency. These findings are also corroborated by DSC, where greater protein-conjugate stability is achieved with the N-3 series and at lower ligand valency.