Enzymatic activation of second-generation dendritic prodrugs: Conjugation of self-immolative dendrimers with poly(ethylene glycol) via click chemistry

Single-triggered disassemble dendrimers were recently developed and introduced as a potential platform for a multi-prodrug. These unique structural dendrimers can release all of their tail units through a self-immolative chain fragmentation initiated by a single cleavage at the dendrimer's core. There are several examples for the bioactivation of first-generation self-immolative dendritic prodrugs. However, enzymatic activation failed for second-generation self-immolative dendrimers. The hydrophobic large molecular structure of the dendritic prodrugs results in aggregation under aqueous conditions and prevented the enzyme from reaching the triggering substrate. Here we show a simple solution for the enzymatic activation of second-generation self-immolative dendrimers. Poly(ethylene glycol) (PEG) was conjugated to the dendritic platform via click chemistry. The poly(ethylene glycol) tails significantly decreased the hydrophobic properties of the dendrimers and thereby prevented aggregate formation. We designed and synthesized a dendritic prodrug with four molecules of the anticancer agent camptothecin and a trigger that can be activated by penicillin-G-amidase. The PEG5000-conjugated, self-immolative dendritic prodrug was effectively activated by penicillin-G-amidase under physiological conditions and free camptothecin was released to the reaction media. Cell-growth inhibition assays demonstrated increased toxicity of the dendritic prodrug upon incubation with the enzyme.