AminoBODIPY Conjugates for Targeted Drug Delivery Systems and Real-Time Monitoring of Drug Release

In this work, we report two concepts of drug delivery based on small-molecule drug conjugates with the ability of specific targeting and drug release monitoring via ratiometric fluorescence. The functionality of these concepts has been verified by two model systems consisting of three parts: (i) fluorescent aminoBODIPY for real-time detection of conjugate cleavage, (ii) a c(RGDfK) peptide specific for α_vβ₃ integrin receptors targeting angiogenesis in most solid tumors or redBODIPY for conjugate cleavage monitoring via FRET, and (iii) pegylated-2-phenyl-3-hydroxy-4(1H)-quinolinone (3HQ) as a model drug. The model drug release is based on a self-immolative disulfide linker sensitive to environments containing thiols, especially glutathione, which is overexpressed in cancer cells. The results show effective thiol-mediated cleavage of the fluorescent reporter and the subsequent liberation of the drug in a tube. The conjugate with c(RGDfK) was confirmed to penetrate the cells via interaction with integrin receptors. Drug release from this conjugate is possible to monitor inside the cells. Further, the synthetic approach to the conjugates and the method of fluorescence monitoring of the drug release have also been described.