In an attempt to increase the residence time of PSMA-targeted theranostics inside the prostate cancer cells and tumors, we designed and prepared a CPTA-PSMATA resembling PSMA-617 by adding a well-known cysteine protease inhibitor (E-64) to the conjugate. Lysosomal proteases, including cysteine, serine, and aspartic families of hydrolytic enzymes, are expressed in high concentrations in the lysosomes and are responsible for the catabolism of proteins inside the cell [165, 278]. We proposed that after successful internalization of the PSMA-targeted conjugates into the cells, they will be conveyed to the endolysosomes. In these endolysosomal compartments, the E-64 moiety will covalently bind to cysteine proteases such as cysteine cathepsins, thereby forming high molecular weight conjugates
