Various embodiments of the present invention pertain to therapeutic compositions that comprise: (1) an active agent (e.g., paclitaxel); and (2) a nanoparticle (e.g., gold nanoparticle). In such embodiments, the active agent is covalently linked to the nanoparticle through a cleavable linker (e.g., a linker containing a hydrazone species). Other embodiments of the present invention pertain to methods of treating a condition in a subject by administering the above-described therapeutic compositions to the subject.