A POLYMERIC DRUG-DELIVERY SYSTEM FOR THE SIMULTANEOUS DELIVERY OF DRUGS ACTIVATABLE BY ENZYMES AND OR LIGHT

Three water soluble copolymers based on N-(2-hydroxypropyl)methacrylam ide were prepared. Copolymer I contains adriamycin, a chemotherapeutic agent, attached via enzymatically degradable oligopeptide (glycylphen ylalanylleucylglycine; G-F-L-G) side chains. The other two copolymers contained the photosensitizer, meso-chlorin e6 monoethylene diamine di sodium salt (Mce6). In Copolymer II, the chlorin is attached via the d egradable G-F-L-G sequence, and it was bound by the nondegradable glyc yl spacer in Copolymer III. Initially, the copolymers were characteriz ed separately in vitro and in vivo. Combinations of the copolymer boun d chemotherapeutic agent and each of the copolymer bound photosensitiz ers were then assessed for antitumor effect in vivo. Localization/rete ntion studies (A/J mice; Neuro 2A neuroblastoma solid tumor) were perf ormed with the two copolymers containing Mce6 as well as the free drug . Results of these experiments demonstrated a very different tumor upt ake profile for the two copolymers. While the free drug was rapidly cl eared from tumor tissue, the copolymer containing Mce6 attached via th e nondegradable bond was retained for an extended period; drug concent rations in the tumor were high even after 5 days. On the other hand, a high concentration of the copolymer containing Mce6 bound via the deg radable sequence was taken up by the tumor, yet its concentration in t he tumor was substantially diminished at 48 h after administration. Th is shows indirect evidence of in vivo cleavage of Mce6 from the copoly mer in the lysosomal compartment which is supported by direct evidence of cleavage by cathepsin B (a lysosomal enzyme) in vitro. Antitumor e ffects were assessed on Neuro 2A neuroblastoma induced in A/J mice for all three copolymers. Photodynamic therapy (PDT) proved the copolymer with Mce6 bound via the degradable oligopeptide sequence to be a more effective photosensitizer in vivo than the other chlorin containing c opolymer. The difference in activity was consistent with the results o btained by photophysical analyses in which the free drug had a higher quantum yield of singlet oxygen generation than the polymer bound drug in buffer. The quantum yield of singlet oxygen generation increased w ith the enzymatic cleavage of the chlorin from the copolymer. Conditio ns were subsequently determined for which chemotherapy or PDT would sh ow some antitumor effect, yet be incapable of curing tumors. Finally, combination therapy experiments were performed in which the copolymer bound adriamycin was mixed with either of the copolymer bound chlorin compounds and injected intravenously (i.v.) into the tail veins of mic e. A time lag was allowed for optimal uptake in the tumor and for the adriamycin to begin to take effect, after which light (650 nm) was app lied to activate the photosensitizer. Tumor cures were obtained with t he combination therapy that could not be achieved by either chemothera py or PDT alone.