7-ethyl-10-hvdroxycamptothecin Nano-drug System For Tumor Targeted Delivery

Tumor-targeted drug accumulation and tumor-responsive drug release are desirable characteristics for efficacious drug delivery systems (DDS). Due to the enhanced permeability and retention (EPR) effect of tumor, nanoparticles (NPs) could selectively accumulate in tumor tissues during blood circulation. Meanwhile, the unique structure and metabolic features of tumor tissues have provided opportunities to design DDS with tumor-triggered drug release. Nanosized DDS may also significantly improve other properties of small molecular drugs such as water solubility, in vivo bioavailability, etc. All these advantages have promoted significantly the research on development of nanoscale DDS to improve the therapeutic effect of anticancer agents. SN38(7-ethyl-10-hydroxy-camptothecin) is the active metabolite of Irinotecan (CPT-11), which has100-1000fold more potent cytotoxicity in vitro compared to Irinotecan. Unfortunately, SN38cannot be administered directly, due to its extremely low solubility in any physiologically compatible and pharmaceutically acceptable solvents.The first part of this thesis aimed to develop an efficacious SN38-delivery system potentially useful for clinics. Inspired by the cancer heterogeneity and frequently elevated levels of reducing glutathione (GSH) and oxidizing reactive oxygen species (ROS) in tumor cells, we herein successfully prepared a novel GSH//ROS-dual responsive SN38prodrug, named as OEG-2S-SN38, through attaching a very low molecular weight oligo (ethylene glycol)(OEG) chain selected as the hydrophilic part to hydrophobic SN38via ester bond and thioether linker. In aqueous solution OEG-2S-SN38formed nanocapsules with diameter of～100nm, and showed greatly improved solubility and stability, with drug loading as high as35%(wt.%). Moreover, these nanocapsule were stable in PBS but released SN38promptly either via thiolysis in GSH-overexpressing cells or enhanced hydrolysis in ROS-overproducing cells. Most importantly, OEG-2S-SN38exhibited more potent antitumor activity than Irinotecan against a panel of human tumor cell lines, BCap37human breast xenograft tumors as well as autochthonous colon cancer. These encouraging data merit further preclinical and clinical investigation on this novel SN38delivery system.The sizes of nano-drugs greatly impact their biological behaviors, e.g. circulation time and therapeutic efficacies. However, available literature is not able to isolate a number of intertwined factors to specifically look into the impacts of size, and thus it is difficult to draw definitive guidelines. In the second part of this thesis, we successfully established a novel way to prepare size-tunable NPs from the same block copolymer, and thus provided an ideal single-variant model system for further studies. Briefly, amphiphilic SN38prodrug polymers PEGx-P(HEMASN38)y, with controlled chain lengths, was synthesized using PEG as initiator and SN38as monomer through atom transfer radical polymerization (ATRP). Surprisingly, by simply altering the fabrication conditions, PEGx-P(HEMASN38)y with same composition self-assembled to form a series of NPs with diameter ranging from30to300nm. Further studies indicate that the length of PEG chain but not P(HEMASN38) chain, significantly affected the circulation time of the NPs. The size of the NPs was found to strongly affect their in vitro and in vivo properties. For instance, the circulation time of NPs significantly increased upon the increase of diameter between30-170nm, but further increase of diameter decreased the circulation time. Moreover, NPs with100nm diameter exhibited as high as20%Injected Dose/g in tumor tissue, around6-8folds of those induced by NPs with30nm diameter, indicating that prolonged circulation time may increase the tumor-targeted drug accumulation. Further biodistribution studies showed that NPs with30nm diameter were mainly captured by the liver, NPs with100nm diameter evenly distributed among various organs, while those with160nm diameter mainly filtrated into spleen. In vivo, NPs with100nm diameter showed significantly improved antitumor efficacy than those with30nm diameter in BCap37xenograft tumors. However, interestingly, the rebounding on the tumor size after stop of drug administration was more significant in animals exposed to NPs with100nm diameter, which may attribute to better penetration capability of smaller NPs into tumors. Finally, in4T1metastatic tumor model, administration of NPs with100nm diameter led to better or equal survival rates compared to those with30nm diameter. These findings will provide valuable information for better understanding of the impact of size on the biological behaviors of NPs, as well as for designing more effective tumor-targeting nano-delivery systems.