A multi-stimuli responsive nanoparticulate SN38 prodrug for cancer chemotherapy

Modification of drug delivery systems (DDSs) with stimuli-responsive elements could significantly increase the tumor-specific delivery of anticancer drugs. Herein we synthesized a novel multiple stimuli-responsive SN38 prodrug, named PEG-S-S-SN38, by conjugating PEG (M_W: 2000) and SN38 with disulfide bonds and carbonic ester linkages as linkers for efficient delivery of SN38. The amphiphilic PEG-S-S-SN38, with a high SN38 loading content, could self-assemble into nanoparticles (NPs) with a stable diameter of ∼73 nm. PEG-S-S-SN38 NPs release SN38 very slowly at physiological pH, while they quickly release SN38 in the presence of GSH, esterase and H₂O₂, all of which are abundant in the cytoplasm of cancer cells. PEG-S-S-SN38 NPs could be quickly internalized into tumor cells, achieve vesicular escape and nuclear localization, and exhibit remarkable in vitro anticancer activity similar to SN38. Encouragingly, PEG-S-S-SN38 NPs exhibit the same effects on cell cycle regulations as SN38 in vitro. Most importantly, the inhibition rate of tumor growth induced by PEG-S-S-SN38 NPs in a xenograft tumor model reached 72.49% ± 6.26%, which was nearly double that of the corresponding clinical drug CPT-11 (38.64% ± 13.04%) at a dosage equivalent to 10 mg kg^-1 SN38. Our data suggest that the multi-stimuli responsiveness of PEG-S-S-SN38 NPs remarkably enhances their therapeutic activity against heterogeneous or mixed cell population in tumors, making this new DDS a promising alternative to CPT-11 for cancer treatment.