For intravenous (i.v.) injection of a water-insoluble antitumor drug, SN-38, we have successfully developed SN-38-incorporated polymeric micelles, NK012. SN-38 was incorporated into polymeric micelles thorough the polymer-drug complex formation by covalent bonding between polyethylene glycol poly (glutamic acid) block copolymers and SN-38. The particle size of NK012 was approximately 20 nm, with a narrow size distribution. NK012 inhibited the cell growth of the cancer cell lines in vitro with an IC50 range of 1.5 - 50 nM by MTT assay. The growth-inhibitory effects of NK012 are 500 - 1000 fold more potent than those of CPT-11, whereas the IC50 values of NK012 were 2-3 fold higher than those of SN-38. NK012 showed significantly potent antitumor activity on a human colo rectal cancer cell line HT-29 xenograft as compared with CPT-11. The enhanced and prolonged distribution of free SN-38 in the tumor was observed after injection of NK012, probably due to sustained release from micellar nanoparticles. To verify whether NK012 enhances its anti-tumor activity by the EPR (enhanced permeability and retention) effect, we used vascular endothelial growth factor-secreting cells (SBC-3/VEGF; VEGF transfectant). In vitro, NK012 exhibited almost equivalent cytotoxicity against SBC-3/Neo (mock transfectant) and SBC-3/VEGF. In vivo antitumor activity assay demonstrated that NK012 and CPT-11 had significant anti-tumor activity against bulky SBC-3/Neo and SBC-3/VEGF tumor (1500 mm3), but complete tumor regression was observed only in SBC-3/VEGF bearing mice treated with NK012. NK012 eradicated bulky SBC-3/VEGF tumors in all mice at both low dose (10 mg/kg, i.v. day1, 5, 9) and high dose (20 mg/kg, i.v. day 1, 5, 9) group. About 10% treatment-related body weight loss was observed in mice treated with NK012 (20 mg/kg) and CPT-11 (30 mg/kg). In the drug distribution analysis, increased accumulation of SN-38 in SBC-3/VEGF tumor was observed at 1, 6, 24, 72, and 168 hr after i.v. administration of NK012 as compared with that in SBC-3/Neo (∼20-fold higher). These results suggest that NK012 could be promising formation of SN-38 and markedly enhanced its anti-tumor activity thorough the EPR effect in highly VEGF-secreting tumors.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]