Evaluation of cancer-targeting, pharmacokinetics and antitumor activity of liposomal methotrexate with transferrin ligand, MBP-Y003.

Tadashi Fujisawa(1), Mieko Nagasawa(1), Chizuko Hashimoto(1), Kazushi Okada(1), Mikihiko Naito(2), Donghyun Kim(1), Daniel D. Von Hoff(3).

(1)Mebiopharm Co., Ltd., Tokyo, Japan, (2)The University of Tokyo, Tokyo, Japan,

(3)Tgen, Phoenix, AZ

Purpose:

MBP-Y003 is a novel liposomal methotrexate (MTX) modified with N-glutaryl phosphatidylethanolamine (NGPE) to avoid entrapment in the reticuloendothelial system and to enhance retention in blood. Transferrin (Tf) is adopted as a ligand to introduce an active targeting function to the liposome. For evaluating potency of clinical use, we investigated in vitro cancer-targeting, retention in blood in mice and efficacy of MBP-Y003 in human tumor-bearing mice.

Methods:

Growth inhibitory activity to six kinds of human tumor cell line was compared using Tf conjugated liposomal MTX with non-Tf conjugated liposomal MTX. The binding of Tf of MBP-Y003 to the Tf receptor (Tf-R), and internalization were observed by Confocal Laser Microscopy using human tumor cells. MBP-Y003 and MTX were administered as a single iv dose of 30 mg/kg to evaluate blood retention in normal mice. MTX concentrations were measured in serum by fluorescence polarization immunoassay. The antitumor efficacy of MBP-Y003 (iv) and MTX (ip) was investigated in a human tumor xenograft model at each maximum tolerated dose (MTD) of 5 mg/kg and 45 mg/kg q4d x 3, respectively.

Results:

Tf conjugated liposomal MTX MBP-Y003 showed higher growth inhibitory activity than non-Tf conjugated liposomal MTX in all cell lines that were tested. Regarding the binding between Tf of MBP-Y003 and Tf-R, at first, the binding of Tf-R and Tf was observed at the cell surfaces, and then internalized into the cytoplasm in a time dependent fashion. AUC0-24h and Cmax of total plasma MTX concentrations in the MBP-Y003 group were significantly higher than those in MTX group. Plasma terminal half-life of MBP-Y003 was also substantially improved compared to the naked MTX. The MBP-Y003 5 mg/kg group showed 89% tumor growth inhibition against PC-3 tumor in nude mice compared with the control group. The antitumor activity achieved with MBP-Y003 was also better than mice treated with standard MTX at 45 mg/kg. No death or change in clinical signs was observed in any group. It was concluded that retention in blood and anti-tumor effects of MBP-Y003 were significantly greater than those of standard MTX.

Conclusion:

Present results suggest that MBP-Y003 has cancer-targeting activity via Tf - Tf-R interaction. MBP-Y003 has enhanced systemic exposure and efficacy compared to standard MTX at doses that appear well tolerated.