A novel water-soluble N-succinyl-chitosan-mitomycin C conjugate prepared by direct carbodiimide coupling: Physicochemical properties, antitumor characteristics and systemic retention

The preparation of a water-soluble conjugate of mitomycin C (MMC) with N-succinyl-chitosan (Suc) by direct carbodiimide coupling was attempted. Smaller amounts of EDC, more advanced succinylated Suc (Suc(II)) and a shorter coupling reaction time were selected as reaction conditions. Almost half the obtained conjugate was water-soluble. The water-soluble conjugate, named Suc(II)-MMC, showed a high drug content of more than 10% (w/w). Suc(II)-MMC exhibited pH-dependent drug release, i.e. MMC release rate constants at 37°C were 0.007, 0.018 and 0.114 (h^-1) at pH 6.2, 7.4 and 9.0, respectively. The addition of mouse plasma barely accelerated the release of MMC. Suc(II)-MMC was very stable at low temperatures (7°C), but showed gel-formation when left to stand at that temperature for 2 weeks. Gel- formation was not observed during standard in vitro and in vivo operations. Suc(II)-MMC showed less toxicity than MMC and a strong in vivo antitumor effect against Sarcoma 180 when administered IV at a high dose. MMC disappeared quickly from the systemic circulation after IV administration, while Suc(II)-MMC was retained at a high concentration of more than 15% of the dose/ml in plasma, even 8 h after IV administration.