CDDP-carboxylate complex

We introduced CDDP into the micelle system where CDDP was complexed with carboxyl groups on PEG-PAsp to form a metal complex micelle (Fig. 3a). The complex spontaneously forms a micelle with a very narrow size distribution having an average diameter of 20 nm [57]. The PEG-PAsp(CDDP) micelles showed an environment responsive drug release behavior. They are stable in distilled water at room temperature, yet in contrast, an exchange between the chloride ion and cisplatin occurred in 150 mM NaCl, resulting in the sustained release of the drug for over 50 h [58]. 

Thus, extension of the blood circulation time of the micelles as well as a regulated release rate of the CDDP from the micelle was concluded to be necessary to achieve a more effective anti-tumor activity. This was eventually achieved using PEG-PGlu instead of PEG-PAsp. Here, CDDP was loaded in the micelle in a similar manner to the PEG-PAsp metal complexation with the ligand substitution reaction between CDDP and the carboxylic group of PEG-PGlu (Fig. 3b) [60]. The formed micelle had a very narrow size distribution with an approximately 30 nm diameter. The PEG-PGlu(CDDP) micelle showed a more sustained release of CDDP (half-value period > 90 h) than... 

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