Biol. Pharm. Bull., 31(1),103-110, January 2008

Regular Articles

Synthesis of Poly(vinyl alcohol)-Doxorubicin Conjugates Containing cis-Aconityl Acid-Cleavable Bond and Its Isomer Dependent Doxorubicin Release

Atsufumi KAKINOKI,^a Yoshiharu KANEO,^*,a Yuka IKEDA,^a Tetsuro TANAKA,^a and Kahee FUJITA^b

^a Laboratory of Biopharmaceutics, Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University; Fukuyama, Hiroshima 729-0292, Japan: and ^b Department of Molecular Medicinal Sciences, Graduate School of Biomedical Sciences, Nagasaki University; Nagasaki 852-8521, Japan. * To whom correspondence should be addressed. e-mail: kaneo@fupharm.fukuyama-u.ac.jp

Aconityl-doxorubicin (ADOX) was synthesized by the modified method of Shen and Ryser. Two isomers of cis-ADOX (cis-configuration) and trans-ADOX (trans-configuration) were generated in the reaction of DOX and cis-aconitic anhydride. These products were separated completely by using HPLC and analyzed by TOF-MS spectroscopy and ¹H- and ¹³C-NMR experiments. The yields of cis-ADOX and trans-ADOX were 36.3 and 44.8%, respectively. The free γ-carboxylic group of ADOX molecule was coupled to poly(vinyl alcohol) (PVA) via ethylenediamine spacer, resulting the macromolecular conjugates of PVA-cis-ADOX and PVA-trans-ADOX, respectively. The DOX content of the conjugates estimated by the hydrolysis method detected the aglycone of DOX which can be estimated as the PVA-bound DOX selectively was 4.4 w/w% which was similar to 4.6 w/w% by the ordinary UV method. Both PVA-cis-ADOX and PVA-trans-ADOX were very stable at neutral pH, but the release of DOX was increased markedly under acidic conditions. Half-life of the release of DOX from PVA-cis-ADOX at pH 5.0 was 3 h which was 4.7-fold shorter than that from PVA-trans-ADOX (14 h). The cytotoxicities of PVA-cis-ADOX and PVA-trans-ADOX were evaluated by using J774.1 cells employing a [³H]uridine incorporation assay as a measure of RNA synthesis. A significant difference in antitumor activity between PVA-cis-ADOX and PVA-trans-ADOX was observed where the former was much active than the later. It was suggested that the conjugate enters the cells and reaches the lysosomal/endosomal compartment, and that the aconityl spacer releases DOX from the conjugate in the acidic compartment of lysosomes/endosomes due to the participation of a free carboxylic group.

Key words poly(vinyl alcohol); doxorubicin; acid-sensitive spacer; macromolecular prodrug; cytotoxicity; cellular uptake