Encapsulation and release of rhodium(II) citrate and its association complex with hydroxypropyl-β-cyclodextrin from biodegradable polymer microspheres

Rhodium(II) carboxylates and their derivatives constitute a promising class of second-generation transition metal compounds with anticancer properties. While most transition metal anticancer compounds chelate DNA and cause extensive chromosomal damage, rhodium(II) carboxylates act on the enzyme DNA polymerase alpha and hence cause minimal chromosomal damage. Rhodium(II) citrate, a recent member of the rhodium(II) carboxylate family is highly promising as an antitumor agent. However, due to its high water solubility, a high systemic dose is necessary to achieve efficacy. In this paper, we have explored the complexation of rhodium(II) citrate with hydroxypropyl-beta-cyclodextrin as a means to improve encapsulation and release kinetics from poly(dl-lactic-co-glycolic) acid (PLGA) and poly(anhydride) microspheres. We observed that complexation of rhodium(II) citrate with hydroxypropyl-beta-cyclodextrin significantly increased both the encapsulation efficiency and duration of release in both polymer systems.