Colon-Specific Drug Delivery Based on a Cyclodextrin Prodrug: Release Behavior of Biphenylylacetic Acid from Its Cyclodextrin Conjugates in Rat Intestinal Tracts after Oral Administration

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Abstract
An antiinflammatory drug biphenylylacetic acid (BPAA) as a model drug was selectively conjugated onto one of the primary hydroxyl groups of alpha-, beta-, and gamma-cyclodextrins (CyDs) through an ester or amide linkage, and the in vivo drug release behavior of these prodrugs in rat gastrointestinal tracts after oral administration was investigated. The CyD prodrugs were stable in rat stomach and small intestine and negligibly absorbed from these tracts. Three to six hours after the oral administration, most of the prodrugs had moved to the cecum and colon. The alpha- and gamma-CyD amide prodrugs were hydrolyzed to the maltose conjugate in the cecum and colon, and these prodrugs and the conjugate were negligibly absorbed. On the other hand, the alpha- and gamma-CyD ester prodrugs produced BPAA in the cecum and colon, and BPAA appeared in the blood after 3-6 h. Both beta-CyD amide and ester prodrugs released only small or negligible amounts of the maltose conjugate or BPAA in the cecum and colon, within 24 h, probably due to the low solubility in the biological media. Further, the antiinflammatory effect of the gamma-CyD ester prodrug was evaluated using the model of carageenan-induced acute edema in rat paw and compared with those of BPAA alone and the BPAA/beta-CyD complex prepared by the kneading method in a molar ratio of 1:1. In the case of the beta-CyD complex, a rapid antiinflammatory response was observed, compared to BPAA alone, because the drug is mainly absorbed from the small intestine after a fast dissolution of the complex. In sharp contrast, the gamma-CyD ester prodrug needed a fairly long lag time to exhibit the drug activity, because BPAA is produced after the prodrug had reached the cecum and colon. The present results clearly suggest that the CyD prodrug approach can provide a versatile means for constructions of not only colon-specific delivery systems but also delayed-release system of certain drugs.