6A-O-[(4-Biphenylyl)acetyl]-α-, -β-, and -γ-cyclodextrins and 6A-Deoxy-6A-[[(4-biphenylyl)acetyl]amino]-α-, -β-, and -γ-cyclodextrins: Potential Prodrugs for Colon-Specific Delivery

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Abstract
Cyclodextrins (CyDs) are known to be fermented to small saccharides by colonic microflora, whereas they are only slightly hydrolyzable and thus are not easily absorbed in the stomach and small intestine. This property of CyDs is particularly useful for colon-specific delivery of drugs. In this study, an antiinflammatory 4-biphenylylacetic acid (BPAA) was selectively conjugated onto one of the primary hydroxyl groups of α-, β-, and γ-CyDs through an ester or amide linkage, 6A-O-[(4-biphenylyl)acetyl]-α-, -β-, and -γ-CyDs (1−3) and 6A-deoxy-6A-[[(4-biphenylyl)acetyl]amino]-α-, -β-, and -γ-CyDs (4−6). In rat cecal and colonic contents (10%, w/v), 1 and 3 released more than 95% of BPAA within 1−2 h, and 2 released about 50% of the drug within 12 h. The amide prodrugs, 4−6, did not release BPAA in the cecal contents, but gave BPAA/maltose or BPAA/triose conjugates linked through an amide bond. On the other hand, these prodrugs were found to be stable in the contents of rat stomachs and small intestines, in intestinal or liver homogenates, and in rat blood. The serum levels of BPAA increased about 3 h after oral administration of 1 and 3 to rats, accompanying a marked increase in the serum levels, whereas 2 and 4−6 resulted in little increase of the serum levels. These facts suggest that BPAA is released after the ring opening of CyDs followed by the ester hydrolysis, and the BPAA activation takes place site-specifically in the cecum and colon. Therefore, the present CyD prodrug approach provides a versatile means of constructing a novel colon-specific drug delivery system.