Vol. 281, Issue 2, 817-825, 1997

Structure-Activity Relationships of a Series of [D-Ala²]Deltorphin I and II Analogues; in Vitro Blood-Brain Barrier Permeability and Stability¹

Sarah A. Thomas² , Thomas J. Abbruscato, Vincent S. Hau, Terrence J. Gillespie, Joseph Zsigo, Victor J. Hruby and Thomas P. Davis

Departments of Pharmacology (S.A.T., T.J.A., V.S.H., T.J.G., T.P.D.) and Chemistry (J.Z., V.J.H.), The University of Arizona, Tucson, Arizona

[D-Ala²]deltorphins are enzymatically stable, amphibian heptapeptides that have a higher affinity and selectivity for delta-opioid receptors than any endogenous mammalian compound known. This study investigated the in vitro blood-brain barrier permeability, using primary bovine brain microvessel endothelium culture, and the resistance to enzymatic degradation, in mouse 15% brain membrane homogenates and 100% plasma, of [D-Ala²]deltorphin I, [D-Ala²]deltorphin II and several analogues. Derivatives were designed with the addition of N-terminal neutral and basic amino acids or with alterations of the amino acids present within the deltorphin sequences. The results indicated that the N-terminal sequence and the amino acids in position 4 and 5 are critical to deltorphin analogue BBB permeability and biological stability, i.e., t1/2 brain; 4.8 hr- [D-Ala²]deltorphin I; >15 hr- [D-Ala²,Ser⁴,D-Ala⁵]deltorphin. Although, no analogue was found to increase the BBB permeability coefficient (PC; ×10⁴ cm/min) of the parent compounds ([D-Ala²]deltorphin II, PC = 23.49 ± 2.42) analogues were identified: [Arg⁰,D-Ala²]deltorphin II, PC = 19.06 ± 3.73 and [Pro¹,Pro⁰,D-Ala²]deltorphin II, PC = 22.22 ± 5.93; which had similar permeability coefficients, even though they had larger molecular weights and, in the case of the cationic pro-drug, a significantly lower lipophilicity. These analogues provide directions in the development of future pro-drugs for the treatment of pain and this study further clarifies the structure-activity relationship of the deltorphins.