High-potency hybrid compounds related to insulin and amphioxus insulin-like peptide

We describe the synthesis and biological evaluation of five two-chain, insulin-like compounds structurally related both to insulin and to a putative insulin like peptide (ILP) whose sequence was deduced from a cDNA cloned from Branchiostoma californiensis (amphioxus), a primitive vertebrate [Chan, S. J., Cao, Q.-P., & Steiner, D. F. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 9319-9323]. The present compounds feature an A-chain corresponding to the A-domain of the putative amphioxus ILP A-domain, except that amino acid substitutions have been made at positions A2, A3, A5, and/or A8, linked via disulfide bonds to the B-chain of bovine insulin. Amphioxus ILP [2 Ile] A/insulin B, amphioxus ILP [2 Ile, 8 His] A/insulin B, amphioxus ILP [2 Ile, 5 Gln, 8 His] A/insulin B, and amphioxus ILP [2 Ile, 3 Ile, 5 Gln, 8 His] A/insulin B all display insulin-like metabolic activity and growth-promoting activity (mitogenesis) equal to or greater than that of natural insulin. Amphioxus ILP [8 His] A/insulin B shows activity in these assays greater than that of its parent compound, but not as high as compounds featuring Ile rather than Leu at position A2. In contrast, the parent compound of the present analogues, i.e., amphioxus ILP A/insulin B, displays potencies ranging from 4.0 to 9.8% relative to insulin in insulin receptor binding and lipogenesis assays, respectively. This parent compound displayed activity in growth factor assays too low for exact quantitation [Chu, Y.-C., Hu, S. Q., Zong, L., Burke, G. T., Gammeltoft, S., Chan, S. J., Steiner, D. F., & Katsoyannis, P. G. (1994) Biochemistry (in press)].(ABSTRACT TRUNCATED AT 250 WORDS)