Comparison of rates of penetration through insect cuticle of amphiphylic analogs of insect pyrokinin neuropeptides

Rates of penetration through the cuticle of amphiphylic analogs, synthesize d by addition of 6-phenylhexanoic acid or 9-fluoreneacetic acid or 1-pyrene butyric acid to the amino terminus of the pentapeptide Phe-Thr-Pro-Arg-Leu- amide, were assessed by quantitative analysis using reversed phase liquid c hromatography. The analogs effectively penetrated the cuticle of both the a dult American cockroach and tobacco budworm moth. However, the amounts of a nalogs that penetrated the cuticle of the cockroach were significantly lowe r and the rates of penetration were slower than for moth cuticle. Penetrati on of the analogs through the cuticle was dependent upon the size of the li pidic attachment to the pentapeptide. The 6-phenylhexanoic acid analog pene trated most rapidly followed by the 9-fluoreneacetic acid analog and the 1- pyrenebutyric acid analog penetrated slowest. All of the analogs exhibited an initial rapid period of penetration lasting 2-3 h followed by the establ ishment of a steady slow release state which lasted between 9-24 h and was dependent upon both the size and surface area of the aromatic lipidic porti on of the analog and species of insect to which the analog was applied. The results confirmed the hypothesis that the insect cuticle could be employed as a slow release device for delivery of analogs of insect neuropeptides. (C) 1999 by Elsevier Science Inc.