Analogs of SRIF which are selective for SSTR1 in contrast to the other cloned SRIF receptors. These analogs are useful in determining the tissue and cellular expression of the
receptor SSTR1 and its biological role in the endocrine, exocrine and
nervous system, as well as in regulating
tumor growth. SRIF analog peptides, such as des-AA1,2,5[D-Trp8, NαMeIAmp9, Tyr11]-SRIF and counterparts incorporating Cbm at the N-terminus and / or NαSer13, inhibit the binding of a universal SRIF
radioligand to the cloned human
receptor SSTR1, but they do not bind with significant affinity to human SSTR2, SSTR3, SSTR4 or SSTR5. By incorporating an iodinated
tyrosine in position-2 or in position-11 in these SSTR1-selective SRIF analogs, a labeled compound useful in
drug-screening methods is provided. The N-terminus accommodates bulky moieties without loss of selectivity, and a carbamoyl
moiety or a conjugating agent that will accept a radioactive
nuclide or will link to a cytotoxin may be present at the N-terminus.