Rational design, synthesis, and biological evaluation of novel growth hormone releasing factor analogues

Abstract

Since its initial discovery in 1982, growth hormone-releasing factor (GRF) has been the subject of intense investigation. This interest was prompted by the potential application of GRF for stimulating growth in dwarf humans and for performance enhancement in livestock. Substantial research has been focused upon the development of potent, long-acting analogs as therapeutics. Herein is described a summary of the cumulative efforts of various laboratories endeavoring in this quest. The rationale utilized in GRF analog development is discussed: 1) determination of bioactive core, 2) evaluation of secondary structure, and 3) elucidation of degradation pathways (chemical and enzymatic). Using this information, several series of linear (unnatural and natural sequence) and cyclic GRF analogs were designed, synthesized, and evaluated. Stimulated by the constraints of commercial production, innovative, alternative methods of synthesis were explored: solid-phase, solution-phase, enzymatic, and recombinant. To date, the most promising candidate for drug development is [His1, Val2, Gln8, Ala15, Leu27]-hGRF(1-32)-OH. This natural sequence analog, consisting of rodent and human sequences, incorporates the bioactive core, preferred secondary structure, resistance to chemical and enzymatic degradation; with the added benefit of amenability to large-scale recombinant synthesis.

Synthesis and biological evaluation of antagonists of growth hormone-releasing hormone with high and protracted in vivo activities

“…Subsequent studies confirmed the essential role of D-Arg 2 substitution for generating GH-RH antagonistic activity (3)(4)(5). Given the preponderant ␣-helical amphiphilic nature of GH-RH (6,27), many attempts were made to stabilize this helical structure and enhance its amphiphilicity in GH-RH analogs (5)(6)(7)(8)(9)(10)(11). Both GH-RH agonistic (5-8) and antagonistic (5, 9-11) peptides with increased biological activities were produced in this way.…”

“…Since the isolation and structural elucidation of human growth hormone-releasing hormone (hGH-RH), various analogs of GH-RH have been synthesized (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11). Most of them were agonists intended for clinical and veterinary applications (5)(6)(7)(8), but there is a greater medical need for antagonistic analogs of GH-RH (12)(13)(14).…”

“…Most of them were agonists intended for clinical and veterinary applications (5)(6)(7)(8), but there is a greater medical need for antagonistic analogs of GH-RH (12)(13)(14). GH-RH antagonists may find use in conditions such as acromegaly, diabetic retinopathy, or diabetic nephropathy (glomerulosclerosis).…”

“…Accordingly, this sequence has been used for development of agonistic and antagonistic GH-RH analogs (2)(3)(4)(5)(6)(7)(8)(9)(10)(11). Replacement of the naturally occur- ]hGH-RH(1-29)NH 2 , the first described GH-RH antagonist (2).…”

Increased activity of antagonists of growth hormone-releasing hormone substituted at positions 8, 9, and 10

“…Many agonistic and antagonistic analogs of GHRH, based on the shortest bioactive sequence of hGHRH(1-29)NH 2 , have been synthesized to elucidate the structure-activity relationships and to increase their biological activity (4)(5)(6)(7)(8)(9)(10)(11)(12)(13). The first reported GHRH antagonist, termed herein as the ''standard antagonist,'' has the chemical structure of [Ac-Tyr 1 , D-Arg 2 ]hGHRH(1-29)NH 2 (7).…”