CJC-1295 Without DAC: What Modified GRF (1-29) Actually Is

Modified GRF (1-29) is a 29-residue peptide: the N-terminal fragment of human growth hormone-releasing hormone, amidated at the C-terminus, with four amino-acid substitutions. The catalogue record gives the sequence as Y-(D-Ala)-DAIFTQSYRKVLAQLSARKLLQDILSR-NH2. It is not a novel hormone and not a distinct receptor ligand - it engages the same GHRH receptor as native GHRH, sermorelin and tesamorelin.

The unmodified version of this fragment already has a name and a clinical history. GHRH(1-29)-NH2 is sermorelin, and it was studied in paediatric endocrinology through the late 1980s and 1990s, including the multicentre randomised comparison against growth hormone published by Neyzi and colleagues. Modified GRF (1-29) is that molecule with four residues swapped for stability.

PubChem does not resolve this compound by name. Noreo's identity record therefore carries the sequence and the substitution list, and deliberately omits formula, molecular weight and CID rather than publishing numbers that cannot be traced to a public record. That is a real limitation on identity verification and worth stating plainly, since the peptide's commercial name gives no help either.

Position 2 is the important one. Dipeptidyl peptidase-4 cleaves GHRH between residues 2 and 3, and that cut removes the N-terminal dipeptide the receptor requires - which is why native GHRH has a half-life measured in minutes. Substituting D-alanine for the natural L-alanine at position 2 presents the enzyme with the wrong stereochemistry. Soule and colleagues measured the consequence directly in normal men in 1994: longer half-life, lower metabolic clearance. Tesamorelin solves the same problem differently, by capping the N-terminus with a trans-3-hexenoyl group instead of altering a residue.

The other three substitutions address chemical rather than enzymatic instability, and the rationale generally given for them is straightforward. Glutamine at position 8 replaces asparagine, which is prone to deamidation and backbone rearrangement. Alanine at position 15 replaces glycine, in a region where reduced backbone flexibility is thought to favour the receptor-binding conformation. Leucine at position 27 replaces methionine, whose thioether side chain oxidises readily.

Taken together the four changes produce a peptide that survives handling and circulation better than the parent fragment while binding the same receptor. What they do not produce is duration on the scale people often assume from the marketing name. Substitutions that resist degradation still leave a peptide of roughly 3,400 daltons subject to renal filtration and distribution, and the receptor-exposure window remains short. Extending that window to days requires a different mechanism entirely, which is what the DAC linker supplies.

The instinctive assumption is that longer action is better, and the GHRH literature does not support that assumption cleanly. Growth hormone is secreted in discrete bursts, shaped by alternating GHRH drive and somatostatin restraint, and several downstream effects appear to depend on the pattern of exposure rather than on total quantity. A receptor agonist that produces a short pulse of stimulation and then clears is, in principle, closer to the physiology.

The evidence for caution about sustained exposure goes back to 1986, when Vance and colleagues infused GHRH continuously in normal men and reported two things happening simultaneously: somatotroph desensitisation, and an increase in the pool of releasable growth hormone. That is not a simple monotonic relationship between stimulus and output. It says the somatotroph responds to a continuous signal differently from an intermittent one, in ways that are not fully characterised even now.

The counterweight is that the same group later found no clear desensitisation or depletion after fourteen days of continuous GHRH administration, and Ionescu and Frohman subsequently showed pulsatile secretion persisting during continuous stimulation by CJC-1295 with DAC. So this is a genuinely contested area rather than a settled argument for the short-acting form. What can be said is that the physiological rationale for a brief receptor-exposure window is real, and it is the honest reason a non-DAC analogue would be chosen for a study design.

CJC-1295 is a code assigned by ConjuChem to a specific molecule, and Jetté and colleagues described it in Endocrinology in 2005. The title names it precisely: the identification of CJC-1295 as a long-lasting GRF analog, among hGRF(1-29)-albumin bioconjugates. The albumin conjugation is not an optional feature of CJC-1295; it is what the code designates.

The tetra-substituted GHRH(1-29) peptide was the scaffold onto which the linker was attached. It existed as an intermediate, not as a marketed compound with its own name. When it later began circulating on its own, it acquired the label 'CJC-1295 without DAC' by back-formation from the compound it was derived from - which is roughly like calling an unlabelled antibody 'the antibody-drug conjugate without the drug'. The phrase describes what is absent rather than what is present.

This has a practical consequence for anyone reading the literature. Searching PubMed for CJC-1295 returns work on the DAC-bearing molecule: Jetté's rodent pharmacology, Teichman's human study of prolonged growth hormone and IGF-1 stimulation, and Ionescu and Frohman on pulsatility. None of it is evidence about the unconjugated peptide, whose pharmacokinetics differ by orders of magnitude. Claims made for 'CJC-1295 no DAC' that cite those papers are citing the wrong compound.

Against CJC-1295 with DAC, the difference is pharmacokinetic and it is large. The DAC version forms a covalent bond with serum albumin through a maleimidopropionic acid linker, which converts a peptide cleared in minutes into one persisting for days. Same receptor, same substituted backbone, entirely different exposure profile - and therefore a different biological question.

Against tesamorelin, the difference is evidence. Tesamorelin is the full 44-residue GHRH sequence protected by an N-terminal acyl group, and it has two completed Phase 3 trials and an approved regulatory label behind it. Modified GRF (1-29) has no trial under its own name at all. The structural relationship is close; the evidential positions are not remotely comparable.

Against ipamorelin, the difference is the receptor. Ipamorelin is a pentapeptide agonist at GHS-R1a, the ghrelin receptor - a separate pathway with its own ligand and its own selectivity questions. Blends pairing a GHRH-receptor agonist with a GHS-R1a agonist exist precisely because the two pathways are distinct, but the rationale for combining them is mechanistic reasoning rather than published outcome data.