CJC-1295 No DAC: GHRH(1-29) Chemistry and Receptor Pharmacology

CJC-1295 No DAC is a synthetic 29-residue peptide corresponding to the biologically active N-terminal fragment of human growth hormone-releasing hormone, carrying four deliberate substitutions. Written as modified GRF (1-29) or tetrasubstituted GRF (1-29), the molecule has the formula C152H252N44O42, a molecular weight of 3367.9 g/mol, and a C-terminal primary amide.

The naming is a frequent source of confusion, and the confusion is chemically meaningful. In the primary literature, the designation CJC-1295 belongs to the compound reported by Jetté and colleagues in 2005: the same tetrasubstituted backbone with an N-epsilon-3-maleimidopropionamide derivative of lysine appended at the C-terminus. That appendage is the drug affinity complex. Material sold as No DAC is the backbone without it, which is why suppliers list the two as separate items and why literature searches on the bare name return work on the conjugate.

Registry identity is unsettled. Two CAS numbers circulate in supplier catalogues for this structure, and both appear as synonyms on the same PubChem record. Because sources disagree on which registry number describes the unconjugated peptide, this overview does not assert one. The unambiguous identifiers are the PubChem CID 56841945, the InChIKey XOZMWINMZMMOBR-HRDSVTNWSA-N, and the formula and mass, all of which are internally consistent with the published sequence.

Modified GRF (1-29) differs from human GHRH(1-29)-NH2 at four positions. D-alanine replaces L-alanine at residue 2, glutamine replaces asparagine at residue 8, alanine replaces glycine at residue 15, and leucine replaces methionine at residue 27. Everything else, including the C-terminal amide, is the native GHRH sequence.

Each change addresses a specific chemical liability documented in the peptide literature. The D-alanine at position 2 removes the stereochemistry that dipeptidyl peptidase IV requires at the P1 site, so the Ala2-Asp3 bond is no longer cleaved. Glutamine at position 8 replaces the asparagine residue that is prone to deamidation and backbone rearrangement in aqueous storage. Leucine at position 27 removes the only sulfur in the molecule, eliminating methionine sulfoxide formation as an oxidative degradation pathway. Alanine at position 15 comes from the medicinal-chemistry series that produced the [X2,Ala15]-GRF(1-29)-NH2 analogues used in the enzymology work described below.

The elemental arithmetic confirms the description. Native GHRH(1-29)-NH2 is C149H246N44O42S at 3357.9 g/mol. Exchanging methionine for leucine subtracts one sulfur and adds one carbon and two hydrogens; the asparagine-to-glutamine and glycine-to-alanine exchanges each add a single methylene. The result is C152H252N44O42 at 3367.9 g/mol, exactly the mass on the PubChem record, and a 10.0 g/mol offset from the unmodified fragment.

The full sequence, using standard three-letter codes, reads Tyr-D-Ala-Asp-Ala-Ile-Phe-Thr-Gln-Ser-Tyr-Arg-Lys-Val-Leu-Ala-Gln-Leu-Ser-Ala-Arg-Lys-Leu-Leu-Gln-Asp-Ile-Leu-Ser-Arg-NH2. The single D-amino acid at position 2 is the reason the molecule cannot be produced by straightforward recombinant expression and is made by solid-phase synthesis.

The GHRH receptor is a class B1 G-protein-coupled receptor on anterior pituitary somatotrophs, and modified GRF (1-29) retains the complete GHRH recognition sequence that engages it. Zhou and colleagues determined a 2.6 angstrom cryo-electron microscopy structure of the human receptor bound to GHRH and heterotrimeric Gs, reconstructed from 307,018 particles, resolving how the peptide N-terminus inserts into the transmembrane core.

The contacts are specific and measurable. The Tyr1 hydroxyl hydrogen-bonds to His210 and Thr213 in transmembrane helix 3, while the Tyr1 main-chain amide contacts Arg357 in helix 7. The Ala2 side chain makes hydrophobic contacts with Leu362 in helix 7 and Asp350 in extracellular loop 3. Asp3 forms a salt bridge with Lys182, a residue the authors describe as fully conserved. Mutagenesis quantified the hierarchy: substituting alanine for Lys182 reduced GHRH potency in cAMP accumulation by roughly 200-fold, whereas the corresponding change at Asp3 reduced it about 4-fold.

That structural picture supplies a rationale for why position 2 tolerates the D-alanine swap while position 3 does not tolerate much at all. The residue-2 side chain contributes only a small hydrophobic contact, so inverting its stereocentre perturbs the binding interface far less than losing the Asp3 salt bridge would. This is an interpretation drawn from the structure rather than a measurement reported for the modified analogue itself, and no published cryo-EM structure of modified GRF (1-29) bound to the receptor exists at the time of writing.

Downstream, the receptor signals through Gs to adenylate cyclase. A 2026 review by Ben-Shlomo and Melmed describes GH transcription and secretion, along with somatotroph lineage development, proliferation and differentiation, as mediated by GHRH signaling through the receptor and driven by raised intracellular cyclic AMP. A 2025 review by Halmos and colleagues extends the picture beyond the pituitary, reporting that splice variant 1 of the receptor retains the greatest similarity to the full-length form, remains functional, and elicits both cAMP signaling and mitogenic activity when stimulated by GHRH. Work published in 2026 on rodent retinal ganglion cells illustrates how consequential that extrapituitary expression can be, with receptor deficiency and receptor activation producing measurably different outcomes in the same injury models.

Native human GHRH is cleaved between residues 2 and 3 by dipeptidyl peptidase IV, and that reaction is the liability modified GRF (1-29) was engineered around. Frohman and colleagues measured an in vivo half-life of 6.8 minutes for GHRH(1-44)-NH2 by HPLC, and the resulting GHRH(3-44)-NH2 metabolite retained under one-thousandth of parent activity.

Bongers and colleagues then measured the reaction directly with purified human placental dipeptidyl peptidase IV. At pH 7.8 and 37 degrees Celsius with an initial substrate concentration of 0.15 mM, initial rates of Ala2-Asp3 cleavage were approximately 5 micromoles per minute per milligram of enzyme, and were essentially identical for GRF(1-44)-NH2, GRF(1-29)-NH2 and GRF(1-20)-NH2. Chain length, in other words, does not protect the bond.

The same study established what does. Peptides carrying a D-configuration residue at P2, P1 or P1', together with desamino-Tyr1 and N-methyl-Tyr1 analogues, were not cleaved at all. Across the [X2,Ala15]-GRF(1-29)-NH2 series, catalytic efficiency ordered as Abu greater than Pro greater than Ala, much greater than Ser, then Gly and Val, with leucine at position 2 by far the poorest substrate. The optimum was a hydrophobic P1 side chain about 0.25 nm long. The D-alanine substitution used in modified GRF (1-29) falls in the not-cleaved category rather than the merely slow one.

One methodological detail from the 1986 work is worth carrying forward into any assay design. Incubating GHRH(1-44)-NH2 with human plasma gave a half-life of 17 minutes when the parent peptide was tracked by HPLC, but 63 minutes when total immunoreactivity was tracked by radioimmunoassay, because the antibody also counted the inactive cleaved product. Immunoassay and chromatography answer different questions about this peptide family.

CJC-1295 No DAC carries no drug affinity complex, and that absence is the entire distinction. The 2005 conjugate appends an N-epsilon-3-maleimidopropionamide derivative of lysine to the C-terminus of this same tetrasubstituted backbone. That maleimide reacts covalently with the free cysteine 34 thiol of serum albumin. Without the appendage, covalent albumin capture cannot occur.

The 2005 work quantified what the appendage buys. Three maleimido derivatives of hGRF(1-29) were bioconjugated to human serum albumin ex vivo; all three showed enhanced in vitro stability against dipeptidyl peptidase IV and were bioactive in a GH secretion assay in cultured rat anterior pituitary cells. In normal male Sprague-Dawley rats, the selected compound produced a 4-fold increase in GH area under the curve over a 2-hour window compared with hGRF(1-29), was still detectable in plasma beyond 72 hours, and appeared on Western blot as an immunoreactive species co-migrating with serum albumin from 15 minutes onward and persisting past 24 hours.

For the unconjugated backbone, none of that circulating reservoir applies. Its persistence in a biological matrix depends only on the intrinsic protease resistance the four substitutions confer. A figure of roughly 30 minutes is widely quoted for this molecule across secondary and commercial sources, but the present survey did not locate a peer-reviewed pharmacokinetic study reporting it as a measured value, so it is recorded here as unverified rather than repeated as fact.

CJC-1295 and the wider GHRH analogue family are recurring targets in anti-doping analytical chemistry, and that literature is where the compound's quantitative detection window is defined. Reported limits of detection in urine span roughly 5 pg/mL to 1 ng/mL depending on extraction chemistry, with liquid chromatography coupled to high-resolution or triple-quadrupole mass spectrometry as the standard platform.

Three method papers bracket the current state. Coppieters and colleagues replaced antibody-based extraction with a simple ultrafiltration preconcentration step ahead of nanoLC-HRMS/MS in 2022, reaching limits of detection between 5 and 25 pg/mL with recoveries of 59 to 115 percent. Cristea and colleagues published a weak cation-exchange solid-phase extraction method with triple-quadrupole UHPLC-MS/MS in 2023, reporting a limit of detection of 0.2 ng/mL and a limit of quantification of 0.6 ng/mL across five GHRH-family analytes. Uçaktürk and Nemutlu published a nano-LC quadrupole/Orbitrap method in 2026 combining ultrafiltration with solid-phase extraction, reporting limits of detection at or below 0.5 ng/mL and limits of identification between 0.5 and 0.75 ng/mL.

Metabolite mapping matters as much as parent sensitivity for a peptide that is cleaved this readily. Memdouh and colleagues characterised the in vitro metabolism of four of the larger GHRH synthetic analogues in fortified urine, identified nineteen major metabolites, synthesised them as reference materials, and built a detection method around them with limits generally at or below the 1 ng/mL performance level. Thomas and colleagues took the opposite approach in 2024, simplifying the extraction chemistry for the entire 2 to 10 kDa peptide window in urine into a single procedure suitable as an initial testing method.

Two practical constraints run through all of this work. Urinary concentrations of GHRH analogues are low and clearance is fast, which is why nano-flow chromatography and preconcentration steps recur. And the analytes are fragile in matrix: the 2022 method paper specifically records that sermorelin and its metabolite degraded rapidly above 4 degrees Celsius and at pH values below 7.

Published handling information for CJC-1295 No DAC is thinner than its analytical literature, and the distinction between the two matters. The material is supplied as a lyophilized powder in 5 mg and 10 mg presentations, and the peer-reviewed guidance that exists concerns behaviour of GHRH analogues in biological matrices rather than storage of the neat solid. Storage figures quoted by suppliers are catalogue specifications, not measurements from published stability studies.

What the method literature does establish is temperature and pH sensitivity in solution. The 2022 ultrafiltration paper records that sermorelin and its principal metabolite degraded rapidly at temperatures above 4 degrees Celsius and at pH values below 7, which argues for cold handling and neutral or slightly alkaline buffers when the analogue family is in solution. Any plasma or serum workflow carries a second constraint: dipeptidyl peptidase IV is active in those matrices, and the 1992 enzymology defines exactly how fast the parent sequence disappears. The four substitutions in this analogue are precisely what remove that route, but they do not confer resistance to other endopeptidases, and the nineteen-metabolite panel from the 2021 study documents what the wider degradation landscape looks like.

For identity confirmation, the computed descriptors are the useful checks. XLogP of minus 10.7, a topological polar surface area of 1450 square angstroms, 52 hydrogen-bond donors and 118 rotatable bonds together describe a highly polar, water-soluble peptide with no expectation of passive membrane permeability. On a mass spectrometer, the monoisotopic mass to verify against a deconvoluted electrospray spectrum is 3365.894 Da, with an average molecular weight of 3367.9 g/mol. The absence of sulfur is a useful negative check: an isotope pattern or elemental analysis showing sulfur indicates the unmodified GHRH(1-29) fragment rather than the tetrasubstituted analogue.