CJC-1295 and Modified GRF(1-29) GHRH Analog Identity: A Research Review of Drug Affinity Complex Albumin Bioconjugation, DPP-IV Resistant Structure, Somatotroph cAMP Signaling and Pulsatile Growth Hormone Secretion

By the Peptide Insider Research Desk

CJC-1295, modified GRF(1-29), and their associated catalogue orthographic variants—cjc-1295 no dac, cjc no dac, cjc with dac, cjc 1295 w dac, cjc without dac, cjc1295 dac, cjc w dac—represent one of the most frequently queried compound families in the research peptide catalogue. This review examines the molecular identity, structural pharmacology, receptor signaling cascade and preclinical-to-clinical evidence base for the tetrasubstituted GHRH analog known as CJC-1295, with particular attention to the Drug Affinity Complex (DAC) bioconjugation strategy that distinguishes the long-acting variant from its non-DAC counterpart.

Molecular Architecture and DPP-IV Resistance Strategy

Native human GHRH is a 44-amino-acid neuropeptide secreted by the arcuate nucleus of the hypothalamus that stimulates growth hormone (GH) synthesis and release from anterior pituitary somatotrophs [1]. The biologically active domain resides entirely within the first 29 residues, designated GRF(1-29), which retains full receptor binding and adenylyl cyclase activation [2]. However, native GRF(1-29) is rapidly inactivated in the circulation by dipeptidyl peptidase IV (DPP-IV; UniProt P27487), which cleaves the Tyr1-Ala2 N-terminal dipeptide bond, yielding biologically inactive GRF(3-29). The resulting plasma half-life of native GRF(1-29) is less than 10 minutes [3][6].

The tetrasubstituted analog addresses each major degradation pathway through four targeted amino acid replacements [2][3]:

• Position 2 — D-Alanine for L-Alanine: The stereochemical inversion at the P1 site of DPP-IV renders the scissile bond refractory to enzymatic hydrolysis, eliminating the primary inactivation pathway.
• Position 8 — Glutamine for Asparagine: Substitution removes the susceptible asparagine side-chain amide, preventing non-enzymatic deamidation that generates isoaspartate and reduces receptor affinity.
• Position 15 — Alanine for Glycine: Introduction of a methyl side chain at this position stabilizes the amphipathic alpha-helical conformation required for high-affinity GHRHR engagement.
• Position 27 — Leucine for Methionine: Replacement of the thioether-containing methionine with the aliphatic leucine eliminates susceptibility to oxidative degradation (methionine sulfoxide formation) during storage and in the oxidative plasma environment.

These modifications collectively extend the unconjugated peptide half-life to approximately 30 minutes while preserving full GHRHR agonist potency [2].

Drug Affinity Complex: Albumin Bioconjugation at Cysteine-34

The distinguishing feature of CJC-1295 proper—as opposed to Modified GRF(1-29), which lacks this element—is the C-terminal Drug Affinity Complex (DAC), a maleimidopropionyl-lysine moiety that enables covalent, irreversible binding to endogenous serum albumin [2][5].

Human serum albumin (HSA; UniProt P02768, ~66.5 kDa) carries a single reduced cysteine at position 34 (Cys34) that presents a free sulfhydryl group accessible to maleimide electrophiles. Upon subcutaneous injection, the reactive maleimide on the DAC linker undergoes a Michael addition with the Cys34 thiol, forming a stable thioether bond. This reaction converts the 3.4 kDa peptide into an approximately 70 kDa albumin-peptide conjugate that is shielded from glomerular filtration (renal clearance threshold ~60 kDa) and further protected from proteolytic degradation by the steric bulk of the albumin carrier [2][5][7].

The pharmacokinetic consequence is dramatic: the DAC-conjugated variant exhibits a functional half-life of 6 to 8 days, compared with approximately 30 minutes for the unconjugated tetrasubstituted peptide [1][2]. This bioconjugation strategy has since been adopted in other peptide therapeutic contexts, where albumin binding is used to extend the circulating residence time of peptide-based agents [7].

GHRH Receptor Signaling: Somatotroph cAMP/PKA Cascade

Both CJC-1295 (DAC) and Modified GRF(1-29) exert their biological effects through the same molecular target: the growth hormone-releasing hormone receptor (GHRHR; UniProt Q02643), a class B1 G protein-coupled receptor (GPCR) expressed predominantly on somatotroph cells of the anterior pituitary [6][8].

Ligand binding to GHRHR activates the stimulatory G protein Gαs, which in turn stimulates adenylyl cyclase to produce cyclic adenosine monophosphate (cAMP) from ATP. Elevated intracellular cAMP activates protein kinase A (PKA), initiating a phosphorylation cascade that opens voltage-gated calcium channels in the somatotroph plasma membrane. The resulting calcium influx triggers exocytosis of preformed GH-containing secretory granules [6][8]. Concurrently, cAMP/PKA signaling activates the transcription factor CREB (cAMP response element-binding protein), which drives transcription of the GH1 gene, replenishing the releasable GH pool over longer time frames [6].

Critically, GHRHR signaling operates in concert with the ghrelin/GH secretagogue receptor (GHSR1a) pathway. Ghrelin receptor activation elevates intracellular calcium through Gαq/phospholipase C/IP3 signaling, and the convergence of the cAMP and calcium pathways at the somatotroph produces a synergistic amplification of GH release that exceeds the sum of either stimulus alone [8][9]. This pharmacological synergism underlies the frequent co-investigation of CJC-1295 and ipamorelin (a selective GHSR1a agonist) in preclinical models.

Pulsatile Growth Hormone Secretion Under Continuous GHRH Receptor Stimulation

A central question in the pharmacology of long-acting GHRH analogs is whether sustained receptor occupancy disrupts the physiological pulsatile pattern of GH release—a pattern characterized by major nocturnal pulses with interpulse nadirs essential for hepatic IGF-1 receptor sensitivity and downstream anabolic signaling [4][10].

Ionescu and Frohman (2006) addressed this question directly by examining GH secretory dynamics during prolonged CJC-1295 exposure. Their investigation demonstrated that pulsatile GH secretion persists during continuous stimulation by CJC-1295, with preserved pulse amplitude and interpulse trough periods [4]. This finding indicates that the somatotroph retains its intrinsic capacity for cyclic degranulation and recovery even under sustained GHRHR agonism—likely because the GH-somatostatin feedback axis continues to impose intermittent inhibition through somatostatin receptor-mediated suppression of cAMP, irrespective of the constant presence of the GHRH agonist [4][10].

Preclinical Evidence

Clinical Evidence: Teichman et al. Phase I Dose-Escalation

The landmark clinical evaluation of CJC-1295 with DAC was reported by Teichman et al. (2006) in a single-dose, dose-escalation study conducted in healthy adult volunteers [1]. Key observations from that investigation include:

• GH Elevation: A single subcutaneous injection produced dose-dependent increases in serum GH levels, with 2- to 10-fold elevations above baseline sustained for 6 or more days post-administration.
• IGF-1 Response: Insulin-like growth factor I (IGF-1) levels increased 1.5- to 3-fold above baseline, with elevations persisting for 9 to 11 days—consistent with the prolonged GH stimulus driving sustained hepatic IGF-1 production.
• Pharmacokinetic Profile: The estimated terminal half-life of CJC-1295 DAC exceeded 5.8 days, supporting the albumin-bioconjugation strategy as an effective half-life extension mechanism.
• Tolerability: Injection-site reactions were the most commonly reported adverse events; no dose-limiting toxicities were identified at the doses tested.

These data confirmed that the DAC-mediated albumin bioconjugation strategy translated from preclinical models to human pharmacology, producing sustained somatotroph stimulation from a single injection [1].

CJC-1295 vs. Modified GRF(1-29): Identity Disambiguation

The research catalogue frequently conflates "CJC-1295" with "Modified GRF(1-29)," and variant query tokens—cjc-1295 without dac, cjc 1295 without dac, cjc-1295 w/ dac, cjc-1295 w/dac, cjc-no dac, cjc1295 no dac, cjc1295 with dac—reflect persistent nomenclature ambiguity. To clarify:

This distinction is pharmacologically significant: the DAC-conjugated form has published dose-response and pharmacokinetic data from controlled clinical investigation, whereas the "no DAC" variant has been studied primarily in preclinical settings, and its human pharmacokinetic profile cannot be reliably extrapolated from the DAC-form data [1][2][4].

Analytical Detection and Regulatory Classification

CJC-1295 is classified as a prohibited substance under the WADA Prohibited List (Section S2, Peptide Hormones). Analytical detection has advanced to immuno-PCR screening capable of detecting CJC-1295 at sub-nanogram-per-milliliter concentrations in biological matrices [11][12][13].

Frequently Asked Questions

What is CJC-1295 and how does it differ from Modified GRF(1-29)?

CJC-1295 (CAS 863288-34-0) is a tetrasubstituted analog of human growth hormone-releasing hormone fragment GRF(1-29) that incorporates a Drug Affinity Complex (DAC) enabling covalent binding to serum albumin at Cys34, extending its functional half-life from approximately 30 minutes to 6-8 days. Modified GRF(1-29) shares the same four amino acid substitutions (D-Ala2, Gln8, Ala15, Leu27) but lacks the DAC moiety, resulting in rapid renal clearance. Both variants activate the GHRH receptor (UniProt Q02643) on anterior pituitary somatotrophs [1][2].

What are the four amino acid substitutions in CJC-1295 and why are they necessary?

The four substitutions are: D-alanine at position 2 (blocks DPP-IV cleavage at the N-terminal dipeptide bond), glutamine at position 8 (prevents asparagine deamidation), alanine at position 15 (stabilizes alpha-helical backbone geometry required for receptor engagement), and leucine at position 27 (prevents methionine oxidation). These modifications collectively confer resistance to enzymatic and chemical degradation while preserving full GHRH receptor agonist potency [2][3].

Does CJC-1295 preserve pulsatile growth hormone secretion?

Ionescu and Frohman (2006) demonstrated that pulsatile GH secretion persists during continuous stimulation by CJC-1295 in a research setting, indicating that the somatostatin-mediated inhibitory feedback axis remains functional and imposes cyclic suppression even under sustained GHRHR agonism. This preservation of pulsatility contrasts with exogenous GH administration, which delivers a pharmacokinetic bolus that bypasses hypothalamic regulation [4][10].

What is the Drug Affinity Complex and how does it extend half-life?

The DAC consists of a maleimidopropionyl-lysine linker appended to the C-terminus of the tetrasubstituted GRF(1-29) peptide. The reactive maleimide undergoes a Michael addition with the Cys34 thiol of circulating human serum albumin (UniProt P02768), forming an irreversible thioether bond. The resulting ~70 kDa conjugate exceeds the renal filtration threshold and is shielded from proteolytic degradation, extending the functional half-life from approximately 30 minutes to 6-8 days [2][5][7].

Where to Source CJC-1295 and Modified GRF(1-29) for Research

Investigators requiring CJC-1295 or Modified GRF(1-29) for preclinical research should verify compound identity (CAS 863288-34-0 for the DAC form), purity specifications (typically greater than or equal to 98% by HPLC), and the presence or absence of the DAC moiety, as the two forms are pharmacologically distinct entities. Research-grade material is available through established suppliers including Short Chain Aminos, BioPep, Catalyst Research, and Apex Research Services. No vendor is assessed or endorsed in this review; sourcing decisions should be guided by certificate of analysis documentation, third-party analytical verification and institutional procurement standards.

Works Cited

1. Teichman SL, Neale A, Lawrence B, Gagnon C, Castaigne JP, Bhatt RS. Prolonged stimulation of growth hormone (GH) and insulin-like growth factor I secretion by CJC-1295, a long-acting analog of GH-releasing hormone, in healthy adults. J Clin Endocrinol Metab. 2006;91(3):799-805. PMID: 16352683.
2. Jette L, Leger R, Thibaudeau K, et al. Human growth hormone-releasing factor (hGRF)1-29-albumin bioconjugates activate the GRF receptor on the anterior pituitary in rats: identification of CJC-1295 as a long-lasting GRF analog. Endocrinology. 2005;146(7):3052-3058. PMID: 15817669.
3. Alba M, Fintini D, Sagazio A, et al. Once-daily administration of CJC-1295, a long-acting growth hormone-releasing hormone (GHRH) analog, normalizes growth in the GHRH knockout mouse. Am J Physiol Endocrinol Metab. 2006;291(6):E1290-E1294. PMID: 16822960.
4. Ionescu M, Frohman LA. Pulsatile secretion of growth hormone (GH) persists during continuous stimulation by CJC-1295, a long-acting GH-releasing hormone analog. J Clin Endocrinol Metab. 2006;91(12):4792-4797. PMID: 17018654.
5. Kuhlmann M, Hamming JBR, Voldum A, et al. An albumin-oligonucleotide assembly for potential combinatorial drug delivery and half-life extension applications. Mol Ther Nucleic Acids. 2017;9:284-291. PMID: 29246307.
6. Mayo KE, Miller T, DeAlmeida V, et al. Regulation of the pituitary somatotroph cell by GHRH and its receptor. Recent Prog Horm Res. 2000;55:237-266. PMID: 11036940.
7. Thorner MO, Chapman IM, Gaylinn BD, Pezzoli SS, Hartman ML. Growth hormone-releasing hormone and growth hormone-releasing peptide as therapeutic agents to enhance growth hormone secretion in disease and aging. Recent Prog Horm Res. 1997;52:215-244. PMID: 9238854.
8. Cunha SR, Mayo KE. Ghrelin and growth hormone (GH) secretagogues potentiate GH-releasing hormone (GHRH)-induced cyclic adenosine 3',5'-monophosphate production in cells expressing transfected GH secretagogue receptor or GHRH receptor. Endocrinology. 2002;143(12):4570-4582. PMID: 12446584.
9. Faidley TD, Leiting B, Pryor KD, et al. Inhibition of dipeptidyl-peptidase IV does not increase circulating IGF-1 concentrations in growing pigs. Exp Biol Med (Maywood). 2006;231(9):1373-1378. PMID: 16946406.
10. Leggett J, Harper E, Waite E, et al. GHRH receptor-targeted botulinum neurotoxin selectively inhibits pulsatile GH secretion in male rats. Endocrinology. 2013;154(10):3688-3699. PMID: 23825127.
11. Barker SA, et al. An immuno polymerase chain reaction screen for the detection of CJC-1295 and other growth-hormone-releasing hormone analogs in equine plasma. Drug Test Anal. 2019;11(6):856-862. PMID: 30489688.
12. Memdouh S, Gavrilovic I, Ng K, et al. Advances in the detection of growth hormone releasing hormone synthetic analogs. Drug Test Anal. 2021;13(11-12):1813-1830. PMID: 34665524.
13. Pont L, Alechaga E, Terrero A, et al. Comparison of magnetic bead surface functionalities for the immunopurification of growth hormone-releasing hormones prior to liquid chromatography-tandem mass spectrometry. J Chromatogr A. 2020;1631:461568. PMID: 32971474.

This article is strictly for research reference; not for human or veterinary use. CJC-1295 and Modified GRF(1-29) are investigational compounds with no approved therapeutic indication. No vendor is assessed or endorsed. Investigators must comply with all applicable institutional, local and national regulations governing peptide acquisition and use in research.