CJC-1295 DAC vs CJC-1295 (No DAC): Complete Comparison

CJC-1295 with DAC and CJC-1295 without DAC share the same core peptide sequence but differ profoundly in their pharmacokinetic behavior and, consequently, their physiological effects on the growth hormone axis. Understanding this distinction is essential for researchers designing experimental protocols involving GHRH-analog stimulation of the somatotropic axis.

The core peptide in both compounds is a modified 29-amino-acid fragment of human GHRH (GRF 1-29) with four amino acid substitutions (Ala2→D-Ala, Asn8→Gln, Ala15→Ala, Met27→Leu) introduced to enhance metabolic stability against dipeptidyl peptidase-IV (DPP-IV) cleavage and methionine oxidation. These substitutions extend the intrinsic half-life from the ~7 minutes of native GHRH to approximately 30 minutes for the tetrasubstituted analog [1].

The DAC version adds a further modification: a maleimidopropionic acid (MPA) linker attached to a lysine residue at position 30, which contains a reactive succinimide group that spontaneously forms a covalent thioether bond with Cys34 of circulating serum albumin. This albumin conjugation protects the peptide from renal clearance and proteolytic degradation, resulting in an approximately 160-fold increase in plasma half-life from ~30 minutes to ~8 days [2].

• CJC-1295 DAC: Half-life ~8 days, continuous GH elevation, albumin-binding
• CJC-1295 no DAC (Mod GRF 1-29): Half-life ~30 min, pulsatile GH release, no albumin binding
• Shared core: Tetrasubstituted GRF(1-29) [D-Ala2, Gln8, Ala15, Leu27]
• GHRH receptor agonist mechanism common to both
• DAC = Drug Affinity Complex (maleimidopropionic acid-based reactive linker)
• Different GH kinetics produce different physiological research outcomes
• No DAC version often combined with GHRP-class co-agonists in research
• DAC version used as single-agent sustained GHRH stimulation tool

CJC-1295 without DAC (Mod GRF 1-29, also termed tetrasubstituted GRF 1-29) is a 29-amino-acid linear peptide with the sequence: 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 molecular formula is approximately C₁₅₂H₂₅₂N₄₄O₄₂ with a molecular weight of ~3367.9 Da. The four substitutions relative to native GRF(1-29) are at positions 2 (Ala→D-Ala), 8 (Asn→Gln), 15 (Gly→Ala), and 27 (Met→Leu) [1].

CJC-1295 with DAC adds a C-terminal lysine residue at position 30 that serves as the attachment point for the DAC linker. The DAC moiety consists of a maleimidopropionic acid (MPA) group connected through a diaminobutyric acid (Dab) spacer, creating a reactive succinimide that undergoes Michael addition with the free thiol of albumin Cys34. The total molecular weight of CJC-1295 DAC (pre-conjugation) is approximately 3647.3 Da. Upon albumin conjugation in vivo, the effective molecular weight exceeds 70 kDa, placing it well above the renal filtration cutoff [2].

Both compounds are produced by solid-phase peptide synthesis using Fmoc chemistry. The DAC version requires additional synthetic steps for incorporation of the Lys30 residue and subsequent conjugation of the MPA-Dab linker. Both are supplied as white to off-white lyophilized powders, soluble in water and aqueous buffers at pH 7–8.

• Mod GRF 1-29 (no DAC): MW ~3367.9 Da, 29 amino acids
• CJC-1295 DAC: MW ~3647.3 Da (pre-conjugation), 30 amino acids + DAC linker
• Core substitutions: D-Ala2, Gln8, Ala15, Leu27 (both forms)
• DAC attachment: Lys30 → MPA-Dab reactive succinimide
• In vivo conjugate MW: >70 kDa (albumin complex)
• Appearance: White lyophilized powder (both)
• Solubility: Aqueous buffers pH 7–8 (both)
• Storage: –20°C desiccated (both)

The Drug Affinity Complex (DAC) technology was developed by ConjuChem Biotechnologies (Montreal, Canada) as a platform for extending the half-life of peptide therapeutics. The technology is based on the principle of in vivo covalent conjugation to endogenous serum albumin, exploiting the uniquely reactive Cys34 thiol on albumin that is accessible for chemical modification while the protein circulates in plasma [3].

The reactive element in the DAC linker is a maleimide group that undergoes a rapid, irreversible Michael addition with the Cys34 thiol under physiological conditions (pH 7.4, 37°C). The reaction is highly selective for the free thiol of albumin due to the nucleophilicity of the cysteine sulfhydryl group and the electrophilic character of the maleimide. The resulting thioether bond is stable under physiological conditions with no significant reversion over the lifetime of the albumin molecule (~19 days in humans).

The albumin conjugation provides half-life extension through multiple mechanisms: (1) the large molecular size of the conjugate (>70 kDa) prevents glomerular filtration, (2) albumin's natural recycling through the FcRn (neonatal Fc receptor) salvage pathway extends the circulatory residence time, and (3) the steric bulk of albumin protects the attached peptide from proteolytic degradation. The CJC-1295 DAC:albumin conjugate retains GHRH receptor binding activity, confirming that the C-terminal conjugation site does not interfere with the N-terminal receptor-binding domain [4].

The pharmacokinetic difference between the two CJC-1295 forms is dramatic and represents the most consequential distinction for research applications. Native human GHRH(1-44) has a plasma half-life of approximately 7 minutes due to rapid DPP-IV cleavage at the Ala2-Asp3 bond. The four substitutions in the tetrasubstituted analog (Mod GRF 1-29) extend this to approximately 30 minutes by conferring DPP-IV resistance and reducing oxidative degradation [1].

CJC-1295 with DAC achieves a dramatically longer half-life of approximately 8 days following subcutaneous administration, as determined in clinical pharmacokinetic studies. In a Phase I/II study, a single subcutaneous injection of CJC-1295 DAC (30–60 µg/kg) produced measurable plasma GH elevations for 6–14 days, with the peptide detectable in plasma for up to 14+ days post-injection [4]. This represents an approximately 160-fold increase over the no-DAC form and enables weekly or biweekly dosing schedules in research protocols.

The pharmacokinetic profiles translate directly into different exposure-time curves. Mod GRF 1-29 produces a rapid spike in plasma concentration that peaks within 15–30 minutes post-injection and is essentially cleared within 2–3 hours, yielding a sharp, discrete pharmacokinetic pulse. CJC-1295 DAC produces a gradual rise to plateau concentrations achieved over 24–48 hours, maintained for several days, with slow decline over the following week.

The distinct pharmacokinetic profiles of the two CJC-1295 forms produce fundamentally different patterns of GH release from pituitary somatotrophs. Mod GRF 1-29, with its ~30-minute half-life, generates a discrete GH pulse that mimics the natural pulsatile pattern of endogenous GHRH release. Each injection produces a GH peak approximately 15–30 minutes post-administration, with GH levels returning to baseline within 2–3 hours [5].

CJC-1295 with DAC, by maintaining sustained GHRH receptor stimulation over days, produces a continuous elevation of baseline GH levels with blunting of the normal pulsatile pattern. Clinical studies reported 2–10-fold elevations in mean 24-hour GH concentrations persisting for 6+ days following a single injection [4]. This continuous GH elevation differs fundamentally from the physiological pattern and from the effect produced by the no-DAC form.

The distinction between pulsatile and continuous GH stimulation has significant implications for downstream signaling. Pulsatile GH release preferentially activates certain STAT5b-dependent gene expression programs in the liver (including IGF-1 production), while continuous GH exposure activates different transcriptional programs. Research comparing these two patterns of GHRH receptor stimulation uses the DAC/no-DAC pair as a pharmacological tool to dissect GH signaling dynamics.

The physiological significance of pulsatile versus continuous GH secretion has been a central question in endocrinology research for decades. Normal GH secretion occurs in 6–12 discrete pulses per day, with the largest pulses occurring during slow-wave sleep. This pulsatile pattern is generated by the alternating release of GHRH and somatostatin from the hypothalamus and is critical for the sex-dimorphic pattern of hepatic gene expression and optimal IGF-1 production [6].

Research using the CJC-1295 DAC/no-DAC comparison directly addresses this fundamental question. Studies have examined whether sustained (DAC-mediated) versus pulsatile (no-DAC) GHRH receptor stimulation produces different effects on IGF-1 levels, body composition, insulin sensitivity, and gene expression in target tissues. In clinical studies, both forms elevated IGF-1 levels, but the kinetic profiles differed: CJC-1295 DAC produced a sustained IGF-1 elevation, while Mod GRF 1-29 produced transient IGF-1 peaks correlated with GH pulses [7].

The continuous GH elevation produced by CJC-1295 DAC raises important research considerations regarding GH receptor desensitization, potential insulin resistance effects (GH is a counter-regulatory hormone), and long-term effects on somatotroph sensitivity. These questions make the DAC/no-DAC pair a valuable research tool for studying GH axis physiology beyond simple GH secretagogue applications.

Both CJC-1295 forms activate the growth hormone-releasing hormone receptor (GHRHR), a class B (secretin family) G protein-coupled receptor expressed primarily on anterior pituitary somatotrophs. The GHRHR couples to Gαs proteins, activating adenylyl cyclase, increasing intracellular cAMP, and stimulating protein kinase A (PKA)-mediated signaling cascades that culminate in GH gene transcription and GH granule exocytosis [8].

The receptor-binding domain of GHRH is located within the N-terminal 29 residues, with positions 1–7 being critical for receptor activation. The four substitutions in the CJC-1295 core sequence do not impair receptor binding affinity, as they are located at positions outside the primary receptor contact domain. Receptor binding studies have confirmed that both the DAC and no-DAC forms exhibit comparable GHRHR binding affinity (Ki in the low nanomolar range), indicating that the DAC modification does not alter intrinsic receptor pharmacology.

An important pharmacological consideration is that GHRH receptor stimulation alone, without concurrent suppression of somatostatin tone, produces submaximal GH release. This is why Mod GRF 1-29 is frequently co-administered with GHRP-class peptides (ipamorelin, GHRP-6, GHRP-2) in research protocols. GHRPs act through the ghrelin receptor (GHS-R1a) and suppress somatostatin release, creating a synergistic amplification of GH pulse amplitude. CJC-1295 DAC, with its sustained action, is less commonly combined with GHRPs because the continuous stimulation pattern differs from the pulsatile paradigm that GHRH/GHRP combinations are designed to amplify.

The choice between CJC-1295 DAC and Mod GRF 1-29 in research protocols depends on the specific experimental question. For studies examining acute GH pulse dynamics, GH pulse-gene expression relationships, or pulsatile secretagogue combinations, Mod GRF 1-29 is the appropriate tool due to its discrete pharmacokinetic profile. For studies requiring sustained GHRH receptor stimulation, extended GH elevation, or reduced injection frequency, CJC-1295 DAC is preferred.

Mod GRF 1-29 is typically administered in research settings at doses of 1–2 µg/kg per injection, with multiple daily administrations to produce discrete GH pulses. The short half-life requires careful timing relative to endpoint measurements. CJC-1295 DAC is administered at doses of 30–60 µg/kg once or twice weekly, with the pharmacokinetic plateau providing a more stable baseline for longitudinal measurements [4].

Storage and handling requirements are similar for both compounds: lyophilized material at –20°C with reconstitution in bacteriostatic water or sterile saline immediately before use. Reconstituted solutions should be stored at 2–8°C and used within 21 days. Both compounds are susceptible to methionine oxidation (despite the Met27→Leu substitution, which addresses the most vulnerable site) and should be protected from light exposure.

Clinical safety data for CJC-1295 DAC derive primarily from Phase I/II studies conducted by ConjuChem Biotechnologies. In these studies involving healthy subjects and GH-deficient adults, the most commonly reported adverse effects were injection site reactions (erythema, induration, pain), transient flushing, and headache. These effects were generally mild and self-limiting [4]. Importantly, cortisol and prolactin levels were not significantly affected, confirming selectivity for the somatotropic axis.

Safety considerations specific to the DAC form include the potential effects of sustained GH elevation on insulin sensitivity. GH is a counter-regulatory hormone that opposes insulin action, and prolonged GH elevation can induce insulin resistance. Clinical monitoring in CJC-1295 DAC studies showed transient elevations in fasting glucose and insulin in some subjects, an expected pharmacological effect of sustained GH exposure that researchers should account for in protocol design [9].

For Mod GRF 1-29, the safety profile reflects its transient pharmacokinetic pattern. The discrete GH pulses produced by individual injections do not cause sustained GH elevation and therefore pose lower risk of chronic GH-excess effects. Injection site reactions and transient flushing remain the most commonly observed effects. Researchers should follow standard peptide handling protocols and be aware that both compounds are potent at microgram-per-kilogram doses.

Explore detailed chemical profiles and research guides for compounds discussed in this article:

• CJC-1295: Complete Research Guide → /learn/cjc-1295-no-dac

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