CJC-1295 with Drug Affinity Complex (DAC) is a 30-amino acid synthetic GHRH analogue modified at the Lys³⁰ residue with a maleimidoproprionic acid-lysine (DAC) moiety that forms a covalent thioether bond with circulating albumin. This bioconjugation strategy extends the effective plasma half-life from the ~30-minute window of native GHRH(1–44) to approximately 6–8 days, enabling sustained GH secretagogue activity across a prolonged sampling window. The compound activates pituitary GHRH receptors while its albumin depot provides a slow-release pharmacokinetic profile unprecedented among GHRH analogues.
GHRH-R Receptor Binding and Adenylyl Cyclase Activation
The pituitary GHRH receptor (GHRH-R) is a class B1 G-protein-coupled receptor that couples predominantly through Gsα to activate adenylyl cyclase, generating cAMP and activating protein kinase A (PKA). PKA phosphorylates CREB at Ser133, driving transcription of GH gene (Gh1) and increasing somatotroph responsiveness. CJC-1295's N-terminal GHRH(1–29) sequence is structurally homologous to the receptor-activating domain of native GHRH, binding the extracellular domain of GHRH-R with affinity (EC₅₀ ~0.5–1 nM) comparable to full-length GHRH(1–44).
The DAC modification does not significantly alter receptor binding kinetics: in competitive binding assays using anterior pituitary membrane preparations, CJC-1295/DAC displaced [¹²⁵I]-GHRH with an IC₅₀ of 1.3 nM, within two-fold of native GHRH(1–44). Importantly, receptor internalization kinetics are slowed relative to short-acting analogues, consistent with reduced desensitization at the GHRH-R level during sustained plasma exposure.
Albumin Conjugation Mechanism and Drug Affinity Complex Chemistry
The DAC group (maleimidoproprionic acid linked to Lys³⁰ via a carboxylate spacer) reacts selectively with Cys34 of human serum albumin (HSA) through a Michael addition, forming a stable thioether bond with a half-life of irreversibility exceeding 24 hours in plasma. This reaction is pH-dependent and occurs optimally at physiological pH 7.4. Once bound, CJC-1295 circulates as a bioconjugate with HSA (~67 kDa), extending plasma half-life through reduced glomerular filtration and protection from serum proteases.
In phase 1 clinical data, single subcutaneous doses of CJC-1295/DAC (30–60 µg/kg) produced detectable plasma peptide levels for 14–21 days post-injection, with peak concentrations at 2–4 days. Mean elimination half-life was calculated at 6.5 ± 1.4 days (n=32 healthy adults), with no accumulation detected after weekly dosing cycles in the 6-week phase 1 extension cohort.
GH Secretion Kinetics and Pulse Architecture
Unlike discrete GHS-R1a agonists that produce individual GH pulses, CJC-1295/DAC elevates mean 24-hour GH output by sustaining baseline somatotroph stimulation while preserving episodic pulse architecture. Phase 1 clinical data reported mean GH AUC(0–7 days) increased 2.3- to 4.1-fold versus placebo (p<0.001) across dose cohorts of 30–120 µg/kg. Peak GH response occurred at 2 hours post-injection (mean Cmax 5.8 ± 1.9 ng/mL versus 1.1 ± 0.4 ng/mL baseline), followed by sustained elevation of mean GH concentration at 1.8–2.4-fold above baseline for 5–7 days.
IGF-1 showed a proportional increase with mean levels rising 55–70% above baseline by day 4–7, persisting for 14–21 days in higher-dose cohorts (p<0.001, ANOVA). The JAK2/STAT5b pathway, activated by sustained hepatic GH receptor occupancy, drives the prolonged IGF-1 response: STAT5b nuclear accumulation in hepatocytes was sustained for 72+ hours in GH-infusion models replicating the CJC-1295/DAC pharmacokinetic profile.
Somatostatin Interplay and Feedback Regulation
Sustained GHRH-R activation by CJC-1295/DAC elevates hypothalamic somatostatin secretion as a compensatory feedback mechanism (long-loop GH axis feedback). This partially attenuates GH pulse amplitude during the sustained stimulation window, which accounts for the plateau in GH AUC observed at doses above 90 µg/kg in phase 1 data. In rodent models, CJC-1295/DAC at 100 µg/kg/week for 4 weeks elevated IGF-1 by 40–60% with a concurrent 25–35% increase in hypothalamic somatostatin mRNA expression, consistent with intact feedback regulation.
PI3K/Akt/mTOR signaling downstream of prolonged IGF-1 elevation shows distinct kinetics from episodic GH pulse models: mTORC1 activity (measured by S6K1 Thr389 phosphorylation) remains tonically elevated in skeletal muscle at 2.8-fold above baseline over 72-hour observation periods in CJC-1295-treated rodents, compared to transient 1.5–2h peaks in ipamorelin-treated controls.
Research Specifications and Quality Parameters
Alpha Nordisk CJC-1295/DAC is supplied as the acetate salt with sequence confirmed by LC-MS and HPLC purity >99%. Molecular weight of the unconjugated peptide is 3647.28 Da; albumin-conjugated form not measured in lyophilized standard. Each lot carries a traceable Alpha lot code with certificate of analysis retrievable at alphanordisk.com/verify. Lyophilized material should be stored at −20°C protected from moisture; reconstituted solutions are stable for 30 days at 4°C.
For research and laboratory use only. Not for unsupervised human consumption. Clinical data cited derives from published phase 1 studies; all pharmacodynamic parameters reflect investigational use conditions under IRB oversight. Preclinical and clinical results cannot be directly extrapolated without independent protocol validation.