CJC-1295 with DAC: Albumin Conjugation Chemistry and Circulating Half-Life

DAC abbreviates drug affinity complex, the bioconjugation platform developed at ConjuChem Biotechnologies. In CJC-1295 with DAC the complex is a single appended residue: a lysine at position 30 whose epsilon-amine carries a 3-maleimidopropionyl group. Everything preceding that lysine is a tetrasubstituted growth hormone-releasing hormone fragment, amidated at the C-terminus.

PubChem record 91971820 confirms the whole construct independently of any supplier description. Reading the systematic name residue by residue gives L-tyrosine followed by a D-configured alanine, then aspartate, alanine, isoleucine, phenylalanine and threonine, with glutamine appearing at position 8, alanine at 15 and leucine at 27. The terminal fragment reads 1-amino-6-[3-(2,5-dioxopyrrol-1-yl)propanoylamino]-1-oxohexan-2-yl, which is a lysine amide bearing a maleimide on its side chain.

Elemental arithmetic ties the two halves together and offers a quick identity check. The unappended tetrasubstituted backbone is C152H252N44O42 at 3367.9 g/mol. Subtracting that from C165H269N47O46 leaves C13H17N3O4, a difference of 279.3 g/mol, which is exactly one lysine residue plus one maleimidopropionyl acyl group after loss of water. A sample whose deconvoluted mass sits 279 units above the backbone carries the appendage; a sample matching the backbone alone does not.

The maleimide ring of CJC-1295 with DAC is an electron-poor alkene that undergoes Michael addition with thiolate anions, and human serum albumin presents exactly one accessible thiol. Cysteine 34 is the only free sulfhydryl among the 35 cysteines of the mature 585-residue protein, the other 34 locked into seventeen disulfide bridges.

Coupling at that residue is therefore selective by default rather than by design, and two properties of the carrier make it an unusually effective anchor. Albumin circulates at roughly 35 to 50 grams per litre, a molar concentration near 0.6 millimolar that vastly exceeds any peptide alongside it, so the maleimide meets Cys34 far more often than any competing nucleophile. Albumin also persists about nineteen days in circulation, a longevity attributable to pH-dependent capture by the neonatal Fc receptor, which diverts endocytosed albumin away from lysosomal degradation and returns it to the extracellular space.

The thiosuccinimide formed by that addition is durable but not inert. Bioconjugation chemists have documented a retro-Michael pathway in which the adduct reverts to free maleimide and free thiol, allowing exchange onto other thiol-bearing molecules, and a competing hydrolysis that opens the succinimide ring irreversibly and locks the linkage in place. Which route dominates depends on the local electronic environment of the linker, one reason newer albumin-binding chemistries have moved toward bromomaleimides and related ring systems.

CJC-1295 with DAC emerged from a 2005 screen of maleimido derivatives of hGRF(1-29) reported by Jetté and colleagues in Endocrinology. Three candidate structures were coupled to human serum albumin outside the animal and compared against the parent fragment for protease resistance, for growth hormone release from cultured rat anterior pituitary cells, and for persistence in rat plasma.

Each conjugate resisted dipeptidyl peptidase IV better than unmodified hGRF(1-29) and still triggered growth hormone secretion in the pituitary cell assay, establishing that a bulky albumin tether at the C-terminus does not abolish recognition at a receptor whose critical contacts lie at the peptide N-terminus. In Sprague-Dawley rats the selected candidate quadrupled the two-hour growth hormone area under the curve against the parent fragment and stayed detectable in plasma past 72 hours. Western blotting placed an immunoreactive species on the albumin band from fifteen minutes onward, direct evidence that capture happens in vivo rather than only in a tube.

A 2006 study in the GHRH knockout mouse tested whether sustained receptor occupancy could substitute for the missing hypothalamic signal. Animals received 2 micrograms at 24, 48 or 72 hour intervals for five weeks beginning at one week of age. The 24-hour schedule restored growth to the range of heterozygous littermates in both mass and body length, while the wider intervals fell short, giving a crude in vivo measure of how long a single quantity of the conjugate keeps the axis engaged.

Human data for CJC-1295 with DAC come from two randomised, placebo-controlled, double-blind ascending-level trials in healthy adults aged 21 to 61, published by Teichman and colleagues in 2006. The trials ran 28 and 49 days across two investigational sites, the second repeating exposure two or three times at weekly or biweekly spacing.

The pharmacokinetic result is the number the compound is known for. Estimated half-life was 5.8 to 8.1 days, an interval that matches the timescale of albumin turnover rather than the timescale of a free peptide. Downstream, mean plasma growth hormone rose two- to tenfold for six days or longer and mean plasma IGF-I rose 1.5- to threefold for nine to eleven days, both scaling with the quantity given. Under the repeated schedule IGF-I stayed above baseline for as long as 28 days. The authors reported no serious adverse reactions, with tolerability described as acceptable at the 30 and 60 microgram per kilogram levels.

A companion study by Ionescu and Frohman asked what continuous receptor stimulation does to the shape of growth hormone output. Healthy men aged 20 to 40 received 60 or 90 micrograms per kilogram and were sampled every 20 minutes for 12 hours one week later. Basal growth hormone rose 7.5-fold, mean growth hormone rose 45 percent and IGF-I rose 45 percent, yet pulse frequency and amplitude were preserved. Sustained agonist presence raised the floor of the rhythm without erasing the rhythm itself, which is a statement about pituitary physiology rather than about any outcome.

CJC-1295 with DAC and the same tetrasubstituted backbone without the appendage are catalogued as separate materials because their kinetics diverge. The four backbone substitutions govern how fast proteases degrade the peptide. The maleimide governs whether a plasma protein carries it at all, and only the second mechanism operates over a timescale of days.

Nomenclature obscures this more than the chemistry does. In the primary literature the designation CJC-1295 refers to the conjugating molecule described in 2005, so a database search on the bare name returns work on the DAC form. The no-DAC label was applied afterwards to distinguish the backbone sold separately, which means published half-life figures, trial results and receptor pharmacology attached to the name CJC-1295 describe the albumin-binding compound unless a source states otherwise.

The distinction also shows up in what degradation studies can and cannot say. A 2023 stability investigation of growth hormone-releasing peptides and GHRH-related fragments found that only some synthetic fragments survived incubation in human blood, trypsin and chymotrypsin well enough to serve as internal standards. Those measurements characterise free peptide in matrix. For the DAC form, the relevant question is how long the albumin carrier lasts, and the carrier outlives any of these fragments by more than an order of magnitude.

CJC-1295 with DAC is a named target in anti-doping analytical chemistry, listed by the World Anti-Doping Agency under growth hormone releasing factors within section S2 of the Prohibited List effective 1 January 2026. That status has driven most of the published method development, and the resulting papers are where quantitative detection figures for this molecule exist.

Equine work supplied the first confirmation method aimed squarely at the conjugate. Timms and colleagues reported in 2019 that immuno-affinity capture followed by tryptic digestion and liquid chromatography tandem mass spectrometry identified CJC-1295 down to 180 picograms per millilitre in one millilitre of plasma. The same group had published an immuno-polymerase chain reaction screen for the wider GHRH analogue family the previous year.

Human urine methods have since converged on high-resolution instruments at nanolitre flow rates. A 2026 method from Uçaktürk and Nemutlu combined ultrafiltration with solid-phase extraction ahead of nano-liquid chromatography on a quadrupole-Orbitrap analyser, covering GHRH and its synthetic analogues including CJC-1295, and reported detection limits at or below 0.5 nanograms per millilitre with identification limits between 0.5 and 0.75 nanograms per millilitre. Separately, capillary electrophoresis with a dimethyl-beta-cyclodextrin selector has been used to resolve GHRH analogues that differ only in the configuration of a single residue, the structural feature that D-alanine at position 2 introduces into this family.

Published handling guidance specific to CJC-1295 with DAC is limited, and the useful constraints come from maleimide chemistry rather than from any stability study of this molecule. The material is supplied as a lyophilized powder in a 5 mg presentation. Storage figures in supplier catalogues are specifications, not peer-reviewed measurements.

The reactive group is the part that fails first. A maleimide ring hydrolyses in aqueous base to the corresponding maleamic acid, an open-chain product that no longer undergoes Michael addition, so alkaline buffers quietly convert the conjugating peptide into a non-conjugating one with no change in appearance. Neutral to slightly acidic aqueous conditions slow that reaction. Free thiols introduced from any source, including reducing agents left over from other workflows, will consume the maleimide directly and compete with whatever carrier protein the experiment intends to label.

For identity confirmation, mass spectrometry gives the cleanest checks. The monoisotopic mass to verify against a deconvoluted electrospray spectrum is 3645.015 Da, with an average molecular weight of 3647.2 g/mol. Two negative controls are worth running alongside. The molecule contains no sulfur, so any sulfur signature in elemental analysis points to an unsubstituted GHRH fragment rather than this analogue. And a species 18 units heavier than expected indicates ring-opened maleamic acid, while a species 279 units lighter indicates the bare tetrasubstituted backbone with no appendage at all. The computed descriptors, XLogP of minus 11.7 and a topological polar surface area of 1540 square angstroms, describe a highly polar molecule with no expectation of passive membrane permeability.