CJC-1295 With DAC vs Without DAC (Mod GRF 1-29): What the DAC Changes

CJC-1295 was the code name for modified GRF(1-29) carrying a maleimidopropionyl drug affinity complex. Over time the code was applied to the underlying peptide without the complex, which is more accurately called modified GRF(1-29) or Mod GRF 1-29. The industry now sells 'CJC-1295 with DAC' and 'CJC-1295 no DAC' as two products, and a great deal of unlabeled 'CJC-1295' is the no-DAC form.

Certus labels both explicitly and states the modification set on the certificate. If a certificate you are reading elsewhere does not say which form it describes, the observed mass will, and the section on mass below explains how.

Sermorelin is GHRH(1-29) with a C-terminal amide, the shortest fragment of the 44-residue growth hormone releasing hormone that retains full activity at the GHRH receptor. Its average molecular weight is 3357.9 Da. It is unmodified, and it degrades quickly: DPP-4 cleaves between residues 2 and 3, and the asparagine at position 8 is prone to rearrangement.

Modified GRF(1-29) keeps the same 29-residue frame and makes four substitutions: D-alanine at position 2 to block DPP-4, glutamine at 8 in place of asparagine to prevent the rearrangement, alanine at 15 in place of glycine, and leucine at 27 in place of methionine to remove the oxidation-prone residue. Its formula is C152H252N44O42 and its molecular weight 3367.9 Da, ten daltons above sermorelin. Both are GHRH receptor agonists; the modified sequence is simply the one that survives in solution and in plasma.

The drug affinity complex is a maleimidopropionyl group attached through a linker to the side chain of the C-terminal lysine. A maleimide is a five-membered ring with a reactive double bond that undergoes Michael addition with a free thiol. In serum, the free thiol it finds is cysteine 34 of albumin, and the reaction tethers the peptide covalently to a carrier protein that circulates for weeks.

The consequence at the receptor is a shift from pulsatile to sustained exposure. That is not simply a longer-lasting version of the same stimulus; it is a categorically different condition, and work on receptor desensitization kinetics or pulse timing needs the no-DAC form for exactly that reason, while sustained-elevation work needs the DAC form.

Chemically, the DAC adds C13H17N3O4 to the peptide. The DAC product has the formula C165H269N47O46 and a molecular weight of 3647.2 Da, which is 279.3 Da above the no-DAC form.

279 Da is an enormous difference at the resolution of electrospray LC-MS, where the certificate tolerance is 1.0 Da. A vial labeled 'with DAC' whose observed mass is 3367.9 Da does not contain the DAC form, whatever the label says, and a vial labeled 'no DAC' at 3647.2 Da does. This is the one case in the catalog where the identity line alone settles a labeling dispute.

There is a subtler defect that the mass also reveals. A maleimide ring hydrolyzes on exposure to water to give a maleamic acid, which adds 18.01 Da and cannot react with a thiol. Hydrolyzed DAC material weighs 3665.2 Da, still clearly not the no-DAC form, but no longer able to bind albumin. It is, functionally, an expensive no-DAC preparation with an inert appendage.

That is why the Certus certificate for CJC-1295 with DAC carries an additional line beyond mass: maleimide integrity by thiol conjugation efficiency against a standard, with a release specification of 90.0 %. The mass proves the DAC is present; the conjugation assay proves it still works.

For the no-DAC form the stability story is ordinary for a 29-mer: store lyophilized at -20 °C protected from light because of the tryptophans, swirl rather than shake because the peptide aggregates under shear, and hold reconstituted stock at 2-8 °C.

The DAC form adds moisture sensitivity on top of that. Maleimide hydrolysis proceeds in any aqueous environment and accelerates above neutral pH, so the cake must be kept desiccated, the sealed vial should reach room temperature before it is opened so that no condensation forms on the cold cake, and reconstitution should happen immediately before the material is needed. Conjugation efficiency declines in solution from the moment diluent is added. Certus ships this product with desiccant regardless of order size, and the release specification of 98.0 % rather than 99.0 % reflects that the DAC synthesis has more steps and more ways to go wrong.

Work that needs a discrete, time-limited GHRH receptor stimulus, including any study of pulse timing, desensitization, or the interaction between GHRH receptor and ghrelin receptor signaling, needs the no-DAC form. Ipamorelin, a selective ghrelin receptor agonist, is the standard partner in that second kind of experiment because the two receptors converge on the same secretory cell through different second-messenger systems.

Work that needs sustained receptor occupancy over days needs the DAC form, and needs it with a verified maleimide. Sermorelin sits alongside both as the minimally engineered comparator: the same 29 residues with none of the modifications, for studies that need to attribute an observation to the substitutions themselves.

For the no-DAC form: HPLC purity against 99.0 %, an observed mass within 1.0 Da of 3367.9, net peptide content, water content, residual trifluoroacetate, endotoxin and sterility. The four substitutions cannot be read from the mass alone (sermorelin is only ten daltons away), so the certificate should state the modification set, and the retention time against a reference standard is the confirming line.

For the DAC form: the same panel against 98.0 %, an observed mass within 1.0 Da of 3647.2, and maleimide integrity by conjugation efficiency. A DAC certificate without a conjugation line has proved that the handle was attached, not that it is still intact.