CJC-1295 vs Ipamorelin vs MK-677: Two Receptors, Three Design Fixes

In 1996, a Merck team cloned the growth hormone (GH) secretagogue receptor. It turned up in pituitary and hypothalamic tissue, but its natural ligand was still unknown [1].

The hormone surfaced three years later, in the stomach of all places. Kojima’s lab pulled a 28-amino-acid peptide out of rat stomach tissue, watched it bind that same receptor, and named it ghrelin (“ghre” is an old Proto-Indo-European root for grow) [2].

So the synthetic keys came first, and the lock’s own key turned up years behind them.

Two of the three compounds in this comparison are keys of exactly that kind. The third one opens a different lock. Most comparison pages blur that. It matters, because each of these molecules was built to patch one weakness in whatever came before it. Spot the weakness and the right experiment usually picks itself.

Two receptors, three molecules

CJC-1295 is GHRH (growth hormone-releasing hormone) with a few deliberate edits. It lands on the GHRH receptor in the anterior pituitary, same as the native hormone.

Ipamorelin and MK-677 skip that receptor entirely. Both hit GHS-R1a, the growth hormone secretagogue receptor, which most people now just call the ghrelin receptor. Raun’s team showed this for ipamorelin with antagonist experiments [3]. Merck’s profiling put MK-677 squarely in the GHRP-6 camp and nowhere near GHRH [4].

CJC-1295 and the 17-minute problem

Native GHRH falls apart fast. Frohman’s lab dropped human GHRH(1-44) into human plasma in vitro and watched it by HPLC: the intact peptide had a half-life of 17 minutes. The leftover fragment, GHRH(3-44), kept under 0.1% of the original activity [5].

The enzyme behind it got named in 1989. Dipeptidylpeptidase IV (DPP-IV) chops off the first two residues, and a D-amino acid at position 1 or 2 is enough to stop it [6]. Campbell’s group at Hoffmann-La Roche found the rest of the soft spots in 1994. Asn8 rearranges in water. Met27 oxidizes. Gly15 swapped for alanine binds the receptor better [7].

Now open CJC-1295 on PubChem and read positions 2, 8, 15 and 27. D-alanine. Glutamine. Alanine. Leucine. Every weak spot on that list got its own patch, which is a satisfying thing to see in one sequence. Strip off the tail and that 29-residue core is what’s normally labeled Mod GRF (1-29), also called CJC-1295 without DAC. Our DAC vs no-DAC comparison gets into that split.

The tail is the DAC part. A lysine at position 30 carries a maleimidopropionyl group, and that group latches covalently onto cysteine 34 of serum albumin. In Jetté’s 2005 rat studies the analog was still in plasma after 72 hours, sitting right on the albumin band in a Western blot. Over a two-hour window it gave four times the GH area under the curve of plain GHRH(1-29) [8].

Those are different measurements: a 17-minute half-life for native GHRH in vitro and detection of the albumin-linked analog in rat plasma at 72 hours.

Alba’s group measured body growth in GHRH knockout mice exposed to CJC-1295. The study compared intervals of 24, 48 and 72 hours and reported normal size only in the 24-hour group [9].

Ipamorelin and the selectivity problem

GHRP-6 and GHRP-2 were the standard ghrelin-receptor tools of the mid-1990s, and both came with a problem. In Raun’s swine work they raised ACTH and cortisol, stress-axis noise you don’t want in a study trying to read GH by itself.

Ipamorelin is a pentapeptide, Aib-His-D-2-Nal-D-Phe-Lys-NH2, out of a Novo Nordisk chemistry program. On rat pituitary cells it ran close to GHRP-6 (EC50 1.3 nmol/L vs 2.2, about 85% of the maximal response).

In Raun’s swine experiments, ACTH and cortisol responses to ipamorelin did not exceed those observed with GHRH, even at more than 200 times the amount associated with a half-maximal GH response [3]. More on the wider family in our ipamorelin vs GHRP-2 vs GHRP-6 piece.

Those hormone measurements came from swine, not a comparison across species.

MK-677 and the peptide problem

Merck aimed somewhere else. They wanted a non-peptide scaffold that could still engage the receptor, and MK-677 (L-163,191) was what came out. In rat pituitary cells, it stimulated GH release at an EC50 of 1.3 nM. In dogs, the study reported increased GH, little change in aldosterone, LH, thyroxine or prolactin, and a small cortisol increase [4].

You may have noticed the number. 1.3 nM again, identical to ipamorelin’s. Different labs, different cell preps, three years apart, so we wouldn’t read anything into the match. Run both in one assay if the comparison matters to you. Same story with cortisol, since one result is from dogs and the other from swine.

Side by side

Matching the compound to the question

The research question determines which properties matter. For CJC-1295, the structural distinction is the albumin-binding DAC group versus the peptide core without that group. Ipamorelin studies measured GH, ACTH and cortisol responses in swine. MK-677 offers a non-peptide scaffold for studying GHS-R1a. Comparisons need to account for assay conditions and species.

CJC-1295 acts at a different receptor from ipamorelin and MK-677. In cell-based comparisons, controls for each receptor help distinguish the signaling readouts.

That receptor Merck cloned in 1996 had no hormone to its name. Two of these compounds were made to switch it on before ghrelin was discovered, and the third was made to outlast a 17-minute enzyme clock somewhere else. Figure out which of those stories your study belongs to, and you’ve picked your compound.

References

1. Howard AD, et al. Science. 1996;273(5277):974-977. PubMed 8688086
2. Kojima M, et al. Nature. 1999;402(6762):656-660. PubMed 10604470
3. Raun K, et al. Eur J Endocrinol. 1998;139(5):552-561. PubMed 9849822
4. Patchett AA, et al. Proc Natl Acad Sci USA. 1995;92(15):7001-7005. PubMed 7624358
5. Frohman LA, et al. J Clin Invest. 1986;78(4):906-913. PubMed 3093533
6. Frohman LA, et al. J Clin Invest. 1989;83(5):1533-1540. PubMed 2565342
7. Campbell RM, et al. Peptides. 1994;15(3):489-495. PubMed 7937325
8. Jetté L, et al. Endocrinology. 2005;146(7):3052-3058. PubMed 15817669
9. Alba M, et al. Am J Physiol Endocrinol Metab. 2006;291(6):E1290-E1294. PubMed 16822960
10. PubChem compound records: CJC-1295 (CID 91971820), ipamorelin (CID 9831659), ibutamoren (CID 178024).

Disclaimer: This content is intended for research purposes only and is not meant to constitute medical advice.