Q: How does Cupid work?


A: Cupid is a peptide & protein delivery system. Our products are composed of two parts. The lead peptide ‘Cupid’ functions as a vehicle to transport the cargo (peptide or protein) through the cell membrane into the cells. Confocal observations indicate the entry process of Cupid is not dependent on endocytosis, like e.g. TAT and Polyarginine, suggesting direct translocation through membrane bilayers.

Once within the cells, the cargo peptide is able to fold into its bioactive form in the cytosol directed by the cells’ own protein folding machinery, as if it had been newly created by the cell itself. The cargo is then free to exert biological effects intrinsic to its structure.


Q: What are the advantages of using Cupid cell penetrating technology?


Cupid technology gives the researcher a new tool to use in conjunction with other approaches. Cupid technology offers the researcher the ability to introduce proteins or parts of proteins into living cells within 1 hour. This approach can offer a huge advantage over genetic manipulation requiring considerable resources in both time and effort, and siRNA experiments which can only hope to deplete whole proteins over many hours or days. Such approaches carry the implicit assumption that the cell will not respond to counteract the changes imposed upon it (e.g. Up-regulate parallel pathways) or that the manipulation does not prove lethal to the cell. Cupid technology, on the other hand, is an acute and controllable process that allows study of both immediate and counteracting processes in real time.


Q: Why use Cupid instead of other cell penetrating peptides?


A: It is known that other cell penetrating peptides such as TAT and polyarginine / lysine enter cells in vesicles through the endocytosis pathway. Such agents are observed within vesicles inside the cells and are essentially therefore trapped within the endocytotic system (Ref 1-3 ).

This raises major questions as to their suitability as agents to deliver bioactive cargoes to the wider cell architecture.

Our proprietary cell penetrating peptide, Cupid, passes through cell membranes of a wide range of living cells including mammalian, plant, plant protoplast, fungal and amoeba. It delivers itself, and any attached cargo, to the cytosol fraction of the cell. Using Cupid coupled to GFP (Green Fluorescent Protein), we have seen no evidence of vesicle formation (indicative of entry via endocytosis) using real-time confocal microscopy. Based on the diffuse pattern of internalized Cupid-GFP we conclude that Cupid enters the cell through interaction with the bilipid layer itself and moves throughout the entire cell.


Q: Are Cupid peptides easy to use?


A: Yes. Cupid cell penetrating peptides are dissolved in water to make a stock solution. This stock is diluted to the desired concentration in cell free media to make a working solution. To start an experiment, simply exchange the working solution with the media containing the cells.


Q: How large a cargo can cupid deliver into living cells?


A: The largest Cupid product we have made contains GFP and a 50kD cargo, the whole being 83 kD kilodaltons in size. We observe this entering living cells and causing them to fluoresce within 1 hour. We believe we have not reached the limit of cargo size.


Q: Are the effects of Cupid peptides reversible?


A: The effect of Cupid cell penetrating peptides should be reversible by simply exchanging the culture media, since all proteins within cells are constantly ‘turned over’ (Half lives will vary from cargo to cargo).


Q: Can I design my own Cupid peptides?


A: At Cupid peptides we specialise exclusively in the manufacture of cell penetrating products. We can undertake to couple Cupid to any peptide or protein. We aim to be very flexible in our arrangements of customised synthesis according to the scale and the exclusivity required. Contact us in confidence.



1) Lundberg M, Wikström S, Johansson M. Cell surface adherence and endocytosis of protein transduction domains. Mol Ther. 2003;8(1):143-150. doi:10.1016/s1525-0016(03)00135-7



2) Palm-Apergi C, Lönn P, Dowdy SF. Do cell-penetrating peptides actually "penetrate" cellular membranes?. Mol Ther. 2012;20(4):695-697. doi:10.1038/mt.2012.40



3) Gestin M, Dowaidar M, Langel Ü. Uptake Mechanism of Cell-Penetrating Peptides. Adv Exp Med Biol. 2017;1030:255-264. doi:10.1007/978-3-319-66095-0_11