Q&A Report: Synthetic Peptide Growth Factors: Forging the Path Forward for Regenerative Medicine, Cell Therapy, and Cellular Agriculture

Dr. Kosuke Minamihata answers questions about the benefits of synthetic peptide growth factors for regenerative medicine and cell therapy.

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What solvent should be used to dissolve PG peptides? Is it soluble in anything other than DMSO?

PG peptides are soluble in general media, but in the case of ultra-trace amounts, such as 2 µg, PG peptides in the medium may adhere to the container and micropipette tip. We recommend using DMSO for solubilization.

What is the degree of residuals in the cell and in the final product?

PG peptides do not directly enter the cells. Therefore, the amount of PG peptide remaining in the final product is expected to be reduced to below the detection limit through medium exchange and washing. However, theoretically, it is possible for PG peptides to enter cells by endocytosis and undergo proliferation and differentiation while still bound to the receptor. Hence, we cannot guarantee that the residual amount of PG peptides will be completely zero. The residual amount of PG peptides is greatly affected by conditions such as the concentration used in the actual process and the washing operations, so it is desirable to evaluate the residual amount of PG peptides in each product. We can conduct a contract analysis of the residual amount of PG peptide in the final product using ultra-sensitive MS or other methods. For more information, please contact us.

What are the shipping conditions/forms of PG peptides?

We ship PG peptides at -20℃. PG peptides are provided as lyophilized products without any additives. All PG peptides are in the acetate salt form.

Do PG peptides and recombinant growth factors have the same mechanism of action?

PG peptides work in the same mechanism of action as recombinant growth factors, and we have confirmed that they show the same activity as growth factors in cell proliferation and differentiation behavior of cultured cells. However, some growth factors also exhibit weak binding to other receptors in addition to their main receptors with strong affinity. Such complex binding behaviors of growth factors may be difficult to reproduce with PG peptides because PG peptides have very high specificity. Therefore, the possibility that growth factors and PG peptides have potentially different physiological activities cannot be completely ruled out.

Have any in vivo animal studies been conducted with PG peptides to ensure their safety? Can they be used for animal studies?

We haven’t conducted in vivo testing of PG peptides yet. So far we only have in vitro cytotoxicity data using cultured cells, showing no toxicity up to 10 μM of PG peptides, which is more than 1000 times the biologically active concentration of PG peptides. We will share the results of the in vivo study of PG peptides in the future when they become available.

Can you comment on the quality control on sterility of PG peptides after production and lyophilization?

Each lot of PG peptides is tested for purity (≧95%) by LC/MS and activity evaluation using cultured cells.

What is the stability of PG peptides?

Firstly, about the long-term storage stability, we have experimental data showing that our PG peptides are stable for over one year at -20℃ in the form of freeze-dried products. This long-term stability test is still ongoing, and we expect to be able to guarantee storage stability for even longer periods in the future. In addition, as our PG peptides are in the form of cyclic peptides containing some non-natural amino acids, they are very stable against degradation by proteases in cultured conditions. Also, PG peptides do not have tertiary structures like proteins, so they are very stable even at high temperatures. Actual experimental data has shown that PG peptides remain stable for one week at 37℃ in serum-free media.

What is the intended scale of manufacturing of PG peptides?

The PG peptides are synthesized by our sister company PeptiStar, and the maximum synthesis scale is up to 10 kg/batch, which means we can essentially accommodate any synthesis scale. Although our current product lineup is only sold on a microgram scale as RUO, we are capable of providing products on a milligram, gram, and even kilogram scale.

Are there any off-target effects of PG peptides? Is any toxicity observed?

During the development phase, we conducted an off-target panel assay against 68 targets and we confirmed that the PG peptide had no effect even at micromolar concentrations, demonstrating high specificity. Additionally, we conducted cytotoxicity assays using HEK293 cells and confirmed that the PG peptide did not exhibit cell toxicity at a concentration of 10 µg. This concentration is more than 1000 times higher than the concentration at which the PG peptide exhibits biological activity, so, under normal usage conditions, we believe tha PG peptides are highly specific and safe.

Is there a difference in activity per molar concentration between PG peptides and recombinant growth factors?

For all PG peptides, the activity per mole concentration is adjusted to the same level of corresponding growth factors.

Given the promising potential of synthetic peptide growth factors, what are some of the challenges that need to be addressed in order to realize their full potential, and where do you see the greatest benefits?

Apart from the price, we believe that the biggest benefit of using PG peptides is the high stability compared with conventional growth factors. There are many companies providing specialized media or media kits for culturing specific types of cells, typically iPSCs or ES cells or some neuron or liver cells. Those specialized products are easy to use and accepted by many researchers. However, growth factors are usually provided as separate supplements because they are unstable and should be added to the media just before use. We are also seeking the possibility of developing such specialized media using our PG peptides, and since our PG peptides are very stable, we anticipate that we can add our peptide into the media and make completely ready-to-use media. We believe that this will make many processes of cell culturing easy and will benefit many people in the cell culturing industry, resulting in the expansion of the use of our PG peptides.

However, the biggest challenge is to increase the number of product line-ups. So far, we have 6 products, but to be honest, those are not major growth factors, rather niche ones. In order to develop media supplemented with our PG peptides, we have to cover all the recombinant growth factors used in such media. Soon, we will have major growth factors like bFGF and EGF, but we still need to develop PG peptides for TGF-β superfamily factors like BMP4, TGF-β1, as well as interleukin series. The challenge is that these growth factors bind to more complex receptors like trimers or even tetramers, so the PG peptides for these factors should also be in such complex forms. We have to develop more to accumulate the knowledge of how to design the peptides, and it will surely take some time, but we will go for it and achieve it as soon as possible.