drug development: hamster and book

The 4 letters of Chinese Hamster

Did you know that nowadays bacteria and mammalian cells, especially hamster cells, produce a wide range of drugs? And who tells them to do so? The answer is the four-letter code of DNA. Biotechnologists spend a lot of time to explore natural DNA sequences of different organisms for production. The Chinese Hamster is a mammalian system and suits well for cell factories because of its similarity to human cells. However, for a long time the knowledge about the hamster DNA sequence had many gaps that needed to be investigated.

The DNA sequence defines the entire information of a cell life. It specifies not only visual characteristics like form or color but it also includes a kind of time schedule and “master plan” for each and every protein: When does a certain protein appear and where does it have its final destination? This information is coded in signal sequences: there are repressing or activating signals, signals for secretion, signals for start and stop of protein production etc. The related signal sequences also help to direct foreign proteins, like those for drug production. Today, Chinese Hamster Ovary cells (CHO) are used to produce approximately 35% of all biopharmaceuticals! For this reason, the biotechnologists are highly interested in the complete sequence of their “workhorses”.

There are different methods to determine the sequence of the DNA bases adenine (A), thymine (T), guanine (G) and cytosin (C). But all of these methods have their limitations and do not provide a complete sequence information. The special feature of a recent publication about the hamster sequence is, that scientists from acib and BOKU Vienna compared data from different methods and combined all mosaic tiles to a comprehensive picture. This bioinformatic approach enabled them to close 95% of all remaining gaps in the hamster genome.

Hamster sequence to design engineering strategies

So far, the efforts to improve CHO cells for production mainly focused on external conditions (e.g. medium or bioreactor optimization). The knowledge about the hamster letter code (DNA) helps a lot to further improve the production cells also on genetic level. The master-plan for proteins can be newly designed and biotechnologists can control where and when their target proteins appear. Especially in mammalian systems it is necessary to activate multiple interacting genes in order to influence the cellular outcome. Back to the letter example: Only changing one word wouldn’t have influence the contents of a book but if you rewrite a complete chapter, the book will tell a new story.

In this context, also the cloning method CRISPR/Cas9 that everyone in biotech community is talking about, can more easily be used to remove repressing signals and allow the activation of a target gene. Quite recently, acib researchers have delivered a proof of concept for the simultaneous integration of multiple genes into the CHO genome and targeted activation of each individual gene by CRISPR/Cas9 application.

What is the advantage?

This procedure saves time, because all DNA elements that researchers want to test, are integrated in one working step only and can be activated in different combinations on demand. In other words: The method opens the door for writing numerous new stories about drug development in CHO!

This work is based on:

Rupp O, MacDonald ML, Li S, et al. A reference genome of the Chinese hamster based on a hybrid assembly strategy. Biotechnology and Bioengineering. 2018;119:2087–2100. https://doi.org/10.1002/bit.26722

Peter Eisenhut, Gerald Klanert, Marcus Weinguny, Laurenz Baier, Vaibhav Jadhav, Daniel Ivansson, Nicole Borth, A CRISPR/Cas9 based engineering strategy for overexpression of multiple genes in Chinese hamster ovary cells, Metabolic Engineering, Volume 48, 2018, Pages 72-81, ISSN 1096-7176, https://doi.org/10.1016/j.ymben.2018.05.017

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