Digging deeper into the secrets of the secretome

Written by:

Diane Hatton

Director of Cell Line Development and Engineering, Biopharmaceuticals Development, BioPharmaceuticals R&D

Lovisa Holmberg-Schiavone

Director of Cell Line Development and Engineering, Biopharmaceuticals Development, BioPharmaceuticals R&D

Steve Rees

Vice President Discovery Biology, Discovery Sciences, BioPharmaceuticals R&D

Three years into our collaborations with the KTH Royal Institute of Technology (KTH), Stockholm, to make and test proteins secreted by cells, we are seeing the first promising impact on our R&D portfolio. As we extend these collaborations, we are identifying potential targets for future interventions across our core therapy areas.

Scientists at the KTH are world leaders in the expression of recombinant proteins in mammalian cells. In our collaborations, we are developing novel expression systems to help us manufacture antibody therapeutics and create a library of all human secreted proteins (the secretome). Many thousands of proteins are secreted from cells to the surrounding environment as well as into the bloodstream where they play an active role in cell-to-cell communication. We are creating a collection of all known human secreted proteins, to allow us to investigate the role of these proteins in disease. The initiative is a key element of our strategy at AstraZeneca to enhance the way we validate drug targets and produce biotherapeutics, with the aim of further increasing our success rate for delivery of new medicines to patients.

Our collaborations with KTH involves two distinct but complementary secretome research projects.

Developing and interrogating a world-class secretome library

In the first phase of this project, KTH scientists identified, produced and purified most of the 2,000 proteins we want for our secretome library.

We have been screening this protein library in cell-based assays to identify potential new drug targets. From the first seven screens, one promising protein is already the focus of a new drug project, with two more hot on its heels. We are delighted with this success rate, which signals the potential for achieving our goal of contributing two to three new drug projects per year from this collaboration.

Through the extension of this collaboration, KTH will start adding recently identified and difficult-to-express proteins to our secretome library, and provide samples in larger quantities to support our long-term research. As far as we know, no one else is attempting secretome exploration on this scale and intensity.

New insights from early assays

We developed a cellular model for loss of identity (dedifferentiation) of pancreatic beta cells which can result in failed insulin production and diabetes. In this assay, we showed that fibroblast growth factor (FGF) proteins play an important role in beta cell dedifferentiation and are exploring the FGF receptor as a potential target in diabetes.

We also developed an assay to screen our secretory proteins for their stabilising and destabilising effects on regulatory T (Treg) cells of the immune system. We identified two members of a protein family, one of which destabilises a Treg cell receptor while the other stabilises it – with potential opportunities in cancer and respiratory disease respectively.

In cardiovascular disease, cardiac progenitor cell (CPC) assays used to screen the secretome proteins have provided new insights into receptor binding of FGF proteins. This approach has the potential for identifying new ways of stimulating CPC proliferation and cardiac regeneration after a heart attack, or for heart failure therapy.

As we move forward, we hope to work with academic and other researchers with relevant biological systems for our assays through our Open Innovation initiative.

Focusing on novel cell-culture systems for the manufacture of therapeutic proteins

The first phase of our second collaboration with KTH focused on exploring novel mammalian cell technologies and culture methods to enhance large-scale production of secreted proteins that hold potential as biological medicines. Therapeutic proteins include native and engineered human proteins, such as monoclonal antibodies, fusion-proteins and bispecific antibodies. These ‘biologics’ can be exquisitely engineered to specifically bind to target molecules in the human body and are being advanced in the clinic for the treatment of many diseases, including cancer, with the potential to address significant unmet medical need. At present, most complex therapeutic proteins are produced by secretion from Chinese hamster ovary (CHO) cells, but it is technically difficult to express some of these proteins in CHO cells. This in turn impacts the ability to bring these innovative candidate medicines to patients in a time- and cost-effective way.

In collaboration with KTH scientists, we are developing human cell lines to produce secreted proteins that are difficult to express in CHO cells and also to understand the underlying biological and molecular characteristics that limit production in CHO cells. Based on these results, we plan to develop novel human cell line systems to produce biologics and also to engineer our CHO cell lines for better performance. Together, we are also exploring how to grow and maximise production from the optimised human cell lines by developing novel continuous-culture production systems instead of the traditional fed-batch operations that are employed currently. This has the potential to make the manufacture of therapeutic proteins more sustainable, reducing production costs and improving the uniformity of product, thus benefitting patients.

In the extension of this project, we plan not only to continue developing cell lines and culture systems for new classes of difficult-to-express secreted proteins, but also to explore these platforms for the production of even more complex biological products – notably viruses. Viruses have exciting promise for gene therapy applications and, importantly, offer the prospect of a ‘cure’ for some diseases. Many of the lessons learned in producing secreted proteins in cell culture are now being put to good use in addressing the even greater challenges of virus production.

Synergy and transparency in action

Bringing together complementary knowledge and expertise both internally and externally in these collaborations is enabling us to make exciting progress in translating the science of the secretome into potential biological therapies of tomorrow. As we make our results available to the wider scientific community through multiple publications, we are pleased with the synergistic outcomes of our joint endeavours.