Building Bacterial Drug Factories | The Scientist Magazine® todayheadline

Bacteria have complex molecular machines that help them drive disease. Scientists can now leverage these machines to treat disease instead. 

Cammie Lesser, a microbiologist at Mass General Research Institute, devised a way to hijack a bacterial secretion system and move it into Escherichia coli, making the bacteria release therapeutic molecules. In an interview with The Scientist, Lesser described how multidisciplinary perspectives opened the door to bacteria-enabled drug delivery.

How did you come up with the idea to use bacteria for drug delivery?

I study secretion machinery in pathogens, especially Shigella, which has a type III secretion system to release molecules into host cells. E. coli, however, rarely secrete proteins extracellularly, unless researchers insert secretion systems from different species. Many years ago, my lab started moving type III secretion systems into a laboratory strain of E. coli. We realized that if we transferred the secretion machinery without the tip, it would secrete therapeutic proteins into the bacteria’s surroundings.

What makes bacteria well suited for this application?

Although the secretion machinery is made of around 20 different proteins, everything is adjacent in the genome, which makes it compact. In the PRObiotic Type 3 secretion E. coli Therapeutic (PROT₃EcT) platform that we developed, we captured those pieces of DNA and moved them from Shigella into E. coli.¹ Then, we added a regulator so that we can control its expression, and finally we added our payloads. The system is modular and you can mix and match its components.

What types of therapeutic molecules can you deliver?

We primarily work with nanobodies, although we have shown that other proteins can be secreted too. Nanobodies are single domain antibodies present in camelids, such as alpacas and camels, but also in sharks. They are generally very stable and they have decent binding affinity, so they are growing in popularity as therapeutics. We used PROT₃EcT to deliver nanobodies that bind to and neutralize tumor necrosis factor alpha (TNF-?) to stop inflammation from developing in a mouse model of intestinal bowel disorder (IBD).¹ 

In a recent study, we used PROT₃EcT to target enterohemorrhagic E. coli (EHEC).² You cannot give antibiotics to patients who have EHEC, because the drugs induce a stress response that causes the bacteria to release more toxin.

Luis Ángel Fernández at the Autonomous University of Madrid identified a nanobody that blocks the protein needed for EHEC infection.³ He showed that it worked in vitro, and we demonstrated that PROT₃EcT can deliver this nanobody in vivo for prophylaxis in an EHEC mouse model.

What are the advantages of PROT₃EcT over conventional drug delivery approaches?

It is nice to deliver drugs where you exactly want them, which is the gut in the case of IBD and gastrointestinal infections. You can think of the bacteria as little factories that are pumping out the therapeutic at the site of disease to prevent off-target effects.

How might you improve PROT₃EcT in future work?

In the EHEC study, the infection was delayed, but we want to cure the infection. There is also a big movement in the IBD field to have bacteria turn on and off when they sense inflammation. It would be really cool if someone with IBD could take a probiotic once a week, and the bacteria would hang out in their gut and recognize when inflammation arises. Then they could start releasing nanobodies.

Another big challenge to resolve with these bacteria-based therapies, before they go into humans, is biocontainment. It is really vital that we have molecular kill switches so that if someone is shedding bacteria, they do not get into the sewage system and grow.

It is good to have people bringing different perspectives to this field, and I think that is why PROT₃EcT got a lot of excitement. Our expertise in understanding secretion machinery was essential in order to build this system.

This interview has been condensed and edited for clarity.