If you could program a cell to do anything, what would you have it do?

Such is the perennial challenge of synthetic biology – to program living entities and biological materials to achieve novel function. How does this apply to healthcare? Engineered viruses that target and destroy infectious bacteria have spawned startups targeting industrial applications and bacterial infection. Human cells have been rewired to secrete insulin in response to flashes of blue light. This might lead to an implant for diabetics that monitors blood glucose and secretes insulin on demand – an artificial pancreas. Other biomedical examples are gene circuits that detect and kill cancer cells and regulates chemical levels in blood to prevent gout.

Most of these applications are created by combining parts. Much like electrical engineers build circuits with resistors and capacitors, synthetic biologists hook up elements that control gene expression, sensors for inputs like chemicals and light, and actuators like toxin release or gene transcription.

Biology unfortunately gets in the way. Putting these parts together isn’t predictable – most parts are not well characterized, meaning a biologist can’t model the response of his circuit. This is why independent organizations like the Parts Registry are leading the effort to characterize parts. Some startups like Gingko Bioworks can even build and test the circuits for your application.

An even bigger challenge is what to do with the synthetic components once you build them. If you build a genetic circuit, how do you safely introduce it into a live organism safely and effectively? How do you make sure it still works in this new environment? How do you prevent it from mutating into something useless, or worse, harmful?

Due to these challenges the field is still waiting for its killer app. So far large-scale biosynthesis has taken most of the attention. Genetically engineered organisms can make biofuels out of biomass and even just sunlight and waste CO2. The same principles can be applied to making artemesinin, a critical drug for malaria, vaccines, and other protein therapeutics like antibodies.

But when can we inject modified cells and circuits into humans to treat and cure diseases that aren’t as treatable with drugs? The field is getting there – Intrexon is working on a cancer treatment in which synthetic DNA molecules are injected around a tumor. A patient takes a pill and activates the DNA, stimulating the immune system to destroy the tumor.

Clearly there are numerous issues and barriers to applying synthetic biology to biomedicine. What can we do with the tools available now to get around these barriers?

Written by Allen Cheng, a Founding Hacker for Hacking Medicine.

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