Synthetic biologists extend the life of cancer fighting circuitry in microbes

Bioengineers at the University of California San Diego have developed a method to significantly reduce the incidence of environmental degradation.

Most of the circuits that synthetic biologists insert into microbes break or vanish entirely from the microbes after a certain period of time-to-date because of various mutations. But in the September 6, 2019 issue of the journal Science, the UC San Diego researchers showed that they can keep going for much longer.

The key to this approach is the researchers' ability to completely replace one genetic-circuit-carrying sub-population with another, while keeping the circuit running.

"We've shown that we can stabilize genetic circuits without getting into the business of fighting evolution," said UC San Diego bioengineering and biology professor Jeff Hasty, the corresponding author on the study. "Once we stopped fighting evolution at the level of individual cells, we were able to keep a metabolically-expensive genetic circuit going as long as we want."

The circuit San Diego UC researchers used in the Science This group, and others, are actively using new types of cancer therapies.

However, the reality today is that the gene is not in place, but the reality today is that the gene is going to be in the microbe. "days, weeks, or months, even with the best circuit-stabilization approaches, it's just a matter of time." Michael Liao, said UC San Diego bioengineering Ph.D. student and the first author on the Science paper. "Our work shows us another way forward, not just in theory, but in practice." We've shown that it's possible to keep track of busting mutations at bay.

If the team 's method can be tested for living systems, the implications could be significant for many fields, including cancer therapy, bioremediation, and bioproduction of useful proteins and chemical components.

Rock Paper Scissors

To actually build a "reset button" for the mutation clock, the researchers focused on the dynamics of strains of microbes, rather than trying to hold selective pressures at the level of individual cells. The researchers demonstrated their community-level engineering system using three sub-populations of E. coli with a "rock-paper-scissors" power dynamic. This means that the "rock" can kill the "scissors" but will be killed by the "paper" strain.

Most published work tends to focus on stabilization strategies that act at the level of single cells. While some of these approaches may be sufficient in a given context, the evolution dictates that these approaches will naturally tend to stop working at some point. However, since the rock-paper-scissors (RPS) stabilization acts at a community level, it can be coupled with any of the systems that act on a single cell level to drastically extend their lifespan.

Making Cancer Drugs and Delivering them to Tumors

In 2016 in NatureUC San Diego researchers led by Hasty, along with colleagues at MIT, described a "synchronized lysis circuit" that could be used to deliver cancer-killing drugs that are produced by those that accumulate in and around tumors. This led the UC San Diego group to focus on the synchronized Science.

These coordinated explosions only occur once in a while, but the quorum sensing functionality also comes into play in the genetic circuitry. After the explosion, the 10% of the bacterial population that did not explode starts growing again. When the population density becomes more quorum sensing, another drug-delivery is triggered and the process encoded by the researchers' synchronized lysis circuit restarts.

The challenge, however, is that this cancer killing genetic circuit-and other genetic circuits created by synthetic biologists-eventually stop working in the bacteria. The culprit. Mutations driven by the process of evolution.

"The fact that some bugs naturally grow in tumors and we can engineer them to produce and deliver therapies in the body is a game-changer for synthetic biology," said Hasty. "But there is still work to do, but we're showing that we can swap populations and keep the circuit running." "This is a big step forward for synthetic biology."

Biomedical Research Advances

Tal Danino, now a professor at Columbia University, who also published a seminal work on the development of quorum sensing for synthetic biology as part of his Ph.D. at UC San Diego.

"Talently demonstrated that they can be used to deliver immunosuppressive drugs to patients and to prevent them from becoming infected." "The results are fascinating." They also highlight how important it is, "said Hasty.

The current approach is not limited to a three-strain system. Individual sup-populations of microbes, for example, which can be used to treat different types of cancer.

The researchers studied the dynamics of populations using microfluidic devices that allow for controlled interactions between different subpopulations. They also demonstrated the system is robust when tested in larger wells.

One next step will be made with the standard approach to stabilize approaches and demonstrate the system in live animal models.

"We are converging on an extremely stable drug delivery platform with wide applicability for bacterial therapies," said Hasty.

Hasty, Din, and Danino are co-founders of GenCirq, a company which seeks to transfer this and related work to the clinic.