New York, NY — March 17, 2022 — Columbia Engineering researchers report developing a “cloaking” system that temporarily hides therapeutic bacteria from the immune system, allowing them to more effectively deliver drugs to tumors and kill cells. tumors in mice. By manipulating the DNA of the microbes, they programmed gene circuits that control the surface of the bacteria, building a molecular “mantle” that encapsulates the bacteria.
“The really exciting thing about this work is that we are able to dynamically control the system,” said Tal Danino, associate professor of biomedical engineering, who co-directed the study in collaboration with Kam Leong, Samuel H. Sheng Professor of biomedical engineering. “We can adjust how long bacteria survive in human blood and increase the maximum tolerable dose of bacteria. We also showed that our system opens up a new bacteria delivery strategy where we can inject bacteria into an accessible tumor and have them migrate in a controllable way to distal tumors as metastases, cancer cells that spread to other parts of the body. “
For the study published today by Nature Biotechnology, the researchers focused on capsular polysaccharides (CAPs), sugar polymers that coat bacterial surfaces. In nature, CAP helps many bacteria protect themselves from attack, including the immune system. “We hijacked the CAP system of a probiotic E. coli strain Nissle 1917, “said Tetsuhiro Harimoto, a PhD student in Danino’s lab, co-lead author of the study.” With CAP, these bacteria can temporarily evade immune attack; without CAP, they lose encapsulation protection and they can be eliminated in the body. So we decided to try to build an effective on / off switch. “
An on / off switch for the immune system
To do this, the researchers designed a new CAP system, which they call inducible CAP, or iCAP. They control the iCAP system by giving it an external signal, a small molecule called IPTG, which allows for programmable and dynamic alteration of E. coli cell surface. Because iCAP alters bacterial interactions with immune systems (such as blood clearance and phagocytosis) directly, the team found that they could control how long bacteria can survive in human blood by regulating the amount of IPTG they give. to iCAP E. coli. In effect, they created an “on / off” switch that controls how the immune system responds to therapeutic bacteria.
Finding the right balance
Although the use of bacteria for therapy is a new alternative approach to treating a wide range of cancers, there are a number of challenges, most notably their toxicity. Unlike many traditional drugs, these bacteria are alive and can proliferate within the body. They are also detected by the body’s immune system as foreign and dangerous, causing a high inflammatory response – too many bacteria means high toxicity due to excessive inflammation – or rapid killing of bacteria – too few bacteria mean no therapeutic efficacy.
Jaeseung Hahn, postdoctoral researcher in the Danino and Leong laboratories who co-directed the project, noted: “In clinical studies, these toxicities have been shown to be the critical problem, limiting the amount we can dose the bacteria and compromising effectiveness. Some studies had to be stopped due to severe toxicity ”.
Hit the mark
Ideal bacteria should be able to evade the immune system upon entry into the body and efficiently reach the tumor. And once they are in the tumor, they need to be eliminated elsewhere in the body to minimize toxicity. The team used mouse tumor models to show that, through iCAP, they could increase the maximum tolerable dose of bacteria by 10-fold. They encapsulated the E. coli effort to allow it to evade the immune system and reach the tumor. Since they did not give IPTG in the body, the E. coli iCAP lost its encapsulation over time and was easier to clear elsewhere in the body, thus minimizing toxicity.
To test the effectiveness, the researchers then designed E. coli iCAP to produce an anticancer toxin and were able to reduce tumor growth in mouse models of colorectal and breast cancer more than in the control group without the iCAP system.
The team also demonstrated controllable bacterial migration within the body. Previous studies have shown that low levels of bacteria escape from tumors as the tumor grows. For this new study, the Columbia team used iCAP to show that they can control the leakage of bacteria from a tumor, as well as their translocation to other tumors. They injected E. coli iCAP in a tumor, fed the mice with IPTG-containing water, activated iCAP within a tumor, and saw E. coli iCAP escapes and migrates to non-injected tumors.
The path forward
The group is exploring a number of research areas. There are more than 80 different types of PACs that exist only for E. coli and even more so for other bacterial species that could be engineered using similar approaches. Furthermore, CAP isn’t the only molecule bacteria have on their surface, and other surface molecules could be controlled in a similar way. Furthermore, while in this example iCAP is controlled by an externally supplied IPTG, other control systems such as biosensors could be used to autonomously control the surface properties of therapeutic bacteria.
The team, also affiliated with the Herbert Irving Comprehensive Cancer Center and the Columbia Data Science Institute, notes that clinical translation is the next big challenge they would like to address. “Although there is a good deal of laboratory research showing various ways to engineer microbes, it is very difficult to apply these powerful therapies to an animal or a complex human body. We have shown proofs of concept in mouse models, but since humans humans are 250 times more sensitive to bacterial endotoxins than mice, we expect our results to have an even greater effect on human patients than on mice, ”said Harimoto.
Leong added, “Bacterial cancer therapy has unique advantages over conventional drug therapy, such as efficient targeting of tumor tissue and programmable drug delivery. The potential toxicity has limited its full potential. The cloaking approach presented in this study can address this critical problem. “