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Cyborg Bacteria: Challenging Synthetic Biology and Drug Delivery

Authored by Angelica Bernal, Biomedical Engineering '25

What do arthritis, multiple sclerosis, and cancer have in common? These pathologies involve malfunctioning of the immune system and can be alleviated with the delivery of certain drugs, including cytokines, to modulate the immune system. However, the delivery of these therapeutic factors is an ongoing challenge in immunotherapy.

There are three main issues when treatment is delivered through a direct injection: the necessity of constant administration due to the drug’s short half-life, the poor ability of the drug to target tissue, and side effects due to a systemic spread of the drug [1]. Therefore, a key question is: How can one make the delivery of therapeutic factors more efficient with these complications in mind?

Rather than administering the therapeutic factors to the patient by injection, recent studies focus on engineering mammalian cells to produce these drugs, reducing administration frequency. However, there are concerns that these engineered cells can disrupt the environment through genetic transfer [2]. Engineering these cells to need specific ligands from their designed environment or to self-destruct if they leave this environment are some solutions [2]. Still, they do not address the possibility of “mutagenic drift, environmental supplementation, and horizontal gene transfer” [3]. In response, a study by Mandell et al. developed genomically recoded organisms with a nonstandard amino acid and redesigned enzymes to require this amino acid for proper functioning [3]. This proposal is beneficial in that this safety consideration can be performed when engineering the cells.

Another rising approach is to use nanovectors: small particles like nanovesicles, virus-like particles, and oncolytic viruses that can transport therapeutic molecules to improve their delivery [1]. The main consideration with these vectors is their biocompatibility and immunogenicity, that is, whether they activate a response from the immune system. If they do, the immune system could degrade the engineered cells or therapeutic factors inside, making the treatment less effective [1]. A way to make vectors less immunogenic is by "functionalizing nanoparticles with non-immunogenic hydrophilic polymers” [1]. For example, Ravi Ghanta et al. utilized modified alginate to make less immunogenic capsules to deliver paracrine factors [4]. Consequently, these design decisions highlight the importance of biomaterials in immunomodulation.

So far, these scientific advances did not fully combine the used biomaterials with the engineered cells, but a recent study has reimagined this approach. At the start of 2023, Contreras-Llano et al. proposed the development of “cyborg cells,” where “hydrogel cross-linking inside bacterial cytoplasm . . . can create nonreplicating yet metabolically active entities” [5]. One of the main advantages of these cells is their usage of poly(ethylene glycol) diacrylate monomer, which generates little immune response from the body [5]. Similarly, the hydrogel crosslinking results in a porous scaffold, which may aid in the diffusion of therapeutic factors [5]. Besides its ability to undergo metabolism and its lack of replication, this platform was successfully implemented with various bacteria strains, including E. coli BL21, E. coli MG1655, and Nissle 1917 [5]. Consequently, this technology has potential in drug delivery by having the flexibility of living cells, the nonreplicating safety of biomaterials, and a wide application range.

Still, there are plenty of biosafety and efficiency considerations for this platform. As suggested by Contreras-Llano et al., future work should focus on studying the biochemical basis for the lack of division of these cyborg cells [5]. This knowledge will help predict how the hydrogelation of the bacterial cytoplasm will interact with enzymes in a living organism. Additionally, having an insight into the lifespan of these cyborg cells is critical as they demonstrate resistance to peroxide (which is often present in the immune system response), high pH, and cell wall-targeting antibiotics [5]. It would be worthwhile to investigate how, if at all, the human body will discard these cyborg cells once they perform their functions, considering that the utilized biomaterial is nondegradable.

Most importantly, there is the issue of immunogenicity and invasion of cancer cells. Contreras-Llano et al. found that these cyborg cells with polyethylene glycol (PEG) as their biomaterial and with the help of the Invasin protein could invade about 34% of the present tumor cells [5]. In their separate study, Briolay et al. note that the lack of interactions of PEG with immune cells could result in “decreased internalization by tumor cells,” which would explain the observed invasion rate [1]. They also highlight that anti-PEG antibodies could decrease the efficiency of nanovectors using PEG [1]. Hence, it might be helpful to experiment with other biomaterials; for instance, Briolay et al. emphasize the efficiency of utilizing stealth coatings that dissolve once inside the tumor [1]. In a different approach, the Ghanta et al. study utilized a modified version of alginate with a triazole-triazole-thiomorpholine dioxide (TMTD) group that “significantly reduces macrophage adherence and subsequent activation” [4]. Although the immune response might seem to clash with the efficiency of tumor invasion, there are various approaches to optimize this technology based on the particular treatment goal of this cyborg cell platform.

Overall, the fields of biomaterials and bioengineering have been closely collaborating to advance drug delivery and immunomodulation. The unique approach of hybrid cyborg cells holds promise in being the next step in addressing both biosafety and efficiency concerns. Still, with a new advance comes novel challenges. Hence, previous studies exploring the connection between biomaterials, polymer coatings, and the immune response prove essential in the optimization of new drug delivery platforms, like the novel cyborg cells.

Works Cited

  1. Briolay, T., Petithomme, T., Fouet, M., Nguyen-Pham, N., Blanquart, C., & Boisgerault, N. (2021). Delivery of cancer therapies by synthetic and bio-inspired nanovectors. Molecular Cancer, 20(55), 1-24.

  2. Simon, A. J., & Ellington, A. D. (2016). Recent advances in synthetic biosafety. F1000 Research, 5(F1000 Faculty Rev), 1-9.

  3. Mandell, D. J., Lajoie, M. J., Mee, M. T., Takeuchi, R., Kuznetsov, G., Norville, J. E., Gregg, C. J., Stoddard, B. L., & Church, G. M. (2015). Biocontainment of genetically modified organisms by synthetic protein design. Nature, 518(7537): 55-60. doi:10.1038/nature14121.

  4. Ghanta, R. K., Aghlara-Fotovat, S., Pugazenthi, A., Ryan, C. T., Singh, V. P., Mathison, M., Jarvis, M. I., Mukherjee, S., Hernandez, A., & Veiseh O. (2020). Immune-modulatory alginate protects mesenchymal stem cells for sustained delivery of reparative factors to ischemic myocardium. Biomaterials Science, 8(18), 5061-5070. doi: 10.1039/d0bm00855a.

  5. Contreras-Llano, L. E., Liu, Y., Henson, T., Meyer, C. C., Baghdasaryan, O., Khan, S., Lin, C., Wang, A., Hu, C. J., & Tan, C. (2023). Engineering Cyborg Bacteria Through Intracellular Hydrogelation. Advanced Science, 2204175, Early View.

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