Team:Virginia/Relevance

Minicells share a number of properties with both liposomes and bacteria that potentially enable all three to act as targeted drug-delivery vesicles. However, minicells not only meet the standards set by both liposomes and bacteria, but confer numerous advantages over both. These advantages establish minicells as the safer and more favorable alternative.

Since minicells form directly from E. coli, they share a number of properties. However, minicells are unlike E. coli in that they lack chromosomal DNA, stripping them of their ability to divide. Lacking the ability to divide means that minicells cannot proliferate and cause an infection. This also, compared to a bacteria, allows minicells to be cleared by the body’s immune system much faster. Instead of DNA, minicells retain plasmids, which can allow them to still express some select genes. Because of the way they are formed, minicells also retain the cytosolic and plasma membrane components of the parent E. coli, allowing processes like gene expression to continue.

Liposomes are highly-customizable artificial vessels that encapsulate material in a plasma membrane, making viable options for reducing drug toxicity, while increasing site-specificity. However, there are a number of liposome qualities that are either matched or improved by minicells. These similarities and differences, in most cases, establish minicells as the better alternative over liposomes.

Similarities include reduced drug toxicity, increased drug stability, and increased therapeutic index via encapsulation. They both allow for greater targeting by site-specific ligands, which reduces collateral damage to sensitive organs. Additionally, either has the potential to be made safe for human administration through various surface proteins.

The minicell advantage, on the other hand, comes from the fact that minicells are directly derived from E. coli, whereas liposomes are artificially created. Since liposomes are artificially made, the membrane has a significant loss of stability, decreased half-life, and tendency to leak small, cytosolic elements. Instead, minicells are directly formed from E. coli, which would not be able to survive if their membranes were unstable or leaky. Although E. coli are gram-negative, there is still an advantage that comes from the thin layer of peptidoglycan, which protects the cell.This greatly increases stability, increases half-life and reduces leakiness.

Liposomes also have a high production cost. Our team’s efforts, within the iGEM competition’s goals, will make the minicell-creating process very simple and accessible. The minicell biobrick has an IPTG-inducible promoter, which upon exposure to IPTG causes the following FtsZ gene to overexpress and the E. coli to divide unevenly, thereby making minicells. Therefore, using only E. coli, the minicell biobrick, and IPTG, virtually anyone can make minicells and continue forward with this promising chassis.

Sources:

• Akbarzadeh, Abolfazl et al. “Liposome: Classification, Preparation, and Applications.” Nanoscale Research Letters. 8 (2013).
• MacDiarmid, Jennifer A. et al. “Bacterially Derived 400 nm Particles for Encapsulation and Cancer Cell Targeting of Chemotherapeutics.” Cancer Cell. 11 (2007): 431-445.
• Oja, Conrad D. et al. “Influence of dose on liposome clearance: critical role of blood proteins.” Biochimica et Biophysica Acta. 1281 (1996): 31-37.
• Ricci, Maurizio et al. “Development of liposomal capreomycin sulfate formulations: Effects of formulation variables on peptide encapsulation.” International Journal of Pharmaceutics. 311 (2006): 127-181.
• Sharma, Amarnath, and Sharma, Uma S. “Liposomes in Drug Delivery: Progress and Limitations.” International Journal of Pharmaceutics. 154 (1997):123-140.