Magnetic Attraction

For solid tumor therapy, not that much, according to Sylvain Martel, Professor of Nanorobotics Laboratory in the Department of Computer Engineering, Polytechnique Montreal, Canada. Martel and his colleagues aim to take on solid tumors with magnetic fields and bacteria to deliver cancer drugs (1). Here, we present a summary of the work.

• Surgery may be impossible for some solid tumors; in these cases, treatment options may be limited to pharmacotherapy. But systemic administration is typically associated with side-effects. Worse, the drug may not reach the deep, hypoxic regions of tumors in quantities sufficient for a therapeutic effect.
• Autonomous drug-loaded vehicles that transport and release drug within the hypoxic region of the tumor could circumvent this problem. But tumor ingress is size-limited (2 microns or less), which makes nanorobots at this scale impractical, especially considering the functionality they would require for locating and penetrating tumors, and for transporting and releasing drugs.
• Bacteria could provide an answer: some species, such as Magnetococcus marinus, have evolved to seek low oxygen levels, and can be engineered to carry drug-loaded nanoliposomes on their surface. Furthermore, M. marinus strain MC-1 contains magnetic iron-oxide nanocrystals and consequently tends to swim along magnetic field lines. Drug-loaded MC-1 bacteria can be directed towards tumors by application of an external magnetic field, and once inside the tumor, autonomously seek hypoxic regions.
• The strategy can result in around 55 percent of injected drug reaching the tumor as compared with one to two percent with conventional systemic injection, and therefore would be expected to enhance the therapeutic effects and decrease side effects as compared with systemic pharmacotherapy (1).

Martel’s approach to using bacteria as drug mules is expected to soon enter primate models, but initially it was seen as “science fiction”. One of the most difficult challenges of the work has been changing people’s mentality. Martel says, “Why does robotics have to be all about plastic and metal components? Why can’t we use biological components in medical nanorobotics?”