Roles of Nanoparticles during Magnetic Resonance Navigation and Bacterial Propulsion for Enhanced Drug Delivery in Tumors

It is well known that the uses of nanoparticles (NPs) can enhance medical imaging, diagnostics, and drug delivery. But for these applications and for drug delivery in particular, the difficulty in targeting specific organs in the body limits the role of these NPs for medical interventions. In cancer therapy for instance, systemic injections of drug-loaded nanoparticles result into an increase of toxicity in the body coupled with a reduction of the therapeutic outcome due to a lack of efficient targeting. Therefore, although the small size of drug-loaded NPs allows them to preferentially accumulate at tumor sites because tumors lack an effective lymphatic drainage system, most of the NPs may not reach the tumor sites but would rather reach healthy organs through systemic circulations. Hence, the challenge would be to deliver the higher percentage of the drug close enough to the tumor sites while avoiding systemic circulations. This can be achieved by adding an additional capability known as Magnetic Resonance Navigation (MRN) to the NPs without compromising their potentials for medical imaging, diagnostics, and drug delivery. MRN used for targeted drug delivery relies on magnetic nanoparticles (MNPs) embedded in therapeutic magnetic microcarriers (TMMCs) where such MNPs being fully saturated in a high homogeneous magnetic field, allow the induction of a pulling force through the use of 3D directional gradients for vascular navigation along a pre-planned path. Although the effectiveness of MRN is independent of the depth at which it operates unlike the use of an external magnet, travel is limited to larger diameter blood vessels. As such, MRN is complemented by bacterial propulsion where drug-loaded MC-1 magnetotactic bacteria (MTB) relying on a chain of NPs known as magnetosomes for directional control and previously transported through MR-compatible microcarriers, are being considered as vehicles capable of reaching the tumor sites through the microvasculature.