2011 Joint AAPM/COMP Meeting
John Weaver
For more information about the American Association of Physicists in Medicine, visit aapm.org/

Magnetic nanoparticles have many diagnostic and therapeutic applications. We have
developed methods of interrogating the microscopic environment surrounding magnetic
nanoparticles that can be used in vivo. This set of methods is termed magnetic
spectroscopy of nanoparticle Brownian motion (MSB) and is capable of evaluating any
physical effect that affects the Brownian motion of the nanoparticles; e.g., temperature,
viscosity, and chemical binding. MSB is capable of human use throughout the body.
Two applications where these methods show significant promise are in planning
nanoparticle cancer therapy and ovarian cancer screening.

Cancer therapy using magnetic nanoparticles activated with an alternating magnetic field
preferentially kills cancer cells both in vitro and in vivo. In vitro experiments have shown
that the microscopic proximity of the nanoparticle to the targeted cells is of central
importance when activating the nanoparticles, that is, nanoparticles that are in vesicles
are more cytotoxic than those in the media surrounding the cells. Therefore, it is
important to understand where the nanoparticles are before magnetic field activation. We
have applied MSB to directly measure the nanoparticle microscopic state. Specifically,
the progression of nanoparticle endocytosis can be monitored rapidly and non-invasively.
Once the nanoparticles are in intracellular vesicles, they are more effective cytotoxic
agents when activated with an external magnetic field.

Ovarian cancer screening is another application of magnetic nanoparticles that shows
significant promise. Ovarian cancer has a high cure rate if found early but a very poor
survival rate if found at an advanced state. Unfortunately ovarian cancer is rarely found
early so an effective early detection method would save many lives. Dendrites or
phagocytes quickly phagocytose magnetic nanoparticles injected into the peritoneal
cavity. Cytokine signaling draws phagocytes to malignancies and they bring the
endocytosed magnetic nanoparticles with them. MSB methods have been used to detect
the resulting collection of magnetic nanoparticles. The result is immunologic
nanoparticle targeting. Magnetic detection of the nanoparticles in a unique genetic
mouse model for ovarian cancer has shown the method can identify microscopic ovarian
malignancies.

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