Biofunctionalized magnetic-vortex microdiscs for targeted cancer-cell destruction

Journal name:
Nature Materials
Volume:
9,
Pages:
165–171
Year published:
DOI:
doi:10.1038/nmat2591
Received
Accepted
Published online
Corrected online

Abstract

Nanomagnetic materials offer exciting avenues for probing cell mechanics and activating mechanosensitive ion channels, as well as for advancing cancer therapies. Most experimental works so far have used superparamagnetic materials. This report describes a first approach based on interfacing cells with lithographically defined microdiscs that possess a spin-vortex ground state. When an alternating magnetic field is applied the microdisc vortices shift, creating an oscillation, which transmits a mechanical force to the cell. Because reduced sensitivity of cancer cells toward apoptosis leads to inappropriate cell survival and malignant progression, selective induction of apoptosis is of great importance for the anticancer therapeutic strategies. We show that the spin-vortex-mediated stimulus creates two dramatic effects: compromised integrity of the cellular membrane, and initiation of programmed cell death. A low-frequency field of a few tens of hertz applied for only ten minutes was sufficient to achieve ~90% cancer-cell destruction in vitro.

At a glance

Figures

  1. The concept of targeted magnetomechanical cancer-cell destruction using disc-shaped magnetic particles possessing a spin-vortex ground state.
    Figure 1: The concept of targeted magnetomechanical cancer-cell destruction using disc-shaped magnetic particles possessing a spin-vortex ground state.

    The microdiscs are biofunctionalized with anti-human-IL13α2R antibody, specifically targeting human glioblastoma cells. When an alternating magnetic field is applied, the magnetic discs oscillate, compromising membrane integrity and initiating spin-vortex-mediated programmed cell death.

  2. Magnetic-vortex microdiscs can be distantly actuated by the application of small-amplitude and low-frequency a.c. magnetic fields.
    Figure 2: Magnetic-vortex microdiscs can be distantly actuated by the application of small-amplitude and low-frequency a.c. magnetic fields.

    a, Reflection optical microscope image of the dried suspension of 60-nm-thick, ~1-μm-diameter 20:80 iron–nickel (permalloy) discs coated with a 5-nm-thick layer of gold on each side. The discs were prepared by means of magnetron sputtering and optical lithography. b, Micromagnetic model of magnetic-vortex spin distribution. The magnetic vortex consists of a ~10-nm-diameter, perpendicularly magnetized vortex core (Supplementary Fig. S4B), and an in-plane flux-closure spin arrangement with zero net magnetization in the remanent state. c, Dependence of the light-intensity modulation ΔI=ImaxImin owing to the field-driven disc alignment (ed) on the applied field frequency f. Inset, A representative time variation of the intensity I of the laser beam travelling through the vial containing the aqueous disc solution subjected to an a.c. magnetic field.

  3. A low-frequency spatially uniform magnetic field applied to the MDs-mAb-cell complex results in compromised integrity of the cellular membrane and cell death.
    Figure 3: A low-frequency spatially uniform magnetic field applied to the MDs–mAb–cell complex results in compromised integrity of the cellular membrane and cell death.

    a, Magnetic-field-induced cell death of the MD–mAb towards N10 cells and MD-IgG loss of cell-membrane integrity using a cellular LDH test for different field frequencies. No remarkable LDH release was observed when MDs functionalized with the isotype-matched negative control IgG1 were applied. Error bars denote the standard deviation for experiments across six wells. be, Optical images of control (b,d) and treated (c,e) N10 glioma cells. A 90Oe–20Hz magnetic field was applied for 10min. The treated cells are rounded off with membrane shrinkage and a loss of membrane integrity.

  4. Comparison of representative atomic force microscope amplitude error, height and cross-section scans for the control and treated cells.
    Figure 4: Comparison of representative atomic force microscope amplitude error, height and cross-section scans for the control and treated cells.

    a, The control N10 cells appear as ~500-nm-thick, rough and elongated shapes with well-defined ~1-μm-high nuclei at their centres. b, The treated cells are characterized by a smoother surface, thickening, shape rounding, rather abrupt edges and an apparent flattening and fractioning of the genetic material storing organelle—the nucleus. The blue and red curves show the cross-section profiles across the centre of the cell along horizontal and vertical directions, respectively. The scan size is 50×50 μm2.

  5. Magnetic-vortex-mediated mechanical stimuli trigger intracellular biochemical pathways activating programmed cell death.
    Figure 5: Magnetic-vortex-mediated mechanical stimuli trigger intracellular biochemical pathways activating programmed cell death.

    a, Apoptosis of the N10 cells induced by an a.c. magnetic field. be, Images of negative control (b,c) and MD-mAb-functionalized cells subjected to 20Hz–90Oe a.c. fields for 10 min and TUNEL stained 4h after the magnetic-field exposure (d,e). The control cells with well-organized chromatin structures have a blue fluorescence, whereas the treated cells are stained with a dark orange–brown dye owing to chromatin fragmentation—an indication of apoptosis. The proportion of apoptotic populations was calculated by counting a total of 1,000 nuclei in each group using optical microscope images. Error bars denote the standard deviation for experiments across six wells. Asterisks indicate that differences between experimental groups and negative controls were considered significant at p<0.05.

  6. Optical imaging of intracellular calcium.
    Figure 6: Optical imaging of intracellular calcium.

    The N10 cells were preloaded with calcium indicator Fluo-4-AM dye (λex=488nm, λem=520nm), green, whereas cell nuclei were stained with Hoechst 33342 (λex=350nm), blue. a, Cell optical images. bd, Fluorescent cell images: snapshots at 0, 7 and 10min application of alternating magnetic field of 10Hz–90Oe. Yellow arrows show representative calcium flashes or spikes.

Change history

Corrected online 13 January 2010
In the version of this Article originally published, the following sentence in the caption of Fig. 5 should have been written as: “Images of negative control (b,c) and MD-mAb-functionalized cells subjected to 20Hz–90Oe a.c. fields for 10 min and TUNEL stained 4h after the magnetic-field exposure (d,e)” This has been corrected in all versions of this Article.

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Author information

Affiliations

  1. Materials Sciences Division, Argonne National Laboratory, Argonne, Illinois 60439, USA

    • Dong-Hyun Kim,
    • Samuel D. Bader &
    • Valentyn Novosad
  2. Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA

    • Elena A. Rozhkova,
    • Samuel D. Bader &
    • Tijana Rajh
  3. The Brain Tumor Center, The University of Chicago Pritzker School of Medicine, Chicago, Illinois 60637, USA

    • Ilya V. Ulasov &
    • Maciej S. Lesniak

Contributions

V.N. and E.A.R. conceived the experimental idea. M.S.L. advanced the conceptual design for the glioma cell targeting. I.V.U. performed in vitro and cell cytotoxicity studies. D.-H.K. and V.N. fabricated the magnetic microdiscs and carried out the magnetic characterization and micromagnetic modelling. D.-H.K. and E.A.R. ran the biofunctionalization experiments. D.-H.K. carried out atomic force and optical microscopy characterizations. E.A.R. and I.V.U. designed and analysed the intracellular Ca imaging experiments. D.-H.K., E.A.R., I.V.U., T.R., S.D.B., M.S.L. and V.N. analysed the data and wrote the manuscript.

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The authors declare no competing financial interests.

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