(625b) Exploiting Serum Interactions with Cationic Biomaterials Enables Label-Free Circulating Tumor Cell Isolation

Exploiting Serum Interactions with
Cationic Biomaterials Enables Label-Free Circulating Tumor Cell Isolation

Michael J. Mitchell¹, Carlos A. Castellanos²,
Michael R. King²

¹Department of Chemical Engineering, Koch
Institute for Integrative Cancer Research, MIT, Cambridge, MA 02139

²Department of Biomedical Engineering, Cornell
University, Ithaca, NY 14853

Introduction: 
The ability to isolate circulating tumor cells (CTCs) from patient blood
at high purity will facilitate the development of effective personalized
medicine regimens for patients with metastatic cancer. Our lab has developed
microscale flow devices with immobilized cell adhesion molecules to both
isolate CTCs from patient blood and deliver therapeutics to cancer cells (1-3).
Improving upon current isolation methods is challenged by (1) the lack of
adhesion receptors common to a broad range of CTCs, and (2) low CTC capture due
to leukocyte bio-fouling onto capture surfaces. Herein, we evaluated the effect
of charged polymer coated surfaces on differential capture of CTCs under flow.

Materials and Methods: Microscale flow devices were
functionalized with cationic polymer by incubation with 0.025 - 0.1% (w/v)
aqueous poly-L-lysine (PLL). Functionalized surfaces were characterized using
dynamic light scattering, AFM, TEM, circular dichroism
spectroscopy, and contact angle goniometry.  Cells were suspended in PBS buffer containing
up to 1% (w/v) human albumin and perfused through microscale devices at a flow
rate of 0.008 mL/min for 10 minutes using a motorized syringe pump and
monitored via an inverted microscope. 
Micrographs and video of cell adhesion were used to measure cancer cell
capture and purity.

Results and Discussion: 
PLL-functionalized surfaces were able to differentially capture cancer
cells and leukocytes suspended in albumin-containing buffers (Fig. 1A - B). Leukocyte
capture significantly decreased on surfaces when cells were suspended in 1%
(w/v) albumin solution, while the number of cancer cells captured remained
unchanged.  Cell suspensions from metastatic prostate
cancer patients were processed on PLL-coated surfaces and  putative CTCs identified on basis
of DAPI, cytokeratin, and CD45 staining (Fig 1 C).

Figure 1: PLL functionalized
surfaces differentially capture cancer cells and leukocytes under flow. Number of firmly adhered cancer cells (A) and leukocytes (B) per
180,000² um. ***P<0.0001. *P <0.01. NS: not
significant. (C) Number of prostate cancer cells captured from blood of
metastatic cancer patients and representative images of CTCs. CTCs were
confirmed on basis of DAPI, cytokeratin (CK), and CD45 staining. Scale bar: 5
um.

Conclusions: 
We have shown that PLL functionalized surfaces contribute to
differential capture of cancer cells under flow.  While both cancer cells and leukocytes
adhesively interact with polylysine, the addition of albumin
to buffer solution acts to repel leukocytes while maintaining cancer cell
capture, which has the potential to improve applications for the isolation of
rare CTC populations of interest, for the development of effective personalized
medicine regimens.

References:

1.  Mitchell MJ, Castellanos CA, King MR. Surfactant
functionalization induces robust, differential adhesion of tumor cells and
blood cells to charged nanotube-coated biomaterials under flow. Biomaterials. 2015; 56:179-186.

2.  Mitchell MJ, Wayne E, Rana K, Schaffer
CB, King MR. TRAIL-coated leukocytes that kill cancer cells in the circulation.
PNAS. 2014; 111:
930-935.

3. Mitchell MJ, Castellanos
CA, King MR. Immobilized surfactant‐nanotube complexes support selectin‐mediated
capture of viable circulating tumor cells in the absence of capture
antibodies. Journal of Biomedical Materials Research Part A. 2015; 103:3407-3418.