In vivo quantitation of rare circulating tumor cells by multiphoton intravital flow cytometry

doi:10.1073/pnas.0703875104

In vivo quantitation of rare circulating tumor cells by multiphoton intravital flow cytometry

*Department of Chemistry and
^†Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907; and
^‡Division of Medical Oncology, Mayo Clinic, Rochester, MN 55905

Edited by Mark T. Groudine, Fred Hutchinson Cancer Research Center, Seattle, WA, and approved May 31, 2007 (received for review April 30, 2007)

Abstract

Quantitation of circulating tumor cells (CTCs) constitutes an emerging tool for the diagnosis and staging of cancer, assessment of response to therapy, and evaluation of residual disease after surgery. Unfortunately, no existing technology has the sensitivity to measure the low numbers of tumor cells (<1 CTC per ml of whole blood) that characterize minimal levels of disease. We present a method, intravital flow cytometry, that noninvasively counts rare CTCs in vivo as they flow through the peripheral vasculature. The method involves i.v. injection of a tumor-specific fluorescent ligand followed by multiphoton fluorescence imaging of superficial blood vessels to quantitate the flowing CTCs. Studies in mice with metastatic tumors demonstrate that CTCs can be quantitated weeks before metastatic disease is detected by other means. Analysis of whole blood samples from cancer patients further establishes that human CTCs can be selectively labeled and quantitated when present at ≈2 CTCs per ml, opening opportunities for earlier assessment of metastatic disease.

Footnotes

^§To whom correspondence should be addressed at:
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907.
E-mail: plow{at}purdue.edu
Author contributions: W.H., L.C.H., J.-X.C., and P.S.L. designed research; W.H. and H.W. performed research; W.H. contributed new reagents/analytic tools; W.H. analyzed data; and W.H., L.C.H., J.-X.C., and P.S.L. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviations:

CTC,

circulating tumor cells;

FR,

folate receptor;

DiIC18 (3),

1,1′-dioctadecyl-3, 3,3′,3′-tetramethylindocarbocyanine perchlorate.