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Noninvasive Detection of Lentiviral-Mediated Choline Kinase Targeting in a Human Breast Cancer Xenograft

Johns Hopkins University In Vivo Cellular Molecular Imaging Center Program, The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland

Requests for reprints: Zaver M. Bhujwalla, Department of Radiology, The Johns Hopkins University School of Medicine, Room 208C, Traylor Building, 720 Rutland Avenue, Baltimore, MD 21205. Phone: 410-955-9698; Fax: 410-614-1948; E-mail: zaver{at}mri.jhu.edu.

Key Words: choline kinase • breast cancer • magnetic resonance imaging • lentivirus • shRNA

Elevated phosphocholine (PC) and total choline (tCho) metabolites are widely established characteristics of most cancer cells, including breast cancer. Effective silencing of choline kinase (chk), the enzyme that converts choline to PC, is associated with reduced tumor growth. The functional importance and down-regulation of chk using RNA interference has been previously established. Here, we report on the preclinical evaluation of lentiviral vector–mediated down-regulation of chk using short hairpin RNA (shRNA) in established tumors derived from human breast cancer cells. Concentrated lentivirus expressing shRNA against chk was injected i.v. in the tail vein of MDA-MB-231 tumor-bearing female severe combined immunodeficient mice. Transduction efficiency in cells and tumors in vivo was assessed optically by enhanced green fluorescent protein expression and additionally from chk mRNA and protein levels. An 80% reduction in chk mRNA and protein was achieved following 90% transduction efficiency in cells. After transduction with chk-shRNA, ¹H magnetic resonance spectroscopy (MRS) of cell and tumor extracts showed decreases in PC and tCho levels (P < 0.01 and 0.05, respectively) in comparison with controls. PC levels were monitored noninvasively by ³¹P MRS in tumors and by ¹H MRS in cell and tumor tissue extracts. Noninvasive ³¹P MR spectra of chk-shRNA–transduced tumors in vivo showed lower PC and phosphomonoester levels that were associated with reduced tumor growth and proliferation. This study shows the use of lentiviral vectors to target chk in a human breast cancer xenograft and noninvasive MRS detection of this targeting. [Cancer Res 2009;69(8):3464–71]