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BioMed Research International
Volume 2013 (2013), Article ID 503095, 7 pages
http://dx.doi.org/10.1155/2013/503095
Research Article

Affinity Labeling of Membrane Receptors Using Tissue-Penetrating Radiations

1Nuclear Medicine, University of Texas MD Anderson Cancer Center, Houston, TX 77030-4009, USA
2Neuro-Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030-4009, USA
3Department of Radiology, Johns Hopkins Medical Institutions, Baltimore, MD 21205, USA
4University of Texas MD Anderson Cancer Center, 1400 Pressler, Unit 1483, Houston, TX 77030-4009, USA
5Addiction Research Center, National Institute of Drug Abuse, Baltimore, MD 21224, USA
6U.S. Consumer Product Safety Commission, Bethesda, MD 20814, USA
7Neuropharmacology, Yerkes National Primate Research Center of Emory University, Atlanta, GA 30322, USA
8Radiology, Psychiatry, Neuroscience, Environmental Health Science, and Carey Business School, Johns Hopkins Medical Institutions, Baltimore, MD 21205, USA

Received 15 April 2013; Revised 6 June 2013; Accepted 13 June 2013

Academic Editor: Mei-Hsiu Liao

Copyright © 2013 Franklin C. Wong et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Photoaffinity labeling, a useful in vivo biochemical tool, is limited when applied in vivo because of the poor tissue penetration by ultraviolet (UV) photons. This study investigates affinity labeling using tissue-penetrating radiation to overcome the tissue attenuation and irreversibly label membrane receptor proteins. Using X-ray (115 kVp) at low doses (<50 cGy or Rad), specific and irreversible binding was found on striatal dopamine transporters with 3 photoaffinity ligands for dopamine transporters, to different extents. Upon X-ray exposure (115 kVp), RTI-38 and RTI-78 ligands showed irreversible and specific binding to the dopamine transporter similar to those seen with UV exposure under other conditions. Similarly, gamma rays at higher energy (662 keV) also affect irreversible binding of photoreactive ligands to peripheral benzodiazepine receptors (by PK14105) and to the dopamine (D2) membrane receptors (by azidoclebopride), respectively. This study reports that X-ray and gamma rays induced affinity labeling of membrane receptors in a manner similar to UV with photoreactive ligands of the dopamine transporter, D2 dopamine receptor (D2R), and peripheral benzodiazepine receptor (PBDZR). It may provide specific noninvasive irreversible block or stimulation of a receptor using tissue-penetrating radiation targeting selected anatomic sites.