Expression of functional folate receptors by human parathyroid cells Collin J. Weber, MD, DMSci, a Susan M€ uller, DMD, b,c Susan A. Safley, PhD, a Kereen B. Gordon, MS, a Praveen Amancha, PhD, d,e Francois Villinger, DVM, PhD, d,e Vernon M. Camp, BA (CNMT) Nuclear Medicine TCB, f Malgorzata Lipowska, PhD, f Jyotirmay Sharma, MD, a Cristina M€ uller, PhD, g Roger Schibli, PhD, g,h Philip S. Low, PhD, i Christopher P. Leamon, PhD, j and Raghuveer K. Halkar, MD, f Atlanta, GA, Villigen-PSI and Zurich, Switzerland, and West Lafayette, IN Background. Human pituitary adenomas express folate receptors (FR); therefore, we hypothesized that parathyroid (PT) tumors also might express FR, whereas normal human thyroids might not. The purpose of our study was to characterize the functionality of FRs on human PT tumors, with the goal of developing an imaging tool that would concentrate in PT more than in the thyroid. Methods. Human PTs and thyroids were evaluated for FR expression by immunohistochemistry. Expression of genes for FRa and FRb was measured with the Illumina Human HT-12 Expression Bead Chips and verified by quantitative reverse-transcription polymerase chain reaction. Folate incorporation by PT cells versus normal thyroid cells was determined by incubation with 99m Technetium ( 99m Tc)(CO) 3 -folate and 99m Tc-Etarfolatide, and uptake was determined by gamma counting. Specific targeting of FRs was demonstrated by blocking with cold folate. A549 cells and Jurkat cells served as FR-negative controls, and KB cells and HeLa cells were FR-positive controls. Results. On immunohistochemistry and Western blotting, human PT cells expressed FRs, whereas human thyroid cells did not. The FRa gene was expressed in all PTs analyzed, and the FRb gene was expressed by most. Uptake of 99m Tc(CO) 3 -folate was increased in PT cells versus thyroid cells. There was dose-dependent uptake of 99m Tc-etarfolatide, and uptake was inhibited by preincubation with cold folate, confirming FR-mediated binding. Conclusion. This is the first report of the expression and functionality of FRs on human PT cells. These findings suggest that 99m Tc-folate holds potential for localization of PT tumors preoperatively and their treatment. (Surgery 2013;154:1385-93.) From the Departments of Surgery, a Pathology and Laboratory Medicine, b Otolaryngology Head and Neck Surgery, Division of Nuclear Medicine, c and Pathology, d Emory University, Atlanta, GA; Yerkes National Primate Research Center, e Atlanta, GA; Department of Radiology and Imaging Sciences, f Emory University, Atlanta, GA; Center for Radiopharmaceutical Sciences ETH-PSI-USZ, g Paul Scherrer Institute, Villigen-PSI, Switzerland; Department of Chemistry and Applied Biosciences, h Institute of Pharmaceutical Sciences, ETH Zurich, Zurich, Switzerland; Department of Chemistry, i Purdue University, and Endocyte Inc, j West Lafayette, IN PRIMARY HYPERPARATHYROIDISM (PHPT) is a common endocrine disorder, present in approximately 1% of the adult U.S. population. 1 The exact incidence of PHPT is difficult to ascertain, although it is esti- mated to occur in 2–3 per 1,000 women and 1 in 1,000 men in the United States with increasing dis- ease incidence after age 55. Up to 85% cases of PHPT are caused by a single PT adenoma, whereas multiple PT hyperplasia and adenomas account for the remaining cases. Less than 1% of PHPT cases are attributed to PT cancer (PT CA), but PT CA no longer is a rare illness, and there is no effective oncologic therapy for PT CA, which often is fatal. 2 For a majority of patients, operation for PT is effective and uncomplicated. However, preopera- tive and intraoperative localization of PT neo- plasms can be challenging in part because current imaging methodologies are suboptimal, failing to identify the PT tumor in as many as 30% of patients. 3 In scenarios such as reoperative para- thyroidectomy for persistent or recurrent Supported by Emory Molecular and Translational lmaging Research Center (EMTIC) Pilot Project and Emory University Department of Surgery Parathyroid Research Fund. Accepted for publication June 26, 2013. Reprint requests: Collin J. Weber, MD, DMSci, Department of Surgery, 101 Woodruff Circle, Suite 5105, Emory University School of Medicine, Atlanta, GA 30322. E-mail: cweber@ emory.edu. 0039-6060/$ - see front matter Ó 2013 Mosby, Inc. All rights reserved. http://dx.doi.org/10.1016/j.surg.2013.06.045 SURGERY 1385