Cancers 2019, 11, 1748; doi:10.3390/cancers11111748 www.mdpi.com/journal/cancers Article [ 18 F] Clofarabine for PET Imaging of Hepatocellular Carcinoma Olga Sergeeva 1 , Vladimir Kepe 2 , Yifan Zhang 1 , Galen A. Miller-Atkins 3 , Jonathan D. Keynon 4 , Renuka Iyer 5 , Sandra Sexton 5 , Amad Awadallah 6 , Wei Xin 6 , Yogen Saunthararajah 7 , E. Ricky Chan 3 and Zhenghong Lee 1,2, * 1 Radiology, Case Western Reserve University, Cleveland, OH 44106, USA; oxs57@case.edu (O.S.); yxz137@case.edu (Y.Z.) 2 Nuclear Medicine, Cleveland Clinic, Cleveland, OH 44195, USA; KEPEV@ccf.org 3 Institute for Computational Biology, Cleveland, OH 44106, USA; gmillera92@gmail.com (G.A.M.-A.); erc6@case.edu (E.R.C.) 4 Biology, Case Western Reserve University, Cleveland, OH 44106, USA; jdk39@case.edu 5 Medical Oncology, Rowell Park Comprehensive Cancer Center, Buffalo, NY 14263, USA; renuka.iyer@roswellpark.org (R.I.); sandra.sexton@roswellpark.org (S.S.) 6 Pathology, University Hospitals Cleveland Medical Center, Cleveland, OH 44106, USA; aawada@yahoo.com (A.A.); wxx10@case.edu (W.X.) 7 Hematology & Oncology, Cleveland Clinic, Cleveland, OH 44195, USA; saunthy@ccf.org * Correspondence: zxl11@case.edu; Tel.: +1-216-844-7920 Received: 21 September 2019; Accepted: 5 November 2019; Published: 7 November 2019 Abstract: Clinical diagnosis of hepatocellular carcinoma (HCC) relies heavily on radiological imaging. However, information pertaining to liver cancer treatment such as the proliferation status is lacking. Imaging tumor proliferation can be valuable in patient management. This study investigated 18 F-labeled clofarabine ([ 18 F]CFA) targeting deoxycytidine kinase (dCK) for PET imaging of dCK-dependent proliferation in HCC. Since clinical PET scans showed a high liver background uptake of [ 18 F]CFA, the aim of this study was to reduce this liver background uptake. A clinically relevant animal model of spontaneously developed HCC in the woodchucks was used for imaging experiments. Several modifiers were tested and compared with the baseline PET scan: Forodesine, probenecid, and cold clofarabine, all applied before the hot [ 18 F]CFA injection to evaluate the reduction in liver background uptake. Application of forodesine before hot [ 18 F]CFA injection did not reduce the background uptake. Instead, it increased the background by 11.6– 36.3%. Application of probenecid also increased the liver background uptake by 16.6–32.1%. Cold CFA application did reduce the liver background uptake of [ 18 F]CFA, comparing to the baseline scan. Combining cold CFA with [ 18 F]CFA for PET imaging of liver cancers is a promising strategy, worthy of further clinical evaluation. Keywords: hepatocellular carcinoma; PET imaging; tumor proliferation 1. Introduction Hepatocellular carcinoma (HCC) is the third leading cause of cancer-related death worldwide, and is the only cancer whose incidence is increasing in the United States [1]. Clinical diagnosis of HCC relies heavily on radiological imaging with contrast enhanced CT or MRI for detecting typical vascular patterns. However, these findings are often supplemented by biopsies for histopathology evaluation and confirmation, especially for patients without cirrhosis, where most guidelines recommend biopsy. A significant limitation of these standard imaging modalities is the lack of direct and biological information pertaining to the treatment of liver cancer, such as tumor proliferation. The proliferative status of a tumor can be probed by PET imaging for treatment monitoring,