Technetium 99 m – Labeled VQ Peptide : A New Imaging Agent for the Early Detection of Tumors or

There is a critical need to develop diagnostic procedures enabling early detection of tumors while at a curable stage. Technetium 99m (Tc)-labeled VQ peptide (Tc-HYNIC-VQ) identified through screening phage display peptide libraries against fresh human colonic adenomas was prepared and evaluated for tumor detection. Tc-HYNIC-VQ was prepared by a non-SnCl2 method with more than 99% radiochemical purity. The biodistribution in the HT-29 tumor model showed that although the absolute tumor uptake values were relatively low (0.60 6 0.09, 0.41 6 0.09, 0.36 6 0.18, and 0.19 6 0.08 %ID/g at 0.5, 1, 2, and 4 hours postinjection, respectively), the tumor uptake was higher than that of any of the other organs except for the kidneys at any time point examined, which led to the high tumor to nontarget ratios. The tumors and inflammation were clearly visualized with high contrast. Although the mechanism of accumulation of radiolabeled VQ peptide in tumors and inflammation needs to be further investigated, TcHYNIC-VQ is a promising imaging agent for the early detection of tumors or premalignancies, at least for screening patients with a high risk of developing cancers. M OLECULAR IMAGING is often defined as the visualization, characterization, and measurement of biologic processes at the molecular and cellular levels in humans and other living systems. By noninvasively characterizing tumor biology, molecular imaging is now playing an indispensable role in tumor diagnosis, therapy monitoring, and prognostic evaluation. Among all the imaging modalities, optical imaging, positron emission tomography (PET), and single-photon emission computed tomography (SPECT) stand out because of their high sensitivity. PET and SPECT are commonly used in routine clinical practice and trials. Colorectal cancer is the third most common cancer in the United States, causing nearly 1 in 10 cancer-related deaths. This high incidence results from the limitations of conventional endoscopic screening, which reveals only anatomic changes. Moreover, flat lesions or lesions originating either from polyposis syndromes or from inflammatory bowel diseases are usually missed by routine endoscopy, which significantly retards the early detection of premalignant lesions and the effective prevention of this disease. Therefore, it is urgent to develop new methods to identify high-risk individuals and detect early changes in the population. A number of biomarkers involved in the physiologic or pathologic events in carcinogenesis and subsequent development of cancer are under investigation to be the targets for early detection. Although less specific when compared to antibodies to these biomarkers, peptides are typically less immunogenic, are much easier to penetrate into tissues and clear rapidly from the blood, and are more convenient to produce. The identification and optimization of tumor biomarker–targeted peptides guarantee a new approach to developing probes for tumor detection and staging. Recently, a series of reports regarding peptides identified from phage display have shown proof of principle that certain cancer-specific phage library–derived probes can be developed for the detection of premalignant From the Medical Isotopes Research Center, Medical and Healthy Analytical Center, and Department of Radiation Medicine, School of Basic Medical Sciences, Peking University, Beijing, China; and the Department of Nuclear Medicine, Peking Union Medical College Hospital, Beijing, China. Address reprint requests to: Fan Wang PhD, Medical Isotopes Research Center, Peking University, 38# Xueyuan Road, Beijing 100191, China; e-mail: wangfan@bjmu.edu.cn. DOI 10.2310/7290.2012.00047 # 2013 Decker Publishing 318 Molecular Imaging, Vol 12, No 5 (July–August 2013): pp 318–326 tissues and solid tumors at an early stage by optical means. VRPMPLQ (Val-Arg-Pro-Met-Pro-Leu-Gln [VQ]) is a heptapeptide sequence first identified by Hsiung and colleagues by screening phage display peptide libraries against fresh human colonic adenomas. In vitro studies showed that binding of VQ peptide to HT-29 human colon cells was around 20-fold greater than its binding to Hs738.st/int nonmalignant human intestinal cells. In vivo studies indicated that the fluoresceinconjugated VQ peptide bound more strongly to dysplastic colonocytes than to adjacent normal cells in the same subject. It is suggested that VQ is a promising targeting molecule of probes for the early detection of colorectal cancer and potentially of other epithelial malignancies. In this study, we present the synthesis and evaluation of Tc-HYNIC-VQ (HYNIC 5 6-hydrazinonicotinamide) as a SPECT radiotracer for tumor imaging in five different xenografted tumor-bearing animal models (HT-29 human colon cancer, CL187 human colon cancer, BGC823 human gastric cancer, U87MG human glioma, and UM-SCC-22B human head and neck cancer). These tumors were clearly visualized with high contrast. Given that patients with chronic inflammatory bowel disease are at increased risk for developing malignancy due to undetected dysplastic lesions, and that the mediators and cellular effectors of inflammation are important constituents of the local environment of tumors, we subsequently explored the capability of Tc-HYNIC-VQ to image inflammation. The main objective of this study was to assess the potential of Tc-HYNIC-VQ for the early detection of tumors or premalignancies. Materials and Methods All commercially available chemical reagents were of analytic grade and used without further purification. Trisodium triphenylphosphine-3,39,399-trisulfonate (TPPTS) and tricine were purchased from Sigma-Aldrich (St. Louis, MO). HYNIC-VQ peptide and HYNIC-QV peptide, QLMRPPV (Gln-Leu-Met-Arg-Pro-Pro-Val [QV], a scrambled peptide), were custom-made by GL Biochem (Shanghai) Ltd. NaTcO4 was obtained from a commercial Mo/Tc generator (Beijing Atom High Tech Co., Ltd., Beijing, China).