Open camera or QR reader and scan code to access this article and other resources online. Synthesis, Quality Control, and Bench-to-Bed Translation of a New [ 68 Ga]Ga-Labeled NOTA-Conjugated Bisphosphonate for Imaging Skeletal Metastases by Positron Emission Tomography Sudipta Chakraborty, 1,2 Sucheta Chatterjee, 2,3 Rubel Chakravarty, 1,2 Haldhar D. Sarma, 4 Raviteja Nanabala, 5 Dibakar Goswami, 2,3 Ajith Joy, 5 and Maroor Raghavan Ambikalamajan Pillai 5 Abstract Background: Early detection of skeletal metastasis is of great interest to determine the prognosis of cancer. Positron emission tomography-computed tomography (PET-CT) imaging provides a better temporal and spec- tral resolution than single photon emission computed tomography-computed tomography (SPECT-CT) imag- ing, and hence is more suitable to detect small metastatic lesions. Although [ 18 F]NaF has been approved by U.S. FDA for a similar purpose, requirement of a medical cyclotron for its regular formulation restricts its extensive utilization. Efforts have been made to find suitable alternative molecules that can be labeled with 68 Ga and used in PET-CT imaging. Objective: The main objective of this study is to synthesize and evaluate a new [ 68 Ga]Ga-labeled NOTA- conjugated geminal bisphosphonate for its potential use in early detection of skeletal metastases using PET-CT. Methods: The authors performed a multistep synthesis of a new NOTA-conjugated bisphosphonic acid using thiourea linker and radiolabeled the molecule with 68 Ga. The radiolabeled formulation was evaluated for its in vitro stability, affinity for hydroxyapatite (HA) particles, preclinical biodistribution in animal models, and PET-CT imaging in patients. Results: The bifunctional chelator (NOTA)-conjugated bisphosphonate was synthesized with 97.8% purity and radiolabeled with 68 Ga in high yield (>98%). The radiolabeled formulation was found to retain its stability in vitro to the extent of >95% up to 4 h in physiological saline and human serum. The formulation also showed high affinity for HA particles in vitro with K d = 907 – 14 mL/g. Preclinical biodistribution studies in normal Wistar rats demonstrated rapid and almost exclusive skeletal accumulation of the complex. PET-CT imaging in a patient confirmed its ability to detect small metastatic skeletal lesions. Conclusions: The newly synthesized [ 68 Ga]Ga-labeled NOTA-conjugated bisphosphonate is a promising ra- diotracer for PET-CT imaging for skeletal metastases. Keywords: bone metastases, PET, bisphosphonates, bifunctional chelator, NOTA, 68 Ga 1 Radiopharmaceuticals Division, Bhabha Atomic Research Centre (BARC), Mumbai, India. 2 Homi Bhabha National Institute (HBNI), Mumbai, India. 3 Bio Organic Division, Bhabha Atomic Research Centre (BARC), Mumbai, India. 4 Radiation Biology and Health Sciences Division, Bhabha Atomic Research Centre (BARC), Mumbai, India. 5 Molecular Group of Companies, Ernakulam, India. Address correspondence to: Sudipta Chakraborty; Radiopharmaceuticals Division, Bhabha Atomic Research Centre (BARC); Trombay, Mumbai 400085, India E-mail: sudipta@barc.gov.in CANCER BIOTHERAPY AND RADIOPHARMACEUTICALS Volume 39, Number 1, 2024 ª Mary Ann Liebert, Inc. DOI: 10.1089/cbr.2023.0077 92 Downloaded by National Institutes of Health Library Package (NIH) from www.liebertpub.com at 02/15/24. For personal use only.