David Ranganathan

Microfluidic radiolabeling of biomolecules with PET radiometals

INTRODUCTION A robust, versatile and compact microreactor has been designed, fabricated and tested for the labeling of bifunctional chelate conjugated biomolecules (BFC-BM) with PET radiometals. METHODS The developed microreactor was used to radiolabel a chelate, either 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) or 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) that had been conjugated to cyclo(Arg-Gly-Asp-DPhe-Lys) peptide, with both ⁶⁴Cu and ⁶⁸Ga respectively. The microreactor radiolabeling conditions were optimized by varying temperature, concentration and residence time. RESULTS Direct comparisons between the microreactor approach and conventional methods showed improved labeling yields and increased reproducibility with the microreactor under identical labeling conditions, due to enhanced mass and heat transfer at the microscale. More importantly, over 90% radiolabeling yields (incorporation of radiometal) were achieved with a 1:1 stoichiometry of bifunctional chelate biomolecule conjugate (BFC-BM) to radiometal in the microreactor, which potentially obviates extensive chromatographic purification that is typically required to remove the large excess of unlabeled biomolecule in radioligands prepared using conventional methods. Moreover, higher yields for radiolabeling of DOTA-functionalized BSA protein (Bovine Serum Albumin) were observed with ⁶⁴Cu/⁶⁸Ga using the microreactor, which demonstrates the ability to label both small and large molecules. CONCLUSIONS A robust, reliable, compact microreactor capable of chelating radiometals with common chelates has been developed and validated. Based on our radiolabeling results, the reported microfluidic approach overall outperforms conventional radiosynthetic methods, and is a promising technology for the radiometal labeling of commonly utilized BFC-BM in aqueous solutions.

Long-term evaluation of TiO2-based 68Ge/68Ga generators and optimized automation of [68Ga]DOTATOC radiosynthesis

Interest in using (68)Ga is rapidly increasing for clinical PET applications due to its favorable imaging characteristics and increased accessibility. The focus of this study was to provide our long-term evaluations of the two TiO(2)-based (68)Ge/(68)Ga generators and develop an optimized automation strategy to synthesize [(68)Ga]DOTATOC by using HEPES as a buffer system. This data will be useful in standardizing the evaluation of (68)Ge/(68)Ga generators and automation strategies to comply with regulatory issues for clinical use.

Radiosynthesis of clinical doses of 68Ga-DOTATATE (GalioMedix™) and validation of organic-matrix-based 68Ge/68Ga generators

INTRODUCTION 68Ga-DOTATATE is a radiolabeled peptide-based agonist that targets somatostatin receptors overexpressed in neuroendocrine tumors. Here, we present our results on validation of organic matrix 68Ge/68Ga generators (ITG GmbH) applied for radiosynthesis of the clinical doses of 68Ga-DOTATATE (GalioMedixTM). METHODS The clinical grade of DOTATATE (25 μg±5 μg) compounded in 1 M NaOAc at pH=5.5 was labeled manually with 514±218 MBq (13.89±5.9 mCi) of 68Ga eluate in 0.05 N HCl at 95°C for 10 min. The radiochemical purity of the final dose was validated using radio-TLC. The quality control of clinical doses included tests of their osmolarity, endotoxin level, radionuclide identity, filter integrity, pH, sterility and 68Ge breakthrough. RESULTS The final dose of 272±126 MBq (7.35±3.4 mCi) of 68Ga-DOTATATE was produced with a radiochemical yield (RCY) of 99%±1%. The total time required for completion of radiolabeling and quality control averaged approximately 35 min. This resulted in delivery of 50%±7% of 68Ga-DOTATATE at the time of calibration (not decay corrected). CONCLUSIONS 68Ga eluted from the generator was directly applied for labeling of DOTA-peptide with no additional pre-concentration or pre-purification of isotope. The low acidity of 68Ga eluate allows for facile synthesis of clinical doses with radiochemical and radionuclide purity higher than 98% and average activity of 272±126 MBq (7.3±3 mCi). There is no need for post-labeling C18 Sep-Pak purification of final doses of radiotracer. Advances in knowledge and implications for patient care. The clinical interest in validation of 68Galabeled agents has increased in the past years due to availability of generators from different vendors (Eckert-Ziegler, ITG, iThemba), favorable approach of U.S. FDA agency to initiate clinical trials, and collaboration of U.S. centers with leading EU clinical sites. The list of 68Ga-labeled tracers evaluated in clinical studies should growth because of the sensitivity of PET technique, the simplicity of the shakebake approach for the dose preparation and reliability of 68Ge/68Ga generators. Our studies have confirmed the reproducible elution profile, and high reliability of ITG GmbH generators required for routine doses preparation according to FDA recommendations.

Peptide Receptor Radionuclide Therapy With 177Lu-Octreotate in Patients With Somatostatin Receptor Expressing Neuroendocrine Tumors: Six Yearsʼ Assessment

Objectives Peptide receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogues is a promising treatment for patients with inoperable, well to moderately differentiated metastatic neuroendocrine tumors (NETs). In continuation of our novel study with the radionuclide lutetium 177Lu, we now present further results of 177Lu DOTATATE therapy in managing NETs and other somatostatin receptor–expressing tumors in a larger and more diverse patient group. Patients and Methods One hundred forty-four consecutive patients (85 men and 59 women; age range, 11–87 years; mean age, 58.5 years) with histologically confirmed NET were enrolled. One hundred forty-three patients received at least 1 cycle of treatment. Among them, 132 were deemed evaluable by having at least 1 cycle of treatment and a posttreatment MRI or CT scan for assessment based on modified Response Evaluation Criteria in Solid Tumors. Response to therapy was evaluated in terms of progression-free survival, overall survival, as well as radiologic, biochemical, and clinical responses. Further, analysis of symptoms was reviewed during therapy and also in subsequent follow-ups for safety evaluation. Renal, gastrointestinal (GI), hepatic, and hematological adverse events were evaluated using National Cancer Institute common toxicities criteria V4.03, through full blood panels, as well as consultation with patients for any symptoms and/or adverse events. Results As of July 2016, median progression-free survival was about to be reached. Of 28 patients who have completed 177Lu DOTATATE therapy (completion of 4 or more cycles of treatment and all designated follow-ups), no patient showed complete response (CR), 8 patients (28.57%) showed partial response (PR), 16 patients (57.14%) showed stable disease (SD), and progressive disease (PD) was observed in 4 patients (14.28%). The objective response rate (CR + PR) of this group was 28.57% (n = 8) with a cumulative disease control (CR + PR + SD) of 85.71% (n = 24). Among 132 evaluable patients, assessment of treatment response using modified Response Evaluation Criteria in Solid Tumors criteria revealed CR in none of the patients, PR in 12 patients (9.09%), SD in 66 patients (50%), whereas PD, which included patients who passed away, was observed in 54 patients (40.90%), yielding an objective response rate of 9.09% (n = 12) and a cumulative disease control rate of 59.09% (n = 78). Symptoms including abdominal pain, diarrhea, flushing, and fatigue improved in over 50% of the patients, whereas weight loss improved in 28.26% of the patients. No grade 3 or grade 4 renal toxicities were found, though eleven grade 3 and five grade 4 hematological as well as three grade 3 hepatotoxicities were reported. Grade 3 hematotoxicity lasted an average of 2.7 months, and grade 4 lasted for only 0.9 months, whereas grade 3 hepatotoxicity lasted an average of 3.1 months. Conclusions 177Lu-octreotate peptide receptor radionuclide therapy has shown promising potential as a safe and effective targeted therapy in inoperable, well to moderately differentiated metastatic neuroendocrine cancers. The results of the multicenter randomized clinical trial conducted in United States and Europe are concordant with current study.