In-Line Radiolabeling: A Novel Continuous-Flow System for Commercial-Scale Protein Labeling

Abstract

A key limitation in developing radiotherapeutic proteins is the expense of manufacturing the drug in small batches using traditional reaction vessels. Removing limitations on the quantity of protein labeled at any one time significantly decreases the cost of production, and nowhere is the need for cost-effective radiotherapeutics more acute than in the treatment of cancer. Methods: We describe a novel method that can rapidly radiolabel, theoretically, unlimited amounts of protein, without causing significant damage to binding potency or structural integrity. Our process controls the reaction rate for the isotope and reactants as they simultaneously flow through a reaction tube. Results: We have demonstrated proof of principle by labeling nearly a gram of antibody with 481 GBq (13 Ci) of 131 I during a single 30-min reaction run. Conclusion: Simple to construct, our system is already used to manufacture a radiolabeled antibody, both in the United States and in India, as part of clinical trials to treat glioblastoma multiforme. Modified, this system may be also applicable for nonradioactive labeling.

Radiochemistry

“…Whilst many procedures are automated, and new schemes for automation are continually being introduced (see below), there is much scope for improved procedures and for seeking new intermediates. Basic methods, like halogen exchange for a [F 18 ]fluoride anion, in the presence of Kryptofix [222], have been used in the labelling of nifedipine derivatives, 110 benzodiazepine receptors 111 and 6-fluoro-3,4-dihydroxy-L-phenylalanine 112 (this compound can also be labelled 113 by the use of [F 18 ]difluorine gas). Many new methods utilise nucleophilic attack by the [F 18 ]fluoride anion on 'good leaving groups' (such as tosyl or triflate) 114,115 this strategy has been used in the labelling of 2 116 -or 6 117 -[F 18 ]-6-deoxy-D-glucose and PBR111 118 (used for imaging a translocator protein).…”

“…A continuous flow system has been described 222 for labelling proteins with radioiodine isotopes. The standard procedures for labelling continue to be exploited, such as halogen-radioiodine exchange which has been used to prepare [I 125 ]iodouracil derivatives, 223 6-deoxy-6-[I 131 ]iodo-L-ascorbic acid 224 and 1-(6-deoxy-6-iodo-b-Dgalactopyranosyl)-2-nitroimidazole.…”