Abstract 1646: Synthesis of [11C]onapristone for clinical investigation

Background: Onapristone is a type I anti-progestin, which prevents the progesterone receptor (PR) monomers from dimerizing, inhibits ligand-induced phosphorylation and prevents association of the PR with its co-activators, thus preventing PR-induced transcription. Onapristone has the potential to treat patients with endometrial cancer, breast cancer, uterine sarcomas, a potential subset of ovarian cancer, prostate cancer and other tumors in which the progesterone receptor plays a role in growth, proliferation and metastasis. [11C]-radiolabeled onapristone and its visualization via PET-scan, coupled with pharmacokinetic (PK) studies, has the potential to determine tissue-specific and blood PK parameters including tumor/tissue and plasma concentrations, whole body distribution and half-life of onapristone. The aim of this study is the development of a rapid Good Manufacturing Product (GMP) synthesis of parentally administered [11C]onapristone. Methods: The production of [11C]-labeled radiopharmaceuticals used a Tracerlab® FX c-Pro (GEMS) synthesis module. Carbon-11 was produced at Institut Curie-Hôpital René Huguenin via the 14N(p,α)11C nuclear reaction using a PETTrace cyclotron (GEMS) equipped with a carbon-11 target. Carbon-11 is delivered from the cyclotron as [11C]CO2 in the synthesis module, and reduced to [11C]CH4. Methane is halogenated to [11C]CH3I and converted to [11C]methyl triflate (CH3OTf). To prepare [11C]onapristone, the module was loaded with 1mg of N-desmethyl-onapristone (Arno Therapeutics) and 500µL of DMSO in the reaction vessel (Sigma®). [11C]CH3OTf was bubbled into the reaction vessel and heated at +50°C for 10 minutes. The reaction mixture was then diluted with 1 ml of mobile phase and purified using a semi-preparative HPLC column: Sunfire C18 5µm 250X10mm (Waters®), mobile phase: acetonitrile (Sigma®)/water (Waters®) 50/50 v/v; flow rate 4 mL/min. The product fraction was collected in 40mL of sterile water and was passed through a C18 SEP PAK (Waters®). This fraction was eluted with isotonic saline (Braun®) and ethanol (Sigma®). The resulting formulation was passed through a 0.22µm sterilizing filter into a sterile dose vial. Results: 10 tests were performed. Time of synthesis was 50 minutes. The amount of carbon-11 delivered was 12-14GBq for the irradiation parameters as follows: 10 min; 10µA. The decay-corrected yield of reducing [11C]CO2 to [11C]CH4 was >99%. The yields of preparing [11C]CH3I were 27-29%. Time retention of [11C]onapristone was 8.5-9.5 minutes and the non-decay-corrected radiolabelling yields were 1-2%. Conclusions: We have successfully developed a fully-automated production of [11C]onapristone ready for use in clinical trials. Citation Format: Olivier Madar, Julien Fouque, Stefan Proniuk, Keyvan Rezai, Samuel Huguet, Alexander Zukiwski, Erard M. Gilles, Alice S. Bexon, François Lokiec. Synthesis of [11C]onapristone for clinical investigation. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1646. doi:10.1158/1538-7445.AM2014-1646