Automated production of a sphingosine-1 phosphate receptor 1 (S1P1) PET radiopharmaceutical [¹¹C]CS1P1 for human use

Highlights

• Automated production of [¹¹C]CS1P1 was performed by a two-step-one-pot procedure under cGMP conditions.

• [¹¹C]CS1P1 was achieved with high molar activity and radiochemical purity.

• The procedure can be applied for a routine production of [¹¹C]CS1P1.

• The radiopharmaceutical [¹¹C]CS1P1 meets all quality control criteria for human use.

Abstract

Automated synthesis of a radiopharmaceutical 3-((2-fluoro-4-(5-(2′-methyl-2-(trifluoromethyl)-[1,1′-biphenyl]-4-yl)-1,2,4-oxadiazol-3-yl)benzyl) (methyl-¹¹C)amino)propanoic acid ([¹¹C]CS1P1) for PET imaging sphingosine-1 phosphate receptor 1 (S1P1) was accomplished by a two-step-one-pot procedure in a Siemens CTI methylation automated module using TR-19 cyclotron. The synthesis of [¹¹C]CS1P1 was successfully validated under current Good Manufacturing Practices (cGMP) conditions, resulting in a consistent average radiochemical yield of ∼15%, molar activity of ∼3129 GBq/μmol (decay corrected to end of bombardment, EOB), and radiochemical purity > 95%. The radiopharmaceutical product meets all quality control criteria for human use for an Investigational New Drug (IND) application to permit human studies.

Introduction

Sphingosine-1-phosphate receptor 1 (S1P1), originally named as endothelial differentiation gene 1 (EDG1) is a protein encoded by the S1P1 gene in humans. It belongs to a sphingosine-1-phosphate receptor family, which has five subtypes (S1P1-5). S1P1 plays an important role in regulating vascular and lymphatic systems, immune system, central nervous system (CNS), and oncogenesis by binding with a bioactive signaling molecule sphingosine 1-phosphate (S1P) (Allende et al., 2003; Garris et al., 2013; Lee et al., 1999; Matloubian et al., 2004; Pham et al., 2008; Rutherford et al., 2013). Interest in S1P1 has increased with the recent approval by the USA Food and Drug Administration (FDA) of the first orally administered S1P receptor-targeted drug for multiple sclerosis (MS). This drug, FTY720 (Fingolimod) (Fig. 1), a sphingosine analogue, acts as an S1P1 modulator after phosphorylation by sphingosine kinase in vivo, in which it engages the S1P1, leading to internalization and subsequent degradation of the S1P1, thereby leading to lymphocyte sequestration in lymph nodes. This prevents them from moving into the CNS and causing a relapse of MS (Brinkmann, 2009; Cohen and Chun, 2011). The success of treating MS using FTY720 has triggered abundant research efforts to investigate the role of S1P1 in the pathogenesis and progression of MS and other inflammatory diseases (Camp et al., 2015; Choi et al., 2011; Gonzalez-Cabrera et al., 2012; Li et al., 2016; Liu et al., 2018).

Positron emission tomography (PET) provides a unique non-invasive medical imaging technique to visualize, characterize, and measure the biological processes in humans and other living subjects. It has become an indispensable tool for many diseases in oncology, cardiology, and neurology. Using suitable radiotracers, PET is used widely in preclinical and clinical investigations to directly quantify the expression of target proteins in vivo for guiding the therapeutic drug development (Das, 2015). In our preclinical research, we developed and evaluated a promising C-11 radiolabeled radiotracer, 3-((2-fluoro-4-(5-(2′-methyl-2-(trifluoromethyl)-[1,1′-biphenyl]-4-yl)-1,2,4-oxadiazol-3-yl)benzyl) (methyl-¹¹C)amino)propanoic acid ([¹¹C]CS1P1) (Fig. 1) targeting S1P1. In vivo animal studies demonstrated that [¹¹C]CS1P1 has the capability of imaging S1P1 expression that reflects the inflammatory response in three different models of inflammatory diseases including MS, neointimal hyperplasia, and vascular inflammation (Jin et al., 2017; Liu et al., 2016, 2017; 2018). To explore the clinical utilization of [¹¹C]CS1P1 for human use, [¹¹C]CS1P1 needs to be prepared under current Good Manufacturing Practices (cGMP) using an automated synthesis module to meet FDA regulation of radiopharmaceutical. Herein, we report our efforts on the automated production of [¹¹C]CS1P1 in our institutional cGMP facilities.