Development of Novel Analogs of the Monocarboxylate Transporter Ligand FACH and Biological Validation of One Potential Radiotracer for Positron Emission Tomography (PET) Imaging

oleh: Masoud Sadeghzadeh, Barbara Wenzel, Daniel Gündel, Winnie Deuther-Conrad, Magali Toussaint, Rareş-Petru Moldovan, Steffen Fischer, Friedrich-Alexander Ludwig, Rodrigo Teodoro, Shirisha Jonnalagadda, Sravan K. Jonnalagadda, Gerrit Schüürmann, Venkatram R. Mereddy, Lester R. Drewes, Peter Brust

Format: Article
Diterbitkan: MDPI AG 2020-05-01

Deskripsi

Monocarboxylate transporters 1-4 (MCT1-4) are involved in several metabolism-related diseases, especially cancer, providing the chance to be considered as relevant targets for diagnosis and therapy. [<sup>18</sup>F]FACH was recently developed and showed very promising preclinical results as a potential positron emission tomography (PET) radiotracer for imaging of MCTs. Given that [<sup>18</sup>F]FACH did not show high blood-brain barrier permeability, the current work is aimed to investigate whether more lipophilic analogs of FACH could improve brain uptake for imaging of gliomas, while retaining binding to MCTs. The 2-fluoropyridinyl-substituted analogs <b>1</b> and <b>2</b> were synthesized and their MCT1 inhibition was estimated by [<sup>14</sup>C]lactate uptake assay on rat brain endothelial-4 (RBE4) cells. While compounds <b>1</b> and <b>2</b> showed lower MCT1 inhibitory potencies than FACH (IC<sub>50</sub> = 11 nM) by factors of 11 and 25, respectively, <b>1</b> (IC<sub>50</sub> = 118 nM) could still be a suitable PET candidate. Therefore, <b>1</b> was selected for radiosynthesis of [<sup>18</sup>F]<b>1</b> and subsequent biological evaluation for imaging of the MCT expression in mouse brain. Regarding lipophilicity, the experimental log D<sub>7.4</sub> result for [<sup>18</sup>F]<b>1</b> agrees pretty well with its predicted value. In vivo and in vitro studies revealed high uptake of the new radiotracer in kidney and other peripheral MCT-expressing organs together with significant reduction by using specific MCT1 inhibitor α-cyano-4-hydroxycinnamic acid. Despite a higher lipophilicity of [<sup>18</sup>F]<b>1</b> compared to [<sup>18</sup>F]FACH, the in vivo brain uptake of [<sup>18</sup>F]<b>1</b> was in a similar range, which is reflected by calculated BBB permeabilities as well through similar transport rates by MCTs on RBE4 cells. Further investigation is needed to clarify the MCT-mediated transport mechanism of these radiotracers in brain.