Abstract 4234: Elucidating structure-activity relationships of SIRT2 and fluoroalkyl chain length to identify the lead candidate substrate radiotracer for PET imaging

Histone deacetylases (HDACs) play a pivotal role in epigenetic regulation through post translational modifications of histone core and other critical proteins in cellular pathways. The HDACs class III, sirtuins (SIRTs) 1-7, possess limited deacetylase activity. Each of these nicotinamide dinucleotide (NAD+) dependent enzymes have unique structures of catalytic sites that prefer larger lysine-modifying groups as substrates (i.e., glutaryl, succinyl, lipoyl, crotanyl, myristoyl). In particular, SIRT2 is a key regulator of nuclear H4K16 and cytoplasmic alpha-tubulin proteins, thereby acting as a mitotic exit regulator. From the literature, it is clear that SIRT2 plays a pivotal role in the regulation of cancers, so much so that it may switch between tumor suppressor and regulator at different stages of tumor progression. For this reason, SIRT2 has been identified as a possible target for cancer therapy but due to the pleiotropic roles of SIRT2 under normal and pathologic conditions, it is important to assess its activity during pharmacomodulation (i.e. activation or inhibition). Therefore, non-invasive PET imaging using SIRT2-specific substrate-type radiotracers may aid in the development of new SIRT2 inhibitors for therapy of cancer. Herein, we report novel synthesis of a focused library of compounds to assess the structure activity relationship (SAR) of SIRT2 with fluoroalkyl chain length varying between 3 and 16 carbons. The preliminary screening was performed with the tert-butyloxycarbonyl-lysine-aminomethylcoumarin (Boc-lys-AMC) backbone and Fluor-de-lys assay [1] to determine the chain length for optimal SIRT2 catalytic efficiency. Based on the analysis of Michealis-Menten kinetics of each substrate, myristoyl (14-carbon carboxylic acid) was cleaved most efficiently, followed by 12-fluorododecanoic and 10-fluorodecanoic acids (kcat/km = 4E-3, 1E-4, 8.9E-5 s-1uM-1, respectively). For in vivo PET imaging radiotracer development, we linked the 12-fluorododecanoic acid with the aminohexanoicanilide (AHA) backbone [2]. This compound was developed with a terminal bromine (precursor), iodine, fluorine, and F-18 (12-[18F]DDAHA). In vitro cellular uptake studies demonstrated a three-fold increase in accumulation of 12-[18F]DDAHA in U87 glioma cells as compared to MiaPaCa, MDA-MB-231, and MCF10A cell lines. The increased accumulation in the U87 glioma cells indicates that this compound may prove useful for detection of brain gliomas and for monitoring therapies with novel SIRT2 specific inhibitors. This insight into the catalytic activity of SIRT2 provides a basis for the development of a SIRT2-specific PET imaging agent to further probe the role of SIRT2-mediated epigenetic regulation in normal physiology and cancer. Citation Format: Robin E. Bonomi, Aleksandr Shavrin, Vadim Popov, Thomas Mangner, Juri G. Gelovani. Elucidating structure-activity relationships of SIRT2 and fluoroalkyl chain length to identify the lead candidate substrate radiotracer for PET imaging. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4234.