Abstract 112: Synthesis and preclinical evaluation of radiolabeled alisertib as an investigational aurora kinase A PET tracer

Abstract

Abstract Background: High expression of the aurora kinase A (AURKA) protein is associated with colorectal adenoma-to-carcinoma progression and with poor prognosis of patients with stage III colorectal cancer (CRC) and patients with CRC liver metastases. Several agents have been developed that specifically target AURKA kinase activity, among those the investigational agent alisertib. To identify CRC patients with high AURKA expression levels a dedicated imaging method would be preferred, since only then a whole body assessment of AURKA expression in primary tumors as well as in metastases can be achieved. Positron emission tomography (PET) using a dedicated radiotracer allows for this. To this end, [3H]alisertib has been synthesized for in vitro experiments and [11C]alisertib for in vivo imaging with PET in xenograft mouse models. Methods: [3H]alisertib was synthesized starting from [3H]methyl nosylate under similar conditions as [11C]alisertib, which was synthesized starting from [11C]CH3I in a two-step procedure, purified and formulated within 45 minutes. Four CRC cell lines with different levels of AURKA expression were selected, HCT116, SW480, SW1398 and Caco-2, and the in vitro dynamic uptake of [3H]alisertib in these cell lines was measured before and after siRNA-mediated AURKA downmodulation. Next, the uptake of [11C]alisertib was assessed with PET in xenografted mice using the same four CRC cell lines. Results: The synthesis of [3H]alisertib was optimized to an overall yield of 42%, while an overall yield of 23 ± 4%, starting from [11C]CH3I, was obtained in an optimized synthesis of [11C]alisertib. The CRC cell line with high expression of AURKA, Caco-2, showed a significantly higher uptake of [3H]alisertib compared to the lower expressing AURKA CRC cell lines, HCT116, SW480 and SW1398. In addition, the uptake of [3H]alisertib was reduced in all cell lines upon downmodulation of AURKA. The stability of [11C]alisertib in rodents was determined at 97.8% ± 1.3% intact tracer in blood at 45 minutes after iv injection (n=4). Preliminary data using a HCT116 xenograft mouse model indicated a tumor-to-background ratio of 1.56 ± 0.12, with an uptake of 1.00 %ID/g at 90 minutes after injection. PET studies with the SW480, SW1398 and Caco-2 xenografts are currently in progress. Conclusions: Both [3H]alisertib and [11C]alisertib were obtained with good purity and yield. In vitro studies using [3H]alisertib indicate good correlation of cellular uptake with AURKA expression. [11C]alisertib is stable in vivo and HCT116 xenografted mice show a fair tumor uptake of [11C]alisertib. Citation Format: Joost Verbeek, Jeroen ACM Goos, Albert A. Geldof, Annemieke C. Hiemstra, Otto S. Hoekstra, Gerrit A. Meijer, Steven Stroud, Daniel Bradley, Remond JA Fijneman, Albert D. Windhorst. Synthesis and preclinical evaluation of radiolabeled alisertib as an investigational aurora kinase A PET tracer. [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 112. doi:10.1158/1538-7445.AM2014-112