Doxorubicin-[18F]Fluorobenzamide: Automated synthesis for Chemofilter Development

1003 Introduction: Doxorubicin (DOX) is a cyctotoxic anthracycline chemotherapy drug which is used in the treatment of a variety of cancers. Transarterial chemoembolization (TACE) delivery of DOX, used primarily for non-resectable hepatocellular carcinoma, is highly effective with a linear dose response curve. DOX systemic toxicity limits the cumulative applied dose. One developing method to curb the systemic toxicity following intra-arterial delivery of DOX involves the installation of a filter downstream of the tumors to trap excess DOX. Doxorubicin-[18F]Fluorobenzamide ([18F]FB-DOX) synthesis was automated to enable the development of a platform for evaluating the filter devices in vitro and in vivo. Herein, we describe the evaluation of [18F]FB-DOX in ion exchange (IEX) and DNA based solid phase adsorbents and validate [18F]FB-DOX as a surrogate for DOX in this application. Methods: [18F]Fluoride ion, prepared on a GE PETtrace via a 18O(p,n)18F reaction, was loaded onto the Sofie ELIXYS FLEX/ CHEM system and trapped on a Waters QMA cartridge. The [18F]fluoride was eluted with Kryptofix [2,2,2] and KHCO3 and azeotropically dried with acetonitrile. A solution of 4-(ethoxycarbonyl)-N,N,N-trimethylbenzenaminium trifluoromethanesulfonate salt in acetonitrile was reacted with the [18F]fluoride and the resulting fluorinated ethyl ester was saponified with tetrapropylammonium hydroxide. Further reaction with TSTU to produced [18F]succinimidyl fluorobenzoate ([18F]SFB) which was diluted with 0.1% acetic acid, trapped on an Oasis HLB cartridge, washed with 0.1% acetic acid and eluted into a second reactor with acetonitrile. The [18F]SFB was dried and reacted with doxorubicin HCl and trimethylamine in DMF. [18F]FB-DOX was purified by reverse phase HPLC. The purified tracer was then concentrated using a C-18 light Sep-Pak, eluted, and formulated in PBS/ 5% ethanol. Two Rezorian cartridges, one empty and one containing either DNA or IEX resin were connected in series. DOX solution (20 µg/ mL in 50 mL PBS) spiked with either [18F]FB-DOX or [18F]SFB, non-binding control, were prepared. Each solution was then pushed via syringe pump (30 mL/min) through the cartridges and the eluant was recirculated 2 more times. New cartridges were used for each solution and resin. Dynamic imaging of the flow experiments was conducted in a Siemens InVeon microPET. Results: [18F]FB-DOX was prepared on a Sofie ELIXYS FLEX/ CHEM in 12.7 ± 5.9% decay corrected yield (n = 4, 0.6- 1.6 GBq) in 129 min, comparable in yield to the previously reported [18F]FB-DOX using a different approach [1]. Flow studies showed minimal binding of [18F]SFB to either IEX or DNA resins, 5.2 and 4.3% respectively for the controls. [18F]FB-DOX was trapped in both resins, 42% on the IEX and 69.5% on the DNA. Dynamic images of the flow experiment were acquired and showed the increased accumulation of [18F]FB-DOX with each pass through both resins. Conclusions: [18F]FB-DOX tracer synthesis from [18F]SFB, a new approach, gave sufficient yield for both in vitro and in vivo studies using the ELIXYS FLEX/ CHEM system. In vitro testing indicated that the tracer was adsorbed along with native DOX from a PBS solution. Control studies with [18F]SFB showed that trapping was specific for the [18F]FB-DOX conjugate and showed that the tracer functions as a radioactive surrogate for DOX trapping. Acknowledgements: This study was funded by the National Cancer Institute, grant R01CA194533. [1] Kumar, P. et al. Curr.Radiopharm.2016, 9, 215-221.