Optimization of Radiochemical Reactions using Droplet Arrays

Summary

This method describes the use of a novel high-throughput methodology, based on droplet chemical reactions, for the rapid and economical optimization of radiopharmaceuticals using nanomole amounts of reagents.

Abstract

Current automated radiosynthesizers are designed to produce large clinical batches of radiopharmaceuticals. They are not well suited for reaction optimization or novel radiopharmaceutical development since each data point involves significant reagent consumption, and contamination of the apparatus requires time for radioactive decay before the next use. To address these limitations, a platform for performing arrays of miniature droplet-based reactions in parallel, each confined within a surface-tension trap on a patterned polytetrafluoroethylene-coated silicon "chip", was developed. These chips enable rapid and convenient studies of reaction parameters including reagent concentrations, reaction solvent, reaction temperature and time. This platform permits the completion of hundreds of reactions in a few days with minimal reagent consumption, instead of taking months using a conventional radiosynthesizer.

Introduction

Positron-emission tomography (PET) radiopharmaceuticals are widely used as research tools to monitor specific in vivo biochemical processes and study diseases, and for the development of new drugs and therapies. Moreover, PET is a critical tool for diagnosing or staging disease and monitoring a patient's response to therapy^1,2,3. Due to the short half-life of PET radioisotopes (e.g., 110 min for fluorine-18-labeled radiopharmaceuticals) and radiation hazard, these compounds are prepared using specialized automated systems operating behind radiation shielding and must be p....

Protocol

CAUTION: This protocol involves the handling of radioactive materials. Experiments should not be undertaken without the necessary training and personal protective equipment and approval from the radiation safety office at your organization. Experiments should be performed behind radiation shielding, preferably in a ventilated hot cell

1. Fabrication of multi-reaction chips

NOTE: Batches of multi-reaction microdroplet chips are fabricated from 4" silicon wafers usi.......

Discussion

Due to limitations of conventional radiochemistry systems that allow only one or a small number of reactions per day and consume a significant quantity of reagents per data point, only a tiny portion of the overall reaction parameter space can be explored in practice, and many times results are reported with no repeats (n=1). Compared to conventional systems, this multi-reaction droplet radiosynthesis platform makes it practical to accomplish more comprehensive and rigorous studies of radiosynthesis conditions while cons.......

Materials

Name	Company	Catalog Number	Comments
2,3-dimethyl-2-butanol (thexyl alcohol)	Sigma-Aldrich	594-60-5	98%
Acetone	KMG Chemicals		Cleanroom LP grade
Ammonium formate (NH4HCO2)	Sigma-Aldrich	540-69-2	97%
Anhydrous acetonitrile (MeCN)	Sigma-Aldrich	75-05-8	99.80%
Ceramic heater	Watlow	Utramic CER-1-01-0093	25 mm x 25 mm
Cerenkov imaging chamber	Custom built		Other instruments can be used for TLC plate readout including: small animal in vivo optical imaging system, 2D radio-TLC scanner, 1D radio-TLC scanner
DI water	Sigma-Aldrich	7732-18-5
Disposable transfer pipets, 3 mL	Falcon	13-680-50
Dose calibrator	Capintec, Inc.	CRC-25 PET
Fallypride	ABX Advanced Biochemical Compounds	1560.0010.000	Fallypride reference standard, >95%
[18F]fluoride in [18O]H2O	UCLA Ahmanson Biomedical Cyclotron Facility		Due to short half-life this must be obtained from local radiochemistry lab or commercial radiopharmacy
Glass cover plates (76.2 mm x 50.8 mm x 1 mm thick)	C&A Scientific	6101
Headway spin coater	Headway Research, Inc.	PWM50-PS-R790 Sipinner system	PWM50-control box, PS-motor, R790-bowl
High temperature oven	Carbolite	HTCR 6 28
Hot plate	Thermo Scientific	Super-Nuova HP133425
Isopropanol (IPA)	KMG Chemicals		Cleanroom LP grade
Mask aligner	Karl Suss	MA/BA6
Methanol (MeOH)	Sigma-Aldrich	67-56-1	≥99.9%
Microcentrifuge tube	Eppendorf	0030 123.301	500 µL, colorless, polypropylene
Micropipette (0.5-10 µL)	Labnet	BioPette P3940-10
Micropipette (100-1000 µL)	Labnet	BioPette P3940-1000
Micropipette (10-100 µL)	Labnet	BioPette P3940-100
Micropipette tips (0.1-10 µL)	USA Scientific Inc Tips	11113810
Micropipette tips (2-200 µL)	BrandTech	13-889-143
Micropipette tips (50-1000 µL)	BrandTech	13-889-145
Photoresist developer solution	MicroChem	MEGAPOSIT MF-26A
Positive photoresist	MicroChem	MEGAPOSIT 220-7.0
Reactive-ion etcher (RIE)	Oxford Instruments	Plasma Lab 80 Plus
Silicon wafer cutter	Euro Tool	CSCB-431.00
Silicon wafer; 4" diameter	Silicon Valley Microelectronics Inc.	0017227-048	P type, boron doped, thickness 525 ± 25 µm
Teflon AF 2400	Chemours	D14896765	1% solids
Tetrabutylammonium bicarbonate (TBAHCO3)	ABX Advanced Biochemical Compounds	808	Aqueous solution stabilized with ethanol, 0.075 M
Themal conducting paste	OMEGA	OT-201-2
TLC plates	Merck KGaA	1.05554.0001	Silica gel 60 F254, 50 mm x 60 mm, aluminum back
Tosyl-fallypride	ABX Advanced Biochemical Compounds	1550.004.000	Fallypride precursor, >90%
Trimethylamine (TEA)	Sigma-Aldrich	75-50-3	≥ 99%
Tweezers	Cole-Parmer	UX-07387-08	Stainless steel, fine tip