A β-Camera Integrated with a Microfluidic Chip for Radioassays Based on Real-Time Imaging of Glycolysis in Small Cell Populations

Abstract

An integrated β-camera and microfluidic chip was developed that is capable of quantitative imaging of glycolysis radioassays using 18F-FDG in small cell populations down to a single cell. This paper demonstrates that the integrated system enables digital control and quantitative measurements of glycolysis in B-RafV600E–mutated melanoma cell lines in response to specific B-Raf inhibition. Methods The β-camera uses a position-sensitive avalanche photodiode to detect charged particle–emitting probes within a microfluidic chip. The integrated β-camera and microfluidic chip system was calibrated, and the linearity was measured using 4 different melanoma cell lines (M257, M202, M233, and M229). Microfluidic radioassays were performed with cell populations ranging from hundreds of cells down to a single cell. The M229 cell line has a homozygous B-RafV600E mutation and is highly sensitive to a B-Raf inhibitor, PLX4032. A microfluidic radioassay was performed over the course of 3 days to assess the cytotoxicity of PLX4032 on cellular 18F-FDG uptake. Results The β-camera is capable of imaging radioactive uptake of 18F-FDG in microfluidic chips. 18F-FDG uptake for a single cell was measured using a radioactivity concentration of 37 MBq/mL during the radiotracer incubation period. For in vitro cytotoxicity monitoring, the β-camera showed that exposure to 1 µM PLX4032 for 3 days decreased the 18F-FDG uptake per cell in highly sensitive M229 cells, compared with vehicle controls. Conclusion The integrated β-camera and microfluidic chip can provide digital control of live cell cultures and allow in vitro quantitative radioassays for multiple samples simultaneously.

A Continuously Infused Microfluidic Radioassay System for the Characterization of Cellular Pharmacokinetics

“…Furthermore, the uptake values obtained with CIMR are indirect estimations compared with the previous in-culture microfluidic radioassay using a loading and flushing protocol (11). Adapting the infusion profile of CIMR with flushing of the tracer allows the pure event density of cells to be measured, and the uptake values we calculated were consistent with the continuously measured CIMR uptake (Supplemental Fig.…”

“…Nevertheless, the significant correlations between the relative uptake ratios (0.5/5 and 2.5/5 mM) for the two types of measurements demonstrated the consistency of the relative relations between them. As many studies investigate the relative differences under certain interventions, the systematic bias between CIMR and conventional uptake may not change the results if all the investigations are performed using in-culture measurement (11). Smaller variations were achieved with in-culture measurement using CIMR than with conventional uptake experiments.…”

“…Thus, the measurements are restricted to several discontinuous time points, and a dynamic acquisition over time is still not possible. In addition, the medium-exchange procedure requires a compromise between the completeness of the exchange and maintenance of a stable culture environment (11,12). Application of this technique to less adhesive cell lines is therefore limited.…”

“…In another approach, the automatic measurement of real-time tracer binding was achieved on a radioimmunoassay system using a rotating cell dish (10). Vu et al developed a microfluidic radioassay system (BetaBox) that integrates a microfluidic chip with a position-sensitive b-camera (11). That system allows multiple radioassays of a small cell population directly in a culture environment.…”

High-Resolution Radioluminescence Microscopy of 18F-FDG Uptake by Reconstructing the β-Ionization Track

“…Only a few methods have demonstrated the ability to visualize the uptake of radionuclide probes with single-cell resolution. One of these methods uses a bsensitive avalanche photodiode to measure radionuclide uptake in small groups of cells, cultured in 16 microfluidic chambers (8). An experiment showed that the avalanche photodiode could measure signal from a single cell in the chamber.…”