Assessment of cellular responses in three‐dimensional cell cultures through chemical exchange saturation transfer and ¹H MRS

Abstract

Metabolic responses to physiological changes have been detected using chemical exchange saturation transfer (CEST) imaging in clinical settings. Similarly to other MRI techniques, the CEST technique was based originally on phantoms from buffer solutions and was then further developed through animal experiments. However, CEST imaging can capture certain dynamics of metabolism that solution phantoms cannot model. Cell culture phantoms can fill the gap between buffer phantoms and animal models. In this study, we used 1 H NMR and CEST in a B 0 field of 9.4 T to investigate HEK293T cells from two-dimensional (2D) cultures, three-dimensional (3D) cultures, and 3D cultures seeded with cell spheroids. Two CEST dips were observed: the magnitude of the amine dip at 2.8 ppm increased during the incubation period, whereas the hydroxyl dip at 1.2 ppm remained approximately the same or modestly increased. We also observed a CEST dip at 2.8 ppm from the 2D culture responding dramatically to doxorubicin treatment. By cross-validating with pH values and the concentrations of amine and hydroxyl protons extracted through 1 H NMR, we observed that they did not correspond to an increase in the amine pool. We believe that the denaturation or degradation of proteins from the fetal bovine serum increased the size of the amine pool. Although 3D culture conditions can be further improved, our study suggests that 3D cultures have the potential to bridge studies of solution phantoms and those on animals.

Special issue on chemical exchange saturation transfer MRI

“…33 Also, to bridge the gap between solution phantoms and in vivo studies, Wu et al showed that 2D and 3D cell culture phantoms can play an important role in interpreting many CEST signals. 34 Here, they showed that CEST signals in cell culture phantoms were sensitive to incubation time over several days. 34 In conclusion, it is fair to say that the submission of 18 review articles and 9 research manuscripts reflects that the CEST MRI field is active and continuing to grow.…”

“…34 Here, they showed that CEST signals in cell culture phantoms were sensitive to incubation time over several days. 34 In conclusion, it is fair to say that the submission of 18 review articles and 9 research manuscripts reflects that the CEST MRI field is active and continuing to grow. We hope that this special issue will increase the interest in the different saturation transfer methods even further, and following the example of APTw MRI lead to important clinical applications.…”

“…Bo et al used a newly synthesized exogeneous CEST agent, namely imidazole‐4,‐5‐dicarboxyamide (I45DC), for depicting perfusion and pH changes in kidney, and observed differences in contrast kinetics and pH between obstructed and unobstructed kidneys in a mouse model 33 . Also, to bridge the gap between solution phantoms and in vivo studies, Wu et al showed that 2D and 3D cell culture phantoms can play an important role in interpreting many CEST signals 34 . Here, they showed that CEST signals in cell culture phantoms were sensitive to incubation time over several days 34 …”

“…Also, to bridge the gap between solution phantoms and in vivo studies, Wu et al showed that 2D and 3D cell culture phantoms can play an important role in interpreting many CEST signals 34 . Here, they showed that CEST signals in cell culture phantoms were sensitive to incubation time over several days 34 …”