Optimization of in vivo cell tracking methods with long-lived radionuclides for PET imaging

Abstract

Stem cell transplantation and cell therapy are the standard treatments for many diseases; however, many suffer from complications, and the therapeutic efficiency can be challenging to predict. The off-target accumulation of the transplanted cells can cause some of these shortcomings. Tracking of infused cells with PET and SPECT imaging can provide the information to understand better the cells’ behaviour in vivo to predict and possibly reduce the risk of complications. Standard cell administration via intravenous or intraarterial injection risks the accumulation of cells in the lungs and the liver. An alternative intra-arterial catheter delivery system enables direct delivery to the target site, reducing off-target accumulation while potentially increasing treatment efficiency. This technique is more invasive; hence, the procedure’s safety must be validated.

The focus of Paper I was to develop protocols to synthesise the PET tracers [89Zr]Zr-(oxinate)4 and [89Zr]Zr-DFO-NCS, followed by a proof of concept labelling of cells. Both radiotracers were produced in less than two hours with limited toxic chemicals and RCY >95% without purification. Both radiotracers labelled cells with high efficiency. Our new protocols improved the feasibility of these radiotracers. Further evaluation regarding cellular toxicity and in vivo stability is needed. In Paper II, we evaluated [89Zr]Zr-(oxinate)4 and [89Zr]Zr-DFO-NCS for cell tracking in rats using PET imaging. Cells labelled with [89Zr]Zr-(oxinate)4 show significantly higher uptake in the liver, while cells labelled with [89Zr]Zr-DFO-NCS had a high signal in the lungs. Concluding that [89Zr]Zr(oxinate)4 provides a more accurate view of the cells’ location, further studies are required to determine the location of the [89Zr]Zr-DFO-NCS labelled cell. In Paper III: A final evaluation of the leakage of [89Zr]Zr-(oxinate)4 and the location of [89Zr]Zr-DFO-NCS labelled cells. The cellular proliferation, viability and radioactive leakage were established in vitro. The protocols were adjusted accordingly: adding a 30-minute wash step after labelling with [89Zr]Zr-(oxinate)4 and reducing the DFO-NCS concentration by 400 fold. The location of the cells was confirmed with flow cytometry ex vivo. Most of the [89Zr]Zr-(oxinate)4 leakage occurred within one hour after labelling and was shown to be reduced by the addition of a longer wash step. High concentrations of DFO-NCS disrupt cell migration in vivo. Paper IV: Administrating cells via intra-arteria catheter was evaluated in two steps. First, in vitro, mimicking the transplantation procedure of [111In]In-(oxinate)3 labelled macrophages through a catheter, and assessing the procedures’ influence on the cells by flow cytometry. Secondly, administer radiolabelled macrophages via intra-arteria catheter delivery into rabbit brain. The procedure’s safety was observed by angiography, MRI and SPECT imaging. Unactivated macrophages are too sensitive and unsuitable for such rough handling. The activated macrophages show fewer adverse effects and are a more appropriate choice. There were no signs of tissue damage or thromboembolic events caused by the cell administration and no lingering accumulation of cells in the brain. Cell administration through the intra-arteria catheter is a prominent administration technique for cell transplantation.