Abstract
PurposeAlmost all radiolabellings of antibodies with 89Zr currently employ the hexadentate chelator desferrioxamine (DFO). However, DFO can lead to unwanted uptake of 89Zr in bones due to instability of the resulting metal complex. DFO*-NCS and the squaramide ester of DFO, DFOSq, are novel analogues that gave more stable 89Zr complexes than DFO in pilot experiments. Here, we directly compare these linker-chelator systems to identify optimal immuno-PET reagents.MethodsCetuximab, trastuzumab and B12 (non-binding control antibody) were labelled with 89Zr via DFO*-NCS, DFOSq, DFO-NCS or DFO*Sq. Stability in vitro was compared at 37 °C in serum (7 days), in formulation solution (24 h ± chelator challenges) and in vivo with N87 and A431 tumour-bearing mice. Finally, to demonstrate the practical benefit of more stable complexation for the accurate detection of bone metastases, [89Zr]Zr-DFO*-NCS and [89Zr]Zr-DFO-NCS-labelled trastuzumab and B12 were evaluated in a bone metastasis mouse model where BT-474 breast cancer cells were injected intratibially.Results[89Zr]Zr-DFO*-NCS-trastuzumab and [89Zr]Zr-DFO*Sq-trastuzumab showed excellent stability in vitro, superior to their [89Zr]Zr-DFO counterparts under all conditions. While tumour uptake was similar for all conjugates, bone uptake was lower for DFO* conjugates. Lower bone uptake for DFO* conjugates was confirmed using a second xenograft model: A431 combined with cetuximab. Finally, in the intratibial BT-474 bone metastasis model, the DFO* conjugates provided superior detection of tumour-specific signal over the DFO conjugates.ConclusionDFO*-mAb conjugates provide lower bone uptake than their DFO analogues; thus, DFO* is a superior candidate for preclinical and clinical 89Zr-immuno-PET.
Highlights
Positron emission tomography with 89Zr-labelled antibodies (89Zr-immuno-PET) is a valuable tool to characterise the in vivo behaviour of monoclonal antibodies as well as other drugs with slow clearance from the blood, such as other types of proteins, mAb conjugates, nanoparticles and cells
When the four radioimmunoconjugates were incubated with serum for a week in a CO2 incubator at 37 °C, [89Zr]ZrDFO*-NCS-trastuzumab (94 ± 0%) and [89Zr]Zr-desferrioxamine B (DFO)*Sqtrastuzumab (100 ± 0%) presented a higher radiochemical purity than [89Zr]Zr-DFOSq-trastuzumab (87 ± 1%) and [89Zr]ZrDFO-NCS-trastuzumab (81 ± 1%) (Fig. 2)
A similar stability trend was exhibited by the immunoreactivity binding assay results: while initially all radioimmunoconjugates presented at least 95% binding, this decreased after 1 week at 37 °C to 90 ± 1 and 96 ± 1% for [89Zr]Zr-DFO*-NCS-trastuzumab and [89Zr]Zr-DFO*Sq-trastuzumab, respectively, while [89Zr]ZrDFOSq-trastuzumab and [89Zr]Zr-DFO-NCS-trastuzumab presented 80 ± 1 and 74 ± 1% immunoreactivity, respectively
Summary
Positron emission tomography with 89Zr-labelled antibodies (89Zr-immuno-PET) is a valuable tool to characterise the in vivo behaviour of monoclonal antibodies (mAbs) as well as other drugs with slow clearance from the blood, such as other types of proteins, mAb conjugates, nanoparticles and cells. A resolution to this problem is important since non-specific bone uptake will provide an increased radiation burden to the patient and may contribute to the misidentification of bone metastases These challenges have prompted the development of a variety of octadentate chelators for 89Zr that should result in increased stability of the 89Zr complexes [13,14,15,16,17,18,19]. DFO*-NCS [20] and DFOSq [21], both derivatives of DFO, showed preliminary improvements in performance in vitro and in vivo compared with DFO and are currently under consideration for clinical use
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
