Abstract
Background: Treatment with immune checkpoint inhibitors has improved both progressionfree survival and overall survival in a subset of patients with tumors. However, the selection of patients who benefit from immune checkpoint inhibitor treatment remains challenging. Positron Emission Tomography (PET) is a non-invasive molecular imaging tool that offers a promising alternative to the current IHC for detecting the PD-L1 expression in malignant cells in vivo, enabling patient selection and predicting the response to individual patient immunotherapy treatment.
Objectives: Herein, we report the development of novel [18F]labeled pyridine-2-carboxamide derivatives [18F]2 and [18F]3 as small-molecule probes for imaging immune checkpoint (PD-1/PD-L1) in cancer using PET.
Methods and Results: [18F]2 and [18F]3 were prepared by a one-step radiofluorination in 44 ± 5% and 30 ± 4% radiochemical yield and > 98% radiochemical purity for a potential clinical translation. The total synthesis time, including HPLC purification, was less than 45 min. [18F]2 and [18F]3 showed excellent stability in injection solution and a significant accumulation and retention in PD-1/PD-L1 expressing MDA-MB-231 breast cancer and in HeLa cervix carcinoma cells (2- 5 cpm/1000 cells). In addition, autoradiographic analysis and inhibition experiments on tumor slices confirm the potential of both compounds as specific imaging probes for the PD-1/PD-L1 axis in tumors.
Conclusion: The in vitro evaluation in PD-L1 expressing cells together with results from autoradiographic analysis in PD-L1 positive tumor sections, suggest that [18F]2 and [18F]3 could be potential imaging probes for assessing PD-L1 expression in tumors and warrant further biological evaluations in vivo.
Graphical Abstract
[http://dx.doi.org/10.1158/2159-8290.CD-18-0367] [PMID: 30115704]
[http://dx.doi.org/10.1093/intimm/dxu095] [PMID: 25323844]
[http://dx.doi.org/10.1146/annurev.immunol.26.021607.090331] [PMID: 18173375]
[http://dx.doi.org/10.1073/pnas.192461099] [PMID: 12218188]
[http://dx.doi.org/10.1056/NEJMoa1507643] [PMID: 26412456]
[http://dx.doi.org/10.1016/S0140-6736(15)01281-7] [PMID: 26712084]
[http://dx.doi.org/10.1016/S0140-6736(16)32517-X] [PMID: 27979383]
[http://dx.doi.org/10.1038/nrclinonc.2017.88] [PMID: 28653677]
[http://dx.doi.org/10.1002/anie.201707816] [PMID: 28971564]
[http://dx.doi.org/10.1007/s00103-020-03221-9] [PMID: 33001218]
[http://dx.doi.org/10.1038/s41571-019-0218-0] [PMID: 31092901]
[http://dx.doi.org/10.1016/j.ctrv.2016.06.002] [PMID: 27310708]
[http://dx.doi.org/10.7150/thno.38339] [PMID: 32042331]
[http://dx.doi.org/10.1200/JCO.2016.67.2477] [PMID: 27863197]
[http://dx.doi.org/10.1007/s11307-018-1254-3] [PMID: 30030697]
[http://dx.doi.org/10.2967/jnumed.116.188029] [PMID: 28522743]
[http://dx.doi.org/10.1007/s00259-017-3691-7] [PMID: 28389693]
[http://dx.doi.org/10.2967/jnumed.117.193011] [PMID: 28596157]
[http://dx.doi.org/10.1038/s41591-018-0255-8] [PMID: 30478423]
[http://dx.doi.org/10.1038/s41467-018-07131-y] [PMID: 30405135]
[http://dx.doi.org/10.1016/j.bbrc.2016.12.156] [PMID: 28025143]
[http://dx.doi.org/10.1177/1536012119852189] [PMID: 31187691]
[http://dx.doi.org/10.3390/molecules24112071] [PMID: 31151293]
[http://dx.doi.org/10.1016/j.bmcl.2020.127572] [PMID: 32979488]
[http://dx.doi.org/10.1016/j.ejps.2021.105964] [PMID: 34375678]
[http://dx.doi.org/10.1021/acs.jmedchem.1c01682] [PMID: 35188766]
[http://dx.doi.org/10.1021/acs.jmedchem.7b01788] [PMID: 29400967]
[http://dx.doi.org/10.1021/jo00362a044]
[http://dx.doi.org/10.1016/j.tetlet.2010.09.134]
[http://dx.doi.org/10.1021/ja0646895] [PMID: 17165796]
[http://dx.doi.org/10.1021/jo7021229] [PMID: 18166063]
[http://dx.doi.org/10.18632/oncotarget.8730] [PMID: 27083005]
[http://dx.doi.org/10.3892/ol.2019.10903] [PMID: 31612048]
[http://dx.doi.org/10.1158/0008-5472.CAN-14-3477] [PMID: 25977331]
[http://dx.doi.org/10.1186/2051-1426-2-S3-P102]
[http://dx.doi.org/10.18632/oncotarget.22888] [PMID: 29535806]
[http://dx.doi.org/10.3390/cells10082151] [PMID: 34440920]
[http://dx.doi.org/10.1038/s41419-021-03449-6] [PMID: 33558476]
[http://dx.doi.org/10.1038/s41598-021-85329-9] [PMID: 33707569]
[http://dx.doi.org/10.2220/biomedres.40.243] [PMID: 31839668]
[http://dx.doi.org/10.3390/ph12010018] [PMID: 30678341]