TY - JOUR

T1 - Radiolabeling of a polypeptide polymer for intratumoral delivery of alpha-particle emitter, 225Ac, and beta-particle emitter, 177Lu

AU - Shalgunov, Vladimir

AU - Engudar, Gokce

AU - Bohrmann, Lennart

AU - Wharton, Luke

AU - Maskell, Keiran

AU - Johann, Kerstin

AU - Barz, Matthias

AU - Schaffer, Paul

AU - Herth, Matthias M.

AU - Radchenko, Valery

N1 - Funding Information: TRIUMF receives funding via a contribution agreement with the National Research Council Canada . We would like to thank Dr's Patrick Causey, Randy Perron and Denise Gendron (Canadian Nuclear Laboratories, ON, Canada) for providing purified 225 Ac for radiolabeling studies. VS was supported by the Lundbeck Foundation , grant number R303-2018-3567 . This work was supported through the NSERC Discovery Grant ( RGPIN-2018-04997 (VR)), from the Natural Sciences and Engineering Research Council of Canada. We also would like to thank Prof. Justin Wilson (Cornell University, Ithaca, NY, USA) for providing macropa-NCS and Prof. Chris Orvig and Prof. Urs Hafeli (University of British Columbia, Vancouver, BC, Canada) for their support. Funding Information: TRIUMF receives funding via a contribution agreement with the National Research Council Canada. We would like to thank Dr's Patrick Causey, Randy Perron and Denise Gendron (Canadian Nuclear Laboratories, ON, Canada) for providing purified 225Ac for radiolabeling studies. VS was supported by the Lundbeck Foundation, grant number R303-2018-3567. This work was supported through the NSERC Discovery Grant (RGPIN-2018-04997 (VR)), from the Natural Sciences and Engineering Research Council of Canada. We also would like to thank Prof. Justin Wilson (Cornell University, Ithaca, NY, USA) for providing macropa-NCS and Prof. Chris Orvig and Prof. Urs Hafeli (University of British Columbia, Vancouver, BC, Canada) for their support. Publisher Copyright: © 2021 Elsevier Inc.

PY - 2022

Y1 - 2022

N2 - Introduction: Radiotherapy of cancer requires both alpha- and beta-particle emitting radionuclides, as these radionuclide types are efficient at destroying different types of tumors. Both classes of radionuclides require a vehicle, such as an antibody or a polymer, to be delivered and retained within the tumor. Polyglutamic acid (pGlu) is a polymer that has proven itself effective as a basis of drug-polymer conjugates in the clinic, while its derivatives have been used for pretargeted tumor imaging in a research setup. trans-Cyclooctene (TCO) modified pGlu is suitable for pretargeted imaging or therapy, as well as for intratumoral radionuclide therapy. In all cases, it becomes indirectly radiolabeled via the bioorthogonal click reaction with the tetrazine (Tz) molecule carrying the radionuclide. In this study, we report the radiolabeling of TCO-modified pGlu with either lutetium-177 (177Lu), a beta-particle emitter, or actinium-225 (225Ac), an alpha-particle emitter, using the click reaction between TCO and Tz. Methods: A panel of Tz derivatives containing a metal ion binding chelator (DOTA or macropa) connected to the Tz moiety directly or through a polyethylene glycol (PEG) linker was synthesized and tested for their ability to chelate 177Lu and 225Ac, and click to pGlu-TCO. Radiolabeled 177Lu-pGlu and 225Ac-pGlu were isolated by size exclusion chromatography. The retention of 177Lu or 225Ac by the obtained conjugates was investigated in vitro in human serum. Results: All DOTA-modified Tzs efficiently chelated 177Lu resulting in average radiochemical conversions (RCC) of >75%. Isolated radiochemical yields (RCY) for 177Lu-pGlu prepared from 177Lu-Tzs ranged from 31% to 55%. TLC analyses detected <5% unchelated 177Lu for all 177Lu-pGlu preparations over six days in human serum. For 225Ac chelation, optimized RCCs ranged from 61 ± 34% to quantitative for DOTA-Tzs and were quantitative for the macropa-modified Tz (>98%). Isolated radiochemical yields (RCY) for 225Ac-pGlu prepared from 225Ac-Tzs ranged from 28% to 51%. For 3 out of 5 225Ac-pGlu conjugates prepared from DOTA-Tzs, the amount of unchelated 225Ac stayed below 10% over six days in human serum, while 225Ac-pGlu prepared from macropa-Tz showed a steady release of up to 37% 225Ac. Conclusion: We labeled TCO-modified pGlu polymers with alpha- and beta-emitting radionuclides in acceptable RCYs. All 177Lu-pGlu preparations and some 225Ac-pGlu preparations showed excellent stability in human plasma. Our work shows the potential of pGlu as a vehicle for alpha- and beta-radiotherapy of tumors and demonstrated the usefulness of Tz ligation for indirect radiolabeling.

AB - Introduction: Radiotherapy of cancer requires both alpha- and beta-particle emitting radionuclides, as these radionuclide types are efficient at destroying different types of tumors. Both classes of radionuclides require a vehicle, such as an antibody or a polymer, to be delivered and retained within the tumor. Polyglutamic acid (pGlu) is a polymer that has proven itself effective as a basis of drug-polymer conjugates in the clinic, while its derivatives have been used for pretargeted tumor imaging in a research setup. trans-Cyclooctene (TCO) modified pGlu is suitable for pretargeted imaging or therapy, as well as for intratumoral radionuclide therapy. In all cases, it becomes indirectly radiolabeled via the bioorthogonal click reaction with the tetrazine (Tz) molecule carrying the radionuclide. In this study, we report the radiolabeling of TCO-modified pGlu with either lutetium-177 (177Lu), a beta-particle emitter, or actinium-225 (225Ac), an alpha-particle emitter, using the click reaction between TCO and Tz. Methods: A panel of Tz derivatives containing a metal ion binding chelator (DOTA or macropa) connected to the Tz moiety directly or through a polyethylene glycol (PEG) linker was synthesized and tested for their ability to chelate 177Lu and 225Ac, and click to pGlu-TCO. Radiolabeled 177Lu-pGlu and 225Ac-pGlu were isolated by size exclusion chromatography. The retention of 177Lu or 225Ac by the obtained conjugates was investigated in vitro in human serum. Results: All DOTA-modified Tzs efficiently chelated 177Lu resulting in average radiochemical conversions (RCC) of >75%. Isolated radiochemical yields (RCY) for 177Lu-pGlu prepared from 177Lu-Tzs ranged from 31% to 55%. TLC analyses detected <5% unchelated 177Lu for all 177Lu-pGlu preparations over six days in human serum. For 225Ac chelation, optimized RCCs ranged from 61 ± 34% to quantitative for DOTA-Tzs and were quantitative for the macropa-modified Tz (>98%). Isolated radiochemical yields (RCY) for 225Ac-pGlu prepared from 225Ac-Tzs ranged from 28% to 51%. For 3 out of 5 225Ac-pGlu conjugates prepared from DOTA-Tzs, the amount of unchelated 225Ac stayed below 10% over six days in human serum, while 225Ac-pGlu prepared from macropa-Tz showed a steady release of up to 37% 225Ac. Conclusion: We labeled TCO-modified pGlu polymers with alpha- and beta-emitting radionuclides in acceptable RCYs. All 177Lu-pGlu preparations and some 225Ac-pGlu preparations showed excellent stability in human plasma. Our work shows the potential of pGlu as a vehicle for alpha- and beta-radiotherapy of tumors and demonstrated the usefulness of Tz ligation for indirect radiolabeling.

KW - Lu

KW - Ac

KW - Polyglutamic acid

KW - Polypeptides

KW - Targeted radionuclide therapy

KW - Tetrazine ligation

U2 - 10.1016/j.nucmedbio.2021.11.001

DO - 10.1016/j.nucmedbio.2021.11.001

M3 - Journal article

C2 - 34839209

AN - SCOPUS:85119931849

VL - 104-105

SP - 11

EP - 21

JO - Nuclear Medicine and Biology

JF - Nuclear Medicine and Biology

SN - 0969-8051

ER -