Features and Practical Aspects of Radiochemical Purity Determination of Receptor-Specific Lu-177 Radiopharmaceuticals as Exemplified by [¹⁷⁷Lu]Lu–PSMA-617

Radiochemical purity (RCP) is one of the key quality criteria for radiopharmaceuticals (RPs) used in clinical practice. The results of RCP measurements depend on the analytical technique, as well as detection parameters, which are specific to a particular analytical system. When reviewing literature data on the  synthesis, pharmaceutical development, preclinical and clinical trials of the same radiopharmaceutical by different authors, one may note significant variability in the RCP values obtained. Hence, it is important to carefully select analysis parameters and study their influence on the results. The aim of the study was to compare previously published and self-developed procedures for RCP analysis of ¹⁷⁷Lu-RPs in terms of their efficiency in the  detection and quantification of possible radiochemical impurities, as well as to  determine the  analytical system parameters that have a  significant impact on the interpretation of the analysis results, using [¹⁷⁷Lu]Lu–PSMA-617 as a case study. Materials and methods: the study used samples of [¹⁷⁷Lu]Lu–PSMA-617 with a volume activity of lutetium-177 of 150–4800 MBq/mL, containing 10–100 µmol/L of the PSMA-617 precursor and 30 mmol/L of sodium acetate as a buffering solution (pH 4.5). The samples were tested by high-performance liquid chromatography (HPLC) and thin-layer chromatography in the conditions described in the literature and developed in the course of the work. Results: the study showed a significant influence of the chosen analytical procedure on the results of [¹⁷⁷Lu]Lu–PSMA-617 RCP assessment. The profile of possible radiochemical impurities requires the use of high-resolution HPLC techniques. Conclusions: the analytical procedure developed and applied by the authors is quite effective. The results of RCP assessment are influenced by the detection system parameters, such as the length and inner diameter of the flow cell and the means of analytical signal processing (peak extraction parameters, smoothing parameters, and noise subtraction/suppression). This fact necessitates validation considering the characteristics of a particular analytical system and demonstrates the need to assess interlaboratory precision in the framework of the implementation and verification of analytical procedures.

1. Dolgin E. Radioactive drugs emerge from the shadows to storm the market. Nat Biotechnol. 2018;36(12):1125–7. https://doi.org/10.1038/nbt1218-1125

2. Sgouros G, Bodei L, McDevitt MR, Nedrow JR. Radiopharmaceutical therapy in cancer: clinical advances and challenges. Nat Rev Drug Discov. 2020;19(9):589–608. https://doi.org/10.1038/s41573-020-0073-9

3. Herrero Álvarez N, Bauer D, Hernández-Gil J, Lewis JS. Recent advances in radiometals for combined imaging and therapy in cancer. ChemMedChem. 2021;16(19): 2909–41. https://doi.org/10.1002/cmdc.202100135

4. Banerjee S, Pillai MRA, Russ Knapp FF. Lutetium-177 therapeutic radiopharmaceuticals: linking chemistry, radiochemistry, and practical applications. Chem Rev. 2015;115(8):2934–74. https://doi.org/10.1021/cr500171e

5. Hennrich U, Kopka K. Lutathera®: the first FDA- and EMA-approved radiopharmaceutical for peptide receptor radionuclide therapy. Pharmaceuticals. 2019;12(3):114. https://doi.org/10.3390/ph12030114

6. Kratochwil C, Fendler WP, Eiber M, Baum R, Bozkurt MF, Czernin J, et al. EANM procedure guidelines for radionuclide therapy with ¹⁷⁷Lu-labelled PSMA-ligands (¹⁷⁷LuPSMA-RLT). Eur J Nucl Med Mol Imaging. 2019;46(12): 2536–44. https://doi.org/10.1007/s00259-019-04485-3

7. Ferdinandus J, Violet J, Sandhu S, Hofman MS. Prostate-specific membrane antigen theranostics: therapy with lutetium-177. Curr Opin Urol. 2018;28(2):197–204. https://doi.org/10.1097/mou.0000000000000486

8. Emmett L, Willowson K, Violet J, Shin J, Blanksby A, Lee J. Lutetium ¹⁷⁷PSMA radionuclide therapy for men with prostate cancer: a review of the current literature and discussion of practical aspects of therapy. J Med Radiat Sci. 2017;64(1):52–60. https://doi.org/10.1002/jmrs.227

9. Chakraborty S, Vimalnath KV, Chakravarty R, Sarma HD, Dash A. Multidose formulation of readyto-use ¹⁷⁷Lu–PSMA-617 in a centralized radiopharmacy set-up. Appl Radiat Isot. 2018;139:91–7. https://doi.org/10.1016/j.apradiso.2018.04.033

10. de Zanger RMS, Chan HS, Breeman WAP, de Blois E. Maintaining radiochemical purity of [¹⁷⁷Lu]Lu–DOTA-PSMA-617 for PRRT by reducing radiolysis. J Radioanal Nucl Chem. 2019;321:285–91. https://doi.org/10.1007/s10967-019-06573-y

11. de Blois E, Chan HS, Konijnenberg M, de Zanger R, Breeman WAP. Effectiveness of quenchers to reduce radiolysis of (111)In- or (177)Lu-labelled methionine-containing regulatory peptides. Maintaining radiochemical purity as measured by HPLC. Curr Top Med Chem. 2013;12(23):2677–85. https://doi.org/10.2174/1568026611212230005

12. de Blois E, Chan HS, de Zanger R, Konijnenberg M, Breeman WAP. Application of single-vial ready-foruse formulation of ¹¹¹In- or ¹⁷⁷Lu-labelled somatostatin analogs. Appl Radiat Isot. 2014;85:28–33. https://doi.org/10.1016/j.apradiso.2013.10.023

13. Mathur A, Prashant V, Sakhare N, Chakraborty S, Vimalnath KV, Mohan RK, et al. Bulk scale formulation of therapeutic doses of clinical grade ready-to-use ¹⁷⁷Lu-DOTA-TATE: the intricate radiochemistry aspects. Cancer Biother Radiopharm. 2017;32(7):266–73. https://doi.org/10.1089/cbr.2017.2208

14. Chakraborty S, Chakravarty R, Shetty P, Vimalnath KV, Sen IB, Dash A. Prospects of medium specific activity (177)Lu in targeted therapy of prostate cancer using (177)Lu-labeled PSMA inhibitor. J Labelled Comp Radiopharm. 2016;59(9):364–71. https://doi.org/10.1002/jlcr.3414

15. Wieczorek Villas Boas CA, Pereira Dias LA, Nakamura Matsuda MM, Bortoleti de Araújo E. Stability in the production and transport of 177Lu labelled PSMA. Brazilian J Radiat Sci. 2021;9(1):1–12. https://doi.org/10.15392/bjrs.v9i1.1619

16. Martin S, Tönnesmann R, Hierlmeier I, Maus S, Rosar F, Ruf J, et al. Identification, characterization, and suppression of side products formed during the synthesis of [¹⁷⁷Lu]Lu–PSMA-617. J Med Chem. 2021;64(8):4960–71. https://doi.org/10.1021/acs.jmedchem.1c00045

17. Zaknun JJ, Bodei L, Mueller-Brand J, Pavel ME, Baum RP, Hörsch D, et al. The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours. Eur J Nucl Med Mol Imaging. 2013;40(5):800–16. https://doi.org/10.1007/s00259-012-2330-6

18. Kodina GE, Malysheva, AO, Larenkov AA, Bruskin AB. Possible impurities in radiopharmaceuticals and corresponding test methods. Vedomosti Nauchnogo tsentra ekspertizy sredstv meditsinskogo primeneniya. Regulyatornye issledovaniya i ekspertiza lekarstvennykh sredstv = Bulletin of the Scientific Centre for Expert Evaluation of Medicinal Products. Regulatory Research and Medicine Evaluation. 2022;12(3):244–62 (In Russ.) https://doi.org/10.30895/1991-2919-2022-12-3-244-262

19. Mu L, Hesselmann R, Oezdemir U, Bertschi L, Blanc A, Dragic M, et al. Identification, characterization and suppression of side-products formed during the synthesis of high dose 68 GaDOTA-TATE. Appl Radiat Isot. 2013;76:63–9. https://doi.org/10.1016/j.apradiso.2012.07.022

20. Larenkov AA, Maruk AYa, Kodina GE. Intricacies of the determination of the radiochemical purity of ⁶⁸Ga preparations: possibility of sorption of ionic ⁶⁸Ga species on reversed-phase columns. Radiochemistry. 2018;60: 625–33. https://doi.org/10.1134/S1066362218060103

21. Maruk AYu, Larenkov A.A. Determination of ionic 68 Ga impurity in radiopharmaceuticals: major revision of radio-HPLC methods. J Radioanal Nucl Chem. 2020;323: 189–95. https://doi.org/10.1007/s10967-019-06964-1

22. Liu S, Edwards DS. Bifunctional chelators for therapeutic lanthanide radiopharmaceuticals. Bioconjug Chem. 2001;12(1):7–34. https://doi.org/10.1021/bc000070v

23. Breeman WAP. Practical aspects of labeling DTPA-and DOTA-peptides with ⁹⁰Y, ¹¹¹In, ¹⁷⁷Lu, ⁶⁸Ga for peptide-receptor scintigraphy and peptide-receptor radionuclide therapy in preclinical and clinical applications. University of New Mexico Health Sciences Center, College of Pharmacy; 2012. https://pharmacyce.unm.edu/program_information/freelessonfiles/vol16lesson5.pdf

24. Breeman WAP, Chan SH, de Zanger RMS, Konijnenberg MK, de Blois E. Overview of development and formulation of ¹⁷⁷Lu-DOTA-TATE for PRRT. Curr Radiopharm. 2016;9(1):8–18. https://doi.org/10.2174/1874471008666150313111131