Pretargeted radioimmunotherapy and SPECT imaging of peritoneal carcinomatosis using bioorthogonal click chemistry: probe selection and first proof-of-concept

Abstract

Rationale: Pretargeted radioimmunotherapy (PRIT) based upon bioorthogonal click chemistry has been investigated for the first time in the context of peritoneal carcinomatosis using a CEA-targeting 35A7 mAb bearing trans-cyclooctene (TCO) moieties and several 177Lu-labeled tetrazine (Tz) radioligands. Starting from three Tz probes containing PEG linkers of varying lengths between the DOTA and Tz groups (i.e. PEGn = 3, 7, or 11, respectively, for Tz-1, Tz-2, and Tz-3), we selected [177Lu]Lu-Tz-2 as the most appropriate for pretargeted SPECT imaging and demonstrated its efficacy in tumor growth control. Methods: An orthotopic model of peritoneal carcinomatosis (PC) was obtained following the intraperitoneal (i.p.) injection of A431-CEA-Luc cells in nude mice. Tumor growth was assessed using bioluminescence imaging. Anti-CEA 35A7 mAb was grafted with 2-3 TCO per immunoglobulin. Pretargeted SPECT imaging and biodistribution experiments were performed to quantify the activity concentrations of [177Lu]Lu-Tz-1-3 in tumors and non-target organs to determine the optimal Tz probe for the PRIT of PC. Results: The pharmacokinetic profiles of [177Lu]Lu-Tz-1-3 alone were determined using both SPECT imaging and biodistribution experiments. These data revealed that [177Lu]Lu-Tz-1 was cleared via both the renal and hepatic systems, while [177Lu]Lu-Tz-2 and [177Lu]Lu-Tz-3 were predominantly excreted via the renal system. In addition, these results illuminated that the longer the PEG linker, the more rapidly the Tz radioligand was cleared from the peritoneal cavity. The absorbed radiation dose corresponding to pretargeting with 35A7-TCO followed 24 h later by [177Lu]Lu-Tz-1-4 was higher for tumors following the administration of [177Lu]Lu-Tz-2 (i.e. 0.59 Gy/MBq) compared to either [177Lu]Lu-Tz-1 (i.e. 0.25 Gy/MBq) and [177Lu]Lu-Tz-3 (i.e. 0.18 Gy/MBq). In a longitudinal PRIT study, we showed that the i.p. injection of 40 MBq of [177Lu]Lu-Tz-2 24 hours after the systemic administration of 35A7-TCO significantly slowed tumor growth compared to control mice receiving only saline or 40 MBq of [177Lu]Lu-Tz-2 alone. Ex vivo measurement of the peritoneal carcinomatosis index (PCI) confirmed that PRIT significantly reduced tumor growth (PCI = 15.5 ± 2.3 after PRIT vs 30.0 ± 2.3 and 30.8 ± 1.4 for the NaCl and [177Lu]Lu-Tz-2 alone groups, respectively). Conclusion: Our results clearly demonstrate the impact of the length of PEG linkers upon the biodistribution profiles of 177Lu-labeled Tz radioligands. Furthermore, we demonstrated for the first time the possibility of using bioorthogonal chemistry for both the pretargeted SPECT and PRIT of peritoneal carcinomatosis.

Pretargeted Theranostics

“…The most promising probe was used in a treatment approach and a projected dose of 40 MBq was applied. This resulted in a significant slow-down of tumor progression, for up to 13 days, after which the tumors started to grow again, albeit much slower as compared to the control group [52].…”

Recent Advances in the Development of Tetrazine Ligation Tools for Pretargeted Nuclear Imaging

“…Several methods have been developed within the last decade, spanning from chelator to nucleophilic substitution approaches. However, relatively few approaches have been described for radiolabeling Tzs with therapeutic nuclides [25,104,[135][136][137][138][139]. We believe new therapeutic and theranostic Tzs will emerge for pretargeting strategies within the next years.…”

Harnessing 64 Cu/ 67 Cu for a theranostic approach to pretargeted radioimmunotherapy

“…Broadly speaking, this methodology consists of four steps: 1) the administration of a monoclonal antibody (mAb)-TCO immunoconjugate; 2) an interval period during which the antibody accumulates at the tumor and clears from the blood; 3) the injection of a small molecule Tz-based radioligand; and 4) the in vivo click ligation between two components, followed by the rapid clearance of any excess radioligand. This strategy has proven highly effective for pretargeted PET imaging (36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49) as well as pretargeted radioimmunotherapy (PRIT) using beta-emitting ( 177 Lu) and alpha-emitting ( 225 Ac) radionuclides (50)(51)(52)(53)(54)(55). Yet as the field stands poised to make the jump from the laboratory to the clinic, it stands to reason that the development of a theranostic approach to Tz/TCO pretargeting could prove instrumental in ensuring the future success of this modality.…”