177-Lu-DOTA-cG250(Ludwig Institute for Cancer Research)

There have been predictions that the use of the macrocyclic chelating agent 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) in zirconium-89 (⁸⁹Zr) immuno-positron emission tomography (⁸⁹Zr-immunoPET) could enhance the in vivo stability of ⁸⁹Zr radioimmunoconjugates. However, conjugating [⁸⁹Zr]Zr-DOTA to a monoclonal antibody (mAb) remains a challenge as the heat treatment required for [⁸⁹Zr]Zr-DOTA chelation can lead to thermal denaturation of the mAb moieties. We developed a method for synthesizing [⁸⁹Zr]Zr-DOTA-mAb based on a tetrazine (Tz)-conjugated bifunctional DOTA derivative 2,2',2″-(10-(1-(4-(1,2,4,5-tetrazin-3-yl)phenyl)-3,21,26-trioxo-6,9,12,15,18-pentaoxa-29-carboxy-2,22,25-triazanonacosane-29-yl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (DOTAGA-Tz) and the inverse electron-demand Diels-Alder (IEDDA) click chemistry reaction where trans-cyclooctene-modified mAbs are conjugated to [⁸⁹Zr]Zr-DOTAGA without being exposed to heat. The stability of IEDDA-derived [⁸⁹Zr]Zr-DOTAGA-trastuzumab was confirmed by in vitro, ex vivo, and in vivo testing and comparative analysis against the conventional deferoxamine (DFO) counterpart [⁸⁹Zr]Zr-DFO-trastuzumab. The in vivo immunoPET imaging using [⁸⁹Zr]Zr-DOTAGA-trastuzumab clearly visualized human epidermal growth factor receptor 2-positive malignancies in murine xenograft models. Greater tumor contrast was observed from [⁸⁹Zr]Zr-DOTAGA-trastuzumab at a 72-h delayed scan compared with [⁸⁹Zr]Zr-DFO-trastuzumab. These findings suggest that our IEDDA ligation approach can be an effective means of synthesizing [⁸⁹Zr]Zr-DOTA-mAb and can enhance the theranostic potential of ⁸⁹Zr-immunoPET in DOTA-mediated radioimmunotherapy.

The aim of this study was to evaluate the biodistribution and dosimetry of lutetium-177-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (177Lu-DOTA)-rituximab in CD20+ non-Hodgkin’s lymphoma and other hematological malignancies treated with rituximab.

The standard dosimetry protocol was used, with cold rituximab infusion, then a diagnostic activity of 177Lu-DOTA-rituximab. Planar images were acquired at multiple time points. Normal organs and tumor dosimetry were performed by using organ and tumor-specific regions of interest and whole-body counts were obtained serially after pixel matched, background, scatter, and attenuation correction. The mean radiation absorbed doses were obtained from OLINDA/EXM v2.1.1 and ORIGIN software.

A total of 22 patients were included in this study. Prolonged blood pool clearance of 177Lu-DOTA-rituximab with long residence time in the blood pool and normal organs were observed. The whole body effective half-life was 104.5 ± 22 h. The mean total body radiation absorbed dose was 0.208 ± 0.03 mGy/MBq and the mean total body effective dose was 0.196 ± 0.05 mGy/MBq of 177Lu-DOTA-rituximab. The mean radiation absorbed doses of 0.613 ± 0.21, 1.68 ± 2, 1.01 ± 0.42, and 0.136 ± 0.02mGy/MBq were seen for the liver, spleen, kidneys, and bone marrow, respectively. Tumor lesion uptake was noticed in two patients with tumor radiation absorbed doses were 0.842 mGy/MBq in one and 9.9 mGy/MBq in the other patient. A strong correlation was obtained between the cumulative activities of radiation-absorbed doses derived from ORIGIN and OLINDA software methods at a significant P value less than 0.001.

The results of our study demonstrated favorable biodistribution and dosimetry of indigenously produced 177Lu-DOTA-rituximab in patients with CD20+ lymphoma. These results can be used for future studies of radioimmunotherapy employing 177Lu-DOTA-rituximab.