Theranostic pretargeted radioimmunotherapy of colorectal cancer xenografts in mice using picomolar affinity 86Y- or 177Lu-DOTA-Bn binding scFv C825/GPA33 IgG bispecific immunoconjugates

Abstract

Purpose GPA33 is a colorectal cancer (CRC) antigen with unique retention properties after huA33-mediated tumor targeting. We tested a pre-targeted radioimmunotherapy (PRIT) approach for CRC using a tetravalent bispecific antibody with dual specificity for GPA33 tumor antigen and DOTA-Bn (radiolanthanide metal) complex. Methods PRIT was optimized in vivo by titrating sequential intravenous doses of huA33-C825, the dextran-based clearing agent (CA), and the C825-haptens 177Lu-or 86Y-DOTA-Bn in mice bearing the SW1222 subcutaneous (s.c.) CRC xenograft model. Results Using optimized PRIT, therapeutic indices (TIs) for tumor radiation absorbed dose of 73 (tumor/blood) and 12 (tumor/kidney) were achieved. Estimated absorbed doses (cGy/MBq) to tumor, blood, liver, spleen, and kidney for single-cycle PRIT were 65.8, 0.9 (TI: 73), 6.3 (TI: 10), 6.6 (TI: 10), and 5.3 (TI: 12), respectively. Two cycles of PRIT treatment (66.6 or 111 MBq 177Lu-DOTA-Bn) were safe and effective, with 9/9 complete responses of established s.c. tumors (100–700 mm3) and 2/9 alive without recurrence >140 d. Tumor log kill in this model was estimated to be 2.1–3.0 based time to 500-mm3 tumor recurrence. In addition, PRIT dosimetry/diagnosis was performed by PET imaging of the positron-emitting DOTA-hapten 86Y-DOTA-Bn. Conclusions We have developed anti-GPA33 PRIT, as a triple-step theranostic strategy for pre-clinical detection, dosimetry and safe targeted radiotherapy of established human colorectal mouse xenografts.

Curative Multicycle Radioimmunotherapy Monitored by Quantitative SPECT/CT-Based Theranostics, Using Bispecific Antibody Pretargeting Strategy in Colorectal Cancer

“…In our preliminary studies with anti-GPA33 DOTA-PRIT and SW1222, dose escalation resulted in progressive tumor response, and that toxicity was not limiting (8). At lower tumor doses (;40-70 Gy), treatment led to complete responses (e.g., we observed 4/4 complete responses for a 2-cycle treatment regimen of 55.5 MBq per cycle) but was ultimately subcurative and resulted in 2 distinct recurrence phenotypes: outgrowth of antigen-positive tumor with the same rate of growth as controls (seen in 3/4); and a histologic senescence pattern that resulted in dormant tumor, in which antigenexpressing cell growth arrested after 1-2 doublings (seen in 1/4; observed at 140 d after injection).…”

“…The anti-GPA33 DOTA-PRIT bispecific antibody huA33-C825 (210 kDa) was expressed and purified as described by Cheal et al (8). A treatment cycle of anti-GPA33 DOTA-PRIT consisted of 3 separate intravenous injections via the tail vein: 0.25 mg of huA33-C825 at 228 h, then 62.5 mg of clearing agent at 24 h, and 55 MBq of 177 Lu-DOTA-Bn at 0 (8).…”

“…All animal experiments were done in accordance with protocols approved by the Institutional Animal Care and Use Committee of Memorial Sloan Kettering Cancer Center, following National Institutes of Health guidelines for animal welfare. Technical details regarding cell culture and animal models were previously described by Cheal et al (8).…”

Preclinical optimization of antibody‐based radiopharmaceuticals for cancer imaging and radionuclide therapy—Model, vector, and radionuclide selection

“…High doses of 177 Lu (2.5–7.4 GBq) were well tolerated with transient grades 3–4 thrombocytopenia in 10 % of the patients (134). On a preclinical level, the use of a tetravalent bispecific antibody with dual specificity for the GPA33 antigen and 177 Lu-DOTA-Bn complex or the use of the inverse electron-demand Diels-Alder reaction between a transcyclooctene conjugate and a radiolabelled ( 177 Lu) Tetrazine-DOTA derivative, both resulted in significant therapeutic response in human xenografts with dosimetry suggesting amenability to clinical translation (34,135). Finally, when possible, compartmental-RIT can be considered to deliver high dose to the tumor and reduce non-specific toxicity.…”

Bioorthogonal Masking of Circulating Antibody–TCO Groups Using Tetrazine-Functionalized Dextran Polymers

“…18–22 With importance for the study presented herein, the use of dextran-based clearing agents has previously been reported in pretargeting applications using a DOTA-containing hapten and anti-DOTA-bispecific mAbs. 18,19,21,22 Using a fusion protein with affinity for CD20 and DOTA, Orcutt et al demonstrated in pretargeted radioimmunotherapy (PRIT) experiments improved target-to-background ratios when a nonradioactive dextran-DOTA-Yttrium construct was injected prior to the radioligand. 21 The dextran construct was injected 1 day after the administration of the fusion protein and 1 h before the injection of the 90 Y-labeled biotin small molecule effector probe.…”