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We studied the effect of varying specific activity of [68Ga]DKFZ-PSMA11 ([68Ga]DP11) on repeated imaging of prostate-specific membrane antigen-positive (PSMA+) xenograft tumors. Athymic nude mice bearing PC3-PIP (PSMA+) and PC3 (PSMA−) bilateral flank tumors were assessed to study intra- and inter-day repeatability of [68Ga]DP11 imaging in mice administered [68Ga]DP11 or [67Ga]DP11 (as a dilution tracer) using imaging and biodistribution studies. Region of interest (ROI) analysis of the [68Ga]DP11 imaging study indicated that the uptake was constant on the same day or consecutive days. Prior imaging with [68Ga]DP11 did not significantly influence the subsequent uptake of [68Ga]DP11. Uptake of [68Ga]DP11 (60 min) and [67Ga]DP11 (24 h) in PC3-PIP tumors was 12.37 ± 4.19 %ID/g and 12.49 ± 6.88 %ID/g, respectively; [68Ga]DP11 was 13.83 ± 3.77 and 17.76 ± 1.84 on same-day and 15.98 ± 5.82 %ID/g on second-day imaging. This study demonstrates that [68Ga]DP11, in a given PSMA+ lesion, is constant under several same-day or serial-day imaging conditions.

GPA33 is a colorectal cancer (CRC) antigen with unique retention properties after huA33-mediated tumor targeting. We tested a pretargeted radioimmunotherapy (PRIT) approach for CRC using a tetravalent bispecific antibody with dual specificity for GPA33 tumor antigen and DOTA-Bn–(radiolanthanide metal) complex. PRIT was optimized in vivo by titrating sequential intravenous doses of huA33-C825, the dextran-based clearing agent, and the C825 haptens 177Lu-or 86Y-DOTA-Bn in mice bearing the SW1222 subcutaneous (s.c.) CRC xenograft model. 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 (66.6 or 111 MBq 177Lu-DOTA-Bn) were safe and effective, with a complete response of established s.c. tumors (100 – 700 mm3) in nine of nine mice, with two mice alive without recurrence at >140 days. Tumor log kill in this model was estimated to be 2.1 – 3.0 based on 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. We have developed anti-GPA33 PRIT as a triple-step theranostic strategy for preclinical detection, dosimetry, and safe targeted radiotherapy of established human colorectal mouse xenografts.

We developed a new approach to bioluminescent T cell imaging using a membrane-anchored form of the Gaussia luciferase (GLuc) enzyme, termed extGLuc, which we could stably express in both mouse and human primary T cells. In vitro, extGLuc+ cells emitted significantly higher bioluminescent signal when compared to cells expressing GLuc, Renilla luciferase (RLuc) or membrane-anchored RLuc (extRLuc). In vivo, mouse extGLuc+ T cells showed higher bioluminescent signal when compared to GLuc+ and RLuc+ T cells. Application of this imaging approach to human T cells genetically modified to express tumor-specific chimeric antigen receptors (CARs) enabled us to show in vivo CAR-mediated T cell accumulation in tumor, T cell persistence over time and concomitant imaging of T cells and tumor cells modified to express firefly luciferase. This sensitive imaging technology has application to many in vivo cell-based studies in a wide array of mouse models.