Detection and therapy of neuroblastoma minimal residual disease using [64/67Cu]Cu-SARTATE in a preclinical model of hepatic metastases

Abstract

Background A major challenge to the long-term success of neuroblastoma therapy is widespread metastases that survive initial therapy as minimal residual disease (MRD). The SSTR2 receptor is expressed by most neuroblastoma tumors making it an attractive target for molecularly targeted radionuclide therapy. SARTATE consists of octreotate, which targets the SSTR2 receptor, conjugated to MeCOSar, a bifunctional chelator with high affinity for copper. Cu-SARTATE offers the potential to both detect and treat neuroblastoma MRD by using [ 64 Cu]Cu-SARTATE to detect and monitor the disease and [ 67 Cu]Cu-SARTATE as the companion therapeutic agent. In the present study, we tested this theranostic pair in a preclinical model of neuroblastoma MRD. An intrahepatic model of metastatic neuroblastoma was established using IMR32 cells in nude mice. The biodistribution of [ 64 Cu]Cu-SARTATE was measured using small-animal PET and ex vivo tissue analysis. Survival studies were carried out using the same model: mice (6–8 mice/group) were given single doses of saline, or 9.25\xa0MBq (250\xa0µCi), or 18.5\xa0MBq (500\xa0µCi) of [ 67 Cu]Cu-SARTATE at either 2 or 4\xa0weeks after tumor cell inoculation. Results PET imaging and ex vivo biodistribution confirmed tumor uptake of [ 64 Cu]Cu-SARTATE and rapid clearance from other tissues. The major clearance tissues were the kidneys (15.6\u2009±\u20095.8% IA/g at 24\xa0h post-injection, 11.5\u2009±\u20092.8% IA/g at 48\xa0h, n \u2009=\u20093/4). Autoradiography and histological analysis confirmed [ 64 Cu]Cu-SARTATE uptake in viable, SSTR2-positive tumor regions with mean tumor uptakes of 14.1–25.0% IA/g at 24\xa0h. [ 67 Cu]Cu-SARTATE therapy was effective when started 2\xa0weeks after tumor cell inoculation, extending survival by an average of 13\xa0days (30%) compared with the untreated group (mean survival of control group 43.0\u2009±\u20098.1\xa0days vs. 55.6\u2009±\u20099.1\xa0days for the treated group; p \u2009=\u20090.012). No significant therapeutic effect was observed when [ 67 Cu]Cu-SARTATE was started 4\xa0weeks after tumor cell inoculation, when the tumors would have been larger (control group 14.6\u2009±\u20098.5\xa0days; 9.25\xa0MBq group 9.5\u2009±\u20091.6\xa0days; 18.5\xa0MBq group 15.6\u2009±\u20094.1\xa0days; p \u2009=\u20090.064). Conclusions Clinical experiences of peptide-receptor radionuclide therapy for metastatic disease have been encouraging. This study demonstrates the potential for a theranostic approach using [ 64/67 Cu]Cu-SARTATE for the detection and treatment of SSTR2-positive neuroblastoma MRD.