CD38-specific immunoPET imaging for multiple myeloma diagnosis and therapeutic monitoring: preclinical and first-in-human studies

Purpose CD38 is a glycoprotein highly specific to multiple myeloma (MM). Therapeutics using antibodies targeting CD38 have shown promising efficacy. However, the efficient stratification of patients who may benefit from daratumumab (Dara) therapy and timely monitoring of therapeutic responses remain significant clinical challenges. To address these issues, we developed a novel nanobody-based PET tracer, [Ga-68]Ga-TOHP-CD3813, which exhibits rapid clearance from the blood and rapid accumulation in targeted tumor lesions, facilitating the detection of CD38 expression in murine models of MM and lymphoma. Furthermore, we conducted the world's first-in-human trials using CD38-targeted nanobodies to validate and assess the clinical imaging effectiveness of [Ga-68]Ga-TOHP-CD3813 in guiding cancer immunotherapy. Materials and methods We prepared a new PET imaging probe based on a CD38-targeted nanobody CD3813, [Ga-68]Ga-TOHP-CD3813, via the site-specific radiolabeling for noninvasive PET imaging of CD38 expression. [Ga-68]Ga-TOHP-CD3813 was assessed for its affinity and specificity to CD38 and its ability to image CD38 expression in MM and lymphoma xenograft models. Biodistribution and the relationship between tumor uptake and CD38 expression were evaluated. Subsequently, we conducted a translational PET imaging of 2 MM patients using [Ga-68]Ga-TOHP-CD3813, while compared with [F-18]FDG PET/CT head-to-head. Dosimetry was also calculated based on the animal data. Results TOHP-CD3813 retained a high affinity for CD38 with a KD of 0.0826 nmol/L. [Ga-68]Ga-TOHP-CD3813 was successfully synthesized at room temperature within 10 min, exhibiting optimal radiochemical properties. Preclinical assessments revealed rapid blood clearance, high CD38 affinity, and significant uptake in CD38-positive xenograft mouse models (6.50 +/- 2.69%ID/g). [Ga-68]Ga-TOHP-CD3813 showed pronounced accumulation in the kidneys and bladder, with moderate liver uptake, indicating its potential as a viable clinical PET radiotracer for diagnosing MM. Additionally, in first-in-human trials, [Ga-68]Ga-TOHP-CD3813 PET/CT provides a substantial improvement over [F-18]FDG PET/CT for the visualization of MM. Conclusions [Ga-68]Ga-TOHP-CD3813, with its high affinity, specificity, and robust imaging capabilities, rapidly and specifically accumulates in tumors with high CD38 expression, offering a significant advantage over [F-18]FDG PET/CT for visualizing MM and enabling same-day PET imaging. Initial human trial results are promising, suggesting its potential as a companion diagnostic tool for optimizing CD38-targeted treatments in tumors. Ongoing larger trials aim to further confirm these findings.