Pharmacokinetic Positron Emission Tomography Imaging of an Optimized CD38-Targeted 68Ga-Labeled Peptide in Multiple Myeloma: A Pilot Study.

Multiple myeloma (MM) is an incurable disease characterized by its clinical and prognostic heterogeneity. Despite conventional chemotherapy and autologous hematopoietic stem cell transplantation, the management of relapsed and refractory MM disease poses significant challenges, both medically and socioeconomically. CD38, highly expressed on the surface of MM cells, serves as a distinct tumor biological target in MM. Peptides offer advantages over antibodies, enabling precise tumor imaging and facilitating early tumor diagnosis and dynamic immunotherapy monitoring. In this study, we developed PF381, a CD38-targeted peptide, and investigated its role in diagnosis, biodistribution, and dosimetry through ⁶⁸Ga-labeling for preclinical evaluation in tumor-bearing models. We screened a microchip-based combinatorial chemistry peptide library to obtain the amino acid sequence of PF381. Affinity for human CD38 was evaluated by SPRi. PF381 was conjugated with DOTA for radiolabeling with ⁶⁸Ga, and the complex was characterized by HPLC. PET imaging was performed in murine tumor models after the administration of [⁶⁸Ga]Ga-DOTA-PF381. Biodistribution analysis compared CD38-positive H929 and CD38-negative U266 tumors, and human radiation dosimetry was estimated. Tumor sections were stained for CD38 expression. SPRi showed that PF381 had a high affinity for CD38 with a KD of 2.49 × 10^-8 M. HPLC measured a radiolabeling efficiency of 78.45 ± 7.91% for [⁶⁸Ga]Ga-DOTA-PF381, with >98% radiochemical purity. PET imaging revealed rapid and persistent accumulation of radioactivity in CD38-positive H929 tumors, contrasting with negligible uptake in CD38-negative U266 tumors. Biodistribution confirmed higher uptake in H929 tumors (0.75 ± 0.03%ID/g) vs U266 (0.26 ± 0.08%ID/g, P < 0.001). The kidney received the highest radiation dose (3.57 × 10^-02 mSv/MBq), with an effective dose of 1.41 × 10^-02 mSv/MBq. Immunofluorescence imaging supported PET and biodistribution findings. We developed a novel peptide targeting CD38 and proved that ⁶⁸Ga-labeled PF381 had rapid targeting and good tumor penetration capabilities. Therefore, ⁶⁸Ga-labeled PF381 could achieve high sensitivity in vivo imaging for CD38-positive hematological malignancies.