Breast cancer (BrCa) ranks as the most prevalent malignant neoplasm affecting women worldwide. The expression of programmed death-ligand 1 (PD-L1) in BrCa has recently emerged as a biomarker for immunotherapy response, but traditional immunohistochemistry (IHC)-based methods are hindered by spatial and temporal heterogeneity. Noninvasive and quantitative PD-L1 imaging using appropriate radiotracers can serve to determine PD-L1 expression in tumors. This study aims to demonstrate the viability of PET imaging with 64Cu-labeled Durvalumab (abbreviated as Durva) to assess PD-L1 expression using a murine xenograft model of breast cancer. Durvalumab, a human IgG1 monoclonal antibody against PD-L1, was assessed for specificity in vitro in two cancer cell lines (MDA-MB-231 triple-negative breast cancer cell line and AsPC-1 pancreatic cancer cell line) with positive and negative PD-L1 expression by flow cytometry. Next, we performed the in vivo evaluation of 64Cu-NOTA-Durva in murine models of human breast cancer by PET imaging and ex vivo biodistribution. Additionally, mice bearing AsPC-1 tumors were employed as a negative control. Tumor uptake was quantified based on a 3D region-of-interest (ROI) analysis of the PET images and ex vivo biodistribution measurements, and the results were compared against conventional IHC testing. The radiotracer uptake was evident in MDA-MB-231 tumors and showed minimal nonspecific binding, corroborating IHC-derived results. The results of the biodistribution showed that the MDA-MB-231 tumor uptake of 64Cu-NOTA-Durva was much higher than 64Cu-NOTA-IgG (a nonspecific radiolabeled IgG). In Conclusion, 64Cu-labeled Durvalumab PET/CT imaging offers a promising, noninvasive approach to evaluate tumor PD-L1 expression.
The development of inert, biocompatible chelation methods is required to harness the emerging positron emitting radionuclide 45Ti for radiopharmaceutical applications. Herein, we evaluate the Ti(IV)-coordination chemistry of four catechol-based, hexacoordinate chelators using synthetic, structural, computational, and radiochemical approaches. The siderophore enterobactin (Ent) and its synthetic mimic TREN-CAM readily form mononuclear Ti(IV) species in aqueous solution at neutral pH. Radiolabeling studies reveal that Ent and TREN-CAM form mononuclear complexes with the short-lived, positron-emitting radionuclide 45Ti(IV), and do not transchelate to plasma proteins in vitro and exhibit rapid renal clearance in naïve mice. These features guide efforts to target the 45Ti isotope to prostate cancer tissue through the design, synthesis, and evaluation of Ent-DUPA, a small molecule conjugate composed of a prostate specific membrane antigen (PSMA) targeting peptide and a monofunctionalized Ent scaffold. The [45Ti][Ti(Ent-DUPA)]2- complex forms readily at room temperature. In a tumor xenograft model in mice, selective tumor tissue accumulation (8±5 %, n=5), and low off-target uptake in other organs is observed. Overall, this work demonstrates targeted imaging with 45Ti(IV), provides a foundation for advancing the application of 45Ti in nuclear medicine, and reveals that Ent can be repurposed as a 45Ti-complexing cargo for targeted nuclear imaging applications.
Prostatic Neoplasms , Siderophores , Humans , Male , Animals , Mice , Siderophores/chemistry , Enterobactin/metabolism , Titanium/chemistry , Off-Label Use , Prostatic Neoplasms/metabolism , Radioisotopes
Cobalt-55 and -58m form a theranostic pair that has relevant properties for cancer research. We report a cation exchange chromatography/extraction chromatography method that separates cyclotron-produced 55/58mCo from 54/57Fe in <1.5 h, recovers >85% Co and achieves [55Co]Co-NOTA and -DOTA AMA 89 ± 48 and 35 ± 7 MBq/nmol (EOB), respectively. Cobalt-55 and -58m were quantitatively labeled to functionalized NOTA at 106 and 50 MBq/nmol (EOB), respectively, corroborating measured AMA. This method is faster than previously published methods and achieves better [55/58mCo]Co-NOTA and -DOTA AMA.
