Evaluation of 134Ce/134La as a PET Imaging Theranostic Pair for 225Ac α-Radiotherapeutics.

225Ac-targeted α-radiotherapy is a promising approach to treating malignancies, including prostate cancer. However, α-emitting isotopes are difficult to image because of low administered activities and a low fraction of suitable γ-emissions. The in vivo generator 134Ce/134La has been proposed as a potential PET imaging surrogate for the therapeutic nuclides 225Ac and 227Th. In this report, we detail efficient radiolabeling methods using the 225Ac-chelators DOTA and MACROPA. These methods were applied to radiolabeling of prostate cancer imaging agents, including PSMA-617 and MACROPA-PEG4-YS5, for evaluation of their in vivo pharmacokinetic characteristics and comparison to the corresponding 225Ac analogs. Methods: Radiolabeling was performed by mixing DOTA/MACROPA chelates with 134Ce/134La in NH4OAc, pH 8.0, at room temperature, and radiochemical yields were monitored by radio-thin-layer chromatography. In vivo biodistributions of 134Ce-DOTA/MACROPA.NH2 complexes were assayed through dynamic small-animal PET/CT imaging and ex vivo biodistribution studies over 1 h in healthy C57BL/6 mice, compared with free 134CeCl3 In vivo, preclinical imaging of 134Ce-PSMA-617 and 134Ce-MACROPA-PEG4-YS5 was performed on 22Rv1 tumor-bearing male nu/nu-mice. Ex vivo biodistribution was performed for 134Ce/225Ac-MACROPA-PEG4-YS5 conjugates. Results: 134Ce-MACROPA.NH2 demonstrated near-quantitative labeling with 1:1 ligand-to-metal ratios at room temperature, whereas a 10:1 ligand-to-metal ratio and elevated temperatures were required for DOTA. Rapid urinary excretion and low liver and bone uptake were seen for 134Ce/225Ac-DOTA/MACROPA. NH2 conjugates in comparison to free 134CeCl3 confirmed high in vivo stability. An interesting observation during the radiolabeling of tumor-targeting vectors PSMA-617 and MACROPA-PEG4-YS5-that the daughter 134La was expelled from the chelate after the decay of parent 134Ce-was confirmed through radio-thin-layer chromatography and reverse-phase high-performance liquid chromatography. Both conjugates, 134Ce-PSMA-617 and 134Ce-MACROPA-PEG4-YS5, displayed tumor uptake in 22Rv1 tumor-bearing mice. The ex vivo biodistribution of 134Ce-MACROPA.NH2, 134Ce-DOTA and 134Ce-MACROPA-PEG4-YS5 corroborated well with the respective 225Ac-conjugates. Conclusion: These results demonstrate the PET imaging potential for 134Ce/134La-labeled small-molecule and antibody agents. The similar 225Ac and 134Ce/134La-chemical and pharmacokinetic characteristics suggest that the 134Ce/134La pair may act as a PET imaging surrogate for 225Ac-based radioligand therapies.

Organ-specific fuel rewiring in acute and chronic hypoxia redistributes glucose and fatty acid metabolism.

Oxygen deprivation can be detrimental. However, chronic hypoxia is also associated with decreased incidence of metabolic syndrome and cardiovascular disease in high-altitude populations. Previously, hypoxic fuel rewiring has primarily been studied in immortalized cells. Here, we describe how systemic hypoxia rewires fuel metabolism to optimize whole-body adaptation. Acclimatization to hypoxia coincided with dramatically lower blood glucose and adiposity. Using in vivo fuel uptake and flux measurements, we found that organs partitioned fuels differently during hypoxia adaption. Acutely, most organs increased glucose uptake and suppressed aerobic glucose oxidation, consistent with previous in vitro investigations. In contrast, brown adipose tissue and skeletal muscle became "glucose savers," suppressing glucose uptake by 3-5-fold. Interestingly, chronic hypoxia produced distinct patterns: the heart relied increasingly on glucose oxidation, and unexpectedly, the brain, kidney, and liver increased fatty acid uptake and oxidation. Hypoxia-induced metabolic plasticity carries therapeutic implications for chronic metabolic diseases and acute hypoxic injuries.

Prostate-Specific Membrane Antigen Targeted Deep Tumor Penetration of Polymer Nanocarriers.

Tumoral uptake of large-size nanoparticles is mediated by the enhanced permeability and retention (EPR) effect, with variable accumulation and heterogenous tumor tissue penetration depending on the tumor phenotype. The performance of nanocarriers via specific targeting has the potential to improve imaging contrast and therapeutic efficacy in vivo with increased deep tissue penetration. To address this hypothesis, we designed and synthesized prostate cancer-targeting starPEG nanocarriers (40 kDa, 15 nm), [89Zr]PEG-(DFB)3(ACUPA)1 and [89Zr]PEG-(DFB)1(ACUPA)3, with one or three prostate-specific membrane antigen (PSMA)-targeting ACUPA ligands. The in vitro PSMA binding affinity and in vivo pharmacokinetics of the targeted nanocarriers were compared with a nontargeted starPEG, [89Zr]PEG-(DFB)4, in PSMA+ PC3-Pip and PSMA- PC3-Flu cells, and xenografts. Increasing the number of ACUPA ligands improved the in vitro binding affinity of PEG-derived polymers to PC3-Pip cells. While both PSMA-targeted nanocarriers significantly improved tissue penetration in PC3-Pip tumors, the multivalent [89Zr]PEG-(DFB)1(ACUPA)3 showed a remarkably higher PC3-Pip/blood ratio and background clearance. In contrast, the nontargeted [89Zr]PEG-(DFB)4 showed low EPR-mediated accumulation with poor tumor tissue penetration. Overall, ACUPA conjugated targeted starPEGs significantly improve tumor retention with deep tumor tissue penetration in low EPR PC3-Pip xenografts. These data suggest that PSMA targeting with multivalent ACUPA ligands may be a generally applicable strategy to increase nanocarrier delivery to prostate cancer. These targeted multivalent nanocarriers with high tumor binding and low healthy tissue retention could be employed in imaging and therapeutic applications.