Aminopeptidase N (APN, CD13) is a transmembrane ectopeptidase involved in many crucial cellular functions. Besides its role as a peptidase, APN also mediates signal transduction and is involved in the activation of matrix metalloproteinases (MMPs). MMPs function in tissue remodeling within the extracellular space and are therefore involved in many human diseases, such as fibrosis, rheumatoid arthritis, tumor angiogenesis, and metastasis, as well as viral infections. However, the exact mechanism that leads to APN-driven MMP activation is unclear. It was previously shown that extracellular 14-3-3 adapter proteins bind to APN and thereby induce the transcription of MMPs. As a first step, we sought to identify potential 14-3-3–binding sites in the APN sequence. We constructed a set of phosphorylated peptides derived from APN to probe for interactions. We identified and characterized a canonical 14-3-3–binding site (site 1) within the flexible, structurally unresolved N-terminal APN region using direct binding fluorescence polarization assays and thermodynamic analysis. In addition, we identified a secondary, noncanonical binding site (site 2), which enhances the binding affinity in combination with site 1 by many orders of magnitude. Finally, we solved crystal structures of 14-3-3σ bound to mono- and bis-phosphorylated APN-derived peptides, which revealed atomic details of the binding mode of mono- and bivalent 14-3-3 interactions. Therefore, our findings shed some light on the first steps of APN-mediated MMP activation and open the field for further investigation of this important signaling pathway.

Radiolabeled small-molecule DOTA-haptens can be combined with antitumor/anti-DOTA bispecific antibodies (BsAbs) for pretargeted radioimmunotherapy (PRIT). For optimized delivery of the theranostic - and β-emitting isotope ¹⁷⁷Lu with DOTA-based PRIT (DOTA-PRIT), bivalent Gemini (DOTA-Bn-thiourea-PEG4-thiourea-Bn-DOTA, aka (3,6,9,12-tetraoxatetradecane-1,14-diyl)bis(DOTA-benzyl thiourea)) was developed. Methods: Gemini was synthesized by linking 2 S-2-(4-isothiocyanatobenzyl)-DOTA molecules together via a 1,14-diamino-PEG4 linker. [¹⁷⁷Lu]Lu-Gemini was prepared with no-carrier-added ¹⁷⁷LuCl₃ to a molar-specific activity of 123 GBq/μmol and radiochemical purity of more than 99%. The specificity of BsAb-¹⁷⁷Lu-Gemini was verified in vitro. Subsequently, we evaluated biodistribution and whole-body clearance for [¹⁷⁷Lu]Lu-Gemini and, for comparison, our gold-standard monovalent [¹⁷⁷Lu]Lu-S-2-(4-aminobenzyl)-DOTA ([¹⁷⁷Lu]Lu-DOTA-Bn) in naïve (tumor-free) athymic nude mice. For our proof-of-concept system, a 3-step pretargeting approach was performed with an established DOTA-PRIT regimen (anti-GPA33/anti-DOTA IgG-scFv BsAb, a clearing agent, and [¹⁷⁷Lu]Lu-Gemini) in mouse models. Results: Initial in vivo studies showed that [¹⁷⁷Lu]Lu-Gemini behaved similarly to [¹⁷⁷Lu]Lu-DOTA-Bn, with almost identical blood and whole-body clearance kinetics, as well as biodistribution and mouse kidney dosimetry. Pretargeting [¹⁷⁷Lu]Lu-Gemini to GPA33-expressing SW1222 human colorectal xenografts was highly effective, leading to absorbed doses of [¹⁷⁷Lu]Lu-Gemini for blood, tumor, liver, spleen, and kidneys of 3.99, 455, 6.93, 5.36, and 14.0 cGy/MBq, respectively. Tumor–to–normal tissue absorbed-dose ratios (i.e., therapeutic indices [TIs]) for the blood and kidneys were 114 and 33, respectively. In addition, we demonstrate that the use of bivalent [¹⁷⁷Lu]Lu-Gemini in DOTA-PRIT leads to improved TIs and augmented [¹⁷⁷Lu]Lu-Gemini tumor uptake and retention in comparison to monovalent [¹⁷⁷Lu]Lu-DOTA-Bn. Finally, we established efficacy in SW1222 tumor-bearing mice, demonstrating that a single injection of anti-GPA33 DOTA-PRIT with 44 MBq (1.2 mCi) of [¹⁷⁷Lu]Lu-Gemini (estimated tumor-absorbed dose, 200 Gy) induced complete responses in 5 of 5 animals and a histologic cure in 2 of 5 (40%) animals. Moreover, a significant increase in survival compared with nontreated controls was noted (maximum tolerated dose not reached). Conclusion: We have developed a bivalent DOTA-radiohapten, [¹⁷⁷Lu]Lu-Gemini, that showed improved radiopharmacology for DOTA-PRIT application. The use of bivalent [¹⁷⁷Lu]Lu-Gemini in DOTA-PRIT, as opposed to monovalent [¹⁷⁷Lu]Lu-DOTA-Bn, allows curative treatments with considerably less administered ¹⁷⁷Lu activity while still achieving high TIs for both the blood (>100) and the kidneys (>30).

DOVER, DE (August 31, 2022) – On Aug. 31, the U.S. Food and Drug Administration (FDA) granted Emergency Use Authorization to Pfizer and Moderna for their new bivalent boosters, meaning vaccine could start shipping to states that pre-ordered as early as Friday.  The Centers for Disease Control and Prevention’s (CDC) advisory committee meets Thursday and Friday, Sept. 1 and 2, […]

DOVER, DE (September 16, 2022) – The Delaware Division of Public Health (DPH) is pleased to share declines in hospitalizations, test positivity rates and the 7-day average of new positive COVID-19 cases continued for the second month in a row.  Deaths also remain low. However, COVID-19 is still circulating in the community, and at higher levels […]

DOVER, DE (October 14, 2022) – The Delaware Division of Public Health (DPH) reports that the 7-day average of new positive COVID-19 cases has decreased for the third consecutive month. Deaths remain low, and hospitalization rates are holding steady. According to the Centers for Disease Control and Prevention’s (CDC) COVID-19 Community Levels data tracker, which factors in data on hospitalizations […]

"The first batch of staff were trained at French labs," she said, adding that its equipment is tested every year by internationally recognised third parties.