Multimodal imaging of capsid and cargo reveals differential brain targeting and liver detargeting of systemically-administered AAVs

The development of gene delivery vehicles with high organ specificity when administered systemically is a critical goal for gene therapy. We combine optical and positron emission tomography (PET) imaging of 1) reporter genes and 2) capsid tags to assess the temporal and spatial distribution and transduction of adeno-associated viruses (AAVs). AAV9 and two engineered AAV vectors (PHP.eB and CAP-B10) that are noteworthy for maximizing blood-brain barrier transport were compared. CAP-B10 shares a modification in the 588 loop with PHP.eB, but also has a modification in the 455 loop, added with the goal of reducing off-target transduction. PET and optical imaging revealed that the additional modifications retained brain receptor affinity. In the liver, the accumulation of AAV9 and the engineered AAV capsids was similar (∼15% of the injected dose per cc and not significantly different between capsids at 21 h). However, the engineered capsids were primarily internalized by Kupffer cells rather than hepatocytes, and liver transduction was greatly reduced. PET reporter gene imaging after engineered AAV systemic injection provided a non-invasive method to monitor AAV-mediated protein expression over time. Through comparison with capsid tagging, differences between brain localization and transduction were revealed. In summary, AAV capsids bearing imaging tags and reporter gene payloads create a unique and powerful platform to assay the pharmacokinetics, cellular specificity and protein expression kinetics of AAV vectors in vivo, a key enabler for the field of gene therapy.

A Clinical PET Imaging Tracer ([18F]DASA-23) to Monitor Pyruvate Kinase M2-Induced Glycolytic Reprogramming in Glioblastoma

PURPOSE

Pyruvate kinase M2 (PKM2) catalyzes the final step in glycolysis, a key process of cancer metabolism. PKM2 is preferentially expressed by glioblastoma (GBM) cells with minimal expression in healthy brain. We describe the development, validation, and translation of a novel PET tracer to study PKM2 in GBM. We evaluated 1-((2-fluoro-6-[18F]fluorophenyl)sulfonyl)-4-((4-methoxyphenyl)sulfonyl)piperazine ([18F]DASA-23) in cell culture, mouse models of GBM, healthy human volunteers, and patients with GBM.

EXPERIMENTAL DESIGN

[18F]DASA-23 was synthesized with a molar activity of 100.47 ± 29.58 GBq/μmol and radiochemical purity >95%. We performed initial testing of [18F]DASA-23 in GBM cell culture and human GBM xenografts implanted orthotopically into mice. Next, we produced [18F]DASA-23 under FDA oversight, and evaluated it in healthy volunteers and a pilot cohort of patients with glioma.

RESULTS

In mouse imaging studies, [18F]DASA-23 clearly delineated the U87 GBM from surrounding healthy brain tissue and had a tumor-to-brain ratio of 3.6 ± 0.5. In human volunteers, [18F]DASA-23 crossed the intact blood-brain barrier and was rapidly cleared. In patients with GBM, [18F]DASA-23 successfully outlined tumors visible on contrast-enhanced MRI. The uptake of [18F]DASA-23 was markedly elevated in GBMs compared with normal brain, and it identified a metabolic nonresponder within 1 week of treatment initiation.

CONCLUSIONS

We developed and translated [18F]DASA-23 as a new tracer that demonstrated the visualization of aberrantly expressed PKM2 for the first time in human subjects. These results warrant further clinical evaluation of [18F]DASA-23 to assess its utility for imaging therapy-induced normalization of aberrant cancer metabolism.

Fully-automated radiosynthesis of the amyloid tracer [11C] PiB via direct [11C]CO2 fixation-reduction

BACKGROUND

The β-amyloid radiotracer [11C] PiB is extensively used for the Positron Emission Tomography (PET) diagnosis of Alzheimer's Disease and related dementias. For clinical use, [11C] PiB is produced using the 11C-methylation method ([11C] Methyl iodide or [11C] methyl triflate as 11C-methylation agents), which represents the most employed 11C-labelling strategy for the synthesis of 11C-radiopharmaceuticals. Recently, the use of direct [11C]CO2 fixation for the syntheses of 11C-tracers has gained interest in the radiochemical community due to its importance in terms of radiochemical versatility and for permitting the direct employment of the cyclotron-produced precursor [11C]CO2. This paper presents an optimised alternative one-pot methodology of [11C]CO2 fixation-reduction for the rapid synthesis of [11C] PiB using an automated commercial platform and its quality control.

RESULTS

[11C] PiB was obtained from a (25.9 ± 13.2)% (Average ± Variation Coefficient, n = 3) (end of synthesis, decay corrected) radiochemical yield from trapped [11C]CO2 after 1 min of labelling time using PhSiH3 / TBAF as the fixation-reduction system in Diglyme at 150 °C. The radiochemical purity was higher than 95% in all cases, and the molar activity was (61.4 ± 1.6) GBq/μmol. The radiochemical yield and activity (EOS) of formulated [11C] PiB from cyclotron-produced [11C]CO2 was (14.8 ± 12.1)%, decay corrected) and 9.88 GBq (± 6.0%), respectively. These are higher values compared to that of the 11C-methylation method with [11C]CH3OTf (~ 8.3%).

CONCLUSIONS

The viability of the system PhSiH3 / TBAF to efficiently promote the radiosynthesis of [11C] PiB via direct [11C]CO2 fixation-reduction has been demonstrated. [11C] PiB was obtained through a fully automated radiosynthesis with a satisfactory yield, purity and molar activity. According to the results, the one-pot methodology employed could reliably yield sufficiently high tracer amounts for preclinical and clinical use.

An efficient preparation of labelling precursor of [11C]L-deprenyl-D2 and automated radiosynthesis

Background

The synthesis of [¹¹C]L-deprenyl-D₂ for imaging of astrocytosis with positron emission tomography (PET) in neurodegenerative diseases has been previously reported. [¹¹C]L-deprenyl-D₂ radiosynthesis requires a precursor, L-nordeprenyl-D₂, which has been previously synthesized from L-amphetamine as starting material with low overall yields. Here, we present an efficient synthesis of L-nordeprenyl-D₂ organic precursor as free base and automated radiosynthesis of [¹¹C]L-deprenyl-D₂ for PET imaging of astrocytosis. The L-nordeprenyl-D₂ precursor was synthesized from the easily commercial available and cheap reagent L-phenylalanine in five steps. Next, N-alkylation of L-nordeprenyl-D₂ free base with [¹¹C]MeOTf was optimized using the automated commercial platform GE TRACERlab® FX C Pro.

Results

A simple and efficient synthesis of L-nordeprenyl-D₂ precursor of [¹¹C]L-deprenyl-D₂ as free base has been developed in five synthetic steps with an overall yield of 33%. The precursor as free base has been stable for 9 months stored at low temperature (−20 °C). The labelled product was obtained with 44 ± 13% (n = 12) (end of synthesis, decay corrected) radiochemical yield from [¹¹C]MeI after 35 min synthesis time. The radiochemical purity was over 99% in all cases and specific activity was (170 ± 116) GBq/μmol.

Conclusions

A high-yield synthesis of [¹¹C]L-deprenyl-D₂ has been achieved with high purity and specific activity. L-nordeprenyl-D₂ precursor as free amine was applicable for automated production in a commercial synthesis module for preclinical and clinical application.

Synthesis and biological properties of new 5-nitroindazole derivatives

A series of new 3-alkoxy- or 3-hydroxy-1-[omega-(dialkylamino)alkyl]-5-nitroindazoles have been synthesized and their trichomonacidal, antichagasic and antineoplastic properties studied. Five derivatives (5, 6, 8, 9 and 17) showed remarkable trichomonacidal activity against Trichomonas vaginalis at 10 microg/mL concentration. Three compounds (8, 10, 11) exhibited interesting antichagasic activity and these same compounds moderate antineoplastic activity against TK-10 and HT-29 cell lines. Unspecific cytotoxicity against macrophages has also been evaluated and only compounds 9, 10 and 11 resulted cytotoxic at the higher dose evaluated (100 microg/mL), loosing cytotoxicity at lower doses. QSAR studies have been carried out. X-ray crystallographic study of compound 8 has been performed.