A generator-produced gallium-68 radiopharmaceutical for PET imaging of myocardial perfusion

Lipophilic cationic technetium-99m-complexes are widely used for myocardial perfusion imaging (MPI). However, inherent uncertainties in the supply chain of molybdenum-99, the parent isotope required for manufacturing 99Mo/99mTc generators, intensifies the need for discovery of novel MPI agents incorporating alternative radionuclides. Recently, germanium/gallium (Ge/Ga) generators capable of producing high quality 68Ga, an isotope with excellent emission characteristics for clinical PET imaging, have emerged. Herein, we report a novel 68Ga-complex identified through mechanism-based cell screening that holds promise as a generator-produced radiopharmaceutical for PET MPI

A blood-based diagnostic test incorporating plasma Aβ42/40 ratio, ApoE proteotype, and age accurately identifies brain amyloid status: Findings from a multi cohort validity analysis

BACKGROUND: The development of blood-based biomarker tests that are accurate and robust for Alzheimer\u27s disease (AD) pathology have the potential to aid clinical diagnosis and facilitate enrollment in AD drug trials. We developed a high-resolution mass spectrometry (MS)-based test that quantifies plasma Aβ42 and Aβ40 concentrations and identifies the ApoE proteotype. We evaluated robustness, clinical performance, and commercial viability of this MS biomarker assay for distinguishing brain amyloid status. METHODS: We used the novel MS assay to analyze 414 plasma samples that were collected, processed, and stored using site-specific protocols, from six independent US cohorts. We used receiver operating characteristic curve (ROC) analyses to assess assay performance and accuracy for predicting amyloid status (positive, negative, and standard uptake value ratio; SUVR). After plasma analysis, sites shared brain amyloid status, defined using diverse, site-specific methods and cutoff values; amyloid PET imaging using various tracers or CSF Aβ42/40 ratio. RESULTS: Plasma Aβ42/40 ratio was significantly (p \u3c 0.001) lower in the amyloid positive vs. negative participants in each cohort. The area under the ROC curve (AUC-ROC) was 0.81 (95% CI = 0.77-0.85) and the percent agreement between plasma Aβ42/40 and amyloid positivity was 75% at the optimal (Youden index) cutoff value. The AUC-ROC (0.86; 95% CI = 0.82-0.90) and accuracy (81%) for the plasma Aβ42/40 ratio improved after controlling for cohort heterogeneity. The AUC-ROC (0.90; 95% CI = 0.87-0.93) and accuracy (86%) improved further when Aβ42/40, ApoE4 copy number and participant age were included in the model. CONCLUSIONS: This mass spectrometry-based plasma biomarker test: has strong diagnostic performance; can accurately distinguish brain amyloid positive from amyloid negative individuals; may aid in the diagnostic evaluation process for Alzheimer\u27s disease; and may enhance the efficiency of enrolling participants into Alzheimer\u27s disease drug trials

Cerenkov Radiation Energy Transfer (CRET) Imaging: A Novel Method for Optical Imaging of PET Isotopes in Biological Systems

Positron emission tomography (PET) allows sensitive, non-invasive analysis of the distribution of radiopharmaceutical tracers labeled with positron (β(+))-emitting radionuclides in small animals and humans. Upon β(+) decay, the initial velocity of high-energy β(+) particles can momentarily exceed the speed of light in tissue, producing Cerenkov radiation that is detectable by optical imaging, but is highly absorbed in living organisms.To improve optical imaging of Cerenkov radiation in biological systems, we demonstrate that Cerenkov radiation from decay of the PET isotopes (64)Cu and (18)F can be spectrally coupled by energy transfer to high Stokes-shift quantum nanoparticles (Qtracker705) to produce highly red-shifted photonic emissions. Efficient energy transfer was not detected with (99m)Tc, a predominantly γ-emitting isotope. Similar to bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET), herein we define the Cerenkov radiation energy transfer (CRET) ratio as the normalized quotient of light detected within a spectral window centered on the fluorophore emission divided by light detected within a spectral window of the Cerenkov radiation emission to quantify imaging signals. Optical images of solutions containing Qtracker705 nanoparticles and [(18)F]FDG showed CRET ratios in vitro as high as 8.8±1.1, while images of mice with subcutaneous pseudotumors impregnated with Qtracker705 following intravenous injection of [(18)F]FDG showed CRET ratios in vivo as high as 3.5±0.3.Quantitative CRET imaging may afford a variety of novel optical imaging applications and activation strategies for PET radiopharmaceuticals and other isotopes in biomaterials, tissues and live animals

CRET <i>in vitro</i> was dependent on Qtracker705 nanoparticle concentration.

<p>(<b>A</b>) IVIS 100 images of 96-well assay plates using either a <510 nm filter (left) or a >590 nm filter (right). Note the red “hot pixel” from an annihilation event detected by the CCD camera in one image (left), and the presence of minimally detectable CRET emitted from the wells containing 200 nM Qtracker705, but no [¹⁸F]FDG, due to contaminating radioactive emissions from adjacent wells (right). Qtracker705 nanoparticles show no CRET when imaged in isolation in the absence of [¹⁸F]FDG. (<b>B</b>) Plot of photon flux from either the <510 nm filter (□) or the >590 filter (▪) with increasing concentrations of Qtracker705 nanoparticles. (<b>C</b>) Plot of CRET ratios versus concentration of Qtracker705 nanoparticles (dashed line is a linear fit of the data: y = 0.036x+1.3; R² = 0.897).</p

CRET imaging of pseudotumor phantoms in live animals <i>in vivo</i>.

<p>(<b>A</b>) Subcutaneous pseudotumors of 500 nM Qtracker705-impregnated Matrigel (closed arrow) and PBS-impregnated Matrigel (open arrow) in opposing flanks of <i>nu/nu</i> mice were imaged with an IVIS 100 using open, <510 nm (blue), 500–570 nm (green), and >590 nm (red) filters 30 minutes following tail-vein injection of [¹⁸F]FDG (17.6 MBq; 475 µCi). (<b>B</b>) The calculated CRET image.</p

Characterization of ⁶⁷Ga-labeled 5a <i>in cellulo</i>.

<p><b>A.</b> Cellular accumulation of <b>5a</b> in human MCF-7 cells (Pgp-) and stably transfected MCF-7/<i>MDR1</i> (Pgp+) cells. <i>Inset</i>: Immunodetectable levels of Pgp in plasma membrane preparations using mAb C219; MCF-7 cells (lane 1) and MCF-7/<i>MDR1</i> cells (lane 2). Arrows demarcate Pgp (170 kDa) and γ-tubulin (γ-t) loading control. <b>B.</b> Cellular accumulation of <b>5a</b> in KB-3–1 cells (Pgp-) and KB-8–5 (Pgp+). Shown are net uptakes at 90 min (fmol (mg protein)⁻¹ (nM₀)⁻¹) using control buffer in the absence (open column) or presence (solid column) of the MDR modulator LY335979 (1 µM). Each column represents the mean of 4 determinations; bar denotes ±SEM.</p