89Zr-leukocyte labelling for cell trafficking: in vitro and preclinical investigations.

BACKGROUND: The non-invasive imaging of leukocyte trafficking to assess inflammatory areas and monitor immunotherapy is currently generating great interest. There is a need to develop more robust cell labelling and imaging approaches to track living cells. Positron emission tomography (PET), a highly sensitive molecular imaging technique, allows precise signals to be produced from radiolabelled moieties. Here, we developed a novel leukocyte labelling approach with the PET radioisotope zirconium-89 (89Zr, half-life of 78.4 h). Experiments were carried out using human leukocytes, freshly isolated from whole human blood. RESULTS: The 89Zr-leukocyte labelling efficiency ranged from 46 to 87% after 30-60 min. Radioactivity concentrations of labelled cells were up to 0.28 MBq/1 million cells. Systemically administered 89Zr-labelled leukocytes produced high-contrast murine PET images at 1 h-5 days post injection. Murine biodistribution data showed that cells primarily distributed to the lung, liver, and spleen at 1 h post injection, and are then gradually trafficked to liver and spleen over 5 days. Histological analysis demonstrated that exogenously 89Zr-labelled human leukocytes were present in the lung, liver, and spleen at 1 h post injection. However, intravenously injected free [89Zr]Zr4+ ion showed retention only in the bone with no radioactivity in the lung at 5 days post injection, which implied good stability of radiolabelled leukocytes in vivo. CONCLUSIONS: Our study presents a stable and generic radiolabelling technique to track leukocytes with PET imaging and shows great potential for further applications in inflammatory cell and other types of cell trafficking studies.

Radiopharmaceutical for detecting PSMA - positive metastatic colon cancer: Matched-pair comparison of 18F-BF3-Cy3-ACUPA and 68Ga-PSMA PET/MRI.

Prostate-specific membrane antigen (PSMA) - based radiopharmaceuticals are promising for the evaluation of PSMA-positive non-prostate cancers. In this case study, 18F-BF3-Cy3-ACUPA and 68Ga-PSMA positron emission tomography/magnetic resonance imaging (PET/MRI) were compared in a patient with metastatic colon cancer. Both 18F-BF3-Cy3-ACUPA and 68Ga-PSMA PET/MRI showed biopsy-proven metastatic left external iliac adenopathy, highlighting the feasibility of PSMA uptake in PET/MRI of metastatic nodal disease from colon cancer. Along with imaging evaluation, PSMA-based radiopharmaceuticals may also be used as a surrogate imaging tracer for potential theranostic applications using alpha or beta emitters in the context of PSMA-directed radiopharmaceutical therapy in advanced and progressive colorectal cancer.

Small Molecule, Multimodal, [18F]-PET and Fluorescence Imaging Agent Targeting Prostate-Specific Membrane Antigen: First-in-Human Study.

BACKGROUND: A first-in-human study of [18F]-BF3-Cy3-ACUPA, a small-molecule imaging agent that can be unimolecularly both positron emitting and fluorescent, is conducted to determine its safety, biodistribution, radiation dosimetry, feasibility in tumor detection by preoperative positron emission tomography (PET), as well as its intraoperative fluorescence imaging utility in patients with prostate-specific membrane antigen positive (PSMA+) tumors. METHODS: Ten patients aged 66 ± 7 years received a 6.5 ± 3.2 mCi intravenous injection of [18F]-BF3-Cy3-ACUPA and underwent PET/computed tomography (CT) imaging. Radiation dosimetry of [18F]-BF3-Cy3-ACUPA, normal organ biodistribution, and tumor uptakes were examined. Two patients were prescheduled for radical prostatectomy (RP) with extended pelvic lymphadenectomy approximately 24 hours following [18F]-BF3-Cy3-ACUPA injection and imaging. Without reinjection, intraoperative fluorescence imaging was performed on freshly excised tissue during RP. Frozen sections of excised tissue during RP were submitted for confirmatory histopathology and multiphoton fluorescence and brightfield microscopy. RESULTS: Absorbed doses by organs including the kidneys and salivary glands were similar to 68Ga-PSMA-11 imaging. [18F]-BF3-Cy3-ACUPA physiologic radiotracer accumulation and urinary/biliary excretion closely resembled the distribution of other published PSMA tracers including [18F]-JK-PSMA-7, [18F]-PSMA-1007, [18F]-DCFPyL, and [18F]-DCFBC. 19F-BF3-Cy3-ACUPA was retained in PSMA+ cancer tissues in patients for at least 24 hours, allowing for intraoperative fluorescence assessment of the prostate and of the embedded prostate cancer without contrast reinjection. After 24 hours, the imaging agent mostly decayed or cleared from the blood pool. Preoperative PET and fluorescence imaging findings were confirmed with final histopathology and multiphoton microscopy. CONCLUSION: Our first-in-human results demonstrate that [18F]-BF3-Cy3-ACUPA is safe and feasible in humans. Larger trials with this PET tracer are expected to further define its capabilities and its clinical role in the management of PSMA+ tumors, especially in prostate cancer.

PET, image-guided HDAC inhibition of pediatric diffuse midline glioma improves survival in murine models.

Efforts at altering the dismal prognosis of pediatric midline gliomas focus on direct delivery strategies like convection-enhanced delivery (CED), where a cannula is implanted into tumor. Successful CED treatments require confirmation of tumor coverage, dosimetry, and longitudinal in vivo pharmacokinetic monitoring. These properties would be best determined clinically with image-guided dosimetry using theranostic agents. In this study, we combine CED with novel, molecular-grade positron emission tomography (PET) imaging and show how PETobinostat, a novel PET-imageable HDAC inhibitor, is effective against DIPG models. PET data reveal that CED has significant mouse-to-mouse variability; imaging is used to modulate CED infusions to maximize tumor saturation. The use of PET-guided CED results in survival prolongation in mouse models; imaging shows the need of CED to achieve high brain concentrations. This work demonstrates how personalized image-guided drug delivery may be useful in potentiating CED-based treatment algorithms and supports a foundation for clinical translation of PETobinostat.

A near-infrared probe for non-invasively monitoring cerebrospinal fluid flow by 18F-positron emitting tomography and fluorescence.

PURPOSE: Knowing the precise flow of cerebrospinal fluid (CSF) is important in the management of multiple neurological diseases. Technology for non-invasively quantifying CSF flow would allow for precise localization of injury and assist in evaluating the viability of certain devices placed in the central nervous system (CNS). METHODS: We describe a near-infrared fluorescent dye for accurately monitoring CSF flow by positron emission tomography (PET) and fluorescence. IR-783, a commercially available near-infrared dye, was chemically modified and radiolabeled with fluorine-18 to give [18F]-IR783-AMBF3. [18F]-IR783-AMBF3 was intrathecally injected into the rat models with normal and aberrant CSF flow and evaluated by the fluorescence and PET/MRI or PET/CT imaging modes. RESULTS: IR783-AMBF3 was clearly distributed in CSF-containing volumes by PET and fluorescence. We compared IR783-AMBF3 (fluorescent at 778/793 nm, ex/em) to a shorter-wavelength, fluorescein equivalent (fluorescent at 495/511 nm, ex/em). IR783-AMBF3 was superior for its ability to image through blood (hemorrhage) and for imaging CSF-flow, through-skin, in subdural-run lumboperitoneal shunts. IR783-AMBF3 was safe under the tested dosage both in vitro and in vivo. CONCLUSION: The superior imaging properties of IR783-AMBF3 could lead to enhanced accuracy in the treatment of patients and would assist surgeons in non-invasively diagnosing diseases of the CNS.

A lysosome specific, acidic-pH activated, near-infrared Bodipy fluorescent probe for noninvasive, long-term, in vivo tumor imaging.

Long-term, in vivo, fluorescent cell tracking probes are useful for understanding complex cellular processes including tissue regeneration, communication, development, invasion, and cancer metastasis. A near-infrared fluorescent, water-soluble probe is particularly important for studying these biological events and processes. Herein, a lysosome specific, near-infrared Bodipy probe with increased fluorescent intensity in the acidic, lysosome environment is reported. This Bodipy probe is packaged in a nanoparticle using DSPE-PEG2000. The resulting nanoparticle is intravenously delivered to a tumor xenograft, where the fluorescent Bodipy becomes useful for non-invasive, long-term, in vivo fluorescent tumor imaging for periods greater than 36 days. These long-term, in vitro and in vitro tracking data indicate that the described Bodipy nanoparticles hold great potential for monitoring biological processes.

Correction: An, F., et al. A Conjugate of Pentamethine Cyanine and 18F as a Positron Emission Tomography/Near-Infrared Fluorescence Probe for Multimodality Tumor Imaging. Int. J. Mol. Sci. 2017, 18, 1214.

The authors wish to make the following corrections to this paper [...].

An [18F]-Positron Emitting Fluorophore Allows Safe Evaluation of Small Molecule Distribution in the CSF, CSF Fistulas, and CNS Device Placement.

The small molecule fluorescein is commonly used to guide the repair of cerebral spinal fluid leaks (CSFLs) in the clinic. We modified fluorescein so that it is also visible by positron emission tomography (PET). This probe was used to quantitatively track the fast distribution of small molecules in the CSF of rats. We tested this probe in models relevant to the clinical diagnosis and treatment of central nervous system (CNS) diseases that affect CSF flow. In this study, fluorescein was radiolabeled with fluorine-18 to produce Fc-AMBF3. [18/19F]-Fc-AMBF3 was introduced at trace quantities (13.2 nmols, 100 µCi) intrathecally (between L5 and L6) in rats to observe the dynamic distribution and clearance of small molecules in the CSF by both [18F]-PET and fluorescence (FL) imaging. Murine models were used to demonstrate the following utilities of Fc-AMBF3: (1) utility in monitoring the spontaneous CSFL repair of a compression fracture of the cribriform plate and (2) utility in quantifying CSF flow velocity during neurosurgical lumboperitoneal shunt placement. Fc-AMBF3 clearly delineated CSF-containing volumes based on noninvasive PET imaging and in ex vivo FL histology. In vivo morbidity (n = 16 rats, <2.7 mg/kg, 77 times the PET dose) was not observed. The clearance of the contrast agent from the CNS was rapid and quantitative (t1/2 = 33.8 ± 0.6 min by FL and t1/2 = 26.0 ± 0.5 min by PET). Fc-AMBF3 was cleared from the CSF through the vasculature and/or lymphatic system that supplies the cribriform plate and the temporal bone. Fc-AMBF3 can be used to diagnose CSFLs, image CSFL repair, and determine the CSF flow velocity in the CNS or through lumboperitoneal shunts by PET/FL imaging. In conclusion, Fc-AMBF3 PET imaging has been demonstrated to safely and dynamically quantitate CSF flow, diagnose fistulas associated with the CSF space, and approximate the clearance of small molecules in the CSF.

A Fluorescent, [18F]-Positron-Emitting Agent for Imaging Prostate-Specific Membrane Antigen Allows Genetic Reporting in Adoptively Transferred, Genetically Modified Cells.

Clinical trials involving genome-edited cells are growing in popularity, where CAR-T immunotherapy and CRISPR/Cas9 editing are more recognized strategies. Genetic reporters are needed to localize the molecular events inside these cells in patients. Specifically, a nonimmunogenic genetic reporter is urgently needed as current reporters are immunogenic due to derivation from nonhuman sources. Prostate-specific membrane antigen (PSMA) is potentially nonimmunogenic due to its natural, low-level expression in select tissues (self-MHC display). PSMA overexpression on human prostate adenocarcinoma is also visible with excellent contrast. We exploit these properties in a transduced, two-component, Human-Derived, Genetic, Positron-emitting, and Fluorescent (HD-GPF) reporter system. Mechanistically analogous to the luciferase and luciferin reporter, PSMA is genetically encoded into non-PSMA expressing 8505C cells and tracked with ACUPA-Cy3-BF3, a single, systemically injected small molecule that delivers positron emitting fluoride (18F) and a fluorophore (Cy3) to report on cells expressing PSMA. PSMA-lentivirus transduced tissues become visible by Cy3 fluorescence, [18F]-positron emission tomography (PET), and γ-scintillated biodistribution. HD-GPF fluorescence is visible at subcellular resolution, while a reduced PET background is achieved in vivo, due to rapid ACUPA-Cy3-BF3 renal excretion. Co-transduction with luciferase and GFP show specific advantages over popular genetic reporters in advanced murine models including, a "mosaic" model of solid-tumor intratumoral heterogeneity and a survival model for observing postsurgical recurrence. We report an advanced genetic reporter that tracks genetically modified cells in entire animals and with subcellular resolution with PET and fluorescence, respectively. This reporter system is potentially nonimmunogenic and will therefore be useful in human studies. PSMA is a biomarker of prostate adenocarcinoma and ACUPA-Cy3-BF3 potential in radical prostatectomy is demonstrated.

Real-Time, in Vivo Correlation of Molecular Structure with Drug Distribution in the Brain Striatum Following Convection Enhanced Delivery.

The blood-brain barrier (BBB) represents a major obstacle in delivering therapeutics to brain lesions. Convection-enhanced delivery (CED), a method that bypasses the BBB through direct, cannula-mediated drug delivery, is one solution to maintaining increased, effective drug concentration at these lesions. CED was recently proven safe in a phase I clinical trial against diffuse intrinsic pontine glioma (DIPG), a childhood cancer. Unfortunately, the exact relationship between drug size, charge, and pharmacokinetic behavior in the brain parenchyma are difficult to observe in vivo. PET imaging of CED-delivered agents allows us to determine these relationships. In this study, we label different modifications of the PDGFRA inhibitor dasatinib with fluorine-18 or via a nanofiber-zirconium-89 system so that the effect of drug structure on post-CED behavior can accurately be tracked in vivo, via PET. Relatively unchanged bioactivity is confirmed in patient- and animal-model-derived cell lines of DIPG. In naïve mice, significant individual variability in CED drug clearance is observed, highlighting a need to accurately understand drug behavior during clinical translation. Generally, the half-life for a drug to clear from a CED site is short for low molecular weight dasatinib analogs that bare different charge; 1-3 (1, 32.2 min (95% CI: 27.7-37.8), 2, 44.8 min (27.3-80.8), and 3, 71.7 min (48.6-127.6) minutes) and is much longer for a dasatinib-nanofiber conjugate, 5, (42.8-57.0 days). Positron emission tomography allows us to accurately measure the effect of drug size and charge in monitoring real-time drug behavior in the brain parenchyma of live specimens.

18F-Positron Emitting/Trimethine Cyanine-Fluorescent Contrast for Image-Guided Prostate Cancer Management.

[18/19F]-4, an anionic GCPII/PSMA inhibitor for image-guided intervention in prostate cancer, is described. [19F]-4 is radiolabeled with a radiochemical yield that is ≥27% and a molar activity of 190 ± 50 mCi/µmol in a <1 h, one-step, aqueous isotopic exchange reaction. [19F]-4 allows PSMA expression to be imaged by fluorescence (FL) and [18F]-PET. PC3-PIP (PSMA-positive, EC50 = 6.74 ± 1.33 nM) cancers are specifically delineated in mice that bear 3 million (18 mg) PC3-PIP and PC3 (control, PSMA-negative) cells. Colocalization of [18/19F]-4 PET, fluorescence, scintillated biodistribution, and PSMA expression are observed.

18F-Radiolabeled Panobinostat Allows for Positron Emission Tomography Guided Delivery of a Histone Deacetylase Inhibitor.

Histone deacetylase (HDAC) inhibition is becoming an increasingly popular approach to treat cancer, as HDAC overexpression is common in many malignancies. The blood-brain barrier (BBB) prevents systemically delivered drugs from reaching brain at effective concentration, making small-molecule-HDAC inhibition in brain tumors particularly challenging. To circumvent the BBB, novel routes for administering therapeutics are being considered in the clinic, and a need exists for drugs whose deliveries can be directly imaged, so that effective delivery across the BBB can be monitored. We report chemistry for radiolabeling the HDAC inhibitor, panobinostat, with fluoride-18 (compound-1). Like panobinostat, compound 1 retains nanomolar efficacy in diffuse intrinsic pontine glioma (DIPG IV and XIII) cells (IC50 = 122 and 108 nM, respectively), with lesser activity against U87 glioma. With a favorable therapeutic ratio, 1 is highly selective to glioma and demonstrates considerably less toxicity toward healthy astrocyte controls (IC50 = 5265 nM). Compound 1 is stable in aqueous solution at physiological pH (>7 days, fetal bovine serum), and its delivery can be imaged by positron emission tomography (PET). Compound 1 is synthesized in two steps, and employs rapid, late-stage aqueous isotopic exchange 18F-radiochemistry. PET is used to image the in vivo delivery of [18F]-1 to the murine central nervous system via convection enhanced delivery.

A Murine Model for Quantitative, Real-Time Evaluation of Convection-Enhanced Delivery (RT-CED) Using an 18[F]-Positron Emitting, Fluorescent Derivative of Dasatinib.

The blood brain barrier can limit the efficacy of systemically delivered drugs in treating neurological malignancies; therefore, alternate routes of drug administration must be considered. The Abl-kinase inhibitor, dasatinib, is modified to give compound 1 ([18F]-1) so that 18F-positron emission tomography (PET) and fluorescent imaging can both be used to observe drug delivery to murine orthotopic glioma. In vitro Western blotting, binding studies (IC50 = 22 ± 5 nmol/L), and cell viability assays (IC50 = 46 ± 30 nmol/L) confirm nanomolar, in vitro effectiveness of [18F]-1, a dasatinib derivative that is visible by 18F-PET and fluorescence. [18F]-1 is used to image dynamic direct drug delivery via two different drug delivery techniques to orthotopic murine brainstem glioma (mBSG) bearing mice. Convection enhanced delivery (CED) delivers higher concentrations of drug to glioma-containing volumes versus systemic, tail-vein delivery. Accurate delivery and clearance data pertaining to dasatinib are observed, providing personalized information that is important in dosimetry and redosing. Cases of missed drug delivery are immediately recognized by PET/CT, allowing for prompt intervention in the case of missed delivery. Mol Cancer Ther; 16(12); 2902-12. ©2017 AACR.

An [18F]-Positron-Emitting, Fluorescent, Cerebrospinal Fluid Probe for Imaging Damage to the Brain and Spine.

Fluorescein is modified to bear 18F so that it can act as both a positron emitter, and a fluorophore, allowing detection by positron emission tomography (PET), scintillation, and fluorescent imaging (FL). [18F]-2 is injected into the intrathecal space of rats and used to observe the cerebrospinal fluid (CSF) that bathes the brain and spine. Injury in three different applications is visualized with [18F]-2: 1) detection of a 0.7 mm paranasal-sinus CSF leak (CSFL); 2) detection of 0.5 mm puncture damage to the thoracic spine (acute spinal cord injury); and 3) detection of intracerebral hemorrhage/edema because of traumatic brain injury. In all models, the location of injury is visualized with [18F]-2 at high resolution. [18F]-2 PET imaging may be a superior alternative to current clinical contrast myelography and 131I, 111In or 99mTc radionuclide cisternography. Like fluorescein, [18F]-2 may also have other uses in diagnostic or fluorescence guided medicine.

A Conjugate of Pentamethine Cyanine and 18F as a Positron Emission Tomography/Near-Infrared Fluorescence Probe for Multimodality Tumor Imaging.

The novel synthesis of a dual-modality, pentamethine cyanine (Cy5) fluorescent, 18F positron emission tomography (PET) imaging probe is reported. The probe shows a large extinction coefficient and large quantum yield in the biologically transparent, near-infrared window (650-900 nm) for in vivo fluorescent imaging. This fluorophore bears the isotope, 18F, giving a 18F-PET/near-infrared fluorescent (NIRF), bi-modal imaging probe, that combines the long-term stability of NIRF and the unlimited penetration depth of PET imaging. The bi-modal probe is labeled with 18F in a quick, one-step reaction, which is important in working with the rapid decay of 18F. The bi-modal probe bears a free carboxyl group, highlighting a PET/NIRF synthon that can be conjugated onto many advanced biomolecules for biomarker-specific in vivo dual-modal PET/NIR tumor imaging, confocal histology, and utility in multi-fluorophore, fluorescence-guided surgery. Its potential in vivo biocompatibility is explored in a quick proof-of-principal in vivo study. The dye is delivered to A549 xenograft flank-tumors to generate PET and NIRF signals at the tumor site. The tumor distribution is confirmed in ex vivo gamma counting and imaging. Pentamethine cyanine (Cy5) has the ability to preferentially accumulate in tumor xenografts. We substitute the PET/NIRF probe for Cy5, and explore this phenomenon.

Dual PET and Near-Infrared Fluorescence Imaging Probes as Tools for Imaging in Oncology.

OBJECTIVE: The purpose of this article is to summarize advances in PET fluorescence resolution, agent design, and preclinical imaging that make a growing case for clinical PET fluorescence imaging. CONCLUSION: Existing SPECT, PET, fluorescence, and MRI contrast imaging techniques are already deeply integrated into the management of cancer, from initial diagnosis to the observation and management of metastases. Combined positron-emitting fluorescent contrast agents can convey new or substantial benefits that improve on these proven clinical contrast agents.