Frank I. Lin

The Fate and Toxicity of Raman-Active Silica-Gold Nanoparticles in Mice

Gold-core nanoparticles designed for imaging by Raman spectroscopy in patients are generally nontoxic in mice, causing only temporary liver inflammation when given intravenously. Minimal Toxicity of Nanoparticles for Raman Imaging Nanoparticles are just the right size to interact with molecules and cells. But how best to harness them as tools in the service of medicine? The authors of this paper have pursued one application: nanoparticles created to image specific cells and molecules from inside living animals—and eventually patients—via Raman spectroscopy, a method based on inelastic light scattering. Although the Raman effect is weak, a gold core inside the nanoparticles boosts the Raman signal enough so that it can be detected inside living tissue. To prepare the ground for use of these nanoparticles in imaging colorectal cancer in patients, Thakor et al. thoroughly tested their toxicity in mice. When introduced through the colon, these gold-core nanoparticles did not cross the gut lining into the body of the mice, a result that bodes well for their future as diagnostic and treatment vehicles for gut diseases. The authors first followed the fate of the silica-gold nanoparticles after the intravenous injection of a high dose into mice. Although their intravenous injection did cause temporary inflammation and some apoptosis in the liver 24 hours later, the nanoparticles were taken up by macrophages in the liver and spleen and eventually cleared from the body through the reticulo-endothelial system. A comprehensive survey of the mice revealed no ill effects of the nanoparticles on their general health or behavior. Their ECGs, blood pressure and heart rate were normal, and a panel of measurements of blood cells and chemistry revealed no effect of the particles. When the authors administered the nanoparticles into the colon, through the rectum, there was minimal evidence that the particles even passed into the animals’ circulation. Even the limited reaction in the liver seen after intravenous administration was absent and the particles were cleared within 5 minutes. The silica-gold nanoparticle tested in this paper can be coated with specific targeting molecules; the addition of one of these—a heptapeptide—did not increase the toxicity after treatment via the colon. These results set the stage for Raman spectroscopic imaging of these targeted, gold-core nanoparticles in diagnosis of colorectal cancer or other disease of hollow viscera. Attachment of premalignant cancer specific targeting groups to the particle would allow detection of early lesions with a endoscopic Raman probe, an approach that could be extended to other clinical situations. Raman spectroscopy is an optical imaging method that is based on the Raman effect, the inelastic scattering of a photon when energy is absorbed from light by a surface. Although Raman spectroscopy is widely used for chemical and molecular analysis, its clinical application has been hindered by the inherently weak nature of the Raman effect. Raman-silica-gold-nanoparticles (R-Si-Au-NPs) overcome this limitation by producing larger Raman signals through surface-enhanced Raman scattering. Because we are developing these particles for use as targeted molecular imaging agents, we examined the acute toxicity and biodistribution of core polyethylene glycol (PEG)–ylated R-Si-Au-NPs after different routes of administration in mice. After intravenous administration, PEG-R-Si-Au-NPs were removed from the circulation by macrophages in the liver and spleen (that is, the reticuloendothelial system). At 24 hours, PEG-R-Si-Au-NPs elicited a mild inflammatory response and an increase in oxidative stress in the liver, which subsided by 2 weeks after administration. No evidence of significant toxicity was observed by measuring clinical, histological, biochemical, or cardiovascular parameters for 2 weeks. Because we are designing targeted PEG-R-Si-Au-NPs (for example, PEG-R-Si-Au-NPs labeled with an affibody that binds specifically to the epidermal growth factor receptor) to detect colorectal cancer after administration into the bowel lumen, we tested the toxicity of the core nanoparticle after administration per rectum. We observed no significant bowel or systemic toxicity, and no PEG-R-Si-Au-NPs were detected systemically. Although additional studies are required to investigate the long-term effects of PEG-R-Si-Au-NPs and their toxicity when carrying the targeting moiety, the results presented here support the idea that PEG-R-Si-Au-NPs can be safely used in living subjects, especially when administered rectally.

Prospective comparison of combined 18F-FDG and 18F-NaF PET/CT vs. 18F-FDG PET/CT imaging for detection of malignancy

PurposeTypically, 18F-FDG PET/CT and 18F-NaF PET/CT scans are done as two separate studies on different days to allow sufficient time for the radiopharmaceutical from the first study to decay. This is inconvenient for the patients and exposes them to two doses of radiation from the CT component of the examinations. In the current study, we compared the clinical usefulness of a combined 18F-FDG/18F-NaF PET/CT scan with that of a separate 18F-FDG-only PET/CT scan.MethodsThere were 62 patients enrolled in this prospective trial. All had both an 18F-FDG-alone PET/CT scan and a combined 18F-FDG/18F-NaF PET/CT scan. Of the 62 patients, 53 (85%) received simultaneous tracer injections, while 9 (15%) received 18F-NaF subsequent to the initial 18F-FDG dose (average delay 2.2 h). Images were independently reviewed for PET findings by two Board-Certified nuclear medicine physicians, with discrepancies resolved by a third reader. Interpreters were instructed to only report findings that were concerning for malignancy. Reading the 18F-FDG-only scan first for half of the patients controlled for order bias.ResultsIn 15 of the 62 patients (24%) neither the 18F-FDG-only PET/CT scan nor the combined 18F-FDG/18F-NaF PET/CT scan identified malignancy. In the remaining 47 patients who had PET findings of malignancy, a greater number of lesions were detected in 16 of 47 patients (34%) using the combined 18F-FDG/18F-NaF PET/CT scan compared to the 18F-FDG-only PET/CT scan. In 2 of these 47 patients (4%), the 18F-FDG-only scan demonstrated soft tissue lesions that were not prospectively identified on the combined study. In 29 of these 47 patients (62%), the combined scan detected an equal number of lesions compared to the 18F-FDG-only scan. Overall, 60 of all the 62 patients (97%) showed an equal or greater number of lesions on the combined scan than on the 18F-FDG-only scan.ConclusionThe current study demonstrated that 18F-FDG and 18F-NaF can be combined in a single PET/CT scan by administering the two radiopharmaceuticals simultaneously or in sequence on the same day. In addition to patient convenience and reduced radiation exposure from the CT component, the combined 18F-FDG/18F-NaF PET/CT scan appeared to increase the sensitivity for detection of osseous lesions compared to the 18F-FDG-only PET/CT scan in the studied population.

Current concepts and future directions in radioimmunotherapy.

Radioimmunotherapy relies on the principles of immunotherapy, but expands the cytotoxic effects of the antibody by complexing it with a radiation-emitting particle. If we consider radioimmunotherapy as a step beyond immunotherapy of cancer, the step was prompted by the (relative) failure of the latter. The conventional way to explain the failure is a lack of intrinsic killing effect and a lack of penetration into poorly vascularized tumor masses. The addition of a radioactive label (usually a β-emitter) to the antibody would improve both. Radiation is lethal and the type of radiation used (beta rays) has a sufficient range to overcome the lack of antibody penetration. At present, the most successful (and FDA approved) radioimmunotherapy agents for lymphomas are anti-CD20 monoclonal antibodies. Rituximab (Rituxan(®)) is a chimeric antibody, used as a non-radioactive antibody and to pre-load the patient when Zevalin(®) is used. Zevalin(®) is the Yttrium-90 ((90)Y) or Indium-111 ((111)In) labeled form of Ibritumomab Tiuxetan. Bexxar(®) is the Iodine-131 ((131)I) labeled form of Tositumomab. Ibritumomab Tiuxetan and Tositumomab are murine anti-CD20 monoclonal antibodies, not chimeric antibodies. Promising research is being done to utilize radioimmunotherapy earlier in the treatment algorithm for lymphoma, including as initial, consolidation, and salvage therapies. However, despite more than 8 years since initial regulatory approval, radioimmunotherapy still has not achieved widespread use due to a combination of medical, scientific, logistic, and financial barriers. Other experimental uses for radioimmunotherapy include other solid tumors to treat infections. Optimization can potentially be done with pre-targeting and bi-specific antibodies. Alpha particle and Auger electron emitters show promise as future radioimmunotherapy agents but are mostly still in pre-clinical stages.

Functional imaging signature of patients presenting with polycythemia/paraganglioma syndromes

Pheochromocytoma/paraganglioma (PPGL) syndromes associated with polycythemia have previously been described in association with mutations in the von Hippel–Lindau gene. Recently, mutations in the prolyl hydroxylase gene (PHD) 1 and 2 and in the hypoxia-inducible factor 2 α (HIF2A) were also found to be associated with multiple and recurrent PPGL. Such patients also presented with PPGL and polycythemia, and later on, some presented with duodenal somatostatinoma. In additional patients presenting with PPGL and polycythemia, no further mutations have been discovered. Because the functional imaging signature of patients with PPGL–polycythemia syndromes is still unknown, and because these tumors (in most patients) are multiple, recurrent, and metastatic, the goal of our study was to assess the optimal imaging approach using 4 different PET radiopharmaceuticals and CT/MRI in these patients. Methods: Fourteen patients (10 women, 4 men) with confirmed PPGL and polycythemia prospectively underwent 68Ga-DOTATATE (13 patients), 18F-FDG (13 patients), 18F-fluorodihydroxyphenylalanine (18F-FDOPA) (14 patients), 18F-fluorodopamine (18F-FDA) (11 patients), and CT/MRI (14 patients). Detection rates of PPGL lesions were compared between all imaging studies and stratified between the underlying mutations. Results: 18F-FDOPA and 18F-FDA PET/CT showed similar combined lesion-based detection rates of 98.7% (95% confidence interval [CI], 92.7%–99.8%) and 98.3% (95% CI, 90.9%–99.7%), respectively. The detection rates for 68Ga-DOTATATE (35.3%; 95% CI, 25.0%–47.2%), 18F-FDG (42.3; 95% CI, 29.9%–55.8%), and CT/MRI (60.3%; 95% CI, 48.8%–70.7%) were significantly lower (P < 0.01), irrespective of the mutation status. Conclusion: 18F-FDOPA and 18F-FDA are superior to 18F-FDG, 68Ga-DOTATATE, and CT/MRI and should be the radiopharmaceuticals of choice in this rare group of patients.

Imaging of subclinical haemopoiesis after stem-cell transplantation in patients with haematological malignancies: A prospective pilot study

BACKGROUND Haemopoietic stem-cell transplantation (HSCT) eradicates host haemopoiesis before venous infusion of haemopoietic stem cells (HSCs). The pathway to cellular recovery has been difficult to study in human beings because of risks associated with interventions during aplasia. We investigated whether 18F-fluorothymidine (18F-FLT) imaging was safe during allogenic HSCT and allowed visualisation of early cellular proliferation and detection of patterns of cellular engraftment after HSCT. METHODS Eligible patients were aged 18-55 years, had high-risk haematological malignancies. All patients underwent myeloablation followed by HSCT. The imaging primary endpoint was detection of early subclinical engraftment after HSCT with 18F-FLT PET or CT. Imaging was done 1 day before and 5 or 9, and 28 days, and 1 year after HSCT. This study is registered with ClinicalTrials.gov, number NCT01338987. FINDINGS Between April 1, 2014, and Dec 31, 2015, 23 patients were enrolled and assessable for toxic effects after completing accrual. 18F-FLT was not associated with any adverse events or delayed engraftment. 18F-FLT imaging objectively identified subclinical bone-marrow recovery within 5 days of HSC infusion, which was up to 20 days before engraftment became clinically evident. Quantitatively, 18F-FLT intensity differed significantly between myeloablative infusion before HSCT and subclinical HSC recovery (p=0·00031). 18F-FLT biodistribution over time revealed a previously unknown path of cellular recovery of haemopoiesis in vivo that mirrored fetal ontogeny. INTERPRETATION 18F-FLT allowed quantification and tracking of subclinical bone-marrow repopulation in human beings and revealed new insights into the biology of HSC recovery after HSCT. FUNDING National Institutes of Health, Bens Run/Bens Gift, Albert and Elizabeth Tucker Foundation, Mex Frates Leukemia Fund, Jones Family fund, and Oklahoma Center for Adult Stem Cell Research.