Deepak Behera

Triblock copolymer coated iron oxide nanoparticle conjugate for tumor integrin targeting

A key challenge in developing nanoplatform-based molecular imaging is to achieve an optimal pharmacokinetic profile to allow sufficient targeting and to avoid rapid clearance by the reticuloendothelial system (RES). In the present study, iron oxide nanoparticles (IONPs) were coated with a PEGylated amphiphilic triblock copolymer, making them water soluble and function-extendable. These particles were then conjugated with a near-infrared fluorescent (NIRF) dye IRDye800 and cyclic Arginine-Glycine-Aspartic acid (RGD) containing peptide c(RGDyK) for integrin alpha(v)beta(3) targeting. In vitro binding assays confirmed the integrin-specific association between the RGD-particle adducts and U87MG glioblastoma cells. Successful tumor homing in vivo was perceived in a subcutaneous U87MG glioblastoma xenograft model by both magnetic resonance imaging (MRI) and NIRF imaging. Ex vivo histopathological studies also revealed low particle accumulation in the liver, which was attributed to their compact hydrodynamic size and PEGylated coating. In conclusion, we have developed a novel RGD-IONP conjugate with excellent tumor integrin targeting efficiency and specificity as well as limited RES uptake for molecular MRI.

A 18F-Labeled Saxitoxin Derivative for in Vivo PET-MR Imaging of Voltage-Gated Sodium Channel Expression Following Nerve Injury

Both chronic and neuropathic pain conditions are associated with increased expression of certain voltage-gated sodium ion channel (NaV) isoforms in peripheral sensory neurons. A method for noninvasive imaging of these channels could represent a powerful tool for investigating aberrant expression of NaV and its role in pain pathogenesis. Herein, we describe the synthesis and evaluation of a positron emission tomography (PET) radiotracer targeting NaVs, the design of which is based on the potent, NaV-selective inhibitor saxitoxin. Both autoradiography analysis of sciatic nerves excised from injured rats as well as whole animal PET-MR imaging demonstrate that a systemically administered [(18)F]-labeled saxitoxin derivative concentrates at the site of nerve injury, consistent with upregulated sodium channel expression following axotomy. This type of PET agent has potential use for serial monitoring of channel expression levels at injured nerves throughout wound healing and/or following drug treatment. Such information may be correlated with pain behavioral analyses to help shed light on the complex molecular processes that underlie pain sensation.

Evaluation of σ-1 Receptor Radioligand 18F-FTC-146 in Rats and Squirrel Monkeys Using PET

The noninvasive imaging of σ-1 receptors (S1Rs) could provide insight into their role in different diseases and lead to novel diagnostic/treatment strategies. The main objective of this study was to assess the S1R radiotracer 18F-FTC-146 in rats. Preliminary squirrel monkey imaging and human serum/liver microsome studies were performed to gain information about the potential of 18F-FTC-146 for eventual clinical translation. Methods: The distribution and stability of 18F-FTC-146 in rats were assessed via PET/CT, autoradiography, γ counting, and high-performance liquid chromatography (HPLC). Preliminary PET/MRI of squirrel monkey brain was conducted along with HPLC assessment of 18F-FTC-146 stability in monkey plasma and human serum. Results: Biodistribution studies showed that 18F-FTC-146 accumulated in S1R-rich rat organs, including the lungs, pancreas, spleen, and brain. Pretreatment with known S1R compounds, haloperidol, or BD1047, before radioligand administration, significantly attenuated 18F-FTC-146 accumulation in all rat brain regions by approximately 85% (P < 0.001), suggesting radiotracer specificity for S1Rs. Similarly, PET/CT and autoradiography results demonstrated accumulation of 18F-FTC-146 in rat brain regions known to contain S1Rs and that this uptake could be blocked by BD1047 pretreatment. Ex vivo analysis of 18F-FTC-146 in the brain showed that only intact radiotracer was present at 15, 30, and 60 min, whereas rapid metabolism of residual 18F-FTC-146 was observed in rat plasma. Preliminary monkey PET/MRI studies demonstrated specific accumulation of 18F-FTC-146 in the brain (mainly in cortical structures, cerebellum, and vermis) that could be attenuated by pretreatment with haloperidol. HPLC of monkey plasma suggested radioligand metabolism, whereas 18F-FTC-146 appeared to be stable in human serum. Finally, liver microsome studies revealed that 18F-FTC-146 has a longer half-life in human microsomes, compared with rodents. Conclusion: Together, these results indicate that 18F-FTC-146 is a promising tool for visualizing S1Rs in preclinical studies and that it has potential for mapping these sites in the human brain.

(18)F-FDG PET/MRI can be used to identify injured peripheral nerves in a model of neuropathic pain.

We demonstrated increased 18F-FDG uptake in injured peripheral nerves in a model of neuropathic pain using small-animal PET/MRI. Methods: A neuropathic pain model in rats was created by spared-nerve injury of the left sciatic nerve. Sham-operated rats without nerve injury were used as a control. The presence of pain was confirmed by testing for allodynia. Sequential small-animal 18F-FDG PET and MRI scans of the thighs were obtained and coregistered. Autoradiography was performed on harvested nerves and muscle. Results: The group with spared-nerve injury showed the development of allodynia in the operated limb (P < 0.001). Increased 18F-FDG uptake was observed on both PET/MRI (P < 0.001) and autoradiography (P < 0.005) in the operated nerve in this group. 18F-FDG uptake in the nerves correlated well with allodynia (ρ = −0.59; P < 0.024). Conclusion: Animals with neuropathic pain show increased 18F-FDG uptake in the affected nerve. Small-animal PET/MRI can be effectively used to localize 18F-FDG uptake in peripheral nerves.

In vivo USPIO Magnetic Resonance Imaging Shows That Minocycline Mitigates Macrophage Recruitment to a Peripheral Nerve Injury

BackgroundMinocycline has proven anti-nociceptive effects, but the mechanism by which minocycline delays the development of allodynia and hyperalgesia after peripheral nerve injury remains unclear. Inflammatory cells, in particular macrophages, are critical components of the response to nerve injury. Using ultrasmall superparamagnetic iron oxide-magnetic resonance imaging (USPIO-MRI) to monitor macrophage trafficking, the purpose of this project is to determine whether minocycline modulates macrophage trafficking to the site of nerve injury in vivo and, in turn, results in altered pain thresholds.ResultsAnimal experiments were approved by Stanford IACUC. A model of neuropathic pain was created using the Spared Nerve Injury (SNI) model that involves ligation of the left sciatic nerve in the left thigh of adult Sprague–Dawley rats. Animals with SNI and uninjured animals were then injected with/without USPIOs (300 μmol/kg IV) and with/without minocycline (50 mg/kg IP). Bilateral sciatic nerves were scanned with a volume coil in a 7 T magnet 7 days after USPIO administration. Fluid-sensitive MR images were obtained, and ROIs were placed on bilateral sciatic nerves to quantify signal intensity. Pain behavior modulation by minocycline was measured using the Von Frey filament test. Sciatic nerves were ultimately harvested at day 7, fixed in 10% buffered formalin and stained for the presence of iron oxide-laden macrophages. Behavioral measurements confirmed the presence of allodynia in the neuropathic pain model while the uninjured and minocycline-treated injured group had significantly higher paw withdrawal thresholds (p < 0.011). Decreased MR signal is observed in the SNI group that received USPIOs (3.3+/−0.5%) compared to the minocycline-treated SNI group that received USPIOs (15.2+/−4.5%) and minocycline-treated group that did not receive USPIOs (41.2+/−2.3%) (p < 0.04). Histology of harvested sciatic nerve specimens confirmed the presence USPIOs at the nerve injury site in the SNI group without minocycline treatment.ConclusionAnimals with neuropathic pain in the left hindpaw show increased trafficking of USPIO-laden macrophages to the site of sciatic nerve injury. Minocycline to retards the migration of macrophages to the nerve injury site, which may partly explain its anti-nociceptive effects. USPIO-MRI is an effective in vivo imaging tool to study the role of macrophages in the development of neuropathic pain.

Synthesis of ligand-functionalized water-soluble [18F]YF3 nanoparticles for PET imaging

We report a simple, efficient synthesis of novel (18)F-labeled imaging agents based on YF3 nanoparticles. Targeting ligands and antitumor drug molecules can be introduced onto the YF3 nanoparticles in a one-pot synthesis. The (18)F-labeling reaction proceeds in aqueous solutions at room temperature with excellent radiolabeling yields (>80%) in a very short time (5-10 min). (18)F-labeled YF3 nanoparticles displayed high stability in mouse and human serum, and their application for mapping lymph nodes in live rats after local injection has also been demonstrated.

Oral manganese as an MRI contrast agent for the detection of nociceptive activity

The ability of divalent manganese to enter neurons via calcium channels makes manganese an excellent MRI contrast agent for the imaging of nociception, the afferent neuronal encoding of pain perception. There is growing evidence that nociceptive neurons possess increased expression and activity of calcium channels, which would allow for the selective accumulation of manganese at these sites. In this study, we show that oral manganese chloride leads to increased enhancement of peripheral nerves involved in nociception on T1‐weighted MRI. Oral rather than intravenous administration was chosen for its potentially better safety profile, making it a better candidate for clinical translation with important applications, such as pain diagnosis, therapy and research. The spared nerve injury (SNI) model of neuropathic pain was used for the purposes of this study. SNI rats were given, sequentially, increasing amounts of manganese chloride (lowest, 2.29 mg/100 g weight; highest, 20.6 mg/100 g weight) with alanine and vitamin D3 by oral gavage. Compared with controls, SNI rats demonstrated increased signal‐to‐background ratios on T1‐weighted fast spin echo MRI, which was confirmed by and correlated strongly with spectrometry measurements of nerve manganese concentration. We also found the difference between SNI and control rats to be greater at 48 h than at 24 h after dosing, indicating increased manganese retention in addition to increased manganese uptake in nociceptive nerves. This study demonstrates that oral manganese is a viable method for the imaging of nerves associated with increased nociceptive activity. Copyright

Neuropathic pain mechanisms and imaging.

Molecular and cellular imaging of neuropathic pain, utilizing the myriad of receptors and inflammatory mediators involved in nociceptive activity, is a promising approach toward objectively identifying peripheral pain generators. Neuropathic conditions arise from injured and inflamed nerves, which have been shown to elaborate several molecular and cellular elements that give rise to the neuropathic phenotype and can be exploited for imaging purposes. As such, in vivo approaches to image neuropathic pain mechanisms include imaging voltage-gated sodium channels with radiolabeled saxitoxin, calcium signaling with manganese-enhanced magnetic resonance imaging, and inflammatory changes and nerve metabolism with (18)F-fluorodeoxyglucose. Imaging approaches exploiting other mediators of nociceptive activity, such as substance P (neurokinin-1) receptor, sigma-1 receptor, and macrophages, have shown promising early advances in animal models. By combining the sensitivity and specificity of molecular imaging with the high anatomical, spatial and contrast resolution afforded by computed tomography and MRI, radiologists can potentially identify sites of nerve injury or neuroinflammation that are implicated as peripheral pain drivers with greater accuracy and confidence. In addition to guiding therapy, these approaches will aid in new drug designs for analgesia and more individualized treatment options.

Postpartum ovarian vein thrombosis presenting as ureteral obstruction

Ovarian vein thrombosis (OVT) is a relatively uncommon but serious postpartum complication. Although infrequent, OVT may progress to involve the inferior vena cava, the renal vein or may cause sepsis and septic pulmonary embolism, all of which are potentially life-threatening. Clinical misdiagnosis is common, and, unfortunately, most affected women undergo laparotomy for possible appendicitis. We present an interesting case of OVT presenting as ureteral obstruction in a postpartum woman who was in her early 20s. Knowledge of this entity and clinical suspicion for its occurrence, in a puerperal patient with fever and abdominal pain not responding to antibiotics, should guide clinicians to appropriate diagnosis and treatment, avoiding misdiagnosis, unnecessary laparotomy and potential complications.

[18F]FDG PET/MRI of patients with chronic pain alters management: early experience

The chronic pain sufferer is currently faced with a lack of objective tools to identify the source of their pain. The overarching goal is to develop clinical [18F]FDG PET/MRI methods to more accurately localize sites of increased neuronal and muscular metabolism or inflammation as it relates to neurogenic sources of pain and to ultimately improve outcomes of chronic pain sufferers. The aims are to 1) correlate imaging findings with location of pain symptomology, 2) predict location of symptoms based on imaging findings alone and 3) to determine whether the imaging results affect current management decisions. Six patients suffering from chronic lower extremity neuropathic pain (4 complex regional pain syndrome, 1 chronic sciatica and 1 neuropathic pain) have been imaged with a PET/MRI system (time-of-flight PET; 3.0T bore) from mid thorax through the feet. All patients underwent PET/MR imaging one hour after a injection of 10mCi [18F]FDG. Two radiologists evaluated PET/MR images (one blinded and the other unblinded to patient exam/history). ROI analysis showed focal increased [18F]FDG uptake in affected nerves and muscle (approx 2-4 times more) over background tissue in various regions of the body in 5 of 6 patients at the site of greatest pain symptoms and other areas of the body (SUVmax of Target 0.9-4.2 vs. Background 0.2-1.2). The radiologist blind to the patient history/exam was able to correctly identify side/location of the symptoms in 5 out of 6 patients. Imaging results were reviewed with the referring physician, who then determined whether a modification in the management plan was needed: 1/6 no change, 2/6 mild modification (e.g., additional diagnostic test ordered) and 3/6 significant modification.