Super-resolution application of generative adversarial network on brain time-of-flight MR angiography: image quality and diagnostic utility evaluation.

OBJECTIVES: To develop a generative adversarial network (GAN) model to improve image resolution of brain time-of-flight MR angiography (TOF-MRA) and to evaluate the image quality and diagnostic utility of the reconstructed images. METHODS: We included 180 patients who underwent 1-min low-resolution (LR) and 4-min high-resolution (routine) brain TOF-MRA scans. We used 50 patients' datasets for training, 12 for quantitative image quality evaluation, and the rest for diagnostic validation. We modified a pix2pix GAN to suit TOF-MRA datasets and fine-tuned GAN-related parameters, including loss functions. Maximum intensity projection images were generated and compared using multi-scale structural similarity (MS-SSIM) and information theoretic-based statistic similarity measure (ISSM) index. Two radiologists scored vessels' visibilities using a 5-point Likert scale. Finally, we evaluated sensitivities and specificities of GAN-MRA in depicting aneurysms, stenoses, and occlusions. RESULTS: The optimal model was achieved with a lambda of 1e5 and L1 + MS-SSIM loss. Image quality metrics for GAN-MRA were higher than those for LR-MRA (MS-SSIM, 0.87 vs. 0.73; ISSM, 0.60 vs. 0.35; p.adjusted < 0.001). Vessels' visibility of GAN-MRA was superior to LR-MRA (rater A, 4.18 vs. 2.53; rater B, 4.61 vs. 2.65; p.adjusted < 0.001). In depicting vascular abnormalities, GAN-MRA showed comparable sensitivities and specificities, with greater sensitivity for aneurysm detection by one rater (93% vs. 84%, p < 0.05). CONCLUSIONS: An optimized GAN could significantly improve the image quality and vessel visibility of low-resolution brain TOF-MRA with equivalent sensitivity and specificity in detecting aneurysms, stenoses, and occlusions. KEY POINTS: • GAN could significantly improve the image quality and vessel visualization of low-resolution brain MR angiography (MRA). • With optimally adjusted training parameters, the GAN model did not degrade diagnostic performance by generating substantial false positives or false negatives. • GAN could be a promising approach for obtaining higher resolution TOF-MRA from images scanned in a fraction of time.

Qualitative and Quantitative Assessment of Nonlocal Means Reconstruction Algorithm in a Flexible PET Scanner.

OBJECTIVE. Flexible PET (fxPET) was designed to fit existing MRI systems. The newly modified nonlocal means (NLM) algorithm is combined with the 3D dynamic row-action maximum likelihood algorithm (DRAMA). We investigated qualitative and quantitative acceptability of fxPET images reconstructed by modified NLM compared with whole-body (WB) PET/CT images and conventional 3D DRAMA reconstruction alone. MATERIALS AND METHODS. Fifty-nine patients with known or suspected malignancies underwent WB PET/CT scanning approximately 1 hour after the injection of 18F-FDG, after which they underwent fxPET scanning. Two readers rated the quality of fxPET images by consensus. Detection rate (the proportion of lesions found on PET), maximal standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), tumor-to-normal liver ratio (TNR), and background liver signal-to-noise ratio (SNR) were compared among the three datasets. RESULTS. Higher image quality was obtained by modified NLM reconstruction than by conventional reconstruction without statistical significance. The detection rate was comparable among three datasets. SUVmax was significantly higher, and MTV and TLG were significantly lower in the modified NLM dataset (p < 0.002) than in the other two datasets, with significantly positive correlations (p < 0.001; Spearman rank correlation coefficient, 0.87-0.99). The TNRs in modified NLM images were significantly larger than in the other datasets (p < 0.05). The background SNRs in modified NLM images were comparable with those in WB PET/CT images, and significantly higher than in the conventional fxPET images (p < 0.005). CONCLUSION. The modified NLM algorithm was clinically acceptable, yielding higher TNR and background SNR compared with conventional reconstruction. Image quality and the lesion detection rate were comparable in this population.

Prognostic Value of Quantitative Parameters of 18F-FDG PET/CT for Patients With Angiosarcoma.

OBJECTIVE. The purpose of this study was to evaluate quantitative parameters in 18F-FDG PET/CT in terms of correlation with histologic grade and overall survival in patients with angiosarcoma. MATERIALS AND METHODS. The cases of 16 patients with histologically confirmed angiosarcoma who had undergone pretreatment FDG PET/CT were retrospectively analyzed. Maximum standardized uptake value for the primary tumor (pSUVmax), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) for the whole body, tumor-to-blood ratio (TBR) for the primary tumor, and summed ratios of tumor-to-blood glycolytic activity for all lesions (whole-body TLG ratio) were calculated. Tumors were divided into high grade and low grade, according to the pathologic results. Correlations between these metabolic parameters and tumor grade were investigated. The prognostic value of these parameters and various clinicopathologic factors with respect to overall survival was assessed with the Cox proportional hazards regression model. RESULTS. Histopathologic examination revealed 10 high-grade and six low-grade tumors. Among the quantitative parameters, pSUVmax (p < 0.0001) and primary TBR (p = 0.0003) were significantly higher for high-grade tumors than for low-grade tumors. Ten patients died during follow-up (median survival time, 19.6 months). Higher pSUVmax (p = 0.040), MTV (p = 0.016), whole-body TLG (p = 0.010), primary TBR (p = 0.019), and whole-body TLG ratio (p = 0.007) correlated significantly with poorer overall survival. Single lesion at initial diagnosis (p = 0.0008) and performance of curative surgery (p = 0.0008) were strong favorable prognostic factors for overall survival, but histologic grade was not identified as a significant predictor. CONCLUSION. In angiosarcoma, high-grade tumors had significantly higher pSUVmax and primary TBR at FDG PET/CT. All quantitative parameters evaluated in this study were found to be significant prognostic factors for overall survival.

Radiolabeled Human Monoclonal Antibody 067-213 has the Potential for Noninvasive Quantification of CD73 Expression.

BACKGROUND: CD73 is an ectonucleotidase regulating extracellular adenosine concentration and plays an important role in adenosine-mediated immunosuppressive pathways. The efficacy of CD73-targeted therapy depends on the expression levels of CD73; therefore, monitoring CD73 status in cancer patients would provide helpful information for selection of patients who would benefit from CD73-targeted therapy. Here, we evaluated the ability of 111In-labeled antibody 067-213, which has high affinity for human CD73, to act as a noninvasive imaging probe. METHODS: Cell binding and competitive inhibition assays for 111In-labeled 067-213 were conducted using MIAPaCa-2 (high CD73 expression) and A431 (low CD73 expression) cells. For in vivo assessments, biodistribution and SPECT/CT studies were conducted in MIAPaCa-2 and A431 tumor-bearing mice. To estimate the absorbed dose in humans, biodistribution and SPECT/CT studies were conducted in healthy rats. RESULTS: 111In-labeled 067-213 bound to MIAPaCa-2 and A431 cells in a CD73-dependent manner and the affinity loss after 111In-labeling was limited. Biodistribution and SPECT/CT studies with 111In-labeled 067-213 in mice showed high uptake in MIAPaCa-2 tumors and lower uptake in A431 tumors. In rats, the probe did not show high uptake in normal organs, including endogenously CD73-expressing organs. The estimated absorbed doses in humans were reasonably low. CONCLUSIONS: 111In-labeled 067-213 showed CD73-expression-dependent tumor uptake and low uptake in normal organs and tissues. Radiolabeled 067-213 holds promise as an imaging probe for noninvasive evaluation of CD73 expression levels in patients. Our data encourage further clinical studies to clarify a role for CD73 monitoring in patients receiving CD73-targeted immune therapy.

Therapeutic efficacy evaluation of radioimmunotherapy with 90 Y-labeled anti-podoplanin antibody NZ-12 for mesothelioma.

Podoplanin is a type I transmembrane sialomucin-like glycoprotein that is highly expressed in malignant mesothelioma. The rat-human chimeric antibody NZ-12 has high affinity for human podoplanin and antibody-dependent cellular cytotoxicity and is applicable for radioimmunotherapy (RIT) to enhance the antitumor effect. In the present study, we evaluated the in vivo and in vitro properties of radiolabeled NZ-12 and the antitumor effect of RIT with 90 Y-labeled NZ-12 in an NCI-H226 (H226) malignant mesothelioma xenograft mouse model. 111 In-labeled NZ-12 bound specifically to H226 cells with high affinity, and accumulation was high in H226 tumors but low in major organs. RIT with 90 Y-labeled NZ-12 significantly suppressed tumor growth and prolonged survival without body weight loss and obvious adverse effects. Higher podoplanin expression levels were observed in human mesothelioma specimens, suggesting higher tumor accumulation of 90 Y-labeled NZ-12 in patients compared with the H226 tumor xenografts. Our findings suggest that 90 Y-labeled NZ-12 is a promising RIT agent as a new therapeutic option for malignant mesothelioma that warrants further clinical studies to evaluate the dosimetry and efficacy in patients.

Initial evaluation of PET/CT with 18 F-FSU-880 targeting prostate-specific membrane antigen in prostate cancer patients.

This first-in-man study was carried out to evaluate the safety, whole-body distribution, dose estimation, and lesion accumulation of 18 F-FSU-880, a newly developed probe targeting prostate-specific membrane antigen. Six prostate cancer patients with known metastatic lesions underwent serial whole-body PET/computed tomography (CT) with 18 F-FSU-880. Blood and urine were analyzed before and after PET/CT. Accumulation of 18 F-FSU-880 in organs and metastatic lesions in serial PET images were evaluated by measuring the standardized uptake values. From the biodistribution data, the organ doses and whole-body effective dose were calculated using OLINDA/EXM software was developed by Dr. Michael Stabin of Vanderbilt University, Nashville, Tennessee, USA. 18 F-FSU-880 PET/CT could be carried out without significant adverse effects. High physiological uptake was observed in the salivary/lachrymal glands and kidneys. The effective dose was calculated to be 0.921 × 10-2 mSv/MBq. Known metastatic lesions were clearly visualized with high image contrast that increased with time, except in 1 patient, whose bone metastases were well-controlled and inactive. The PET/CT with 18 F-FSU-880 could be carried out safely and could clearly visualize active metastatic lesions. The present results warrant further clinical studies with a larger number of cases to verify the clinical utility of 18 F-FSU-880 PET/CT in the management of prostate cancer patients.

Increased 14C-acetate accumulation in IDH-mutated human glioblastoma: implications for detecting IDH-mutated glioblastoma with 11C-acetate PET imaging.

PURPOSE: Recently, the potential value of isocitrate dehydrogenase (IDH) mutation as a prognostic marker in glioblastomas has been established. Glioblastomas are classified by their IDH mutation status under the 2016 WHO classification system. However, noninvasive diagnostic methods for the mutation status in glioblastoma patients have not been established so far. The purpose of this study was to evaluate the difference of acetate metabolism between in glioblastomas with wild-type IDH and in those with IDH mutation by comparing the uptake of 14C-acetate using genetically engineered glioblastoma cell lines in vitro and in vivo. METHODS: We established glioblastoma cells (U251) expressing IDH1 R132H and examined the cell uptake of [1-14C]acetate. Biodistribution studies and an autoradiographic study for U251 cell tumor-bearing mice (BALB/c-nu/nu) with or without the IDH1 mutation were performed 1 h after [1-14C]acetate administration. RESULTS: Significantly higher uptake of [1-14C]acetate was observed in U251/IDH1 R132H cells than in U251/IDH1 wild-type cells both in vitro (10.11 ± 0.94 vs. 4.26 ± 0.95%dose/mg, p = 0.0047) and in vivo (0.97 ± 0.14 vs. 0.66 ± 0.05%ID/g; p = 0.0037). Tumor-to-muscle ratios were also significantly higher in U251/IDH1 R132H tumors (3.36 ± 0.41 vs. 1.88 ± 0.59, p = 0.0030). The autoradiographic study shows the entirely higher radioactivity of the U251/IDH1 R132H tumor tissue section than that of the U251/IDH1 Wild-type tumor. CONCLUSIONS: In vitro and in vivo studies demonstrated that the uptake of radiolabeled acetate was significantly higher in IDH-mutated cells than in IDH-wild-type cells.

Enhanced intestinal 2-deoxy-2-[18F]fluoro-D-glucose uptake under metformin is not fully suppressed by loperamide.

OBJECTIVE: This study investigated whether the metformin (Met)-induced enhanced intestinal uptake of 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG) is reduced by loperamide, a long-acting anti-diarrheal agent. METHODS: Mean 18F-FDG uptake in the mouse small intestine and colon with Met exposure was compared with that in control mice. In the Met group, high-dose (1.0 mg/kg body weight) and low-dose (0.1 mg/kg body weight) loperamide were introduced, and 18F-FDG uptake in the small intestine and colon was compared with that of control mice administered high-dose loperamide. The percent injected dose of 18F-FDG per gram of tissue (%ID/g) in the extracted tissues was then determined. RESULTS: 18F-FDG uptake increased significantly in the small intestine (0.64±0.06 vs. 1.01±0.15, p=0.040) and, especially, the colon (0.46±0.13 vs. 2.16±0.51, p<0.001) after Met exposure. Neither high-dose nor low-dose loperamide significantly reduced 18F-FDG uptake in the small intestine (0.82±0.31 vs. 0.84±0.22, p=0.93 and 0.78±0.25 vs. 0.70±0.15, p=0.13, respectively) or colon (2.13±0.41 vs. 1.67±0.55, p=0.063 and 1.77±0.39 vs. 1.80±0.25, p=0.56, respectively). The colonic %ID/g was significantly higher in Met groups irrespective of loperamide introduction than in control group, whereas the significant difference in the small intestine was observed only between Met and control groups. CONCLUSION: Metformin increased 18F-FDG uptake in intestines especially in colon. Loperamide administration partially, but not sufficiently, suppresses the Met-induced increased colonic uptake of 18F-FDG.

Efficacy Evaluation of Combination Treatment Using Gemcitabine and Radioimmunotherapy with 90Y-Labeled Fully Human Anti-CD147 Monoclonal Antibody 059-053 in a BxPC-3 Xenograft Mouse Model of Refractory Pancreatic Cancer.

The poor prognosis of pancreatic cancer requires the development of more effective therapy. CD147 expresses in pancreatic cancer with high incidence and has a crucial role in invasion and metastasis. We developed a fully human monoclonal antibody (059-053) with high affinity for CD147. Here we evaluated the efficacy of combined treatment using radioimmunotherapy (RIT) with 90Y-labeled 059-053 and gemcitabine in a BxPC-3 xenograft mouse model. Expression of CD147 and matrix metalloproteinase-2 (MMP2) in BxPC-3 tumors was evaluated. In vitro and in vivo properties of 059-053 were evaluated using 111In-labeled 059-053 and a pancreatic cancer model BxPC-3. Tumor volume and body weight were periodically measured in mice receiving gemcitabine, RIT, and both RIT and gemcitabine (one cycle and two cycles). High expression of CD147 and MMP2 was observed in BxPC-3 tumors and suppressed by 059-053 injection. Radiolabeled 059-053 bound specifically to BxPC-3 cells and accumulated highly in BxPC-3 tumors but low in major organs. Combined treatment using RIT with gemcitabine (one cycle) significantly suppressed tumor growth and prolonged survival with tolerable toxicity. The two-cycle regimen had the highest anti-tumor effect, but was not tolerable. Combined treatment with 90Y-labeled 059-053 and gemcitabine is a promising therapeutic option for pancreatic cancer.

Synthesis and evaluation of 11C-labeled coumarin analog as an imaging probe for detecting monocarboxylate transporters expression.

Upregulated monocarboxylate transporters (MCTs) in tumors are considered diagnostic imaging targets. Herein, we synthesized the positron emission tomography probe candidates coumarin analogs 2 and 3, and showed 55 times higher affinity of 2 for MCTs than a representative MCT inhibitor. Whereas [11C]2 showed low tumor accumulation, probably due to adduct formation with plasma proteins, [11C]2 showed high initial brain uptake, suggesting that the scaffold of 2 has properties that are preferable in imaging probes for the astrocyte-neuron lactate shuttle. Although further optimization of 2 is required, our findings can be used to inform the development of MCT-targeted imaging agents.

Immunotargeting of Integrin α6ß4 for Single-Photon Emission Computed Tomography and Near-Infrared Fluorescence Imaging in a Pancreatic Cancer Model.

To explore suitable imaging probes for early and specific detection of pancreatic cancer, we demonstrated that α6ß4integrin is a good target and employed single-photon emission computed tomography (SPECT) or near-infrared (NIR) imaging for immunotargeting. Expression levels of α6ß4were examined by Western blotting and flow cytometry in certain human pancreatic cancer cell lines. The human cell line BxPC-3 was used for α6ß4-positive and a mouse cell line, A4, was used for negative counterpart. We labeled antibody against α6ß4with Indium-111 ((111)In) or indocyanine green (ICG). After injection of(111)In-labeled probe to tumor-bearing mice, biodistribution, SPECT, autoradiography (ARG), and immunohistochemical (IHC) studies were conducted. After administration of ICG-labeled probe, in vivo and ex vivo NIR imaging and fluorescence microscopy of tumors were performed. BxPC-3 tumor showed a higher radioligand binding in SPECT and higher fluorescence intensity as well as a delay in the probe washout in NIR imaging when compared to A4 tumor. The biodistribution profile of(111)In-labeled probe, ARG, and IHC confirmed the α6ß4specific binding of the probe. Here, we propose that α6ß4is a desirable target for the diagnosis of pancreatic cancer and that it could be detected by radionuclide imaging and NIR imaging using a radiolabeled or ICG-labeled α6ß4antibody.

The predictive value of preoperative 18F-fluorodeoxyglucose PET for postoperative recurrence in patients with localized primary gastrointestinal stromal tumour.

OBJECTIVES: To assess the potential value of preoperative 18F-FDG PET to predict postoperative recurrence of solitary localized primary gastrointestinal stromal tumour (GIST) after radical resection. METHODS: A total of 46 patients with primary GIST who received preoperative 18F-FDG PET and underwent complete resection without neoadjuvant therapy were retrospectively studied. PET findings, including ring-shaped uptake and intense uptake, were compared with Joensuu risk grades using Fisher's exact test. The prognostic value of the preoperative clinico-imaging variables-age ≥60 years, male, ring-shaped uptake, intense uptake, tumour size >5 cm, heterogeneous CT attenuation and lower gastrointestinal origin-and Joensuu high risk for recurrence-free survival was evaluated using log-rank test and multivariate Cox regression analysis. RESULTS: Ring-shaped uptake and intense uptake were significantly associated with Joensuu high risk. Univariate analysis showed that ring-shaped uptake, intense uptake, size >5 cm and Joensuu high risk were significantly associated with inferior recurrence-free survival. Multivariate analysis showed that ring-shaped uptake (P = 0.004) and Joensuu high risk (P = 0.021) were independent adverse prognostic factors of postoperative recurrence. CONCLUSIONS: Ring-shaped uptake on preoperative 18F-FDG PET may be a potential predictor of postoperative tumour recurrence of localized primary GISTs. KEY POINTS: • Clinical course of resectable solitary localized primary GISTs varies widely. • Ring-shaped uptake is an independent adverse prognostic factor of postoperative recurrence. • Preoperative 18 F-FDG PET may help predict postoperative recurrence of GISTs.

Clinical, Morphologic, and Pathologic Features Associated With Increased FDG Uptake in Schwannoma.

OBJECTIVE: The objective of this study was to investigate the clinical, morphologic, and pathologic features associated with increased 18F-FDG uptake in benign schwannomas. MATERIALS AND METHODS: Twenty-two schwannomas in 22 patients (age range, 25-81 years) who had FDG PET or PET/CT scans and subsequently underwent surgical re-section were retrospectively analyzed. The maximum standardized uptake value (SUVmax) was compared with patient age, sex, tumor location (gastrointestinal vs nongastrointestinal origin), tumor size, gross appearance, intratumoral cellularity, intratumoral infiltration of inflammatory cells, presence of peritumoral lymphoid cuffs, and expression status of glucose transporters 1 and 3 on tumor cells. RESULTS: The SUVmax of schwannomas ranged from 1.5 to 17.3 (median, 3.7). Significantly higher SUVmax was observed in gastrointestinal schwannomas (n = 4) compared with nongastrointestinal schwannomas (n = 18, p = 0.007) and in schwannomas with peritumoral lymphoid cuffs (n = 5) compared with those without peritumoral lymphoid cuffs (n = 17, p = 0.001). A significant correlation was seen between tumor location and the presence of peritumoral lymphoid cuffs (p < 0.001). Age, sex, tumor size, gross appearance, intratumoral cellularity, intratumoral inflammatory cell infiltration, and expression status of glucose transporters 1 and 3 on tumor cells had no significant correlation with SUVmax. CONCLUSION: Gastrointestinal schwannomas and schwannomas with peritumoral lymphoid cuffs may be associated with elevated FDG uptake. Knowledge of the features of schwannomas associated with increased uptake may be helpful to avoid misinterpretation of benign schwannomas as malignancy.

Passive and electro-assisted delivery of hydrogel nanoparticles in solid tumors, visualized by optical and magnetic resonance imaging in vivo.

The present study describes a development of nanohydrogel, loaded with QD(705) and manganese (QD(705)@Nanogel and QD(705)@Mn@Nanogel), and its passive and electro-assisted delivery in solid tumors, visualized by fluorescence imaging and magnetic resonance imaging (MRI) on colon cancer-grafted mice as a model. QD(705)@Nanogel was delivered passively predominantly into the tumor, which was visualized in vivo and ex vivo using fluorescent imaging. The fluorescence intensity increased gradually within 30 min after injection, reached a plateau between 30 min and 2 h, and decreased gradually to the baseline within 24 h. The fluorescence intensity in the tumor area was about 2.5 times higher than the background fluorescence. A very weak fluorescent signal was detected in the liver area, but not in the areas of the kidneys or bladder. This result was in contrast with our previous study, indicating that FITC@Mn@Nanogel did not enter into the tumor and was detected rapidly in the kidney and bladder after i.v. injection [J. Mater. Chem. B 2013, 1, 4932-4938]. We found that the embedding of a hard material (as QD) in nanohydrogel changes the physical properties of the soft material (decreases the size and negative charge and changes the shape) and alters its pharmacodynamics. Electroporation facilitated the delivery of the nanohydrogel in the tumor tissue, visualized by fluorescent imaging and MRI. Strong signal intensity was recorded in the tumor area shortly after the combined treatment (QD@Mn@Nanogel + electroporation), and it was observed even 48 h after the electroporation. The data demonstrate more effective penetration of the nanoparticles in the tumor due to the increased permeability of blood vessels at the electroporated area. There was no rupture of blood vessels after electroporation, and there were no artifacts in the images due to a bleeding.

Prognostic value of (18) F-fluoroazomycin arabinoside PET/CT in patients with advanced non-small-cell lung cancer.

This study evaluated the prognostic value of positron emission tomography/computed tomography (PET/CT) using (18) F-fluoroazomycin arabinoside (FAZA) in patients with advanced non-small-cell lung cancer (NSCLC) compared with (18) F-fluorodeoxyglucose (FDG). Thirty-eight patients with advanced NSCLC (stage III, 23 patients; stage IV, 15 patients) underwent FAZA and FDG PET/CT before treatment. The PET parameters (tumor-to-muscle ratio [T/M] at 1 and 2 h for FAZA, maximum standardized uptake value for FDG) in the primary lesion and lymph node (LN) metastasis and clinical parameters were compared concerning their effects on progression-free survival (PFS) and overall survival (OS). In our univariate analysis of all patients, clinical stage and FAZA T/M in LNs at 1 and 2 h were predictive of PFS (P = 0.021, 0.028, and 0.002, respectively). Multivariate analysis also indicated that clinical stage and FAZA T/M in LNs at 1 and 2 h were independent predictors of PFS. Subgroup analysis of chemoradiotherapy-treated stage III patients revealed that only FAZA T/M in LNs at 2 h was predictive of PFS (P = 0.025). The FDG PET/CT parameters were not predictive of PFS. No parameter was a significant predictor of OS. In patients with advanced NSCLC, FAZA uptake in LNs, but not in primary lesions, was predictive of treatment outcome. These results suggest the importance of characterization of LN metastases in advanced NSCLC patients.

γ-PARCEL: Control of Molecular Release Using γ-Rays.

We previously have developed the photoresponsive tetra-gel and nanoparticles for controlling the function of the encapsulated substance by UV irradiation. However, the penetration ability of the UV is not high enough. Here, we developed a radiation-responsive tetra-gel and nanoparticle based on γ-ray-responsive X-shaped polyethylene glycol (PEG) linker with a disulfide bond. The nanoparticle could retain small molecules and biomacromolecules. γ-Rays were used as a trigger signal because of their higher penetrating ability. This allowed a spatiotemporal release and control of the encapsulated substances from the nanoparticle in the deeper region, which is impossible by using light exposure (ultraviolet, visible, and near-infrared).

Development of the Fibronectin-Mimetic Peptide KSSPHSRN(SG)5RGDSP as a Novel Radioprobe for Molecular Imaging of the Cancer Biomarker α5ß1 Integrin.

α5ß1 Integrin, a fibronectin receptor, is becoming a pertinent therapeutic target and a promising prognostic biomarker for cancer patients. The aim of this study was to functionalize an α5ß1-specific fibronectin-mimetic peptide sequence KSSPHSRN(SG)5RGDSP (called PR_b) as a positron emission tomography (PET) probe. PR_b was modified by addition of a ß-alanine residue, conjugated with 2-S-(4-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA), and radiolabeled with (18)F based on the chelation of (18)F-aluminum fluoride. A control probe was produced by glycine to alanine substitution in the RGD motif of PR_b. Cell binding and blocking assays, autoradiographic evaluation of tissue binding and blocking, dynamic PET scans, and a biodistribution study were conducted using cell lines and murine tumor models with determined expression levels of α5ß1 and other related integrins. (18)F-PR_b was produced with a labeling yield of 22.3±1.9% based on (18)F-F(-), a radiochemical purity of >99%, and a specific activity of 30-70 GBq/µmol; it exhibited α5ß1-binding activity and specificity in vitro, ex vivo, and in vivo, and had a rapid blood clearance and a predominant renal excretion pathway. In vivo α5ß1-positive tumors could be clearly visualized by (18)F-PR_b PET imaging. Both imaging and biodistribution studies suggested higher uptake of (18)F-PR_b in α5ß1-positive tumors than in α5ß1-negative tumors and higher α5ß1-positive tumor uptake of (18)F-PR_b than the control probe. In contrast, there was no significant difference seen in the contralateral muscle uptake. A PET radioprobe, (18)F-PR_b, was developed de novo and potentially can be used for noninvasive detection of α5ß1 expression in tumors.

Evaluation of thermo-triggered drug release in intramuscular-transplanted tumors using thermosensitive polymer-modified liposomes and MRI.

Multi-modal thermo-sensitive polymer-modified liposomes (MTPLs) containing an anticancer drug, MR contrast agent, and fluorescent dye have been investigated as "theranostic" nanodevices that can be used to monitor drug delivery in cancer therapy. Here, we measured the physical characteristics of MTPLs, observed the dynamics of MTPLs in vivo, visualized heat-triggered drug release using MRI, and evaluated the treatment effects of the MTPLs with and without heating. In vitro experiments demonstrated that the MTPLs released drugs at temperatures above 41°C. In vivo MTPLs accumulated in tumor tissue, with the accumulation maximized for 4-12hours. MR signal in the tumor was significantly elevated after mild heating for 15 minutes, indicating release of the contrast agent from the MTPLs was facilitated by heat-triggering. Tumor size after treatment with MTPLs and heating was significantly smaller than those of the control groups. In conclusion, MTPLs with MRI are useful for low-invasive cancer theranostics.

Inhibition of radical reactions for an improved potassium tert-butoxide-promoted (11) C-methylation strategy for the synthesis of α-(11) C-methyl amino acids.

α-(11) C-Methyl amino acids are useful tools for biological imaging studies. However, a robust procedure for the labeling of amino acids has not yet been established. In this study, the (11) C-methylation of Schiff-base-activated α-amino acid derivatives has been optimized for the radiosynthesis of various α-(11) C-methyl amino acids. The benzophenone imine analog of methyl 2-amino butyrate was (11) C-methylated with [(11) C]methyl iodide following its initial deprotonation with potassium tert-butoxide (KOtBu). The use of an alternative base such as tetrabutylammonium fluoride, triethylamine, and 1,8-diazabicyclo[5.4.0]undec-7-ene did not result in the (11) C-methylated product. Furthermore, the KOtBu-promoted (11) C-methylation of the Schiff-base-activated amino acid analog was enhanced by the addition of 1,2,4,5-tetramethoxybenzene or 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and inhibited by the addition of 1,10-phenanthroline. These results suggest that inhibition of radical generation induced by KOtBu improves the α-(11) C-methylation of the Schiff-base-activated amino acids. The addition of a mixture of KOtBu and TEMPO to a solution of Schiff-base-activated amino acid ester and [(11) C]methyl iodide provided optimal results, and the tert-butyl ester and benzophenone imine groups could be readily hydrolyzed to give the desired α-(11) C-methyl amino acids with a high radiochemical conversion. This strategy could be readily applied to the synthesis of other α-(11) C-methyl amino acids.

Density-tunable conjugation of cyclic RGD ligands with polyion complex vesicles for the neovascular imaging of orthotopic glioblastomas.

Introduction of ligands into 100 nm scaled hollow capsules has great potential for diagnostic and therapeutic applications in drug delivery systems. Polyethylene glycol-conjugated (PEGylated) polyion complex vesicles (PICsomes) are promising hollow nano-capsules that can survive for long periods in the blood circulation and can be used to deliver water-soluble macromolecules to target tissues. In this study, cyclic RGD (cRGD) peptide, which is specifically recognized by αVß3 and αvß5 integrins that are expressed at high levels in the neovascular system, was conjugated onto the distal end of PEG strands on PICsomes for active neovascular targeting. Density-tunable cRGD-conjugation was achieved using PICsomes with definite fraction of end-functionalized PEG, to substitute 20, 40, and 100% of PEG distal end of the PICsomes to cRGD moieties. Compared with control-PICsomes without cRGD, cRGD-PICsomes exhibited increased uptake into human umbilical vein endothelial cells. Intravital confocal laser scanning microscopy revealed that the 40%-cRGD-PICsomes accumulated mainly in the tumor neovasculature and remained in the perivascular region even after 24 h. Furthermore, we prepared superparamagnetic iron oxide (SPIO)-loaded cRGD-PICsomes for magnetic resonance imaging (MRI) and successfully visualized the neovasculature in an orthotopic glioblastoma model, which suggests that SPIO-loaded cRGD-PICsomes might be useful as a MRI contrast reagent for imaging of the tumor microenvironment, including neovascular regions that overexpress αVß3 integrins.