Hitchhiking Nanoparticles: Mesenchymal Stem Cell-Mediated Delivery of Theranostic Nanoparticles

Nanotechnology has emerged as a promising solution to permanent elimination of cancer. However, nanoparticles themselves lack specificity to tumors. Due to enhanced migration to tumors, mesenchymal stem cells (MSCs) were suggested as cell-mediated delivery vehicles of nanoparticles. In this study, we have constructed a complex composed of photoluminescent quantum dots (QDs) and a photosensitizer chlorin e6 (Ce6) to obtain multifunctional nanoparticles, combining cancer diagnostic and therapeutic properties. QDs serve as energy donors-excited QDs transfer energy to the attached Ce6 via Förster resonance energy transfer, which in turn generates reactive oxygen species. Here, the physicochemical properties of the QD-Ce6 complex and singlet oxygen generation were measured, and the stability in protein-rich media was evaluated, showing that the complex remains the most stable in protein-free medium. In vitro studies on MSC and cancer cell response to the QD-Ce6 complex revealed the complex-loaded MSCs' potential to transport theranostic nanoparticles and induce cancer cell death. In vivo studies proved the therapeutic efficacy, as the survival of tumor-bearing mice was statistically significantly increased, while tumor progression and metastases were slowed down.

Cancer causes metabolic perturbations associated with reduced insulin-stimulated glucose uptake in peripheral tissues and impaired muscle microvascular perfusion

BACKGROUND

Redirecting glucose from skeletal muscle and adipose tissue, likely benefits the tumor's energy demand to support tumor growth, as cancer patients with type 2 diabetes have 30% increased mortality rates. The aim of this study was to elucidate tissue-specific contributions and molecular mechanisms underlying cancer-induced metabolic perturbations.

METHODS

Glucose uptake in skeletal muscle and white adipose tissue (WAT), as well as hepatic glucose production, were determined in control and Lewis lung carcinoma (LLC) tumor-bearing C57BL/6 mice using isotopic tracers. Skeletal muscle microvascular perfusion was analyzed via a real-time contrast-enhanced ultrasound technique. Finally, the role of fatty acid turnover on glycemic control was determined by treating tumor-bearing insulin-resistant mice with nicotinic acid or etomoxir.

RESULTS

LLC tumor-bearing mice displayed reduced insulin-induced blood-glucose-lowering and glucose intolerance, which was restored by etomoxir or nicotinic acid. Insulin-stimulated glucose uptake was 30-40% reduced in skeletal muscle and WAT of mice carrying large tumors. Despite compromised glucose uptake, tumor-bearing mice displayed upregulated insulin-stimulated phosphorylation of TBC1D4^Thr642 (+18%), AKT^Ser474 (+65%), and AKT^Thr309 (+86%) in muscle. Insulin caused a 70% increase in muscle microvascular perfusion in control mice, which was abolished in tumor-bearing mice. Additionally, tumor-bearing mice displayed increased (+45%) basal (not insulin-stimulated) hepatic glucose production.

CONCLUSIONS

Cancer can result in marked perturbations on at least six metabolically essential functions; i) insulin's blood-glucose-lowering effect, ii) glucose tolerance, iii) skeletal muscle and WAT insulin-stimulated glucose uptake, iv) intramyocellular insulin signaling, v) muscle microvascular perfusion, and vi) basal hepatic glucose production in mice. The mechanism causing cancer-induced insulin resistance may relate to fatty acid metabolism.

Tunable and amplified Raman gold nanoprobes for effective tracking (TARGET): in vivo sensing and imaging

We describe the development of a highly tunable, physiologically stable, and ultra-bright Raman probe, named as TARGET (Tunable and Amplified Raman Gold Nanoprobes for Effective Tracking), for in vitro and in vivo surface-enhanced Raman scattering (SERS) applications. The TARGET structure consists of a gold core inside a larger gold shell with a tunable interstitial gap similar to a "nanorattle" structure. The combination of galvanic replacement and the seed mediated growth method was employed to load Raman reporter molecules and subsequently close the pores to prevent leaking and degradation of reporters under physiologically extreme conditions. Precise tuning of the core-shell gap width, core size, and shell thickness allows us to modulate the plasmonic effect and achieve a maximum electric-field (E-field) intensity. The interstitial gap of TARGET nanoprobes can be designed to exhibit a plasmon absorption band at 785 nm, which is in resonance with the dye absorption maximum and lies in the "tissue optical window", resulting in ultra-bright SERS signals for in vivo studies. The results of in vivo measurements of TARGETs in laboratory mice illustrated the usefulness of these nanoprobes for medical sensing and imaging.

Noninvasive Evaluation of Metabolic Tumor Volume in Lewis Lung Carcinoma Tumor-Bearing C57BL/6 Mice with Micro-PET and the Radiotracers 18F-Alfatide and 18F-FDG: A Comparative Analysis

Purpose

To explore the value of a new simple lyophilized kit for labeling PRGD₂ peptide (¹⁸F-ALF-NOTA-PRGD₂, denoted as ¹⁸F-alfatide) in the determination of metabolic tumor volume (MTV) with micro-PET in lewis lung carcinoma (LLC) tumor-bearing C57BL/6 mice verified by pathologic examination and compared with those using ¹⁸F-fluorodeoxyglucose (FDG) PET.

Methods

All LLC tumor-bearing C57BL/6 mice underwent two attenuation-corrected whole-body micro-PET scans with the radiotracers ¹⁸F-alfatide and ¹⁸F-FDG within two days. ¹⁸F-alfatide metabolic tumor volume (V_RGD) and ¹⁸F-FDG metabolic tumor volume (V_FDG) were manually delineated slice by slice on PET images. Pathologic tumor volume (V_Path) was measured in vitro after the xenografts were removed.

Results

A total of 37 mice with NSCLC xenografts were enrolled and 33 of them underwent ¹⁸F-alfatide PET, and 35 of them underwent ¹⁸F-FDG PET and all underwent pathological examination. The mean ± standard deviation of V_Path, V_RGD, and V_FDG were 0.59±0.32 cm³ (range,0.13~1.64 cm³), 0.61±0.37 cm³ (range,0.15~1.86 cm³), and 1.24±0.53 cm³ (range,0.17~2.20 cm³), respectively. V_Path vs. V_RGD, V_Path vs. V_FDG, and V_RGD vs. V_FDG comparisons were t = -0.145, P = 0.885, t = -6.239, P<0.001, and t = -5.661, P<0.001, respectively. No significant difference was found between V_Path and V_RGD. V_FDG was much larger than V_RGD and V_Path. V_RGD seemed more approximate to the pathologic gross tumor volume. Furthermore, V_Path was more strongly correlated with V_RGD (R = 0.964,P<0.001) than with V_FDG (R = 0.584,P<0.001).

Conclusions

¹⁸F-alfatide PET provided a better estimation of gross tumor volume than ¹⁸F-FDG PET in LLC tumor-bearing C57BL/6 mice.

Mouse Hepatic Tumor Vascular Imaging by Experimental Selective Angiography

PURPOSE

Human hepatocellular carcinoma (HCC) has unique vascular features, which require selective imaging of hepatic arterial perfusion and portal venous perfusion with vascular catheterization for sufficient evaluation. Unlike in humans, vessels in mice are too small to catheterize, and the importance of separately imaging the feeding vessels of tumors is frequently overlooked in hepatic tumor models. The purpose of this study was to perform selective latex angiography in several mouse liver tumor models and assess their suitability.

MATERIALS AND METHODS

In several ectopic (Lewis lung carcinoma, B16/F10 melanoma cell lines) and spontaneous liver tumor (Albumin-Cre/MST1fl/fl/MST2fl/fl, Albumin-Cre/WW45fl/fl, and H-ras12V genetically modified mouse) models, the heart left ventricle and/or main portal vein of mice was punctured, and latex dye was infused to achieve selective latex arteriography and/or portography.

RESULTS

H-ras12V transgenic mice (a HCC and hepatic adenoma model) developed multiple liver nodules that displayed three different perfusion patterns (portal venous or hepatic artery perfusion predominant, mixed perfusion), indicating intra-tumoral vascular heterogeneity. Selective latex angiography revealed that the Lewis lung carcinoma implant model and the Albumin-Cre/WW45fl/fl model reproduced conventional angiography findings of human HCC. Specifically, these mice developed tumors with abundant feeding arteries but no portal venous perfusion.

CONCLUSION

Different hepatic tumor models showed different tumor vessel characteristics that influence the suitability of the model and that should be considered when designing translational experiments. Selective latex angiography applied to certain mouse tumor models (both ectopic and spontaneous) closely simulated typical characteristics of human HCC vascular imaging.

Enhanced in vivo antitumor efficacy of poorly soluble PDT agent, meso-tetraphenylporphine, in PEG-PE-based tumor-targeted immunomicelles

Poorly soluble photosensitizer, meso-tetraphenylporphine (TPP), was solubilized using the polymeric micelles prepared from polyethylene glycol-phosphatidyl ethanolamine conjugate (PEG-PE). TPP-loaded PEG-PE micelles have been additionally modified with tumor-specific monoclonal 2C5 antibody (mAb 2C5), which resulted in significantly improved anticancer effect of the drug under the PDT conditions against murine Lewis lung carcinoma (LLC) In vivo in female C57BL/6 mice. Fourteen days after tumor inoculation, the mice with more than 2 mm diameter tumors were given an intravenous injection of 1 mg/kg of free TPP or TPP loaded into control PEG-PE micelles or into mAb 2C5-PEG-PE tumor-targeted immunomicelles. Twenty-four hours after the administration, the animals were anesthetized, and tumor sites were illuminated with light (630 nm) for 12 min. Microscopic evaluation of tumor response was conducted in some mice 24 h after light irradiation, and tumor size was followed in the remaining animals for another 35 days. The attachment of mAb 2C5 to TPP-loaded immunomicelles provided the maximum level of tumor growth inhibition. Enhanced tumor accumulation of TPP-loaded mAb 2C5-PEG-PE-immunomicelles was confirmed by gamma-imaging studies. The modification of the TPP-loaded polymeric micelles with tumor-specific antibodies could be used as a general approach to enhance the efficacy of PDT.

Correlation of contrast-enhanced ultrasound with two distinct types of blood vessels for the assessment of angiogenesis in lewis lung carcinoma

OBJECTIVE

The aim of our study was to evaluate tumor angiogenesis in Lewis lung carcinoma (LLC) of mice using a contrast-enhanced ultrasound (CEUS) examination, and to determine the correlation of contrast-enhanced ultrasonographic parameters with different blood vessel markers of microvessel density (MVD).

MATERIALS AND METHODS

Subcutaneous Lewis lung carcinomas were established in 25 mice, which were evaluated by contrast-enhanced US using SonoVue (a second-generation US contrast agent). The results were recorded as digital video images and the time-intensity curves and hemodynamic parameters were analyzed. Pathological tumor specimens were obtained just after US examination. Tumor specimens were stained with hematoxylin and eosin (H & E) and expression of CD31 and CD34, the different endothelial cell markers, was determined by immunohistochemical straining. Then the relationship between the CEUS parameters and the level of MVD was analyzed.

RESULTS

Two distinct types of microvessels were identified in Lewis lung carcinoma: differentiated (CD34 +) and undifferentiated (CD31 +) vessels. A significant correlation was found between CEUS parameters and undifferentiated MVD (CD31 + vessels) in LLC (P < 0.05). There was a reverse correlation between the different MVDs.

CONCLUSION

The study showed that among the distinct types of vasculature (CD31 + and CD34 +) in Lewis lung carcinoma, the former correlated with the CEUS parameters. Therefore, CEUS using a second-generation US contrast agent may be useful for the evaluation of tumor angiogenesis of LLC of mice.

Positron emission tomography imaging of tumors expressing the human chemokine receptor CXCR4 in mice with the use of 64Cu-AMD3100

PURPOSE

Expression of CXCR4 in cancers has been correlated with poor prognosis and increased metastasis. Quantifying CXCR4 expression non-invasively might aid in prognostication and monitoring therapy. We evaluated a radiolabeled antagonist of CXCR4, ⁶⁴Cu-AMD3100, as a positron-emitting imaging agent.

PROCEDURES

CXCR4-transfected or non-transfected cell lines were injected into mice to form xenografts. Accumulation of ⁶⁴Cu-AMD3100 in tumors was analyzed by small-animal PET and biodistribution assays.

RESULTS

⁶⁴Cu-AMD3100 accumulated in CXCR4-expressing, but not CXCR4-negative, tumors. For CXCR4-expressing tumors, tumor-to-blood and tumor-to-muscle ratios were 23-41 and 50-59, respectively, depending on tumor type. Excess of unlabeled Cu-AMD3100 or AMD3100 significantly reduced ⁶⁴Cu-AMD3100 accumulation in CXCR4-expressing tumors. Human-absorbed dose calculations predicted a dose limit of 444 MBq.

CONCLUSIONS

CXCR4 can be imaged in tumors using ⁶⁴Cu-AMD3100. Dosimetry studies suggest that imaging in humans is feasible. We conclude that ⁶⁴Cu-AMD3100 should be investigated as a potential agent for imaging and quantifying CXCR4 in tumors.

Radioactive synthesis and biodistribution study of beta-elemene-99mTc(CO)3 conjugates

Beta-elemene, (5S,7R,10S)-(-)-(1-methyl-1-vinyl-2,4-diisopropenylcyclohexane), is an anticancer agent from traditional Chinese herbal medicine. Three novel (99m)Tc(CO)(3)-beta-elemene conjugates were synthesized successfully, and compared with beta-elemene exhibited improved water solubility. A biodistribution and micro single photon emission computed tomography image study showed there is a visible accumulation in Lewis lung cancer tumors.

Morphological study of early-stage lung cancer using synchrotron radiation

In the present study the feasibility of applying synchrotron radiation to the morphological study of early-stage lung cancer has been investigated. Lewis lung cancer was implanted and grown in a nude mouse for different periods, and imaged using phase-contrast synchrotron X-rays. Morphological differences were clearly shown between the normal lung and cancerous tissues at this early stage. Irregular and tortuous angiogenesis were found in the periphery region of the developing lung cancer. Results from this study indicate that synchrotron X-rays can be used for imaging cancer development and progression with minimal invasion.

The effect of electromagnetic field and local inductive hyperthermia on nonlinear dynamics of the growth of transplanted animal tumors

AIM

To examine the effects of electromagnetic field with amplified magnetic component and local inductive hyperthermia (IH) on nonlinear dynamics of the growth of animal tumors.

MATERIALS AND METHODS

Guerin carcinoma, Lewis lung carcinoma, sarcoma 45, Walker 256 carcinosarcoma and Pliss lymphosarcoma were studied. The animal tumors were exposed inside of loop aerial, 3 cm in diameter locally for 30 min. Parameters of electromagnetic irradiation (EI): frequency 40 MHz, magnetic intensity 72 A/m, electric intensity 200 V/m and the output power 50 W. The temperature measured by immersion of thermocouple inside the center of the tumor didn't exceed 38.5-39.5 degrees C. Nonlinear dynamics of the growth of animal tumors was analyzed by autocatalytic equation. The heterogeneity of ultrasonic image of the tumor was analyzed by Moran spatial autocorrelation.

RESULTS

The strongest inhibition effect under the influence of EI was in Pliss lymphosarcoma and sarcoma 45. The growth stimulation of animal tumors after EI was recorded in Walker 256 carcinosarcoma. The use of mild IH increased the blood flow in the tumor of Guerin carcinoma.

CONCLUSION

These results are important for clinical application because they testify the necessity of optimization of schemes for local EI during anticancer neoadjuvant therapy with the use of drugs or magnetic nanoparticles. The use of mild IH as a basis for the monotherapy of malignant tumors is not expedient.

Non-invasive screening of lung nodules in mice comparing a novel volumetric computed tomography with a clinical multislice CT

In vivo imaging of small animal models will play an increasingly important role in cancer research, as new imaging systems that employ non-invasive protocols and offer high-resolution capability become available. A flat-panel volumetric computed tomograph (fpvCT) was evaluated to determine if minimally invasive protocols can be used to provide the spatial resolution required for lung imaging in small animals. The detection of small pulmonary nodules in a Lewis carcinoma model was investigated, and fpvCT was compared with a multislice computed tomograph (MSCT). Five C57/BL6 mice with Lewis lung carcinoma were monitored with both modalities over two weeks. Sensitivity of the systems was measured by comparing the results with histology, and the incidence of first visualization of the tumors in the two systems was determined. Compared to MSCT, fpvCT proved its superior sensitivity in detection of lung nodules. Due to its isotropic resolution and a significant reduction of partial volume effects, early detection and reasonable determination of growth in very small tumors was only possible with fpvCT. fpvCT is a high-resolution imaging system that proved its ability to perform in vivo monitoring of a pulmonary lung tumor model in mice. This permits longitudinal investigations in small animals for cancer research.

Enhanced tumor visualization by gamma-scintigraphy with 111In-labeled polychelating-polymer-containing immunoliposomes

Here, we have prepared long-circulating PEGylated liposomes heavily loaded with 111In via the liposome-incorporated polylysine-based (PLL-based) polychelating amphiphilic polymer (PAP) and additionally modified with the monoclonal antibody 2C5 (mAb 2C5) possessing the nucleosome-restricted (NS-restricted) specificity and capable of specific recognition of a broad variety of live cancer cells via the cancer cell surface bound NSs. These liposomes have been tested as a tumor-specific contrast agent for the gamma-scintigraphic visualization of model tumors in mice. The tumor accumulation of mAb 2C5 modified liposomes prepared in this study was significantly (3-to-5-fold) higher than in the neighboring muscle tissue at all times after administration (6, 24, and 48 h) in mice bearing murine Lewis lung carcinoma (LLC) and human HT-29 tumors. The whole body direct gamma-imaging of LLC tumor bearing mice at different times has demonstrated the superior in vivo tumor accumulation of the targeted mAb 2C5 modified PAP-containing PEGylated liposomes compared to nontargeted liposomal control formulations, which resulted in better and faster tumor imaging as shown with LLC-bearing mice.

Noninvasive assessment of tumor vasculature response to radiation-mediated, vasculature-targeted therapy using quantified power Doppler sonography: implications for improvement of therapy schedules

OBJECTIVE

Stereotactic radiotherapy (ablative radiation) is a modality that holds considerable promise for effective treatment of intracranial and extracranial malignancies. Although tumor vasculature is relatively resistant to small fractionated doses of ionizing radiation, large ablative doses of ionizing radiation lead to effective demise of the tumor vasculature. The purpose of this study was (1) to noninvasively monitor and compare tumor physiologic parameters in response to ablative radiation treatments and (2) to use these noninvasive parameters to optimize the schedule of administration of radiation therapy.

METHODS

Lewis lung carcinoma tumors were implanted into C57BL/6 mice and treated with ablative radiation. The kinetics of change in physiologic parameters of a response to single-dose 20-Gy treatments was measured. Parameters studied included tumor blood flow, apoptosis, and proliferation rates. Serial tumor sections were stained to correlate noninvasive Doppler assessment of tumor blood flow with microvasculature histologic findings.

RESULTS

A single administration of 20 Gy led to an incomplete tumor vascular response, with subsequent recovery of tumor blood flow within 4 days after treatment. Sustained reduction of tumor blood flow by administering the successive ablative radiation treatment before tumor blood flow recovery led to a 3-fold tumor growth delay. The difference in tumor volumes at each measurement time point (every 2 days) was statistically significant (P=.016).

CONCLUSIONS

This study suggests a rational design of schedule optimization for radiation-mediated, vasculature-directed treatments guided by noninvasive assessment of tumor blood flow levels to ultimately improve the tumor response.

Antibiofouling Polymer-Coated Superparamagnetic Iron Oxide Nanoparticles as Potential Magnetic Resonance Contrast Agents for in Vivo Cancer Imaging

We report the fabrication and characterization of antifouling polymer-coated magnetic nanoparticles as nanoprobes for magnetic resonance (MR) contrast agents. Magnetite superparamagnetic iron oxide nanoparticles (SPION) were coated with the protein- or cell-resistant polymer, poly(TMSMA-r-PEGMA), to generate stable, protein-resistant MR probes. Coated magnetic nanoparticles synthesized using two different preparation methods (in situ and stepwise, respectively) were both well dispersed in PBS buffer at a variety of pH conditions (pH 1-10). In addition, dynamic light scattering data revealed that their sizes were not altered even after 24 h of incubation in 10% serum containing cell culture medium, indicative of a lack of protein adsorption on their surfaces. When the antibiofouling polymer-coated SPION were incubated with macrophage cells, uptake was significantly lower in comparison to that of the popular contrast agent, Feridex I.V., suggesting that the polymer-coated SPION can be long-circulated in plasma by escaping from uptake by the reticular endothelial system (RES) such as macrophages. Indeed, when the coated SPION were administered to tumor xenograft mice by intravenous injection, the tumor could be detected in T2-weighted MR images within 1 h as a result of the accumulation of the nanomagnets within the tumor site. Although the poly(TMSMA-r-PEGMA)-coated SPION do not have any targeting ligands on their surface, they are potentially useful for cancer diagnosis in vivo.

Comparative evaluation of FET and FDG for differentiating lung carcinoma from inflammation in mice

BACKGROUND

Clinical FDG/PET (2-deoxy-2-18F-fluoro-D-glucose/positron emission tomography) studies encounter difficulties in detecting early stage lung cancers. The aim of this study was to evaluate the ability of O-2-18F-fluoroethyl-L-tyrosine (FET) and FDG to differentiate between inflammation and lung carcinoma in mice.

MATERIALS AND METHODS

Sixty-four C57BL/6 mice were inoculated with 2x10(6) LLC1 lung carcinoma cells in the right hind flank on day 0 and were then injected with 0.1 mL turpentine in the left thigh muscle on day 3. The progress of inflammation and tumor in mice was longitudinally monitored by FDG/microPET. The biodistribution study, pharmacokinetic evaluation and whole-body autoradiography of FET and FDG were performed on day 8 after tumor inoculation.

RESULTS

The FDG uptakes in tumor and inflammatory lesions were 4.42-fold and 3.53-fold (n = 4) higher, respectively, than that in muscle at 90 min post-injection and the tumor-to-inflammation ratio was 1.25. For FET/microPET, the tumor uptake was 2.07-fold and 2.07-fold (n = 4) higher than those in muscle and inflammatory lesions at 90 min post-injection, respectively. The distribution half-life (t1/2,alpha) and the elimination half-life (t1/2,beta) of FET were 39 min and 205 min, respectively, in mice.

CONCLUSION

FDG delineated both tumor and inflammation, while FET accumulated in tumor to a significantly higher extent. Our results demonstrated the potential of FET to distinguish epidermoid lung carcinoma from inflammatory lesions in mice.

Synthesis and evaluation of 4-[18F]fluorothalidomide for the in vivo studies of angiogenesis

In this study, we prepared 2-(2,6-dioxopiperidin-3-yl)-4-[(18)F]fluoroisoindole-1,3-dione (4-[(18)F]fluorothalidomide; [(18)F]1) for the in vivo studies of angiogenesis. Radiochemical synthesis of [(18)F]1 was carried out by labeling 4-trimethylammoniumthalidomide trifluoromethanesulfonate with nBu(4)N[(18)F]F in dimethyl sulfoxide (DMSO), followed by reverse-phase HPLC purification. Decay-corrected radiochemical yield of [(18)F]1 was 50-60%, with an effective specific activity of 42-120 GBq/micromol (end of synthesis). Incubation of the radioligand with human umbilical vein endothelial cells (HUVEC-C; American Type Culture Collection) showed a time-dependent increase in the uptake of the radioligand, and the uptake was inhibited by 8-11% in the presence of 10 microM thalidomide, indicating nonspecific binding of the radioligand. Positron emission tomography (PET) images of mice implanted with tumors in their right flanks revealed a marked accumulation of radioactivity in the livers, kidneys and bladders of the mice, and brain uptake appeared at approximately 40 min after injection. However, no radioactivity uptake was detected in the implanted tumor. Thin-layer chromatography (TLC), HPLC and LC-MS analyses of mouse liver microsomal metabolites of [(18)F]1 and 1 with or without nicotinamide adenine dinucleotide phosphate (NADPH) clearly revealed that the radioligand did not go through metabolic activation but underwent nonenzymatic hydrolysis at physiological pH. Therefore, these results would appear to indicate that [(18)F]1 may not be suitable for the in vivo studies of angiogenesis at least in mice, although it was reported that thalidomide and/or its hydrolysis products may be responsible for its activity in humans.

Longitudinal evaluation of tumor metastasis by an FDG-microPet/microCT dual-imaging modality in a lung carcinoma-bearing mouse model

BACKGROUND

Histological methods are used to define the growth and response to various treatments of lung carcinoma in mice. The aim of the study was to evaluate a quantitative and 3D-tomographic microPET/microCT dual-image modality using 18F-fluorodeoxyglucose (FDG) to monitor the tumor progression in an experimental metastasis mouse model.

MATERIALS AND METHODS

Six normal mice were subjected to FDG-microPET/microCT image scan to present the normal thorax morphology. Twenty-one 8-week-old male C57BL/6 mice were inoculated with 1 x 10(6) Lewis lung carcinoma cells (LLC1) through the lateral tail vein. FDG-microPET/microCT scans were performed on days 0, 5, 9, 13 and 18 (n=6) to monitor the growth of the tumor. MicroPET and microCT images were further used to monitor the metastasis of the lung carcinoma to the liver. Fifteen mice were sacrificed for biodistribution on days 0, 5, 9, 13 and 18 after the inoculation of lung carcinoma cells.

RESULTS

The FDG-microPET/microCT dual-image modality showed that the growth of the tumor could be monitored longitudinally. The standard uptake value (SUV) of FDG increased from 0.63 +/- 0.05 on day 0 to 1.03 +/- 0.15 on day 18, reflecting the growth of the tumor in mice. The tumors located in the lung and liver could be clearly visualized by the fusion of microPET and microCT images, and further confirmed by whole-body autoradiography or H&E stain.

CONCLUSION

By FDG-microPET, the increase in SUV provided an alternative for assessing the growth of a tumor in vivo. Our results suggest that the growth progression of lung carcinoma can be identified using the FDG-microPET/microCT dual-image modality longitudinally in mice.

Potential applications of flat-panel volumetric CT in morphologic and functional small animal imaging

Noninvasive radiologic imaging has recently gained considerable interest in basic and preclinical research for monitoring disease progression and therapeutic efficacy. In this report, we introduce flat-panel volumetric computed tomography (fpVCT) as a powerful new tool for noninvasive imaging of different organ systems in preclinical research. The three-dimensional visualization that is achieved by isotropic high-resolution datasets is illustrated for the skeleton, chest, abdominal organs, and brain of mice. The high image quality of chest scans enables the visualization of small lung nodules in an orthotopic lung cancer model and the reliable imaging of therapy side effects such as lung fibrosis. Using contrast-enhanced scans, fpVCT displayed the vascular trees of the brain, liver, and kidney down to the subsegmental level. Functional application of fpVCT in dynamic contrast-enhanced scans of the rat brain delivered physiologically reliable data of perfusion and tissue blood volume. Beyond scanning of small animal models as demonstrated here, fpVCT provides the ability to image animals up to the size of primates.

Effects of anesthetic agents and fasting duration on 18F-FDG biodistribution and insulin levels in tumor-bearing mice

Small-animal PET has opened the way for imaging (18)F-FDG uptake in murine tumor models, but the need for anesthesia raises concern over its potential influence on (18)F-FDG kinetics. We thus investigated such effects on cultured cells and on tumor-bearing mice after short- and long-term fasting.

METHODS

Lewis lung carcinoma (LLC) cells and cardiomyoblasts were treated for 2 h with a 100 micromol/L concentration of xylazine, ketamine, xylazine plus ketamine (Xy/Ke), or pentobarbital and were measured for (18)F-FDG uptake. LLC tumor-bearing C57BL6 mice that had been kept fasting for either 4 or 20 h were injected with Xy/Ke, pentobarbital, or saline and were administered 1.8 MBq of (18)F-FDG 15 min later. Biodistribution studies and plasma glucose and insulin assays were performed 45 min after injection. Separate anesthetized and control mice underwent (18)F-FDG PET.

RESULTS

(18)F-FDG uptake in LLC cells was unaffected by anesthetic agents, whereas xylazine and ketamine caused a small increase of uptake in cardiomyoblasts. In mice kept fasting 4 h, Xy/Ke induced a marked elevation of (18)F-FDG activity (percentage injected dose [%ID]) in blood (6.8 +/- 0.9%ID/g vs. 1.1 +/- 0.6%ID/g) and kidneys while decreasing myocardial uptake (2.3 +/- 1.3%ID/g vs. 4.7 +/- 1.8%ID/g). Target-to-blood ratios were significantly reduced. Pentobarbital caused a moderate increase in blood activity (2.5 +/- 0.8%ID/g), decreased myocardial uptake (2.8 +/- 0.5%ID/g), and reduced target-to-blood ratios. PET images of mice kept fasting 4 h were consistent with the biodistribution data. Insulin levels were lower with Xy/Ke and higher with pentobarbital. In mice kept fasting 20 h, Xy/Ke and pentobarbital increased blood (18)F-FDG activity (5.5 +/- 2.2 and 4.9 +/- 0.9%ID/g vs. 2.4 +/- 0.3%ID/g) and reduced target-to-blood ratios, but these changes were substantially attenuated, compared with those in mice kept fasting 4 h. In addition, insulin levels were low and unaffected by anesthesia.

CONCLUSION

Xy/Ke anesthesia markedly elevates blood (18)F-FDG activity and reduces tumor uptake ratios through inhibition of insulin release in mice kept fasting 4 h, whereas pentobarbital induces a similar but less severe response through insulin resistance. These metabolic effects, however, are substantially attenuated after 20 h of fasting. Hence both the choice of anesthetic and the duration of fasting have important effects on (18)F-FDG kinetics and PET images of tumor-bearing mice and should be considered when such studies are performed.

Effects of extracellular Na+ and Ca2+ ions and Ca2+ channel modulators on the cell-associated activity of 99mTc-MIBI and 99mTc-tetrofosmin in tumour cells

Our aim was to determine whether the Ca2+ ion or cell membrane Ca2+ and Na+/Ca2+ ion transport systems are involved in maintaining the cell-associated activity of technetium-99m-hexakis-methoxy-isobutyl-isonitrile (99mTc-MIBI) and technetium-99m-ethylene-bis[bis(2-ethoxyethyl)phosphin] (99mTc-tetrofosmin) in tumour cell lines. The cell-associated activities of 99mTc-MIBI and 99mTc-tetrofosmin were assessed in various buffers, with or without Na+ and/or with different concentrations of Ca2+, in Lewi's murine lung cell carcinoma and human glioma cell lines. Different Ca2+ channel modulators, such as verapamil, flunarizine and 3,4-dichlorobenzamil (DCB), were used to assess the effect of Ca2+ channels on the cell-associated activity of 99mTc-MIBI and 99mTc-tetrofosmin. Despite significant differences between cell lines, the cell-associated activity of 99mTc-MIBI was higher in buffers without extracellular Ca2+ and Na+. The cell-associated activity of 99mTc-MIBI was significantly lower in all buffers containing high concentrations of Ca2+ in both cell lines. The cell-associated activity of Tc-tetrofosmin was also significantly higher in buffers without Ca2+, and was significantly decreased in buffers with high concentrations of Ca2+. All modulators significantly increased the cell-associated activity of 99mTc-MIBI in both cell lines in all buffers. All modulators increased the cell-associated activity of 99mTc-tetrofosmin, particularly in buffers containing Ca2+. The cell-associated activities of both 99mTc-MIBI and 99mTc-tetrofosmin may be dependent on verapamil-, flunarizine- and DCB-sensitive Ca2+ channels.

Preferential accumulation of (3)H-tetraphenylphosphonium in non-small cell lung carcinoma in mice: comparison with (99m)Tc-MIBI

We have previously shown enhanced accumulation of the delocalized lipophilic cation (11)C-triphenylmethylphosphonium in canine brain glioma, suggesting its potential use for tumor staging in humans using PET. Here, we extend our studies of phosphonium cations to nonbrain tumors and characterize the biodistribution and tumor specificity of (3)H-tetraphenylphosphonium ((3)H-TPP) in non-small cell lung carcinoma in mice.

METHODS

(3)H-TPP accumulation in isolated malignant lung nodules of the Lewis lung carcinoma (LLC) cell line, in LLC-bearing lung, and in control lung was measured at various intervals after inoculation. Tumor uptake and biodistribution of (3)H-TPP were compared with those of (99m)Tc-methoxyisobutylisonitrile (MIBI).

RESULTS

(3)H-TPP accumulation in LLC nodules at 14 d was significantly greater than that in controls, peaked at 21 d, and declined to lower values at 28 d after injection. At 21 d after injection, (3)H-TPP uptake in LLC nodules was greater than that in control lung tissue and in LLC-bearing lung tissue-by 549% and 230%, respectively-whereas (99m)Tc-MIBI nodule uptake was greater by 90% and 30%, respectively.

CONCLUSION

The high tumor accumulation and sensitivity to the phase of tumor development suggest the potential use of radiolabeled phosphonium analogs for in vivo tumor staging and as a tool for investigating tumor evolution.

Lung carcinoma imaging using a synthetic laminin derivative radioiodinated peptide YIGSR

The synthetic laminin pentapeptide tyrosyl-isoleucyl-glycyl-seryl-arginine (YIGSR) binds to a metastasis associated high-affinity laminin receptor. The aim of this study was to investigate if the radiolabeled peptide can be considered as a basis for a potential tumor-imaging radiopharmaceutical.

METHODS

Iodine-131-labeled YIGSR was injected in mice inoculated with Lewis Lung carcinoma, as well as in normal controls. The experimental animals were imaged on a gamma camera 10 hr after peptide administration. The same peptide was also labeled with 125I and administered to tumor-bearing and normal mice. At various time-points after peptide administration, the experimental animals were killed, and the radioactivity in the tumor, lung, liver and spleen was measured. Microscopic autoradiography was performed in histological sections of the same tissues.

RESULTS

The tumor and the spleen of tumor-bearing animals were imaged on a gamma camera. No significant blood-pool background was detected. No other organ except urinary bladder and thyroid was imaged in normal animals. The peptide was retained on tumor and spleen of tumor-bearing animals. Twenty-four hours after peptide administration, the tumor, lung, liver and spleen of animals with tumors contained significantly more radioactivity than the same tissues of equally treated normal controls. The radiolabeled peptide YIGSR was detected by microscopic autoradiography on the surface of certain tumor cells, but not on the surface of any normal cell.

CONCLUSION

Although extensive research is still required, the peptide YIGSR can be considered as a basis for the development of a receptor specific radiopharmaceutical useful for the in vivo estimation of the metastatic potential of tumors. This radiopharmaceutical may be helpful in staging and prognostic-related decisions on cancer treatment.