Magnetic resonance imaging of the pancreas and pancreatic tumors in a mouse orthotopic model of human cancer

Monitoring longitudinal disease progression in a novel murine Kit tumor model using high-field MRI

Animal models are an indispensable platform used in various research disciplines, enabling, for example, studies of basic biological mechanisms, pathological processes and new therapeutic interventions. In this study, we applied magnetic resonance imaging (MRI) to characterize the clinical picture of a novel N-ethyl-N-nitrosourea-induced Kit-mutant mouse in vivo. Seven C3H Kit^N824K/WT mutant animals each of both sexes and their littermates were monitored every other month for a period of twelve months. MRI relaxometry data of hematopoietic bone marrow and splenic tissue as well as high-resolution images of the gastrointestinal organs were acquired. Compared with controls, the mutants showed a dynamic change in the shape and volume of the cecum and enlarged Peyer´s patches were identified throughout the entire study. Mammary tumors were observed in the majority of mutant females and were first detected at eight months of age. Using relaxation measurements, a substantial decrease in longitudinal relaxation times in hematopoietic tissue was detected in mutants at one year of age. In contrast, transverse relaxation time of splenic tissue showed no differences between genotypes, except in two mutant mice, one of which had leukemia and the other hemangioma. In this study, in vivo MRI was used for the first time to thoroughly characterize the evolution of systemic manifestations of a novel Kit-induced tumor model and to document the observable organ-specific disease cascade.

Effective bowel motion reduction in mouse abdominal MRI using hyoscine butylbromide

PURPOSE

Bowel motion is a significant source of artifacts in mouse abdominal MRI. Fasting and administration of hyoscine butylbromide (BUSC) have been proposed for bowel motion reduction but with inconsistent results and limited efficacy assessments. Here, we evaluate these regimes for mouse abdominal MRI at high field.

METHODS

Thirty-two adult C57BL/6J mice were imaged on a 9.4T scanner with a FLASH sequence, acquired over 90 min with ~19 s temporal resolution. During MRI acquisition, 8 mice were injected with a low-dose and 8 mice with a high-dose bolus of BUSC (0.5 and 5 mg/kg, respectively). Eight mice were food deprived for 4.5-6.5 hours before MRI and another group of eight mice was injected with saline during MRI acquisition. Two expert readers reviewed the images and classified bowel motion, and quantitative voxel-wise analyses were performed for identification of moving regions. After defining the most effective protocol, high-resolution T₂ -weighted and diffusion-weighted images were acquired from 4 mice.

RESULTS

High-dose BUSC was the most effective protocol for bowel motion reduction, for up to 45 min. Fasting and saline protocols were not effective in suppressing bowel motion. High-resolution abdominal MRI clearly demonstrated improved image quality and ADC quantification with the high-dose BUSC protocol.

CONCLUSION

Our data show that BUSC administration is advantageous for abdominal MRI in the mouse. Specifically, it endows significant bowel motion reduction, with relatively short onset timings after injection (~8.5 min) and relatively long duration of the effect (~45 min). These features improve the quality of high-resolution images of the mouse abdomen.

Identification of variable stages in murine pancreatic tumors by a multiparametric approach employing hyperpolarized 13 C MRSI, 1 H diffusivity and 1 H T1 MRI

This study explored the usefulness of multiple quantitative MRI approaches to detect pancreatic ductal adenocarcinomas in two murine models, PAN-02 and KPC. Methods assayed included 1 H T1 and T2 measurements, quantitative diffusivity mapping, magnetization transfer (MT) 1 H MRI throughout the abdomen and hyperpolarized 13 C spectroscopic imaging. The progress of the disease was followed as a function of its development; studies were also conducted for wildtype control mice and for mice with induced mild acute pancreatitis. Customized methods developed for scanning the motion- and artifact-prone mice abdomens allowed us to obtain quality 1 H images for these targeted regions. Contrasts between tumors and surrounding tissues, however, were significantly different. Anatomical images, T2 maps and MT did not yield significant contrast unless tumors were large. By contrast, tumors showed statistically lower diffusivities than their surroundings (≈8.3 ± 0.4 x 10-4 for PAN-02 and ≈10.2 ± 0.6 x 10-4 for KPC vs 13 ± 1 x 10-3 mm2 s-1 for surroundings), longer T1 relaxation times (≈1.44 ± 0.05 for PAN-02 and ≈1.45 ± 0.05 for KPC vs 0.95 ± 0.10 seconds for surroundings) and significantly higher lactate/pyruvate ratios by hyperpolarized 13 C MR (0.53 ± 0.2 for PAN-02 and 0.78 ± 0.2 for KPC vs 0.11 ± 0.04 for control and 0.31 ± 0.04 for pancreatitis-bearing mice). Although the latter could also distinguish early-stage tumors from healthy animal controls, their response was similar to that in our pancreatitis model. Still, this ambiguity could be lifted using the 1 H-based reporters. If confirmed for other kinds of pancreatic tumors this means that these approaches, combined, can provide a route to an early detection of pancreatic cancer.

Non-invasive dynamic monitoring initiation and growth of pancreatic tumor in the LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre (KPC) transgenic mouse model

The LSL-Kras^G12D/+;LSL-Trp53^R172H/+;Pdx-1-Cre (KPC) mouse is one of the most widely used transgenic models to evaluate tumor characteristics and to develop novel therapies for pancreatic ductal adenocarcinoma (PDAC). There is no report of the effective systemic evaluation of longitudinal KPC tumor imitation and growth. Therefore, we aimed to characterize the initiation and progression of pancreatic cancer in KPC mice using longitudinal multiparametric magnetic resonance imaging (MRI) approaches and overall survival. Ten KPC mice were used to develop spontaneous PDAC and monitored by MRI. Tumor growth was evaluated using weekly acquired MRI data. The relationship between diffusion-weighted MRI (DW-MRI) imaging biomarkers (apparent diffusion coefficient - ADC) and tumor fibrosis measurement by pathological methods was assessed by Pearson correlation coefficient. Six KPC mice developed spontaneously pancreatic tumors at the age of 20.0 ± 2.9 weeks with a relatively short life span (6.8 ± 1.8 weeks). The tumors could be detected by MRI with a minimum diameter of 3.88 ± 1.18 mm (range, 2.18-5.20 mm), showing a rapid growth curve according to both the longest diameter (1.63 ± 0.52 mm/week) and tumor volume (148.77 ± 80.87 mm³)/week. Pathological results confirmed that the tumors display histopathological features of human pancreatic cancer. A strong correlation between ADC values and fibrosis measurements was observed (R = -0.825, P = .043). Our results show that the initiation and progression of pancreatic tumor in KPC mice can be evaluated by longitudinally non-invasive dynamic MRI approaches. The findings will be the fundamental KPC background data for developing novel therapeutic approaches, in particular for evaluation of response to novel treatments.

Evaluation of pancreatic tumor development in KPC mice using multi-parametric MRI

Background

Pancreatic ductal adenocarcinoma (PDA) is a fatal disease with very poor prognosis. Development of sensitive and noninvasive methods to monitor tumor progression in PDA is a critical and unmet need. Magnetic resonance imaging (MRI) can noninvasively provide information regarding underlying pathophysiological processes such as necrosis, inflammatory changes and fibrotic tissue deposition.

Methods

A genetically engineered KPC mouse model that recapitulates human PDA was used to characterize disease progression. MR measures of T₁ and T₂ relaxation times, magnetization transfer ratio (MTR), diffusion and chemical exchange saturation transfer were compared in two separate phases i.e. slow and rapid growth phase of tumor. Fibrotic tissue accumulation was assessed histologically using Masson’s trichrome staining. Pearson correlation coefficient (r) was computed to assess the relationship between the fibrotic tissue accumulation and different MR parameters.

Results

There was a negative correlation between amide proton transfer signal intensity and tumor volume (r = − 0.63, p = 0.003) in the slow growth phase of the tumor development. In the terminal stage of rapid growth phase of the tumor development MTR was strongly correlated with tumor volume (r = 0.62, p = 0.008). Finally, MTR was significantly correlated with % fibrosis (r = 0.87; p < 0.01), followed by moderate correlation between tumor volume (r = 0.42); T₁ (r = − 0.61), T₂ (r = − 0.61) and accumulation of fibrotic tissue.

Conclusions

Here we demonstrated, using multi-parametric MRI (mp-MRI), that MRI parameters changed with tumor progression in a mouse model of PDA. Use of mp-MRI may have the potential to monitor the dynamic changes of tumor microenvironment with increase in tumor size in the transgenic KPC mouse model of pancreatic tumor.

Electronic supplementary material

The online version of this article (10.1186/s40644-018-0172-6) contains supplementary material, which is available to authorized users.

Noninvasive characterization of pancreatic tumor mouse models using magnetic resonance imaging

The preclinical models of pancreatic adenocarcinoma provide an alternative means for determining the mechanisms of malignancy and possibilities for treatments, thus representing a resource of immense potential for cancer treatment in medicine. To evaluate different tumor models, quantifiable magnetic resonance imaging (MRI) techniques can play a significant role in identifying valuable in vivo biomarkers of tumor characteristics. We characterized three models of pancreatic cancer with multiparametric MRI techniques. Tumor stromal density of each tumor was measured using diffusion-weighted imaging and magnetization transfer (MT-MRI). Histologic measurement showed a similar trend with tumor fibrosis levels. Results indicated that MRI measurements can serve as a valuable tool in identifying and evaluating tumor characteristics.

Characterization of a rat orthotopic pancreatic head tumor model using three-dimensional and quantitative multi-parametric MRI

The purpose of this study was to investigate the reliability of 3D isotropic MRI and quantitative multi-parametric MRI characterization on an orthotopic pancreatic head tumor model in rats. 3D isotropic T₂ -weighted MRI was performed as a routine for tumor longitudinal follow-up and volume estimation. Common bile duct diameter was measured from 3D multiplanar reconstruction. Quantitative multi-parametric measurements including pixel-wise T₂ , T₁ relaxivity, apparent diffusion coefficient (ADC) and apparent diffusion kurtosis mapping were performed twice throughout tumor growth. Semi-quantitative and quantitative analyses based on an extended Tofts model were applied to region-of-interest-based dynamic contrast-enhanced imaging, followed by contrast ratio measurement on standard contrast-enhanced imaging. Moreover, low-level texture-based analysis was inspected for T₂ , T₁ , ADC and contrast ratio measurements. Results indicated that multi-parametric MRI showed good reproducibility for tumor characterization; the measurements were not affected by tumor growth. Tumor growth was further confirmed with histology examinations. To conclude, state-of-the-art clinical MRI techniques were translated to this preclinical tumor model with high reliability, and have paved the way for translational oncology studies on this tumor model.

In vivo biodistribution and passive accumulation of upconversion nanoparticles in colorectal cancer models via intraperitoneal injection

Cit-UCNPs after IP injection exhibited significantly different biological processes from those after IV injection. The passive-tumour targeting effectiveness of cit-UCNPs via the IP route was higher than that via the IV route.

Cathepsin S-cleavable, multi-block HPMA copolymers for improved SPECT/CT imaging of pancreatic cancer

This work continues our efforts to improve the diagnostic and radiotherapeutic effectiveness of nanomedicine platforms by developing approaches to reduce the non-target accumulation of these agents. Herein, we developed multi-block HPMA copolymers with backbones that are susceptible to cleavage by cathepsin S, a protease that is abundantly expressed in tissues of the mononuclear phagocyte system (MPS). Specifically, a bis-thiol terminated HPMA telechelic copolymer containing 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Three maleimide modified linkers with different sequences, including cathepsin S degradable oligopeptide, scramble oligopeptide and oligo ethylene glycol, were subsequently synthesized and used for the extension of the HPMA copolymers by thiol-maleimide click chemistry. All multi-block HPMA copolymers could be labeled by (177)Lu with high labeling efficiency and exhibited high serum stability. In vitro cleavage studies demonstrated highly selective and efficient cathepsin S mediated cleavage of the cathepsin S-susceptible multi-block HPMA copolymer. A modified multi-block HPMA copolymer series capable of Förster Resonance Energy Transfer (FRET) was utilized to investigate the rate of cleavage of the multi-block HPMA copolymers in monocyte-derived macrophages. Confocal imaging and flow cytometry studies revealed substantially higher rates of cleavage for the multi-block HPMA copolymers containing the cathepsin S-susceptible linker. The efficacy of the cathepsin S-cleavable multi-block HPMA copolymer was further examined using an in vivo model of pancreatic ductal adenocarcinoma. Based on the biodistribution and SPECT/CT studies, the copolymer extended with the cathepsin S susceptible linker exhibited significantly faster clearance and lower non-target retention without compromising tumor targeting. Overall, these results indicate that exploitation of the cathepsin S activity in MPS tissues can be utilized to substantially lower non-target accumulation, suggesting this is a promising approach for the development of diagnostic and radiotherapeutic nanomedicine platforms.

Gd(III)-Dithiolane Gold Nanoparticles for T1-Weighted Magnetic Resonance Imaging of the Pancreas

Pancreatic adenocarcinoma has a 5 year survival of approximately 3% and median survival of 6 months and is among the most dismal of prognoses in all of medicine. This poor prognosis is largely due to delayed diagnosis where patients remain asymptomatic until advanced disease is present. Therefore, techniques to allow early detection of pancreatic adenocarcinoma are desperately needed. Imaging of pancreatic tissue is notoriously difficult, and the development of new imaging techniques would impact our understanding of organ physiology and pathology with applications in disease diagnosis, staging, and longitudinal response to therapy in vivo. Magnetic resonance imaging (MRI) provides numerous advantages for these types of investigations; however, it is unable to delineate the pancreas due to low inherent contrast within this tissue type. To overcome this limitation, we have prepared a new Gd(III) contrast agent that accumulates in the pancreas and provides significant contrast enhancement by MR imaging. We describe the synthesis and characterization of a new dithiolane-Gd(III) complex and a straightforward and scalable approach for conjugation to a gold nanoparticle. We present data that show the nanoconjugates exhibit very high per particle values of r1 relaxivity at both low and high magnetic field strengths due to the high Gd(III) payload. We provide evidence of pancreatic tissue labeling that includes MR images, post-mortem biodistribution analysis, and pancreatic tissue evaluation of particle localization. Significant contrast enhancement was observed allowing clear identification of the pancreas with contrast-to-noise ratios exceeding 35:1.

Molecular Imaging of Pancreatic Cancer with Antibodies

Development of novel imaging probes for cancer diagnostics remains critical for early detection of disease, yet most imaging agents are hindered by suboptimal tumor accumulation. To overcome these limitations, researchers have adapted antibodies for imaging purposes. As cancerous malignancies express atypical patterns of cell surface proteins in comparison to noncancerous tissues, novel antibody-based imaging agents can be constructed to target individual cancer cells or surrounding vasculature. Using molecular imaging techniques, these agents may be utilized for detection of malignancies and monitoring of therapeutic response. Currently, there are several imaging modalities commonly employed for molecular imaging. These imaging modalities include positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance (MR) imaging, optical imaging (fluorescence and bioluminescence), and photoacoustic (PA) imaging. While antibody-based imaging agents may be employed for a broad range of diseases, this review focuses on the molecular imaging of pancreatic cancer, as there are limited resources for imaging and treatment of pancreatic malignancies. Additionally, pancreatic cancer remains the most lethal cancer with an overall 5-year survival rate of approximately 7%, despite significant advances in the imaging and treatment of many other cancers. In this review, we discuss recent advances in molecular imaging of pancreatic cancer using antibody-based imaging agents. This task is accomplished by summarizing the current progress in each type of molecular imaging modality described above. Also, several considerations for designing and synthesizing novel antibody-based imaging agents are discussed. Lastly, the future directions of antibody-based imaging agents are discussed, emphasizing the potential applications for personalized medicine.

Missed pancreatic ductal adenocarcinoma: Assessment of early imaging findings on prediagnostic magnetic resonance imaging

OBJECTIVE

To investigate the early imaging findings and growth rate of pancreatic ductal adenocarcinoma (PDAC), and to assess whether MR imaging detects early PDAC better than CT.

MATERIALS AND METHODS

The institutional review board approved this retrospective study and waived the requirement for informed consent. Twenty-two patients were included, and two radiologists, by consensus, assessed the presence of focal lesions, interruption of the main pancreatic duct (MPD), MPD dilatation, and pancreatitis, volume doubling time (VDT) of PDAC on prediagnostic MR imaging. Two other observers independently reviewed three image sets (CT images, unenhanced MR images, and unenhanced and contrast-enhanced MR images) for the detection of early PDAC. Paired Wilcoxon signed rank test and receiver operating characteristic (ROC) curve analysis were used for statistical analyses.

RESULTS

In 20 (90.9%) patients, prediagnostic MR exams showed abnormality, and all of them showed focal lesions on the first abnormal prediagnostic MR exams. Thirteen lesions (65%) showed no MPD interruption and one lesion (5%) was accompanied by pancreatitis. The mean VDT of PDAC was 151.7 days (range, 18.3-417.8 days). Diagnostic performance of unenhanced MR images (Az, 0.971-0.989) and combined unenhanced and contrast-enhanced MR images (Az, 0.956-0.963) was significantly better than that of CT images (Az, 0.565-0.583; p<0.01) for both observers,

CONCLUSION

The most common early imaging finding of PDAC on prediagnostic MR exams was a focal lesion with no MPD interruption with a mean volume doubling time of five months. MR imaging was superior to CT for the detection of early PDAC.

In vivo proton MR spectroscopy of pancreatic neuroendocrine tumors in a multiple endocrine neoplasia type 1 conditional knockout mouse model

PURPOSE

MR spectroscopy (MRS) can improve diagnosis and follow treatment in cancer. However, no study has yet reported application of in vivo (1)H-MRS in malignant pancreatic lesions. This study quantitatively determined whether in vivo (1)H-MRS on multiple endocrine neoplasia type 1 (Men1) conditional knockout (KO) mice and their wild type (WT) littermates could detect differences in total choline (tCho) levels between tumor and control pancreas.

METHODS

Relative tCho levels in pancreatic tumors or pancreata from KO and WT mice were determined using in vivo (1)H-MRS at 9.4 T. The levels of Cho-containing compounds were also quantified using in vitro (1)H-NMR on extracts of pancreatic tissues from KO and WT mice, respectively, and on extracts of pancreatic tissues from patients with pancreatic neuroendocrine tumors (PNETs).

RESULTS

tCho levels measured by in vivo (1)H-MRS were significantly higher in PNETs from KO mice compared to the normal pancreas from WT mice. The elevated choline-containing compounds were also identified in pancreatic tumors from KO mice and tissues from patients with PNETs via in vitro (1)H-NMR.

CONCLUSION

These results indicate the potential use of tCho levels estimated via in vivo (1)H-MRS in differentiating malignant pancreatic tumors from benign tumors.

Comparison of self-gated and prospectively triggered fast low angle shot (FLASH) sequences for contrast-enhanced magnetic resonance imaging of the liver at 9.4 T in a rat model of colorectal cancer metastases

OBJECTIVE

The aim of this study was to compare a retrospectively self-gated fast low angle shot sequence (RSG-FLASH) with a prospectively triggered fast low angle shot sequence (PT-FLASH) using an external trigger device for dynamic contrast-enhanced magnetic resonance imaging of the liver at 9.4 T in a rat model of colorectal cancer metastases.

MATERIALS AND METHODS

In 10 rats with hepatic metastases, we acquired an axial RSG-FLASH sequence through the liver. A FLASH sequence with prospective triggering (PT-FLASH) using an external trigger device was acquired at the same location with the same imaging parameters. After intravenous injection of 0.2 mmol/kg body weight of Gd-DTPA, alternating acquisitions of both sequences were performed at 4 consecutive time points.Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and lesion enhancement were obtained for liver tumors and parenchyma. In addition, we assessed the total acquisition times of the different imaging approaches for each acquisition, including triggering and gating. Two independent readers performed a qualitative evaluation of each sequence. Statistical analyses included paired t tests and Wilcoxon matched pairs signed rank tests.

RESULTS

No statistically significant differences in SNR, CNR, or lesion enhancement were observed. Qualitative assessments of the sequences were comparable. However, acquisition times of PT-FLASH were significantly longer (mean [SD], 160.6 [25.7] seconds; P < 0.0001) and markedly variable (minimum, 120 seconds; maximum, 209 seconds), whereas the RSG-FLASH approach demonstrated a constant mean (SD) acquisition time of 59.0 (0) seconds.

CONCLUSIONS

The RSG-FLASH and PT-FLASH sequences do not differ qualitatively or quantitatively regarding SNR, CNR, and lesion enhancement for magnetic resonance imaging of the liver in the rats at 9.4 T. However, the variability of acquisition times for the PT-FLASH sequences is a major factor of inconsistency, and we therefore consider this approach as inappropriate for dynamic contrast-enhanced studies with multiple-measurement time points. In contrast, the RSG-FLASH sequence represents a fast, consistent, and reproducible technique suitable for contrast-agent kinetic studies in experimental small-animal imaging of the abdomen.

A non-invasive method of quantifying pancreatic volume in mice using micro-MRI

In experimental models of pancreatic growth and recovery, changes in pancreatic size are assessed by euthanizing a large cohort of animals at varying time points and measuring organ mass. However, to ascertain this information in clinical practice, patients with pancreatic disorders routinely undergo non-invasive cross-sectional imaging of the pancreas using magnetic resonance imaging (MRI) or computed tomography (CT). The aim of the current study was to develop a thin-sliced, optimized sequence protocol using a high field MRI to accurately calculate pancreatic volumes in the most common experimental animal, the mouse. Using a 7 Telsa Bruker micro-MRI system, we performed abdominal imaging in whole-fixed mice in three standard planes: axial, sagittal, and coronal. The contour of the pancreas was traced using Vitrea software and then transformed into a 3-dimensional (3D) reconstruction, from which volumetric measurements were calculated. Images were optimized using heart perfusion-fixation, T1 sequence analysis, and 0.2 to 0.4 mm thick slices. As proof of principle, increases in pancreatic volume among mice of different ages correlated tightly with increasing body weight. In summary, this is the first study to measure pancreatic volumes in mice, using a high field 7 Tesla micro-MRI and a thin-sliced, optimized sequence protocol. We anticipate that micro-MRI will improve the ability to non-invasively quantify changes in pancreatic size and will dramatically reduce the number of animals required to serially assess pancreatic growth and recovery.

Metastatic pancreatic cancer is dependent on oncogenic Kras in mice

Pancreatic cancer is one of the deadliest human malignancies, and its prognosis has not improved over the past 40 years. Mouse models that spontaneously develop pancreatic adenocarcinoma and mimic the progression of the human disease are emerging as a new tool to investigate the basic biology of this disease and identify potential therapeutic targets. Here, we describe a new model of metastatic pancreatic adenocarcinoma based on pancreas-specific, inducible and reversible expression of an oncogenic form of Kras, together with pancreas-specific expression of a mutant form of the tumor suppressor p53. Using high-resolution magnetic resonance imaging to follow individual animals in longitudinal studies, we show that both primary and metastatic lesions depend on continuous Kras activity for their maintenance. However, re-activation of Kras* following prolonged inactivation leads to rapid tumor relapse, raising the concern that Kras*-resistance might eventually be acquired. Thus, our data identifies Kras* as a key oncogene in pancreatic cancer maintenance, but raises the possibility of acquired resistance should Kras inhibitors become available for use in pancreatic cancer.

Empirical mathematical model for dynamic manganese-enhanced MRI of the murine pancreas for assessment of β-cell function

Autoimmune ablation of pancreatic β-cells and alteration of its microvasculature may be a predictor of Type I diabetes development. A dynamic manganese-enhanced MRI (MEMRI) approach and an empirical mathematical model were developed to monitor whole pancreatic β-cell function and vasculature modifications in mice. Normal and streptozotocin-induced diabetic FVB/N mice were imaged on a 9.4T MRI system using a 3D magnetization prepared rapid acquisition gradient echo pulse sequence to characterize low dose manganese kinetics in the pancreas head, body and tail. Average signal enhancement in the pancreas (head, body, and tail) as a function of time was fit by a novel empirical mathematical model characterizing contrast uptake/washout rates and yielding parameters describing peak signal, initial slope, and initial area under the curve. Signal enhancement from glucose-induced manganese uptake was fit by a linear function. The results demonstrated that the diabetic pancreatic tail had a significantly lower contrast uptake rate, smaller initial slope/initial area under the curve, and a smaller rate of Mn uptake following glucose activation (p<0.05) compared to the normal pancreatic tail. These observations parallel known patterns of β-cell loss and alteration in supportive vasculature associated with diabetes. Dynamic MEMRI is a promising technique for assessing β-cell functionality and vascular perfusion with potential applications for monitoring diabetes progression and/or therapy.

Targeted imaging of breast tumor progression and therapeutic response in a human uMUC-1 expressing transgenic mouse model

The ability to monitor breast cancer initiation and progression on the molecular level would provide an effective tool for early diagnosis and therapy. In the present study, we focused on the underglycosylated MUC-1 tumor antigen (uMUC-1), which is directly linked to tumor progression from pre-malignancy to advanced malignancy in breast cancer and has been identified as the independent predictor of local recurrence and tumor response to chemotherapy. We investigated whether changes in uMUC-1 expression during tumor development and therapeutic intervention could be monitored non-invasively using molecular imaging approach with the uMUC-1-specific contrast agent (MN-EPPT) detectable by magnetic resonance and fluorescence optical imaging. This was done in mice that express human uMUC-1 tumor antigen (MMT mice) and develop spontaneous mammary carcinoma in a stage-wise fashion. After the injection of MN-EPPT there was a significant reduction in average T2 relaxation times of the mammary fat pad between pre-malignancy and cancer. In addition, T2 relaxation times were already altered at pre-malignant state in these mice compared to non-tumor bearing mice. This indicated that targeting uMUC-1 could be useful for detecting pre-malignant transformation in the mammary fat pad. We also probed changes in uMUC-1 expression with MN-EPPT during therapy with doxorubicin (Dox). We observed that tumor delta-T2s were significantly reduced by treatment with Dox indicating lower accumulation of MN-EPPT. This correlated with a lower level of MUC-1 expression in the Dox-treated tumors, as confirmed by immunoblotting. Our study could provide a very sensitive molecular imaging approach for monitoring tumor progression and therapeutic response.

Magnetic resonance imaging for pancreatic ductal adenocarcinomas induced by N-nitrosobis (2-oxopropyl) amine in Syrian golden hamsters

OBJECTIVES

This study aimed to study magnetic resonance imaging (MRI) findings of pancreatic ductal adenocarcinomas (PDAs) induced by N-nitrosobis (2-oxopropyl) amine (BOP) in Syrian hamsters.

METHODS

A total of 101 female hamsters, 8 weeks old, were randomized into 3 groups. They were randomized into a BOP-treated group (n = 80; with weekly subcutaneous injections of BOP [10 mg/kg body weight] for 7 consecutive weeks), a saline-treated group (n = 16), and an untreated group (n = 5). Hamsters underwent abdominal MRI on 1.5-T MR scanners with a dedicated animal radiofrequency coil. Findings of the tumor from the MRI were compared those from histology.

RESULTS

Pancreata in the saline-treated and in the untreated groups were normal. In the BOP-treated group, there were 23 and 31 BOP-induced PDAs on macroscopy and microscopy, respectively. Of the PDAs detected on macroscopy, 65.2% were depicted on MRI. As early as 13 and 19 weeks after the first injection of BOP, PDAs in hamsters were found on histology and MRI, respectively. Moreover, the tumor volume on MRI was correlated with the tumor weights excised (r = 0.96, P = 0.000, n = 15).

CONCLUSIONS

N-nitrosobis (2-oxopropyl) amine successfully induced PDAs in hamsters. Magnetic resonance imaging has the ability to detect healthy pancreas and PDAs in hamsters and has the potential to monitor the development of PDAs.

Tumour size measurement in a mouse model using high resolution MRI

BACKGROUND

Animal models are frequently used to assess new treatment methods in cancer research. MRI offers a non-invasive in vivo monitoring of tumour tissue and thus allows longitudinal measurements of treatment effects, without the need for large cohorts of animals. Tumour size is an important biomarker of the disease development, but to our knowledge, MRI based size measurements have not yet been verified for small tumours (10-2-10-1 g). The aim of this study was to assess the accuracy of MRI based tumour size measurements of small tumours on mice.

METHODS

2D and 3D T2-weighted RARE images of tumour bearing mice were acquired in vivo using a 7 T dedicated animal MR system. For the 3D images the acquired image resolution was varied. The images were exported to a PC workstation where the tumour mass was determined assuming a density of 1 g/cm(3), using an in-house developed tool for segmentation and delineation. The resulting data were compared to the weight of the resected tumours after sacrifice of the animal using regression analysis.

RESULTS

Strong correlations were demonstrated between MRI- and necropsy determined masses. In general, 3D acquisition was not a prerequisite for high accuracy. However, it was slightly more accurate than 2D when small (<0.2 g) tumours were assessed for inter- and intraobserver variation. In 3D images, the voxel sizes could be increased from 1603 μm(3) to 2403 μm(3) without affecting the results significantly, thus reducing acquisition time substantially.

CONCLUSIONS

2D MRI was sufficient for accurate tumour size measurement, except for small tumours (<0.2 g) where 3D acquisition was necessary to reduce interobserver variation. Acquisition times between 15 and 50 minutes, depending on tumour size, were sufficient for accurate tumour volume measurement. Hence, it is possible to include further MR investigations of the tumour, such as tissue perfusion, diffusion or metabolic composition in the same MR session.

Visualization of mouse pancreas architecture using MR microscopy

Pancreatic diseases, which include diabetes, pancreatitis, and pancreatic cancer, are often difficult to detect and/or stage, contributing to a reduced quality of life and lifespan for patients. Thus, there is need for a technology that can visualize tissue changes in the pancreas, improve understanding of disease progression, and facilitate earlier detection in the human population. Because of low spatial resolution, current clinical magnetic resonance imaging (MRI) at low field strength has yet to fully visualize the exocrine, endocrine, vascular, and stromal components of the pancreas. We used high field strength magnetic resonance microscopy (μMRI) to image mouse pancreas ex vivo without contrast agents at high spatial resolution. We analyzed the resulting high-resolution images using volume rendering to resolve components in the pancreas, including acini, islets, blood vessels, and extracellular matrix. Locations and dimensions of pancreatic components as seen in three-dimensional μMRI were compared with histological images, and good correspondence was found. Future longitudinal studies could expand on the use of in vivo μMRI in mouse models of pancreatic diseases. Capturing three-dimensional structural changes through μMRI could help to identify early cellular and tissue changes associated with pancreatic disease, serving as a mode of improved detection in the clinic for endocrine and exocrine pathologies.

Targeted nanogels: a versatile platform for drug delivery to tumors

Although nanoparticle-based drug delivery formulations can improve the effectiveness and safety of certain anticancer drugs, many drugs, due to their chemical composition, are unsuitable for nanoparticle loading. Here, we describe a targeted nanogel drug delivery platform that can (i) encapsulate a wide range of drug chemotypes, including biological, small molecule, and cytotoxic agents; (ii) display targeting ligands and polymeric coatings on the surface; (iii) enhance drug retention within the nanogel core after photo-cross-linking; and (iv) retain therapeutic activity after lyophilization allowing for long-term storage. For therapeutic studies, we used integrin αvβ3-targeted lipid-coated nanogels with cross-linked human serum albumin in the core for carrying therapeutic cargoes. These particles exhibited potent activity in tumor cell viability assays with drugs of distinct chemotype, including paclitaxel, docetaxel, bortezomib, 17-AAG, sorafenib, sunitinib, bosutinib, and dasatinib. Treatment of orthotopic breast and pancreas tumors in mice with taxane-loaded nanogels produced a 15-fold improvement in antitumor activity relative to Abraxane by blocking both primary tumor growth and spontaneous metastasis. With a modifiable surface and core, the lipid-coated nanogel represents a platform technology that can be easily adapted for specific drug delivery applications to treat a wide range of malignant diseases.

In vivo imaging of pancreatic tumours and liver metastases using 7 Tesla MRI in a murine orthotopic pancreatic cancer model and a liver metastases model

Background

Pancreatic cancer is the fourth leading cause of tumour death in the western world. However, appropriate tumour models are scarce. Here we present a syngeneic murine pancreatic cancer model using 7 Tesla MRI and evaluate its clinical relevance and applicability.

Methods

6606PDA murine pancreatic cancer cells were orthotopically injected into the pancreatic head. Liver metastases were induced through splenic injection. Animals were analyzed by MRI three and five weeks following injection. Tumours were detected using T2-weighted high resolution sequences. Tumour volumes were determined by callipers and MRI. Liver metastases were analyzed using gadolinium-EOB-DTPA and T1-weighted 3D-Flash sequences. Tumour blood flow was measured using low molecular gadobutrol and high molecular gadolinium-DTPA.

Results

MRI handling and applicability was similar to human systems, resolution as low as 0.1 mm. After 5 weeks tumour volumes differed significantly (p < 0.01) when comparing calliper measurments (n = 5, mean 1065 mm³+/-243 mm³) with MRI (mean 918 mm³+/-193 mm³) with MRI being more precise. Histology (n = 5) confirmed MRI tumour measurements (mean size MRI 38.5 mm²+/-22.8 mm² versus 32.6 mm²+/-22.6 mm² (histology), p < 0,0004) with differences due to fixation and processing of specimens. After splenic injection all mice developed liver metastases with a mean of 8 metastases and a mean volume of 173.8 mm³+/-56.7 mm³ after 5 weeks. Lymphnodes were also easily identified. Tumour accumulation of gadobutrol was significantly (p < 0.05) higher than gadolinium-DTPA. All imaging experiments could be done repeatedly to comply with the 3R-principle thus reducing the number of experimental animals.

Conclusions

This model permits monitoring of tumour growth and metastasis formation in longitudinal non-invasive high-resolution MR studies including using contrast agents comparable to human pancreatic cancer. This multidisciplinary environment enables radiologists, surgeons and physicians to further improve translational research and therapies of pancreatic cancer.

Oncogenic Ras/Src cooperativity in pancreatic neoplasia

Pancreas cancer is one of the most lethal malignancies and is characterized by activating mutations of Kras, present in 95% of patients. More than 60% of pancreatic cancers also display increased c-Src activity, which is associated with poor prognosis. Although loss of tumor suppressor function (for example, p16, p53, Smad4) combined with oncogenic Kras signaling has been shown to accelerate pancreatic duct carcinogenesis, it is unclear whether elevated Src activity contributes to Kras-dependent tumorigenesis or is simply a biomarker of disease progression. Here, we demonstrate that in the context of oncogenic Kras, activation of c-Src through deletion of C-terminal Src kinase (CSK) results in the development of invasive pancreatic ductal adenocarcinoma (PDA) by 5-8 weeks. In contrast, deletion of CSK alone fails to induce neoplasia, while oncogenic Kras expression yields PDA at low frequency after a latency of 12 months. Analysis of cell lines derived from Ras/Src-induced PDA's indicates that oncogenic Ras/Src cooperativity may lead to genomic instability, yet Ras/Src-driven tumor cells remain dependent on Src signaling and as such, Src inhibition suppresses growth of Ras/Src-driven tumors. These findings demonstrate that oncogenic Ras/Src cooperate to accelerate PDA onset and support further studies of Src-directed therapies in pancreatic cancer.

Imaging tumor variation in response to photodynamic therapy in pancreatic cancer xenograft models

PURPOSE

A treatment monitoring study investigated the differential effects of orthotopic pancreatic cancer models in response to interstitial photodynamic therapy (PDT), and the validity of using magnetic resonance imaging as a surrogate measure of response was assessed.

METHODS AND MATERIALS

Different orthotopic pancreatic cancer xenograft models (AsPC-1 and Panc-1) were used to represent the range of pathophysiology observed in human beings. Identical dose escalation studies (10, 20, and 40J/cm) using interstitial verteporfin PDT were performed, and magnetic resonance imaging with T2-weighted and T1-weighted contrast were used to monitor the total tumor volume and the vascular perfusion volume, respectively.

RESULTS

There was a significant amount of necrosis in the slower-growing Panc-1 tumor using high light dose, although complete necrosis was not observed. Lower doses were required for the same level of tumor kill in the faster-growing AsPC-1 cell line.

CONCLUSIONS

The tumor growth rate and vascular pattern of the tumor affect the optimal PDT treatment regimen, with faster-growing tumors being relatively easier to treat. This highlights the fact that therapy in human beings shows a heterogeneous range of outcomes, and suggests a need for careful individualized treatment outcomes assessment in clinical work.

RBBP9: a tumor-associated serine hydrolase activity required for pancreatic neoplasia

Pancreatic cancer is one of the most lethal malignancies. To discover functionally relevant modulators of pancreatic neoplasia, we performed activity-based proteomic profiling on primary human ductal adenocarcinomas. Here, we identify retinoblastoma-binding protein 9 (RBBP9) as a tumor-associated serine hydrolase that displays elevated activity in pancreatic carcinomas. Whereas RBBP9 is expressed in normal and malignant tissues at similar levels, its elevated activity in tumor cells promotes anchorage-independent growth in vitro as well as pancreatic carcinogenesis in vivo. At the molecular level, RBBP9 activity overcomes TGF-beta-mediated antiproliferative signaling by reducing Smad2/3 phosphorylation, a previously unknown role for a serine hydrolase in cancer biology. Conversely, loss of endogenous RBBP9 or expression of mutationally inactive RBBP9 leads to elevated Smad2/3 phosphorylation, implicating this serine hydrolase as an essential suppressor of TGF-beta signaling. Finally, RBBP9-mediated suppression of TGF-beta signaling is required for E-cadherin expression as loss of the serine hydrolase activity leads to a reduction in E-cadherin levels and a concomitant decrease in the integrity of tumor cell-cell junctions. These data not only define a previously uncharacterized serine hydrolase activity associated with epithelial neoplasia, but also demonstrate the potential benefit of functional proteomics in the identification of new therapeutic targets.

Noninvasive assessment of pancreatic beta-cell function in vivo with manganese-enhanced magnetic resonance imaging

Loss of beta-cell function in type 1 and type 2 diabetes leads to metabolic dysregulation and inability to maintain normoglycemia. Noninvasive imaging of beta-cell function in vivo would therefore provide a valuable diagnostic and research tool for quantifying progression to diabetes and response to therapeutic intervention. Because manganese (Mn(2+)) is a longitudinal relaxation time (T1)-shortening magnetic resonance imaging (MRI) contrast agent that enters cells such as pancreatic beta-cells through voltage-gated calcium channels, we hypothesized that Mn(2+)-enhanced MRI of the pancreas after glucose infusion would allow for noninvasive detection of beta-cell function in vivo. To test this hypothesis, we administered glucose and saline challenges intravenously to normal mice and mice given high or low doses of streptozotocin (STZ) to induce diabetes. Serial inversion recovery MRI was subsequently performed after Mn(2+) injection to probe Mn(2+) accumulation in the pancreas. Time-intensity curves of the pancreas (normalized to the liver) fit to a sigmoid function showed a 51% increase in signal plateau height after glucose stimulation relative to saline (P < 0.01) in normal mice. In diabetic mice given a high dose of STZ, only a 9% increase in plateau signal intensity was observed after glucose challenge (P = not significant); in mice given a low dose of STZ, a 20% increase in plateau signal intensity was seen after glucose challenge (P = 0.02). Consistent with these imaging findings, the pancreatic insulin content of high- and low-dose STZ diabetic mice was reduced about 20-fold and 10-fold, respectively, compared with normal mice. We conclude that Mn(2+)-enhanced MRI demonstrates excellent potential as a means for noninvasively monitoring beta-cell function in vivo and may have the sensitivity to detect progressive decreases in function that occur in the diabetic disease process.

In vivo imaging of a diabetogenic CD8+ T cell response during type 1 diabetes progression

Type 1 diabetes is preceded by a long, protracted period of pancreatic islet inflammation by autoreactive lymphocytes. Noninvasive imaging of islet inflammation prior to the onset of hyperglycemia might have diagnostic and therapeutic implications, but this is not currently possible. Here, MRI is used to track, noninvasively, the accumulation diabetogenic CD8+ T-cells during type 1 diabetes progression in nonobese diabetic (NOD) mice. The contrast agent is an MRI probe (MN-NRP-V7) that specifically labels CD8+ T-cells recognizing residues 206-214 of islet-specific glucose-6-phosphatase catalytic subunit related protein (IGRP(206-214)) in the context of the major histocompatibility complex (MHC) class I molecule H-2K(d). This probe consists of superparamagnetic iron oxide nanoparticles (MN) coated with K(d) molecules presenting NRP-V7, a high-avidity mimotope of IGRP(206-214). NOD mice of different ages (5, 8, 15, and 24 weeks) were imaged by MRI before and after a single intravenous injection of MN-NRP-V7 or unmodified MN nanoparticles. MN-NRP-V7 accumulation, as determined by semiquantitative MRI analysis of pancreas-associated T(2) relaxation time, was antigen-specific, age-dependent, and well correlated with the numbers of MN-NRP-V7-labeled CD8+ T-cells recovered from the pancreata of the treated mice. Antigen/MHC-coupled nanoparticles represent a promising new avenue for noninvasive imaging of lymphocyte inflammation in organ-specific autoimmunity and transplantation.

Nanoparticle-mediated drug delivery to tumor vasculature suppresses metastasis

Integrin alphanubeta3 is found on a subset of tumor blood vessels where it is associated with angiogenesis and malignant tumor growth. We designed an alphanubeta3-targeted nanoparticle (NP) encapsulating the cytotoxic drug doxorubicin (Dox) for targeted drug delivery to the alphanubeta3-expressing tumor vasculature. We observed real-time targeting of this NP to tumor vessels and noted selective apoptosis in regions of the alphanubeta3-expressing tumor vasculature. In clinically relevant pancreatic and renal cell orthotopic models of spontaneous metastasis, targeted delivery of Dox produced an antimetastatic effect. In fact, alphanubeta3-mediated delivery of this drug to the tumor vasculature resulted in a 15-fold increase in antimetastatic activity without producing drug-associated weight loss as observed with systemic administration of the free drug. These findings reveal that NP-based delivery of cytotoxic drugs to the alphanubeta3-positive tumor vasculature represents an approach for treating metastatic disease.

Noninvasive magnetic resonance imaging of the development of individual colon cancer tumors in rat liver

Monitoring tumor development is essential for the understanding of mechanisms involved in tumor progression and to determine efficacy of therapy. One of the evolving approaches is longitudinal noninvasive magnetic resonance imaging (MRI) of tumors in experimental models. We applied high-resolution MRI at 7 Tesla to study the development of colon cancer tumors in rat liver. MRI acquisition was triggered to the respiratory cycle to minimize motion artifacts. A special radio frequency (RF) coil was designed to acquire detailed T1-weighted and T2-weighted images of the liver. T2-weighted images identified hyperintense lesions representing tumors with a minimum diameter of 2 mm, enabling the determination of growth rates and morphological aspects of individual tumors. It is concluded that high-resolution MRI using a dedicated RF coil and triggering to the respiratory cycle is an excellent tool for quantitative and morphological analysis of individual diffusely distributed tumors throughout the liver. However, at present, MRI requires expensive equipment and expertise and is a time-consuming methodology. Therefore, it should preferably be used for dedicated applications rather than for high-throughput assessment of total tumor load in animals.

In vivo imaging of tumor response to therapy using a dual-modality imaging strategy

In vivo assessment of the outcome of cancer therapy is hampered by the paucity of imaging probes that target tumors specifically and noninvasively. The importance of such probes increases with the continuous development of chemotherapeutics and the necessity to evaluate their effectiveness in a clinical setting. We have recently reported on a dual-modality imaging probe specifically targeting the underglycosylated mucin-1 tumor-specific antigen (uMUC-1), which is one of the early hallmarks of tumorigenesis in a wide variety of tumors. This probe consists of crosslinked superparamagnetic iron oxide nanoparticles (CLIO) for MR imaging, modified with Cy5.5 dye (for near infrared optical fluorescence imaging (NIRF)), and has peptides (EPPT), specifically recognizing uMUC-1, attached to the nanoparticle's dextran coat. In the present study, we demonstrated that this probe could not only detect orthotopically implanted preclinical models of adenocarcinomas but could also track tumor response to chemotherapy in vivo in real time. Considering the high cost associated with the development and testing of new cancer therapeutics and the need for accurate, noninvasive assessment of their effectiveness, we believe that the developed probe represents a valuable research tool relevant to clinical discovery.

A New Class of Macrocyclic Lanthanide Complexes for Cell Labeling and Magnetic Resonance Imaging Applications

Lanthanide complexes have wide applications in biochemical research and biomedical imaging. We have designed and synthesized a new class of macrocyclic lanthanide chelates, Ln/DTPA-PDA-C(n), for cell labeling and magnetic resonance imaging (MRI) applications. Two lipophilic Gd3+ complexes, Gd/DTPA-PDA-C(n) (n = 10, 12), labeled a number of cultured mammalian cells noninvasively at concentrations as low as a few micromolar. Cells took up these agents rapidly and showed robust intensity increases in T1-weighed MR images. Labeled cells showed normal morphology and doubling time as control cells. In addition to cultured cells, these agents also labeled primary cells in tissues such as dissected pancreatic islets. To study the mechanism of cellular uptake, we applied the technique of diffusion enhanced fluorescence resonance energy transfer (DEFRET) to determine the cellular localization of these lipophilic lanthanide complexes. After loading cells with a luminescent complex, Tb/DTPA-PDA-C10, we observed DEFRET between the Tb3+ complex and extracellular, but not intracellular, calcein. We concluded that these cyclic lanthanide complexes label cells by inserting two hydrophobic alkyl chains into cell membranes with the hydrophilic metal binding site facing the extracellular medium. As the first imaging application of these macrocyclic lanthanide chelates, we labeled insulin secreting beta-cells with Gd/DTPA-PDA-C12. Labeled cells were encapsulated in hollow fibers and were implanted in a nude mouse. MR imaging of implanted beta-cells showed that these cells could be followed in vivo for up to two weeks. The combined advantages of this new class of macrocyclic contrast agents ensure future imaging applications to track cell movement and localization in different biological systems.

Magnetic resonance imaging for detection and analysis of mouse phenotypes

With the enormous and growing number of experimental and genetic mouse models of human disease, there is a need for efficient means of characterizing abnormalities in mouse anatomy and physiology. Adaptation of magnetic resonance imaging (MRI) to the scale of the mouse promises to address this challenge and make major contributions to biomedical research by non-invasive assessment in the mouse. MRI is already emerging as an enabling technology providing informative and meaningful measures in a range of mouse models. In this review, recent progress in both in vivo and post mortem imaging is reported. Challenges unique to mouse MRI are also identified. In particular, the needs for high-throughput imaging and comparative anatomical analyses in large biological studies are described and current efforts at handling these issues are presented.

Magnetic resonance imaging in an orthotopic rat model: blockade of epidermal growth factor receptor with EMD72000 inhibits human pancreatic carcinoma growth

The purpose of our research was to investigate the antiangiogenic effect of the epidermal growth factor receptor monoclonal antibody (anti-EGF-R MAB) EMD72000, in an orthotopic human pancreatic carcinoma model in rats, assessed by magnetic resonance (MR) imaging using angiogenic surrogate markers in comparison with histopathologic findings. Human pancreatic adenocarcinoma cells L3.6pl were injected orthotopically in the pancreas of 12 athymic nude rats. Through a 21-day course, groups of 6 rats were treated intraperitoneally with either EMD72000 or with saline solution for control animals. Dynamic contrast-enhanced MR imaging was performed before and after the treatment to assess microvascular permeability, estimated by the endothelial transfer coefficient (KPS) and fractional plasma volumes (fPV) of the pancreatic tumors. EMD72000-treated animals showed significantly less tumor volume progression (1,080 mm3 +/- 1,244; p = 0.012) and significantly lower values for microvascular permeability (KPS = 4.2 ml min(-1) 100 ml(-1) of tissue +/- 2.8; p = 0.015), fractional plasma volume (fPV = 0.018 ml ml(-1) of tissue +/- .015; p = 0.003) and microvessel density (MVD = 13 +/- 4 (0.159 mm2); p = 0.001) than saline-treated animals (6,544 mm3 +/- 5,202; 9.5 ml min(-1) 100 ml(-1) of tissue +/- 4.3, 0.056 ml ml(-1) of tissue +/- 0.019 and 25 +/- 5 (0.159 mm2), respectively). KPS and fPV values showed moderate positive correlation with MVD (r = 0.5, p = 0.103; r = 0.6, p = 0.065, respectively). Intraperitoneal injection of EMD72000 inhibits orthotopic human pancreatic carcinoma growth in rats. Antiangiogenic effects of anti-EGF-R MAB EMD72000 can be quantified and monitored noninvasively by dynamic MR imaging.

Mouse MRI: Concepts and Applications in Physiology

The purpose of this review is to provide an introduction to the rapidly expanding field of mouse magnetic resonance imaging (MRI). It is by no means meant to be all-inclusive but rather to provide a brief introduction to the basics of MRI theory, provide some insight into the basic experiments that can be performed in mice by using MRI, and bring to light some factors to consider when planning a mouse MRI experiment.