Prostate cancer tumor grade differentiation with dynamic contrast-enhanced MR imaging in the rat: comparison of macromolecular and small-molecular contrast media--preliminary experience

Manganese-Based Targeted Nanoparticles for Postoperative Gastric Cancer Monitoring via Magnetic Resonance Imaging

Postoperative recurrence is a common and severe problem in the treatment of gastric cancer; consequently, a prolonged course of chemotherapy treatment is inevitable. Monitoring by imaging could provide an accurate evaluation of the therapeutic effects, which would be beneficial to guide a treatment strategy adjustment over time. However, current imaging technologies remain insufficient for the continuous postoperative monitoring of gastric cancer. In this case, molecular imaging offers an efficient strategy. Targetable contrast agents are an essential part of molecular imaging, which could greatly enhance the accuracy and quality of monitoring. Herein, we synthesized a Mn-based contrast agent for magnetic resonance imaging (MRI) of gastric cancer monitoring. Initially, small-sized Mn3O4 nanoparticles (NPs) were synthesized. Then, a functionalized polyethylene glycol (PEG) lipid was attached to the surface of the Mn3O4 NPs, to improve biocompatibility. The targetable MRI contrast agent (Mn3O4@PEG-RGD NPs) was further prepared by the conjugation of the arginine-glycine-aspartic acid (RGD) peptides. The completed Mn3O4@PEG-RGD NPs had the small size of 7.3 ± 2.7 nm and exhibited superior colloidal stability in different solution environments. In addition, Mn3O4@PEG-RGD NPs exhibited reliable biotolerance and low toxicity both in vitro and in vivo. Imaging experiments amply demonstrated that Mn3O4@PEG-RGD NPs could efficiently accumulate in gastric cancer tissues and cells via RGD mediation, and immediately significantly increased the MRI effects. Through this study, we can conclude that Mn3O4@PEG-RGD NPs have the potential to be a novel MRI contrast agent for the postoperative monitoring of gastric cancer.

Gd-AAZTA-MADEC, an improved blood pool agent for DCE-MRI studies on mice on 1 T scanners

A novel MRI blood-pool contrast agent (Gd-AAZTA-MADEC) has been compared with established blood pool agents for tumor contrast enhanced images and angiography. Synthesis, relaxometric properties, albumin binding affinity and pharmacokinetic profiles are reported. For in vivo studies, angiographic images and tumor contrast enhanced images were acquired on mice with benchtop 1T-MRI scanners and compared with MS-325, B22956/1 and B25716/1. The design of this contrast agent involved the elongation of the spacer between the targeting deoxycholic acid moiety and the Gd-AAZTA imaging reporting unit that drastically changed either the binding affinity to albumin (KA(HSA) = 8.3 × 10(5) M(-1)) and the hydration state of the Gd ion (q = 2) in comparison to the recently reported B25716/1. The very markedly high binding affinity towards mouse and human serum albumins resulted in peculiar pharmacokinetics and relaxometric properties. The NMRD profiles clearly indicated that maximum efficiency is attainable at magnetic field strength of 1 T. In vivo studies showed high enhancement of the vasculature and a prolonged accumulation inside tumor. The herein reported pre-clinical imaging studies show that a great benefit arises from the combination of a benchtop MRI scanner operating at 1 T and the albumin-binding Gd-AAZTA-MADEC complex, for pursuing enhanced angiography and improved characterization of tumor vascular microenvironment.

High-field small animal magnetic resonance oncology studies

This review focuses on the applications of high magnetic field magnetic resonance imaging (MRI) and spectroscopy (MRS) to cancer studies in small animals. High-field MRI can provide information about tumor physiology, the microenvironment, metabolism, vascularity and cellularity. Such studies are invaluable for understanding tumor growth and proliferation, response to treatment and drug development. The MR techniques reviewed here include (1)H, (31)P, chemical exchange saturation transfer imaging and hyperpolarized (13)C MRS as well as diffusion-weighted, blood oxygen level dependent contrast imaging and dynamic contrast-enhanced MRI. These methods have been proven effective in animal studies and are highly relevant to human clinical studies.

Magnetic resonance imaging (MRI) contrast agents for tumor diagnosis

This review focuses on MRI contrast agents for tumor diagnosis. Several types of low molecular weight Gd3+-based complexes and dextran-coated superparamagnetic iron oxide (SPIO) nanoparticles have been used for clinical tumor diagnosis as longitudinal relaxation time (T1) and transverse relaxation time (T2) MRI contrast agents, respectively. To further improve the sensitivity of MRI, new types of chelates for T1 MRI contrast agents and combination of low molecular weight T1 MRI contrast agents with different types of carriers have been investigated. Different types of materials for forming secure coating layers of SPIO and novel superparamagnetic particles with higher relaxivity values have been explored. Various types of ligands were applied to improve the capability to target tumor for both T1 and T2 contrast agents. Furthermore, MRI contrast agents for detection of tumor metabolism were also pursued.

Targeted biodegradable dendritic MRI contrast agent for enhanced tumor imaging

Highly sensitive and safe contrast agents (CAs) are essential for magnetic resonance imaging (MRI) to achieve accurate tumor detection and imaging. Dendrimer-based macromolecular MRI contrast agents are advantageous owing to their tumor-targeting ability, enhanced imaging contrast and enlarged imaging window. However, most of them have drawbacks of non-degradability and thereby long-term retention in body and toxicity. Herein, a tumor-targeting biodegradable dendritic CA (DCA) (FA-PEG-G2-DTPA-Gd) was prepared from a polyester dendrimer conjugated with gadolinium (Gd) chelates and PEG chains with distal folic acid. The DCA had a high longitudinal relaxivity up to 17.1mM(-1)s(-1), 4 times higher than the clinically used CA Magnevist. The MRI contrasted by FA-PEG-G2-DTPA-Gd outlined the inoculated tumor more clearly, and had much higher contrast enhancement for a much longer time than Magnevist. More importantly, the biodegradable FA-PEG-G2-DTPA-Gd gave much less Gd retentions in all the organs or tissues than non-degradable DCAs. Thus, the high efficiency in MRI contrast enhancement and low Gd retention merit it a promising CA for contrast enhanced tumor MRI.

Computed tomography and magnetic resonance imaging

Imaging in Oncology is rapidly moving from the detection and size measurement of a lesion to the quantitative assessment of metabolic processes and cellular and molecular interactions. Increasing insights into cancer as a complex disease with involvement of the tumor stroma in tumor pathobiological processes have made it clear that for successful control of cancer, treatment strategies should not only be directed at the tumor cells but also targeted at the tumor microenvironment. This requires understanding of the complex molecular and cellular interactions in cancer tissue. Recent developments in imaging technology have increased the possibility to image various pathobiological processes in cancer development and response to treatment. For computed tomography (CT) and magnetic resonance imaging (MRI) various improvements in hardware, software, and imaging probes have lifted these modalities from classical anatomical imaging techniques to techniques suitable to image and quantify various physiological processes and molecular and cellular interactions. Next to a more general overview of possible imaging targets in oncology this chapter provides an overview of the various developments in CT and MRI technology and some specific applications.

Imaging hypoxia in gliomas

Hypoxia plays a central role in tumour development, angiogenesis, growth and resistance to treatment. Owing to constant developments in medical imaging technology, significant advances have been made towards in vitro and in vivo imaging of hypoxia in a variety of tumours, including gliomas of the central nervous system. The aim of this article is to review the literature on imaging approaches currently available for measuring hypoxia in human gliomas and provide an insight into recent advances and future directions in this field. After a brief overview of hypoxia and its importance in gliomas, several methods of measuring hypoxia will be presented. These range from invasive monitoring by Eppendorf polarographic O(2) microelectrodes, positron electron tomography (PET) tracers based on 2-nitroimidazole compounds [(18)F-labelled fluoro-misonidazole ((18)F-MISO) or 1-(2-[((18))F]fluoro-1-[hydroxymethyl]ethoxy)methyl-2-nitroimidazole (FRP-170)], (64)Cu-ATSM Cu-diacetyl-bis(N4-methylthiosemicarbazone) (Cu-ATSM) or (99m)Tc- and (68)Ga-labelled metronidazole (MN) agents to advanced MRI methods, such as blood oxygenation level dependent (BOLD) MRI, oxygen-enhanced MRI, diffusion-weighted MRI (DWI-MRI), dynamic contrast-enhanced MRI (DCE-MRI) and (1)H-magnetic resonance spectroscopy.

Perfusion computed tomography assessments of peri-enhancing brain tissue in high-grade gliomas

PURPOSE

This study was undertaken to identify tumoural infiltration of peri-enhancing brain tissue in patients with glioblastoma by means of perfusion computed tomography (PCT) parameters, cerebral blood volume (CBV) and permeability surface (PS).

MATERIALS AND METHODS

Eight patients with surgically treated glioblastoma who were eligible for radiotherapy and nine patients with brain metastases from lung and breast cancer underwent CT before and after injection of contrast medium. CBV and PS were calculated in the contrast-enhancing lesion area, in the area of perilesional oedema and in the normal-appearing white matter (NAWM), normalised to contralateral symmetrical areas.

RESULTS

No significant differences were found for normalised CBV (nCBV) and nPS in NAWM regions between metastasis and glioma. Significant differences in nPS (p<0.005) were found between the typically vasogenic oedema surrounding the metastases and signal alteration surrounding the glial neoplasm. On the contrary, no significant differences were detected in the same areas for nCBV.

CONCLUSIONS

PCT can analyse the histopathological substrate underlying the hypodense peritumoural halo and differentiate between vasogenic oedema and neoplastic infiltration on the basis of the PS parameter. In our study, PS was more informative than CBV. These findings can be used to integrate plans for radiation therapy and/or surgery.

Evaluation of tumor angiogenesis in a mouse PC-3 prostate cancer model using dynamic contrast-enhanced sonography

OBJECTIVES

The purpose of this study was to evaluate tumor angiogenesis in a mouse xenograft model injected with human PC-3 prostate cancer cells using contrast-enhanced sonography.

METHODS

Sixteen nude mice were injected with human prostate cancer cells on the back or the flank. Contrast-enhanced sonography was performed with a 5- to 12-MHz broadband linear transducer after a 500-μL bolus injection of a sonographic contrast agent composed of lipid shells and sulfur hexafluoride. Contrast-enhanced sonograms were obtained by the pulse inversion coded harmonic technique with a low mechanical index of 0.07. A region of interest was drawn to encompass the tumor, and time-intensity curves were acquired. After fitting the curve by a gamma variate function, the maximum intensity, area under the curve for up to 50 seconds, time to peak, shape parameter, and scale parameter were derived. The tumor volume, percentage of vascular endothelial growth factor expression, and CD31-positive vessel count (microvessel density) were correlated with the parameters derived from the time-intensity curve.

RESULTS

The maximum intensity was positively correlated with the microvessel density with statistical significance (r = 0.552; P = .03). The percentage of vascular endothelial growth factor expression did not have any correlation with the parameters from the curve.

CONCLUSIONS

Contrast-enhanced sonography can reflect tumor vascularity in a prostate cancer animal model. Sonography of tumor angiogenesis may permit functional assessment of the tumor vasculature and provide an imaging biomarker for tumor responses to antiangiogenic therapies.

Assessment of tumor angiogenesis: dynamic contrast-enhanced MRI with paramagnetic nanoparticles compared with Gd-DTPA in a rabbit Vx-2 tumor model

The purpose of this study was to evaluate the suitability of a macromolecular MRI contrast agent (paramagnetic nanoparticles, PNs) for the characterization of tumor angiogenesis. Our aim was to estimate the permeability of PNs in developing tumor vasculature and compare it with that of a low molecular weight contrast agent (Gd-DTPA) using dynamic contrast-enhanced MRI (DCE). Male New Zealand white rabbits (n = 5) underwent DCE MRI 12-14 days after Vx-2 tumor fragments were implanted into the left hind limb. Each contrast agent (PNs followed by Gd-DTPA) was evaluated using a DCE protocol and transendothelial transfer coefficient (K(i)) maps were calculated using a two-compartment model. Two regions of interest (ROIs) were located within the tumor core and hindlimb muscle and five ROIs were placed within the tumor rim. Comparisons were performed using repeated measures analysis of variance (ANOVA). The K(i) values estimated using PNs were significantly lower than those obtained for Gd-DTPA (p = 0.018). When PNs and Gd-DTPA data were analyzed separately, significant differences were identified among tumor rim ROIs for PNs (p < 0.0001), but not for Gd-DTPA data (p = 0.34). The mean K(i) for the tumor rim was significantly greater than that of either the core or the hindlimb muscle for both contrast agents (p < 0.05 for each comparison). In summary, the extravasation of Gd-DTPA was far greater than that of PNs, suggesting that PNs can reveal regional differences in tumor vascular permeability that are not otherwise apparent with clinical contrast agents such as Gd-DTPA. These results suggest that PNs show potential for the noninvasive delineation of tumor angiogenesis.

Macromolecular and dendrimer-based magnetic resonance contrast agents

Magnetic resonance imaging (MRI) is a powerful imaging modality that can provide an assessment of function or molecular expression in tandem with anatomic detail. Over the last 20-25 years, a number of gadolinium-based MR contrast agents have been developed to enhance signal by altering proton relaxation properties. This review explores a range of these agents from small molecule chelates, such as Gd-DTPA and Gd-DOTA, to macromolecular structures composed of albumin, polylysine, polysaccharides (dextran, inulin, starch), poly(ethylene glycol), copolymers of cystamine and cystine with GD-DTPA, and various dendritic structures based on polyamidoamine and polylysine (Gadomers). The synthesis, structure, biodistribution, and targeting of dendrimer-based MR contrast agents are also discussed.

Polydisulfide Based Biodegradable Macromolecular Magnetic Resonance Imaging Contrast Agents

Macromolecular Gd(III) complexes are advantageous over small molecular Gd(III) complexes in contrast enhanced magnetic resonance imaging (MRI) because of their prolonged blood circulation and preferential tumor accumulation. However, macromolecular contrast agents have not been approved for clinical applications because of the safety concerns related to their slow body excretion. Polydisulfide Gd(III) complexes have been designed and developed as biodegradable macromolecular MRI contrast agents to alleviate the concerns by facilitating the clearance of Gd(III) complexes from the body. These agents initially behave as macromolecular agents and result in superior contrast enhancement in the vasculature and tumor tissues. They can then be readily degraded in vivo into small molecular chelates that can rapidly excrete from the body via renal filtration after the MRI examinations. Various polydisulfide Gd(III) complexes have been prepared as biodegradable macromolecular MRI contrast agents. These agents have resulted in strong contrast enhancement in the vasculature and tumor tissue in animal models with minimal long-term tissue accumulation comparable to small molecular contrast agents. Polydisulfide Gd(III) complexes are promising for further clinical development as safe and effective biodegradable macromolecular MRI contrast agents for cardiovascular and cancer imaging. The review summarizes the chemistry and properties of polydisulfide Gd(III) complexes.

Tumor characterization with dynamic contrast enhanced magnetic resonance imaging and biodegradable macromolecular contrast agents in mice

PURPOSE

To investigate the efficacy of polydisulfide-based biodegradable macromolecular contrast agents of different degradability and molecular weight for tumor characterization based on angiogenesis using dynamic contrast enhanced MRI (DCE-MRI).

METHODS

Biodegradable macromolecular MRI contrast agents, Gd-DTPA cystamine copolymers (GDCC) and Gd-DTPA cystine copolymers (GDCP), with molecular weight of 20 and 70 KDa were evaluated for tumor characterization. Gd(DTPA-BMA) and a prototype of macromolecular contrast agent, albumin-(Gd-DTPA), were used as controls. The DCE-MRI studies were performed in nude mice bearing MDA PCa 2b and PC-3 human prostate tumor xenografts. Tumor angiogenic kinetic parameters including endothelium transfer coefficient (K(trans)) and fractional tumor plasma volume (f(PV)) were calculated from the DCE-MRI data using a two-compartment model and compared between the two different tumor models for each contrast agent.

RESULTS

There was no significant difference in the f(PV) values between two tumor models estimated with the same agent except for GDCC-70. The K(trans) values in both tumor models decreased with the increase of molecular weight of contrast agents. With the same high molecular weight (70 KDa), GDCC-70 showed a higher K(trans) values than GDCP-70 due to high degradability of the former in both tumor models (p < 0.05). The K(trans) values of MDA PCa 2b tumors were significantly higher than those of PC-3 tumors estimated by Gd(DTPA-BMA), GDCC-20, GDCC-70, GDCP-70, and albumin-(Gd-DTPA) (p < 0.05).

CONCLUSIONS

The polydisulfide-based biodegradable macromolecular MRI contrast agents are promising in tumor characterization and differentiation with dynamic contrast enhanced MRI.

Brain tumor hypoxia: tumorigenesis, angiogenesis, imaging, pseudoprogression, and as a therapeutic target

Hypoxia is implicated in many aspects of tumor development, angiogenesis, and growth in many different tumors. Brain tumors, particularly the highly aggressive glioblastoma multiforme (GBM) with its necrotic tissues, are likely affected similarly by hypoxia, although this involvement has not been closely studied. Invasion, apoptosis, chemoresistance, resistance to antiangiogenic therapy, and radiation resistance may all have hypoxic mechanisms. The extent of the influence of hypoxia in these processes makes it an attractive therapeutic target for GBM. Because of their relationship to glioma and meningioma growth and angiogenesis, hypoxia-regulated molecules, including hypoxia inducible factor-1, carbonic anhydrase IX, glucose transporter 1, and vascular endothelial growth factor, may be suitable subjects for therapies. Furthermore, other novel hypoxia-regulated molecules that may play a role in GBM may provide further options. Emerging imaging techniques may allow for improved determination of hypoxia in human brain tumors to better focus therapeutic treatments; however, tumor pseudoprogression, which may be prompted by hypoxia, poses further challenges. An understanding of the role of hypoxia in tumor development and growth is important for physicians involved in the care of patients with brain tumors.

Characterization of tumor angiogenesis with dynamic contrast-enhanced MRI and biodegradable macromolecular contrast agents in mice

The efficacy of polydisulfide-based biodegradable macromolecular contrast agents for characterizing tumor angiogenesis was investigated in a mouse model using dynamic contrast-enhanced MRI (DCE-MRI). Biodegradable macromolecular MRI contrast agents, gadopentetate dimeglumine (Gd-DTPA) cystamine copolymers (GDCC), and Gd-DTPA cystine copolymers (GDCP), with molecular weights of 20 and 70 kDa were used in the study. Gadodiamide (Gd [DTPA-BMA]) and albumin labeled with Gd-DTPA [albumin-(Gd-DTPA)] were used as the controls. The DCE-MRI studies were performed in nude mice bearing prostate tumor xenografts from the MDA-PCa-2b cell line. Tumor angiogenic kinetic parameters, including endothelial transfer coefficient (K(PS)), fractional tumor plasma volume (f(PV)), and permeability surface area product (PS), were estimated from the DCE-MRI data using a two-compartment model. The K(PS) and f(PV) values estimated by the biodegradable macromolecular contrast agents were between those estimated by Gd(DTPA-BMA) and albumin-(Gd-DTPA). The parameters estimated by the agent with a slow degradation rate and high molecular weight, GDCP-70 (K(PS) = 2.09 +/- 0.50 ml/min/100 cc and f(PV) = 0.075 +/- 0.021), were closer to those by albumin-(Gd-DTPA) (K(PS) = 1.43 +/- 0.64 ml/min/100 cc and f(PV) = 0.044 +/- 0.007) than by other agents with relatively low molecular weight or rapid degradation rate. The polydisulfide-based biodegradable macromolecular contrast agents are promising for characterizing tumor vascularity and angiogenesis with DCE-MRI.

Quantitative estimation of permeability surface-area product in astroglial brain tumors using perfusion CT and correlation with histopathologic grade

BACKGROUND AND PURPOSE

Glioma angiogenesis and its different hemodynamic features, which can be evaluated by using perfusion CT (PCT) imaging of the brain, have been correlated with the grade and the aggressiveness of gliomas. Our hypothesis was that quantitative estimation of permeability surface area product (PS), cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) in astroglial brain tumors by using PCT will correlate with glioma grade. High-grade gliomas will show higher PS and CBV as compared with low-grade gliomas.

MATERIALS AND METHODS

PCT was performed in 32 patients with previously untreated astroglial tumors (24 high-grade gliomas and 8 low-grade gliomas) by using a total acquisition time of 170 seconds. World Health Organization (WHO) glioma grades were compared with PCT parameter absolute values by using Student or nonparametric Wilcoxon 2-sample tests. Receiver operating characteristic (ROC) analyses were also done for each of the parameters.

RESULTS

The differences in PS, CBV, and CBF between the low- and high-grade tumor groups were statistically significant, with the low-grade group showing lower mean values than the high-grade group. ROC analyses showed that both CBV (C-statistic 0.930) and PS (C-statistic 0.927) were very similar to each other in differentiating low- and high-grade gliomas and had higher predictability compared with CBF and MTT. Within the high-grade group, differentiation of WHO grade III and IV gliomas was also possible by using PCT parameters, and PS showed the highest C-statistic value (0.926) for the ROC analyses in this regard.

CONCLUSIONS

Both PS and CBV showed strong association with glioma grading, high-grade gliomas showing higher PS and CBV as compared with low-grade gliomas. Perfusion parameters, especially PS, can also be used to differentiate WHO grade III from grade IV in the high-grade tumor group.

Vascular permeability during antiangiogenesis treatment: MR imaging assay results as biomarker for subsequent tumor growth in rats

PURPOSE

To prospectively evaluate in rats the acute change in tumor vascular leakiness (K(PS)) assayed at magnetic resonance (MR) imaging after a single dose of the angiogenesis inhibitor bevacizumab as a predictive biomarker of tumor growth response after a prolonged treatment course.

MATERIALS AND METHODS

Institutional animal care and use committee approval was obtained. Seventeen female rats with implanted human breast cancers underwent dynamic albumin-(Gd-DTPA)(30)-enhanced MR imaging followed by an initial dose of bevacizumab or saline (as a control). Treatment was continued every 3rd day, for a total of four doses at five possible dose levels: 0 mg bevacizumab (n = 4 [control rats]), 0.1 mg bevacizumab (n = 3), 0.25 mg bevacizumab (n = 2), 0.5 mg bevacizumab (n = 5), and 1.0 mg bevacizumab (n = 3). A second MR imaging examination was performed 24 hours after the initial dose to enable calculation of the acute change in MR imaging-assayed leakiness, or Delta K(PS). This acute change in K(PS) at MR imaging was correlated with tumor growth response for each cancer at the completion of the 11-day treatment course. For statistical analyses, an unpaired two-tailed t test, analysis of variance, and linear regression analyses were used.

RESULTS

The MR imaging-assayed change in tumor microvascular leakiness, tested as a potential biomarker, correlated strongly with tumor growth rate (R(2) = 0.74, P < .001). K(PS) and tumor growth decreased significantly in all bevacizumab-treated cancers compared with these values in control group cancers (P < .05).

CONCLUSION

The MR imaging-assayed acute change in vascular leakiness after a single dose of bevacizumab was an early, measurable predictive biomarker of tumor angiogenesis treatment response.

Polydisulfide Gd(III) chelates as biodegradable macromolecular magnetic resonance imaging contrast agents

Macromolecular gadolinium (Gd)(III) complexes have a prolonged blood circulation time and can preferentially accumulate in solid tumors, depending on the tumor blood vessel hyperpermeability, resulting in superior contrast enhancement in magnetic resonance (MR) cardiovascular imaging and cancer imaging as shown in animal models. Unfortunately, safety concerns related to these agents’ slow elimination from the body impede their clinical development. Polydisulfide Gd(III) complexes have been designed and developed as biodegradable macromolecular magnetic resonance imaging (MRI) contrast agents to facilitate the clearance of Gd(III) complexes from the body after MRI examinations. These novel agents can act as macromolecular contrast agents for in vivo imaging and excrete rapidly as low-molecular-weight agents. The rationale and recent development of the novel biodegradable contrast agents are reviewed here. Polydisulfide Gd(III) complexes have relatively long blood circulation time and gradually degrade into small Gd(III) complexes, which are rapidly excreted via renal filtration. These agents result in effective and prolonged in vivo contrast enhancement in the blood pool and tumor tissue in animal models, yet demonstrate minimal Gd(III) tissue retention as the clinically used low-molecular-weight agents. Structural modification of the agents can readily alter the contrast-enhancement kinetics. Polydisulfide Gd(III) complexes are promising for further clinical development as safe, effective, biodegradable macromolecular MRI contrast agents for cardiovascular and cancer imaging, and for evaluation of therapeutic response.

Prostate cancer: accurate determination of extracapsular extension with high-spatial-resolution dynamic contrast-enhanced and T2-weighted MR imaging--initial results

PURPOSE

To prospectively compare the sensitivity and specificity of high-spatial-resolution dynamic contrast material-enhanced magnetic resonance (MR) imaging with those of high-spatial-resolution T2-weighted MR imaging, performed with an endorectal coil (ERC), for assessment of extracapsular extension (ECE) and staging in patients with prostate cancer, with histopathologic findings as reference.

MATERIALS AND METHODS

The study was approved by the institutional internal review board; a signed informed consent was obtained. MR imaging of the prostate at 1.5 T was performed with combined surface coils and ERCs in 32 patients (mean age, 65 years; range, 42-78 years) before radical prostatectomy. High-spatial-resolution T2-weighted fast spin-echo and high-spatial-resolution dynamic contrast-enhanced three-dimensional gradient-echo images were acquired with gadopentetate dimeglumine. Dynamic contrast-enhanced MR images were analyzed with a computer-generated color-coded scheme. Two experienced readers independently assessed ECE and tumor stage. MR imaging-based staging results were compared with histopathologic results. For the prediction of ECE, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Staging accuracy was determined with the area under the receiver operating characteristic curve (AUC) by using the Wilcoxon-Mann-Whitney index of diagnostic accuracy.

RESULTS

The mean sensitivity, specificity, PPV, and NPV for assessment of ECE with the combined data sets for both readers were 86%, 95%, 90%, and 93%, respectively. The sensitivity of MR images for determination of ECE was significantly improved for both readers (>25%) with combined data sets compared with T2-weighted MR images alone. The combined data sets had a mean overall staging accuracy for both readers of 95%, as determined with AUC. Staging results for both readers were significantly improved (P<.05) with the combined data sets compared with T2-weighted MR images alone.

CONCLUSION

The combination of high-spatial-resolution dynamic contrast-enhanced MR imaging and T2-weighted MR imaging yields improved assessment of ECE and better results for prostate cancer staging compared with either technique independently.

Magnetic resonance imaging enhancement of normal tissues and tumors using macromolecular Gd-based cascade polymer contrast agents: preclinical evaluations

OBJECTIVES

We sought to compare magnetic resonance imaging (MRI) enhancement using 4 novel macromolecular polyethyleneglycol (PEG)-based cascade-polymer gadolinium contrast agents (macromolecular contrast media) in normal soft tissues and a breast cancer model.

MATERIALS AND METHODS

Four candidate PEG cascade polymers with effective molecular weights of 74, 82, 106, and 132 kDa, respectively, and T1-relaxivities of 8.1, 9.1, 9.7, and 10.0, respectively (at 2 Tesla and 37 degrees C in HEPES buffer), initially were used to characterize liver and kidney MRI-enhancement patterns in normal Sprague-Dawley rats (n = 4-5 per contrast agent). Kinetic analysis of dynamic MRI enhancement was used in 8 nude rats bearing MDA-MB 435 breast cancers to estimate fractional plasma volume and apparent endothelial leakiness (K) in tumors and muscle.

RESULTS

Soft-tissue enhancement patterns followed closely the blood enhancement over the course of 30-50 minutes with estimated blood half-lives between 23 and 73 minutes, which varied with effective molecular weights. The 2 smaller compounds yielded measurable leaks in normal muscle [K = 204 and 56 microL/(min.100 cm), respectively], whereas the 2 larger molecules did not leak in muscle [K = 0 microL/(min.100 cm)]; however, MRI-assayed leakiness of tumor vessels with respect to those 2 larger macromolecular contrast media was 68 +/- 27 and 16 +/- 8 microL/(min.100 cm), respectively.

CONCLUSIONS

Two relatively large (effective molecular weight >82 kDa) PEG-based cascade polymer contrast agents were well-suited for MRI quantification of tissue plasma volume and for differentiating leaky cancer microvessels from nonleaky normal vessels.

Dynamic contrast enhanced MRI of mouse fibrosarcoma using small-molecular and novel macromolecular contrast agents

The aim of the study was a comparison of 2 novel macromolecular contrast agents, Gadomer-17 and Polylysine-Gd-DTPA, with commercially available Gd-DTPA in determining the quality of tumor microvasculature by dynamic contrast enhanced MRI. Three groups of 5 mice with SA-1 tumors were studied. To each group of animals one contrast agent was administered; i.e. the first group got Gd-DTPA, the second group Gadomer-17 and the third group Polylysine-Gd-DTPA. To perform dynamic contrast enhanced MRI a standard keyhole approach was used by which consecutive signal intensity change due to contrast agent accumulation in the tumor was measured. From the obtained data, tissue permeability surface area product PS and fractional blood volume BV were calculated on a pixel-by-pixel basis. PS and BV values were calculated for each contrast agent. Based on the values, contrast agents were classified according to their performance in characterizing tumor microvasculature. Results of our study suggest that Gadomer-17 and Polylysine-Gd-DTPA are significantly superior to Gd-DTPA in characterizing tumor microvasculature.

MRI tumor characterization using Gd-GlyMe-DOTA-perfluorooctyl-mannose-conjugate (Gadofluorine M), a protein-avid contrast agent

The rationale and objectives were to define the MRI tumor-characterizing potential of a new protein-avid contrast agent, Gd-GlyMe-DOTA-perfluorooctyl-mannose-conjugate (Gadofluorine M; Schering AG, Berlin, Germany) in a chemically induced tumor model of varying malignancy. Because of the tendency for this agent to form large micelles in water and to bind strongly to hydrophobic sites on proteins, it was hypothesized that patterns of dynamic tumor enhancement could be used to differentiate benign from malignant lesions, to grade the severity of malignancies and to define areas of tumor necrosis. Gadofluorine M, 0.05 mmol Gd kg(-1), was administered intravenously to 28 anesthetized rats that had developed over 10 months mammary tumors of varying degrees of malignancy as a consequence of intraperitoneal administration of N-ethyl-N-nitrosourea (ENU), 45-250 mg kg(-1). These tumors ranged histologically from benign fibroadenomas to highly undifferentiated adenocarcinomas. Dynamic enhancement data were analyzed kinetically using a two-compartment tumor model to generate estimates of fractional plasma volume (fPV), apparent fractional extracellular volume (fEV*) and an endothelial transfer coefficient (K(PS)) for this contrast agent. Tumors were examined microscopically for tumor type, degree of malignancy (Scarff-Bloom-Richardson score) and location of necrosis. Eighteen tumor-bearing rats were successfully imaged. MRI data showed an immediate strong and gradually increasing tumor enhancement. K(PS) and fEV*, but not fPV obtained from tumors correlated significantly (p < 0.05) with the SBR tumor grade, r = 0.65 and 0.56, respectively. Estimates for K(PS) and fEV* but not fPV were significantly lower in a group consisting of benign and low-grade malignant tumors compared with the group of less-differentiated high-grade tumors (1.61 +/- 0.64 vs 3.37 +/- 1.49, p < 0.01; 0.45 +/- 0.17 vs 0.78 +/- 0.24, p < 0.01; and 0.076 +/- 0.048 vs 0.121 +/- 0.088, p = 0.24, respectively). It is concluded that the protein-avid MRI contrast agent Gadofluorine M enhances tumors of varying malignancy depending on the tumor grade, higher contrast agent accumulation for more malignant lesions. The results show potential utility for differentiating benign and low-grade malignant lesions from high-grade cancers.

Pharmacokinetics, biodistribution and contrast enhanced MR blood pool imaging of Gd-DTPA cystine copolymers and Gd-DTPA cystine diethyl ester copolymers in a rat model

PURPOSE

To investigate plasma pharmacokinetics and biodistribution of biodegradable polydisulfide Gd(III) complexes, Gd-DTPA cystine copolymers (GDCP) and Gd-DTPA cystine diethyl ester copolymers (GDCEP) and their efficacy as blood pool MRI contrast agents in comparison with a nondegradable macromolecular agent, Gd-DTPA 1,6-hexanediamine copolymers (GDHC).

METHODS

The pharmacokinetics and biodistribution of GDCP and GDCEP with molecular weight of 35 KDa were investigated in Sprague-Dawley rats after intravenous administration at a dose of 0.1 mmol Gd/kg. GDHC with the same molecular weight was used as a control. The Gd content in the plasma and various tissues and organs were determined by the ICP-OES. Plasma pharmacokinetic parameters were calculated by using a two-compartment model. The contrast enhanced blood pool MR imaging of the agents was evaluated in Sprague-Dawley rats on a Siemens Trio 3T MR scanner.

RESULTS

The biodegradable macromolecular agents, GDCP and GDCEP, had faster blood pool clearance than the nondegradable GDHC. The long-term Gd(III) tissue retention of the biodegradable polydisulfide agents was substantially lower than the nondegradable macromolecular agent. Both GDCP and GDCEP resulted in significant blood pool enhancement for the first 2 min post-injection and more rapid disappearance of the enhancement over time than GDHC. The negatively charged GDCP had prolonged enhancement duration as compared to GDCEP. The structure and biodegradability of the macromolecular contrast agents significantly affected their pharmacokinetics and blood pool contrast enhancement.

CONCLUSION

Both GDCP and GDCEP provided effective contrast enhancement for MR imaging of the blood pool. The accumulation of toxic Gd(III) ions in the body was greatly reduced with GDCP and GDCEP as compared to the nondegradable control.

Prostate dynamic contrast-enhanced MRI with simple visual diagnostic criteria: is it reasonable?

The purpose of this study was to evaluate the accuracy of prostate cancer localization with simple visual diagnostic criteria using dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI). A total of 46 consecutive patients with biopsy-proven prostate cancer underwent prostate 1.5 T MRI with pelvic phased-array coils before prostatectomy. Besides the usual T2-weighted sequences, a 30-s DCE sequence was acquired three times after gadoterate injection. On DCE images, all early enhancing lesions of the peripheral zone were considered malignant. In the central gland, only early enhancing lesions appearing homogeneous or invading the peripheral zone were considered malignant. Three readers specified the presence of cancer in 20 prostate sectors and the location of distinct tumors. Results were compared with histology; p < 0.05 was considered significant. For localization of cancer in the sectors, DCE imaging had a significantly higher sensitivity [logistic regression, odds ratio (OR): 3.9, p < 0.0001] and a slightly but significantly lower specificity (OR: 0.57, p < 0.0001). Of the tumors >0.3 cc, 50-60% and 78-81% were correctly depicted with T2-weighted and DCE imaging, respectively. For both techniques, the depiction rate of tumors >0.3 cc was significantly influenced by the Gleason score (most Gleason </=6 tumors were overlooked), but not by the tumor volume.

CONCLUSION

DCE-MRI using pelvic phased-array coils and simple visual diagnostic criteria is more sensitive for tumor localization than T2-weighted imaging.

Macromolecular MRI contrast agents for imaging tumor angiogenesis

Angiogenesis has long been accepted as a vital process in the growth and metastasis of tumors. As a result it is the target of several novel anti-cancer medications. Consequently, there is an urgent clinical need to develop accurate, non-invasive imaging techniques to improve the characterization of tumor angiogenesis and the monitoring of the response to anti-angiogenic therapy. Macromolecular MR contrast media (MMCM) offer this diagnostic potential by preferentially exploiting the inherent hyperpermeable nature of new tumor vessels compared with normal vessels. Over the last 10-15 years many classes of MMCM have been developed. When evaluated with dynamic contrast enhanced (DCE) MRI, a number of MMCM have demonstrated in vivo imaging properties that correlate with ex vivo histological features of angiogenesis. The enhancement patterns with some MMCM have been reported to correlate with tumor grade, as well as show response to anti-angiogenic and anti-vascular drugs. Future applications of MMCM include targeted angiogenesis imaging and drug delivery of anti-cancer 'payloads'. Herein we discuss the best known MMCMs along with their advantages and disadvantages.

Biodegradable cystamine spacer facilitates the clearance of Gd(III) chelates in poly(glutamic acid) Gd-DO3A conjugates for contrast-enhanced MR imaging

Poly(L-glutamic acid) (PGA)-cystamine-[gadolinium (Gd)-DO3A] was prepared in high yield with a high Gd-DO3A conjugation efficiency. Approximately 55% of the carboxylic groups in PGA were loaded with Gd-DO3A via cystamine as the spacer. Cystamine can be readily cleaved by endogenous thiols to release the Gd(III) chelates from the conjugate facilitating Gd(III) excretion after the magnetic resonance imaging (MRI). The contrast-enhanced MRI with PGA-cystamine-(Gd-DO3A) was investigated in mice bearing MDA-MB-231 breast carcinoma xenografts. PGA-1,6-hexanediamine-(Gd-DO3A), a paramagnetic polymer conjugate of a nondegradable spacer, was used as a control. Both conjugates resulted in similar contrast enhancement in the heart, vasculature, liver and kidneys in the first hour post injection. More substantial signal intensity reduction was observed for PGA-cystamine-(Gd-DO3A) in these organs than PGA-1,6-hexanediamine-(Gd-DO3A) due to release of the Gd chelates from PGA-cystamine-(Gd-DO3A) after the cleavage of the disulfide spacer by the endogenous thiols. Both conjugates resulted in similar tumor enhancement with approximately 70% increased signal intensity in the tumor periphery and 10-40% increased signal intensity in tumor interstitium. No cross-reaction was observed between PGA-cystamine-(Gd-DO3A) and human serum albumin, a plasma protein containing a cysteine residue. PGA-cystamine-(Gd-DO3A) resulted in significantly lower Gd(III) tissue retention than PGA-1,6-hexanediamine-(Gd-DO3A) 10 days after the injection in the mice (P<.05). The conjugation of Gd(III) chelates to biomedical copolymers via the degradable disulfide spacer resulted in significant contrast enhancement in the blood pool and tumor tissue but minimal long-term Gd(III) tissue retention.

Effect of size and charge on pharmacokinetics and in vivo MRI contrast enhancement of biodegradable polydisulfide Gd(III) complexes

The purpose of this study is to investigate how the structures of polydisulfide Gd(III) complexes affect their pharmacokinetics and in vivo contrast enhancement as biodegradable macromolecular MRI contrast agents. A negatively charged polydisulfide Gd(III) complex, (Gd-DTPA)-cystine copolymers (GDCP), and a neutral agent, (Gd-DTPA)-cystine diethyl ester copolymers (GDCEP), with different molecular weights were prepared and characterized. The MRI contrast enhancement of the agents was studied in mice. Neutral GDCEP showed more rapid degradation than negatively charged GDCP in the blood plasma. Consequently, GDCP resulted in more significant and prolonged contrast enhancement in the blood pool and liver than GDCEP. The size of GDCEP did not significantly affect its in vivo contrast enhancement due to rapid degradation and clearance from the blood circulation. The increase in the molecular weight of GDCP resulted in prolonged in vivo contrast enhancement in the blood pool. The structural modification of polydisulfide Gd(III) complexes resulted in biodegradable macromolecular MRI contrast agents with different degradability and in vivo contrast enhancement.

Hypoxia in the tumorigenesis of gliomas and as a potential target for therapeutic measures

✓ In this article, the author provides a brief description of the role of hypoxia in the tumorigenesis of gliomas and suggests potential ways of exploiting this role to design treatment modalities. Tumor hypoxia predicts the likelihood of metastases, tumor recurrence, resistance to chemotherapy and radiation therapy, invasive potential, and decreased patient survival for many human malignancies. Various methods of measurement of tumor hypoxia are discussed, including direct measurement and imaging methods.

The role of hypoxia-responsive molecules, especially hypoxia-inducible factor-1 (HIF-1), in glioma tumorigenesis is explored. Treatment modalities regulated by hypoxia are proposed and some potential strategies reviewed. The progression of a low-grade astrocytoma to a glioblastoma multiforme may be mediated by hypoxia-induced phenotypic changes and subsequent clonal selection of cells that overexpress hypoxia-responsive molecules, such as HIF-1. In this model, intratumoral hypoxia causes genetic changes that produce a microenvironment that selects for cells of a more aggressive phenotype.

Magnetic Resonance Macromolecular Agents for Monitoring Tumor Microvessels and Angiogenesis Inhibition

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) using macromolecular contrast media enables assessments of the tumor vasculature based on the differential distribution of the contrast agent within normal and pathologic tissues. Quantitative assays of both morphologic and functional properties can provide useful diagnostic insight into tissue angiogenesis. The use of MRI enhanced with macromolecular agents for the characterization of tumor microvessels has been experimentally demonstrated in a range of malignant tumor types. Kinetic analysis of DCE-MRI data can be used to estimate microvascular permeability and tumor blood volume. By measuring these functional tumor properties, an accurate, noninvasive, and quantitative description of the microcirculation of individual tumors can be acquired, improving the specificity of imaging examinations for cancer diagnosis and for treatment and follow up. The noninvasive MRI assessment of tumor angiogenesis can be applied in the diagnostic differentiation between benign and malignant tumors and can also provide means for in vivo monitoring of antitumor therapy. In this review, the potential clinical applications and limitations of various macromolecular contrast agents applied for evaluations of tumor angiogenesis, with and without drug interventions, are discussed.

Innovative Diagnostik in der Früherkennung und beim Staging des lokalisierten Prostatakarzinoms

Prostate cancer is the most common malignancy in males. Men aged 50 years and older are recommended to undergo an annual digital rectal examination (DRE) and determination of prostate-specific antigen (PSA) in serum for early detection. Fortunately, disease-specific mortality continues to decline as a result of advances in screening, staging, and patient awareness. However, about 30% of men with a clinically organ-confined disease show evidence of extracapsular extension or seminal vesicle invasion on pathological analysis. Consequently, there is a need for more accurate diagnostic tools for planning tailored treatment. A variety of modern imaging techniques has been implemented in an attempt to obtain more precise staging, thereby allowing for more detailed counseling, and instituting optimum therapy. This review highlights developments in prostate cancer imaging that may improve staging and treatment planning for prostate cancer patients.

Dynamic contrast-enhanced and diffusion MRI show rapid and dramatic changes in tumor microenvironment in response to inhibition of HIF-1alpha using PX-478

PX-478 is a new agent known to inhibit the hypoxia-responsive transcription factor, HIF-1alpha, in experimental tumors. The current study was undertaken in preparation for clinical trials to determine which noninvasive imaging endpoint(s) is sensitive to this drug's actions. Dynamic contrast-enhanced (DCE) and diffusion-weighted (DW) magnetic resonance imaging (MRI) were used to monitor acute effects on tumor hemodynamics and cellularity, respectively. Mice bearing human xenografts were treated either with PX-478 or vehicle, and imaged over time. DW imaging was performed at three b values to generate apparent diffusion coefficient of water (ADCw) maps. For DCE-MRI, a macromolecular contrast reagent, BSA-Gd-DTPA, was used to determine vascular permeability and vascular volume fractions. PX-478 induced a dramatic reduction in tumor blood vessel permeability within 2 hours after treatment, which returned to baseline by 48 hours. The anti-VEGF antibody, Avastin, reduced both the permeability and vascular volume. PX-478 had no effect on the perfusion behavior of a drug-resistant tumor system, A-549. Tumor cellularity, estimated from ADCw, was significantly decreased 24 and 36 hours after treatment. This is the earliest significant response of ADC to therapy yet reported. Based on these preclinical findings, both of these imaging endpoints will be included in the clinical trial of PX-478.

Contrast-enhanced MRI with new biodegradable macromolecular Gd(III) complexes in tumor-bearing mice

The structures of polydisulfide-based biodegradable macromolecular Gd(III) complexes were modified to improve their in vivo retention time and MRI contrast enhancement. Steric hindrance was introduced around the disulfide bonds to control their access to free thiols in order to alter the degradation rate of the copolymers. Two new macromolecular agents, (Gd-DTPA)-cystine copolymers (GDCP) and (Gd-DTPA)-cystine diethyl ester copolymers (GDCEP), were prepared. Both agents were readily degraded in vitro and in vivo by the disulfide-thiol exchange reaction, but at a slow rate. The introduction of COOH and COOEt groups slowed down the degradation of the copolymers in the incubation with 15 microM cysteine. Metabolic degradation products were identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry in the urine samples from rats injected with the agents. The T(1) relaxivity (r(1)) was 5.43 mM(-1)s(-1) for GDCP, and 5.86 mM(-1)s(-1) for GDCEP, respectively, at 3T. MRI contrast enhancement of both agents was studied in nude mice bearing MDA-BM-231 human breast carcinoma xenografts, on a Siemens Trio 3T scanner. The modified agents resulted in more significant contrast enhancement in the blood pool and tumor periphery than (Gd-DTPA)-cystamine copolymers (GDCC) and a low-molecular-weight control agent, Gd-(DTPA-BMA), at a dose of 0.1 mmol-Gd/kg. The results demonstrate that the structural modification of the biodegradable macromolecular Gd(III) complexes resulted in a relatively slow degradation of the macromolecules and significantly improved in vivo contrast enhancement. The modified agents show promise for use in investigations of blood pool and cancer by contrast-enhanced (CE) MRI.

Early Antiangiogenic Activity of SU11248 Evaluated In vivo by Dynamic Contrast-Enhanced Magnetic Resonance Imaging in an Experimental Model of Colon Carcinoma

PURPOSE

To compare two dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) techniques in terms of their ability in assessing the early antiangiogenic effect of SU11248, a novel selective multitargeted tyrosine kinase inhibitor, that exhibits direct antitumor and antiangiogenic activity via inhibition of the receptor tyrosine kinases platelet-derived growth factor receptor, vascular endothelial growth factor receptor, KIT, and FLT3.

EXPERIMENTAL DESIGN

A s.c. tumor model of HT29 human colon carcinoma in athymic mice was used. Two DCE-MRI techniques were used based, respectively, on macromolecular [Gd-diethylenetriaminepentaacetic acid (DTPA)-albumin] and low molecular weight (Gd-DTPA) contrast agents. The first technique provided a quantitative measurement of transendothelial permeability and fractional plasma volume, accepted surrogate markers of tumor angiogenesis. With the second technique, we quantified the initial area under the concentration-time curve, which gives information related to tumor perfusion and vascular permeability. Experiments were done before and 24 hours after a single dose administration of SU11248.

RESULTS

The early antiangiogenic effect of SU11248 was detected by DCE-MRI with macromolecular contrast agent as a 42% decrease in vascular permeability measured in the tumor rim. The effect was also detected by DCE-MRI done with Gd-DTPA as a 31% decrease in the initial area under the concentration-time curve. Histologic slices showed a statistically significant difference in mean vessel density between the treated and control groups.

CONCLUSIONS

The early antiangiogenic activity of SU11248 was detected in vivo by DCE-MRI techniques using either macromolecular or low molecular weight contrast agents. Because DCE-MRI techniques with low molecular weight contrast agents can be used in clinical studies, these results could be relevant for the design of clinical trials based on new paradigms.

Magnetic resonance characterization of tumor microvessels in experimental breast tumors using a slow clearance blood pool contrast agent (carboxymethyldextran-A2-Gd-DOTA) with histopathological correlation

Carboxymethyldextran (CMD)-A2-Gd-DOTA, a slow clearance blood pool contrast agent with a molecular weight of 52.1 kDa, designed to have intravascular residence for more than 1 h, was evaluated for its potential to characterize and differentiate the microvessels of malignant and benign breast tumors. Precontrast single-slice inversion-recovery snapshot FLASH and dynamic contrast-enhanced MRI using an axial T1-weighted three-dimensional spoiled gradient recalled sequence was performed in 30 Sprague-Dawley rats with chemically induced breast tumors. Endothelial transfer coefficient and fractional plasma volume of the breast tumors were estimated from MRI data acquired with CMD-A2-Gd-DOTA enhancement injected at a dose of 0.1 mmol Gd/kg body weight using a two-compartment bidirectional model of the tumor tissue. The correlation between MRI microvessel characteristics and histopathological tumor grade was determined using the Scarff-Bloom-Richardson method. Using CMD-A2-Gd-DOTA, no significant correlations were found between the MR-estimated endothelial transfer coefficient or plasma volumes with histological tumor grade. Analysis of CMD-A2-Gd-DOTA-enhanced MR kinetic data failed to demonstrate feasibility for the differentiation of benign from malignant tumors or for image-based tumor grading.

Pharmacokinetics and tissue retention of (Gd-DTPA)-cystamine copolymers, a biodegradable macromolecular magnetic resonance imaging contrast agent

PURPOSE

To investigate the pharmacokinetics, long-term tissue retention of Gd(III) ions, and magnetic resonance imaging (MRI) contrast enhancement of extracellular biodegradable macromolecular Gd(III) complexes, (Gd-DTPA)-cystamine copolymers (GDCC), of different molecular weights.

METHODS

The pharmacokinetics of blood clearance and long-term Gd(III) retention of GDCC were investigated in Sprague-Dawley rats. Pharmacokinetic parameters were calculated by using a two-compartment model. The blood pool contrast enhancement of GDCC was evaluated in Sprague-Dawley rats on a Siemens Trio 3T MR scanner. Gd-(DTPA-BMA) was used as a control.

RESULTS

The alpha phase half-life of Gd-(DTPA-BMA) and GDCC with molecular weights of 18,000 (GDCC-18) and 60,000 Da (GDCC-60) was 0.48 +/- 0.16 min, 1.08 +/- 0.24 min, and 1.74 +/- 0.57 min, and the beta phase half-life was 21.2 +/- 5.5 min, 26.5 +/- 5.9 min, and 53.7 +/- 15.9 min, respectively. GDCC had minimal long-term Gd tissue retention comparable to that of Gd-(DTPA-BMA). GDCC resulted in more significant contrast enhancement in the blood pool than Gd-(DTPA-BMA).

CONCLUSIONS

GDCC provides a prolonged blood pool retention time for effective MRI contrast enhancement and then clears rapidly with minimal accumulation of Gd (III) ions. It is promising for further development as a blood pool MRI contrast agent.

Synthesis and characterization of poly(L-glutamic acid) gadolinium chelate: a new biodegradable MRI contrast agent

Most currently evaluated macromolecular contrast agents for magnetic resonance imaging (MRI) are not biodegradable. The goal of this study is to synthesize and characterize poly(l-glutamic acid) (PG) gadolinium chelates as biodegradable blood-pool MRI contrast agents. Two PG chelates of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) were synthesized through the use of difunctional and monofunctional DTPA precursors. The conjugates were characterized with regard to molecular weight and molecular weight distribution, gadolinium content, relaxivity, and degradability. Distributions of the polymeric MRI contrast agents in various organs were determined by intravenous injection of (111)In-labeled polymers into mice bearing murine breast tumors. MRI scans were performed at 1.5 T in mice after bolus injection of the polymeric chelates. PG-Hex-DTPA-Gd, obtained from aminohexyl-substituted PG and DTPA-dianhydride, was partially cross-linked and was undegradable in the presence of cathepsin B. On the other hand, PG-Bz-DTPA-Gd synthesized directly from PG and monofunctional p-aminobenzyl-DTPA(acetic acid-tert-butyl ester) was a linear polymer and was degradable. The relaxivities of the polymers at 1.5 T were 3-8 times as great as that of Gd-DTPA. Both polymers had high blood concentrations and were primarily accumulated in the kidney. However, PG-Bz-DTPA-Gd was gradually cleared from the body and had significantly less retention in the blood, the spleen, and the kidney. MRI with PG-Bz-DTPA-Gd in mice showed enhanced vascular contrast at up to 2 h after the contrast agent injection. The ability of PG-Bz-DTPA-Gd to be degraded and cleared from the body makes it a favorable macromolecular MRI contrast agent.

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.

The Thioredoxin-1 Inhibitor 1-Methylpropyl 2-Imidazolyl Disulfide (PX-12) Decreases Vascular Permeability in Tumor Xenografts Monitored by Dynamic Contrast Enhanced Magnetic Resonance Imaging

Purpose: The purpose of this study was to use dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) to measure changes in tumor xenograft permeability produced by the antitumor thioredoxin-1 (Trx-1) inhibitor 1-methylpropyl 2-imidazolyl disulfide (PX-12) and to assess the relationship to Trx-1 and vascular endothelial growth factor (VEGF) levels.

Experimental Design: DCE-MRI was used to monitor the dynamics of gadolinium-diethylenetriaminepentaacetic acid coupled bovine serum albumin as a macromolecular contrast reagent to measure hemodynamic changes in HT-29 human colon xenografts in immunodeficient mice treated with PX-12. Blood vessel permeability was estimated from the slope of the enhancement curves, and tumor vascular volume fraction from the ordinate. Tumor Trx-1 and VEGF was also measured.

Results: PX-12 caused a rapid 63% decrease in the average tumor blood vessel permeability within 2 hours of administration. The decrease lasted 24 hours and had returned to pretreatment values by 48 hours. The changes in vascular permeability were not accompanied by alterations in average tumor vascular volume fraction. There was a decrease in tumor and tumor-derived VEGF in plasma at 24 hours after treatment with PX-12, but not at earlier time points. However, tumor redox active Trx-1 showed a rapid decline within 2 hours following PX-12 administration that was maintained for 24 hours.

Conclusion: The rapid decrease in tumor vascular permeability caused by PX-12 administration coincided with a decrease in tumor redox active Trx-1 and preceded a decrease in VEGF. DCE-MRI responses to PX-12 in patients of Trx-1 inhibition at early time points and decreased VEGF at later times, may be useful to follow tumor response and even therapeutic benefit.

Dynamic contrast-enhanced magnetic resonance imaging rapidly indicates vessel regression in human squamous cell carcinomas grown in nude mice caused by VEGF receptor 2 blockade with DC101

The purpose of our study was the investigation of early changes in tumor vascularization during antiangiogenic therapy with the vascular endothelial growth factor (VEGF) receptor 2 antibody (DC101) using dynamic contrast-enhanced magnetic resonance imaging (DCE MRI). Subcutaneous heterotransplants of human skin squamous cell carcinomas in nude mice were treated with DC101. Animals were examined before and repeatedly during 2 weeks of antiangiogenic treatment using Gd-DTPA-enhanced dynamic T1-weighted MRI. With a two-compartment model, dynamic data were parameterized in "amplitude" (increase of signal intensity relative to precontrast value) and k(ep) (exchange rate constant). Data obtained by MRI were validated by parallel examinations of histological sections immunostained for blood vessels (CD31). Already 2 days after the first DC101 application, a decrease of tumor vascularization was observed, which preceded a reduction of tumor volume. The difference between treated tumors and controls became prominent after 4 days, when amplitudes of treated tumors were decreased by 61% (P =.02). In line with change of microvessel density, the decrease in amplitudes was most pronounced in tumor centers. On day 7, the mean tumor volumes of treated (153 +/- 843 mm(3)) and control animals (596 +/- 384 mm(3)) were significantly different (P =.03). After 14 days, treated tumors showed further growth reduction (83 +/- 93 mm(3)), whereas untreated tumors (1208 +/- 822 mm(3)) continued to increase (P =.02). Our data underline the efficacy of DC101 as antiangiogenic treatment in human squamous cell carcinoma xenografts in nude mice and indicate DCE MRI as a valuable tool for early detection of treatment effects before changes in tumor volume become apparent.