Preclinical evaluation of gadolinium (III) texaphyrin complex. A new paramagnetic contrast agent for magnetic resonance imaging

Metalloporphyrin Nanoparticles: Coordinating Diverse Theranostic Functions

Metalloporphyrins serve key roles in natural biological processes and also have demonstrated utility for biomedical applications. They can be encapsulated or grafted in conventional nanoparticles or can self-assemble themselves at the nanoscale. A wide range of metals can be stably chelated either before or after porphyrin nanoparticle formation, without the necessity of any additional chelator chemistry. The addition of metals can substantially alter a range of behaviors such as modulating phototherapeutic efficacy; conferring responsiveness to biological stimuli; or providing contrast for magnetic resonance, positron emission or surface enhanced Raman imaging. Chelated metals can also provide a convenient handle for bioconjugation with other molecules via axial coordination. This review provides an overview of some recent biomedical, nanoparticulate approaches involving gain-of-function metalloporphyrins and related molecules.

Motexafin gadolinium: a novel radiosensitizer for brain tumors

Despite advances in the field of oncology, progress for patients with brain metastases and most primary brain tumors has been slow. New efforts to enhance the therapeutic index of radiation therapy are under way, including the use of radiosensitizers. Motexafin gadolinium (Xcytrin) is one such novel agent with several unique properties that enhance the cytotoxic potential of radiation therapy, as well as several chemotherapeutic agents, and possibly has independent cytotoxicity in certain lymphoid malignancies. Motexafin gadolinium is very well tolerated with tumor specific uptake. The rationale for the use of this drug as well as its current and future role as a radiation enhancer in the management of brain tumors is reviewed.

Recent developments in texaphyrin chemistry and drug discovery

Texaphyrins are pentaaza expanded porphyrins with the ability to form stable complexes with a variety of metal cations, particularly those of the lanthanide series. In biological milieus, texaphyrins act as redox mediators and mediate the production of reactive oxygen species (ROS). In this review, newer studies involving texaphyrin complexes targeting several different applications in anticancer therapy are described. In particular, the preparation of bismuth and lead texaphyrin complexes as potential α-core emitters for radiotherapy is detailed, as are gadolinium texaphyrin functionalized magnetic nanoparticles with features that make them of interest as dual-mode magnetic resonance imaging contrast agents and as constructs with anticancer activity mediated through ROS-induced sensitization and concurrent hyperthermia. Also discussed are gadolinium texaphyrin complexes as possible carrier systems for the targeted delivery of platinum payloads.

Texaphyrins and water-soluble zinc(II) ionophores: development, mechanism of anticancer activity, and synergistic effects

Texaphyrins, first prepared by Sessler and coworkers in the 1980s, represent early examples of expanded porphyrins. This class of pentaaza, oligopyrrolic macrocycles demonstrates excellent tumor localization and metal-chelating properties. In biological milieus, texaphyrins act as redox mediators and are able to produce reactive oxygen species. Furthermore, texaphyrins have been shown to upregulate zinc in vivo, an important feature that inspired us to develop new zinc ionophores that might allow the same function to be elicited but via a simpler chemical means. In this review, the basic properties of texaphyrins and the zinc ionophores they helped spawn will be discussed in the cadre of developing an understanding that could lead to the preparation of new, redox-active anticancer agents.

Strategies for Target-Specific Contrast Agents for Magnetic Resonance Imaging

This review describes recent research efforts focused on increasing the specificity of contrast agents for proton magnetic resonance imaging (MRI). Contrast agents play an indispensable role in MRI by enhancing the inherent contrast of images; however, the non-specific nature of current clinical contrast agents limits their usefulness. This limitation can be addressed by conjugating contrast agents or contrast-agent-loaded carriers-including polymers, nanoparticles, dendrimers, and liposomes-to molecules that bind to biological sites of interest. An alternative approach to conjugation is synthetically mimicking biological structures with metal complexes that are also contrast agents. In this review, we describe the advantages and limitations of these two targeting strategies with respect to translation from in vitro to in vivo imaging while focusing on advances from the last ten years.

Gadolinium complexes of chlorin derivatives applicable for MRI contrast agents and PDT

One of the ultimate goals of contrast agent (CA) research in magnetic resonance imaging (MRI) is to identify tumor-seeking materials. Thus, cancer diagnosis by Photodynamic Therapy (PDT) using photosensitizer will be one of the best tools for cancer research. By linking paramagnetic gadolinium [ Gd(III) ] ion to tumor selective chlorin-based photosensitizers, the cancer cell can be easily detected with high sensitivity and cured by appropriate laser irradiation simultaneously. The synthesis of monomer and dimer chlorin derivatives, such as pyropheophorbide-a and purpurin systems, conjugated with Gd(III) diethylenetriaminepentaacetic acid (DTPA) by means of diethylene-triaminepentaacetic dianhydride (caDTPA) for the evaluation as CAs for MRI was described in the present study.

Prolonged intracerebral convection-enhanced delivery of topotecan with a subcutaneously implantable infusion pump

Intracerebral convection-enhanced delivery (CED) of chemotherapeutic agents currently requires an externalized catheter and infusion system, which limits its duration because of the need for hospitalization and the risk of infection. To evaluate the feasibility of prolonged topotecan administration by CED in a large animal brain with the use of a subcutaneous implantable pump. Medtronic Synchromed-II pumps were implanted subcutaneously for intracerebral CED in pigs. Gadodiamide (28.7 mg/mL), with or without topotecan (136 μM), was infused at 0.7 mL/24 h for 3 or 10 days. Pigs underwent magnetic resonance imaging before and at 6 times points after surgery. Enhancement and FLAIR+ volumes were calculated in a semi-automated fashion. Magnetic resonance spectroscopy-based topotecan signature was also investigated. Brain histology was analyzed by hematoxylin and eosin staining and with immunoperoxidase for a microglial antigen. CED of topotecan/gadolinium was well tolerated in all cases (n = 6). Maximum enhancement volume was reached at day 3 and remained stable if CED was continued for 10 days, but it decreased if CED was stopped at day 3. Magnetic resonance spectroscopy revealed a decrease in parenchymal metabolites in the presence of topotecan. Similarly, the combination of topotecan and gadolinium infusion led to a FLAIR+ volume that tended to be larger than that seen after the infusion of gadolinium alone. Histological analysis of the brains showed an area of macrophage infiltrate in the ipsilateral white matter upon infusion with topotecan/gadolinium. Intracerebral topotecan CED is well tolerated in a large animal brain for up to 10 days. Intracerebral long-term CED can be achieved with a subcutaneously implanted pump and provides a stable volume of distribution. This work constitutes a proof of principle for the safety and feasibility for prolonged CED, providing a means of continuous local drug delivery that is accessible to the practicing neuro-oncologist.

Reactive oxygen species: an Achilles' heel of melanoma?

The successful treatment of melanoma has been hampered by the unique biology of this cancer. Fortunately, research to further our understanding of how melanoma cells differ from normal tissues has led to the discovery of potential new avenues of attack. One promising strategy relates to targeting the excess free radicals produced by melanomas. Melanocyte transformation into cancer is associated with significant structural alterations in the melanosome. In addition to pigment production, melanosomes also protect the cell by scavenging free radicals generated by sunlight and cellular metabolism. In melanoma, the disrupted and disorganized melanosome structure reverses this process. Melanosomes found in melanoma produce free radicals, such as hydrogen peroxide, furthering DNA damage. Melanosome generation of reactive oxygen species (ROS), in tandem with those generated by cancer metabolism, activate cellular signal transduction pathways that prevent cell death. ROS activation of proto-oncogene pathways in melanoma contributes to their resistance to chemotherapy. Fortunately, it may be possible to target these free radicals, just as Paris was able to successfully target Achilles' heel. The use of agents that block ROS scavenging, such as ATN-224 and disulfiram, have been explored clinically. A recent randomized Phase II trial with elesclomol, an agent that generates ROS, in combination with paclitaxel led to improved patient survival, suggesting that this may be a viable approach to advance the treatment of melanoma.

Gadolinium texaphyrin (Gd-Tex)-malonato-platinum conjugates: synthesis and comparison with carboplatin in normal and Pt-resistant cell lines

The synthesis of a new PEG-solubilized gadolinium texaphyrin (Gd-Tex) conjugate containing a malonate-Pt(NH(3))(2) moiety is described. The effect of the tumor localizing Gd-Tex macrocycle on platinum activity was evaluated in cell culture. The malonate moiety, analogous to that present in carboplatin, is expected to release an aquated Pt(NH(3))(2) species under physiological conditions. The half-life in phosphate-buffered saline was found to be ca. 3 days at room temperature, and the hydrolytic product released from the conjugate was collected and confirmed as Pt-based by flameless atomic absorption spectrophotometry. Anti-proliferative activity was tested using A549 human lung cancer and A2780 human ovarian cancer cell lines. In both cell lines, the activity of the Gd-Tex conjugate was found to be similar to that of carboplatin. Efficacy against a Pt-resistant ovarian cell line greater than that displayed by carboplatin was also observed.

Molecular MRI of hematopoietic stem-progenitor cells: in vivo monitoring of gene therapy and atherosclerosis

A characteristic feature of atherosclerotic cardiovascular disease is the diffuse involvement of arteries across the entire human body and the presence of multiple, simultaneous lesions. The diffuse nature of this disease creates a unique challenge for early diagnosis and effective treatment. We believe that recent progress in the field of molecular MRI has opened new avenues towards solving the problem. A new technology has been developed that uses molecular MRI to monitor the migration and homing of hematopoietic stem-progenitor cells to injured arteries and atherosclerosis. In this Review, we introduce several novel technical developments in the field of molecular MRI of atherosclerosis, including advanced techniques for magnetic labeling of stem-progenitor cells and molecular MRI of hematopoietic bone marrow cells migrating to injured arteries and homing to atherosclerotic plaques. In addition, we examine molecular MRI of vascular gene therapy mediated by stem-progenitor cells. These new techniques provide the basis for the further development of in vivo MRI techniques to monitor stem-cell-mediated vascular gene therapy for multiple and diffuse atherosclerotic cardiovascular lesions.

Motexafin gadolinium injection for the treatment of brain metastases in patients with non-small cell lung cancer

Despite recent advances in technology, targeting, and chemotherapy, brain metastasis from non-small cell lung cancer (NSCLC) remains a significant problem. The vast majority of patients with this diagnosis undergo whole brain radiation therapy (WBRT). However, outcomes are still quite poor with median survivals measured in only months. In an effort to enhance outcomes from external beam radiation treatments, radiosensitizers have been investigated. Motexafin gadolinium (MGd) (Xcytrin^®, Sunnyvale, CA, USA) is a novel radiation sensitizer with a unique mechanism of action that may increase the therapeutic index of WBRT for patients with brain metastases, particularly in those with NSCLC histologies. Here we review the rationale for the use of this drug as well as its current and future role as a radiation enhancer in the management of NSCLC brain metastasis.

CNS complications of breast cancer: current and emerging treatment options

In general, the development of CNS metastases of breast cancer depends on several prognostic factors, including younger age and a negative hormone receptor status. Also, the presence of a breast cancer 1, early onset (BRCA1) germline mutation and expression of the human epidermal growth factor receptor 2 (Her2/neu) proto-oncogene seem to contribute to an increased rate of development of CNS metastases. The choice of appropriate therapy for brain metastases also depends on prognostic factors, including the age of the patient, the Karnofsky performance score, the number of brain metastases and the presence of systemic disease. Surgery followed by whole brain radiation therapy (WBRT) is generally restricted to ambulant patients with a single brain metastasis without active extracranial disease. In patients who have two to four metastases, stereotactic focal radiotherapy (i.e. radiosurgery) with or without WBRT is usually indicated. In the remainder of patients, WBRT alone provides adequate palliation. Although breast carcinoma is sensitive to chemotherapy, the role of chemotherapy in the treatment of brain metastases is still unclear. Objective responses after cyclophosphamide-based therapies were reported in studies performed in the 1980s. Subgroup analysis of data from a randomised study indicates that survival may improve if WBRT is combined with the radiosensitiser efaproxiral. Interestingly, the Her2/neu antibody trastuzumab, which does not cross the blood-brain barrier, produces systemic responses and enhanced survival, without a clear effect on brain metastases. Breast cancer constitutes the most common solid primary tumour leading to leptomeningeal disease. Clinical symptoms such as cranial nerve dysfunction or a cauda equina syndrome can be treated with local radiotherapy. A randomised study in patients with leptomeningeal disease secondary to breast cancer has revealed that intrathecal chemotherapy is associated with substantially more adverse effects than non-intrathecal treatment, without a clear benefit in terms of response or survival. Intramedullary metastasis is rare but often presents with a rapidly progressive myelopathy. Local radiotherapy may preserve neurological function. Epidural spinal cord metastasis occurs in approximately 4% of patients and can lead to paraplegia. A randomised study has shown that surgical intervention together with local radiotherapy is superior to local radiotherapy alone.

Current issues and perspectives in small rodent magnetic resonance imaging using clinical MRI scanners

Small rodents such as mice and rats are frequently used in animal experiments for several reasons. In the past, animal experiments were frequently associated with invasive methods and groups of animals had to be killed to perform longitudinal studies. Today's modern imaging techniques such as magnetic resonance imaging (MRI) allow non-invasive longitudinal monitoring of multiple parameters. Although only a few institutions have access to dedicated small animal MR scanners, most institutions carrying out animal experiments have access to clinical MR scanners. Technological advances and the increasing field strength of clinical scanners make MRI a broadly available and viable technique in preclinical in vivo research. This review provides an overview of current concepts, limitations, and recent studies dealing with small animal imaging using clinical MR scanners.

Motexafin gadolinium: A novel redox active drug for cancer therapy

Motexafin gadolinium (MGd, Xcytrin) is an aromatic macrocycle that has a strong affinity for electrons, i.e., it is easily reduced. In the presence of oxygen, MGd accepts electrons from various cellular reducing metabolites and forms superoxide and other reactive oxygen species (ROS) by redox cycling. The reaction with NADPH is dramatically accelerated by various oxido-reductases including thioredoxin reductase. In vitro studies with various cancer cell lines have shown an increase in ROS and intracellular free zinc in cells treated with MGd. MGd increases cytotoxicity of ionizing radiation and various chemotherapy agents and may be directly cytotoxic to tumor cells under certain conditions. MGd selectively localizes in tumors, perhaps due to their metabolic perturbations. MGd treatment in murine models enhances tumor response to radiation and chemotherapy agents. In controlled, randomized clinical trials, combining MGd treatment with ionizing radiation improves time to neurologic progression in lung cancer patients with brain metastases. The molecular target for MGd appears to be thioredoxin reductase which, when inhibited, results in cellular redox stress, cytotoxicity and an increase in tumor responsiveness to a variety of treatments.

Motexafin gadolinium modulates levels of phosphorylated Akt and synergizes with inhibitors of Akt phosphorylation

Motexafin gadolinium (MGd, Xcytrin) is a tumor-selective expanded porphyrin that targets oxidative stress-related proteins. MGd treatment of the follicular lymphoma-derived cell line HF-1 resulted in growth suppression and apoptosis whereas MGd treatment of the Burkitt's lymphoma-derived cell line Ramos resulted in growth suppression but not apoptosis. Because phosphorylation status of Akt/protein kinase B is regulated by oxidative stress, we monitored total and phosphorylated Akt (pAkt) in MGd-treated HF-1 and Ramos cells. Levels of pAkt increased within 30 minutes after MGd treatment of HF-1 but after 4 hours began to show a progressive decline to below baseline levels before cells underwent apoptosis. In MGd-treated Ramos cells, pAkt increased approximately 2-fold within 4 hours and remained persistently elevated. Because pAkt activates survival pathways, we determined if MGd-induced cell death could be enhanced by inhibiting phosphorylation of Akt. The addition of specific inhibitors of Akt phosphorylation (Akt inhibitor 1 or SH-5) reduced pAkt levels in MGd-treated HF-1 and Ramos cells and synergistically enhanced MGd-induced cell death. MGd was also evaluated in combination with celecoxib, an inhibitor of Akt phosphorylation, or docetaxel, a microtubule inhibitor that can decrease Akt phosphorylation. The combination of MGd/celecoxib or MGd/docetaxel resulted in decreased Akt phosphorylation and in synergistic cytotoxicity compared with either agent alone. These data point to a potential protective role for pAkt in MGd-induced apoptosis and suggest that MGd activity may be enhanced by combining it with agents that inhibit Akt phosphorylation.

Validation and use of three complementary analytical methods (LC–FLS, LC–MS/MS and ICP–MS) to evaluate the pharmacokinetics, biodistribution and stability of motexafin gadolinium in plasma and tissues

Liquid chromatography-fluorescence (LC-FLS), liquid chromatography-tandem mass spectrometry (LC-MS/MS) and inductively coupled plasma-mass spectrometry (ICP-MS) methods were developed and validated for the evaluation of motexafin gadolinium (MGd, Xcytrin) pharmacokinetics and biodistribution in plasma and tissues. The LC-FLS method exhibited the greatest sensitivity (0.0057 microg mL(-1)), and was used for pharmacokinetic, biodistribution, and protein binding studies with small sample sizes or low MGd concentrations. The LC-MS/MS method, which exhibited a short run time and excellent selectivity, was used for routine clinical plasma sample analysis. The ICP-MS method, which measured total Gd, was used in conjunction with LC methods to assess MGd stability in plasma. All three methods were validated using human plasma. The LC-FLS method was also validated using plasma, liver and kidneys from mice and rats. All three methods were shown to be accurate, precise and robust for each matrix validated. For three mice, the mean (standard deviation) concentration of MGd in plasma/tissues taken 5 hr after dosing with 23 mg kg(-1) MGd was determined by LC-FLS as follows: plasma (0.025+/-0.002 microg mL(-1)), liver (2.89+/-0.45 microg g(-1)), and kidney (6.09+/-1.05 microg g(-1)). Plasma samples from a subset of patients with brain metastases from extracranial tumors were analyzed using both LC-MS/MS and ICP-MS methods. For a representative patient, > or = 90% of the total Gd in plasma was accounted for as MGd over the first hour post dosing. By 24 hr post dosing, 63% of total Gd was accounted for as MGd, indicating some metabolism of MGd.

MRI measurement of the uptake and retention of motexafin gadolinium in glioblastoma multiforme and uninvolved normal human brain

PURPOSE

Motexafin gadolinium (MGd) is an investigational pharmaceutical with radiation enhancing properties. Magnetic Resonance Imaging (MRI) was used to measure brain and tumor MGd levels to evaluate (1) the degree to which MGd passes through the intact blood brain barrier, and (2) the retention of MGd in tumor in patients with glioblastoma multiforme (GBM).

METHODS AND MATERIALS

MRI studies were performed on GBM patients who participated in a phase I clinical trial in which MGd was given during standard fractionated radiation therapy. MGd was administered daily (Monday to Friday) for five or 10 doses as a loading regimen, followed by three times per week dosing as a maintenance schedule. T1-weighted MRI was performed at intervals throughout the course of the MGd administration and radiation therapy in the 33 participating patients. Eleven patients had pre- and post-MGd scans, allowing for study of MGd's normal blood brain barrier penetration. Twenty-two patients had adequate residual tumor for measurements to evaluate MGd retention in tumor during the course of MGd and radiation administration.

RESULTS AND CONCLUSIONS

The studies of uninvolved brain tissue support the conclusion that MGd does not cross the intact blood brain barrier in detectable quantities. The tumor study showed MGd uptake during loading and maintenance without measurably significant fall off on non-dosage days during the maintenance dosing. Although the number of cases is small, the 10-day loading regimen showed greater drug loading and retention compared with the 5 days loading regimen.

Motexafin gadolinium induces mitochondriallymediated caspase-dependent apoptosis

Motexafin gadolinium (MGd, Xcytrin) is a tumor-localizing redox mediator that catalyzes the oxidation of intracellular reducing molecules including NADPH, ascorbate, protein and non-protein thiols, generating reactive oxygen species (ROS). MGd localizes to tumors and cooperates with radiation and chemotherapy to kill tumor cells in tissue culture and animal models. In this report, we demonstrate that MGd triggers the mitochondrial apoptotic pathway in the HF-1 lymphoma cell line as determined by loss of mitochondrial membrane potential, release of cytochrome c from mitochondria, activation of caspase-9 prior to caspase-8, cleavage of PARP and annexin V binding. There was minimal effect on MGd-induced apoptosis by the caspase inhibitor z-VAD-fmk, even though caspase-3 activity (as measured by DEVD-cleavage) was completely inhibited. However, MGd-induced apoptosis was reduced to baseline levels by the more potent caspase inhibitor Q-VD-OPh, demonstrating that MGd-induced apoptosis is indeed caspase-dependent. Apoptosis induced by dexamethasone, doxorubicin and etoposide (mediated through the mitochondrial pathway) was also more sensitive to inhibition by Q-VD-OPh than z-VAD-fmk. Our results demonstrating differential sensitivity of drug-induced apoptosis to caspase inhibitors suggest that the term "caspase-independent apoptosis" cannot be solely defined as apoptosis that is not inhibited by z-VAD-fmk as has been utilized in some published studies.

Mechanisms in photodynamic therapy: Part three-Photosensitizer pharmacokinetics, biodistribution, tumor localization and modes of tumor destruction

Photodynamic therapy (PDT) has been known for over a hundred years, but is only now becoming widely used. Originally developed as cancer therapy, some of its most successful applications are for non-malignant disease. The majority of mechanistic research into PDT, however, is still directed towards anti-cancer applications. In the final part of series of three reviews, we will cover the possible reasons for the well-known tumor localizing properties of photosensitizers (PS). When PS are injected into the bloodstream they bind to various serum proteins and this can affect their phamacokinetics and biodistribution. Different PS can have very different pharmacokinetics and this can directly affect the illumination parameters. Intravenously injected PS undergo a transition from being bound to serum proteins, then bound to endothelial cells, then bound to the adventitia of the vessels, then bound either to the extracellular matrix or to the cells within the tumor, and finally to being cleared from the tumor by lymphatics or blood vessels, and excreted either by the kidneys or the liver. The effect of PDT on the tumor largely depends at which stage of this continuous process light is delivered. The anti-tumor effects of PDT are divided into three main mechanisms. Powerful anti-vascular effects can lead to thrombosis and hemorrhage in tumor blood vessels that subsequently lead to tumor death via deprivation of oxygen and nutrients. Direct tumor cell death by apoptosis or necrosis can occur if the PS has been allowed to be taken up by tumor cells. Finally the acute inflammation and release of cytokines and stress response proteins induced in the tumor by PDT can lead to an influx of leukocytes that can both contribute to tumor destruction as well as to stimulate the immune system to recognize and destroy tumor cells even at distant locations.

Motexafin gadolinium induces oxidative stress and apoptosis in hematologic malignancies

Redox mechanisms have been shown to be important in malignant cell survival and are a system that may be modified for the treatment of hematologic malignancies. Motexafin gadolinium (MGd) is a synthetic expanded porphyrin that selectively accumulates in tumor cells and oxidizes various intracellular metabolites, including ascorbate, nicotinamide adenine dinucleotide phosphate, glutathione, and protein thiols, to generate reactive oxygen species in a process known as futile redox cycling. The rationale for its use in hematologic malignancies is that, like naturally occurring porphyrins, it tends to concentrate selectively in cancer cells, and it has a novel mechanism of action of inducing redox stress and triggering apoptosis in a broad range of malignancies. MGd induces apoptosis in B-cell non-Hodgkin's lymphoma, chronic lymphocytic leukemia, and highly resistant myeloma cell lines. Furthermore, MGd is additive or synergistic with ionizing radiation, several chemotherapy agents, and rituximab in vitro and in vivo tumor models. Through gene expression profiling, various stress-related genes are upregulated in response to MGd, including genes encoding metallothioneins, heat shock proteins, and heme oxygenase. Preliminary results from clinical trials with MGd in hematopoietic malignancies have shown that it is well tolerated, with minimal hematologic side effects in both; it has single agent activity in very heavily pretreated chronic lymphocytic leukemia /small lymphocytic lymphoma patients, and it has induced prompt complete remissions in combination with 90Yttrium-ibritumomab (Y-90 Zevalin; Biogen Idec Inc., Cambridge, MA) for relapsed non-Hodgkin's lymphoma in the first two cohorts of patients enrolled. Various clinical trials studying MGd as a single agent and in combination with radiation and/or chemotherapy for the treatment of hematologic malignancies are ongoing.

Necrosis Avid Contrast Agents

Two categories of necrosis-avid contrast agents (NACAs), namely porphyrin- and nonporphyrin-based complexes, have thus far been discovered as necrosis-targeting markers for noninvasive magnetic resonance imaging (MRI) identification of acute myocardial infarction, assessment of tissue or organ viability, and therapeutic evaluation after interventional therapies. In addition to necrosis labeling, other less-specific functions, such as first-pass perfusion, blood pool contrast effect, hepatobiliary contrast enhancement (CE), adrenal and spleen CE, and renal functional imaging, also are demonstrated with NACAs. Despite various investigations with a collection of clues in favor of certain hypotheses, the mechanisms of such a unique targetability for NACAs still remain to be elucidated. However, a few things have become clear that porphyrin-like structures are not necessary for necrosis avidity and the albumin binding is not the supposed driving force but only a parallel nonspecific feature shared by both NACAs and non-NACA substances. Although the research and development of NACAs still remain in preclinical stage at a relatively small scale, their significance rests upon striking enhancement effects, which may warrant their eventual versatile clinical applications. The present review article is intended to summarize the cumulated facts about the evolving research on this topic, to demonstrate experimental observations for better understanding of the mechanisms, to trigger broader public interests and more intensive research activities, and to advocate, toward both academics and industries, further promotion of preclinical and clinical development of this unique and promising class of contrast agents.

Effects of motexafin gadolinium on DNA damage and X-ray-induced DNA damage repair, as assessed by the Comet assay

PURPOSE

To investigate the effects of motexafin gadolinium (MGd) on the levels of reactive oxygen species (ROS), glutathione (GSH), and DNA damage in EMT6 mouse mammary carcinoma cells. The ability of MGd to alter radiosensitivity and to inhibit DNA damage repair after X-ray irradiation was also evaluated.

METHODS AND MATERIALS

Reactive oxygen species and GSH levels were assessed by 2,7-dichlorofluorescein fluorescence flow cytometry and the Tietze method, respectively. Cellular radiosensitivity was assessed by clonogenic assays. Deoxyribonucleic acid damage and DNA damage repair were assessed in plateau-phase EMT6 cells by the Comet assay and clonogenic assays.

RESULTS

Cells treated with 100 mumol/L MGd plus equimolar ascorbic acid (AA) had significantly increased levels of ROS and a 58.9% +/- 3.4% decrease in GSH levels, relative to controls. Motexafin gadolinium plus AA treatment increased the hypoxic, but not the aerobic, radiosensitivity of EMT6 cells. There were increased levels of single-strand breaks in cells treated with 100 mumol/L MGd plus equimolar AA, as evidenced by changes in the alkaline tail moment (MGd + AA, 6 h: 14.7 +/- 1.8; control: 2.8 +/- 0.9). The level of single-strand breaks was dependent on the length of treatment. Motexafin gadolinium plus AA did not increase double-strand breaks. The repair of single-strand breaks at 2 h, but not at 4 h and 6 h, after irradiation was altered significantly in cells treated with MGd plus AA (MGd + AA, 2 h: 15.8 +/- 3.4; control: 5.8 +/- 0.6). Motexafin gadolinium did not alter the repair of double-strand breaks at any time after irradiation with 10 Gy.

CONCLUSIONS

Motexafin gadolinium plus AA generated ROS, which in turn altered GSH homeostasis and induced DNA strand breaks. The MGd plus AA-mediated alteration of GSH levels increased the hypoxic, but not aerobic, radiosensitivity of EMT6 cells. Motexafin gadolinium altered the kinetics of single-strand break repair soon after irradiation but did not inhibit potentially lethal damage repair in EMT6 cells.

Motexafin gadolinium: a redox-active tumor selective agent for the treatment of cancer

PURPOSE OF REVIEW

Redox regulation has been shown to be an important component of malignant cell survival and is a system that may be pharmacologically manipulated for the treatment of cancer. Motexafin gadolinium is a member of a class of rationally designed porphyrin-like molecules called texaphyrins. The rationale for its use in cancer therapy is that, like naturally occurring porphyrins, it tends to concentrate selectively in cancer cells and it has a novel mechanism of action as it induces redox stress, triggering apoptosis in a broad range of cancers.

RECENT FINDINGS

In vitro studies have shown that motexafin gadolinium is synergistic with radiation and varied chemotherapeutic agents. A phase III international study has shown that the onset of neurologic progression is significantly delayed in patients with brain metastases from lung cancer treated with whole-brain radiation and motexafin gadolinium (compared with radiation alone). Recent preclinical data have shown that motexafin gadolinium alone is cytotoxic to cancers such as multiple myeloma, non-Hodgkin lymphoma, and chronic lymphocytic leukemia through redox and apoptotic pathways. Multiple clinical trials examining motexafin gadolinium as a single agent and in combination with radiation and/or chemotherapy for the treatment of solid and hematopoietic tumors are underway.

SUMMARY

Motexafin gadolinium is a novel tumor-targeted agent that disrupts redox balance in cancer cells by futile redox cycling. Motexafin gadolinium is currently in numerous hematology/oncology clinical trials for use as a single agent and in combination with chemotherapy and/or radiation therapy.

Cell tracking with gadophrin-2: a bifunctional contrast agent for MR imaging, optical imaging, and fluorescence microscopy

The purpose of this study was to assess the feasibility of use of gadophrin-2 to trace intravenously injected human hematopoietic cells in athymic mice, employing magnetic resonance (MR) imaging, optical imaging (OI), and fluorescence microscopy. Mononuclear peripheral blood cells from GCSF-primed patients were labeled with gadophrin-2 (Schering AG, Berlin, Germany), a paramagnetic and fluorescent metalloporphyrin, using established transfection techniques with cationic liposomes. The labeled cells were evaluated in vitro with electron microscopy and inductively coupled plasma atomic emission spectrometry. Then, 1x10(6)-3x10(8) labeled cells were injected into 14 nude Balb/c mice and the in vivo cell distribution was evaluated with MR imaging and OI before and 4, 24, and 48 h after intravenous injection (p.i.). Five additional mice served as controls: three mice were untreated controls and two mice were investigated after injection of unlabeled cells. The contrast agent effect was determined quantitatively for MR imaging by calculating signal-to-noise-ratio (SNR) data. After completion of in vivo imaging studies, fluorescence microscopy of excised organs was performed. Intracellular cytoplasmatic uptake of gadophrin-2 was confirmed by electron microscopy. Spectrometry determined an uptake of 31.56 nmol Gd per 10(6) cells. After intravenous injection, the distribution of gadophrin-2 labeled cells in nude mice could be visualized by MR, OI, and fluorescence microscopy. At 4 h p.i., the transplanted cells mainly distributed to lung, liver, and spleen, and 24 h p.i. they also distributed to the bone marrow. Fluorescence microscopy confirmed the distribution of gadophrin-2 labeled cells to these target organs. Gadophrin-2 is suited as a bifunctional contrast agent for MR imaging, OI, and fluorescence microscopy and may be used to combine the advantages of each individual imaging modality for in vivo tracking of intravenously injected hematopoietic cells.

Effects of texaphyrins on the oxygenation of EMT6 mouse mammary tumors

PURPOSE

To investigate the effects of texaphyrins on the oxygenation of EMT6 mouse mammary tumors in Balb/c Rw mice. Texaphyrins are synthetic, porphyrin-like molecules capable of stably coordinating lanthanide and nonlanthanide metals. Metallotexaphyrin compounds containing gadolinium (MGd), lutetium (MLu), europium (Eu-Tex), dysprosium (Dy-Tex), and manganese (Mn-Tex) were evaluated.

METHODS

Tumor oxygenation was measured using an Eppendorf pO2 histograph when tumors, implanted intradermally in the rear dorsum, reached 150-200 mm3. Oxygen measurements were also made in the leg muscle of tumor-bearing mice, to determine whether changes in oxygenation occurred in nontumor tissue.

RESULTS

Motexafin gadolinium (Xcytrin, MGd) seems to be an effective modulator of tumor oxygen tension. The mean of the median tumor pO2 6 hours after injection of MGd was 8.0 +/- 2.4 mm Hg. The control value was 1.5 +/- 0.4 mm Hg. The oxygen levels within EMT6 tumors were shifted significantly toward higher oxygen tensions 6-8 hours after i.v. injection of 40 micromol/kg MGd, thereby reducing the percentage of severely hypoxic readings (MGd, 6 hours: 44.6 +/- 4.3% <2.5 mm Hg;

CONTROL

69.4 +/- 3.0% <2.5 mm Hg). There was no significant change in the oxygenation of the leg muscle after MGd treatment. Eu-Tex and Mn-Tex increased the tumor oxygenation to a much lesser degree than MGd. MLu, Dy-Tex, and the vehicle (a 5% mannitol solution) did not modulate tumor oxygenation.

CONCLUSIONS

MGd is an effective modulator of tumor oxygenation. The central metal composition of texaphyrin compounds is an important determinant of the effect of the texaphyrins on tumor oxygenation.

Biodistribution Assessment of a Lutetium(III) Texaphyrin Analogue in Tumor-bearing Mice Using NIR Fourier-transform Raman Spectroscopy¶

The use of near-infrared (NIR)-excited Fourier-transform (FT) Raman spectroscopy as a technique for evaluating the extent of photosensitizer localization in tumor (human pancreatic adenocarcinomas)-bearing mice has been tested using lutetium(III) texaphyrin analogue Lu-T2B2Tex. The complex was injected subcutaneously in the form of three injections given during the course of 3 days. The kinetics of biodistribution were then followed over a time scale of 1-6 days. The NIR-FT-Raman spectra of tissue samples obtained from the xenographic tumor, muscle, heart, brain, liver, spleen, kidney and blood were recorded and used to identify the presence of Lu-T2B2Tex in these tissues. Five Raman sensitizer markers were used to estimate the relative content of Lu-T2B2Tex in tumor at various postinjection times. UV-Visible (Vis) absorption spectroscopic detection of this sensitizer in tissue extracts was applied as a conventional method. Both spectroscopic methods were in good agreement with each other and confirm that Lu-T2B2Tex localizes well in tumor tissue. Maximal drug content was observed 3 days after the final injection. This time delay seems to be optimal for tumor irradiation in photodynamic therapy.

Response to motexafin gadolinium and ionizing radiation of experimental rat prostate and lung tumors

PURPOSE

To investigate the responses of two experimental rat tumors to single and fractionated X-ray doses whether or not combined with Motexafin gadolinium (MGd), and the distribution of MGd in R3327-MATLyLu (MLL) tumors using MRI.

METHODS

L44 lung tumor in BN rats and MLL prostate tumor in Copenhagen rats were grown subcutaneously. MGd at concentrations of 8.7 to 25.1 micro mol/kg was administered 2 h before or just before treatments with single and fractionated X-ray doses. Tumor volume growth delay was the endpoint used. The two-dimensional distribution of the MGd concentration in time was analyzed simultaneously in slices through the center of MLL tumors using MRI. Directly after the MRI experiments, tumor sections were stained for cytoplasm, nuclei, and microvessel endothelium.

RESULTS

MGd at different concentrations administered a few minutes or 2 h before X-ray doses produced no radiation enhancement in the two tumor models. The MGd concentration as determined by MRI was maximal 5 min after injection and decreased slowly thereafter. In a representative section at the center of the MLL tumor, the microvessel density is nearly homogeneous and correlates with a nearly homogeneous MGd distribution. Hardly any MGd is taken up in underlying muscle tissue.

CONCLUSION

No radiosensitization was observed for the different irradiation regimens. The distribution of MGd is nearly homogeneous in the MLL tumor and hardly any MGd is taken up in underlying muscles. Our negative results on radiosensitivity in our two tumor models raise questions about the efficacy of MGd as a general radiosensitizing agent.

Dynamic enhancement features of gadophrin-2 on magnetic resonance imaging: an experimental model of VX2 carcinoma and bacterial abscess in rabbit thigh

RATIONALE AND OBJECTIVES

To determine the dynamic enhancement features of malignant tumor and bacterial abscess in rabbits on magnetic resonance imaging (MRI) after injection of gadolinium mesoporphyrin (gadophrin-2) and to correlate them with histopathologic findings.

METHODS

Six VX2 carcinomas and six bacterial abscesses were experimentally induced in either thigh of six rabbits. Dynamic T1-weighted MRI was performed before and 1, 3, 5, 10, 30 minutes and 16, 21, 72 hours after intravenous injection of gadophrin-2 (0.05 mmol/kg). The enhancement ratios of lesions were calculated for each time point. All tumors and abscesses were sectioned along the same plane of MR images for a detailed MRI-histopathologic correlation.

RESULTS

In tumors and abscesses, peripheral-rim enhancement appeared on MRI at 1, 3, 5, 10, 30 minutes after injection of gadophrin-2. The lesions showed peripheral enhancement with irregular central enhancement or diffuse enhancement after 16 and 21 hours, and there was diffuse enhancement of the entire lesion after 72 hours. Enhancement ratios in tumor-necrosis mixed area and the pure necrotic area in VX2 carcinoma and the central cavity in bacterial abscess were significantly lower than that in the compact cellular portion in VX2 carcinoma and the wall of abscess at early phase (P < 0.01). On delayed phase MRI, there was no statistical significance in enhancement ratio of three histologic parts of VX2 carcinoma (P > 0.05) and two histologic parts of abscess (P > 0.05). Rapid enhancement at early phase with diminishing signal intensity at delayed phase is indicative of viable compact tumor and delayed strong enhancement is indicative of necrosis.

CONCLUSION

It is difficult to distinguish an abscess from a tumor on gadophrin-2 enhanced MRI especially when intratumoral necrosis is prominent. However, the trend and degree of enhancement by gadophrin-2 could be helpful in discrimination between viable tumor and tumor necrosis.

Redox cycling by motexafin gadolinium enhances cellular response to ionizing radiation by forming reactive oxygen species

PURPOSE

To examine the mechanism of radiation enhancement by motexafin gadolinium (Gd-Tex) in vitro.

METHODS AND MATERIALS

Oxidation of ascorbate and NADPH by Gd-Tex was evaluated in a neutral buffer. Growth inhibition of human uterine cancer cell line MES-SA was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) dye. Clonogenic assays were used to measure radiation response in MES-SA, A549 human lung carcinoma, E89, a CHO cell line variant deficient in glucose-6-phosphate dehydrogenase activity, and murine lymphoma cell lines LYAR and LYAS.

RESULTS

Gd-Tex catalyzed the oxidation of NADPH and ascorbate under aerobic conditions, forming hydrogen peroxide. Decreased viability was observed in MES-SA cells incubated with Gd-Tex in media containing NADPH or ascorbate. Gd-Tex and ascorbate increased fluorescence in dichlorofluorescin acetate-treated cultures. Synergistic effects on the aerobic radiation response in MES-SA and A549 were seen using Gd-Tex in combination with L-buthionine-(S,R)-sulfoximine (BSO). Incubation with Gd-Tex in the presence of ascorbate increased the aerobic radiation response of E89 and the apoptosis-sensitive B-cell line (LYAS).

CONCLUSIONS

Gd-Tex sensitizes cells to ionizing radiation by increasing oxidative stress as a consequence of futile redox cycling. Optimization of the concentration of ascorbate (or other reducing species) may be required when evaluating Gd-Tex activity in vitro.

Occlusive myocardial infarction: investigation of bis-gadolinium mesoporphyrins-enhanced T1-weighted MR imaging in a cat model

PURPOSE

To test whether bis-gadolinium mesoporphyrins-enhanced magnetic resonance (MR) imaging can accurately depict irreversibly damaged myocardium in occlusive myocardial infarction.

MATERIALS AND METHODS

Ten cats were subjected to 90 minutes of occlusion of the left anterior descending coronary artery. Bis-gadolinium mesoporphyrins-enhanced T1-weighted MR imaging was performed in the cats for 6 hours. Histopathologic examinations with 2'3'5-triphenyl tetrazolium chloride (TTC) staining and electron microscopy were performed on the resected specimens. The time course and pattern of signal intensity enhancement were evaluated. The size of the infarcted myocardium was estimated on the MR images by measuring the size of the signal intensity-enhanced area.

RESULTS

In eight of 10 cats, it was impossible to distinguish infarcted myocardium from normal myocardium at visual inspection of T1-weighted MR images. The contrast ratio between infarcted and normal myocardium did not increase significantly over time. In one of the two remaining cats, a doughnut pattern of signal intensity enhancement was noted. The other cat showed intensely homogeneous enhancement of infarcted myocardium at MR imaging. The size of the area of signal intensity enhancement at MR imaging in these two cats was accurately mapped to that of the infarction on the TTC-stained specimens.

CONCLUSION

Occlusive myocardial infarction cannot be accurately detected at bis-gadolinium mesoporphyrins-enhanced MR imaging.

Effects of Motexafin gadolinium on tumor metabolism and radiation sensitivity

PURPOSE

Experiments were undertaken to determine if metabolic changes induced by Motexafin gadolinium (Gd-Tex(+2), XCYTRIN) predict time intervals between drug and radiation wherein there is enhancement of radiation efficacy.

METHODS AND MATERIALS

We evaluated the effect of Gd-Tex(+2) on tumor metabolism and on tumor growth using a mouse mammary carcinoma model and (31)P nuclear magnetic resonance (NMR) experiments. Response to therapy was evaluated based on time for the tumor to regrow to pretreatment size and also tumor doubling time.

RESULTS

(31)P NMR experiments indicated that Gd-Tex(+2) effected tumor energy metabolism during the first 24 hours postadministration. A decrease in phosphocreatine was noted at 2 (p < 0.04), 6 (p < 0.006), and 24 (p < 0.001) hours post Gd-Tex(+2). A decrease in nucleoside triphosphates was noted only at 2 hours (p < 0.02), with subsequent recovery at 6 hours. Phosphocreatine in control (saline treated) tumors showed a significant decrease only at 24 hours (p < 0.01). Irradiation at 2 and 6 hours post Gd-Tex(+2) induced an enhanced effect compared to radiation alone as measured by analyzing the growth curves, maximum tumor volumes, and the time for the tumors to regrow to their initial volumes. Irradiation at 24 hours post Gd-Tex(+2) induced a modest enhancement in tumor growth delay compared to radiation alone.

DISCUSSION

NMR spectroscopy may be useful for monitoring tumor metabolism after treatment with Gd-Tex(+2) and administering radiation during the time of maximal efficacy of Gd-Tex(+2).

Evaluation by contrast-enhanced MR imaging of the lateral border zone in reperfused myocardial infarction in a cat model

OBJECTIVE

To identify and evaluate the lateral border zone by comparing the size and distribution of the abnormal signal area demonstrated by MR imaging with the infarct area revealed by pathological examination in a reperfused myocardial infarction cat model.

MATERIALS AND METHODS

In eight cats, the left anterior descending coronary artery was occluded for 90 minutes, and this was followed by 90 minutes of reperfusion. ECG-triggered breath-hold turbo spin-echo T2-weighted MR images were initially obtained along the short axis of the heart before the administration of contrast media. After the injection of Gadomer-17 and Gadophrin-2, contrast-enhanced T1-weighted MR images were obtained for three hours. The size of the abnormal signal area seen on each image was compared with that of the infarct area after TTC staining. To assess ultrastructural changes in the myocardium at the infarct area, lateral border zone and normal myocardium, electron microscopic examination was performed.

RESULTS

The high signal area seen on T2-weighted images and the enhanced area seen on Gadomer-17-enhanced T1WI were larger than the enhanced area on Gadophrin-2-enhanced T1WI and the infarct area revealed by TTC staining; the difference was expressed as a percentage of the size of the total left ventricle mass (T2= 39.2 %; Gadomer-17 =37.25 % vs Gadophrin-2 = 29.6 %; TTC staining = 28.2 %; p < 0.05). The ultrastructural changes seen at the lateral border zone were compatible with reversible myocardial damage.

CONCLUSION

In a reperfused myocardial infarction cat model, the presence and size of the lateral border zone can be determined by means of Gadomer-17- and Gadophrin-2-enhanced MR imaging.

Sensitive high-performance liquid chromatographic assay for motexafin gadolinium and motexafin lutetium in human plasma

We present new HPLC methods for the quantitation in human plasma of two investigative metallotexaphyrin agents, motexafin gadolinium (Gd-Tex) and motexafin lutetium (Lu-Tex). Each assay uses: the other texaphyrin analogue as an internal standard; protein precipitation with acetonitrile:methanol (50:50, v/v); an ODS reversed-phase column; an isocratic mobile phase of 100 mM ammonium acetate, pH 4.3:acetonitrile:methanol (59:21:20, v/v/v); and absorbance detection at 470 nm. The Gd-Tex assay has a lower limit of quantitation (LLOQ) of 0.01 microM and is linear between 0.01 and 30 microM. The Lu-Tex assay has an LLOQ of 0.1 microM and is linear between 0.1 and 30 microM. The assays are suited for in vivo preclinical studies and clinical trials because they require minimal amounts of plasma, are sensitive, and involve a 30-mm run time. These assays are important tools for evaluating the potential of Gd-Tex and Lu-Tex as a radiation enhancer and photosensitizer, respectively.

Reversible renal toxicity resulting from high single doses of the new radiosensitizer gadolinium texaphyrin

Gadolinium (III) texaphyrin (Gd-Tex) (NSC 695238) is a potential radiation sensitizer that selectively localizes in tumors and is detectable by magnetic resonance imaging (MRI). In this single-dose phase I trial, reversible renal injury was the dose-limiting toxicity. This report details that renal injury. A single intravenous dose of Gd-Tex was followed 2 hours later by radiation therapy. The Gd-Tex dose was escalated in 13 patient cohorts. Doses ranged from 0.6 to 29.6 mg/kg. The maximum tolerated dosage (MTD) was 22.3 mg/kg. Three patients had grade II and one had grade III acute nonoliguric renal failure at the 22.3 and 29.6 mg/kg dose levels. The injury was always transient, and responded to fluid restriction and renal diet. In all patients, transient green discoloration including urine developed at doses > or =7.1 mg/kg. MRI studies demonstrated image enhancement in the liver, kidneys, and in primary and metastatic tumors in all patients receiving >5.4 mg/kg. It is important that the liver and kidneys be excluded from the radiation volume. Gd-Tex was well tolerated at doses below the MTD. It is important that the liver and kidneys be excluded from the radiation volume. We recommend that 16.7 mg/kg be used as the maximum single dose to obviate even low grade renal toxicity.

Metalloporphyrins-Applications and clinical significance

The fascinating structures of naturally occurring porphyrins and metalloporphyrins have been perfected by nature to give functional dyes par excellence. The important roles these tetrapyrrolic macrocycles play in vital biological processes, in particular photosynthesis (chlorophyll), oxygen transport (hemoglobin), oxygen activation (cytochrome), have led to their characterization as 'pigments of life'. Because porphyrins possess extended π-electron systems and exhibit stability, they are finding use, to an increasing extent, in advanced materials, as components in organic metals, molecular wires, and other devices. In medicine, porphyrins are experiencing a renaissance due to the advent of photodynamic therapy of great promise in the treatment of cancer and dermatological diseases. The interdisciplinary interest porphyrins thus generate has provided the impetus to develop Novel-porphyrin like molecules anticipated to exhibit special properties, by structural variation of the tetrapyrrolic macrocycle, while maintaining a (4n+2)π main conjugation pathway.In addition to their esoteric application in science, porphyrins have been shown to have profound implications for therapeutic purposes. Their photosensitizing properties have led to their utilization in photodynamic therapy. Certain metalloporphyrins such as SnPP are being tested as drugs for the treatment of neonatal jaundice. Metalloporphyrins are serving as SOD mimetics to combat oxidative stress and a range of metalloporphyrin complexes have been proposed as contrast agents for magnetic resonance imaging.

Gadolinium mesoporphyrin as an MR imaging contrast agent in the evaluation of tumors: an experimental model of VX2 carcinoma in rabbits

OBJECTIVE

We determined the enhancement features of experimentally induced malignant tumors on MR imaging with the use of gadolinium mesoporphyrin, a recently developed MR contrast agent that may be necrosis-specific.

MATERIALS AND METHODS

VX2 carcinoma was inoculated into 24 rabbit thighs. T1-weighted contrast-enhanced MR imaging with IV gadopentetate dimeglumine (2-min delay) and gadolinium mesoporphyrin (20-hr delay) was performed 3-4 days (n = 6), 6-7 days (n = 6), 10-11 days (n = 5), and 13-14 days (n = 7) after the implantation of VX2 carcinoma. All tumors were sectioned along the same plane of MR images, and a detailed MR imaging-histopathologic correlation was performed.

RESULTS

Pathologically, areas enhanced with gadolinium mesoporphyrin included necrotic tissue, viable tumor, inflammatory granulation tissue, hemorrhage, and fibrosis. On gadopentetate dimeglumine-enhanced MR images, unenhanced areas of the tumor corresponded with intratumoral necrosis and hemorrhage.

CONCLUSION

Gadolinium mesoporphyrin enhances tumor necrosis on delayed phase MR imaging; however, it is impossible to specifically depict necrosis with gadolinium mesoporphyrin because it also enhances other parts of lesions, including viable tumor.

Irreversibly damaged myocardium at MR imaging with a necrotic tissue-specific contrast agent in a cat model

PURPOSE

To investigate the capability of a necrosis-avid magnetic resonance (MR) contrast agent, bis-gadolinium mesoporphyrins, for assessment of irreversibly damaged myocardium and to evaluate the time course of signal enhancement in the reperfused myocardium.

MATERIALS AND METHODS

Nine cats were subjected to 90 minutes of occlusion of the left anterior descending coronary artery followed by 90 minutes of reperfusion. Contrast material-enhanced T1-weighted spin-echo images were obtained for 12 hours in five cats and 6 hours in four cats. Pathologic examinations of the resected specimens were performed with 2'3'5-triphenyl tetrazolium chloride (TTC) histochemical staining and electron microscopy. The size of enhanced area on MR images was compared with that of irreversibly damaged myocardium with TTC staining. The time course of signal enhancement was evaluated.

RESULTS

The size of enhanced area on MR images was well correlated with that of irreversibly damaged myocardium with TTC staining. Maximum enhancement occurred 1-3 hours after administration of the contrast material, with mean enhancement of 171% that of normal myocardium. Electron microscopic examinations showed severe myocardial damage in the irreversibly damaged myocardium but only mild edematous changes in the reversibly damaged myocardium.

CONCLUSION

MR images enhanced with bis-gadolinium mesoporphyrins provide accurate sizing of irreversibly damaged myocardium with a strong and persistent signal enhancement in the reperfused myocardium.

Phases IB and II multidose trial of gadolinium texaphyrin, a radiation sensitizer detectable at MR imaging: preliminary results in brain metastases

PURPOSE

To evaluate magnetic resonance (MR) imaging results after administration of gadolinium texaphyrin, a tumor-selective radiation sensitizer that is detectable at MR imaging, and to determine an appropriate intravenous dose of gadolinium texaphyrin for repeated injections during radiation therapy, the dose-limiting toxicity of reiterated doses of gadolinium texaphyrin, the maximal tolerated dose, the biolocalization of gadolinium texaphyrin (as assessed at MR examinations), and the response to treatment.

MATERIALS AND METHODS

Ten daily intravenous injections of gadolinium texaphyrin, each followed by whole-brain radiation therapy (total of 10 fractions, 30 Gy), were administered to patients with brain metastases in a multicenter study. At the study institution, 11 patients underwent MR imaging before and after the first injection, after the 10th injection, and 8 weeks after entry into the study.

RESULTS

MR imaging revealed selective drug uptake in metastases, without enhancement of normal brain tissue. In 10 patients, tumor uptake was higher after the 10th injection than after the first injection, which indicated accumulation of gadolinium texaphyrin in metastases. One lesion was visible only after the 10th injection and not at the pretherapeutic MR examination with injection of conventional gadolinium-based contrast material. Response to treatment was defined as a reduction in the size of the metastases between the preinjection MR study and the last MR study; seven patients achieved partial remission with tumor regression exceeding 50% of the initial size, and four achieved a minor response with less than 50% tumor regression.

CONCLUSION

These preliminary results indicate that gadolinium texaphyrin is tumor selective and that brain metastases can be depicted at MR imaging long after the administration of gadolinium texaphyrin.

Delivery of diagnostic agents for magnetic resonance imaging

A review of contrast agents used for magnetic resonance imaging was made with regard to methods of drug delivery using published literature. Since the clinical approval of Gd-DTPA in 1988, there has been extensive research towards developing organ- and tissue-specific contrast agents. Targeting strategies have consistently improved along with improvements in nuclear medicine imaging, and a broad spectrum of potential agents has accumulated. Liver, blood-pool targeted, and, due to their inherent convenience of delivery, intraorally administered gastrointestinal agents have been developed or are being developed. For intravenous contrast agents, collective magnetic labels with modifications for some specificities results in the larger-sized agents which can be an obstacle for the agent in accessing the targeted cells. In conclusion, the next step in the development of specific contrast agents for clinical use is to improve non-specific delivery to the extra-capillary space adjacent to targeted cells.