(18)F-labeled rhodamines as potential myocardial perfusion agents: comparison of pharmacokinetic properties of several rhodamines

INTRODUCTION

We recently reported the development of the [(18)F]fluorodiethylene glycol ester of rhodamine B as a potential positron emission tomography (PET) tracer for myocardial perfusion imaging (MPI). This compound was developed by optimizing the ester moiety on the rhodamine B core, and its pharmacokinetic properties were found to be superior to those of the prototype ethyl ester. The goal of the present study was to optimize the rhodamine core while retaining the fluorodiethyleneglycol ester prosthetic group.

METHODS

A series of different rhodamine cores (rhodamine 6G, rhodamine 101, and tetramethylrhodamine) were labeled with (18)F using the corresponding rhodamine lactones as the precursors and [(18)F]fluorodiethylene glycol ester as the prosthetic group. The compounds were purified by semipreparative HPLC, and their biodistribution was measured in rats. Additionally, the uptake of the compounds was evaluated in isolated rat cardiomyocytes.

RESULTS

As was the case with the different prosthetic groups, we found that the rhodamine core has a significant effect on the in vitro and in vivo properties of this series of compounds. Of the rhodamines evaluated to date, the pharmacologic properties of the (18)F-labeled diethylene glycol ester of rhodamine 6G are superior to those of the (18)F-labeled diethylene glycol esters of rhodamine B, rhodamine 101, and tetramethylrhodamine. As with (18)F-labeled rhodamine B, [(18)F]rhodamine 6G was observed to localize in the mitochondria of isolated rat cardiomyocytes.

CONCLUSIONS

Based on these results, the (18)F-labeled diethylene glycol ester of rhodamine 6G is the most promising potential PET MPI radiopharmaceutical of those that have evaluated to date, and we are now preparing to carry out first-in-human clinical studies with this compound.

Biological characterization of F-18-labeled rhodamine B, a potential positron emission tomography perfusion tracer

INTRODUCTION

Myocardial infarction is the leading cause of death in western countries, and positron emission tomography (PET) plays an increasing role in the diagnosis and treatment planning for this disease. However, the absence of an (18)F-labeled PET myocardial perfusion tracer hampers the widespread use of PET in myocardial perfusion imaging (MPI). We recently reported a potential MPI agent based on (18)F-labeled rhodamine B. The goal of this study was to more completely define the biological properties of (18)F-labeled rhodamine B with respect to uptake and localization in an animal model of myocardial infarction and to evaluate the uptake (18)F-labeled rhodamine B by cardiomyocytes.

METHODS

A total of 12 female Sprague Dawley rats with a permanent ligation of the left anterior descending artery (LAD) were studied with small-animal PET. The animals were injected with 100-150 μCi of (18)F-labeled rhodamine B diethylene glycol ester ([(18)F]RhoBDEGF) and imaged two days before ligation. The animals were imaged again two to ten days post-ligation. After the post-surgery scans, the animals were euthanized and the hearts were sectioned into 1mm slices and myocardial infarct size was determined by phosphorimaging and 2,3,5-triphenyltetrazolium chloride staining (TTC). In addition, the uptake of [(18)F]RhoBDEGF in isolated rat neonatal cardiomyocytes was determined by fluorescence microscopy.

RESULTS

Small-animal PET showed intense and uniform uptake of [(18)F]RhoBDEGF throughout the myocardium in healthy rats. After LAD ligation, well defined perfusion defects were observed in the PET images. The defect size was highly correlated with the infarct size as determined ex vivo by phosphorimaging and TTC staining. In vitro, [(18)F]RhoBDEGF was rapidly internalized into rat cardiomyocytes with ~40 % of the initial activity internalized within the 60 min incubation time. Fluorescence microscopy clearly demonstrated localization of [(18)F]RhoBDEGF in the mitochondria of rat cardiomyocytes.

CONCLUSION

Fluorine-18-labeled rhodamine B diethylene glycol ester ([(18)F]RhoBDEGF) provides excellent image quality and clear delineation of myocardial infarcts in a rat infarct model. In vitro studies demonstrate localization of the tracer in the mitochondria of cardiac myocytes. In combination, these results support the continued evaluation of this tracer for the PET assessment of myocardial perfusion.

Effect of the prosthetic group on the pharmacologic properties of 18F-labeled rhodamine B, a potential myocardial perfusion agent for positron emission tomography (PET)

We recently reported the development of the 2-[(18)F]fluoroethyl ester of rhodamine B as a potential positron emission tomography (PET) tracer for myocardial perfusion imaging. This compound, which was prepared using a [(18)F]fluoroethyl prosthetic group, has significant uptake in the myocardium in rats but also demonstrates relatively high liver uptake and is rapidly hydrolyzed in vivo in mice. We have now prepared (18)F-labeled rhodamine B using three additional prosthetic groups (propyl, diethylene glycol, and triethylene glycol) and found that the prosthetic group has a significant effect on the in vitro and in vivo properties of these compounds. Of the esters prepared to date, the diethylene glycol ester is superior in terms of in vitro stability and pharmacokinetics. These observations suggest that the prosthetic group plays a significant role in determining the pharmacological properties of (18)F-labeled compounds. They also support the value of continued investigation of (18)F-labeled rhodamines as PET radiopharmaceuticals for myocardial perfusion imaging.

Imaging cancer using PET--the effect of the bifunctional chelator on the biodistribution of a (64)Cu-labeled antibody

INTRODUCTION

Use of copper radioisotopes in antibody radiolabeling is challenged by reported loss of the radionuclide from the bifunctional chelator used to label the protein. The objective of this study was to investigate the relationship between the thermodynamic stability of the (64)Cu-complexes of five commonly used bifunctional chelators (BFCs) and the biodistribution of an antibody labeled with (64)Cu using these chelators in tumor-bearing mice.

METHODS

The chelators [S-2-(aminobenzyl)1,4,7-triazacyclononane-1,4,7-triacetic acid (p-NH(2)-Bn-NOTA): 6-[p-(bromoacetamido)benzyl]-1, 4, 8, 11-tetraazacyclotetradecane-N, N', N'', N'''-tetraacetic acid (BAT-6): S-2-(4-aminobenzyl)-1,4,7,10-tetraazacyclododocane tetraacetic acid (p-NH(2)-Bn-DOTA): 1,4,7,10-tetraazacyclododocane-N, N', N", N"'-tetraacetic acid (DOTA): and 1-N-(4-aminobenzyl)-3,6,10,13,16,19-hexaazabicyclo[6.6.6]eicosane-1,8-diamine (SarAr)] were conjugated to the anti-GD2 antibody ch14.18, and the modified antibody was labeled with (64)Cu and injected into mice bearing subcutaneous human melanoma tumors (M21) (n = 3-5 for each study). Biodistribution data were obtained from positron emission tomography images acquired at 1, 24 and 48 hours post-injection, and at 48 hours post-injection a full ex vivo biodistribution study was carried out.

RESULTS

The biodistribution, including tumor targeting, was similar for all the radioimmunoconjugates. At 48 h post-injection, the only statistically significant differences in radionuclide uptake (p < 0.05) were between blood, liver, spleen and kidney. For example, liver uptake of [(64)Cu]ch14.18-p-NH(2)-Bn-NOTA was 4.74 ± 0.77 per cent of the injected dose per gram of tissue (%ID/g), and for [(64)Cu]ch14.18-SarAr was 8.06 ± 0.77 %ID/g. Differences in tumor targeting correlated with variations in tumor size rather than which BFC was used.

CONCLUSIONS

The results of this study indicate that differences in the thermodynamic stability of these chelator-Cu(II) complexes were not associated with significant differences in uptake of the tracer by the tumor. However, there were significant differences in tracer concentration in other tissues, including those involved in clearance of the radioimmunoconjugate (e.g., liver and spleen).

Detection of intestinal inflammation by MicroPET imaging using a (64)Cu-labeled anti-beta(7) integrin antibody

BACKGROUND

The primary function of integrin beta(7) is the recruitment and retention of lymphocytes to the inflamed gut. The aim of this study was to investigate the possibility of imaging colitis radioimmunodetection by targeting the beta(7) integrin with a radiolabeled antibody.

METHODS

FIB504.64, a monoclonal antibody that binds to beta(7) integrin, was conjugated with a bifunctional chelator and labeled with (64)Cu. The antibody (50 microg, 7 MBq) was injected into C57BL/6 mice with experimentally induced colitis (n = 6). MicroPET images were collected at 1, 24, and 48 hours postinjection and the biodistribution was measured at 48 hours by tissue assay. Data were also obtained for a (64)Cu-labeled nonspecific isotype-matched antibody in mice with colitis and (64)Cu-labeled FIB504.64 in healthy mice (n = 5-6).

RESULTS

The microPET images showed higher uptake of (64)Cu-labeled FIB504.64 in the gut of mice with colitis than for either of the controls. This observation was confirmed by the 48-hour ex vivo biodistribution data: the percentage of injected dose per gram of tissue (%ID/g +/- SD) (large intestine) colitis mice with (64)Cu-labeled FIB504.64, 6.49 +/- 2.25; control mice with (64)Cu-labeled FIB504.64, 3.64 +/- 1.12; colitis mice, (64)Cu-labeled nonspecific antibody 3.97 +/- 0.48%ID/g (P < 0.05 between groups).

CONCLUSIONS

The selective uptake of (64)Cu-labeled FIB504.64 antibody in the gut of animals with colitis suggests that integrin beta(7) may be a promising target for radioimmunodetection of this disease, which would aid diagnosis, assessment, and therapy guidance of this disease.

Synthesis of fluorine-18 labeled rhodamine B: A potential PET myocardial perfusion imaging agent

There is considerable interest in developing an (18)F-labeled PET myocardial perfusion agent. Rhodamine dyes share several properties with (99m)Tc-MIBI, the most commonly used single-photon myocardial perfusion agent, suggesting that an (18)F-labeled rhodamine dye might prove useful for this application. In addition to being lipophilic cations, like (99m)Tc-MIBI, rhodamine dyes are known to accumulate in the myocardium and are substrates for Pgp, the protein implicated in MDR1 multidrug resistance. As the first step in determining whether (18)F-labeled rhodamines might be useful as myocardial perfusion agents for PET, our objective was to develop synthetic methods for preparing the (18)F-labeled compounds so that they could be evaluated in vivo. Rhodamine B was chosen as the prototype compound for development of the synthesis because the ethyl substituents on the amine moieties of rhodamine B protect them from side reactions, thus eliminating the need to include (and subsequently remove) protecting groups. The 2'-[(18)F]fluoroethyl ester of rhodamine B was synthesized by heating rhodamine B lactone with [(18)F]fluoroethyltosylate in acetonitrile at 165 degrees C for 30min using [(18)F]fluoroethyl tosylate, which was prepared by the reaction of ethyleneglycol ditosylate with Kryptofix 2.2.2, K(2)CO(3), and [(18)F]NaF in acetonitrile for 10min at 90 degrees C. The product was purified by semi-preparative HPLC to produce the 2'-[(18)F]fluoroethylester in >97% radiochemical purity with a specific activity of 1.3GBq/mumol, an isolated decay corrected yield of 35%, and a total synthesis time of 90min.

Conditional mouse osteosarcoma, dependent on p53 loss and potentiated by loss of Rb, mimics the human disease

Osteosarcoma is the most common primary malignant tumor of bone. Analysis of familial cancer syndromes and sporadic cases has strongly implicated both p53 and pRb in its pathogenesis; however, the relative contribution of these mutations to the initiation of osteosarcoma is unclear. We describe here the generation and characterization of a genetically engineered mouse model in which all animals develop short latency malignant osteosarcoma. The genetically engineered mouse model is based on osteoblast-restricted deletion of p53 and pRb. Osteosarcoma development is dependent on loss of p53 and potentiated by loss of pRb, revealing a dominance of p53 mutation in the development of osteosarcoma. The model reproduces many of the defining features of human osteosarcoma including cytogenetic complexity and comparable gene expression signatures, histology, and metastatic behavior. Using a novel in silico methodology termed cytogenetic region enrichment analysis, we demonstrate high conservation of gene expression changes between murine osteosarcoma and known cytogentically rearranged loci from human osteosarcoma. Due to the strong similarity between murine osteosarcoma and human osteosarcoma in this model, this should provide a valuable platform for addressing the molecular genetics of osteosarcoma and for developing novel therapeutic strategies.

Young women with diabetes: using Internet communication to create stability during life transitions

AIMS AND OBJECTIVES

The aim of the current study was to explore and describe the strategies young women with Type 1 diabetes used to manage transitions in their lives. This paper will describe one aspect of the findings of how women with Type 1 diabetes used the Internet to interact with other people with diabetes and create stability in their lives.

BACKGROUND

Individuals living with diabetes develop a range of different strategies to create stability in their lives and enhance their well-being. Changing social and emotional conditions during life transitions have a major impact on diabetes management. Although the literature indicates that strategies enabling the individuals to cope with transitions are important, they remain under-researched.

DESIGN

Using grounded theory, interviews were conducted with 20 women with Type 1 diabetes. Constant comparative data analysis was used to analyse the data and develop an understanding of how young women with Type 1 diabetes used the Internet to create stability in their lives.

FINDINGS

The findings revealed that the women valued their autonomy and being in control of when and to whom they reveal their diabetic status, especially during life transitions and at times of uncertainty. However, during these times they also required health and social information and interacting with other people. One of the women's main strategies in managing transitions was to use Internet chat lines as a way of obtaining information and communicating with others. This strategy gave women a sense of autonomy, enabled them to maintain their anonymity and interact with other people on their own terms.

CONCLUSIONS

Having meaningful personal interactions, social support and being able to connect with others were fundamental to the women's well being. Most importantly, preserving autonomy and anonymity during such interactions were integral to the way the women with Type 1 diabetes managed life transitions.

RELEVANCE TO CLINICAL PRACTICE

Health professionals need to explore and incorporate Internet communication process or anonymous help lines into their practice as a way to assist people manage their diabetes.

Young women with type 1 diabetes' management of turning points and transitions

The authors used grounded theory to explore and develop a substantive theory to explain how 20 young women with type 1 diabetes managed their lives when facing turning points and undergoing transitions. The women experienced a basic social problem: being in the grip of blood glucose levels (BGLs), which consisted of three categories: (a) the impact of being susceptible to fluctuating BGLs, (b) the responses of other people to the individual woman's diabetes, and (c) the impact of the individual women's diabetes on other people's lives. The women used a basic social process to overcome the basic social problem by creating stability, which involved using three interconnected subprocesses: forming meaningful relationships, enhancing attentiveness to blood glucose levels, and putting things in perspective. Insights into the processes and strategies used by the women have important implications for provision of care and service delivery.

Hepatitis C: a medical and social diagnosis

Hepatitis C has reached epidemic proportions in Australia. Because of its association with injecting drug use, which is a main transmission mode, hepatitis C is a highly stigmatising health condition. In fact, the stigma attached to hepatitis C means hepatitis C is not just a medical diagnosis, but also a social diagnosis. The limited available research indicates hepatitis C-related discrimination is most likely to occur in health care settings. A strategic and evidenced-based approach is required to combat the social impact of hepatitis C.

Gene therapy of prostate cancer with the soluble vascular endothelial growth factor receptor Flk1

A variety of novel therapeutic approaches have emerged recently for the treatment of human cancers. We have coupled two of these therapeutic approaches, gene therapy and antiangiogenic therapy and tested them in two murine prostate cancer models Recombinant adenovirus encoding the ligand-binding ectodomain of the VEGF receptor 2 (Flk1) fused to an Fc domain was administered to SCID mice carrying orthotopic human LNCaP tumors as well as to transgenic (TRAMP) mice with spontaneous prostate tumors. Ad Flk1-Fc injection reduced tumor growth by 66% for orthotopic LNCaP tumors and by 42% for spontaneous tumors in TRAMP mice. Microvessel density in the primary tumors was reduced by 68% and 40% in the two models respectively. A decrease in microvessel density was also observed in lymphatic metastases in Ad Flk1-Fc-treated TRAMP mice and was correlated with a decrease in the frequency of regional metastases in the treated animals. Survival time was also extended in the Ad Flk1-Fc-treated TRAMP mice relative to the control-treated animals. Our results suggest that adenoviral delivery of soluble Flk1 receptor can reduce vascular density and prostate tumor growth and prolong survival time in orthotopically implanted tumors as well as in spontaneous prostate tumors in transgenic animals.

Tumor vascularity: evaluation in a murine model with contrast-enhanced color Doppler US effect of angiogenesis inhibitors

PURPOSE

To determine the ability of contrast material-enhanced ultrasonography (US) to depict tumor growth and vascularity in a murine model of prostate carcinoma treated with an angiogenic inhibitor.

MATERIALS AND METHODS

Thirty-five genetically engineered mice with spontaneously occurring prostate tumors were monitored on a weekly basis with gray-scale and color Doppler US with a 15-MHz linear transducer. Eighteen mice were treated with an adenoviral vector to deliver a soluble form of the Flk1 receptor (VEGFR-2), a vascular endothelial growth factor receptor designed to block tumor angiogenesis. The remaining 17 animals were injected with saline and used as controls. Tumor volumes were calculated on the basis of serial US measurements. Color Doppler US was performed in every tumor before and after intravenous injection of 0.1 mL per kilogram of body weight of a US contrast agent. US images were evaluated for tumor size, pattern of vascularity, and extent of vascularity (vascularity index). Findings at US were correlated with findings at autopsy in 30 animals.

RESULTS

Estimates of tumor volume at US correlated well with tumor measurements at autopsy (r =.89, P <.001). Marked differences in tumor size and slope of increasing tumor volume were evident at US between treated and control mice after treatment (P <.016, analysis of variance). The US contrast agent markedly increased color Doppler US signal intensity with an 800% (from 10% to 12,700%) change in the mean number of color pixels per imaging field, and showed vascularity in areas of tumor not identified on precontrast images in 70% (109 of 156 studies). No correlation was found between the pattern of vascularity or vascularity index before or after contrast material administration and tumor size, treatment status, or histologic assessment of tumor vascularity.

CONCLUSION

Contrast-enhanced US improves visualization of tumor vascularity. However, histologic patterns of tumor vascularity do not correlate with Doppler US depiction of blood flow in these vessels.

Seeking help for chest pain: NIDDM and non-diabetics' responses to three hypothetical scenarios

Seeking medical assistance early during illness is important to decrease the associated morbidity and mortality. A cross sectional survey was carried out to determine how long people with non-insulin dependent diabetes (NIDDM), and a group of non-diabetics would wait before seeking medical advice for chest pain. Self-administered questionnaires were completed by 50 diabetics (22 males, 28 females) age range 42 to 81, mean 64.26 +/- 9.78 from the diabetic outpatient clinic of a major hospital, and 51 non-diabetics, (15 males, 35 females) age range 16 to 84, mean 56.28 +/- 21.6 from a suburban general practice. Both groups were most likely to seek help when experiencing severe pain (56% diabetics, 59% non-DM). Previous heart disease was not a major motivating factor in either group. Subjects with previous chest pain would be more likely to seek help early. Females would be more likely to seek help immediately than males for severe chest pain (p < 0.05). The diabetic group were more likely to seek help immediately than the non-diabetic group (p < 0.05). There was a significant difference in potential help seeking for mild chest pain in diabetic subjects between those with previous history of chest pain and those with no history of chest pain (p < 0.05). There was no significant relationship between help-seeking behaviour and diabetes treatment, duration of diabetes or age (p > 0.05). An important implication for nursing was the absence of a significant relationship between previous diabetes education and potential help-seeking behaviour.

Beliefs about diabetes and diabetic complications

A study of people with non-insulin dependent diabetes found that, generally, they had a good understanding of its complications although over half believed they personally were not vulnerable. Non-diabetic subjects had limited knowledge in this area.

Diabetes shared care: a model

Increases in both the cost of providing quality diabetes care and in the number of people developing diabetes have led to a search for more cost effective models of care. This paper outlines a shared care scheme that has benefits for the patient, the outpatient clinic and the general practitioner.

Sexuality and women with diabetes

Health educators are ideally placed to identify sexual problems and provide sex education for women with diabetes. Important pre-requisites are for the educator to have an understanding of the human sexual response; knowledge of the evidence for sexual dysfunction in diabetic women and to be comfortable with their own sexuality. This paper aims to discuss aspects of female sexuality; the effects of diabetes on female sexuality and sexual responsiveness. The evidence for and possible causes of, sexual dysfunction in diabetic females as documented in the literature are explored and strategies for identifying sexual problems outlined.