Enhanced Extraction of Blood and Tissue Time-Activity Curves in Cardiac Mouse FDG PET Imaging by Means of Constrained Nonnegative Matrix Factorization

We propose an enhanced method to accurately retrieve time-activity curves (TACs) of blood and tissue from dynamic 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) positron emission tomography (PET) cardiac images of mice. The method is noninvasive and consists of using a constrained nonnegative matrix factorization algorithm (CNMF) applied to the matrix (A) containing the intensity values of the voxels of the left ventricle (LV) PET image. CNMF factorizes A into nonnegative matrices H and W, respectively, representing the physiological factors (blood and tissue) and their associated weights, by minimizing an extended cost function. We verified our method on 32 C57BL/6 mice, 14 of them with acute myocardial infarction (AMI). With CNMF, we could break down the mouse LV into myocardial and blood pool images. Their corresponding TACs were used in kinetic modeling to readily determine the [¹⁸F]FDG influx constant (K_i) required to compute the myocardial metabolic rate of glucose. The calculated K_i values using CNMF for the heart of control mice were in good agreement with those published in the literature. Significant differences in K_i values for the heart of control and AMI mice were found using CNMF. The values of the elements of W agreed well with the LV structural changes induced by ligation of the left coronary artery. CNMF was compared with the recently published method based on robust unmixing of dynamic sequences using regions of interest (RUDUR). A clear improvement of signal separation was observed with CNMF compared to the RUDUR method.

Chemical synthesis of fluorinated and iodinated 17β-HSD3 inhibitors and evaluation for imaging prostate cancer tumors and tissue biodistribution

Prostate cancer is the most common cancer among men and the development of new therapeutic agents is needed for its treatment and/or diagnosis. 17β-hydroxysteroid dehydrogenase type 3 (17β-HSD3) is involved in the production of androgens, which stimulates the proliferation of prostate cancer cells. Piperazinomethyl-androsterone sulfonamide derivatives were developed as 17β-HSD3 inhibitors and the concentration of a representative sulfonamide derivative (compound 1) was found to accumulate in prostate tumor tissues relatively to plasma in a mouse xenograft experiment. This finding gives us the opportunity to specifically target the prostate cancer tumors through the development of a radiolabelled version of compound 1 toward targeted molecular radiotherapy or radioimaging diagnosis. The chemical synthesis of fluorinated and iodinated analogs of compound 1 was achieved, leading to a series of compounds with similar levels of inhibition as the initial candidate. From 17β-HSD3 inhibition activity, molecular modeling and mouse plasma-concentration studies, the most promising compound of this series was selected, its ¹⁸F-radiolabelled version (¹⁸F-3) synthesized, and imaging/biodistribution studies engaged. When injected in mice, however, ¹⁸F-3 uptake in the target tissues (LNCaP[17β-HSD3] tumors and testicles) was not sufficient to allow their visualization by positron emission tomography. Plasma concentration values of compounds 3-8 administered orally, however, showed that the para-iodo compound 7 is the most metabolically stable and could therefore be an interesting alternative for radiolabelling and radiotreatment.

The loss of P2X7 receptor expression leads to increase intestinal glucose transit and hepatic steatosis

In intestinal epithelial cells (IEC), it was reported that the activation of the P2X7 receptor leads to the internalization of the glucose transporter GLUT2, which is accompanied by a reduction of IEC capacity to transport glucose. In this study, we used P2rx7 -/- mice to decipher P2X7 functions in intestinal glucose transport and to evaluate the impacts on metabolism. Immunohistochemistry analyses revealed the presence of GLUT2 at the apical domain of P2rx7 -/- jejunum enterocytes. Positron emission tomography and biodistribution studies demonstrated that glucose was more efficiently delivered to the circulation of knockout animals. These findings correlated with increase blood glucose, insulin, triglycerides and cholesterol levels. In fact, P2rx7 -/- mice had increased serum triglyceride and cholesterol levels and displayed glucose intolerance and resistance to insulin. Finally, P2rx7 -/- mice developed a hepatic steatosis characterized by a reduction of Acaca, Acacb, Fasn and Acox1 mRNA expression, as well as for ACC and FAS protein expression. Our study suggests that P2X7 could play a central role in metabolic diseases.

A Novel Positron Emission Tomography (PET) Approach to Monitor Cardiac Metabolic Pathway Remodeling in Response to Sunitinib Malate

Sunitinib is a tyrosine kinase inhibitor approved for the treatment of multiple solid tumors. However, cardiotoxicity is of increasing concern, with a need to develop rational mechanism driven approaches for the early detection of cardiac dysfunction. We sought to interrogate changes in cardiac energy substrate usage during sunitinib treatment, hypothesising that these changes could represent a strategy for the early detection of cardiotoxicity. Balb/CJ mice or Sprague-Dawley rats were treated orally for 4 weeks with 40 or 20 mg/kg/day sunitinib. Cardiac positron emission tomography (PET) was implemented to investigate alterations in myocardial glucose and oxidative metabolism. Following treatment, blood pressure increased, and left ventricular ejection fraction decreased. Cardiac [¹⁸F]-fluorodeoxyglucose (FDG)-PET revealed increased glucose uptake after 48 hours. [¹¹C]Acetate-PET showed decreased myocardial perfusion following treatment. Electron microscopy revealed significant lipid accumulation in the myocardium. Proteomic analyses indicated that oxidative metabolism, fatty acid β-oxidation and mitochondrial dysfunction were among the top myocardial signalling pathways perturbed. Sunitinib treatment results in an increased reliance on glycolysis, increased myocardial lipid deposition and perturbed mitochondrial function, indicative of a fundamental energy crisis resulting in compromised myocardial energy metabolism and function. Our findings suggest that a cardiac PET strategy may represent a rational approach to non-invasively monitor metabolic pathway remodeling following sunitinib treatment.

Endurance training or beta-blockade can partially block the energy metabolism remodeling taking place in experimental chronic left ventricle volume overload

Background

Patients with chronic aortic valve regurgitation (AR) causing left ventricular (LV) volume overload can remain asymptomatic for many years despite having a severely dilated heart. The sudden development of heart failure is not well understood but alterations of myocardial energy metabolism may be contributive. We studied the evolution of LV energy metabolism in experimental AR.

Methods

LV glucose utilization was evaluated in vivo by positron emission tomography (microPET) scanning of 6-month AR rats. Sham-operated or AR rats (n = 10-30 animals/group) were evaluated 3, 6 or 9 months post-surgery. We also tested treatment intervention in order to evaluate their impact on metabolism. AR rats (20 animals) were trained on a treadmill 5 times a week for 9 months and another group of rats received a beta-blockade treatment (carvedilol) for 6 months.

Results

MicroPET revealed an abnormal increase in glucose consumption in the LV free wall of AR rats at 6 months. On the other hand, fatty acid beta-oxidation was significantly reduced compared to sham control rats 6 months post AR induction. A significant decrease in citrate synthase and complex 1 activity suggested that mitochondrial oxidative phosphorylation was also affected maybe as soon as 3 months post-AR.

Moderate intensity endurance training starting 2 weeks post-AR was able to partially normalize the activity of various myocardial enzymes implicated in energy metabolism. The same was true for the AR rats treated with carvedilol (30 mg/kg/d). Responses to these interventions were different at the level of gene expression. We measured mRNA levels of a number of genes implicated in the transport of energy substrates and we observed that training did not reverse the general down-regulation of these genes in AR rats whereas carvedilol normalized the expression of most of them.

Conclusion

This study shows that myocardial energy metabolism remodeling taking place in the dilated left ventricle submitted to severe volume overload from AR can be partially avoided by exercise or beta-blockade in rats.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2261-14-190) contains supplementary material, which is available to authorized users.

[(11)C]-Acetoacetate PET imaging: a potential early marker for cardiac heart failure

The ketone body acetoacetate could be used as an alternate nutrient for the heart, and it also has the potential to improve cardiac function in an ischemic-reperfusion model or reduce the mitochondrial production of oxidative stress involved in cardiotoxicity. In this study, [(11)C]-acetoacetate was investigated as an early marker of intracellular damage in heart failure.

METHODS

A rat cardiotoxicity heart failure model was induced by doxorubicin, Dox(+). [(14)C]-Acetoacetate, a non-positron (β-) emitting radiotracer, was used to characterize the arterial blood input function and myocardial mitochondrial uptake. Afterward, [(11)C]-acetoacetate (β+) myocardial PET images were obtained for kinetic analysis and heart function assessment in control Dox(-) (n=15) and treated Dox(+) (n=6) rats. The uptake rate (K1) and myocardial clearance rate (k2or kmono) were extracted.

RESULTS

[(14)C]-Acetoacetate in the blood was increased in Dox(+), from 2 min post-injection until the last withdrawal point when the heart was harvested, as well as the uptake in the heart and myocardial mitochondria (unpaired t-test, p <0.05). PET kinetic analysis of [(11)C]-acetoacetate showed that rate constants K1, k2 and kmono were decreased in Dox(+) (p <0.05) combined with a reduction of 24% of the left ventricular ejection fraction (p <0.001).

CONCLUSION

Radioactive acetoacetate ex vivo analysis [(14)C], and in vivo kinetic [(11)C] studies provided evidence that [(11)C]-acetoacetate can assess heart failure Dox(+). Contrary to myocardial flow reserve (rest-stress protocol), [(11)C]-acetoacetate can be used to assess reduced kinetic rate constants without requirement of hyperemic stress response. The proposed [(11)C]-acetoacetate cardiac radiotracer in the investigation of heart disease is novel and paves the way to a potential role for [(11)C]-acetoacetate in cardiac pathophysiology.

Angiotensin II-converting enzyme inhibition improves survival, ventricular remodeling, and myocardial energetics in experimental aortic regurgitation

BACKGROUND

Aortic valve regurgitation (AR) is a volume-overload disease causing severe eccentric left ventricular (LV) hypertrophy and eventually heart failure. There is currently no approved drug to treat patients with AR. Many vasodilators including angiotensin-converting enzyme inhibitors have been evaluated in clinical trials, but although some results were promising, others were inconclusive. Overall, no drug has yet been able to improve clinical outcome in AR and the controversy remains. We have previously shown in an animal model that captopril (Cpt) reduced LV hypertrophy and protected LV systolic function, but we had not evaluated the clinical outcome. This protocol was designed to evaluate the effects of a long-term Cpt treatment on survival in the same animal model of severe aortic valve regurgitation.

METHODS AND RESULTS

Forty Wistar rats with AR were treated or untreated with Cpt (1 g/L in drinking water) for a period of 7 months to evaluate survival, myocardial remodeling, and function by echocardiography as well as myocardial metabolism by µ positron emission tomography scan. Survival was significantly improved in Cpt-treated animals with a survival benefit visible as soon as after 4 months of treatment. Cpt reduced LV dilatation and LV hypertrophy. It also significantly improved the myocardial metabolic profile by restoring the level of fatty acids metabolic enzymes and use.

CONCLUSIONS

In a controlled animal model of pure severe aortic valve regurgitation, Cpt treatment reduced LV remodeling and LV hypertrophy and improved myocardial metabolic profile and survival. These results support the need to reevaluate the role of angiotensin-converting enzyme inhibitors in humans with AR in a large, carefully designed prospective clinical trial.

Positron emission tomography detection of human endothelial cell and fibroblast monolayers: effect of pretreament and cell density on 18FDG uptake

Background

The non-destructive assessment and characterization of tridimensional (3D) cell and tissue constructs in bioreactors represents a challenge in tissue engineering. Medical imaging modalities, which can provide information on the structure and function of internal organs and tissues in living organisms, have the potential of allowing repetitive monitoring of these 3D cultures in vitro. Positron emission tomography (PET) is the most sensitive non-invasive imaging modality, capable of measuring picomolar amounts of radiolabeled molecules. However, since PET imaging protocols have been designed almost exclusively for in vivo investigations, suitable methods must be devised to enable imaging of cells or tissue substitutes. As a prior step to imaging 3D cultures, cell radiotracer uptake conditions must first be optimized.

Methods

In this study, human umbilical vein endothelial cells (HUVEC) and human fibroblasts were cultured at different densities and PET was used to non-destructively monitor their glycolytic activity by measuring ¹⁸F-fluorodeoxyglucose (¹⁸FDG) uptake. Various cell preconditioning protocols were investigated by adjusting the following parameters to optimize ¹⁸FDG uptake: glucose starvation, insulin stimulation, glucose concentration, ¹⁸FDG incubation time, cell density and radiotracer efflux prevention.

Results

The conditions yielding optimal ¹⁸FDG uptake, and hence best detection sensitivity by PET, were as follows: 2-hour cell preconditioning by glucose deprivation with 1-hour insulin stimulation, followed by 1-hour ¹⁸FDG incubation and 15-minute stabilization in standard culture medium, prior to rinsing and PET scanning.

Conclusions

A step-wise dependence of ¹⁸FDG uptake on glucose concentration was found, but a linear correlation between PET signal and cell density was observed. Detection thresholds of 36 ± 7 and 21 ± 4 cells were estimated for endothelial cells and fibroblasts, respectively.

Copper-64 labeled sulfophthalocyanines for positron emission tomography (PET) imaging in tumor-bearing rats

Sulfonated metallophthalocyanines ( PcS ) are second generation photosensitizers for photodynamic therapy (PDT) of cancer. Metal-free H 2 PcS are readily labeled with 64 Cu ++ to yield a mixture of sulfonated [64 Cu ] CuPcS suitable for biodistribution studies in tumor-bearing rats by positron emission tomography (PET). Most of the 64 Cu activity was sequestrated within the kidneys (20%ID/g) and liver (12%ID/g) while tumor uptake values remained low (0.2%ID/g). Dissection and counting of individual tissue samples after the 24 h scan confirmed the uptake values derived from the PET images. The procedure can be applied to series of novel PcS to evaluate structure-tumor selectivity relationships as a parameter to select potential agents for photodynamic therapy.

[11C]Acetate rest-stress protocol to assess myocardial perfusion and oxygen consumption reserve in a model of congestive heart failure in rats

This study describes an [(11)C]acetate rest-stress method to obtain an indirect estimate of myocardial blood flow (MBF) and myocardial oxygen consumption (MVO(2)) in rats. Doxorubicin cardiotoxicity was used to test the usefulness of this approach for the assessment of congestive heart failure.

METHODS

[(11)C]Acetate rest-stress studies have been used in clinical research to assess the capacity of the coronary arteries to respond to stress. In this article, we used this approach to assess the cardiotoxicity of doxorubicin in a rat model. The method was first validated in a group of healthy rats and then used to follow the effect of doxorubicin chemotherapy on cardiac function. The effect of doxorubicin on myocardial perfusion and oxygen consumption reserve was measured at rest and under dobutamine stimulation.

RESULTS

Validation of the protocol showed a good correlation between the MBF and MVO(2) (r(2)=.68). The doxorubicin-treated group showed a significant (P=.04) decrease in cardiovascular perfusion reserve at 1.3±0.2 compared with the control animals at 1.6±0.2. Similar results were obtained for the MVO(2) reserve (treated 1.8±0.4 vs. controls 2.3±0.3; P=.02).

CONCLUSIONS

We describe an [(11)C]acetate PET rest-stress protocol for the assessment of congestive heart failure in rats and its application to the follow-up of cardiotoxicity under doxorubicin chemotherapy. This is a rapid and reliable approach to the measurement of cardiac perfusion and oxygen consumption reserve that could be applied to the development of new strategies to reduce the cardiotoxicity of anthracycline.

Image-derived input function in dynamic human PET/CT: methodology and validation with 11C-acetate and 18F-fluorothioheptadecanoic acid in muscle and 18F-fluorodeoxyglucose in brain

Purpose

Despite current advances in PET/CT systems, blood sampling still remains the standard method to obtain the radiotracer input function for tracer kinetic modelling. The purpose of this study was to validate the use of image-derived input functions (IDIF) of the carotid and femoral arteries to measure the arterial input function (AIF) in PET imaging. The data were obtained from two different research studies, one using ¹⁸F-FDG for brain imaging and the other using ¹¹C-acetate and ¹⁸F-fluoro-6-thioheptadecanoic acid (¹⁸F-FTHA) in femoral muscles.

Methods

The method was validated with two phantom systems. First, a static phantom consisting of syringes of different diameters containing radioactivity was used to determine the recovery coefficient (RC) and spill-in factors. Second, a dynamic phantom built to model bolus injection and clearance of tracers was used to establish the correlation between blood sampling, AIF and IDIF. The RC was then applied to the femoral artery data from PET imaging studies with ¹¹C-acetate and ¹⁸F-FTHA and to carotid artery data from brain imaging with ¹⁸F-FDG. These IDIF data were then compared to actual AIFs from patients.

Results

With ¹¹C-acetate, the perfusion index in the femoral muscle was 0.34±0.18 min⁻¹ when estimated from the actual time–activity blood curve, 0.29±0.15 min⁻¹ when estimated from the corrected IDIF, and 0.66±0.41 min⁻¹ when the IDIF data were not corrected for RC. A one-way repeated measures (ANOVA) and Tukey’s test showed a statistically significant difference for the IDIF not corrected for RC (p<0.0001). With ¹⁸F-FTHA there was a strong correlation between Patlak slopes, the plasma to tissue transfer rate calculated using the true plasma radioactivity content and the corrected IDIF for the femoral muscles (vastus lateralis r=0.86, p=0.027; biceps femoris r=0.90, p=0.017). On the other hand, there was no correlation between the values derived using the AIF and those derived using the uncorrected IDIF. Finally, in the brain imaging study with ¹⁸F-FDG, the cerebral metabolic rate of glucose (CMRglc) measured using the uncorrected IDIF was consistently overestimated. The CMRglc obtained using blood sampling was 13.1±3.9 mg/100 g per minute and 14.0±5.7 mg/100 g per minute using the corrected IDIF (r²=0.90).

Conclusion

Correctly obtained, carotid and femoral artery IDIFs can be used as a substitute for AIFs to perform tracer kinetic modelling in skeletal femoral muscles and brain analyses.

Vascular-targeted photodynamic therapy with BF2-chelated Tetraaryl-Azadipyrromethene agents: a multi-modality molecular imaging approach to therapeutic assessment

Background:

Photodynamic therapy (PDT) is a treatment modality for a range of diseases including cancer. The BF₂-chelated tetraaryl-azadipyrromethenes (ADPMs) are an emerging class of non-porphyrin PDT agent, which have previously shown excellent photochemical and photophysical properties for therapeutic application. Herein, in vivo efficacy and mechanism of action studies have been completed for the lead agent, ADMP06.

Methods:

A multi-modality imaging approach was employed to assess efficacy of treatment, as well as probe the mechanism of action of ADPM06-mediated PDT.

Results:

Tumour ablation in 71% of animals bearing mammary tumours was achieved after delivery of 2 mg kg⁻¹ of ADPM06 followed immediately by light irradiation with 150 J cm⁻². The inherent fluorescence of ADPM06 was utilised to monitor organ biodistribution patterns, with fluorescence reaching baseline levels in all organs within 24 h. Mechanism of action studies were carried out using dynamic positron emission tomography and magnetic resonance imaging techniques, which, when taken together, indicated a decrease in tumour vascular perfusion and concomitant reduction in tumour metabolism over time after treatment.

Conclusion:

The encouraging treatment responses in vivo and vascular-targeting mechanism of action continue to indicate therapeutic benefit for this new class of photosensitiser.

Microdeletion 15q13.3: a locus with incomplete penetrance for autism, mental retardation, and psychiatric disorders

BACKGROUND

Microdeletions within chromosome 15q13.3 are associated both with a recently recognised syndrome of mental retardation, seizures, and dysmorphic features, and with schizophrenia.

METHODS AND RESULTS

Based on routine diagnostic testing of approximately 8200 samples using array comparative genomic hybridisation, we identified 20 individuals (14 children and six parents in 12 families) with microdeletions of 15q13.3. Phenotypes in the children included developmental delay, mental retardation, or borderline IQ in most and autistic spectrum disorder (6/14), speech delay, aggressiveness, attention deficit hyperactivity disorder, and other behavioural problems. Both parents were available in seven families, and the deletion was de novo in one, inherited from an apparently normal parent in four, and inherited from a parent with learning disability and bipolar disorder in two families. Of the 14 children, six in five families were adopted, and DNA was available for only one of these 10 biological parents; the deletion was very likely inherited for one of these families with two affected children. Among the unavailable parents, two mothers were described as having mental retardation, another mother as having "mental illness", and one father as having schizophrenia. We hypothesise that some of the unavailable parents have the deletion.

CONCLUSIONS

The occurrence of increased adoption, frequent autism, bipolar disorder, and lack of penetrance are noteworthy findings in individuals with deletion 15q13.3. A high rate of adoption may be related to the presence of the deletion in biological parents. Unconfirmed histories of antisocial behaviours in unavailable biological parents raise the concern that future research may show that deletion 15q13.3 is associated with such behaviours.

A small animal positron emission tomography study of the effect of chemotherapy and hormonal therapy on the uptake of 2-deoxy-2-[F-18]fluoro-D-glucose in murine models of breast cancer

PURPOSE

We used small animal positron emission tomography (PET) imaging to monitor the time-course of tumor metabolic response to hormone and chemotherapy in a murine model of hormone-sensitive breast cancer.

PROCEDURES

Estrogen receptor positive murine mammary carcinomas were inoculated in Balb/c mice. Small animal PET imaging using 2-deoxy-2-[F-18]fluoro-D: -glucose (FDG) was used to assess tumor metabolic activity. Imaging was done before and at days 1, 7, and 14 after the administration of doxorubicin, methotrexate, letrozole, or placebo. The tumor uptake of FDG was calculated from a region-of-interest drawn around the tumor.

RESULTS

All treatments resulted in a decrease in tumor growth rate and end volume compared to untreated control. FDG uptake was also markedly decreased after treatment although a flare reaction was observed on PET at day 7, the intensity of which varied according to the treatment modality.

CONCLUSION

PET imaging is sensitive to detect early changes associated with therapy in murine breast cancer models. A flare reaction was observed 7 days after the initiation of therapy.

PET imaging of apoptosis with 64Cu-labeled streptavidin following pretargeting of phosphatidylserine with biotinylated annexin-V

PURPOSE

In vivo detection of apoptosis is a diagnostic tool with potential clinical applications in cardiology and oncology. Radiolabeled annexin-V (anxV) is an ideal probe for in vivo apoptosis detection owing to its strong affinity for phosphatidylserine (PS), the molecular flag on the surface of apoptotic cells. Most clinical studies performed to visualize apoptosis have used (99m)Tc-anxV; however, its poor distribution profile often compromises image quality. In this study, tumor apoptosis after therapy was visualized by positron emission tomography (PET) using (64)Cu-labeled streptavidin (SAv), following pre-targeting of apoptotic cells with biotinylated anxV.

METHODS

Apoptosis was induced in tumor-bearing mice by photodynamic therapy (PDT) using phthalocyanine dyes as photosensitizers, and red light. After PDT, mice were injected i.v. with biotinylated anxV, followed 2 h later by an avidin chase, and after another 2 h with (64)Cu-DOTA-biotin-SAv. PET images were subsequently recorded up to 13 h after PDT.

RESULTS

PET images delineated apoptosis in treated tumors as early as 30 min after (64)Cu-DOTA-biotin-SAv administration, with tumor-to-background ratios reaching a maximum at 3 h post-injection, i.e., 7 h post-PDT. Omitting the administration of biotinylated anxV or the avidin chase failed to provide a clear PET image, confirming that all three steps are essential for adequate visualization of apoptosis. Furthermore, differences in action mechanisms between photosensitizers that target tumor cells directly or via initial vascular stasis were clearly recognized through differences in tracer uptake patterns detecting early or delayed apoptosis.

CONCLUSION

This study demonstrates the efficacy of a three-step (64)Cu pretargeting procedure for PET imaging of apoptosis. Our data also confirm the usefulness of small animal PET to evaluate cancer treatment protocols.

Dynamic imaging of transient metabolic processes by small-animal PET for the evaluation of photosensitizers in photodynamic therapy of cancer

This study evaluated the potential use of dynamic PET to monitor transient metabolic processes and to investigate the mechanisms of action of new photosensitizing drugs in the photodynamic therapy (PDT) of cancer.

METHODS

Rats bearing 2 mammary tumors received different phthalocyanine-based photosensitizers. The following day, the animals were positioned in a Sherbrooke small-animal PET scanner and continuously infused with 18F-FDG while dynamic images were acquired for 2 h. During that period, one of the 2 tumors was exposed for 30 min to red light delivered by a small diode laser to activate PDT.

RESULTS

18F-FDG time-activity curves during PDT showed distinct transient patterns characterized by a drop and subsequent recovery of tumor 18F-FDG uptake rates. Variations in these rates and response delay parameters revealed tumoral and systemic metabolic processes that correlated with differences in mechanism of action between drugs, that is, direct tumor cell kill or initial vascular shutdown.

CONCLUSION

Real-time follow-up of tumor response to PDT as monitored by dynamic 18F-FDG PET has been shown to correlate with the mechanisms of action of photosensitizing drugs in vivo. This new imaging paradigm can be exploited to monitor a variety of transient cellular and molecular processes as they occur in vivo, enabling the mechanisms of action of therapeutic interventions to be scrutinized and their efficacy predicted in real time.

Breast cancer models to study the expression of estrogen receptors with small animal PET imaging

Different animal models of estrogen positive tumors (ER+) were evaluated for their suitability to follow tumor response after various treatment protocols, using small animal positron emission tomography (PET). ER+ human breast cancer cell lines MCF-7 and T-47D, using MDA-MB-231 as ER-; control, and murine mammary ductal carcinomas MC4-L2, MC4-L3, and MC7-L1, were compared for their in vivo growth rate and retention of ER+ status. Tumor metabolic activity was estimated from the relative uptake (% injected dose/g) of [18F]fluorodeoxyglucose (FDG) uptake, whereas ER content was determined from 16alpha-[18F]fluoroestradiol (FES) retention. F-18 activity values were obtained by small animal PET imaging and confirmed by tissue sampling and radioactivity counting. Reliable uptake measurements could be obtained for tumors of 200 microl or over. The human cell lines grew at a slower rate in vivo and failed to accumulate FES; in contrast, the Balb/c MC7-L1 and MC4-L2 grew well and showed good uptake of both FDG and FES. Chemotherapy and hormone therapy delayed the growth of MC7-L1 and MC4-L2 tumors, confirming their suitability as an ER+ model for therapeutic interventions. MC4-L3 tumors also showed promising results but required the presence of progestative pellets to grow. These data demonstrate that murine MC7-L1 and MC4-L2 tumors are suitable models for the monitoring of ER+ breast cancer therapy using small animal PET imaging.

Scintimammography with 11beta-methoxy-(17alpha,20Z)-[123I]iodovinylestrad iol: a complementary role to 99mTc-methoxyisobutyl isonitrile in the characterization of breast tumors

The aim of this study was to investigate a possible relationship between 99mTc-methoxyisobutyl isonitrile (MIBI) uptake and the estrogen receptor (ER) status of breast tumors as determined by 11beta-methoxy-(17alpha,20Z)-[123I]iodovinylestradi ol (MIVE) scintimammography.

METHODS

Thirteen patients referred for MIVE scintimammography after abnormal mammography or finding of a suspect mass on physical examination were injected intravenously with MIVE. Planar images of the breasts and axillary region were taken with both radiopharmaceuticals and compared with pathologic examination of the tumor tissue and in vitro ER quantification.

RESULTS

The presence of cancerous tissue, as indicated by MIBI uptake, is a prerequisite for the accumulation of MIVE by the breast tumors. There was no statistically significant correlation between the MIBI and MIVE tumor uptake ratios. However, the latter correlate well with the presence of ER, as determined by an in vitro assay.

CONCLUSION

MIVE scans add unique information concerning the tumor ER status in breast cancer patients, which could contribute to a better characterization of the tumor and aid in the selection of the most appropriate treatment protocol.

Biodistribution, dosimetry and metabolism of 11beta-methoxy-(17alpha,20E/Z)-[123I]iodovinylestradiol in healthy women and breast cancer patients

The biodistribution and dosimetry of the 20E and 20Z stereoisomers of 11 beta-methoxy-(17alpha,20)-[123I]iodovinylestradiol (MIVE) were evaluated in six healthy women. Tumor uptake and metabolism of the 20Z isomer were evaluated in 13 women referred after abnormal mammography or after discovery of a suspect mass at physical examination.

METHODS

The radiopharmaceuticals were prepared from their corresponding stannyl intermediates and administrated intravenously. Blood samples were drawn at different time intervals and urine was collected for up to 24 h. Metabolites were detected by radiochromatography. Tissue distribution was followed for up to 24 h by scintigraphic imaging. The dosimetry was computed according to the Medical Internal Radiation Dose scheme.

RESULTS

The 20E and 20Z isomers exhibit similar biodistribution and dosimetry patterns. Chromatographic analysis of plasma samples of healthy volunteers and cancer patients, as well as in vitro plasma incubations, confirmed the in vivo stability of (20Z)-[123I]MIVE. Radioactivity was rapidly cleared from the blood by the liver and excreted through the gut, which received the highest radiation dose (0.211 mGy/MBq). The effective doses for the adult female and male phantom were 0.054 and 0.046 mSv/MBq, respectively. Among the 13 patients imaged with (20Z)-[123I]MIVE, 3 had fibrocystic disease with no focal uptake, 8 had good agreement with in vitro estrogen receptor determination and 2 were false-positive.

CONCLUSION

The radiation dose after intravenous administration of 20E- or (20Z)-[123I]MIVE at imaging dose levels is within acceptable limits. There was a good correlation between uptake of (20Z)-[123I]MIVE and the presence of estrogen receptors in breast cancer patients.

[Benign, diffuse external otitis]

A review of the literature on benign diffuse external otitis was done to throw light on the problems of pathogenesis, etiological factors, and various forms of treatment. A prospective study done on normal adult ear canals and a prospective study of 26 new cases of benign external otitis was done according to clinical criteria elaborated by Senturia to show that Coly-Mycin Otic is a drug to be recommended in the treatment of this disease.