Targeted delivery of cytotoxic proteins to prostate cancer via conjugation to small molecule urea-based PSMA inhibitors

Prostate cancer cells are characterized by a remarkably low proliferative rate and the production of high levels of prostate-specific proteases. Protein-based toxins are attractive candidates for prostate cancer therapy because they kill cells via proliferation-independent mechanisms. However, the non-specific cytotoxicity of these potent cytotoxins must be redirected to avoid toxicity to normal tissues. Prostate-Specific Membrane Antigen (PSMA) is membrane-bound carboxypeptidase that is highly expressed by prostate cancer cells. Potent dipeptide PSMA inhibitors have been developed that can selectively deliver and concentrate imaging agents within prostate cancer cells based on continuous PSMA internalization and endosomal cycling. On this basis, we conjugated a PSMA inhibitor to the apoptosis-inducing human protease Granzyme B and the potent Pseudomonas exotoxin protein toxin fragment, PE35. We assessed selective PSMA binding and entrance into tumor cell to induce cell death. We demonstrated these agents selectively bound to PSMA and became internalized. PSMA-targeted PE35 toxin was selectively toxic to PSMA producing cells in vitro. Intratumoral and intravenous administration of this toxin produced marked tumor killing of PSMA-producing xenografts with minimal host toxicity. These studies demonstrate that urea-based PSMA inhibitors represent a simpler, less expensive alternative to antibodies as a means to deliver cytotoxic proteins to prostate cancer cells.

Translational evaluation of translocator protein as a marker of neuroinflammation in schizophrenia

Positron emission tomography (PET) imaging with radiotracers that target translocator protein 18 kDa (TSPO) has become a popular approach to assess putative neuroinflammatory processes and associated microglia activation in psychotic illnesses. It remains unclear, however, whether TSPO imaging can accurately capture low-grade inflammatory processes such as those present in schizophrenia and related disorders. Therefore, we evaluated the validity of TSPO as a disease-relevant marker of inflammation using a translational approach, which combined neurodevelopmental and neurodegenerative mouse models with PET imaging in patients with recent-onset schizophrenia and matched controls. Using an infection-mediated neurodevelopmental mouse model, we show that schizophrenia-relevant behavioral abnormalities and increased inflammatory cytokine expression are associated with reduced prefrontal TSPO levels. On the other hand, TSPO was markedly upregulated in a mouse model of acute neurodegeneration and reactive gliosis, which was induced by intrahippocampal injection of kainic acid. In both models, the changes in TSPO levels were not restricted to microglia but emerged in various cell types, including microglia, astrocytes and vascular endothelial cells. Human PET imaging using the second-generation TSPO radiotracer [11C]DPA-713 revealed a strong trend towards reduced TSPO binding in the middle frontal gyrus of patients with recent-onset schizophrenia, who were previously shown to display increased levels of inflammatory cytokines in peripheral and central tissues. Together, our findings challenge the common assumption that central low-grade inflammation in schizophrenia is mirrored by increased TSPO expression or ligand binding. Our study further underscores the need to interpret altered TSPO binding in schizophrenia with caution, especially when measures of TSPO are not complemented with other markers of inflammation. Unless more selective microglial markers are available for PET imaging, quantification of cytokines and other inflammatory biomarkers, along with their molecular signaling pathways, may be more accurate in attempts to characterize inflammatory profiles in schizophrenia and other mental disorders that lack robust reactive gliosis.

Detecting Tumor Metastases: The Road to Therapy Starts Here

Metastasis is the complex process by which primary tumor cells migrate and establish secondary tumors in an adjacent or distant location in the body. Early detection of metastatic disease and effective therapeutic options for targeting these detected metastases remain impediments to effectively treating patients with advanced cancers. If metastatic lesions are identified early, patients might maximally benefit from effective early therapeutic interventions. Further, monitoring patients whose primary tumors are effectively treated for potential metastatic disease onset is also highly valuable. Finally, patients with metastatic disease can be monitored for efficacy of specific therapeutic interventions through effective metastatic detection techniques. Thus, being able to detect and visualize metastatic lesions is key and provides potential to greatly improve overall patient outcomes. In order to achieve these objectives, researchers have endeavored to mechanistically define the steps involved in the metastatic process as well as ways to effectively detect metastatic progression. We presently overview various preclinical and clinical in vitro and in vivo assays developed to more efficiently detect tumor metastases, which provides the foundation for developing more effective therapies for this invariably fatal component of the cancerous process.

PET imaging of prostate-specific membrane antigen in prostate cancer: current state of the art and future challenges

BACKGROUND

Prostate-specific membrane antigen (PSMA) is a cell surface enzyme that is highly expressed in prostate cancer (PCa) and is currently being extensively explored as a promising target for molecular imaging in a variety of clinical contexts. Novel antibody and small-molecule PSMA radiotracers labeled with a variety of radionuclides for positron emission tomography (PET) imaging applications have been developed and explored in recent studies.

METHODS

A great deal of progress has been made in defining the clinical utility of this class of PET agents through predominantly small and retrospective clinical studies. The most compelling data to date has been in the setting of biochemically recurrent PCa, where PSMA-targeted radiotracers have been found to be superior to conventional imaging and other molecular imaging agents for the detection of locally recurrent and metastatic PCa.

RESULTS

Early data, however, suggest that initial lymph node staging before definitive therapy in high-risk primary PCa patients may be limited, although intraoperative guidance may still hold promise. Other examples of potential promising applications for PSMA PET imaging include non-invasive characterization of primary PCa, staging and treatment planning for PSMA-targeted radiotherapeutics, and guidance of focal therapy for oligometastatic disease.

CONCLUSIONS

However, all of these indications and applications for PCa PSMA PET imaging are still lacking and require large, prospective, systematic clinical trials for validation. Such validation trials are needed and hopefully will be forthcoming as the fields of molecular imaging, urology, radiation oncology and medical oncology continue to define and refine the utility of PSMA-targeted PET imaging to improve the management of PCa patients.

In vivo markers of inflammatory response in recent-onset schizophrenia: a combined study using [(11)C]DPA-713 PET and analysis of CSF and plasma

Several lines of evidence suggest aberrant immune response in schizophrenia, including elevated levels of cytokines. These cytokines are thought to be produced by activated microglia, the innate immune cells of the central nervous system. However, increase in translocator protein 18 kDa (TSPO), a marker of activated glia, has not been found in patients with chronic schizophrenia using second-generation radiotracers and positron emission tomography (PET)-based neuroimaging. In this study we focused on patients with recent onset of schizophrenia (within 5 years of diagnosis). Quantified levels of TSPO in the cortical and subcortical brain regions using the PET-based radiotracer [(11)C]DPA-713 were compared between the patients and healthy controls. Markers of inflammation, including interleukin 6 (IL-6), were assessed in the plasma and cerebrospinal fluid (CSF) in these participants. We observed no significant change in the binding of [(11)C]DPA-713 to TSPO in 12 patients with recent onset of schizophrenia compared with 14 controls. Nevertheless, the patients with recent onset of schizophrenia showed a significant increase in IL-6 in both plasma (P<0.001) and CSF (P=0.02). The CSF levels of IL-6 were significantly correlated with the levels of IL-6 in plasma within the total study population (P<0.001) and in patients with recent onset of schizophrenia alone (P=0.03). Our results suggest that increased levels of IL-6 may occur in the absence of changed TSPO PET signal in the brains of medicated patients with recent onset of schizophrenia. Future development of PET-based radiotracers targeting alternative markers of glial activation and immune response may be needed to capture the inflammatory signature present in the brains of patients with early-stage disease.

Prostate-specific membrane antigen as a target for cancer imaging and therapy

The prostate-specific membrane antigen (PSMA) is a molecular target whose use has resulted in some of the most productive work toward imaging and treating prostate cancer over the past two decades. A wide variety of imaging agents extending from intact antibodies to low-molecular-weight compounds permeate the literature. In parallel there is a rapidly expanding pool of antibody-drug conjugates, radiopharmaceutical therapeutics, small-molecule drug conjugates, theranostics and nanomedicines targeting PSMA. Such productivity is motivated by the abundant expression of PSMA on the surface of prostate cancer cells and within the neovasculature of other solid tumors, with limited expression in most normal tissues. Animating the field is a variety of small-molecule scaffolds upon which the radionuclides, drugs, MR-detectable species and nanoparticles can be placed with relative ease. Among those, the urea-based agents have been most extensively leveraged, with expanding clinical use for detection and more recently for radiopharmaceutical therapy of prostate cancer, with surprisingly little toxicity. PSMA imaging of other cancers is also appearing in the clinical literature, and may overtake FDG for certain indications. Targeting PSMA may provide a viable alternative or first-line approach to managing prostate and other cancers.

Glia and immune cell signaling in bipolar disorder: insights from neuropharmacology and molecular imaging to clinical application

Bipolar disorder (BD) is a debilitating mental illness characterized by severe fluctuations in mood, sleep, energy and executive functioning. Pharmacological studies of selective serotonin reuptake inhibitors and the monoamine system have helped us to clinically understand bipolar depression. Mood stabilizers such as lithium and valproic acid, the first-line treatments for bipolar mania and depression, inhibit glycogen synthase kinase-3 beta (GSK-3β) and regulate the Wnt pathway. Recent investigations suggest that microglia, the resident immune cells of the brain, provide a physiological link between the serotonin system and the GSK-3β/Wnt pathway through neuroinflammation. We review the pharmacological, translational and brain imaging studies that support a role for microglia in regulating neurotransmitter synthesis and immune cell activation. These investigations provide a model for microglia involvement in the pathophysiology and phenotype of BD that may translate into improved therapies.

GCPII imaging and cancer

Glutamate carboxypeptidase II (GCPII) in the central nervous system is referred to as the prostate-specific membrane antigen (PSMA) in the periphery. PSMA serves as a target for imaging and treatment of prostate cancer and because of its expression in solid tumor neovasculature has the potential to be used in this regard for other malignancies as well. An overview of GCPII/PSMA in cancer, as well as a discussion of imaging and therapy of prostate cancer using a wide variety of PSMA-targeting agents is provided.

Early prediction of anti-epidermal growth factor receptor (EGFR) therapy with 18[F]FDG-PET: A preclinical and clinical correlation

14064

Background: Predictive biomarkers for response to anti-EGFR therapy are of significant clinical importance. We hypothesized that early changes in 18[F]FDG tumor uptake predict response to anti-EGFR therapy. We investigated this in a mice model and correlated these findings with human patients undergoing anti-EGFR therapy. Methods: Mice bearing two head and neck squamous cell cancer (HnNSCC) xenografts (Hep2, Cal27) received vehicle or erlotinib for 3 weeks. 18[F]FDG uptake were imaged with small animal micro- PET at baseline and after 1 week of therapy, and reported in SUVmax. For clinical correlation, human patients with HnNSCC receiving erlotinib were identified from an ongoing clinical trial. 18[F]FDG-PET images were obtained at baseline and after 2 weeks of erlotinib monotherapy. Tumor specimens were obtained by fine-needle aspiration biopsy at the same time as PET. A panel of pharmacodynamic markers (including Ki-67 and pMAPK) were assessed . Results: Hep2 was resistant to erlotinib therapy (Tumor/Control [T/C]: 0.8) while Cal27 was sensitive (T/C: 0.2). SUVmax in the resistant Hep2 xenografts was not significantly different from the control (86% ± 70% of control) while SUVmax in the treated sensitive Cal27 xenografts showed a significant decrease than control (-2% ± 7%). Ki-67 in the treated Hep2 was not significantly different from control while that in Cal27 was <50% of control. For clinical correlation, ki-67 score was higher after 2 weeks in the patient resistant to erlotinib monotherapy by 18[F]FDG-PET (SUVmax increased by 14%, ± 11%) and was lower in the patient who was 18[F]FDG-PET sensitive (SUVmax decreased by 56%, ± 13%). pMAPK decreased in all cases and had a poor correlation with efficacy. Conclusions: Early dynamic changes in 18[F]FDG tumor uptake is predictive of response to anti-EGFR therapy and correlates with changes in ki-67 expression, both in a preclinical and a clinical scenario.

No significant financial relationships to disclose.

Spectroscopic evidence of cerebral axonopathy in patients with "pure" adrenomyeloneuropathy

BACKGROUND

Adrenomyeloneuropathy (AMN) is the adult variant of X-linked adrenoleukodystrophy. The disease pathology is usually limited to spinal cord and peripheral nerves, and when this is the case, it is referred to as "pure" AMN. Histopathology shows cerebral involvement even in pure AMN; however, not much is known about the nature, extent, and clinical relevance of these findings.

OBJECTIVE

To investigate brain involvement in AMN patients with normal MRI, employing multislice MR spectroscopic imaging.

METHODS

Twelve men with pure AMN were compared with 19 age-matched healthy volunteers. Metabolite ratios (N-acetylaspartate [NAA]/choline [Cho], NAA/creatine [Cr], and Cho/Cr) were measured from seven brain regions. Global metabolite ratios were generated as an average of these seven regional ratios. The Expanded Disability Status Scale (EDSS) was used for neurologic evaluation.

RESULTS

The patients with AMN showed reduced global NAA/Cho (AMN 1.40 +/- 0.16 vs controls 1.75 +/- 0.34; p = 0.003)) and global NAA/Cr (AMN 2.32 +/- 0.13 vs controls 2.62 +/- 0.43; p = 0.03). Regionally, NAA/Cho was lowered in the internal capsule (AMN 1.30 +/- 0.20 vs controls 1.69 +/- 0.37; p = 0.002) and in parieto-occipital white matter (AMN 1.45 +/- 0.19 vs controls 1.78 +/- 0.55; p = 0.04). NAA/Cr was lowered in parieto-occipital white matter (AMN 2.34 +/- 0.31 vs controls 2.83 +/- 0.71; p = 0.04). EDSS demonstrated an inverse association with global NAA/Cr (r = -0.65, p = 0.02) and NAA/Cr in centrum semiovale (r = -0.73, p = 0.006) and in parieto-occipital white matter (r = -0.64, p = 0.02). Cho/Cr was not significantly elevated.

CONCLUSIONS

(1)H-MR spectroscopic imaging is able to detect biochemical abnormalities suggestive of axonal damage even in the brains of patients with pure adrenomyeloneuropathy. The axonopathy is most prominent in internal capsule and parieto-occipital white matter and may contribute to clinical disability.

Reliability of normal findings on MR imaging for excluding the diagnosis of vasculitis of the central nervous system

OBJECTIVE

We attempt to determine whether angiography is indicated in patients with suspected central nervous system (CNS) vasculitis who present with negative findings on MR imaging studies.

CONCLUSION

MR imaging findings may be negative in the setting of CNS vasculitis confirmed on angiography, indicating that advanced imaging techniques tailored to detect infarction (i.e., fluid-attenuated inversion recovery, diffusion-weighted, and perfusion imaging) may be necessary to enhance the sensitivity of an MR study and that despite the high sensitivity of MR imaging for CNS vasculitis, angiography may still be required to render an accurate diagnosis.

Positron emission tomography in the detection and management of sarcomatous transformation in neurofibromatosis

Benign neurofibromas undergo sarcomatous transformation in approximately 5% of patients with neurofibromatosis type I. The clinical and radiologic diagnosis of sarcomatous change remains difficult. Positron emission tomography with F-18 fluorodeoxyglucose is a method to assess increased glucose metabolism in malignant tissue such as sarcomas. In this case report, positron emission tomography accurately distinguished malignant from benign neurofibromas. The technique may be useful as a noninvasive screening tool for malignant transformation of neurofibromas.

Chordoid glioma: a neoplasm unique to the hypothalamus and anterior third ventricle

BACKGROUND AND PURPOSE

Chordoid glioma is a new clinicopathologic entity that occurs in the region of the hypothalamus/anterior third ventricle. The aims of this study were to describe the characteristic radiographic features of chordoid glioma, identify specific imaging features that may enable differentiation of chordoid glioma from other suprasellar tumors, and increase neuroradiologists' awareness of this newly described tumor, facilitating prospective diagnosis.

METHODS

CT scans and/or MR images of six patients with chordoid glioma were reviewed retrospectively to determine whether any characteristic radiographic features would emerge. Reports of the clinical presentation, pathologic findings, and radiographic findings of another six patients were reviewed and included, for a total patient population of 12 (mean age +/- SD, 46 +/- 13 years).

RESULTS

Imaging features were strikingly similar for all tumors. In each case, the mass was ovoid, was well circumscribed, was located in the region of the hypothalamus/anterior third ventricle, and enhanced uniformly and intensely. Tumors were hyperdense to gray matter on CT scans and were isointense on T1-weighted MR images and slightly hyperintense on long-TR MR images. In two patients, vasogenic edema extended into the optic tracts, and in three, there was hydrocephalus.

CONCLUSION

Chordoid glioma is a recently described unique histopathologic entity that has been added to the World Health Organization glioma classification scheme and must be included in the differential diagnosis of a suprasellar mass. Distinctive imaging features are its location, ovoid shape, hyperdensity on CT scans, and uniform intense contrast enhancement.

Quantification and minimization of magnetic susceptibility artifacts on GRE images

PURPOSE

The purpose of this work was to determine the optimal imaging parameters for minimization of metallic susceptibility artifacts during gradient echo (GRE) imaging.

METHOD

We performed GRE imaging of titanium screws in a nickel-doped agarose gel phantom, systematically varying several parameters to characterize and quantify susceptibility artifacts.

RESULTS

The greatest reduction in artifact size came from using a short TE; increasing the frequency matrix and decreasing the slice thickness also contributed substantially to reducing the artifact size. Whenever possible, implanted prostheses should be aligned with the main magnetic field to minimize artifact size. Parameters with negligible effect on artifact size included bandwidth, phase encode matrix, and field of view.

CONCLUSION

Radiologists can easily adjust the above parameters in their imaging protocols to improve GRE image quality in patients with implanted metallic devices.

New techniques in MR imaging of brain tumors

The past decade has seen many new MR imaging techniques that have been applied to brain tumor imaging. As MR imaging is applied further to cellular and molecular imaging (e.g., imaging of gene transfer and expression), more possibilities for brain tumor diagnosis and treatment will become evident. The superior contrast, resolution, and lack of need for image coregistration suggest that MR imaging techniques may displace PET as the preeminent modality for studying brain and tumor physiology and chemistry for indications other than receptor-based imaging. Nevertheless, the new MR imaging techniques require further histologic, physiologic, and intraoperative validation in suitable animal models and in clinical studies, and should be used to complement PET. Application of echo-planar imaging and other fast imaging sequences can permit the merger of several MR imaging studies (e.g., perfusion imaging, DWI, and MRS(I) into a typical (1-hour) clinical time slot). Synergistic information provided by these new techniques might soon enable physicians to reach the ultimate goals of noninvasive tumor grading and avoidance of having to obtain a biopsy.

Radiolabeled neuronal nitric oxide synthase inhibitors: synthesis, in vivo evaluation, and primate PET studies

The objectives of this study were to synthesize neuronal nitric oxide synthase (NOS-I)-selective imaging agents based on the 2 potent, selective inhibitors AR-R 17443 [N-(4-((2-((phenylmethyl) (methyl)-amino)ethyl)phenyl)-2-thiophenecarboximidamide)] and AR-R 18512 [(N(2-methyl-1,2,3,4-tetrahydroisoquinoline-7-yl)-2-thiophenecarboxim idamide)] in positron-emitting form and to evaluate regional brain uptake in rodents and primates.

METHODS

[11C]AR-R 17443 and [11C]AR-R 18512 were produced by N-alkylation of the corresponding desmethyl precursors using [11C]iodomethane. Regional brain uptake of [11C]AR-R 17443 and [11C]AR-R 18512 was assayed in rats and NOS-I knockout mice, and PET was performed in baboons. Tracer kinetic modeling used a 2-compartment plasma and brain tissue model.

RESULTS

Yields of [11C]AR-R 17443 and [11C]AR-R 18512 ranged from 8% to 16% at the end of synthesis, with specific activities of 50-178 GBq/micromol (1,350-4,800 Ci/mmol) at the end of synthesis. In rat cerebellum and cortex at 30 min after injection, [11C]AR-R 17443 showed 1.01 +/- 0.01 and 1.63 +/- 0.12 percentage injected dose per gram (%ID/g) uptake, respectively, whereas [11C]AR-R 18512 showed 0.88 +/- 0.01 and 1.30 +/- 0.07 %ID/g uptake, respectively. Attempts to block tracer uptake by pretreatment with the NOS-I-selective inhibitor 7-nitroindazole or the corresponding unlabeled inhibitor (or desmethyl precursor to AR-R 17443 of similar potency) were unsuccessful. A small but significant (20%) decrease in cerebellar uptake of [11C]AR-R 18512 was present in NOS-I knockout mice compared with control mice. PET of [11C]AR-R 18512 in baboons with concurrent regional cerebral blood flow (rCBF) determination before and after administration of blocker showed dose-related decreases in cerebellar uptake that were greater than or equal to decreases in rCBF. Plasma metabolites accounted for 27% of total activity at 30 min after injection. Kinetic modeling of binding potentials revealed a distribution volume of 334 in cerebral blood that dropped 51% after blocker administration.

CONCLUSION

Rodent studies for [11C]AR-R 17443 and [11C]AR-R 18512 showed little evidence of specific NOS-I binding. In baboons, we detected a higher uptake of [11C]AR-R 18512 in the cerebellum than in the cortex (approximately 5%, accounting for decreased rCBF because of blockade), indicating minimal specific binding. Analogs of higher affinity are likely required if this class of agents is to prove viable for PET.

Human skeletal muscle: sodium MR imaging and quantification-potential applications in exercise and disease

PURPOSE

To use sodium 23 magnetic resonance (MR) imaging to quantify noninvasively total sodium in human muscle and to apply the technique in exercise and musculoskeletal disease.

MATERIALS AND METHODS

Total [Na] sodium was determined from the ratio of the relaxation-corrected (23)Na signal intensities measured from short echo-time (0.4 msec) (23)Na images to those from an external saline solution reference. The method was validated with the blinded use of saline solutions of varying sodium concentrations. [Na] was measured in the calf muscles in 10 healthy volunteers. (23)Na MR imaging also was performed in two healthy subjects after exercise, two patients with myotonic dystrophy, and two patients with osteoarthritis.

RESULTS

(23)Na MR imaging yielded a total [Na] value of 28.4 mmol/kg of wet weight +/- 3.6 (SD) in normal muscle, consistent with prior biopsy data. Spatial resolution was 0.22 mL, with signal-to-noise ratio of 10-15. Mean signal intensity elevations were 16% and 22% after exercise and 47% and 70% in dystrophic muscles compared with those at normal resting levels. In osteoarthritis, mean signal intensity reductions were 36% and 15% compared with those in unaffected knee joints.

CONCLUSION

(23)Na MR imaging can be used to quantify total [Na] in human muscle. The technique may facilitate understanding of the role of the sodium-potassium pump and perfusion in normal and diseased muscle.

CNS vasculitis in autoimmune disease: MR imaging findings and correlation with angiography

BACKGROUND AND PURPOSE

MR findings in CNS vasculitis and their correlation with angiography have not been clearly defined. We therefore explored three hypotheses regarding CNS vasculitis associated with autoimmune disease: 1) MR imaging is highly sensitive; 2) a typical MR appearance exists; and, 3) MR and angiographic findings correlate well.

METHODS

We studied 18 patients with CNS vasculitis associated with autoimmune disease, characterized the MR lesions by type, size, number, and location, and correlated the MR findings with those of angiography.

RESULTS

All patients with CNS vasculitis had abnormalities on MR studies. On average, four +/- two lesions per patient were detected on MR images. The lesions were located in the subcortical white matter (n = 20), cortical gray matter (n = 16), deep gray matter (n = 16), deep white matter (n = 9), and cerebellum (n = 9). Only 65% of MR lesions were evident on angiograms; 44% of the lesions revealed on angiograms were detected by MR.

CONCLUSION

MR imaging is sensitive for CNS vasculitis. Lesions attributable to CNS vasculitis in autoimmune disease are distributed nearly equally among cortical, subcortical, and deep gray matter structures. The modest correlation between MR imaging and angiography suggests that the two techniques provide different information about CNS vasculitis and that both types of studies are needed for the complete assessment of damage caused by vascular abnormalities.

Histoplasmosis mimicking vasculitis of the central nervous system

We describe a case of disseminated histoplasmosis that was erroneously diagnosed as central nervous system vasculitis and treated with immunosuppressive therapy. Our case emphasizes the importance of excluding infections before initiating treatment for presumed central nervous system vasculitis. Clinical clues to underlying Histoplasma infections are also discussed.

Sensitivities of noninvasive tests for central nervous system vasculitis: a comparison of lumbar puncture, computed tomography, and magnetic resonance imaging

OBJECTIVE

To determine the sensitivities of lumbar puncture (LP), computed tomography (CT), and magnetic resonance imaging (MRI) for central nervous system (CNS) vasculitis.

METHODS

We reviewed the charts and radiologic studies of 20 patients with angiogram positive CNS vasculitis.

RESULTS

The patients ranged in age from 7-72 years, with a mean of 43.7 +/- 15.5 years. Twelve patients (60%) were women; 8 (40%) were men. Seven had primary angiitis of the CNS (PACNS), 8 had rheumatological illnesses (4 had systemic lupus erythematosus), and 5 had vasculitis due to other diverse etiologies, including 2 who had CNS infections. LP was positive in 8/15 angiographically proven cases, for a sensitivity of 53% [95% confidence interval (CI): 27-79]. The sensitivity of CT was 65% (11/17) (95% CI: 38-86), and that of MRI 75% (12/16) (CI: 48-93). The use of LP plus either CT or MRI was more sensitive than LP alone: for LP and CT, the sensitivity was 92% (11/12) (CI: 62-100), and for LP and MRI, 100% (12/12) (CI: 74-100). The combination of CT and MRI was not more sensitive than either test alone.

CONCLUSION

The sensitivities of LP, CT, and MRI for angiogram positive vasculitis are only modest. CT and MRI may be completely normal in cases of CNS vasculitis when the angiogram is positive. LP and either CT or MRI are of additive benefit in the diagnosis of CNS vasculitis, and should be done before angiography; and, in a patient with both a normal LP and a normal CT or MRI, a CNS angiogram is unlikely to be positive for vasculitis.

Fluorine-substituted corticosteroids: synthesis and evaluation as potential receptor-based imaging agents for positron emission tomography of the brain

We have prepared eight fluorine-substituted corticosteroids representing ligands selective for Type I and Type II corticosteroid receptor subtypes as potential imaging agents for corticosteroid receptor-containing regions of the brain. Receptor binding affinity assays show that fluorine substitution for hydroxyl or hydrogen in these steroids generally results in some reduction in affinity, with the result that the absolute affinity of these fluorine-substituted ligands for receptor is less than that typical for steroid hormones that show receptor-based, target selective uptake in vivo. Five of these compounds were prepared in fluorine-18 labeled form by a simple sulfonate ester displacement reaction, and their tissue distribution was studied in the adrenalectomized rat. There is no selective accumulation nor selective retention of the Type I selective corticosteroids (18F-RU 26752, 21-[18F]fluoroprogesterone, 21-[18F]fluoro-11 beta-hydroxyprogesterone) in either the brain, or other target tissues (pituitary, kidney, liver). The Type II selective corticosteroids (18F-RU 28362, 18F-triamcinolone acetonide) show uptake into the hippocampus which can be partially blocked by a competing ligand; in target tissues outside the brain, the blocking is more complete. All of the 18F-labeled compounds show considerable defluorination, evident as high bone activity levels. These results, coupled with earlier findings in the literature, suggest that radiolabeled corticosteroid receptor ligands with both greater metabolic stability and higher receptor binding affinity and selectivity are needed for imaging corticosteroid receptors in the hippocampus.

Preparation and evaluation of 17-ethynyl-substituted 16 alpha-[18F]fluoroestradiols: selective receptor-based PET imaging agents

We have prepared and studied six new analogs of 16 alpha-fluoroestradiol (FES): 17 alpha- and 17 beta-ethynyl-FES (7 [FEES] and 7a), and the 11 beta-ethyl (8 and 8a) and 11 beta-methoxy (9 and 9a) derivatives, novel estrogen receptor-based PET imaging agents. The relative binding affinity (RBA) for the estrogen receptor (ER) versus FES is increased for 7, 9 and 9a but decreased for 7a, 8 and 8a. All six analogs have been labeled in the 16 alpha position with 18F by the nucleophilic displacement of the corresponding 16 beta-trifluoromethanesulfonate with nBu4N18F. Subsequent ethynylation with lithium trimethylsilylacetylide yielded the FEES analogs (total synthesis time: 120 min; effective specific activity: 200-2400 Ci/mmol). Selective uptake in the uterus was high for [18F]7, [18F]8, [18F]9 and [18F]9a (% ID/g values at 1 h: 11.2, 12.9, 9.9 and 8.3, respectively), while uptake was effectively blocked by coinjection of an excess of unlabeled estradiol. The FEES analogs, [18F]7, [18F]8 and [18F]9, exhibited the highest selectivity, in terms of target (uterus)-to-blood ratios, ever seen amongst estrogen radiopharmaceuticals, 154, 145 and 169, respectively. The analogs [18F]7a and [18F]8a displayed no uptake in the uterus, consistent with their low RBAs. Metabolism studies revealed that most of the uterine activity is unmetabolized while the blood exhibits a rapid and subsequently sustained mixture of metabolites. The muscle shows a metabolic profile intermediate to the uterus and blood. These analogs provide an array of desirable characteristics for the optimal PET imaging of ER-rich target tissues.

Assessment of 21-[18F]fluoro-16 alpha-ethyl-19-norprogesterone as a positron-emitting radiopharmaceutical for the detection of progestin receptors in human breast carcinomas

We have used 21-[18F]fluoro-16 alpha-ethyl-19-norprogesterone (FENP) for imaging progestin receptors by PET in patients with primary carcinoma of the breast. In vitro binding and in vivo tissue distribution studies in rats have shown that FENP has high specific activity, high affinity for progestin receptors, and receptor-mediated uptake in target tissues. Eight patients with primary breast carcinoma were studied. Breast carcinoma was identified correctly in 50% of the patients with progestin-receptor-positive tumors; however, the FENP uptake was not correlated with progestin-receptor levels. We noted a low target-to-background ratio in humans, with high relative activity in the spine, blood pool, and normal breast tissue. Our findings indicate that FENP is not a suitable agent for imaging progestin receptors in humans.

11 beta-methoxy-, 11 beta-ethyl- and 17 alpha-ethynyl-substituted 16 alpha-fluoroestradiols: receptor-based imaging agents with enhanced uptake efficiency and selectivity

We have prepared three analogues of 16 alpha-fluoroestradiol (FES) substituted either with an 11 beta-methoxy group (1, 11 beta-MeO-FES), an 11 beta-ethyl group (2, 11 beta-Et-FES), or a 17 alpha-ethynyl group (3, 17 alpha-ethynyl-FES). These substituents all lower the binding of FES to the serum proteins alphafetoprotein and sex steroid binding protein, but their effect on estrogen receptor binding varies: Receptor binding is increased by the 11 beta-ethyl and 17 alpha-ethynyl groups, but decreased by the 11 beta-methoxy group. These substituents also have a parallel effect on the lipophilicity, and hence the nonspecific binding estimated for these compounds. All three compounds were prepared in fluorine-18 labeled form, at effective specific activities of 90-1600 Ci/mmol, by fluoride ion displacement reactions as done previously with FES. Tissue distribution studies in immature rats show high uptake selectivity by target tissue (uterus) and effective competition by an excess of unlabeled estradiol. Percent injected dose per gram values (% ID/g) at 1 h are 6% for 11 beta-MeO-FES and 11-13% for 11 beta-Et-FES and 17 alpha-ethynyl-FES (FES itself has a % ID/g of 9%). Uptake selectivity in terms of uterus to blood or muscle ratios at 1 h is highest for 11 beta-MeO-FES and 17 alpha-ethynyl-FES (43-149). Metabolic consumption studies show that most activity in uterus is unmetabolized and in blood is rapidly and nearly completely metabolized. In muscle, FES and the substituted estrogens show intermediate levels of metabolic consumption; in some cases activity in muscle extracts is nearly unmetabolized. Thus, the substituents on FES cause major alterations in receptor and nonreceptor binding affinity, uptake efficiency and selectivity, and extent of metabolism. It is not readily clear, however, whether the alterations in uptake efficiency and selectivity are the result of differences in receptor or nonreceptor binding or lipophilicity, or altered patterns of metabolism. Nevertheless, these compounds should be useful in providing a spectrum of uptake properties that could be used for imaging different estrogen-receptor-containing structures.

Target tissue uptake selectivity of three fluorine-substituted progestins: potential imaging agents for receptor-positive breast tumors

We have studied three new fluorine-substituted progestins (1-3) as potential imaging agents for progesterone receptor (PgR)-positive human breast tumors. Two of these are fluorine-substituted analogs of the potent progestin R5020 (promegestone), derived from (21S)-hydroxy R 5020 (RU 27987) and (21R)-hydroxy R 5020 (RU 27988), known metabolites of R 5020, which have affinities for PgR that are 116 and 4%, respectively (relative to R 5020 = 100%). These precursors were protected as their 3,3-dioxolane derivatives and converted to the 21-trifluoromethanesulfonate derivatives. Fluoride ion displacement, followed by acid-catalyzed deprotection, furnished in good yield the epimeric fluoroanalogs, (21S)- and (21R)-fluro R 5020 (1 and 2, affinities for PgR, 11 and 45%, respectively). These compounds were also prepared in 18F labeled form by the same route, in 14-32% overall radiochemical yield (decay corrected; synthesis time 90 min; sp. act. 370-1060 Ci/mmol). In tissue distribution studies in estrogen-primed immature rats, uterus-to-muscle ratios were 4.3 at 1 h for the 21S-epimer and 1.1 for the 21R-epimer, paralleling their relative binding affinities. Considerable metabolic defluorination was observed. The third fluorine-substituted progestin, DU 41165, has a novel retroprogesterone (9 beta, 10 alpha) structure, substituted with fluorine at C-6; its binding affinity is 145% relative to R 5020, and it was prepared in tritium-labeled form by acetylation of DU 41231, the 17 alpha-hydroxy precursor, with [3H]acetic anhydride. In estrogen-primed immature rats, this compound shows uterus-to-muscle ratios of 15 at 1 h, and 18-71 between 2 and 6 h, suggesting that compounds in this retroprogesterone series may be very promising candidates for selective imaging of PgR-positive tissues and tumors.

21-[18F]fluoro-16 alpha-ethyl-19-norprogesterone: synthesis and target tissue selective uptake of a progestin receptor based radiotracer for positron emission tomography

We have synthesized 21-[18F]fluoro-16 alpha-ethyl-19-norprogesterone (FENP), a high affinity ligand for the progesterone receptor, labeled with the positron-emitting radionuclide fluorine-18 (t1/2 = 110 min). The synthesis proceeds in two steps from 21-hydroxy-16 alpha-ethyl-19-norprogesterone and involves [18F]fluoride ion displacement of the 21-trifluoromethanesulfonate (21-triflate). This material is purified by HPLC and is obtained in 4-30% overall yield (decay corrected) within 40 min after the end of bombardment to produce [18F]fluoride ion. The effective specific activity, determined by competitive radioreceptor binding assays, is 700-1400 Ci/mmol. In vivo, [18F]FENP demonstrates highly selective, receptor-mediated uptake by the uterus of estrogen-primed rats; the uterus to blood and uterus to muscle ratios were respectively 26 and 16 at 1 h and 71 and 41 at 3 h after injection. The high target tissue selectivity of this uptake suggests that this compound may be useful for the in vivo imaging of progestin target tissues and receptor-rich tumors (such as human breast tumors) by positron emission tomography.

Uptake of three [3H]progestins by target tissues in vivo: implications for the design of diagnostic imaging agents

We have investigated the tissue distribution of radioactivity for 0.5-4 h following the i.v. injection of three tritium-labeled progestins in estrogen-primed, immature rats. Whereas [3H]progesterone shows minimal uterine uptake (less than 0.7% injected dose per gram; %ID/g), the two higher affinity, synthetic progestins [3H]R 5020 (promegestrone) and [3H]ORG 2058 show highly selective uptake that reaches 4-5% ID/g by 1-3 h. The uterus to non-target tissue activity ratio at 2-4 h is approximately 12-20 for R 5020 and ORG 2058, but less than 2 for progesterone; the uterus to blood activity ratio for R 5020 is also high (approximately 15), but is lower for ORG 2058, possibly due to the accumulation of radiolabeled metabolites in the blood. The uterine uptake is selectively blocked by simultaneous injection of a large dose of unlabeled steroid, indicating that the uptake is mediated by a high affinity, low capacity binding system, presumably the progesterone receptor. Pronounced uptake is also observed by the liver and into fat, but is not receptor-mediated. The highly selective target tissue uptake by the two synthetic steroids, but not by progesterone, indicates that one must have ligands with sufficiently high affinity for the target tissue receptor, as well as low affinity for certain non-receptor binding proteins, in order to obtain adequate contrast between target and non-target tissues in dynamic uptake studies. These guidelines will be important in the development of suitable in vivo imaging agents based on the progesterone receptor.