Preclinical Studies of Gene Replacement Therapy for CDKL5 Deficiency Disorder.

Cyclin dependent kinase-like 5 (CDKL5) Deficiency Disorder (CDD) is a rare neurodevelopmental disorder caused by a mutation in the X-linked CDKL5 gene. CDKL5 is a serine/threonine kinase that is critical for axon outgrowth, dendritic morphogenesis, as well as synapse formation, maturation, and maintenance. This disorder is characterized by early-onset epilepsy, hypotonia, and failure to reach cognitive and motor developmental milestones. Because the disease is monogenic, delivery of the CDKL5 gene to the brain of patients should provide clinical benefit. To this end, we designed a gene therapy vector, adeno-associated virus (AAV)9.Syn.hCDKL5, in which human CDKL5 gene expression is driven by the synapsin promoter. In biodistribution studies conducted in mice, intracerebroventricular (ICV) injection resulted in broader, more optimal biodistribution than did intracisterna magna (ICM) delivery. AAV9.Syn.hCDKL5 treatment increased phosphorylation of EB2, a bona fide CDKL5 substrate, demonstrating biological activity in vivo. Our data provides proof-of-concept that ICV delivery of AAV9.Syn.hCDKL5 to neonatal male Cdkl5 knockout mice reduces pathology and reduces aberrant behavior. Functional improvements were seen at doses of 3e11 to 5e11 vector genomes (vg)/g brain, which resulted in transfection of ≥50% of the neurons. Functional improvements were not seen at lower doses suggesting a requirement for broad distribution for efficacy.

AAV2-hAADC (Eladocagene Exuparvovec) Biodistribution and Expression: Superiority of Intraputaminal versus Intracerebroventricular and Intrathecal (Lumbar) Routes of Administration.

Aromatic L-amino acid decarboxylase deficiency is a genetic disorder of enzyme loss with decreased neurotransmitter synthesis, and it is characterized by symptoms of impaired motor development and cognitive function, hypotonia, dystonia, and oculogyric crises. Though symptomatic severity varies, the majority of patients experience severe motor impairments, including an inability to sit, stand, or walk. One approved therapy for Aromatic L-amino acid decarboxylase deficiency involves intraputaminal delivery of an adeno-associated virus packaging the human Aromatic L-amino acid decarboxylase enzyme (hAADC) cDNA. The objective of this study in monkeys was to determine the acceptability of ICV/IT as minimally invasive dosing options by evaluating hAADC biodistribution and expression following intraputaminal, intracerebroventricular (ICV), or intrathecal (IT, lumbar) administration. Results show that all routes produced comparable CSF transgene levels and were well-tolerated. The intraputaminal route yielded the highest levels of transgene-derived mRNA expression in the putamen, caudate, and globus pallidus, while expression levels in the spinal cord and dorsal root ganglia (DRG, a target of special toxicological concern) were undetectable. In contrast, the highest transgene levels in ICV/IT groups were observed in the spinal cord and DRG, but levels were too low to result in expression in the putamen, caudate, and globus pallidus. Unlike ICV/IT, the intraputaminal route produced no transgene in blood, suggesting a lower likelihood of off-target toxicities. Additionally, intraputaminal dosing resulted in the lowest anti-AAV2 antibody (anti-drug antibody) levels. Together, these data demonstrate the superiority of intraputaminal administration over ICV/IT routes in achieving AAV2-hAADC transgene DNA distribution and mRNA expression in target therapeutic areas while minimizing risk of toxicity.

Effect of LX4211 on glucose homeostasis and body composition in preclinical models.

Treatments that lower blood glucose levels and body weight should benefit patients with type 2 diabetes mellitus (T2DM). We developed LX4211 [(2S,3R,4R,5S,6R)-2-(4-chloro-3-(4-ethoxybenzyl)phenyl)-6-(methylthio)tetrahydro-2H-pyran-3,4,5-triol], an orally available small molecule that decreases postprandial glucose excursions by inhibiting intestinal sodium/glucose cotransporter 1 (SGLT1) and increases urinary glucose excretion (UGE) by inhibiting renal SGLT2. In clinical studies of patients with T2DM, LX4211 appears to act through dual SGLT1/SGLT2 inhibition to improve glycemic control and promote weight loss. Here, we present preclinical studies that explored the ability of LX4211 to improve glycemic control and promote weight loss. We found that 1) LX4211 inhibited in vitro glucose transport mediated by mouse, rat, and dog SGLT1 and SGLT2; 2) a single daily LX4211 dose markedly increased UGE for >24 hours in mice, rats, and dogs; and 3) in the KK.Cg-Ay/J heterozygous (KKA(y)) mouse model of T2DM, LX4211 lowered A1C and postprandial glucose concentrations while increasing postprandial glucagon-like peptide 1 concentrations. Also, long-term LX4211 treatment 1) decreased oral glucose tolerance test (OGTT) glucose excursions, increased OGTT 30-minute insulin concentrations and increased pancreatic insulin content in KKA(y) mice; and 2) decreased weight gain in dogs and rats but not in KKA(y) mice while increasing food consumption in dogs, rats, and KKA(y) mice; in these KKA(y) mice, calories lost through UGE were completely offset by calories gained through hyperphagia. These findings suggest that LX4211 improves glycemic control by dual SGLT1/SGLT2 inhibition in mice as in humans, and that the LX4211-mediated weight loss observed in patients with T2DM may be attenuated by LX4211-mediated hyperphagia in some of these individuals.

Evaluation of LMI1195, a novel 18F-labeled cardiac neuronal PET imaging agent, in cells and animal models.

BACKGROUND: Heart failure has been associated with impaired cardiac sympathetic neuronal function. Cardiac imaging with radiolabeled agents that are substrates for the neuronal norepinephrine transporter (NET) has demonstrated the potential to identify individuals at risk of cardiac events. N-[3-Bromo-4-(3-[18F]fluoro-propoxy)-benzyl]-guanidine (LMI1195) is a newly developed 18F-labeled NET substrate designed to allow cardiac neuronal imaging with the high sensitivity, resolution, and quantification afforded by positron emission tomography (PET). METHODS AND RESULTS: LMI1195 was evaluated in comparison with norepinephrine (NE) in vitro and 123I-meta-iodobenzylguanidine (MIBG) in vivo. The affinity (Ki) of LMI1195 for NET was 5.16 ± 2.83 µmol/L, similar to that of NE (3.36 ± 2.77 µmol/L) in a cell membrane-binding assay. Similarly, LMI1195 uptake kinetics examined in a human neuroblastoma cell line had Km and Vmax values of 1.44 ± 0.76 µmol/L and 6.05 ± 3.09 pmol/million cells per minute, comparable to NE (2.01 ± 0.85 µmol/L and 6.23 ± 1.52 pmol/million cells per minute). In rats, LMI1195 heart uptake at 15 and 60 minutes after intravenous administration was 2.36 ± 0.38% and 2.16 ± 0.38% injected dose per gram of tissue (%ID/g), similar to 123I-MIBG (2.14 ± 0.30 and 2.19 ± 0.27%ID/g). However, the heart to liver and lung uptake ratios were significantly higher for LMI1195 than for 123I-MIBG. In rabbits, desipramine (1 mg/kg), a selective NET inhibitor, blocked LMI1195 heart uptake by 82%, which was more effective than 123I-MIBG (53%), at 1 hour after dosing. Sympathetic denervation with 6-hydroxydopamine, a neurotoxin, resulted in a marked (79%) decrease in LMI1195 heart uptake. Cardiac PET imaging with LMI1195 in rats, rabbits, and nonhuman primates revealed clear myocardium with low radioactivity levels in the blood, lung, and liver. Imaging in rabbits pretreated with desipramine showed reduced heart radioactivity levels in a dose-dependent manner. Additionally, imaging in sympathetically denervated rabbits resulted in low cardiac image intensity with LMI1195 but normal perfusion images with flurpiridaz F 18, a PET myocardial perfusion imaging agent. In nonhuman primates pretreated with desipramine (0.5 mg/kg), imaging with LMI1195 showed a 66% decrease in myocardial uptake. In a rat model of heart failure, the LMI1195 cardiac uptake decreased as heart failure progressed. CONCLUSIONS: LMI1195 is a novel (18)F imaging agent retained in the heart through the NET and allowing evaluation of the cardiac sympathetic neuronal function by PET imaging.

Synthesis and Cardiac Imaging of (18)F-Ligands Selective for ß1-Adrenoreceptors.

A series of potent and selective ß1-adrenoreceptor ligands were identified (IC50 range, 0.04-0.25 nM; ß1/ß2 selectivity range, 65-450-fold), labeled with the PET radioisotope fluorine-18 and evaluated in normal Sprague-Dawley rats. Tissue distribution studies demonstrated uptake of each radiotracers from the blood pool into the myocardium (0.48-0.62% ID/g), lung (0.63-0.97% ID/g), and liver (1.03-1.14% ID/g). Dynamic µPET imaging confirmed the in vivo dissection studies.

Inhibition of sphingosine 1-phosphate lyase for the treatment of rheumatoid arthritis: discovery of (E)-1-(4-((1R,2S,3R)-1,2,3,4-tetrahydroxybutyl)-1H-imidazol-2-yl)ethanone oxime (LX2931) and (1R,2S,3R)-1-(2-(isoxazol-3-yl)-1H-imidazol-4-yl)butane-1,2,3,4-tetraol (LX2932).

Sphingosine 1-phosphate lyase (S1PL) has been characterized as a novel target for the treatment of autoimmune disorders using genetic and pharmacological methods. Medicinal chemistry efforts targeting S1PL by direct in vivo evaluation of synthetic analogues of 2-acetyl-4(5)-(1(R),2(S),3(R),4-tetrahydroxybutyl)-imidazole (THI, 1) led to the discovery of 2 (LX2931) and 4 (LX2932). The immunological phenotypes observed in S1PL deficient mice were recapitulated by oral administration of 2 or 4. Oral dosing of 2 or 4 yielded a dose-dependent decrease in circulating lymphocyte numbers in multiple species and showed a therapeutic effect in rodent models of rheumatoid arthritis (RA). Phase I clinical trials indicated that 2, the first clinically studied inhibitor of S1PL, produced a dose-dependent and reversible reduction of circulating lymphocytes and was well tolerated at dose levels of up to 180 mg daily. Phase II evaluation of 2 in patients with active rheumatoid arthritis is currently underway.

Assessment of 18F-labeled mitochondrial complex I inhibitors as PET myocardial perfusion imaging agents in rats, rabbits, and primates.

PURPOSE: Myocardial extractions of mitochondria complex I (MC-I) inhibitors were high and well correlated with flow. This study assessed the potential of MC-I inhibitors to be developed as myocardial perfusion imaging (MPI) agents. METHODS: RP1003, RP1004, and RP1005 representing three classes of MC-I inhibitor were synthesized and radio-labeled with (18)F. These agents were evaluated for IC(50) values, tissue biodistribution, and cardiac PET imaging. (18)F-RP1004 was further examined for first-pass extraction and by imaging in non-human primates (NHP) and rats following coronary ligation. RESULTS: RP1003, RP1004, and RP1005 exhibited high MC-I inhibitory activity with IC(50) of 3.7, 16.7, and 14.4 nM. Heart uptakes in rats (percent injected dose per gram tissue) at 15 and 60 min after injection were 3.52 +/- 0.36 and 2.68 +/- 0.20 for (18)F-RP1003, 2.40 +/- 0.21 and 2.67 +/- 0.27 for (18)F-RP1004, and 2.28 +/- 0.12 and 1.81 +/- 0.17 for (18)F-RP1005. The heart to lung and liver uptake ratios were favorable for cardiac imaging with these agents. In isolated perfused rabbit hearts, the uptake of (18)F-RP1004 increased from 0.74 +/- 0.19 to 1.68 +/- 0.39 mL/min/g at flow rates of 1.66 to 5.06 mL/min/g. These values were higher than or similar to that of (99m)Tc-sestamibi. Cardiac imaging with these agents in rats and rabbits allowed visualization of the heart with minimal lung interference and rapid liver activity clearance. Imaging with (18)F-RP1004 also showed clear myocardium and marked liver activity washout in the NHP and clear detection of the perfusion-deficit area associated with left coronary artery ligation in the rat. CONCLUSION: MC-I inhibitors have the potential to be a new class of MPI agent.

Molecular imaging of matrix metalloproteinase in atherosclerotic lesions: resolution with dietary modification and statin therapy.

OBJECTIVES: This study sought to evaluate the feasibility of noninvasive detection of matrix metalloproteinase (MMP) activity in experimental atherosclerosis using technetium-99m-labeled broad matrix metalloproteinase inhibitor (MPI) and to determine the effect of dietary modification and statin treatment on MMP activity. BACKGROUND: The MMP activity in atherosclerotic lesions contributes to the vulnerability of atherosclerotic plaques to rupture. METHODS: Atherosclerosis was produced in 34 New Zealand White rabbits by balloon de-endotheliazation of the abdominal aorta and a high-cholesterol diet. In addition, 12 unmanipulated rabbits were used as controls and 3 for blood clearance characteristics. In vivo micro-single-photon emission computed tomography (SPECT) imaging was performed after radiolabeled MPI administration. Subsequently, aortas were explanted to quantitatively measure percent injected dose per gram (%ID/g) MPI uptake. Histological and immunohistochemical characterization was performed and the extent of MMP activity was determined by gel zymography or enzyme-linked immunosorbent assays. RESULTS: The MPI uptake in atherosclerotic lesions (n = 18) was clearly visualized by micro-SPECT imaging; MPI uptake was markedly reduced by administration of unlabeled MPI before the radiotracer (n = 4). The MPI uptake was also significantly reduced after diet withdrawal (n = 6) and fluvastatin treatment (n = 6); no uptake was observed in normal control rabbits (n = 12). The %ID/g MPI uptake (0.10 +/- 0.03%) in the atherosclerotic lesions was significantly higher than the uptake in control aorta (0.016 +/- 0.004%, p < 0.0001). Uptake in fluvastatin (0.056 +/- 0.011%, p < 0.0005) and diet withdrawal groups (0.043 +/- 0.011%, p < 0.0001) was lower than the untreated group. The MPI uptake correlated with immunohistochemically verified macrophage infiltration (r = 0.643, p < 0.0001), and MMP-2 (r = 0.542, p < 0.0001) or MMP-9 (r = 0.578, p < 0.0001) expression in plaques. CONCLUSIONS: The present data show the feasibility of noninvasive detection of MMP activity in atherosclerotic plaques, and confirm that dietary modification and statin therapy reduce MMP activity.

Synthesis and biological evaluation of pyridazinone analogues as potential cardiac positron emission tomography tracers.

A series of fluorinated pyridazinone derivatives with IC50 values ranging from 8 to 4000 nM for the mitochondrial complex 1 (MC1) have been prepared. Structure-activity relationship (SAR) assessment indicated preference of the fluorine label to be incorporated on an alkyl side chain rather than directly on the pyridazinone moiety. Tissue distribution studies of a series of analogues ([18F] 22-28) in Sprague-Dawley (SD) rats identified [18F]27 as the most promising radiotracer with high uptake in cardiac tissue (3.41%ID/g; 30 min post injection) in addition to favorable heart to nontarget organ distribution ratios. MicroPET images of SD rats and nonhuman primates after [18F]27 administration allowed easy assessment of the myocardium through 60 min with minimal lung or liver interference.

Mechanism of uptake and retention of F-18 BMS-747158-02 in cardiomyocytes: a novel PET myocardial imaging agent.

BACKGROUND: BMS-747158-02 is a novel fluorine 18-labeled pyridazinone derivative designed for cardiac imaging. The uptake and retention mechanisms of F-18 BMS-747158-02 in cardiac myocytes were studied in vitro, and the biodistribution of F-18 BMS-747158-02 was studied in vivo in mice. METHODS AND RESULTS: Fluorine 19 BMS-747158-01 inhibited mitochondrial complex I (MC-I) in bovine heart submitochondrial particles with an IC(50) of 16.6 +/- 3 nmol/L that was comparable to the reference inhibitors of MC-1, rotenone, pyridaben, and deguelin (IC(50) of 18.2 +/- 6.7 nmol/L, 19.8 +/- 2.6 nmol/L, and 23.1 +/- 1.5 nmol/L, respectively). F-18 BMS-747158-02 had high uptake in monolayers of neonatal rat cardiomyocytes (10.3% +/- 0.7% of incubated drug at 60 minutes) that was inhibited by 200 nmol/L of rotenone (91% +/- 2%) and deguelin (89% +/- 3%). In contrast, an inactive pyridaben analog, P-070 (IC(50) value >4 micromol/L in MC-1 assay), did not inhibit the binding of F-18 BMS-747158-02 in cardiomyocytes. Uptake and washout kinetics for F-18 BMS-747158-02 in rat cardiomyocytes indicated that the time to half-maximal (t((1/2))) uptake was very rapid (approximately 35 seconds), and washout t((1/2)) for efflux of F-18 BMS-747158-02 was greater than 120 minutes. In vivo biodistribution studies in mice showed that F-18 BMS-747158-02 had substantial myocardial uptake (9.5% +/- 0.5% of injected dose per gram) at 60 minutes and heart-to-lung and heart-to-liver ratios of 14.1 +/- 2.5 and 8.3 +/- 0.5, respectively. Positron emission tomography imaging in the mouse allowed clear cardiac visualization and demonstrated sustained myocardial uptake through 55 minutes. CONCLUSIONS: F-18 BMS-747158-02 is a novel positron emission tomography cardiac tracer targeting MC-I in cardiomyocytes with rapid uptake and slow washout. These characteristics allow fast and sustained accumulation in the heart.

Amino Acid derived enamides: synthesis and aminopeptidase activity.

Recently developed copper-catalyzed coupling methodology has been applied to the synthesis of amino acid derived enamides. Bond formation proved to be strongly influenced by protection strategy and vinyl iodide substitution while tolerant of limited side chain functionality. Assessment of aminopeptidase activity revealed a preference for (E)-1,2-disubstituted constructs.

Synthesis and biological evaluation of the mitochondrial complex 1 inhibitor 2-[4-(4-fluorobutyl)benzylsulfanyl]-3-methylchromene-4-one as a potential cardiac positron emission tomography tracer.

A series of fluorinated chromone analogs with IC50 values ranging from 9 to 133 nM for the mitochondrial complex 1 (MC-I) has been prepared. A structure-activity relationship (SAR) study of the most potent fluorinated chromone analog 10 demonstrated the linkage heteroatom preference of the side chain region of the molecule while maintaining potent MC-I inhibitory activity. Tissue distribution studies 30 min after [(18)F]10 administration to Sprague-Dawley (SD) rats demonstrated high uptake of the radiotracer from the blood pool into the myocardium (2.24% ID/g), kidney (1.93% ID/g), and liver (2.00% ID/g). After 2 h about 66% of the activity in the myocardium at 30 min had been retained, whereas approximately 70% had been cleared from the liver and kidney. MicroPET images of SD rats after [(18)F]10 administration allowed easy assessment of the myocardium through 60 min with minimal lung or liver interference.

Radiolabeled divalent peptidomimetic vitronectin receptor antagonists as potential tumor radiotherapeutic and imaging agents.

The integrin receptor alphavbeta3 is overexpressed on the endothelial cells of growing tumors and on some tumor cells themselves. A radiolabeled alphavbeta3 antagonists belonging to the quinolin-4-one class of peptidomimetics (TA138) was previously shown to exhibit high affinity for integrin alphavbeta3 and high selectivity versus other integrin receptors. 111In-TA138 exhibited high tumor uptake in the c-neu Oncomouse mammary adenocarcinoma model and produced excellent scintigraphic images. This study describes the synthesis of eight divalent versions of TA138 and their evaluation as potential tumor radiotherapeutic agents. The two main variables in this study were the length of the spacer bridging the biotargeting moieties and the total negative charge of the molecules imparted by the cysteic acid pharmacokinetic modifiers. Receptor affinity was evaluated in a panel of integrin receptor affinity assays, and biodistribution studies using the 111In-labeled derivatives were carried out in the c-neu Oncomouse model. All divalent agents maintained the high receptor affinity and selectivity of TA138, and six of the eight 111In derivatives exhibited blood clearance that was faster than 111In-TA138 at 24 h postinjection (PI). All divalent agents exhibited tumor uptake and retention at 24 h PI that was higher than 111In-TA138. Tumor/organ ratios were improved for most of the divalent agents at 24 h PI in critical nontarget organs marrow, kidney, and liver, with the agents having intermediate-length spacers (29-43 A) showing the largest improvement. As an example, 111In-15 showed tumor uptake of 14.3% ID/g at 24 h PI and tumor/organ ratios as follows: marrow, 3.24; kidney, 7.29; liver, 8.51. A comparison of therapeutic indices for 90Y-TA138 and 177Lu-15 indicate an improved therapeutic index for the divalent agent. The implications for radiotherapeutic applications and the mechanism of this multivalent effect are discussed.

Structure-activity relationships of 111In- and 99mTc-labeled quinolin-4-one peptidomimetics as ligands for the vitronectin receptor: potential tumor imaging agents.

The integrin receptor alpha(v)beta(3) is overexpressed on the endothelial cells of growing tumors and on some tumor cells themselves. Radiolabeled alpha(v)beta(3) antagonists have demonstrated potential application as tumor imaging agents and as radiotherapeutic agents. This report describes the total synthesis of eight new HYNIC and DOTA conjugates of receptor alpha(v)beta(3) antagonists belonging to the quinolin-4-one class of peptidomimetics, and their radiolabeling with (99m)Tc (for HYNIC) and (111)In (for DOTA). Tethering of the radionuclide-chelator complexes was achieved at two different sites on the quinolin-4-one molecule. All such derivatives maintained high affinity for receptor alpha(v)beta(3) and high selectivity versus receptors alpha(IIb)beta(3), alpha(v)beta(5), alpha(5)beta(1). Biodistribution of the radiolabeled compounds was evaluated in the c-neu Oncomouse mammary adenocarcinoma model. DOTA conjugate (111)In-TA138 presented the best biodistribution profile. Tumor uptake at 2 h postinjection was 9.39% of injected dose/g of tissue (%ID/g). Activity levels in selected organs was as follows: blood, 0.54% ID/g; liver, 1.94% ID/g; kidney, 2.33% ID/g; lung, 2.74% ID/g; bone, 1.56% ID/g. A complete biodistribution analysis of (111)In-TA138 and the other radiolabeled compounds of this study are presented and discussed. A scintigraphic imaging study with (111)In-TA138 showed a clear delineation of the tumors and rapid clearance of activity from nontarget tissues.

Noninvasive targeted imaging of matrix metalloproteinase activation in a murine model of postinfarction remodeling.

BACKGROUND: Time-dependent activation of matrix metalloproteinases (MMPs) after myocardial infarction (MI) contributes to adverse left ventricular (LV) remodeling; however, noninvasive methods to monitor this process serially are needed. METHODS AND RESULTS: MMP-targeted radiotracers were developed that displayed selective binding kinetics to the active MMP catalytic domain. Initial nonimaging studies were performed with a (111)In-labeled MMP-targeted radiotracer ((111)In-RP782) and negative control compound ((111)In-RP788) in control mice (Ctrl) and in mice 1 week after surgically induced MI. Localization of (111)In-RP782 was demonstrated within the MI by microautoradiography. A 334+/-44% increase (P<0.001 versus Ctrl) in relative retention of (111)In-RP782 was confirmed by gamma well counting of myocardium. Subsequent high-resolution dual-isotope planar and hybrid micro-single-photon emission computed tomography/CT imaging studies with an analogous 99mTc-labeled MMP-targeted radiotracer (99mTc-RP805) and 201Tl demonstrated favorable biodistribution and clearance kinetics of 99mTc-RP805 for in vivo cardiac imaging, with robust retention 1 to 3 weeks after MI in regions of decreased 201Tl perfusion. Gamma well counting yielded a similar approximately 300% increase in relative myocardial retention of 99mTc-RP805 in MI regions (Ctrl, 102+/-9%; 1 week, 351+/-77%; 2 weeks, 291+/-45%; 3 weeks, 292+/-41%; P<0.05 versus Ctrl). Myocardial uptake in the MI region was also significantly increased approximately 5-fold when expressed as percentage injected dose per gram tissue. There was also a significant 2-fold increase in myocardial activity in remote regions relative to control mice, suggesting activation of MMPs in regions remote from the MI. CONCLUSIONS: This novel noninvasive targeted MMP radiotracer imaging approach holds significant diagnostic potential for in vivo localization of MMP activation and tracking of MMP-mediated post-MI remodeling.

Detection of injury-induced vascular remodeling by targeting activated alphavbeta3 integrin in vivo.

BACKGROUND: The alpha(v)beta3 integrin plays a critical role in cell proliferation and migration. We hypothesized that vascular cell proliferation, a hallmark of injury-induced remodeling, can be tracked by targeting alpha(v)beta3 integrin expression in vivo. METHODS AND RESULTS: RP748, a novel 111In-labeled alpha(v)beta3-specific radiotracer, was evaluated for its cell-binding characteristics and ability to track injury-induced vascular proliferation in vivo. Three groups of experiments were performed. In cultured endothelial cells (ECs), TA145, a cy3-labeled homologue of RP748, localized to alpha(v)beta3 at focal contacts. Activation of alpha(v)beta3 by Mn2+ led to increased EC binding of TA145. Left common carotid artery wire injury in apolipoprotein E-/- mice led to vascular wall expansion over a period of 4 weeks. RP748 (7.4 MBq) was injected into groups of 9 mice at 1, 3, or 4 weeks after left carotid injury, and carotids were harvested for autoradiography. Relative autographic intensity, defined as counts/pixel of the injured left carotid area divided by counts/pixel of the uninjured right carotid area, was higher at 1 and 3 weeks (1.8+/-0.1 and 1.9+/-0.2, respectively) and decreased significantly by 4 weeks after injury (1.4+/-0.1, P<0.05). Carotid alpha(v) and beta3 integrin expression was maximal at 1 week and decreased by 4 weeks after injury. The proliferation index, as determined by Ki67 staining, followed a temporal pattern similar to that of RP748 uptake. Dynamic gamma imaging demonstrated rapid renal clearance of RP748. CONCLUSIONS: RP748 has preferential binding to activated alpha(v)beta3 integrin and can track the injury-induced vascular proliferative process in vivo.

Design, synthesis, and evaluation of radiolabeled integrin alpha v beta 3 receptor antagonists for tumor imaging and radiotherapy.

The goal of this research is the development of tumor imaging and radiotherapeutic agents based on targeting of the integrin alpha(v)beta(3) (vitronectin receptor). Macrocyclic chelator DOTA has been conjugated to peptidomimetic vitronectin receptor antagonist SH066 to give TA138. TA138 and (89)Y-TA138 retain antagonist properties and high affinity for integrin alpha(v)beta(3) (IC(50) = 12 and 18 nM, respectively), and good selectivity versus integrin alpha(IIb)beta(3) (IC(50) > 10,000 nM). TA138 forms stable complexes with (111)In and (90)Y in > 95% RCP. (111)In-TA138 demonstrates high tumor uptake in the c-neu Oncomouse (Charles River Laboratories [Charles River, Canada]) mammary adenocarcinoma model (9.39% ID/g at 2 hours PI) and low background activity. Blood clearance is rapid and excretion is renal. Tumors are visible as early as 0.5 hours PI. Radiotherapy studies in the c-neu Oncomouse model demonstrated a slowing of tumor growth at a dose of 15 mCi/m(2), and a regression of tumors at a dose of 90 mCi/m(2).