Development of cancer receptor-specific gold nanoparticles will allow efficient targeting/optimum retention of engineered gold nanoparticles within tumors and thus provide synergistic advantages in oncology as it relates to molecular imaging and therapy. Bombesin (BBN) peptides have demonstrated high affinity toward gastrin-releasing peptide (GRP) receptors in vivo that are overexpressed in prostate, breast, and small-cell lung carcinoma. We have synthesized a library of GRP receptor-avid nanoplatforms by conjugating gold nanoparticles (AuNPs) with BBN peptides. Cellular interactions and binding affinities (IC 50 ) of AuNP-BBN conjugates toward GRP receptors on human prostate cancer cells have been investigated in detail. In vivo studies using AuNP-BBN and its radiolabeled surrogate 198 AuNP-BBN, exhibiting high binding affinity (IC 50 in microgram ranges), provide unequivocal evidence that AuNP-BBN constructs are GRP-receptor-specific showing accumulation with high selectivity in GRP-receptor-rich pancreatic acne in normal mice and also in tumors in prostate-tumor-bearing, severe combined immunodeficient mice. The i.p. mode of delivery has been found to be efficient as AuNP-BBN conjugates showed reduced RES organ uptake with concomitant increase in uptake at tumor targets. The selective uptake of this new generation of GRP-receptor-specific AuNP-BBN peptide analogs has demonstrated realistic clinical potential in molecular imaging via x-ray computed tomography techniques as the contrast numbers in prostate tumor sites are severalfold higher as compared to the pretreatment group (Hounsfield unit = 150).gold nanoparticles | bombesin | gastrin-releasing peptide receptor | prostate cancer | computed tomography imaging

We examined the mechanisms involved in protein kinase C (PKC)-dependent down-regulation of dopamine transporter (DAT) activity and cell surface expression by treating heterologously expressing cells with the clathrin-mediated endocytosis inhibitor concanavalin A (Con A) or the cholesterol depleter/membrane raft disrupter methyl-b-cyclodextrin (MbC) prior to treatment with the PKC activator phorbol 12-myristate, 13-acetate (PMA). Con A blocked PMA-induced surface reductions of DAT but only partially inhibited down-regulation, while MbC partially blocked down-regulation but did not inhibit loss of cell surface DAT, demonstrating that PKC-induced DAT down-regulation occurs by a combination of trafficking and non-trafficking processes. Using density-gradient centrifugation, we found that DATs are distributed approximately equally between Triton-insoluble, cholesterol-rich membrane rafts and Triton-soluble non-raft membranes. DATs in both populations are present at the cell surface and are active for dopamine and cocaine binding. PMA-induced loss of cell surface DAT occurred only from non-raft populations, demonstrating that non-raft DATs are regulated by trafficking events and indicating the likelihood that the cholesteroldependent non-trafficking regulatory mechanism occurs in rafts. PMA did not affect the DAT raft-non-raft distribution but stimulated the phosphorylation of DAT to a substantially greater level in rafts than non-rafts. These findings reveal a previously unknown role for cholesterol in DAT function and demonstrate the presence of distinct subcellular DAT populations that possess multiple regulatory differences that may impact dopaminergic neurotransmission.

Systemic delivery of therapeutic agents to solid tumors is hindered by vascular and interstitial barriers. We hypothesized that prostate tumor specific epigallocatechin-gallate (EGCg) functionalized radioactive gold nanoparticles, when delivered intratumorally (IT), would circumvent transport barriers, resulting in targeted delivery of therapeutic payloads. The results described herein support our hypothesis. We report the development of inherently therapeutic gold nanoparticles derived from the Au-198 isotope; the range of the 198 Au β-particle (approximately 11 mm in tissue or approximately 1100 cell diameters) is sufficiently long to provide cross-fire effects of a radiation dose delivered to cells within the prostate gland and short enough to minimize the radiation dose to critical tissues near the periphery of the capsule. The formulation of biocompatible 198 AuNPs utilizes the redox chemistry of prostate tumor specific phytochemical EGCg as it converts gold salt into gold nanoparticles and also selectively binds with excellent affinity to Laminin67R receptors, which are over expressed in prostate tumor cells. Pharmacokinetic studies in PC-3 xenograft SCID mice showed approximately 72% retention of 198 AuNP-EGCg in tumors 24 h after intratumoral administration. Therapeutic studies showed 80% reduction of tumor volumes after 28 d demonstrating significant inhibition of tumor growth compared to controls. This innovative nanotechnological approach serves as a basis for designing biocompatible target specific antineoplastic agents. This novel intratumorally injectable 198 AuNP-EGCg nanotherapeutic agent may provide significant advances in oncology for use as an effective treatment for prostate and other solid tumors.nanoradiotherapy | tumor metastases | localized therapy | polyphenols | cellular targeting R ecent data have confirmed that the incidence of prostate cancer is the highest among all estimated new cancer cases in American males, nearly double that of lung cancer (1). Globally, prostate cancer continues to be the second leading cause of cancer-related death in men (1). A detailed study involving 77,000 North Americans has shown that 10 y of regular prostate specific antigen (PSA) screening did not save a significant number of lives (2). Therefore, developments of new therapeutic protocols that provide effective control of the growth and propagation of prostate tumors have gained considerable clinical significance in the care and treatment of prostate cancer patients (3). The latest clinical trials on human prostate cancer patients using various experimental drugs further attest that shrinking prostate tumor sizes led to more than doubled survival in 70-80% of patients with aggressive cancers (3). Although a plethora of therapeutic approaches, which include utility of cytotoxic drugs (paclitaxel, estramustine, carboplatin, and doxorubicin) are currently in clinical practice, unfortunately, none of these chemotherapeutic agents offer a clinically efficient, affordable, and toxicologically safe regimen...

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SA4503, a potent sigma(1) receptor agonist, is reported as having 103-fold higher affinity for sigma(1) (IC(50) = 17.4 nM) than sigma(2) (IC(50) = 1,784 nM) sites in guinea pig brain membranes. Modest structural changes appear to have major effects on sigma(1)/sigma(2) selectivity. The fluoroethyl analog, FE-SA4503, is described as having high primary affinity for sigma(2) sites (IC(50) = 2.11 nM) and a weaker interaction with sigma(1) sites (IC(50) = 6.48 nM). SA4503 and FE-SA4503 have been radiolabeled for PET studies, and both bind selectively to sigma(1) receptors in animal and human brain in vivo. We prepared SA4503 and FE-SA4503 as reference compounds for radioligand development efforts. In our hands, SA4503 is 14-fold selective for sigma(1) (K(i) = 4.6 nM) over sigma(2) (K(i) = 63.1 nM) sites in guinea pig brain homogenates. Further, FE-SA4503 exhibits the same 14-fold selectivity for sigma(1) (K(i) = 8.0 nM) over sigma(2) (K(i) = 113.2 nM) receptors. The main differences from previously reported values stem from sigma(2) affinity determinations. This protocol, displacement of [(3)H]DTG binding to sigma(2) sites using (+)-pentazocine (200 nM) to mask sigma(1) sites, was validated by the proper rank order of sigma(2) inhibitory potencies shown by a panel of additional ligands: ifenprodil > haloperidol > DTG >> (+)-pentazocine. Robust Pearson correlation (r = 1.0, P = 0.002; slope = 0.97) was observed for our pK(i) values against those from a prior study by others. The findings have bearing on structure-activity relationships for this active series, and on conclusions that might be drawn from experiments relying upon defined sigma(1)/sigma(2) binding selectivity.

Benztropine and its analogs are tropane ring-containing dopamine uptake inhibitors that produce behavioral effects markedly different from cocaine and other dopamine transporter blockers. We investigated the benztropine binding site on dopamine transporters by covalently attaching a benztropine-based photoaffinity ligand, 125 I]RTI 82 occurs closer to the C terminal in a domain containing transmembrane helices 4-7. Thus, although benztropine and cocaine both contain tropane rings, their binding sites are distinct, suggesting that dopamine transport inhibition may occur by different mechanisms. These results support previously derived structure-activity relationships suggesting that benztropine and cocaine analogs bind to different domains on the dopamine transporter. These differing molecular interactions may lead to the distinctive behavioral profiles of these compounds in animal models of drug abuse and indicate promise for the development of benztropine-based molecules for cocaine substitution therapies.

Recently, we have developed the positron emitting radiotracer N1'-([11C]methyl)naltrindole ([11C]MeNTI) and demonstrated its high selectivity for delta opioid receptors in the mouse brain [Lever et al. (1992) Eur. J. Pharmacol., 216:449-450]. In the present study, we examined the selectivity of [11C]MeNTI for the delta opioid receptor in the human brain, using positron emission tomography (PET). The regional kinetics and distribution as well as the pharmacology confirmed the selectivity of [11C]MeNTI for delta opioid receptor in the human brain. First, the regional kinetics of [11C]MeNTI are in accordance with the density of the delta opioid receptor. Rapid washout in receptor-poor areas and prolonged retention in receptor-rich areas were observed. Second, the regional distribution of [11C]MeNTI correlated well (r = 0.91) with the in vitro distribution of delta opioid sites but not with mu or kappa site densities (r < or = 0.008 or r < or = 0.014, respectively). [11C]MeNTI binding was highest in regions of the neocortex (insular, parietal, frontal, cingulate, and occipital), caudate nucleus, and putamen. Binding was intermediate in the amygdala and lowest in the cerebellum and thalamus. Third, studies using the competitive antagonist naltrexone demonstrated the inhibition of [11C]MeNTI binding. Naltrexone inhibition of [11C]MeNTI binding was most effective in delta receptor-rich regions, and its inhibitory potency correlated well (r = 0.88) with the regional distribution of delta opioid sites. [11C]MeNTI is the first radioligand which selectively labels delta opioid receptors in vivo in the human brain following systemic administration. The availability of [11C]MeNTI will enable a receptor specific analysis of the role of [11C]MeNTI receptors in normal and abnormal human brain.

Alterations in a variety of neurotransmitter systems have been identified in experimental models of epilepsy and in brain tissue from patients with intractable temporal lobe seizures. The availability of new high-affinity radioligands permits the study of some neuroreceptors in vivo with positron emission tomography (PET). We previously characterized the in vivo binding of 11C-carfentanil, a potent and selective mu opiate receptor agonist, and described increases in 11C-carfentanil binding in the temporal neocortex of patients with unilateral temporal lobe epilepsy. These studies have been extended to 11C-diprenorphine, which labels mu, kappa, and delta opiate receptor subtypes. Paired measurements of opiate receptor binding were performed with PET using 11C-carfentanil and 11C-diprenorphine in patients with unilateral temporal lobe seizures. Carfentanil binding, reflecting changes in mu opiate receptors, was increased in the temporal neocortex and decreased in the amygdala on the side of the epileptic focus. Diprenorphine binding, reflecting mu as well as non-mu opiate subtypes, was not significantly different among regions in the focus and nonfocus temporal lobes. Regional glucose metabolism, measured using 18F-2-fluoro-2-deoxyglucose, was decreased in the mesial and lateral aspects of the temporal lobe ipsilateral to the epileptogenic focus. The variation in pattern of carfentanil and diprenorphine binding supports a differential regulation of opiate subtypes in unilateral temporal lobe epilepsy.