Synthesis and estrogen receptor affinity of a 4-hydroxytamoxifen-labeled ligand for diagnostic imaging

Polysaccharide-Drug Conjugates: A Tool for Enhanced Cancer Therapy

Cancer is one of the most widespread deadly diseases, following cardiovascular disease, worldwide. Chemotherapy is widely used in combination with surgery, hormone and radiation therapy to treat various cancers. However, chemotherapeutic drugs can cause severe side effects due to non-specific targeting, poor bioavailability, low therapeutic indices, and high dose requirements. Several drug carriers successfully overcome these issues and deliver drugs to the desired sites, reducing the side effects. Among various drug delivery systems, polysaccharide-based carriers that target only the cancer cells have been developed to overcome the toxicity of chemotherapeutics. Polysaccharides are non-toxic, biodegradable, hydrophilic biopolymers that can be easily modified chemically to improve the bioavailability and stability for delivering therapeutics into cancer tissues. Different polysaccharides, such as chitosan, alginates, cyclodextrin, pullulan, hyaluronic acid, dextran, guar gum, pectin, and cellulose, have been used in anti-cancer drug delivery systems. This review highlights the recent progress made in polysaccharides-based drug carriers in anti-cancer therapy.

Synthesis and growth inhibition activity of fluorinated derivatives of tamoxifen

The design and synthesis of 11 fluorinated derivatives of tamoxifen are described. Growth inhibition values (GI50) on human HT-29, M21, MCF7, and MDA-MB-231 tumor cells are also reported. In general, the GI50 values are similar or slightly higher than tamoxifen with the most active compound on MCF7 cell line having a GI50=3.6μM. Surprisingly, as opposed to tamoxifen, both geometrical isomers behave similarly. We hypothesize that this behavior is due to in vitro isomerization of the compounds.

Influence of charge on cell permeability and tumor imaging of GPR30-targeted 111in-labeled nonsteroidal imaging agents

Recent clinical studies implicate the role of G protein-coupled estrogen receptor, GPR30, in aggressive forms of breast, ovarian, and endometrial cancers. However, the functional role of GPR30 at cellular and molecular levels remains less clear and controversial, particularly its subcellular location. The primary objective of this study was to develop radiolabeled neutral and charged GPR30-targeted nonsteroidal analogues to understand the influence of ligand charge on cell binding, cellular permeability, and in vivo tumor imaging. Therefore, we developed a series of GPR30-targeted (111/113)In(III)-labeled analogues using macrocyclic and acyclic polyamino-polycarboxylate chelate designs that would render either a net negative or neutral charge. In vitro biological evaluations were performed to determine the role of negatively charged analogues on receptor binding and activation using calcium mobilization and phosphoinositide 3-kinase assays. In vivo evaluations were performed on GPR30-expressing human endometrial Hec50 tumor-bearing mice to characterize the biodistribution and potential application of GPR30-targeted imaging agents for translational research. In vitro functional assays revealed an effect of charge, such that only the neutral analogue activated GPR30-mediated rapid signaling pathways. These observations are consistent with expectations for initial rates of membrane permeability and suggest an intracellular rather than the cell surface location of functional receptor. In vivo studies revealed receptor-mediated uptake of the radiotracer in target organs and tumors; however, further structural modifications will be required for the development of future generations of GPR30-targeted imaging agents with enhanced metabolic properties and decreased nonspecific localization to the intestines.

131I labeling of tamoxifen and biodistribution studies in rats

Tamoxifen [TAM ([Z]-2-[4-(1,2-diphenyl-1-di-butenyl)-phenoxy]-N,N-dimethylethanamine)] has been used as an antiestrogen drug for treatment and prevention of human breast cancer. Tamoxifen was labeled with 131I using iodogen as an oxidizing agent. Mass spectroscopy of the cold standard showed that the labeling occurs in ortho position to the phenyl ether position of TAM as expected. Quality control, radiochemical yield and stability were established using the radioelectrophoresis method. The radiolabeled compound maintained its stability throughout working period of 24 h. Scintigraphic imaging was performed and tissue distribution was determined in Albino Wistar rats. According to biodistribution and imaging experiments the radiolabeled compound presented estrogen receptor (ER) specificity and it was uptaken by endometrium as well as breast tissue.

Persistent binding of ligands to the aryl hydrocarbon receptor

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates many of the biological and toxic effects of halogenated aromatic hydrocarbons (HAHs), polycyclic aromatic hydrocarbons (PAHs), and other structurally diverse ligands. While HAHs are several orders of magnitude more potent in producing AhR-dependent biochemical effects than PAHs or other AhR agonists, only the HAHs have been observed to produce AhR-dependent toxicity in vivo. Here we have characterized the dissociation of a prototypical HAH ligand ([(3)H] 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD]) and PAH-like ligand ([(3)H] beta-naphthoflavone [betaNF]) from the guinea pig, hamster, mouse, and rat hepatic cytosolic AhR in order to elucidate the relationship between the apparent ligand-binding affinities and the divergent potency of these chemicals. Both compounds dissociated very slowly from the AhR with the amount of specific binding remaining at 96 h ranging from 53% to 70% for [(3)H]TCDD and 26% to 85% for [(3)H] betaNF, depending upon the species examined. The rate of ligand dissociation was unaffected by protein concentration or incubation temperature. Preincubation of cytosol with 2,3,7,8-tetrachlorodibenzofuran, carbaryl, or primaquine, prior to the addition of [(3)H]TCDD, shifted the apparent IC(50) of these compounds as competitive AhR ligands by approximately 10- to 50-fold. Our results support the need for reassessment of previous AhR ligand-binding affinity calculations and competitive binding analysis since these measurements are not carried out at equilibrium binding conditions. Our studies suggest that AhR binding affinity/occupancy has little effect on the observed differences in the persistence of gene expression by HAHs and PAHs.

Synthesis and biodistribution of fluorine-18-labeled fluorocyclofenils for imaging the estrogen receptor

C4-[18F]Fluorocyclofenil ([18F]FCF, 6) and C3-[18F]fluoroethylcyclofenil ([18F]FECF, 9), two high-affinity nonsteroidal estrogens, were prepared and investigated as potential agents for imaging estrogen receptors (ERs) in breast tumors. Both of these compounds could be prepared conveniently from alkyl methanesulfonate precursors (5,8) by fluoride displacement reactions, and they were obtained in high radiochemical purity and radiochemical yields, with effective specific activities sufficient for in vivo biodistribution studies. While the biodistribution of [18F]FCF (6) in immature female rats showed no selective target tissue uptake, the biodistribution of [18F]FECF (9) showed selective uptake by the uterus, but this uptake could not be blocked by excess estradiol. The poor in vivo biodistribution of these otherwise high-affinity ligands arouses curiosity, and together with recent results on the biodistribution of other nonsteroidal ligands suggests that factors other than receptor binding affinity are important for in vivo imaging of estrogen target tissues and ER-positive breast tumors.