Search

Rationale and Objectives. We have recently developed an iodinated lipid-based contrast agent capable of residing in the blood pool for extended periods of time relative to conventional water-soluble contrast agents. The purpose of this study was to examine the effects of combining this new blood-pool agent (ITG-PEG) with a hepatocyte-selective agent (ITG-LE, Molecular Biosystems) for accurate CT detection of small ( Materials and Methods. Preliminary pharmacokinetic analyses were conducted in SD rats (12) by injection of either I-125-labeled ITG-PEG or I-125-labeled ITG-LE followed by subsequent blood collection and quantification of radioactivity. Preliminary CT studies were conducted in both normal (3) and tumor-bearing NZW rabbits (2). Tumor-bearing rabbits were laparotomized and VX2 cells injected directly into the hepatic parenchyma to produce a total of eight focal lesions (2–10 mm diameter). Animals underwent CT scanning 10 days later with multiple techniques including noncontrast and helical IV enhanced (600 mg I/kg iohexol), and then 24 hours later using both ITG-PEG and ITG-LE (200 mg I/kg). Tissue density measurements (HU) of liver, tumor, and blood (descending aorta) were acquired in each case for comparison. Tumor morphology was verified by gross pathologic inspection. Results. Pharmacokinetic analysis in rats as well as CT studies in normal rabbits revealed that ITG-PEG remains in the blood-pool phase for more than 2 hours following IV administration. In fact, blood density in normal rabbit obtained with ITG-PEG was 95.1 HU ± 5.8 at 120 minutes compared to 90.7 HU ± 6.1 immediately after injection. Although liver enhancement was greater with iohexol (67 HU within 1 minute of injection), than for ITG-PEG/ITG-LE (32 HU, 60 minutes postinjection), liver to lesion ratios favored ITG-PEG/ITG-LE due to significant enhancement of tumor itself with iohexol (+40 HU). Tumor enhancement was minimal with ITG-PEG/ITG-LE. Lesions were subjectively much better defined with ITG-PEG/ITG-LE with sharper edge definition. Conclusion. In these animal models, a new iodinated lipid-based contrast agent composed of both blood pool and hepatocyte-selective components afforded favorable CT imaging results compared to a conventional urographic agent, albeit at one-third the total iodine dose.

Rationale and Objectives. We compared the computed tomography (CT) scanning characteristics of a polyiodinated triglyceride analog with those of a urographic agent to distinguish Morris-7777 hepatoma (MH) cells from normal hepatocytes in rats. Methods. Eighteen Buffalo rats were laparotomized and MH cells injected directly into the hepatic parenchyma or introduced via the portal vein to produce, respectively, focal or diffuse lesions in the liver. Baseline CT scans were obtained 21 days after implantation and prior to intravenous administration of either the polyiodinated triglyceride (45–100 mg l/kg) or the nonionic contrast agent, iohexol (560 mg I/kg). Images were obtained at 0–3 hr and 24 hr. Gross pathologic inspection was performed to validate the imaging results. Results. Hepatomas were nearly isodense with normal liver parenchyma in many of the animals, rendering lesion detection difficult with no contrast agent. The bolus administration of iohexol improved lesion detection in many cases. Lesion conspicuity, however, was significantly improved with the polyiodinated triglyceride at less than one eighth the dose of iohexol. Conclusion. Because of their biochemical nature, polyiodinated triglyceride analogs are specifically cleared by the liver. Consequently, they offer several advantages over nonspecific urographic agents in their ability to enhance lesion conspicuity in this hepatoma model.

Purpose. A formulation methodology for the incorporation of polyiodinated triglyceride (ITG) analogues into a protein-free chylomicron remnant-like emulsion was developed to provide a vehicle for the selective hepatic delivery of these agents for contrast-enhanced X-ray computed tomography (CECT).

Mitotane is used in adrenal cancer as adjuvant therapy, monotherapy or combined with other cytotoxic agents in advanced disease, but only 30% of patients respond. The aim of this study was to define the structural requirements for drug activity and to develop analogs with improved adrenalytic action.Nine analogs of [1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2dichloroethane] (o,p'-DDD) were tested by measuring suppression of cortisol secretion and the presence of inflammatory changes in the dog adrenal and inhibition of cell proliferation and cortisol production by NCI-H295 human adrenal cancer cells.In addition to mitotane, o,p'-DDClBr and o,p'-DDBr(2), were active in vitro and in vitro: Their effects were comparable to that of o,p'-DDD when tested at 50 μM concentration, but o,p'DDBr(2) was significantly more active at the lower 20 μM concentration.A dihalogenated methine carbon is required for adrenalytic activity. A change in the aromatic portion of the mitotane molecule causes loss of activity. Because of its greater activity at lower concentrations, o,p'-DDBr(2) has potential application in the treatment of patients with adrenal cancer.

We have designed and synthesized two radioiodinated analogs of hexadecylphosphocholine in order to evaluate their tumor imaging potential. 12-(m[125I]iodophenyl)dodecyl phosphocholine (NM-324) and hexadecyl-2-[N,N-dimethyl-N-(m[125I]iodobenzyl-ammonium]ethyl phosphate (NM-326) demonstrated the ability of such compounds to localize in and thereby visualize the Walker 256 tumor in rats. However, the tumor avidity of NM-324 was far superior to NM-326. In addition, NM-324 showed excellent tumor localization in athymic mice bearing subcutaneous human tumors.

A triglyceride analog, glycerol-2-palmitoyl-1,3-di-15-(p-iodophenyl)pentadecanoate (DPPG) was synthesized and radiolabeled for evaluation as a potential functional liver scintigraphic agent. Uptake of DPPG was compared in normal, diabetic, tumor-bearing and heparin pretreated rats, revealing differences in uptake and clearance of radioactivity, correlating with hepatic lipase activity of these groups. Similar results were observed by γ -camera scintigraphy. Comparing the uptake of DPPG with that of its fatty acid component, 15-(p-iodophenyl)pentadecanoic acid (IPPA), revealed that the peak uptake of IPPA in the liver was about half that of DPPG. Based upon these findings, DPPG warrants further study as a hepatic radiodiagnostic agent.

Two novel cholesteryl ether derivatives were synthesized and radioiodinated: (1) [125I]cholesteryl m-iodobenzyl ether (125I-CIBE) and (2) [125I]cholesteryl 12-(m-iodophenyl)dodecyl ether (125I-CIDE). These radioiodinated ethers were incorporated into low-density lipoprotein (LDL) by incubating the compounds (solubilized in saline with Tween-20) with isolated LDL or with whole plasma. Such LDL preparations were taken up by cultured fibroblasts in a receptor-dependent manner similar to that of radioiodinated LDL. Upon injection into guinea pigs, 125I-CIBE-labeled guinea pig LDL cleared from the plasma similarly to radioiodinated guinea pig LDL. The primary sites of 125I-CIBE uptake were the adrenal and the liver, and the compound was stable to both hydrolysis and deiodination over 24 h. In summary, 125I-CIBE and 125I-CIDE, like previously described tritiated cholesteryl ethers, appear to be potentially useful tracers of cholesteryl ester uptake. Moreover, these radioiodinated probes have the advantage of being more easily quantitated in tissue samples as well as being detectable by noninvasive scintigraphic imaging.

To assess a surface-modified emulsion as a percutaneous CT lymphographic agent in normal dogs.An iodinated chylomicron remnant-like microemulsion was formulated with a mean particle size of 91.3 nm and an iodine concentration of 91 mg I/mL. Contrast material (2 mL) was injected into the subcutaneous tissues of the metatarsus and metacarpus of six normal dogs to enhance popliteal and cervical lymph nodes, respectively. CT images were acquired at 0, 15, 30, 45, 60, 240, 480, and 1440 minutes.Significant lymph node enhancement occurred in as little as 15 minutes after injection and persisted at least 8 hours. Node opacification was most pronounced at 1 to 4 hours postinjection and exceeded 200 HU in some nodes (precontrast attenuation = 45 HU). Marked enhancement of popliteal efferent lymphatics and of iliac and sacral node groups also occurred indicating distribution to second order nodes. Attenuation of enhanced nodes reverted to precontrast levels by 24 hours.The new surface-modified, chylomicron remnant-like emulsion provided marked, selective enhancement of targeted lymph nodes after subcutaneous administration. Moreover, the formulation produced significant opacification of more distant node groups from a single injection.

Rationale and objectives DHOG-LE is an injectable polyiodinated triglyceride lipid emulsion providing contrast enhancement of the liver in CT. Studies were conducted to characterize the imaging efficacy of various DHOG-LE formulations as a function of both the administered iodine dose and the formulation composition. Materials and methods Four DHOG-LE preparations consisting of either 10, 20, 25, or 30% (w/v) total lipid were administered to anesthetized female Sprague Dawley rats as single intravenous bolus doses of 50, 100, 150, and/or 300 mg I/kg (n = 3 to 6 rats/formulation and dose). A 25% triolein lipid emulsion prepared without iodine was administered as a vehicle control at the highest dose volume (n = 6). Liver enhancement was evaluated as a function of time (0 to 24 hours) after administration of contrast by analyzing regions of interest from sequential body scans. Results At all dose levels, liver enhancement was observed after injection of each DHOG-LE formulation. Regardless of formulation composition, similar enhancement of the liver was noted when administered at an equivalent iodine dose. Liver enhancement increased proportionately with increasing iodine dose. Mean peak intensities for 50, 100, 150, and 300 mg I/kg doses were 78 HU (42% above baseline), 101 HU (84% above baseline), 125 HU (127% above baseline), and 195 HU (255% above baseline), respectively. Liver time-intensity profiles exhibited rapid uptake, prolonged enhancement up to 3 hours, and complete clearance of the majority of the formulations tested by 24 hours. Time and duration of peak intensities were also directly related to iodine dose. Conclusions In the animal model tested, DHOG-LE imaging efficacy was directly related to iodine dose and was independent of formulation composition. Thus, administration of DHOG-LE in highly concentrated lipid preparations minimized administered dose volume and resulted in appreciable liver enhancement, even at the lowest dose of 50 mg I/kg.

It is often impossible to optimally plan therapy for prostate cancer as current imaging is unreliable in determining if the cancer has spread beyond the prostate. Similarly, when prostate cancer recurs, as evidenced by a rising serum PSA level, non-invasively determining the precise location of the recurrence is often impossible. We have developed new radioactive compounds, NM404 and NM412, which are radioiodinated phospholipid ether analogs and have shown that they can localize to prostate cancer in rodent models of prostate cancer. We have recently shown that NM404 (1125 labeled) develops tumor uptake 37 times that of normal muscle, 9 times that of normal prostate and 3-11 times that of normal blood and liver, with 18% ID/g in the tumor at 5 days post injection. This level of targeting is considerably higher than most other radiopharmaceuticals. We also have completed pre clinical toxicology tests with the NM404 and NM412 reagents, which have shown no toxicity in doses up to 200 times that of the planned human dose in both rat and rabbit models. Dosimetry calculations for the radio labeled compounds have been completed. These data have allowed for development of protocols to begin human imaging studies, after appropriate approvals are obtained.

A synthetic lipid emulsion (LE) has been developed with physicochemical properties that closely resemble those of a specific class of naturally-occurring lipoproteins known as chylomicron remnants. The formulation has the potential to serve as a hepatocyte-selective delivery system for any lipophilic or amphipathic compounds that can be associated with the internal lipid phase of the emulsion. In the present studies, a lipophilic polyiodinated triglyceride (ITG) was successfully incorporated into the delivery vehicle to form a stable chylomicron-remnant-like emulsion capable of localizing material to the liver following intravenous injection. The preferred ITG-LE formulation was shown to have a mean particle diameter of less than 200 nm and a particle size stability profile in excess of 12 months. The viscosity, pH, and osmolality of the formulation also appeared favorable for safe and convenient intravenous injection. The particle size profile, chemical properties, and high degree of incorporation of ITG into the emulsion suggest that the ITG-LE formulation holds substantial promise as a hepatocyte-selective imaging agent for computed tomography of the liver. Biodistribution, elimination, and computed tomography (CT) imaging results in animals corroborated the hepatocyte-selective nature of the ITG-LE formulation.

The adrenalytic activity of mitotane ( o , p ′-DDD) has made it useful in the treatment of adrenocortical carcinoma and Cushing's syndrome. In support of a study to develop mitotane analogs as more effective therapeutic agents and as a basis for understanding the toxicity of related compounds in the adrenals, the biotransformations of o , p ′-DDD in adrenocortical homogenate preparations have been studied and compared with those of its m , p ′- and p , p ′-isomers. Aliphatic oxidation to the corresponding acetic acid derivative, o , p ′-, m , p ′- or p , p ′-DDA, was the major transformation for all the preparations. In the comparisons of the DDD isomers, the order of both DDA formation and apparent covalent binding was o , p ′- > m , p ′- > p , p ′-DDD. There was also evidence for α-hydroxylation at the benzylic carbon with subsequent loss of water to form ethylene derivatives. This was a minor pathway for o , p ′-DDD, but was the major pathway for the other two isomers. Thus, while the total yields of metabolites of o , p ′- and m , p ′-DDD were similar and at least twice that of the p , p ′-isomer, their distribution of metabolites differed significantly. The effects of the three isomers on cell growth and cortisol production with the human adrenocortical carcinoma cell line, NCI H-295, followed the same order as their DDA formation and tissue binding. It is proposed that hydroxylation by the adrenal cortex at the β-carbon leads to an adrenalytic effect, whereas hydroxylation at the α-carbon would represent an alternate deactivation pathway.

A series of glyceryl 2-oleoyl 1,3-bis[omega-(3-amino-2,4,6-triiodophenyl)] alkanoates was synthesized, radioiodinated with iodine-125, emulsified, and evaluated for their ability to selectively localize in the liver for potential use as hepatographic agents in computed tomography. All seven analogs displayed rapid liver uptake wherein between 65 and 78% of the injected dose accumulated in the liver by 30 min. Liver values ranged from 46 to 93% 3 h after injection which corresponded to liver to blood ratios ranging from 21 to 450. Moreover, subsequent elimination of radioactivity from the liver was nearly linear with respect to alkyl chain length. Analogs with longer alkyl chain length were eliminated from the liver more rapidly than their shorter chain counterparts. Because of their biochemical similarities to naturally occurring triglycerides, these novel analogs may prove useful not only for high-resolution anatomic imaging of focal liver lesions, but also for evaluating a variety of diffuse diseases known to affect hepatic function and biochemistry.

Summary. Mitotane is an important adrenalytic drug for the treatment of adrenal cancer whose use is limited by toxicity. Reports from another laboratory indicated that a methylated homolog of Mitotane (Mitometh) tested in guinea pigs possessed comparable adrenalytic activity but was less toxic than Mitotane. This observation prompted us to undertake a comparative study of these two drugs on the basis that Mitometh may be a superior agent for the treatment of adrenal cancer. Preliminary studies in guinea pigs failed to show a significant adrenalytic effect for either Mitotane or Mitometh. Thus, we extended the study to 13 mongrel dogs weighing 12-15 kg that were treated daily with Mitometh or Mitotane (50-100 mg/kg) for 6 or 12 days. Cortisol decreased to undetectable levels and adrenocorticotropic hormone (ACTH) rose to 10 times the baseline levels within 72 h in Mitotane-treated animals. Despite the achievement of similar drug levels, Mitometh treatment in dogs failed to suppress cortisol or increase ACTH. To determine whether these differences were due to differences in bioavailability, we measured the relative concentration of Mitotane and Mitometh in homogenates of adrenal cortex obtained from Mitotane- and Mitomethtreated dogs. The adrenal concentration of Mitometh determined in Mitometh--treated dogs was 5 times higher than the concentration of Mitotane measured in Mitotanetreated animals. Whereas the adrenal glands of Mitotanetreated dogs showed hemorrhage and necrosis, the Mitometh-treated animals showed no adrenal damage. Despite the lack of adrenalytic activity, Mitometh maintained its toxicity as demonstrated by microscopic evidence of hepatic necrosis and an increase in hepatic enzymes. The adrenalytic effects of both agents was also studied in vitro using a human functioning adrenal cortical carcinoma cell line, NCI-H295. Whereas Mitotane strongly suppressed cell growth, Mitometh had a weaker effect. We conclude that Mitometh is not likely to be effective in the therapy of adrenal cancer. Moreover, the results of this study are supportive of the view that metabolic transformation of Mitotane is in some way linked to its adrenalytic action.

Two different methods were evaluated for incorporating [125I]cholesteryl iopanoate ([125I]CI), a non-hydrolyzable cholesteryl ester analog, into LDL. The first procedure was an organic solvent delipidation-reconstitution procedure (R[125I-CI]LDL) while the second involved incubation of detergent (Tween-20)-solubilized [125I]CI with whole plasma (D[125I-CI]LDL). R[125I-CI]LDL behaved similar to native LDL in vitro, but was markedly different in vivo, apparently due to a heterogeneity in particle size. D[125I-CI]LDL, however, was metabolized normally both in vitro and in vivo. These results, combined with the residualizing nature of [125I]CI, demonstrate that D[125I-CI]LDL is appropriate for tracing LDL uptake in vivo.

Novel iodinated and radioiodinated 1,2-diacylglycerol analogues are biological reagents for studying the effect of diacylglycerols in the activation of protein kinase C. This calcium-requiring enzyme may be involved in tumor promotion by phorbol diesters and related compounds. Iodinated and radioiodinated 1,2-diacylglycerol analogues, in accordance with the invention, are useful as imaging agents, such as radiopaques and radiopharmaceuticals, and have the general formula: ##STR1## The triglycerol backbone structure is 1,2-disubstituted with one position being occupied by an iodine-containing substituent, preferably an amino-substituted-2,4,6-triiodophenyl aliphatic chain, such as iopanoic acid, or by a monoiodiphenyl aliphatic chain, such as (m-iodophenyl)propanoic acid. The other position may be substituted with saturated and unsaturated long and short aliphatic chains.

Iodinated clonidine derivatives useful, inter alia, as a probe for identification and characterization of α2 -adrenergic receptor sites and as tracers for imaging techniques such as positron emission tomography or computer assisted tomography. Binding competition studies have indicated that p-iodoclonidine, for example, is a particularly efficacious binder for α2 -adrenergic sites.

Novel radioiodinated analogues of naturally-occurring cholestrol esters, arylaliphatic cholesteryl ethers, are selective for low density lipoproteins and have been shown to be successful imaging agents for adrenal glands. The arylaliphatic cholesteryl ethers have the general formula: ##STR1## where X is a radioactive isotope of iodine and n is an integer between 1 and 20. Two illustrative examples, m-iodobenzyl cholesteryl ether and 12-(m-iodophenyl) dodecyl cholesteryl ether, were radiolabeled with 125 I by an isotope exchange reaction. Tissue distribution studies indicate significant accumulation of the cholesteryl ethers in the adrenal glands, and to a lesser extent in the liver. The cholesteryl ethers selectively incorporate into plasma lipoproteins as determined by polyacrylamide gel electrophoresis.

Radioiodinated benzoyl esters and amides of epimeric 20-hydroxy- and 20-aminopregn-5-en-3 beta-ols were synthesized in an effort to find an agent that would be rapidly and selectively taken up by adrenal cortical tissue. Achievement of such a goal would provide a basis for the development of adrenal imaging agents superior to those currently available for clinical use. The iodobenzoyl derivatives were obtained by treating the appropriate epimer with 2-iodobenzoic acid in the presence of dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine. The resulting esters and amides were readily labeled with radioiodine by isotope exchange with sodium iodide-125 in pivalic acid. Tissue distribution studies in female rats revealed that only the esters displayed appreciable adrenal specificity, and the ester having the same configuration at C-20 as cholesterol was significantly better than the corresponding C-20 epimer.

A number of A or B ring modified 20- and 22-azacholesterol analogues (1 and 2, respectively) were synthesized in an attempt to ascertain the structural requirements for inhibition of the cholesterol side-chain cleavage reaction in bovine adrenocortical mitochondrial acetone powder preparations. The inhibition studies of these analogues revealed that (1) the 3-methyl ethers were as active as the parent compounds and that (2) reduction of the delta 5 double bond greatly lessened the inhibitory activity. These studies demonstrated a crucial role of the delta 5 double bond for inhibitory activity, while a free hydroxyl group at C-3 is not essential for this action. Furthermore, as in the parent compounds, 22-azacholesterol analogues were more potent than their 20-azacholesterol counterparts.

A series of cholesteryl phenylalkanoic esters was synthesized in which the acyl moiety served as the carrier for radioiodine. Tissue distribution studies in rats revealed that several of these radioiodinated esters selectively accumulated in steroid-secreting tissues, such as the adrenal cortex and ovary. Furthermore, this selective uptake was shown to correlate with the stability of these esters to in vivo hydrolysis. An unexpected finding was the unusually high propensity of some of these esters to localize in the ovary and thus afford a possible approach to ovarian imaging agents.

A variety of benzoic and aryl aliphatic mono and polyiodinated acids and esters (sterol, triglyceride) were radioiodinated in 55–99% radiochemical yield by isotope exchange with Na 125I in a melt of pivalic acid. In general, the reaction was complete in 1 h at 155°C with little or no substrate decompostion. High specific activity studies afforded 125I-labeled iopanoic acid with a specific activity of over 700 Ci/mmol.

Radioiodinated cholesteryl iopanoate, a nonhydrolyzable cholesteryl ester probe, showed increased uptake into atherosclerotic aortas of cholesterol-fed rabbits in comparison with normal rabbits. Auto-radiography of the aortas showed the radioactivity to be concentrated in areas of visible atherosclerotic involvement. Lipid extraction and thin-layer chromatography of this tissue as well as liver, adrenal, and plasma confirmed the resistance of this probe to hydrolysis. These findings suggest that 125I-cholesteryl iopanoate may prove useful for noninvasively monitoring atherosclerosis in intact laboratory animals.

Several groups have examined the possible use of radioiodinated cholesterol esters to achieve selective uptake of radioactivity in the adrenal cortex and have obtained variable results. This study indicates that the tissue distribution profile varies not only with the type of ester, but also with the vehicle employed for administration. Radioiodinated 19-iodocholesteryl (125-IC), iodocholesteryl palmitate (125-ICP)and iodocholesteryl oleate (125-ICO) were dissolved in either tween vehicle (saline containing 1.6% tween 80 and 10% ethanol) or myristate vehicle (isopropyl myristate-ethanol, 1:5 v/v) and administered i.v. to rats. Irrespective of the agent, considerably more radioactivity appeared in the target organs when the tween vehicle was employed. When the myristate vehicle was used, higher levels of radioactivity appeared in the lung. This finding suggests precipitation of the agents from the myristate vehicle occurred upon administration. In the tween vehicle, 125-ICO showed almost three times greater predilection for adrenal cortex than 125-ICP with levels of activity approaching those seen for 125-IC. Adrenal activity and adrenal to non-target ratios were sufficient for visualization of the adrenals at 5 days after injection of 125-ICO in the tween vehicle. Lipid extraction and TLC analysis of tissue radioactivity revealed that radioactivity in the adrenal and ovary was predominantly in an esterified form. Further analysis of the esters present after injection of 125-ICP showed these to be a mixture of mono and polyunsaturated esters. The site of hydrolysis and subsequent reesterification is an interesting biochemical aspect that remains to be elucidated.

Acylated derivatives of 17 alpha-hydroxyprogesterone were prepared in order to test the hypothesis that dialkylamino alkyl moieties have the effect of transforming progestogens into antiprogestogens. This approach has been successful with certain estrogens. Compounds with other functional groups were synthesized to determine whether these might exert binding influence outside the area occupied by progesterone itself. The compounds were tested for competitive affinity against tritiated progesterone and receptor from rabbit uterus cytosol. The low affinity of all derivatives makes it unlikely that they would be active as antiprogestational agents.The synthesis of potential antiprogestogens is described. Acylated derivatives of 17alpha-hydroxyprogesterone were prepared to test the hyp othesis that dialkylamino alkyl moieties have the effect of transforming progestogens into antiprogestogens. Compounds with other functional groups were synthesized to determine if they might exert binding influence outside the area occupied by progesterone itself. Each compound was tested for competitive affinity against tritiated progester one and receptor from rabbit uterus cytosol. All the derivatives showed low affinity which makes it unlikely that they would be active antiprogestational agents.

Antibody used in a steroid radioimmunoassay raised against a steroid hapten-carrier protein conjugate may recognize both the hapten and the chemical bridge to the protein. Use of the same bridge in the radioisotopic label may lead to higher affinity binding to the label than to the native steroid. Inhibition curves under these conditions are shallow and generally not acceptable for radioimmunoassay procedures. We have developed a radioimmunoassay for androstenedione that employs different bridges at the 11β position of the steroid for the protein conjugate and label. The resulting assay has greatly reduced bridge-binding, has an acceptable slope for the standard curve and is very specific as evidenced by low crossreactivies to other steroids.

A series of glyceryl 1,3-bis- and 1,2,3-tris[omega-(3-amino-2,4,6-triiodophenyl)alkanoates] were synthesized, radioiodinated with iodine-125, and evaluated for their ability to selectively localize in the liver for potential use as hepatographic imaging agents. Of the nine target compounds synthesized and evaluated in rats, glyceryl 1,2,3-tris[3-(3-amino-2,4,6-triiodophenyl)propionate] (5b) displayed rapid and sustained liver specificity. This agent was found to accumulate in the liver in concentrations of 60, 75, and 86% of the administered dose at 5 min, 30 min, and 24 h, respectively. Moreover, the 24-h liver-to-blood ratio of 235 justifies further studies in higher animal species.

The chemistry of DDT and DDD derivatives was explored by studying the steric and electronic effects on the hydrolysis of a variety of substituted diphenylacetaldehyde ethylene glycol cyclic acetals. This investigation demonstrated that ortho substituents, p-nitro, and p-methoxy groups affect the product distribution in different ways. The mechanistic details of this work are discussed.

The relationship between molecular structure and the binding potential of steroids to receptor proteins was investigated. Twenty-four selected steroids were studied in minced incubations of rat pro state tissue. Measurements of the inhibitory effects of the steroids on tbe binding of tritiated 5 α-dihydrotestosterone to the receptor proteins were obtained in the 100,000 × g dialysed supernatant and the purified nuclear component of the prostate cells. The steroids that achieved the highest degree of inhibition were those compounds that exhibited a generally planar geometric shape and were known to possess potent androgenic activity.Several of the compounds were shown to possess a higher degree of inhibition than that of testosterone or 5α-dihydrotestosterone. The data is further supportive of the two step theory that necessitates the complexing of the free steroids to the receptor proteins in the cytosol before transport to the nuclei. Evidence is also suggestive of the presence of 17-esterase activity. The inhibitory effect of the steroids apparently involves the binding, to the intracellular receptors and is not related to the uptake of 5α-dihydrotestosterone into the cell.

A series of omega-(3-amino-2,4,6-triiodophenyl)alkanoic acids and the corresponding 1,3-dipalmitoylglycerol 2-[omega-(3-amino-2,4,6-triiodophenyl)alkanoates] were synthesized, radioiodinated with iodine-125, and evaluated for their ability to selectively localize in the liver for potential use as hepatographic imaging agents. Acid analogues 1d and 1e afforded relatively high levels of radioactivity in the liver (45 and 49% injected dose) 5 min after intravenous administration to rats. These acids displayed a marked propensity to become bound to plasma albumin. In contrast, triacylglycerol analogues 10a and 10c did not become immediately associated with plasma albumin but instead rapidly became associated with plasma lipoproteins and showed a different tissue distribution profile than free acids 1a and 1c. Although long-chain triacylglycerol analogues 10d and 10e exhibited some capacity to accumulate in the liver at 5 and 30 min, respectively, analysis of the plasma revealed significant in vivo ester hydrolysis. It would thus appear that liver radioactivity following administration of 10d and 10e was due to uptake of the free acid and not the intact triacylglycerol. Triacylglycerol analogues 10a and 10c, on the other hand, were taken up intact and showed liver accumulations of 25 and 35% of the administered dose at 30 min.

Steroid radioimmunoassays (RIA) employ antibodies raised against a carrier protein-steroid conjugate. Individual antibodies may recognize the steroid, the protein or the chemical bridge used to Join them together. Use of the same bridge In the tracer results in higher affinity binding of the tracer than the native ligand which in turn results in a loss of sensitivity and precision. We have greatly reduced bridge-binding In a RIA for androstenedione. Conjugates and radioiodinated labels were prepared with either an ester op ether chemical bridge. By using an antibody and the corresponding label with the heterologous bridge very sensitive assays were obtained.

in the Rat. POHLAND, R. C., AND COUNSELL, R. E. (1985). Toxicol. Appl. Pharmacol. 77, 4757. Two radioiodinated probes, ‘%cholesteryl oleate (‘251-CO), a derivative of a natural constituent of lipoproteins, and l-(2-chlorophenyl)-1-(4[‘25I]iodopheny1>2,2-dichloroethane (‘%DDD), an analog of the adrenolytic drug o,p’-DDD (mitotane), were selected to study the role of lipoproteins in drug disposition and to examine the ability of these vehicles to direct foreign molecules to specific tissues. In vivo and in vitro techniques were utilized to associate these probes with rat high density lipoproteins (HDL). Tissue distribution studies indicated that prior incorporation of ‘*%CO into rat HDL increased the uptake of ‘251-C0 by rat adrenal, which was dramatically enhanced when this preparation was administered to animals made hypolipidemic with 4-aminopyrazolo-(3,4)-pyrimidine (CAPP). Acetylation of HDL labeled with ‘2sI-C0 provided evidence that the observed uptake into the adrenal was via a receptormediated process. In contrast with these results, prior association of ‘*‘I-DDD with rat HDL failed to alter the ability of this compound to accumulate in adrenal tissue of normal or hypolipidemic animals. Polyacrylamide gel electrophoresis (PAGE) was utilized to examine the stability of the association of ‘%CO and ‘*‘I-DDD with rat HDL. These results suggested that ‘251-C0 was associated with the lipophilic core of HDL, whereas ‘*‘I-DDD appeared to be partially associated with the suface components of HDL. Saturation of surface components with stable o,p’-DDD offered data to suggest that this binding to apoproteins may disrupt the normal receptor-mediated uptake process. These studies indicate that lipoproteins may effect the distribution and tissue uptake of lipophilic compounds and, conversely, lipophilic molecules can effect the metabolic fate of lipoproteins. The overall result is dependent upon the nature of the association of these lipophilic compounds with lipoproteins which is difficult to predict on the basis of molecular structure alone.

In an effort to visualize whole body cholesteryl ester (CE) deposition using the nuclear medicine imaging technique of gamma camera scintigraphy, 125I-cholesteryl iopanoate (125I-CI), a nonhydrolyzable CE analogue, was used as a marker for CE deposition in atherosclerotic New Zealand white rabbits. Groups of animals were fed either a cholesterol-enriched diet (2%, w/w) or the same diet supplemented with the hypolipidemic drugs colestipol (1%, w/w) and/or clofibrate (0.3%, w/w). Injections of 125I-CI were administered biweekly. At the end of 15 weeks, animals were scintigraphically scanned and sacrificed for tissue analysis. The results demonstrated that while drug treatment had no significant effect on plasma lipid levels, it substantially lessened atherosclerotic involvement in the thoracic-abdominal aorta. These differences in aortic lipid accumulation were reflected in the whole-body scans which showed a reduction in tissue accumulation of 125I-CI in the drug-treated groups. Gamma camera scintigraphy thus represents a rapid means of visualizing tissue CE accumulation which could facilitate the evaluation of lipid-lowering drug efficacy and possible antiatherosclerotic effect.

A series of metyrapone analogues was synthesized for study as inhibitors of steroid 11beta-hydroxylase. Racemic mixtures of the new compounds were evaluated in vitro. Preliminary results revealed several analogues to be effective inhibitors of deoxycorticosterone hydroxylation. 2-(3-pyridyl)propiophenone (13) and alpha,beta-diphenyl-3-pyridineethanol (16) were the most active new compounds. Each was 65% as potent as metyrapone; 3-Pyridyl alpha-3-pyridylbenzyl ketone (3), 2-phenyl-2-(3-pyridyl)acetophenone (4), alpha-(diphenylmethyl)-3-pyridinemethanol (17), and 1,2-di-3-pyridyl-1-propanol (26) were 52, 32, 25, and 41% as inhibitory as metyrapone, respectively. Diphenylmethyl 3-pyridyl ketone (5), benzyl 3-pyridyl ketone (10), 2-(3-pyridyl)acetophenone (12), 2-phenyl-1-(3-pyridyl)-1-propanone (11), alpha,beta-di-3-pyridylphenethyl alcohol (15), and 1,2-di-3-pyridylethanol (27) had less than 25% the activity of metyrapone. All compounds displaying a metyrapone-like inhibition contained appropriately substituted alcoholic or ketonic functions. A phenyl or methyl group alpha to the carbon bearing the oxygen was necessary for appreciable activity. A 3-phridyl group alpha to the carbonyl carbon could be replaced by a phenyl group. For optimal activity, however, the other 3-pyridyl group of metyrapone could not be exchanged for a phenyl group.

Cholesteryl iopanoate, the prototype for a new class of lipid-soluble, site-specific contrast agents, has undergone preliminary evaluation for organic-specific uptake. This report describes the tissue distribution profile of this radioiodinated sterol ester in the rabbit as a function of time following intravenous injection of tracer doses. Selective accumulation of this agent in the liver and adrenal was observed relative to blood and other tissues. Maximum contrast concentration was achieved between 24 and 48 hours postinjection. Analysis of lipid extra of liver, adrenal, and plasma indicated that the compound was relatively resistant to hydrolysis and dehalogenation. The hepatic selectivity and retention of cholesteryl iopanoate support further study of this or related agents for site-specific, contrast-enhanced computed tomography.