New multimeric magnetic resonance imaging agents.

RATIONALE AND OBJECTIVES: The authors investigated the effect of multimerization on the relaxivity of macrocyclic gadolinium (Gd) chelates. The objective was to develop more sensitive magnetic resonance imaging (MRI) contrast agents to study biochemical processes. METHODS: Covalently linked nonionic, macrocyclic, multimeric lanthanide chelates that belong to the classes of dimers, trimers, tetramers, hexamer, and octamer, in the molecular weight range approximately 1 to 5 KDa, were synthesized. The chemical linkage was based on either the amide bond or the 2-hydroxypropylidene bond. Relaxivity values, 20r1, on Gd3+ chelates and hydration numbers, Q, on Tb3+ chelates were determined. RESULTS: Relaxivity values increased with molecular weight and Q values were not affected, the increase in r1 in attributable to the expected increase in the overall rotational correlation time, tau r with an increase in molecular weight. The rigidity of the linkers, which is expected to affect the intrachelate rotational correlation time tau r* that makes a contribution to the overall correlation time, tau r, exerted a noticeable effect. The hydroxyl-based chelates generally had lower r1 values than the amide-based chelates. This is rationalized as arising from the longer and thereby rate-limiting effect of the tau m value for the hydroxyl chelates compared with that reported of the amide-based chelates. This rate limiting effect of tau m becomes a dominant factor controlling attainable enhanced relaxivity when multimers based on traditional chelate designs are used for MRI applications. CONCLUSIONS: Approaches aimed at enhancing relaxivity by modulating the water relaxation time, tau m, will be important for the future development of functional MRI contrast agents for the imaging of biochemical processes.

Radiotoxicity of 17 alpha-[125I]iodovinyl-11 beta-methoxyestradiol in MCF-7 human breast cancer cells.

Therapeutic strategies for human breast cancer using 125I-labeled steroid hormones are clinically attractive in light of the estrogen dependence of many human breast cancers and the favorable microdosimetry resulting from 125I decay. We determined the uptake specific estrogen receptor binding and radiotoxicity of 17 alpha-[125I]iodovinyl-11 beta-methoxyestradiol (125IVME2) in vitro using cultured MCF-7 human breast carcinoma cells. 125IVME2 rapidly enters MCF-7 cells and reaches a plateau in the presence of competing 10(-7) M 17 beta-estradiol. In the absence of competitor, uptake is substantially greater before reaching a plateau. Efflux of 125IVME2 from cells incubated in the absence of estradiol decreases to levels corresponding to specific binding. Under equilibrium conditions and in the absence of competitor, 125IVME2 binds to both specific and nonspecific sites but, in the presence of excess 17 beta-estradiol, the observed binding is nonspecific. 125IVME2 is cytotoxic to exponentially growing MCF-7 cells and produces a survival curve typical of those observed for [125I]iododeoxyuridine and 16 alpha-[125I]iodoestradiol.

Microscopic analysis of arterial microsphere distribution in rabbit liver and hepatic VX2 tumor.

Microspheres conjugated to radioisotopes and chemotherapeutic agents are playing an important investigative and clinical role in the management of metastatic neoplasms. The purpose of our investigation was to histologically assess the basis for regional intra-arterial microsphere therapy, by comparing the spatial distribution of microspheres in the tumor and liver of experimental models of hepatic metastases. Three New Zealand white rabbits with hepatic VX2 tumor implants were arterially injected with hepatic doses of either 15 or 30 million blue-dyed, polystyrene microspheres (27 microns-diameter). Microscopic examination of random liver and tumor samples revealed that 6-12 times as many microspheres were embolized within tumor than in normal liver (p less than 0.002). The majority of microspheres aggregated into clusters of various size within liver and tumor vasculature, though analysis of cluster sizes illustrated an exponentially skewed distribution toward isolated microspheres. Approximately eight times as many clusters were observed in tumor than in liver (p less than 0.008). Finally, a morphometric analysis was used to quantitate the minimal distances separating microsphere clusters, the intercluster distance (ICD). Analysis of over three thousand intercluster measurements revealed a median ICD approximately five times lower in tumor than in liver (p less than 1 x 10(-8)). This microquantitative analysis provides a fundamental description of how regional intra-arterial microsphere therapy allows the targeted delivery of microspheres to neoplastic tissue, to potentially improve the therapeutic index in the treatment of hepatic metastases.

[125I]iodotamoxifen cytotoxicity in cultured human (MCF-7) breast cancer cells.

We evaluated the uptake and radiotoxicity of [125I]iodotamoxifen (125ITAM) in MCF-7 human breast cancer cells in the presence or absence of excess non-radioactive estradiol (E2) or iodotamoxifen (ITAM). Studies in cells under wash-out conditions and in nuclei isolated from previously exposed cells showed that 125ITAM binds estrogen receptor (ER) and antiestrogen binding sites (AEBS) and has the capacity for considerable non-specific binding. The radiotoxicity of 125ITAM was a complex function related to ER content and/or function as well as interactions with ER, AEBS and non-specific binding. Addition of E2 or ITAM abolished ER mediated cell killing. ITAM but not E2 abolished AEBS mediated cytotoxicity. Non-specific binding accounted for considerable cytotoxicity. Although these studies confirm the radiotoxicity of nuclear bound 125I, multiple nuclear binding sites, variability in ER content and function and non-specific binding will all adversely influence ultimate clinical efficacy.

Cytotoxicity of receptor-mediated 16 alpha-[125I]iodoestradiol in cultured MCF-7 human breast cancer cells.

Therapeutic strategies using 125I-labeled steroid hormones are attractive in light of the estrogen dependence of many human breast cancers and the favorable microdosimetry resulting from 125I decay. We determined the uptake, specific estrogen receptor (ER) binding, and cytotoxicity of 16 alpha-[125I]iodoestradiol in cultured MCF-7 human breast cancer cells. The cytotoxicity of receptor-mediated 125I appears to be sufficient in MCF-7 cells to warrant in vivo experimentation. Furthermore, cytotoxicity not specific to ERs is minimal within the dose range necessary for ER saturation and specific cell killing. Competitive toxicity studies using nonradioactive 17 beta-estradiol demonstrate an unequivocal relationship between ER binding and clonogenic viability.

Origin and cytotoxic properties of base propenals derived from DNA.

Base propenals arise from DNA by a Fe(II)-bleomycin-mediated reaction which leads to strand scission. These compounds undergo addition-elimination reactions with thiols and other nucleophilic groups under physiological conditions and form an addition product with glutathione. Thymine- and adenine-N1-propenals inhibit DNA synthesis in HeLa cells; both compounds are cytotoxic [50% inhibiting concentration (IC50) = 1 to 2 microM]. A structurally related nucleoside, thymidine-N3-propenal, designed as a metabolic pathway inhibitor, inhibits growth of HeLa, L1210 leukemia, Lewis lung carcinoma, B16 melanoma, and DLD-1 human colon carcinoma cells in culture (IC50 = 1 to 6 microM). A single injection of this compound, administered on the first day following transplant of L1210 leukemia cells, increased the mean survival time of mice by 50% (T/C = 154). Thymidine-N3-propenal selectively blocks DNA synthesis in HeLa cells and inhibits thymidine kinase (Ki = 5.1 microM) and DNA polymerase-alpha. We suggest that base propenals, rather than damaged DNA, account for some of the cytotoxic effects of bleomycin and that nucleoside propenals represent a novel class of site-directed inhibitors.

Steroids. 2. Synthesis of C-18 functionalized steroids via the Smith-Hughes route.

The total synthesis of a series of racemic C-18 functionalized steroids was carried out in a search for novel estrogen-and/or progestin-receptor agonists or antagonists. The target compound 3,18-dihydroxyestra-1,3,5(10)-triene (2), 13-(2-oxopropyl)gona-4-en-3-one (3), 13-(1-hydroxy-1-prop-2-ynyl)gona-4-en-3-one (4a and 4b) and 13-(1-acetoxy-2-oxo-1-propyl)gona-4-en-3-one (5) are position isomers of the highly biologically active estradiol, progesterone, norethindrone, and 17-acetoxyprogesterone, respectively. Nevertheless the synthetic C-18 functionalized steroids 3-5 showed little activity in the Clauberg and anti-Clauberg assays. Compound 2 showed no antagonism in the postcoital assay despite the fact that it exhibited weak but measurable in vitro receptor-binding activity.

Synthesis and biological activity of a new class of cytotoxic agents: N-(3-oxoprop-1-enyl)-substituted pyrimidines and purines.

The 1-(3-oxoprop-1-enyl) derivatives of thymine and cytosine and the corresponding 9-substituted derivatives of adenine and guanine (products of degradation of DNA by bleomycin, Fe2+, and O2) have been synthesized and tested for biological activity. The thymine and adenine compounds are highly cytotoxic to a variety of tumor cell lines and inhibit macromolecular synthesis in cultured HeLa cells. Structure-activity studies, based primarily on the pyrimidine derivatives, reveal that the most potent inhibition occurs when the propenal group is located on the 3-nitrogen of a 2'-deoxyribonucleoside. The 3-(3-oxoprop-1-enyl) derivatives of thymidine, 2'-deoxyuridine, and 5-iodo-2'-deoxyuridine powerfully and selectively inhibit incorporation of thymidine into DNA at concentrations (IC50 approximately equal to 0.5 microM) comparable to those observed with idoxuridine. Active compounds in this series react readily with nucleophiles containing primary amino and sulfhydryl groups. The results of this study provide a basis for the development of a new class of cytotoxic agents.

Radiographic quality, tube potential, and patient dose.

Measurements were made to determine if there was an optimal kVp that would maximize radiographic contrast for various materials while minimizing average patient dose. Radiographs were made of a 17-cm-thick plexiglass phantom (to simulate a typical abdomen) with added regions of plexiglass, hydroxyapatite, and iodine with peak kilovoltages from 40 to 150 kVp and 2 mm A1 added filtration. Radiographs were also made of a 4-cm-thick plexiglass phantom to simulate a typical breast, with added regions of plexiglass, hydroxyapatite, and fat at a peak kilovoltage from 35 to 100 kVp and with 1 mm added filtration. For the thicker phantom it was found that the contrast per average absorbed dose for the added plexiglass, hydroxyapatite, and iodine increased by about 3, 2, and 0.4, respectively, when going from 50 to 150 kVp. Contrast was measured relative to a reference region on the phantom. Similar data for the thinner phantom showed an increase of about 35% in contrast per average absorbed dose for plexiglass and fat but a decrease by about 30% for hydroxyapatite as the kVp changes from 35 to 100 kVp.

Communicating through satisfied adopters of female sterilization.

Communication patterns between 127 satisfied adopters of female sterilization (agents) and 257 potential adopters of family planning (recipients) were examined in this study conducted in a rural community in southern India. The influence of satisfied adopters relative to other family planning communication agents was evaluated. Satisfied adopters were identified as the most important source of family planning information by 55 percent of agents and 74 percent of recipients. Communication usually occurred between persons of similar caste, occupation, education, and income.