Migration of electrons and holes in crystalline d(CGATCG)-anthracycline complexes X-irradiated at 4 K.

Electrons and holes generated in irradiated DNA migrate to stable trapping sites. Protonation and deprotonation reactions at these sites promote the trapping of electrons and holes, thereby inhibiting further migration. The extent of migration determines the final distribution of damage in irradiated DNA. In this study, electron and hole migration is investigated in a crystalline DNA hexamer intercalated with an anthracycline drug. The intercalator is no further than 2 base pairs away from any DNA base. From EPR measurements, there is no evidence of DNA-centered radicals in the irradiated DNA hexamer. The aromatic region of the anthracycline intercalator evidently sequesters most or all of the electrons and most of the holes. Further hole trapping and radical stabilization appear to occur on the anthracycline's amino sugar group, which is nestled in the minor groove of the hexamer. The relatively large yield of this proposed amino sugar radical suggests that holes generated in the DNA solvation shell migrate to the amino sugar, where they become trapped. This would be the first observation of a radical formed by the direct effect of low-dose, low-LET radiation that is trapped within the DNA helix, yet lies outside of the stacked bases. With respect to holes generated in the DNA bases at 4 K, we conclude that most, if not all, are capable of migrating to an intercalator < or = 2 base pairs away. With respect to dry electrons, we conclude that anthracycline competes effectively for electron trapping over a region of at least 2 base pairs; our experiments cannot distinguish between electron attachment to the bases followed by transfer to the intercalator and direct attachment to the intercalator.

[Mutagenic activity in urine from smokers detected by sister chromatid exchange (SCE) of peripheral lymphocytes].

Mutagenic activity in urine from smokers was detected by SCE. Human peripheral lymphocytes were treated with 50 microliters urine (contain 0.1 mg creatinine) from 63 smokers and 34 non-smokers for SCE analysis. The results showed that there was significantly higher SCE frequencies (7.82 +/- 1.12/cell) of lymphocytes treated with urine of smokers as compared with those of non-smokers (6.49 +/- 1.12/cell) (P less than 0.001). However, the mutagenicity in urine of smokers who smoked 20 cigarettes/day was similar to those of smokers on 10 cigarettes/day. Intake of mutagens from food might be responsible for the low level mutagens in urine of some non-smokers. This test may provide a sensitive, economical bioassay for evaluating cancer risk in smokers.

[Effect of beta-carotene on sister chromatid exchanges induced by MNNG and aflatoxin B1 in V79 cells].

In order to elucidate the mechanism of tumor prevention of beta-carotene, its effect on sister chromatid exchanges (SCE) induced by MNNG in cultured V79 cells, under condition free of the enzyme system to convert beta-carotene into vitamin A, was studied. It was found that SCE level was significantly increased by high doses beta-carotene (10(-5)-10(-4) M) and the enhancement of SCE was restored to its original level by addition of alpha-tocopherol (final concentration 2 micrograms/ml). This may be due to the latter inhibiting the oxidation of beta-carotene and reducing the amount of oxidated carotene, which is toxic for cultured cells. Combination of beta-carotene and alpha-tocopherol at low doses inhibited SCE induced by MNNG (P less than 0.05) but no protective activity was observed when used separately. It was also found that beta-carotene (2 x 10(-7) M) and retinol (16 micrograms/ml) inhibited SCE induced by aflatoxin B1, which is activated by S-9 mixture. The present data clearly show that the antitumor activity of beta-carotene may be attributed to both itself and its degraded compound vitamin A, and may take part in the initiation of carcinogenesis. Combination of beta-carotene and other cancer preventive drugs is more effective and safer than it used individually.

[Sister chromatid exchanges (SCE), chromosomal aberrations and micronuclei of cultured peripheral lymphocytes in patients with lung cancer, miners and non-mining workers of the tin mine in Yunnan].

Determination of SCE frequency, chromosomal aberration and micronucleus rate of cultured peripheral lymphocytes in 32 patients with lung cancer, 33 miners and 40 non-mining workers in Yunnan Tin Mine was carried out. The results showed that the cancer patients had higher SCE incidence, chromosomal aberration and micronucleus rate, the non-mining workers had the least and miners on an intermediate level. There was a significant difference of SCE, chromosomal aberrations and micronucleus rate between patients and non-mining workers (P less than 0.05-0.01). We also found that miners had a significant higher SCE and chromosomal aberration rate but not micronucleus rate as compared with the non-mining workers. We proposed that some carcinogens present in the Yunnan Tin Mine be responsible for the genetic damages in the miners. Chemical drugs may be considered to contribute to the genetic damage in cancer patients who had a tendency toward an increased SCE, chromosomal aberration and micronucleus rate as compared to the miners, though without reaching a statistical significance. We suggested that combination assay of SCE with chromosomal aberration or micronucleus be an useful index for screening of the high risk population and monitoring the chemical drug prevention of lung cancers in Yunnan Tin Mine.

[Effect of sodium selenite on the chromosomal aberration of V 79 cells induced in vitro by MNNG and MNU].

Effect of sodium selenite on chromosomal aberration of V 79 cells induced by MNNG and MNU was studied. Na2SeO3 alone, at the concentration of 10(-7)-10(-4) M, increased the incidence of chromosomal aberration. However, Na2SeO3 at 10(-7)-10(-5) M, having been preincubated with the cells for 4 hours, could reduce the number of cells with chromosomal aberration induced by MNNG. Na2SeO3 at 10(-7)-10(-4) M inhibited mutagenic activity of chromosomal aberration induced by MNU. The same inhibition was observed even sodium selenite was added to the medium simultaneously with this carcinogen. The results indicate that sodium selenite alone, at the concentration range used in this experiment, is an aberration-inducing agent. But when combined with the carcinogen, anti-cancer effect is obtained.

Origin of a Meloidogyne incognita Surface Coat Antigen.

The surface coat (SC) of plant nematodes is thought to originate either from the living hypodermis or from secretory glands associated with the excretory system or nervous system. In this study, we investigated the origin of the SC of Meloidogyne incognita by immunolocalization with a monoclonal antibody raised against the surface coat of the preparasitic juveniles (J2). Under the electron microscope, strong labeling was found on the cuticular surface and in the rectal dilation of the J2, while labeling was absent in other parts of the nematode, including the hypodermis, excretory system, nervous system, and digestive system. Because the rectal glands are known to be the origin of the gelatinous egg matrix produced by adult females of Meloidogyne, we also examined sections of mature females from monoxenic cultures of Arabidopsis thaliana. Labeling of the female occurred in the rectal glands and in the gelatinous matrix exuded from the anus. At the ultrastructural level, gold particles were mainly deposited in multivesicular bodies that appeared to be associated with the Golgi bodies of the rectal glands. Our results suggest that at least one component of the J2 SC originates from the rectal gland cells and that the SC of the J2 shares common epitopes with the gelatinous egg matrix of mature females.

[Investigation of protective effect of selenium on genetic materials among workers exposed to arsenic].

An increased chromosomal aberration and micronuclei rate of cultured lymphocytes among smelter workers in Yunnan Tin Corporation has been associated with exposure to arsenic which might be involved in carcinogenesis of lung cancer in this area. Selenium, as an essential trace element for life, antagonizes the toxic effects of arsenic. The low intake of selenium among workers in this area might increase injurious effects of arsenic in the tissues. The preliminary results showed that the chromosomal aberration rate of cultured lymphocytes in smelter workers was lowered about 46.1% after treatment with selenium 150 micrograms/d for 21 days. It will provide clues for further study on the elimination of toxicity of arsenic among workers who are exposed to arsenic by supplementation of selenium.

[A sensitive, simple and economical bioassay for detecting mutagenicity in human urine by determination of SCE frequency in cultured peripheral lymphocytes].

A bioassay was established for detecting mutagenicity in human urine by determination of SCE frequency in cultured human peripheral lymphocytes. The results showed that the SCE frequencies induced by the urine of smokers were significantly higher than those of nonsmokers (P less than 0.01), while SCE frequencies induced by the urine of 20 cancer patients after chemotherapy (19.44/cell) were much higher than those before treatment (9.92/cell, P less than 0.001). Also, higher SCE frequencies were found in all cancer cases after chemotherapy. The authors suggest that this is a more sensitive, reliable, simple, economical and practical assay for detecting mutagenicity of human urine.

The B-DNA dodecamer at high resolution reveals a spine of water on sodium.

We describe a very accurate addition (called structure X here) to the B-DNA dodecamer family of X-ray structures. Our results confirm the observation of Drew and Dickerson [(1981) J. Mol. Biol. 151, 535-556] that the spine of hydration in AT tract DNA is two layers deep. However, our results suggest that the primary spine is partially occupied by sodium ions. We suggest that many sequence-dependent features of DNA conformation are mediated by site specific binding of cations. For example, preferential localization of cations, as described here within the minor groove of structure X, is probably the structural origin of AT tract bending and groove narrowing. The secondary spine, which does not interact directly with the DNA, is as geometrically regular as the primary spine, providing a model for transmission of sequence information into solvent regions. A fully hydrated magnesium ion located in the major groove of structure X appears to pull cytosine bases partially out from the helical stack, exposing pi-systems to partial positive charges of the magnesium ion and its outer sphere. A partially ordered spermine molecule is located within the major groove of structure X. Dodecamer structures are derived from crystals of [d(CGCGAATTCGCG)]2 in space group P212121 (a = 25 A, b = 40 A, and c = 66 A). On average, those crystals diffracted to around 2.5 A resolution with 2500 unique reflections. Structure X, with the same space group, DNA sequence, and crystal form as the "Dickerson dodecamer", is refined against a complete, low-temperature, 1.4 A resolution data set, with over 11000 reflections. Structure X appears to be conformationally more ordered than previous structures, suggesting that at least a portion of the conformational heterogeneity previously attributed to DNA sequence in fact arises from experimental error.

Structure of a DNA-bisdaunomycin complex.

The application of detailed structural data bases has now culminated in the successful design of a new generation of bisanthracyclines that form ultratight DNA complexes [Chaires, J. B., Leng, F., Przewloka, T., Fokt, I., Ling, Y. H., Perez-Soler, R., & Priebe, W. (1997) J. Med. Chem. 40, 261-266]. Daunomycin dimers were designed to bind to DNA in complexes resembling those of monomers intercalated at adjacent sites. The goal of the work described here was to determine, with X-ray crystallography, if a potent member of this newly designed and synthesized class of bisanthracyclines (WP631) binds as intended. WP631 is composed of two daunomycin molecules, linked N3' to N3' by a xylyl group. We have solved the 2.2 A X-ray crystal structure of a complex of WP631 bound to [d(CGATCG)]2. We demonstrate, on a detailed molecular level, that the WP631 design strategy is a success. The structures of WP631 and two daunomycin molecules bound to [d(CGATCG)]2 provide the unprecedented opportunity for detailed comparison of mono- and bis-intercalated complexes of the same chromophore, allowing us to distinguish effects of mono-intercalation from those of bis-intercalation. Differences are focused primarily in the centers of the complexes. DNA unwinding and other helical distortions propagate more efficiently to the center of the WP631 complex than to the center of the daunomycin complex.