X-ray structure of a DNA decamer containing 7,8-dihydro-8-oxoguanine

We have determined the x-ray structure of a DNA fragment containing 7,8-dihydro-8-oxoguanine (G(O)). The structure of the duplex form of d(CCAGOCGCTGG) has been determined to 1.6-A resolution. The results demonstrate that GO forms Watson-Crick base pairs with the opposite C and that G(O) is in the anti conformation. Structural perturbations induced by C.G(O)anti base pairs are subtle. The structure allows us to identify probable elements by which the DNA repair protein MutM recognizes its substrates. Hydrogen bond donors/acceptors within the major groove are the most likely element. In that groove, the pattern of hydrogen-bond donors/acceptors of C.G(O)anti is unique. Additional structural analysis indicates that conversion of G to G(O) would not significantly influence the glycosidic torsion preference of the nucleoside. There is no steric interaction of the 8-oxygen of G(O) with the phospho-deoxyribose backbone.

Reported myopia in opposite sex twins: a hormonal hypothesis

Two studies have reported poor vision in opposite sex twins (evidenced by wearing glasses or low visual acuity, both of which are interpreted here as evidence of myopia), whereas none have reported an absence of such effects. If these reports are replicable, it would suggest a hormonal effect. There is one report of higher testosterone levels in those suffering from high myopia. A possible mechanism would be if sex hormones in opposite sex pairs transfer from one fetus to the other. There is evidence that sex hormones can cross the placenta, and reports of sex differences in the development of opposite sex twins are consistent with such transfers. If different parts of the eye respond differentially to sex hormones, eyes developing in the unusual hormonal environment of opposite sex twins would be expected to have high myopia rates.

Analysis of the effect of hormones on opposite-sex twin attitudes

Numerous reports in the literature suggest that hormones may transfer from one fetus to another, in humans as in animals. In a large sample of over seven thousand Australian adult twins, it was found that opposite-sex females showed a statistically significant tendency to hold more masculine attitudes than did same-sex female twins. This may be due to post-natal social interaction, but could also be caused by the transfer of testosterone from the male to the female fetus in opposite-sex twins.

The role of cell cycle redistribution in radiosensitization: implications regarding the mechanism of fluorodeoxyuridine radiosensitization

PURPOSE

Radiosensitization has previously been demonstrated in a human colon cancer cell line (HT-29) following a 2 h exposure to low, clinically relevant concentrations (0.05-0.5 microM) of fluorodeoxyuridine (FdUrd) (15). The sensitizer enhancement ratio value (measured at 10% survival) plateaued at approximately 1.7 between 16 and 32 h following removal of drug. Parallel studies investigating the effect of FdUrd on the distribution of cells throughout the cell cycle found that the percentage of cells in early S-phase increased to approximately 70% during the same period that maximal radiosensitization was noted. As a follow-up to these findings, experiments have been designed to investigate the contribution of this early S-phase delay to radiosensitization.

METHODS AND MATERIALS

Synchronized populations of HT-29 cells have been obtained with three separate techniques. Two involve the induction of a reversible metaphase arrest (with high pressure N2O or colcemid) followed by a shakeoff of mitotic cells. The third uses a plant amino acid, mimosine, to induce a reversible block at the G1/S boundary. Flow cytometry was used to analyze the degree of synchrony based on bromodeoxyuridine (BrdUrd) uptake and propidium iodide (PI) staining. Radiation survival curves were obtained on these synchronized populations to investigate changes in radiosensitivity through the cell cycle. Additionally, levels of thymidylate synthase (TS), the primary target of FdUrd cytotoxicity, were measured in each phase of the cell cycle using the TS 106 monoclonal antibody against human TS.

RESULTS

Synchronization with mitotic shakeoff produced relatively pure populations of cells in G1; however, the degree of synchrony in early S-phase was limited both by cells remaining in G1 and by cells progressing into late S-phase. These techniques failed to reveal increased radiosensitivity in early S-phase at 10% survival. An 18 h exposure to mimosine resulted in populations that more closely resembled the early S-phase enrichment following FdUrd exposure and revealed increased radiosensitivity during early S-phase. TS levels were noted to be only 1.3 times higher in S phase than in G0/G1.

CONCLUSION

Radiation survival data from cells synchronized with mitotic shakeoff techniques suggest that early S-phase delay is unlikely to be the primary mechanism of FdUrd radiosensitization. In contrast, the increased sensitivity seen in early S-phase with mimosine synchronized cells is similar to that seen with FdUrd. Although confounding biochemical pertubations cannot be ruled out, these data continue to suggest an association between early S-phase enrichment and radiosensitization. The significance of TS inhibition as a mechanism of FdUrd radiosensitization remains unclear.

4-Hydroxytamoxifen, an active metabolite of tamoxifen, does not alter the radiation sensitivity of MCF-7 breast carcinoma cells irradiated in vitro

The effect of 4-hydroxytamoxifen (4OH-TAM), the potent anti-estrogenic metabolite of tamoxifen, on the radiosensitivity of MCF-7 cells irradiated in vitro was determined. Radiation dose response curves were generated for MCF-7 cells maintained and irradiated in phenol red-free medium containing 10(-10) M estradiol (E2) with or without 10(-7) M 4OH-TAM. Immediately after irradiation cells were transferred to medium containing 10(-10) ME2 supplemented with bovine serum to stimulate colony formation. Estradiol-stimulated cell proliferation was inhibited by 10(-7) M 4OH-TAM, but radiation sensitivity was not significantly altered (p > 0.3). Continued incubation in the absence of E2 for an additional 24 hours after irradiation likewise failed to alter the radiosensitivity of 4OH-TAM-treated MCF-7 cells. These studies indicate that growth-inhibitory concentrations of the anti-estrogen 4OH-TAM do not modify the in vitro radiation sensitivity of this line of human breast carcinoma cells.

Deoxyribonucleoside triphosphate pools and thymidine chemosensitization in human T-cell leukemia

Thymidine kills cells by depleting dCTP stores. The present experiments tested whether deoxycytidine, by replenishing dCTP pools, could prevent thymidine cytotoxicity and thymidine's enhancement of carboplatin killing in two human T-cell acute leukemia cell lines. MOLT3 and JM cells were exposed to combinations of thymidine, deoxycytidine, and carboplatin and then assessed for survival, the magnitude of thymidine-carboplatin chemosensitization, and changes in deoxyribonucleoside triphosphate pools. For both cell lines, deoxycytidine (up to 144.5 micrograms/ml x 24 h) completely restored dCTP pools but only partially protected against thymidine cytotoxicity (100-1000 micrograms/ml x 24 h) and thymidine-carboplatin sensitization (up to 60 micrograms carboplatin/ml during the last hour of thymidine). This contrasts with complete protection in prior studies using other cell types. Thymidine alone markedly increased dTTP and dGTP pools and decreased dCTP; dATP pools underwent a sharp decline which has not been observed before in any cell line. In subsequent studies 0.0336-137.3 micrograms deoxyadenosine/ml partially prevented cytotoxicity and carboplatin sensitization by 300 micrograms thymidine/ml. Together, deoxycytidine and deoxyadenosine completely prevented thymidine-carboplatin sensitization even though dATP and dCTP pools were not entirely returned to normal. These findings are discussed in regard to the unusual sensitivity of T-cell malignancies to thymidine toxicity, mechanisms of cytotoxicity and chemosensitization by thymidine, and the possibility of thymidine selectively sensitizing T-cell malignancies to killing by alkylating agents.

Low pH does not affect the dose response for 5'-amino-5'-deoxythymidine modulation of IdUrd DNA incorporation and radiosensitization in a human bladder cancer cell line

We report that coincubation of 647V cells for one cell cycle with low concentrations (30 microM) of 5'-amino-5'-deoxythymidine increased IdUrd DNA incorporation and radiosensitivity at low extracellular pH (pHe 6.8) in a fashion similar to treatment at normal pHe. IdUrd DNA incorporation is inhibited by high (300 microM) 5'-AdThd concentrations at both normal and low pHe (7.4 and 6.8), resulting in no significant radiosensitization. These results at low pHe were not anticipated based on previously published studies of 5'-AdThd modulation of thymidine kinase (TK) activity and nucleoside cellular uptake. Our results suggest that regulation of intracellular pH (pHi) during the course of one cell cycle negates the 5'-AdThd dose-dependent modulation of TK activity demonstrated previously. Flow cytometric measurement of pHi in 647V cells showed that normal pHi (pH 7.4) was maintained in 647V cells over a 12- to 24-h exposure to low pHe (pH 6.8). Thus the concomitant use of IdUrd and high concentrations of 5'-AdThd (> 30 microM) is unlikely to result in selective in vivo radiosensitization of human tumors under conditions which are intermittently or chronically acidic. However, low concentrations of 5'-AdThd may prove to be an effective in vivo modulator of IdUrd radiosensitization of human tumors under both normal and acidic conditions.

On the correlation of myopia and intelligence

A pleiotropic relationship between intelligence and myopia has been shown to exist. Large eyes (as measured by axial length) have been shown to lead to myopia, and large brains have been shown to be more intelligent. I hypothesized that the myopia/intelligence relationship could arise because a single genetically controlled mechanism affects both brain size and eye size. This hypothesis has testable implications.

Linear-quadratic analysis of radiosensitization by halogenated pyrimidines. I. Radiosensitization of human colon cancer cells by iododeoxyuridine

Radiosensitization by iododeoxyuridine (IdU) is a method of enhancing cell killing in the radiotherapy of human cancers, especially for tumors that proliferate faster than the surrounding normal tissues, such as might appear in brain or liver. We have investigated in vitro the relationship between the amount of thymidine replacement by IdU and the resulting radiosensitization in two human colon cancer cell lines, HCT 116 and HT 29, with differing inherent sensitivities to X rays. The results show that an increase in the initial slope of the cell survival curve was the predominant mode of radiosensitization. In this situation, the emphasis on changes in the initial slope suggest the use of a survival curve model that contains the initial slope as a defined variable, which the traditional single-hit, multitarget model does not. We present our analyses mainly in terms of alpha (initial slope) and changes in surviving fraction at 2 Gy and also as a modified form of sensitizer enhancement ratio that describes the dose-modifying factor of IdU at a single radiation dose of 2 Gy (SER 2 Gy). Iododeoxyuridine is an effective radiosensitizer in both cell lines, but IdU appears especially effective in increasing the initial slope of the more radioresistant line, the HT 29 cells.

Linear-quadratic analysis of radiosensitization by halogenated pyrimidines. II. Radiosensitization of human colon cancer cells by bromodeoxyuridine

As a continuation of the studies in Part I (Miller, Fowler, and Kinsella, Radiat. Res. 131, 000-000, 1992), which examined the radiosensitizing effects of iododeoxyuridine (IdU), similar experiments with bromodeoxyuridine (BrdU) were conducted concurrently to characterize its effects on the shape of the radiation survival curves of cells of two human colon cancer cell lines, HT 29 and HCT 116. The efficiency of radiosensitization by BrdU, expressed as a function of percentage thymidine replacement, was lower when compared to IdU in both cell lines. However, the major radiosensitizing effect of BrdU was manifest as an increase in the initial slope (alpha), just as observed for IdU. However, with BrdU, in contrast to IdU, an increase in curvature (repairable damage) was also evident. Cells of the more radiosensitive line, HCT 116, showed less sensitization by either BrdU or IdU than cells of the more radioresistant line, HT 29. These results were consistent with the proposed mechanism of radiosensitization being an increase in the single-hit character of low-LET radiation. It follows that the radiosensitizing effects of both analogs were largest in the low-dose region of the survival curve.

Radiosensitization by fluorodeoxyuridine: effects of thymidylate synthase inhibition and cell synchronization

The combination of fluoropyrimidines and radiation has resulted in increased control of colorectal cancer in the clinic, but the basic mechanism of the interaction is not understood clearly. Preliminary work in our laboratory showed that 2-h exposures of HT 29 human colon carcinoma cells to relatively low levels of 5-fluorodeoxyuridine resulted in extended thymidylate synthase inhibition after the drug was removed (up to 30 h after treatment with 0.5 microM 5-fluorodeoxyuridine). The low cytotoxicity associated with this treatment simplified efforts to test the effects of extended thymidylate synthase inhibition on radiosensitivity of HT 29 cells. Although thymidylate synthase was completely inhibited at the end of the 2-h exposure, an increase in the radiosensitivity of the cells was not evident until 16 h after the removal of drug. Flow cytometric analysis showed that cells accumulated in early S phase over time, and the increase in radiation sensitivity of the entire population followed the increase of the proportion of cells in early S, a relatively radiosensitive phase of the cell cycle. This treatment schedule was compared with 24-h continuous exposure, and we found that the same maximum increase in radiosensitivity was achieved by both treatment strategies. However, more cytotoxicity was associated with continuous exposure. This study provides evidence that radiosensitization by 5-fluorodeoxyuridine is in part due to alteration of cell kinetics and redistribution of cells throughout the cycle. This information may be useful in the design of less toxic combined chemo- and radiotherapy treatment strategies by limiting systemic exposure to fluoropyrimidines.

Modulation of IdUrd-DNA incorporation and radiosensitization in human bladder carcinoma cells

5' Amino-5'-deoxythymidine (5'-AdThd) has been demonstrated previously to antagonize dTTP-mediated feedback inhibition of purified thymidine kinase from 647V, a human bladder cancer cell line. Low concentrations of 5'-AdThd (3-30 microM) have also been shown to stimulate cellular uptake of iododeoxyuridine (IdUrd) in 647V cells at clinically relevant IdUrd concentrations (2 microM). We report that the combination of 30 microM 5'-AdThd plus 2 microM IdUrd results in a significant increase of IdUrd replacement of thymidine (dThd) (18%) in the DNA of 647V cells over that obtained by exposure to 2 microM IdUrd alone (7.9%). However, increasing the 5'-AdThd concentration to 300 microM inhibited the incorporation of IdUrd into DNA (3%). IdUrd-induced radiosensitization of 647V cells, as measured by clonogenic survival, was enhanced by coincubation with 30 microM 5'-AdThd, while 300 microM 5'-AdThd reduced the IdUrd radiosensitization. Additionally, radiation-induced single strand break generation when IdUrd was incorporated into 647V DNA, as measured by rapid alkaline elution, was also enhanced by coincubation with 30 microM 5'-AdThd, while 300 microM 5'-AdThd resulted in a decrease in the number of single strand breaks produced. In T24, another bladder cancer cell line, and SV-HUC-TT1, a tumorigenic cell line derived from SV-HUC, 3-10 microM 5'-AdThd was also able to enhance IdUrd replacement of dThd in DNA. However, no stimulation of dThd replacement by 5'-AdThd occurred in SV-HUC, a prototypic "normal" bladder urothelial cell line. Since 5'-AdThd is not a substrate for mammalian thymidine kinase and has little or no cytotoxicity in vitro and in vivo, it may be a selective modulator of IdUrd radiosensitization of human bladder carcinoma and should be tested in vivo.

The use of VP16 and cisplatin in the treatment of Merkel cell carcinoma

A 70-year-old male with regionally recurrent Merkel cell cancer obtained a complete remission with three cycles of VP16 and cisplatin. His response was consolidated with local radiation therapy. Two additional patients have been reported to have responded to the same combination. Chemotherapy consisting of either cyclophosphamide, vincristine, and doxorubicin or VP16 and cisplatin should be considered in locally recurrent Merkel cell cancer.

Interaction of deoxyuridine with fluorouracil and dipyridamole in a human colon cancer cell line

We have reported previously that dipyridamole increases the toxicity of 5-fluorouracil and alters fluorouracil metabolism in HCT 116 cells, producing a selective increase in fluorodeoxyuridine monophosphate (FdUMP) levels by blocking the efflux of fluorodeoxyuridine. Dipyridamole also blocks deoxyuridine efflux and prolongs the intracellular half-life of deoxyuridine monophosphate (dUMP). The significance of the effect of dipyridamole on FdUMP and dUMP levels was explored further. In cell growth experiments, 1-50 microM deoxyuridine enhanced the cytotoxicity of 5 microM fluorouracil in a dose-dependent manner, and greater than or equal to 10 microM deoxyuridine increased the augmentation of fluorouracil toxicity produced by 0.5 microM dipyridamole. The effect of deoxyuridine on [6-3H]fluorouracil metabolism was studied. After 4 hr, 25 microM deoxyuridine increased the amount of [3H]FdUMP formed 2- to 4-fold relative to that of fluorouracil +/- dipyridamole alone. The mechanism by which deoxyuridine increased FdUMP was examined by measuring the distribution of [2'-3H]deoxyuridine metabolites following exposure of 25 microM deoxyuridine +/- 5 microM fluorouracil. Tritium appeared in the FdUMP peak at 4 and 24 hr in cells exposed to fluorouracil and deoxyuridine, indicating that [3H]deoxyribose was transferred to fluorouracil. A large buildup of [3H]dUMP was seen in cells exposed to fluorouracil plus deoxyuridine for 4 and 24 hr compared to exposure to [3H]deoxyuridine alone, suggesting that dUMP may also inhibit catabolism of FdUMP. Since the increased FdUMP levels produced by dipyridamole did not appear to correlate with further depletion of thymidine triphosphate pools, the incorporation of [3H]fluorouracil metabolites into nucleic acids was monitored by cesium sulfate density centrifugation. Fluorouracil-RNA increased as a function of time (1, 2 and 13 pmol/10(6) cells after 4, 8 and 24 hr), but fluorouracil-DNA was detected only after 24 hr (0.5 pmol/10(6) cells). Dipyridamole however, did not appear to alter the pattern of incorporation of fluorouracil into either RNA or DNA. Perturbations of endogenous dUMP levels by fluorouracil and dipyridamole were then studied. In cells exposed to fluorouracil alone, dUMP pools were unchanged from control at 2 hr, but they had increased 9-fold by 4 hr (3362 pmol/10(6) cells). Simultaneous exposure to fluorouracil and dipyridamole resulted in a 1.5-fold (566 pmol/10(6) cells) and 13.6-fold (5049 pmol/10(6) cells) increase over control dUMP levels after 2 and 4 hr respectively. The dUMP pools continued to enlarge through 24 hr. The effect of fluorouracil on DNA fragility was examined.(ABSTRACT TRUNCATED AT 400 WORDS)

Central serous choroidopathy misdiagnosed as a manifestation of multiple sclerosis

Visual loss secondary to macular disease can be differentiated from optic nerve lesions relatively easily in the office by simple and reliable noninvasive means. The diagnosis of a medically or surgically treatable lesion can obviate for the patient the often unnecessary anxiety and expense of more extensive studies.

Sarcoidosis mimicking glioma: case report and review of intracranial sarcoid mass lesions

Sarcoidosis may rarely cause a discrete intracranial mass lesion. We report a case originally diagnosed as a malignant glioma because of the uneven enhancement and marked white matter edema seen on computerized tomography. Twenty-two reported cases are analyzed, together wih our own. Major signs and symptoms are similar to those of other intracranial masses. Coexistent meningeal or hypothalamic involvement is often present, but extracranial sarcoidosis may be absent. The radiologic appearance varies and does not permit distinction from neoplasms or other granulomatous diseases. Treatment with steroids alone seems to be the best choice for initial therapy.

CT in the evaluation of spine trauma

Fifteen patients admitted for spine trauma in an 8 month period were studied with computed tomography (CT). All the patients had initial routine plain film screening, and 10 of 15 were also examined with conventional tomography. Five patients sustained vertical fall, axial-load injuries in the thoracolumbar junction region; two others suffered missile injury to the spine. CT provided more information than plain films in all these patients due to its superior imaging of bony detail and its ability to assess soft-tissue damage. In four of these patients, conventional tomography was done but contributed no additional information. Eight other patients sustained complex fractures of the cervical spine. In all but one, the combination of plain films and CT allowed complete evaluation of the injury. In one patient, conventional tomography showed an additional linear fracture one vertebral level below the main region of injury. Plain films and CT allow complete, safe, rapid, easily interpretable evaluation of spine trauma patients in the acute setting. Conventional tomography yields no additional clinically vital information in the acute evaluation of spine trauma, when plain films are abnormal. Its current ability to show finer bony detail than CT can be reserved for evaluating equivocal plain film and CT findings or more complete evaluation (if indicated) after the patient is clinically stable.

The role of computed tomography in the evaluation of neck masses

Application of computed tomography (CT) to neck masses has received little attention. The authors reviewed 10 cervical masses studied with CT as well as conventional imaging modalities. CT was extremely useful in defining both the osseous and soft-tissue extent of the lesion. In several instances, CT was able to show the relationship of the tumor to the spinal canal. When combined with angiography, CT demonstrated the relationship of the major cervical vascular channels to the lesion. Pathological conditions included neurofibroma, chordoma, branchial cleft cyst, neuroblastoma, lymphoma, neurilemmoma, and metastatic carcinoma.

The angiographic features of extraabdominal desmoid tumors

Extraabdominal desmoid tumors are nonencapsulated locally invasive neoplasms of fibrous tissue. The angiographic features include arterial stretching, neovascularity, and tumor staining (4 of 6 cases in this series). Although benign, these tumors are difficult to cure because they tend to recur locally.

Duodenal involvement with Crohn's disease: a spectrum of radiographic abnormality

The clinical and radiographic features of 22 cases of duodenal Crohn's disease were analyzed. The presenting clinical findings in the majority suggested peptic disease rather than regional enteritis. There was no cases of isolated duodenal Crohn's disease but a spectrum of radiographic abnormalities was produced by duodenal involvement with Crohn's disease which simulated a variety of clinical entities. A radiographic examination of the small bowel or colon was useful to confirm a diagnosis of Crohn's disease when duodenal abnormalities were suggestive.

Extra-axial posterior fossa lesions simulating intra-axial lesions on computed tomography

Differentiation of extra- from intra-axial posterior fossa lesions is sometimes not possible on computed tomography. Six cases are presented wherein the lesion appeared to be intra-axial on computed tomograms yet angiographically and surgically proved to be extra-axial. False localization on computed tomography occurs with slowly growing masses which burrow into brain parenchyma.

Dissociation of prelycopersene pyrophosphate synthetase from phytoene synthetase complex of tomato fruit plastids

The partially purified phytoene synthetase enzyme complex obtained from tomato fruit plastids dissociates into two or more subunit species on chromatography in low ionic strength buffer on DEAE-cellulose. One of these subunits prelycopersene pyrophosphate synthetase, has a molecular weight of approximately 40,000, whereas the phytoene synthetase complex has a molecular weight of 200,000. The prelycopersene pyrophosphate synthetase catalyzes the conversion of isopentenyl pyrophosphate to geranylgeranyl and prelycopersene pyrophosphates. The identities of these substances were established by thin layer chromatography in several solvent systems. The formation of both geranylgeranyl and prelycopersene pyrophosphates by this enzyme supports earlier results with cruder enzyme systems which suggested that these compounds are intermediates in the synthesis of phytoene.