Visualization of nonreciprocal chromosome exchanges in irradiated human fibroblasts by fluorescence in situ hybridization

A long-standing controversy in radiation cytogenetics is the precise mechanism for the formation of chromosome exchanges. The classical breakage-and-reunion hypothesis suggested by Stadler and developed by Sax was challenged in 1959 by Revell, who proposed that radiation produced an "unstable lesion" which could interact with another such lesion to form an exchange. A difference between the predictions of these two theories is that the breakage-and-reunion hypothesis would allow the two broken ends of a chromosome to join with contemporary broken ends in different chromosomes, thereby producing nonreciprocal exchanges involving more than two chromosomes. This would not occur according to the Revell theory, which demands pairwise commital to the exchange. The ability to "paint" a whole chromosome using fluorescence in situ hybridization allows a discrimination between reciprocal and nonreciprocal chromosome exchanges. We scored metaphases in AG1522 human fibroblasts irradiated in G1 phase with 6 Gy and hybridized to chromosomes 1, 4, or 8. Of the complete exchanges involving one of these chromosomes, 26% were found to possess either one or three centromeres in the exchange pair. Since we could rule out any significant contribution of complex exchanges (i.e., those involving more than one break per chromosome), these one- and three-centromere exchange pairs must have arisen from a nonreciprocal exchange. Because an equal number of nonreciprocal exchanges would be expected to have a total of two centromeres, this suggests that approximately 50% of all exchanges at this dose were nonreciprocal. These data support the breakage-and-reunion hypothesis and are incompatible with the standard form of the exchange hypothesis of Revell.

Tumor-specific, schedule-dependent interaction between tirapazamine (SR 4233) and cisplatin

Tirapazamine (SR 4233), a benzotriazine di-N-oxide, a potent and selective killer of hypoxic cells, is currently in Phase I clinical trials with the expectation that it will be combined with radiation therapy. However, because of the likelihood that hypoxic tumor cells may also be resistant to some commonly used chemotherapeutic agents, we have tested tirapazamine in combination with cisplatin (c-DDP) in the mouse RIF-1 tumor. A large, schedule-dependent enhancement of tumor cell killing was observed both in vivo and in vitro, with a maximal response observed when the SR 4233 was given 2-3 h before c-DDP. Assay of serum blood urea nitrogen levels following treatment with these two drugs indicates that SR 4233 does not enhance the kidney damage which can result from high doses of c-DDP. Leukopenia induced by the two drugs in combination was equal to that predicted from an additive effect of the responses to the individual drugs. Also, there was no change in the systemic toxicity of c-DDP (as judged by 50% lethal dose) when SR 4233 was combined with c-DDP at a dose and timing that produced the maximum tumor interaction. These observations point to a promising new combination therapy with considerable therapeutic advantage.

Identification of some clinically significant actinomycetes

Early recognition of infections caused by actinomycetes tend to be highly dependent on at least a tentative diagnosis derived from microbiological tests, since the clinical symptoms can be difficult to interpret. Reliable identification of clinically significant actinomycetes depends upon the application of taxonomic techniques that are not yet widely used in clinical laboratories. The value of rapid enzyme, chemical and molecular fingerprinting techniques is exemplified by their application to the identification of representatives of clinically significant actinomycete taxa.

Chromosomal radiosensitivity at intrachromosomal telomeric sites

Telomeric DNA is composed of highly conserved sequences which are present at the termini of chromosomes as well as at intrachromosomal locations. Here, we studied a Chinese hamster ovary (CHO) cell line, BL-10, with highly stable amplified telomeric DNA at the termini as well as at intrachromosomal locations. We show that intrachromosomal or interstitial telomeric sites in this cell line and in another CHO cell line, HA-I, are radiosensitive in that they are more prone to breakage than would be expected based on the percentage of the genome composed of telomeric sequences. The frequency of breakage at interstitial telomeric sites is 4.3 to 8.3 times higher than that in the CHO genome overall. These conclusions are reached by both conventional cytogenetic analysis of two CHO cell lines which have the same survival rates after exposure to ionizing radiation, and by use of double fluorescence in situ hybridization (FISH) with a pan-telomere-specific probe and a CHO chromosome-specific library in the same metaphase cells after irradiation.

The influence of irradiation of the tumor bed on tumor hypoxia: measurements by radiation response, oxygen electrodes, and nitroimidazole binding

SCCVII carcinomas and RIF-1 sarcomas were transplanted and grown in the unirradiated (control tumors) or preirradiated tissue of mice. Tumor oxygenation was measured when the tumors were in the size range 50-150 mm3 using three different methods. The tumors growing in tissues preirradiated with 20 Gy were significantly more hypoxic than the control tumors for both tumor types. Radiobiologically hypoxic fractions of these tumors were approximately 10 times higher than those of the controls. The relative [3H]misonidazole binding of the tumors transplanted into irradiated tissue was approximately five times (P < 0.01) higher in SCCVII tumors or approximately two times (P < 0.05) higher in RIF-1 tumors than that of the controls. The pO2 histographs measured directly by a polarographic microelectrode were more hypoxic (P < 0.001) and changed from bimodal to unimodal in pattern in the tumors transplanted into irradiated tissue compared to those of the controls. The increase of the relative [3H]misonidazole binding in the tumors transplanted into irradiated tissue compared to that of the controls was similar to the increase of the cumulative frequency of pO2 below 10.0 mm Hg for both the SCCVII and the RIF-1 tumors. The data suggest that the majority of tumor cells with pO2 values below 5.0 mm Hg were clonogenic in the SCCVII tumors while only a small portion of tumor cells with pO2 below 5.0 mm Hg were clonogenic in the control RIF-1 tumors. Increased hypoxia caused by preirradiation of the tumor bed is a useful model in evaluating the efficacy of various treatments affected by tumor oxygenation levels. The model is also useful in evaluating techniques for measuring oxygen levels.

Further evidence of functional differentiation within biceps brachii

This study investigated whether the two heads of Biceps Brachii could be functionally differentiated during rapid supination movements with different degrees of elbow flexion, shoulder axial rotation and load. Surface electromyograms, recorded from the long and short heads of Biceps Brachii, were utilised to identify changes in the intensity of muscle contraction. Based upon an analysis of sixteen subjects, the results indicated that joint position (muscle length), but not load, significantly (p < 0.05) influenced the relationship between the contraction intensities of the two heads. Specifically, increasing the length of the Biceps Brachii promoted increased activation of the long head in relation to the short head in producing rapid supination motions. It was concluded that functional differentiation within the two heads of Biceps Brachii was present in motions involving its distal insertion.

Sound Velocities in Olivine at Earth Mantle Pressures

The independent elastic constants of an upper mantle mineral, San Carlos olivine [(Mg(1.8)Fe(0.2))SiO(4)], were measured from 0 to 12.5 gigapascals. Evidence is offered in support of the proposition that the explicit temperature dependence of the bulk modulus is small over the range of temperatures and pressures thought to prevail above the 400-kilometer discontinuity, and thus the data can be extrapolated to estimate the properties of olivine under mantle conditions at a depth of 400 kilometers. In the absence of high-temperature data at high pressures, estimates are made of the properties of olivine under mantle conditions to a depth of 400 kilometers. In contrast with low-pressure laboratory data, the predicted covariance of shear and compressional velocities as a function of temperature nearly matches the seismically estimated value for the lower mantle.

Acute lung injury at Baragwanath ICU. An eight-month audit and call for consensus for other organ failure in the adult respiratory distress syndrome

To test the expanded definition of acute lung injury (ALI), we prospectively, over a period of 8 months, studied all adult ICU admissions who fitted the definition. Our study consisted of 83 patients with the adult respiratory distress syndrome (ARDS) and 60 with mild to moderate ALI. Sepsis and trauma were the most common diagnoses on admission. The overall mortality rate was 45 percent for ARDS and 38 percent in the other group. Mortality rose significantly with associated other organ failure, the incidence of which was as follows: hepatic, 39 percent; cardiac, 38 percent; hematologic, 22 percent; renal, 21 percent; neurologic, 5 percent. Sepsis syndrome eventually occurred in 73 percent and septic shock in 38 percent of all cases of ALI. We found the expanded definition a useful grading system and consider this definition of ARDS to be currently the best. There are, however, problems with the determination of lung compliance, the effect of inverse ratio ventilation, and the lack of consensus in defining other organ failure.

SR 4233 (tirapazamine): a new anticancer drug exploiting hypoxia in solid tumours

SR 4233 (3-amino-1,2,4-benzotriazine 1,4-dioxide, WIN 59075, tirapazamine) is the lead compound in a new class of bioreductive anticancer drugs, the benzotriazine di-N-oxides. It is currently undergoing Phase I clinical testing. The preferential tumour cell killing of SR 4233 is a result of its high specific toxicity to cells at low oxygen tensions. Such hypoxic cells are a common feature of solid tumours, but not normal tissues, and are resistant to cancer therapies including radiation and some anticancer drugs. The killing of these tumour cells by SR 4233, particularly when given on multiple occasions, can increase total tumour cell killing by fractionated irradiation by several orders of magnitude without increasing toxicity to surrounding normal tissues. Topics covered in this review include the rationale for developing a hypoxic cytotoxic agent, the cytotoxicity of SR 4233 as a function of oxygen concentration, the mechanism of action of the drug and its intracellular target and the in vivo evidence that the drug may be useful as an adjunct both to radiotherapy and chemotherapy. Finally, the major unanswered questions on the drug are outlined.

Cutaneous Nocardia farcinica infection in a nonimmunocompromised patient: case report and review

Nocardia farcinica, the etiologic agent of bovine farcy, is microbiologically related to but distinct from Nocardia asteroides. N. farcinica is noted for its propensity to cause serious systemic infection in both normal and immunocompromised hosts and its marked degree of resistance to multiple antimicrobial agents. We present a case in which a nonimmunocompromised patient who sustained a contaminated facial laceration developed an abscess due to N. farcinica with underlying osteomyelitis. The severity of the infection necessitated surgical debridement followed by administration of intravenous amikacin therapy. The isolate was susceptible to amikacin and trimethoprim-sulfamethoxazole but resistant to erythromycin in vitro. Therapy with trimethoprim-sulfamethoxazole was started but was discontinued because of the patient's intolerance to the drug. Intramuscular amikacin was substituted, resulting in complete resolution of the infection. The history, epidemiology, and microbiological characteristics of this interesting and unusual microorganism are reviewed.

Rhodococcus species fatal infection in an immunocompetent host

A 24-year-old woman had fatal pneumonia-associated adult respiratory distress syndrome caused by Rhodococcus species. Histological examination of lung biopsy tissue showed intracellular coccobacillary microorganisms. Antimicrobial susceptibility tests on the patient's blood isolate showed that it was resistant to clindamycin and norfloxacin but susceptible to several other antimicrobial agents. Also, the isolate's biochemical reactions and pattern of RNA gene-containing restriction fragments were significantly different from those of the 20 recognized Rhodococcus species, suggesting that this patient's infection was caused by an as yet uncharacterized Rhodococcus species. Of the 17 human cases of nonequi Rhodococcus species infection reported to date (including the current case), nine patients were immunocompetent, five had disseminated infection, and four died. Further studies will be required to unequivocally establish the species status of this patient's Rhodococcus isolate biochemically and genetically.

Influences of closure, occlusion, and size on the perception of fragmented pictures

Two experiments examined the ability to recognize a repeated figure in stimuli where only fragments of the figures were presented. Fragments were either closed or open regions presented either with or without an occluder that filled the spaces between the fragments (Experiment 1). Recognition performance was significantly better for open fragments, with or without an occluder, contrary to previous assertions that the occluder is the important factor for recognition. When stimulus size was varied, an occluder hindered recognition performance in the smallest size condition relative to unoccluded stimuli, which were equally easy to recognize across all size conditions (Experiment 2). The size results support the idea of size invariance in object naming. The difficulty in the smallest occluded condition is discussed in terms of differences in global and local processing depending on visual angle and sparsity.

Moving phantom visibility as a function of fundus pigmentation

Moving phantom visibility was measured for subjects with a fundus classified as either lightly or darkly pigmented. The phantom-inducing pattern was a black-and-white square-wave grating drifting continuously from left to right, with a black horizontal occluder interrupting the middle of the grating. Moving phantom visibility was significantly reduced for darker relative to lighter pigmented subjects. The results show that fundus pigmentation can influence the perception of illusory contours and surfaces (i.e., phantoms). This finding supports and expands on previous research concerning fundus pigmentation influences on real contour perception.

Characterization of the DNA double strand break repair defect in scid mice

The scid mutation in CB-17 mice confers a profound immunodeficiency, resulting from an inability to rearrange immunoglobulin and T-cell receptor genes during lymphocyte development. Moreover, we and others have recently demonstrated in these scid mice a hypersensitivity to the lethal effects of ionizing radiation and a defect in DNA double strand break rejoining. In this report, we further characterize the radiosensitivity and repair defect in cells from scid mice. In order to determine whether scid cells were specifically sensitive to agents that produce double strand breaks, restriction enzymes RsaI and Sau3AI were introduced into scid and parental C.B-17 cells by electroporation. scid cells were 2-fold more sensitive than C.B-17 cells to both the blunt and the staggered end cuts produced by these restriction enzymes. However, the scid cells proficiently ligated both staggered and blunt ends of transfected plasmids. To determine whether the extent of DNA rejoining in scid cells was dependent on the initial dose of gamma-rays, final levels of DNA double strand break rejoining in scid and C.B-17 cells were quantitated by asymmetric field inversion gel electrophoresis. The results indicate an apparent difference in repair levels dependent on the dose of gamma-rays, ranging from 75% rejoining at 10 Gy to 40% rejoining at 50 Gy. In contrast, > 90% rejoining was observed in control C.B-17 cells at all doses. Delineating the links between these aberrant recombinational events, abnormal V(D)J recombination, and double strand break repair defects, will aid in the understanding of the basic mechanisms involved in these processes.

Metabolism of the bioreductive cytotoxin SR 4233 by tumour cells: enzymatic studies

SR 4233 (3-amino-1,2,4-benzotriazine 1,4-dioxide) is an anti-tumour agent that has a highly selective toxicity to hypoxic cells. In this study we delineate the role of several different bioreductive enzymes in the metabolism of SR 4233 by two tumour cell lines HT 1080 (human fibrosarcoma) and SCCVII (mouse carcinoma). Enzyme kinetics demonstrates similar KM of HT 1080 and SCCVII cell sonicates and differing Vmax. Among all cofactors tested, NADPH was the most important one in reducing SR 4233 by both tumour cell sonicates. NADH was the second most important cofactor while hypoxanthine and N-methylnicotinamide were less involved in the reduction of SR 4233. Carbon monoxide inhibited the reduction by about 60% suggesting that cytochrome P-450 may play a major role in the reduction of SR 4233 under hypoxia in both SCCVII and HT 1080 cells. DT diaphorase is also involved, particularly in HT 1080 cells, in this drug reduction. The level of functional cytochrome P-450, cytochrome P-450 reductase activity and DT diaphorase activity in both cell lines were assayed. These enzyme levels were all higher in SCCVII cells than in HT 1080 cells. This result correlated the higher Vmax of SR 4233 reduction in SCCVII cells than in HT 1080 cells.

Primary lymphocutaneous nocardiosis caused by an unusual species of Nocardia: Nocardia transvalensis

We present the first case of lymphocutaneous nocardiosis caused by Nocardia transvalensis and the seventh report of infection caused by this microorganism. The patient was allergic to sulfonamides but responded to amikacin and cefotaxime and later to erythromycin. The treatment and criteria for differentiation of cutaneous Nocardia species infection are discussed.

Lack of differential radiosensitization of hypoxic cells in a mouse tumor at low radiation doses per fraction by cisplatin

Korbelik and Skov (Radiat. Res. 119, 145-156, 1989) have reported that cis-diamminedichloroplatinum (II) (cisplatin) shows substantial preferential radiosensitization of hypoxic cells in vitro at low radiation doses (1-4 Gy), and that the interaction seen with low doses of radiation is greatly diminished at high radiation doses. If such an interaction occurred with fractionated irradiation in vivo, it would be extremely important to radiation therapy, since the sensitizer enhancement ratios achievable in the low-dose region are higher than those achievable with current hypoxic cell radiosensitizers. We have tested this possibility in an experimental mouse tumor using fractionated irradiation under conditions in which the response of the tumor was determined by either its aerobic or its hypoxic cells. RIF-1 tumors were irradiated with 10 fractions of 1-4 Gy every 12 h with cisplatin given either as 12 mg/kg once before the first radiation dose or as 1.2 mg/kg at various times prior to each radiation dose. The tumors were irradiated with or without a clamp applied 2-3 min before each radiation dose. The effectiveness of the treatments was assayed by regrowth delay. Cisplatin caused a similar regrowth delay when used alone in both clamped and nonclamped tumors and produced a similar additive or supra-additive interaction when used with the 10 fractionated radiation schedule whether the tumors were hypoxic or aerobic. Our data suggest that cisplatin does not show any preferential radiosensitization of hypoxic cells with low-dose multifraction irradiation in this tumor, although a clear schedule-dependent interaction between the drug and radiation was seen for both aerobic and hypoxic tumors.