Effects of spermine on the detection of induced forward mutation at the Can1 locus in yeast: evidence for selection against canavanine-resistant mutants.

The effect of exogenous spermine tetrahydrochloride (0.5 mg/ml) on hydrazine- and nitrous acid-induced forward mutation to canavanine resistance (CAN1 leads to can1, normal to defective arginine permease) was examined in stationary-phase haploid Saccharomyces cerevisiae. Post-treatment cell division (specifically DNA replication) is required for hydrazine mutagenesis at this locus, whereas nitrous acid mutagenesis exhibits, in addition, a significant post-treatment-independent component. Spermine addition only during mutagenic treatments in buffer did not affect mutagen cytotoxicity, but did result in a slight yet consistent decrease in induced mutation frequencies. Addition of spermine to the yeast extract--peptone--dextrose (YEPD) post-treatment growth medium resulted in dramatic reductions of induced mutation frequencies, which could be alleviated by pregrowth in spermine-containing YEPD. Such a medium was found to cause an apparent temporary growth inhibition for almost 40 h, after which the growth rate of the culture increased rapidly. Cultures "recovering" from spermine inhibition were no longer inhibitable by spermine in fresh medium, suggesting an outgrowth of spontaneous and/or induced spermine-resistant derivatives. Genetic analysis of one isolate revealed a single dominant nuclear gene conferring resistance by some means other than defective spermine uptake. Growth of this mutant was only slightly inhibited by spermine (20% increase in doubling time), while mutation expression remained high. Results of competitive growth experiments indicated that spermine-containing YEPD exerted a selection pressure against canavanine-resistant cells, while YEPD by itself did not. The mechanism for this selection is not presently understood. With respect to replication-dependent induced mutation at CAN1, our initial observation of a strong apparent antimutagenic action of spermine was found to be best explained by this specific selection against can1 mutants. This underscores the need for caution in the interpretation of experiments designed to study physiological modification of mutagenic potential.     

Skeletal Scintigraphy

Skeletal scintigraphy, using phosphates or diphosphonates labeled with technetium 99m, is a sensitive method of detecting bone abnormalities. The most important and most frequent role of bone scanning is evaluating the skeletal areas in patients who have a primary cancer, especially a malignant condition that has a tendency to spread to bone areas. The bone scan is superior to bone radiographs in diagnosing these abnormalities; 15 percent to 25 percent of patients with breast, prostate or lung cancer, who have normal roentgenograms, also have abnormal scintigrams due to metastases. The majority of bone metastases appear as hot spots on the scan and are easily recognized. The incidence of abnormal bone scans in patients with early stages (I and II) of breast cancer varies from 6 percent to 26 percent, but almost invariably those patients with scan abnormalities have a poor prognosis and should be considered for additional therapies. Progression or regression of bony lesions can be defined through scanning, and abnormal areas can be identified for biopsy. The incidence of metastases in solitary scan lesions in patients with known primary tumors varies from 20 percent to 64 percent. Bone scintigraphy shows positive uptake in 95 percent of cases with acute osteomyelitis. Stress fractures and trauma suspected in battered babies can be diagnosed by scanning before there is radiological evidence. The procedure is free from acute or long-term side effects and, except in cases of very young patients, sedation is seldom necessary.Although the test is sensitive, it is not specific and therefore it is difficult to overemphasize the importance of clinical, radiographic, biochemical and scanning correlation in each patient.     

Electrochemical treatment of mouse and rat fibrosarcomas with direct current

Electrochemical treatment (ECT) of cancer utilizes direct current to produce chemical changes in tumors. ECT has been suggested as an effective alternative local cancer therapy. However, a methodology is not established, and mechanisms are not well studied. In vivo studies were conducted to evaluate the effectiveness of ECT on animal tumor models. Radiation-induced fibrosarcomas were implanted subcutaneously in 157 female C3H/HeJ mice. Larger rat fibrosarcomas were implanted on 34 female Fisher 344 rats. When the spheroidal tumors reached 10 mm in the mice, two to five platinum electrodes were inserted into the tumors at various spacings and orientations. Ten rats in a pilot group were treated when their ellipsoidal tumors were about 25 mm long; electrode insertion was similar to the later part of the mouse study, i.e., two at the base and two at the center. A second group of 24 rats was treated with six or seven electrodes when their tumors were about 20 mm long; all electrodes were inserted at the tumor base. Of the 24 rats, 12 of these were treated once, 10 were treated twice, and 2 were treated thrice. All treated tumors showed necrosis and regression for both mice and rats; however, later tumor recurrence reduced long-term survival. When multiple treatments were implemented, the best 3 month mouse tumor cure rate was 59.3%, and the best 6 month rat tumor cure rate was 75.0%. These preliminary results indicate that ECT is effective on the radiation-induced fibrosarcoma (RIF-1) mouse tumor and rat fibrosarcoma. The effectiveness is dependent on electrode placement and dosage. Bioelectromagnetics 18:14–24, 1997. © 1997 Wiley-Liss, Inc.     

TP53 tumor suppressor protein in normal human fibroblasts does not respond to 837 MHz microwave exposure.

The TP53 tumor suppressor protein (formerly known as p53) responds to a wide variety of environmental insults. To evaluate the safety of cellular telephones, TP53 responses in human fibroblast cells were studied after exposure to 837 MHz microwaves. Cells were exposed in a temperature-controlled transverse electromagnetic (TEM) chamber to a specific absorption rate (SAR) of 0.9 or 9.0 W/kg at 837 MHz continuous-wave (CW) microwave irradiation for 2 h. The TP53 protein levels were measured by Western blot at 2, 8, 24 and 48 h after treatment. The TP53 protein levels in microwave-treated cells, sham-treated cells, and untreated cells remained unchanged relative to each other at all times tested (Fisher test and Student-Newman-Keuls test, P > 0.05). No morphological alterations were observed in microwave-treated cells compared to sham-treated cells. We conclude that TP53 protein expression levels in cultured human fibroblast cells do not change significantly during a 48-h period after exposure to 837 MHz continuous microwaves for 2 h at SAR levels of 0.9 or 9.0 W/kg.     

Genomic changes and HPV type in cervical carcinoma

To identify chromosomal regions that may include the loci of abnormally expressed cellular genes and may be specifically altered depending on the histological subtype of the tumor, we studied primary cervical carcinoma using CGH and HPV genotyping. Eighty-seven percent of the primary tumors were positive for DNA of a "high-risk" HPV type (e.g., 16 or 18). In the cervical carcinomas, without reference to histologic subtype, overrepresentation of chromosome 3q was the most consistent chromosomal aberration with underrepresentation of chromosome 3p also a frequent finding. Chromosome arms 1q, 5p, 20q, and Xq were overrepresented in many tumors and 3p loss and 5p, 8q, and 16q gain were only associated with squamous cell carcinoma in this series.     

Ca2+ oscillations and the cell cycle at fertilisation of mammalian and ascidian eggs

At fertilisation of mammalian and ascidian eggs the sperm induces a series of Ca2+ oscillations. These Ca2+ oscillations are triggered by a sperm-borne Ca2+-releasing factor whose identity is still unresolved. In both mammals and ascidians Ca2+ oscillations in eggs are associated with the period leading up to exit from meiosis and entry into the first embryonic cell cycle. Thus, in mammals Ca2+ oscillations continue for several hours but are complete by within 30 min in the ascidian. In mammals and ascidians Ca2+ oscillations stop at around the time when pronuclei form in the 1-cell embryo. There is evidence to show that cell cycle factors are important in regulating the fertilisation Ca2+ signal. If the formation of pronuclei is blocked either in mammals (by spindle disruption) or in ascidians (by clamping maturation promoting factor levels high) then Ca2+ oscillations continue indefinitely. Here, we explore the nature of the sperm Ca2+-releasing factor and examine the relationship between cell cycle resumption and the control of Ca2+ oscillations at fertilisation.