Gene amplification in fibroblasts from ataxia telangiectasia (AT) patients and in X-ray hypersensitive AT-like Chinese hamster mutants.

In search of functions involved in the regulation of gene amplification, and given the relevance of chromosome breakage in initiating the process, we analyzed the gene amplification ability of cells hypersensitive to inducers of DNA double-strand breaks and defective in cell cycle control: two human fibroblast strains derived from patients affected by ataxia telangiectasia (AT) and two hamster mutant cell lines belonging to complementation group XRCC8 of the rodent X-ray-sensitive mutants. These mutants are considered hamster models of AT cells. To measure gene amplification, the frequency and the rate of occurrence of N-(phosphonacetyl)-L-aspartate resistant cells were determined. In both hamster mutants, these two parameters were increased by about an order of magnitude compared with parental cells, suggesting that amplification ability was increased by the genetic defect. In primary AT fibroblasts, as in normal human fibroblasts, gene amplification was undetectable and a block in the G(1) phase of the cell cycle was induced upon PALA treatment. These results suggest that in AT fibroblasts, where only the ATM gene is mutated, ATM-independent mechanisms prevent gene amplification, while, in the immortalized hamster cell lines, which are already permissive for gene amplification, the AT-like defect increases the probability of gene amplification.

Two extended arrays of a satellite DNA sequence at the centromere and at the short-arm telomere of Chinese hamster chromosome 5.

We have cloned a Chinese hamster chromosome-specific repeated sequence (SatCH5). This satellite is composed of a 33-bp unit organized in two extended tandem arrays. It is localized at the centromere and at the short-arm subtelomere of chromosome 5. Altogether, SatCH5 covers about 1-2 Mb per diploid genome and is not present in other species, including the Syrian hamster and mouse. Since it is known in the Chinese hamster and numerous other vertebrate species that telomeric (TTAGGG)n repeats are localized at the centromeres of several chromosomes, we studied the localization of SatCH5 relative to (TTAGGG)n sequences. Using two-color fluorescence in situ hybridization on stretched chromosomes and on DNA fibers, we have shown that at the centromere of chromosome 5 SatCH5 and the (TTAGGG)n arrays are contiguous. SatCH5 is the first chromosome-specific repetitive sequence located at both the pericentromeric and subtelomeric regions of the same chromosome.

Clinical trial of high doses of Bay I 7433 (Copovithane).

Bay i 7433 (Copovithane) is a biological response modifier with antitumour activity in vivo, but no cytotoxic or cytostatic effect in vitro. A clinical trial of the compound at doses of 15g/m2/week was carried out for six weeks in 10 patients with various forms of cancer. Tolerance was good: no systemic toxicity was observed but local inflammation occurred in two cases at the site of injection. No objective antitumour response was observed.

Kinetics of penetration and clearance of mezlocillin in the bronchopulmonary tract.

Mezlocillin is an expanded spectrum semisynthetic penicillin for parenteral administration, with a good activity against a wide range of pathogenic bacteria including most anaerobes. The pharmacokinetic parameters of mezlocillin were determined in serum and sputum at the first and the seventh day of treatment with 1 g/im/12 h in patients suffering from bronchopulmonary infections. In a second group of volunteer patients who had to undergo surgery for lung cancer, mezlocillin levels in pulmonary tissue and the corresponding serum levels were determined at different times after drug administration. The data obtained made it possible to obtain information on the penetration and clearance of this drug in the bronchopulmonary tract in comparison with that of the serum. The pharmacokinetic behaviour of mezlocillin ensures an efficient antibacterial action in the respiratory tract.