No abstract

Genes coding for production of the K1 polysaccharide capsule of Escherichia coli have been cloned. Complementation, insertion, and deletion analyses were used to localize the K1 genes and demonstrated that a minimum of 9 kilobases of DNA split into at least two gene blocks is involved in synthesis and assembly of the capsule. One of the gene blocks is responsible for biosynthesis of the polysaccharide, and the other is responsible for extracellular appearance of capsular material. Using cloned K1 genes as probes in Southern blot experiments, we detected homology to DNA from strains of E. coli capsular types K92, K7, and K100. In contrast, no homology was apparent between K1 genes and DNA from meningococcus group B, although the K1 and group B capsules are chemically and immunologically identical.

The 23 kilobase multiple drug resistance r determinant (r-det) of the R plasmid NRl is an IS 1-mediated transposon, Tn267 1. Drug-resistant Escherichia coli transductants isolated after infection with bacteriophage P 1 : : Tn267 1 derivatives carry the intact r-det in their chromosomes. Independently isolated transductants carry the r-det at different locations on the chromosome. From the E. coli chromosome, Tn267 1 can transpose to various locations on the phage P7 genome. Throughout these processes, r-det is maintained as a stable unit. Various possible molecular mechanisms, which all might contribute with characteristic frequencies to the transposition of Tn267 1, are discussed. The results presented are relevant to the understanding of mechanisms for a wide spreading of drug resistance genes.

The novel cisplatin analogue D-17872 was studied for its anticancer activity using in vivo and in vitro preclinical models. The compound at the sublethal dose of 215 mg/kg (ca. 50% of the approximate LD50) induced no nephrotoxic effect strong enough to increase the blood urea level in rats. It had good in vivo antitumor efficacy against murine P388 (max. ILS: D-17872 132%, cisplatin 55%) and L1210 leukemia (max. ILS: D-17872 43%, cisplatin 38%), L5222 leukemia of the rat (max. ILS: D-17872 163%, cisplatin 163%) and murine B16 melanoma. Activity against P388 leukemia substantially exceeded that of cisplatin. Moreover, the M5076 reticulum cell sarcoma implanted into the subrenal capsule and the DMBA-induced mammary tumor of the rat were inhibited by D-17872 to a greater extent than by cisplatin (min. T/C: D-17872 -3%, cisplatin 11%). Using clonogenic microassays, D-17872 was active in vitro against a variety of human and rodent tumor cell lines, albeit at higher concentrations than cisplatin (IC50 values: D-17872 2.6-12.7 mumol/l, cisplatin 0.13-0.42 mumol/l). Apart from its cytotoxic action it was able to induce in vitro differentiation of the human HL-60 and K562 and of the murine M1-T22 cell lines, while cisplatin induced differentiation only in the HL-60 cell line. Thus D-17872 exhibited a pharmacological and toxicological profile different from that of the parent compound. The results suggest that induction of differentiation contributes to the antineoplastic efficacy of this novel cisplatin derivative.

The so-called hematopoietic stem cells from mouse and human bone marrow can be induced in vitro to form colonies, provided that the appropriate hormones (colony stimulating factors, CSFs) and culture conditions have been selected. Such hematopoietic colony cultures are of interest for in vitro cytotoxicity testing of a great number of drugs. In fact, it has been increasingly recognized that serious side effects of many drugs involve injury to hematopoietic organs. Moreover, several hormones and inhibitors (including chalones) that regulate hematopoiesis have attracted clinical interest and their identity can be determined by such in vitro cultures. Therefore hematopoietic stem cells seem to provide identified targets to assay for either stimulatory, inhibitory, or cytotoxic drug effects.