Antimicrobial effects of novel siderophores linked to beta-lactam antibiotics.

As a strategy to increase the penetration of antibiotic drugs through the outer membrane of gram-negative pathogens, facilitated transport through siderophore receptors has been frequently exploited. Hydroxamic acids, catechols, or very close isosteres of catechols, which are mimics of naturally occurring siderophores, have been used successfully as covalently linked escorting moieties, but a much wider diversity of iron binding motifs exists. This observation, coupled to the relative lack of specificity of siderophore receptors, prompted us to initiate a program to identify novel, noncatechol siderophoric structures. We screened over 300 compounds for their ability to (1) support growth in low iron medium of a Pseudomonas aeruginosa siderophore biosynthesis deletion mutant, or (2) compete with a bactericidal siderophore-antibiotic conjugate for siderophore receptor access. From these assays we identified a set of small molecules that fulfilled one or both of these criteria. We then synthesized these compounds with functional groups suitable for attachment to both monobactam and cephalosporin core structures. Siderophore-beta-lactam conjugates then were tested against a panel of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus strains. Although several of the resultant chimeric compounds had antimicrobial activity approaching that of ceftazidime, and most compounds demonstrated very potent activity against their cellular targets, only a single compound was obtained that had enhanced, siderophore-mediated antibacterial activity. Results with tonB mutants frequently showed increased rather than decreased susceptibilities. suggesting that multiple factors influenced the intracellular concentration of the drugs.

Expression of chimeric granulocyte-macrophage colony-stimulating factor/interleukin 2 receptors in human cytotoxic T lymphocyte clones results in granulocyte-macrophage colony-stimulating factor-dependent growth.

Adoptive immunotherapy with ex vivo-expanded antigen-specific cytotoxic T lymphocytes (CTLs) has been shown to clear viral infections and eliminate tumors in murine models. Clinical trials have also reported promising data for the use of adoptive immunotherapy to treat cytomegalovirus (CMV) and Epstein-Barr viral (EBV) infections in bone marrow transplant recipients. For these indications, the need for ex vivo-expanded CTLs is often short lived, until the immune system is reconstituted by the donor transplant. In chronic disease settings, increased longevity of adoptively transferred CTLs and generation of memory will be necessary. The additional administration of helper functions normally supplied by antigen-specific T helper (Th) cells will probably be essential for long-term survival of adoptively transferred CTLs. Toward this goal of supplying helper functions, we transduced human CTLs with chimeric GM-CSFR/IL-2R receptors that deliver an IL-2 signal on binding GM-CSF. Clones expressing the chimeric receptors proliferated in response to GM-CSF. Stimulation with antigen induced GM-CSF production and resulted in an autocrine growth loop such that the CTL clones proliferated in the absence of exogenous cytokines. This type of genetic modification has potential for increasing the circulating half-life and, by extension, the efficacy of ex vivo-expanded CTLs.

Alternate promoter selection within a human cytomegalovirus immediate-early and early transcription unit (UL119-115) defines true late transcripts containing open reading frames for putative viral glycoproteins.

The human cytomegalovirus open reading frames (ORFs) UL119 through UL115 (UL119-115) are located downstream of the immediate-early 1 and 2 transcription units. The promoter upstream of UL119 is active at all times after infection and drives the synthesis of a spliced 3.1-kb mRNA. The viral mRNA initiates in UL119, contains UL119-117 and UL116, and terminates just downstream of UL115. True late transcripts that are detected only after viral DNA synthesis originate from this transcription unit. True late mRNAs of 2.1 kb, containing ORFs UL116 and UL115, and 1.2 kb, containing ORF UL115 only, are synthesized. The true late viral mRNAs are 3' coterminal with the 3.1-kb mRNA. This transcription unit is an example of late promoters nested within an immediate-early-early transcription unit. The gene products of UL119-117, UL116, and UL115 are predicted to be glycoproteins. Efficient expression of the downstream ORFs at late times after infection may be related to alternate promoter usage and downstream cap site selection.

A class III transcription factor composed of RNA.

It is generally assumed that the machinery that transcribes genes is composed entirely of polypeptides. However, in vitro transcription by silkworm RNA polymerase III requires a transcription factor that is not a polypeptide. This component, TFIIIR, is distinct from the previously identified transcription components: RNA polymerase III, and the accessory factors TFIIIA, TFIIIB, TFIIIC, and TFIIID. The newly discovered TFIIIR is a macromolecule that appears to be composed of RNA. It is resistant to heat, detergent, phenol, protease, and deoxyribonuclease, but it is sensitive to alkali and ribonuclease.

Identification and characterization of the human cytomegalovirus immediate-early region 2 gene that stimulates gene expression from an inducible promoter.

The human cytomegalovirus (HCMV) XbaI E cloned DNA fragment of approximately 20 kilobases can complement an adenovirus mutant (dl312) defective in the E1a viral gene product (D. J. Spector and M. J. Tevethia, Virology 151:329-338, 1986). This viral DNA fragment contains three immediate-early (IE) genes between 0.709 and 0.751 map units (M. F. Stinski, D. R. Thomsen, R. M. Stenberg, and L. C. Goldstein, J. Virol. 46:1-14, 1983). Two of the IE genes, IE1 and IE2, were isolated and tested for a role in regulating viral gene expression. Since HCMV early and late promoters require additional characterization, the chloramphenicol acetyl transferase (cat) gene, driven by the adenovirus E2 promoter, was used as an indicator of gene expression. cat expression from this heterologous viral promoter was shown to be stimulated by HCMV at early times after infection. The IE1 gene product did not function independently in activating this promoter. The IE2 gene products could independently stimulate the expression of a plasmid of a plasmid when the cat gene was placed downstream of the inducible E2 promoter (E2CAT). Five proteins of different sizes have been predicted to originate from IE2, depending on mRNA splicing. The protein products specified by the IE2 gene were characterized with an antibody to a synthetic peptide according to the open reading frame of exon 2. Three of the five proteins are encoded by exon 2. Three viral proteins of 82, 54, and 28 kilodaltons (kDa) were detected. The exons contained in the region designated as IE2a have open reading frames that could code for two of the smaller proteins of 27 and 30 kDa. This region, when driven by the HCMV enhancer, could independently stimulate gene expression from E2CAT to a high level. A plasmid with the HCMV enhancer upstream of exons, that could code for the HCMV IE2 proteins of 48 and 51 kDa, as well as 27- and 30-kDa proteins, also stimulated E2CAT expression but at a lower level. The activity of this plasmid was augmented by the IE1 gene product, despite the fact that the latter gene product alone was inactive. It is proposed that the HCMV IE region 2 gene products are involved in the regulation of viral or host cell promoters either independently or in combination with other HCMV IE proteins.

Multiple spliced and unspliced transcripts from human cytomegalovirus immediate-early region 2 and evidence for a common initiation site within immediate-early region 1.

Human cytomegalovirus immediate-early (IE) region 2 (0.732 to 0.740 map unit) begins 35 nucleotides downstream of IE region 1 (Stenberg et al., J. Virol. 49:190-199, 1984). A series of mRNAs that have different splicing patterns are transcribed from region 2. There is an unspliced 1,589-nucleotide exon present in minor amounts and two spliced exons (836 and 289 nucleotides) present in larger amounts. The IE region 2 exons were found to be spliced onto the first three exons of region 1. Therefore, under IE conditions the region 1 promoter-regulatory region can promote transcription of region 2. Promoter sequences (i.e., CAAT and TATA boxes) are found upstream of the 5' end of IE region 2 but presumably function poorly at IE times after infection. The transcriptional regulation of these IE genes and the possible functional roles of the proteins are discussed. We postulate that a series of unique but related proteins are made from the region 2 transcripts. Some of these proteins should contain the same 169 amino-terminal residues as the major IE 72-kilodalton protein encoded by IE region 1 (Stenberg et al., J. Virol. 49:190-199, 1984). Variations in the amino acid sequences of the region 2 proteins could occur at either the amino terminus, the carboxy terminus, or both termini.