Christine E. Salomon

Natural products as leads for tuberculosis drug development

New therapeutics are urgently needed to combat the immense disease burden of tuberculosis and related mycobacterial diseases worldwide. Natural products continue to provide leads for the development of novel drugs to treat the rapidly growing numbers of patients with multi- and extensively-drug resistant tuberculosis. This review presents natural products and synthesized analogues with anti-mycobacterial activity published between 2006 through 2009. Structure activity relationships, synthetic analogues and newly reported activities of known compounds reported during this period are also included.

Structure and Cytotoxicity of Arnamial and Related Fungal Sesquiterpene Aryl Esters

We report on the structure elucidation of arnamial, a new Delta(2,4)-protoilludane everninate ester from the fungus Armillaria mellea, and on the apoptotic activity of arnamial as well as the cytotoxic activity of structurally related compounds on selected human cancer cells. Arnamial showed cytotoxicity against Jurkat T cells, MCF-7 breast adenocarcinoma, CCRF-CEM lymphoblastic leukemia, and HCT-116 colorectal carcinoma cells at IC50 = 3.9, 15.4, 8.9, and 10.7 microM, respectively, and the related aryl ester melledonal C showed cytotoxic activity against CCRF-CEM cells (IC50 = 14.75 microM). [1,2-13C2]Acetate feeding supports a polyketide origin of the orsellinic acid moiety of arnamial.

Growth inhibition and apoptosis in cancer cells induced by polyphenolic compounds of Acacia hydaspica : Involvement of multiple signal transduction pathways

Acacia hydaspica R. Parker is known for its medicinal uses in multiple ailments. In this study, we performed bioassay-guided fractionation of cytotoxic compounds from A. hydaspica and investigated their effects on growth and signaling activity in prostate and breast cancer cell lines. Four active polyphenolic compounds were identified as 7-O-galloyl catechin (GC), catechin (C), methyl gallate (MG), and catechin-3-O-gallate (CG). The four compounds inhibited prostate cancer PC-3 cell growth in a dose-dependent manner, whereas CG and MG inhibited breast cancer MDA-MB-231 cell growth. All tested compounds inhibited cell survival and colony growth in both cell lines, and there was evidence of chromatin condensation, cell shrinkage and apoptotic bodies. Further, acridine orange, ethidium bromide, propidium iodide and DAPI staining demonstrated that cell death occurred partly via apoptosis in both PC-3 and MDA-MB-231 cells. In PC-3 cells treatment repressed the expression of anti-apoptotic molecules Bcl-2, Bcl-xL and survivin, coupled with down-regulation of signaling pathways AKT, NFκB, ERK1/2 and JAK/STAT. In MDA-MB-231 cells, treatment induced reduction of CK2α, Bcl-xL, survivin and xIAP protein expression along with suppression of NFκB, JAK/STAT and PI3K pathways. Our findings suggest that certain polyphenolic compounds derived from A. hydaspica may be promising chemopreventive/therapeutic candidates against cancer.

Pharmacophore and structure–activity relationships of integrase inhibition within a dual inhibitor scaffold of HIV reverse transcriptase and integrase

Rational design of dually active inhibitors against human immunodeficiency virus (HIV) reverse transcriptase (RT) and integrase (IN) has proved viable with 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT) type of non-nucleoside RT inhibitors (NNRTIs). To establish the pharmacophore and study the structure-activity relationships (SAR) of integrase inhibition within a previously disclosed RT/IN dual inhibitor scaffold, new analogues featuring substitution at different sites of the HEPT ring were designed and synthesized. These studies have revealed an IN inhibition pharmacophore that is merged with the known RT pharmacophore through a shared C-6 benzyl group. Further SAR also demonstrated that optimal IN inhibition within our dual inhibitor scaffold requires a regiospecific (N-1) diketoacid (DKA)-carrying pendant with a certain length.

Biosynthesis of ubiquinone compounds with conjugated prenyl side chains

ABSTRACT Enzymatic steps from two different biosynthetic pathways were combined in Escherichia coli, directing the synthesis of a new class of biomolecules—ubiquinones with prenyl side chains containing conjugated double bonds. This was achieved by the activity of a C30 carotenoid desaturase, CrtN, from Staphylococcus aureus, which exhibited an inherent flexibility in substrate recognition compared to other carotenoid desaturases. By utilizing the known plasticity of E. colis native ubiquinone biosynthesis pathway and the unusual activity of CrtN, modified ubiquinone structures with prenyl side chains containing conjugated double bonds were generated. The side chains of the new structures were confirmed to have different degrees of desaturation by mass spectrometry and nuclear magnetic resonance analysis. In vivo 14C labeling and in vitro activity studies showed that CrtN desaturates octaprenyl diphosphates but not the ubiquinone compounds directly. Antioxidant properties of conjugated side chain ubiquinones were analyzed in an in vitro β-carotene-linoleate model system and were found to be higher than the corresponding unmodified ubiquinones. These results demonstrate that by combining pathway steps from different branches of biosynthetic networks, classes of compounds not observed in nature can be synthesized and structural motifs that are functionally important can be combined or enhanced.

Subinhibitory Antibiotic Concentrations Mediate Nutrient Use and Competition among Soil Streptomyces

Though traditionally perceived as weapons, antibiotics are also hypothesized to act as microbial signals in natural habitats. However, while subinhibitory concentrations of antibiotics (SICA) are known to shift bacterial gene expression, specific hypotheses as to how SICA influence the ecology of natural populations are scarce. We explored whether antibiotic ‘signals’, or SICA, have the potential to alter nutrient utilization, niche overlap, and competitive species interactions among Streptomyces populations in soil. For nine diverse Streptomyces isolates, we evaluated nutrient utilization patterns on 95 different nutrient sources in the presence and absence of subinhibitory concentrations of five antibiotics. There were significant changes in nutrient use among Streptomyces isolates, including both increases and decreases in the capacity to use individual nutrients in the presence vs. in the absence of SICA. Isolates varied in their responses to SICA and antibiotics varied in their effects on isolates. Furthermore, for some isolate-isolate-antibiotic combinations, competition-free growth (growth for an isolate on all nutrients that were not utilized by a competing isolate), was increased in the presence of SICA, reducing the potential fitness cost of nutrient competition among those competitors. This suggests that antibiotics may provide a mechanism for bacteria to actively minimize niche overlap among competitors in soil. Thus, in contrast to antagonistic coevolutionary dynamics, antibiotics as signals may mediate coevolutionary displacement among coexisting Streptomyces, thereby hindering the emergence of antibiotic resistant phenotypes. These results contribute to our broad understanding of the ecology and evolutionary biology of antibiotics and microbial signals in nature.

Pathogen variation and urea influence selection and success of Streptomyces mixtures in biological control.

Success in biological control of plant diseases remains inconsistent in the field. A collection of well-characterized Streptomyces antagonists (n = 19 isolates) was tested for their capacities to inhibit pathogenic Streptomyces scabies (n = 15 isolates). There was significant variation among antagonists in ability to inhibit pathogen isolates and among pathogens in their susceptibility to inhibition. Only one antagonist could inhibit all pathogens, and antagonist-pathogen interactions were highly specific, highlighting the limitations of single-strain inoculum in biological control. However, the collection of pathogens could be inhibited by several combinations of antagonists, suggesting the potential for successful antagonist mixtures. Urea generally increased effectiveness of antagonists at inhibiting pathogens in vitro (increased mean inhibition zones) but its specific effects varied among antagonist-pathogen combinations. In greenhouse trials, urea enhanced the effectiveness of antagonist mixtures relative to individual antagonists in controlling potato scab. Although antagonist mixtures were frequently antagonistic in the absence of urea, all n= 2 and n = 3 antagonist-isolate combinations were synergistic in the presence of urea. This work provides insights into the efficacy of single- versus multiple-strain inocula in biological control and on the potential for nutrients to influence mixture success.

Antiproliferative activities of halogenated thieno[3,2-d]pyrimidines

The in vitro evaluation of thieno[3,2-d]pyrimidines identified halogenated compounds 1 and 2 with antiproliferative activity against three different cancer cell lines. A structure activity relationship study indicated the necessity of the chlorine at the C4-position for biological activity. The two most active compounds 1 and 2 were found to induce apoptosis in the leukemia L1210 cell line. Additionally, the compounds were screened against a variety of other microbial targets and as a result, selective activity against several fungi was also observed. The synthesis and preliminary biological results are reported herein.

Sagitol, a pyridoacridine alkaloid from the sponge Oceanapia sagittaria

The sponge Oceanapia sagittaria from Palau contained the known sponge metabolite dercitamide (1) and a new pyridoacridine alkaloid sagitol (2). The structure of sagitol (2) was determined by interpretation of spectral data and confirmed by oxidation of dercitamide (1). CD measurements suggest that sagitol (2) is not an artifact.

Synthesis and evaluation of N-alkyl-9-aminoacridines with antibacterial activity.

A series of 9-alkylaminoacridines were synthesized and evaluated for activity against two strains of methicillin-resistant and one strain of methicillin-sensitive Staphylococcus aureus. Results are presented that show a clear structure activity relationship between the N-alkyl chain length and antibacterial activity with peak MIC99 values of 2-3 μM for alkyl chains ranging from 10 to 14 carbons in length. Although prior work has linked the function of acridine-based compounds to intercalation and topoisomerase inhibition, the present results show that 9-alkylaminoacridines likely function as amphiphilic membrane-active disruptors potentially in a similar manner as quaternary ammonium antimicrobials.