John H. Cardellina

The guttiferones, HIV-inhibitory benzophenones from Symphonia globulifera, Garcinia livingstonei, Garcinia ovalifolia and Clusia rosea

Abstract Extracts from species of the tropical plant genera Symphonia , Garcinia and Clusia (Guttiferae) have yielded a series of new polyisoprenylated benzophenone derivatives named guttiferones A–E (1–5). Structural assignments were based on detailed spectral analysis. These compounds inhibit the cytophatic effects of in vitro HIV infection.

A marine Micrococcus produces metabolites ascribed to the sponge Tedania ignis

Extracts of the spongeTedania ignis have been reported to contain several diketopiperazines. As part of an investigation of the commensal and symbiotic microflora of sponges, we have consistently isolated, from specimens ofT. ignis, aMicrococcus sp. which produces diketopiperazines in laboratory cultural media. This is the first demonstration that a bacterium associated with a sponge produces secondary metabolites ascribed to the sponge host.

ANTIVIRAL ACTIVITY OF CULTURED BLUE‐GREEN ALGAE (CYANOPHYTA)1

Lipophilic and hydrophilic extracts from approximately 600 strains of cultured cyanophytes, representing some 300 species, were examined for antiviral activity against three pathogenic viruses. Approximately 10% of the cultures produced substances that caused significant reduction in cytopathic effect normally associated with viral infection. The screening program identified the order Chroococcales as commonly producing antiviral agents.

Cytotoxic and tubulin-interactive hemiasterlins from Auletta sp. and Siphonochalina spp. sponges.

Chemical and biological investigations of extracts from the sponge genus Auletta and two collections of Siphonochalina sp. have shown these organisms to be producers of the potent hemiasterlin class of antitumor agents. In addition to the previously known hemiasterlin (1) and hemiasterlin A (2), a new analogue, hemiasterlin C (3), was isolated and identified. The structures of 1 and 2 were assigned based on comparison to literature values, and 3 was identified on the basis of 1H NMR, 13C NMR, COSY, HSQC, and HMBC experiments. The cytotoxic and antitubulin activities of 1-3 were evaluated. In a comparative assay for inhibition of tubulin polymerization, the hemiasterlins were more potent than dolastatin 15 and equipotent with cryptophycin 1, but were somewhat less potent than dolastatin 10.

Centaureidin, a cytotoxic flavone from Polymnia fruticosa, inhibits tubulin polymerization

Abstract The characteristics pattern of differential cytotoxicity of a crude extract of the tropical plant Polymnia fruticosa was found to be similar to those of known tubulin-interactive compounds. Fractionation of the extract led to centraureidin as the major cytotoxic principle. Centaureidin inhibited tubulin polymerization, inhibited the binding of [3H]-colchicine to tubulin, and induced mitotic figure formation in whole cells at cytotoxic concentrations. This is the first known example of a flavone with antimitotic activity.

Cellular Inhibition of Checkpoint Kinase 2 (Chk2) and Potentiation of Camptothecins and Radiation by the Novel Chk2 Inhibitor PV1019 [7-Nitro-1H-indole-2-carboxylic acid {4-[1-(guanidinohydrazone)-ethyl]-phenyl}-amide]

Chk2 is a checkpoint kinase involved in the ataxia telangiectasia mutated pathway, which is activated by genomic instability and DNA damage, leading to either cell death (apoptosis) or cell cycle arrest. Chk2 provides an unexplored therapeutic target against cancer cells. We recently reported 4,4′-diacetyldiphenylurea-bis(guanylhydrazone) (NSC 109555) as a novel chemotype Chk2 inhibitor. We have now synthesized a derivative of NSC 109555, PV1019 (NSC 744039) [7-nitro-1H-indole-2-carboxylic acid {4-[1-(guanidinohydrazone)-ethyl]-phenyl}-amide], which is a selective submicromolar inhibitor of Chk2 in vitro. The cocrystal structure of PV1019 bound in the ATP binding pocket of Chk2 confirmed enzymatic/biochemical observations that PV1019 acts as a competitive inhibitor of Chk2 with respect to ATP. PV1019 was found to inhibit Chk2 in cells. It inhibits Chk2 autophosphorylation (which represents the cellular kinase activation of Chk2), Cdc25C phosphorylation, and HDMX degradation in response to DNA damage. PV1019 also protects normal mouse thymocytes against ionizing radiation-induced apoptosis, and it shows synergistic antiproliferative activity with topotecan, camptothecin, and radiation in human tumor cell lines. We also show that PV1019 and Chk2 small interfering RNAs can exert antiproliferative activity themselves in the cancer cells with high Chk2 expression in the NCI-60 screen. These data indicate that PV1019 is a potent and selective inhibitor of Chk2 with chemotherapeutic and radiosensitization potential.

Zerumbone, an HIV-Inhibitory and Cytotoxic Sesquiterpene of Zingiber Aromaticum and Z. Zerumbet

Abstract Zerumbone and 3“,4”-O-diacetylafzelin were isolated from organic extracts of rhizomes of Zingiber aromaticum (Zingiberaceae), and zerumbone and 4-O-acetylafzelin were obtained from organic extracts of entire plants of Z. zerumbet. Zerumbone exhibited HIV-inhibitory and cytotoxic activities, while the afzelins were inactive in both assays.

‘Biomimetic’ oxidative dimerization of korupensamine A: Completion of the first total synthesis of michellamines A, B, and C

Abstract A first synthetic access to michellamine A (1), a C2-symmetric antiviral naturally occurring quateraryl, is described, by oxidative ‘dimeriza

Identification of a Bis-guanylhydrazone [4,4'-Diacetyldiphenylurea-bis(guanylhydrazone); NSC 109555] as a novel chemotype for inhibition of Chk2 kinase.

Chk2 is a protein kinase involved in the ATM-dependent checkpoint pathway (http://discover.nci.nih.gov/mim). This pathway is activated by genomic instability and DNA damage and results in either cell cycle arrest, to allow DNA repair to occur, or cell death (apoptosis). Chk2 is activated by ATM-mediated phosphorylation and autophosphorylation and in turn phosphorylates its downstream targets (Cdc25A, Cdc25C, BRCA1, p53, Hdmx, E2F1, PP2A, and PML). Inhibition of Chk2 has been proposed to sensitize p53-deficient cells as well as protect normal tissue after exposure to DNA-damaging agents. We have developed a drug-screening program for specific Chk2 inhibitors using a fluorescence polarization assay, immobilized metal ion affinity-based fluorescence polarization (IMAP). This assay detects the degree of phosphorylation of a fluorescently linked substrate by Chk2. From a screen of over 100,000 compounds from the NCI Developmental Therapeutics Program, we identified a bis-guanylhydrazone [4,4′-diacetyldiphenylureabis(guanylhydrazone); NSC 109555] as a lead compound. In vitro data show the specific inhibition of Chk2 kinase activity by NSC 109555 using in vitro kinase assays and kinase-profiling experiments. NSC 109555 was shown to be a competitive inhibitor of Chk2 with respect to ATP, which was supported by docking of NSC 109555 into the ATP binding pocket of the Chk2 catalytic domain. The potency of NSC 109555 was comparable with that of other known Chk2 inhibitors, such as debromohymenialdisine and 2-arylbenzimidazole. These data define a novel chemotype for the development of potent and selective inhibitors of Chk2. This class of drugs may ultimately be useful in combination with current DNA-damaging agents used in the clinic.

Cell type-specific, topoisomerase II-dependent inhibition of hypoxia-inducible factor-1alpha protein accumulation by NSC 644221.

Purpose: The discovery and development of small-molecule inhibitors of hypoxia-inducible factor-1 (HIF-1) is an attractive, yet challenging, strategy for the development of new cancer therapeutic agents. Here, we report on a novel tricyclic carboxamide inhibitor of HIF-1α, NSC 644221. Experimental Design: We investigated the mechanism by which the novel compound NSC 644221 inhibited HIF-1α. Results: NSC 644221 inhibited HIF-1–dependent, but not constitutive, luciferase expression in U251-HRE and U251-pGL3 cells, respectively, as well as hypoxic induction of vascular endothelial growth factor mRNA expression in U251 cells. HIF-1α, but not HIF-1β, protein expression was inhibited by NSC 644221 in a time- and dose-dependent fashion. Interestingly, NSC 644221 was unable to inhibit HIF-1α protein accumulation in the presence of the proteasome inhibitors MG132 or PS341, yet it did not directly affect the degradation of HIF-1α as shown by experiments done in the presence of cyclohexamide or pulse-chase labeling using [35S]methionine. In contrast, NSC 644221 decreased the rate of HIF-1α translation relative to untreated controls. Silencing of topoisomerase (topo) IIα, but not topo I, by specific small interfering RNA completely blocked the ability of NSC 644221 to inhibit HIF-1α. The data presented show that topo II is required for the inhibition of HIF-1α by NSC 644221. Furthermore, although NSC 644221 induced p21 expression, γH2A.X, and G2-M arrest in the majority of cell lines tested, it only inhibited HIF-1α in a distinct subset of cells, raising the possibility of pathway-specific “resistance” to HIF-1 inhibition in cancer cells. Conclusions: NSC 644221 is a novel HIF-1 inhibitor with potential for use as both an analytic tool and a therapeutic agent. Our data provide a strong rationale for pursuing the preclinical development of NSC 644221 as a HIF-1 inhibitor.