Ross E. Longley

Tubulin polymerizing activity of dictyostatin-1, a polyketide of marine sponge origin.

Dictyostatin-1 had previously been isolated from a marine sponge of the genus Spongia sp. and described as a cytotoxic agent to murine and human cancer cells, but its mechanism of activity was unknown. In a routine screening assay used to detect cytotoxic compounds of marine origin, dictyostatin-1 was identified as a highly active component in an extract from a Lithistida sponge and exploration into its pharmacology was pursued. Initial studies demonstrated that dictyostatin-1 arrested cells in the G(2)/M phase of the cell cycle. Staining of these cells with antitubulin revealed cells having multiple aster formations and microtubule matrix bundling patterns similar to that seen in cells exposed to paclitaxel. Dictyostatin-1 was able to induce the polymerization of purified bovine brain tubulin in vitro and the polymerized tubulin remained stable at cold temperatures. Dictyostatin-1 also proved to be highly potent in two paclitaxel-resistant human cancer cell lines expressing active P-glycoprotein. Together, these results indicate that dictyostatin-1 is a potent inducer of tubulin polymerization and retains activity in cells expressing the P-glycoprotein efflux pump.

Discodermolide—a New, Marine-derived Immunosuppressive Compound: I. In Vitro Studies

The in vitro immunosuppressive properties of a novel, marine-derived compound, discodermolide, are reported here. Discodermolide suppressed the proliferative responses of splenocytes in the murine two-way mixed lymphocyte reaction (MLR) and concanavalin A stimulated cultures, with IC50 values of 0.24 μM and 0.19 μM, respectively. There was no evidence of cyto-toxicity for murine splenocytes at concentrations of discodermolide as high as 1.26 μM. Similarly, discodermolide suppressed the proliferative responses of human peripheral blood leukocytes (PBL) in the two-way MLR, and Con A and phytohemagglutinin mitogenesis. The IC50 values were 5.65 μM, 28.02 μM, and 30.12 μM for the MLR, Con A, and PHA mitogenic responses, respectively. There was no evidence of cytotozicity toward human PBL at discodermolide concentrations as high as 80.64 μM. Discodermolide was equally effective, compared with cyclosporine, in suppressing the PMA-ionomycin induced proliferation of purified, murine T cells, with IC50 values of 9.0 nM and 14.0 nM for discoder molide and CsA, respectively. The production of IL-2 by PMA-ionomycin stimulated T cells was not inhibited by discodermolide; however, the percentage of IL-2 receptor-bearing cells as measured by immunofluorescence with 7D4 antibody, specific for the 55-kDa chain (p55) comprising the murine IL-2 receptor, was reduced. The expression of a similar chain comprising the human IL-2 receptor (Tac antigen, p55) by PHA or Con-A-stimulated PBL was similarly suppressed by discodermolide. The precise mechanism of action of discodermolide remains to be elucidated.

Immunosuppression by discodermolide.

In summary, discodermolide, a novel, marine-derived compound, is a potent in vitro and in vivo immunosuppressive agent. Discodermolide blocks cellular proliferation in lymphoid and nonlymphoid cells. This blocking action is not due to cytotoxicity. Blockage of cell proliferation by discodermolide appears to occur at the G2/M interface of the cell cycle, similar to that observed with other types of antiproliferative drugs (i.e., doxorubicin). The cell cycle block appears to be reversible, as cells recover normal cycling patterns within 48 h after removal of the compound. Additional work with this compound is targeted towards determining the exact nature of discodermolides mitotic block and is currently under way.

Semisynthetic analogues of the microtubule-stabilizing agent discodermolide: Preparation and biological activity

A series of 12 semisynthetic discodermolide analogues, 2-13, have been prepared using natural (+)-discodermolide (1) and evaluated for in vitro cytotoxicity against cultured murine P-388 leukemia and A-549 human adenocarcinoma cells. These semisynthetic analogues showed a significant variation of cytotoxicity and confirmed the importance of the C-7 through C-19 molecular fragment for potency. Specifically, these analogues suggested the importance of the C-11 and C-17 hydroxyl groups and the C-13 double bond for the potency of discodermolide. The preparation, structure elucidation, and biological activity of these new analogues are described.

Antiproliferative and immunosuppressive properties of microcolin A, a marine-derived lipopeptide

The immunosuppressive effects of microcolin A, a lipopeptide extracted from the marine blue green alga Lyngbya majuscula were investigated. Microcolin A suppressed concanavalin A (IC50 = 5.8 nM), phytohemagglutinin (IC50 = 12.5 nM) and lipopolysaccharide (IC50 = 8.0 nM) induced proliferation of murine splenocytes. Mixed lymphocyte reaction (IC50 = 5.0 nM), anti-IgM (mu-chain specific) (IC50 = 10.0 nM), and phorbol 12-myristate 13-acetate plus ionomycin (IC50 = 5.8 nM) stimulation of murine splenocytes were all similarly suppressed by microcolin A. The inhibitory activity of microcolin A was time-dependent and reversible and was not associated with a reduction in cell viability. Moreover, microcolin A not only inhibited IL-2 production and IL-2 receptor expression by concanavalin A activated splenocytes, but also suppressed in vitro antibody responsiveness to keyhole limpet hemocyanin. These results indicate that microcolin A is a potent immunosuppressive and antiproliferative agent.

Eryloside E from an atlantic sponge Erylus goffrilleri

Abstract A glycoside, which we call eryloside E ( 1 ), was isolated from the marine sponge Erylus goffrilleri and characterized by spectroscopic methods. Eryloside E possesses a rare penasterol nucleus with a t -butyl substituent on the side chain and three sugar molecules attached through carbons 3 and 30.

Induction of apoptosis in mouse thymocytes by microcolin A and its synthetic analog

Microcolin A (Mic-1), a marine-derived compound, has been shown to be a novel antiproliferative and immunosuppressive agent. We investigated the ability of Mic-1 and its chemosynthetic analog, microcolin A3 (Mic-3), to induce apoptosis in murine thymocytes. Following incubation of the cells with Mic-1 (10-100 nM) or Mic-3 (10-100 nM), internucleosomal DNA fragmentation in apoptotic cells was detected by agarose gel electrophoresis and the diphenylamine (DPA) assay; the presence of hypodiploid nuclei assessed by propidium iodide (PI) staining; and the percentages of apoptotic and necrotic cells quantified by morphological observation and fluorescein labeled annexin-V binding. Our results show that both Mic-1 and Mic-3 are potent inducers of apoptosis in thymocytes depending on drug concentration and time of exposure, with Mic-3 being more potent than Mic-1 in the induction of apoptosis. Furthermore, flow cytometric analysis using monoclonal antibodies specific to thymocyte subpopulations showed that the proportion of the early immature CD4+ CD8+ T-cell subpopulation in thymocytes was selectively decreased by both agents with a corresponding increase of other subpopulations, indicating that CD4+ CD8+ T cells are the most likely targets of Mic-1 and Mic-3. These in vitro results suggest that the antiproliferative and immunosuppressive properties of both compounds are possibly associated with apoptosis-inducing events and imply that they may have additional potential value as antineoplastic agents.

Tubercidin, A Cytotoxic Agent from the Marine Sponge Caulospongia biflabellata

Tubercidin (1), a known nucleoside antibiotic, was isolated as the major metabolite from a marine sponge Caulospongia biflabellata. Compound 1 exhibited potent cytotoxic activity against P388 and A549 tumor cells. The isolation, structure elucidation and biological activities of tubercidin (1) are described. This is the first report of the isolation of tubercidin from a marine organism.

6-Hydroxydiscodermindole, A New Discodermindole from the Marine Sponge Discodermia polydiscus

6-Hydroxydiscodermindole (2), a new discodermindole analogue, has been isolated from the deep-water marine sponge Discodermia polydiscus. It showed marginal in vitro cytotoxicity against cultured murine P388 leukemia cells. The isolation, structure elucidation and cytotoxicity of 6-hydroxydiscodermindole (2) is described.