-
[show abstract]
[hide abstract]
ABSTRACT: During the course of a mechanism-based screening program designed to identify new microtubule-disrupting agents from natural products, we identified a crude extract from Tacca chantrieri that initiated Taxol-like microtubule bundling. Bioassay-directed purification of the extract yielded the highly oxygenated steroids taccalonolides E and A. The taccalonolides caused an increased density of cellular microtubules in interphase cells and the formation of thick bundles of microtubules similar to the effects of Taxol. Mitotic cells exhibited abnormal mitotic spindles containing three or more spindle poles. The taccalonolides were evaluated for antiproliferative effects in drug-sensitive and multidrug-resistant cell lines. The data indicate that taccalonolide E is slightly more potent than taccalonolide A in drug-sensitive cell lines and that both taccalonolides are effective inhibitors of cell proliferation. Both taccalonolides are poorer substrates for transport by P-glycoprotein than Taxol. The ability of the taccalonolides to circumvent mutations in the Taxol-binding region of beta-tubulin was examined using the PTX 10, PTX 22, and 1A9/A8 cell lines. The data suggest little cross-resistance of taccalonolide A as compared with Taxol, however, the data from the PTX 22 cell line indicate a 12-fold resistance to taccalonolide E, suggesting a potential overlap of binding sites. Characteristic of agents that disrupt microtubules, the taccalonolides caused G(2)-M accumulation, Bcl-2 phosphorylation, and initiation of apoptosis. The taccalonolides represent a novel class of plant-derived microtubule-stabilizers that differ structurally and biologically from other classes of microtubule-stabilizers.
Cancer Research 07/2003; 63(12):3211-20. · 7.86 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Symplostatin 1, an analog of dolastatin 10, was recently isolated from cyanobacteria of the genus Symploca. Symplostatin 1 is a potent inhibitor of cell proliferation with IC(50) values in the low nanomolar range and it exhibits efficacy against a variety of cancer cell types. Symplostatin 1 caused the formation of abnormal mitotic spindles and accumulation of cells in metaphase at concentrations that had only minor effects on interphase microtubules. At higher concentrations, symplostatin 1 caused the loss of interphase microtubules. Cell cycle analysis revealed that symplostatin 1 caused G(2)/M arrest, consistent with its effects on mitotic spindles. Symplostatin 1 initiated the phosphorylation of Bcl-2, formation of micronuclei and activation of caspase 3, indicating induction of apoptosis. The cellular effects of symplostatin 1 are consistent with other antimitotic tubulin-targeting drugs. Tubulin polymerization experiments indicated that symplostatin 1 potently inhibits the assembly of purified tubulin, suggesting that tubulin may be its intracellular target. Some microtubule-targeting agents are reported to have antiangiogenic activity and therefore the effects of symplostatin 1 on endothelial cell proliferation and invasion were evaluated. Symplostatin 1 was found to be a potent inhibitor of both endothelial cell proliferation and invasion. Because of its potent and broad activity in vitro, symplostatin 1 was evaluated in vivo. Symplostatin 1 was active against murine colon 38 and murine mammary 16/C; however, it was poorly tolerated and the mice were slow to recover from the toxicity. The data indicate that symplostatin 1 has a mechanism of action similar to dolastatin 10.
International Journal of Cancer 05/2003; 104(4):512-21. · 5.44 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 2-Methoxyestradiol (2-ME2) is a natural estrogen metabolite that, while devoid of estrogenic effects, has both antiangiogenic and antitumor effects. 2-ME2 is currently being evaluated in Phase I and Phase II clinical trials for the treatment of multiple types of cancer. Novel analogues of 2-ME2 were tested for activities that predict antiangiogenic and antitumor effects. Selected analogues were tested for inhibitory activity against endothelial cell proliferation and invasion. The results show that these analogues are effective inhibitors of endothelial cell activities that may predict antiangiogenic activity, and one analogue, 2-methoxy-14-dehydroestradiol (14-dehydro-2-ME2), was 6-15-fold more potent than the parental compound in these assays. The analogues were also evaluated for inhibition of proliferation and cytotoxicity against multiple tumor cell lines and found to be potent and effective. 14-Dehydro-2-ME2 was approximately 15-fold more potent than 2-ME2 against various tumor cell lines, and 2-methoxy-15-dehydroestradiol was particularly effective against DU 145 and PC3 prostate cancer cell lines. In vivo antitumor activity was observed for the three analogues tested in the murine xenograft MDA-MB-435 model; however, 2-ME2 provided no antitumor activity in this trial. The two most effective analogues, 14-dehydro-2-ME2 and 2-methoxyestradiol-15 alpha,16 alpha-acetonide, provided 29.4% and 26.7% inhibition of tumor burden, respectively. Mechanism of action studies indicate that the analogues cause mitotic spindle disruption, mitotic arrest, microtubule depolymerization, and inhibition of the assembly of purified tubulin similar to the effects of 2-ME2. Consistent with antimitotics that inhibit the dynamic instability of tubulin and initiate apoptosis, these novel 2-ME2 analogues cause Bcl-2 phosphorylation and activation of mitogen-activated protein kinase signaling pathways.
Cancer Research 05/2003; 63(7):1538-49. · 7.86 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The syntheses and antimitotic activity of several novel 2-methoxyestradiol analogs are described. Structural modifications investigated include introduction of additional unsaturation in rings B and D; inversion at C-13; and substitution at the C-2, C-15, C-16, and C-7 alpha positions. Of 15 analogs synthesized, 2 have demonstrated superior biological activities compared to 2-methoxyestradiol.
Steroids 01/2003; 67(13-14):1079-89. · 2.83 Impact Factor
