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6. Increased intracellular Ca2+ signaling caused by the antitumor agent helenalin and its analogues.

Author

Powis, Garth, Gallegos, Alfred, Abraham, Robert, Ashendel, Curtis, Zalkow, Leon, Grindey, Gerald, Bonjouklian, Rosanne, Powis, G, Gallegos, A, Abraham, R T, Ashendel, C L, Zalkow, L H, Grindey, G B, and Bonjouklian, R

Abstract

The antitumor sesquiterpene lactone helenalin, which is found in species of the plant genus Helenium, caused a marked potentiation of the increases in intracellular free Ca2+ concentration ([Ca2+]i) produced by mitogens such as vasopressin, bradykinin, and platelet-derived growth factor in Swiss mouse 3T3 fibroblasts. Removing external Ca2+ partly attenuated the increased [Ca2+]i responses caused by helenalin. The increased [Ca2+]i responses occurred at concentrations of helenalin that inhibited cell proliferation. At higher concentrations, helenalin inhibited the [Ca2+]i responses. No change in resting [Ca2+]i was caused by helenalin even at high concentrations. Other helenalin analogues also increased the [Ca2+]i response. Helenalin did not inhibit protein kinase C (PKC) and PKC appeared to play a minor role in the effects of helenalin on [Ca2+]i responses in intact cells. Studies with saponin-permeabilized HT-29 human colon carcinosarcoma cells indicated that helenalin caused an increased accumulation of Ca2+ into nonmitochondrial stores and that the potentiating effect of helenalin on mitogen-stimulated [Ca2+]i responses was due in part to an increase in the inositol-(1,4,5)-trisphosphate-mediated release of Ca2+ from these stores. [ABSTRACT FROM AUTHOR]

Published
1994
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16. Syntheses and Biological Activities of a Novel Group of Steroidal Derived Inhibitors for Human CDC25A Protein Phosphatase<SUP>1</SUP><BBR RID="jm0004401b00001">

Author

Peng, H., Xie, W., Otterness, D. M., Cogswell, J. P., McConnell, R. T., Carter, H. L., Powis, G., Abraham, R. T., and Zalkow, L. H.

Abstract

Silica gel supported pyrolysis of an azido-homo-oxa steroid led to rearrangement, presumably by a mechanism similar to that of solution phase Schmidt fragmentation, to produce a group of novel inhibitors for the oncogenic cell cycle regulator Cdc25A phosphatase. Cyano-containing acid 17, one of the best inhibitors in this group, inhibited the activity of Cdc25A protein phosphatase reversibly and noncompetitively with an IC50 value of 2.2 μM. Structure−activity relationships revealed that a phosphate surrogate such as a carboxyl or a xanthate group is required for inhibitory activity, and a hydrophobic alkyl chain, such as the cholesteryl side chain, contributes greatly to the potency. Without the cyano group, acid 26 and xanthate 27 were found to be more selective over Cdc25A (IC50 = 5.1 μM and 1.1 μM, respectively) than toward CD45 (IC50 > 100 μM, in each case), a receptor protein tyrosine phosphatase. Several of these inhibitors showed antiproliferative activities in the NCI 60-human tumor cell line screen. These steroidal derived Cdc25 inhibitors provide unique leads for the development of dual-specificity protein phosphatase inhibitors.

Published
2001

20. Evidence for the formation of exoand endoaziridines in the reaction of cis–endoand cis–exo-bicyclo[2•2•1]-5-heptene-2,3-dicarboxylic anhydride and benzenesulfonyl azide

Author

Oehlschlager, A. C. and Zalkow, L. H.

Abstract

Benzenesulfonyl azide has been found to react with cis–endoand cis–exobicyclo[2•2•1]-5-heptene-2,3-dicarboxylic anhydride to give in both cases, predominantly the more hindered endoaziridine in addition to the exoaziridine in apparent violation of the "exo-addition rule" (3). The stereochemistry of the aziridine rings were determined by nuclear magnetic resonance analysis and by conversion of the endo-aziridine-exo-anhydride to 2-endo-benzenesulfonamidobicyclo[2•2•1]heptane. The endo-aziridine-endo-anhydride has been previously (4) converted into a lactone-N-benzenesulfonyl-lactam.

Published
1969
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