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Grundlagen: Tetrocarcin-A (TC-A) ist eine von Actinomyceten erzeugte Substanz mit antibiotischer Wirkung, TC-A ist bisher ausschließlich an einem Cervix-Carcinom Zellsystem getestet und kann dabei eo ipso Apoptose induzieren, eine Sensitierung entlang dem CD95/Fas Signalweg und eine Steigerung der proapoptotischen Wirkung klassischer zytotoxischer Substanzen bewirken (Nakashima et al., Cancer Res. 2000, Vol 60, p. 1229-35). In hämatologischen Tumoren liegt häufig eine Bcl-2 Überexpression als (Mit-)Ursache gestörter Spontanapoptose und reduzierter Zytostatikasensitivität vor. Substanzen, die Bcl-2-Funktionen überwinden oder davon unabhängig wirken können, haben daher Bedeutung für die Entwicklung neuer therapeutischer Wirkkombinationen. Methodik: Es wurde daher anhand einer T-ALL-Zelllinie (i.e. CCRF-CEM) die proapoptotische Effizienz von TC-A in einem hämatologischen Tumorsystem überprüft, der entsprechende Signalweg charakterisiert und die Interferenz mit der Bcl-2-Funktion überprüft. Dies erfolgte durch Messung von PI/AnnexinV doppelpositiven Zellen und Western-Blot-Analysen. Die T-ALL-Zell-Linie wurde im Wildtyp und nach Transfektion mit Bcl-2 untersucht. Ergebnisse: In der Vektor-Kontrolllinie mit geringer basaler Bcl-2-Expression kam es durch die Stimulation mit zunehmender Konzentration von TC-A und in Abhängigkeit von der Inkubationsdauer zu einer Zunahme der Apoptoseinduktion, gekennzeichnet durch die Aktivierung eines mitochondriellen Apoptoseweges. Dieser konnte durch Aktivierung von Bid, den Zusammenbruch des mitochondriellen Transmembran-Potentials, die Spaltung der Caspasen 2, 3, 6, 8, 9, PARP und anschließende DNA-Fragmentation charakterisiert werden. Bcl-2-Überexpression konnte einen nur partiellen Schutz gegen die TC-A-Wirkung entfalten Schlußfolgerungen: TC-A könnte somit in Leukosen eine Bcl-2-unabhängige Wirkung besitzen und somit zur Erweiterung/Verbesserung zytotoxischer Medikation beitragen. [ABSTRACT FROM AUTHOR]

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Copyright of Acta Medica Austriaca is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the past decade, it was concluded from a number of investigations that death domain-containing members of the tumor necrosis factor-receptor (TNF-R) family and their ligands such as Fas/FasL and TNF-related apoptosis-inducing ligand (TRAIL)-R/TRAIL are essential for maintaining an intact immune system for surveillance against infection and cancer development and that nondeath domain-containing members such as CD30 or CD40 are involved in the fine tuning of this system during the selection process of the lymphatic system. In line with this conclusion are the observations that alterations in structure, function, and regulation of these molecules contribute to autoimmunity and cancer development of the lymphoid system. Besides controlling size and function of the lymphoid cell pool, Fas/FasL and TRAIL-R/TRAIL regulate myelopoiesis and the dendritic cell functions, and severe alterations of these lineages during the outgrowth and expansion of the lymphoid tumors have been reported. It is the aim of this review to summarize what is currently known about the complex role of these two death receptor/ligand systems in normal, disturbed, and neoplastic hemato-/lymphopoiesis and to point out how such knowledge can be used in developing novel, therapeutic options and the problems that will have to be faced along the way.

Tetrocarcin-A (TC-A), an antibiotic agent isolated from actinomycetes, has recently been described to antagonize Bcl-2 functions, thereby sensitizing tumor cells to cell death signals under control of Bcl-2. In this study, we analyzed the direct proapoptotic effect of TC-A in the B-chronic lymphocytic leukemia (B-CLL) model. We focused on the signal cascade triggered by TC-A in B-CLL cells and identified activated mitochondrial as well as endoplasmatic reticulum (ER) stress signals. The expression levels of known effector molecules mediating mitochondrial signaling, such as Bax and Bid, and the antagonistic molecule Bcl-2 did not influence sensitivity of B-CLL cells to TC-A. Furthermore, the molecular chaperone and sensor of ER stress, HSP70, though significantly up-regulated in B-CLL cells undergoing TC-A-triggered apoptosis, was ineffective to exert its anti-apoptotic function described in multiple cell death pathways. Autologous T cells of B-CLL patients were significantly less sensitive to TC-A as were also T cells from healthy donors when compared with their normal B-cell fraction. Furthermore, sensitivity of B-CLL cells to TC-A treatment in vitro was dependent neither on the expression levels of CD38-a prognostic factor for survival of B-CLL patients as well as for their response to therapy-nor on the clinical stage or pretreatment status of patients. From our data showing that TC-A induced a cell death pathway via ER stress preferentially in B cells and that it acted independently of important markers of drug sensitivity and of clinical markers, we conclude that TC-A might represent an attractive candidate drug for further evaluation in preclinical trials.

During the last decade, the concerted effort of numerous scientific groups has expanded our understanding of the finely tuned network present within bone marrow for the regulation of the hematopoietic system. This network, comprising humoral and cellular cross talk, is responsible for the adaptation of hematopoietic populations to demands as they arise. Major components of this control system are death receptors and their specific ligands, which eliminate superfluous cells once they have fulfilled their respective functions. The important role of Fas (CD95/Apo-1), one member of this death receptor family, in the regulation of T- and B-cell functions has been established. Alteration of Fas expression and/or function in lymphoid cells may contribute to the development of autoimmunity and/or neoplastic diseases. In addition to controlling lymphoid compartments, Fas is also involved in the regulation of myeloid cell functions. More recently, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its specific receptors (TRAIL-R) have been identified as further members of this death receptor/ligand family. The TRAIL-R/TRAIL system is of vital importance for the maturation and functioning of immune effector cells of lymphoid, as well as myeloid, origin. In the present review, we have summarized current knowledge about both death receptor/ligand systems in the expansion and functioning of cells from the myeloid compartments, highlighted their role in normal hematopoiesis, and assessed their alterations in pathologic or neoplastic conditions.

The T-ALL cell lines CCRF-CEM and Jurkat were studied for their sensitivity toward apoptosis induced by tetrocarcin-A (TC-A), an antibacterial and antitumor agent isolated from the actinomycete Micromonospora. This substance promoted cell death via a mitochondrial signaling pathway, that is, by activation of Bid and Bax, loss of the mitochondrial transmembrane potential, release of cytochrome c, and activation of effector caspases, even under conditions of Bcl-2 overexpression. Furthermore, sensitivity to TC-A was not dependent on expression of wild-type caspase-8. In contrast, this apoptotic pathway was inhibited markedly by pretreatment of cells with cycloheximide, an inhibitor of de novo protein synthesis. cDNA microarray chip analysis revealed that TC-A induced a significant up-regulation of members of the heat shock protein family known to be involved in the endoplasmic reticulum (ER)-stress-induced apoptotic program. The activation of caspase-12, the central inducer caspase involved in ER-stress by TC-A treatment, is in concordance with this result. These results show that, in T-ALL cells, TC-A induces an apoptotic machinery via mitochondrial and ER signaling, which is not inhibited by aberrant expression/function of important regulators of death receptor- and drug-induced apoptosis.