title: Apoptosis induction by the dual-action DNA- and protein-reactive antitumor drug irofulven is largely Bcl-2-independent.
abstract: The overexpression of Bcl-2 is implicated in the resistance of cancer cells to apoptosis. This study explored the potential of irofulven (hydroxymethylacylfulvene, HMAF, MGI 114, NSC 683863), a novel DNA- and protein-reactive anticancer drug, to overcome the anti-apoptotic properties of Bcl-2 in HeLa cells with controlled Bcl-2 overexpression. Irofulven treatment resulted in rapid (12hr) dissipation of the mitochondrial membrane potential, phosphatidylserine externalization, and apoptotic DNA fragmentation, with progressive changes after 24hr. Bcl-2 overexpression caused marginal or partial inhibition of these effects after treatment times ranging from 12 to 48hr. Both Bcl-2-dependent and -independent responses to irofulven were abrogated by a broad-spectrum caspase inhibitor. Despite the somewhat decreased apoptotic indices, cell growth inhibition by irofulven was unaffected by Bcl-2 status. In comparison, Bcl-2 overexpression drastically reduced apoptotic DNA fragmentation by etoposide, acting via topoisomerase II-mediated DNA damage, but had no effect on apoptotic DNA fragmentation by helenalin A, which reacts with proteins but not DNA. Irofulven retains its pro-apoptotic and growth inhibitory potential in cell lines that have naturally high Bcl-2 expression. Collectively, the results implicate multiple mechanisms of apoptosis induction by irofulven, which may differ in time course and Bcl-2 dependence. It is possible that the sustained ability of irofulven to induce profound apoptosis and to block cell growth despite Bcl-2 overexpression may be related to its dual reactivity with both DNA and proteins.
authors.affiliation: Department of Radiation Oncology, University of Texas Health Science Center, 13960 Omicron Drive, San Antonio, TX 78245, USA.
authors.forename: Maryanne C S
authors.initials: MC
authors.lastname: Herzig
authors.forename: Alex V
authors.initials: AV
authors.lastname: Trevino
authors.forename: Huiyun
authors.initials: H
authors.lastname: Liang
authors.forename: Richard
authors.initials: R
authors.lastname: Salinas
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Waters
authors.forename: John R
authors.initials: JR
authors.lastname: MacDonald
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Woynarowska
authors.forename: Jan M
authors.initials: JM
authors.lastname: Woynarowski
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D053938:DNA Fragmentation / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D012717:Sesquiterpenes / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D019253:Proto-Oncogene Proteins c-bcl-2; D012717:Sesquiterpenes; C102714:irofulven