Rottlerin potentiates camptothecin-induced cytotoxicity in human hormone refractory prostate cancers through increased formation and stabilization of topoisomerase I-DNA cleavage complexes in a PKCδ-independent pathway
Journal
Biochemical Pharmacology
Journal Volume
84
Journal Issue
1
Pages
59-67
Date Issued
2012
Author(s)
Abstract
Combination therapy, which can optimize killing activity to cancers and minimize drug resistance, is a mainstream therapy against hormone-refractory prostate cancers (HRPCs). Rottlerin, a natural polyphenolic component, synergistically increased PC-3 (a HRPC cell line) apoptosis induced by camptothecin (a topoisomerase I inhibitor). Using siRNA technique to knockdown protein kinase C-δ (PKCδ), the data showed that rottlerin-mediated synergistic effect was PKCδ-independent, although rottlerin has been used as a PKCδ inhibitor. Rottlerin potentiated camptothecin-induced DNA fragmentation at S phase and ATM phosphorylation at Ser 1981. The effect was correlated to apoptosis (r 2 = 0.9). To detect upstream signals, the data showed that camptothecin acted on and stabilized topoisomerase I-DNA complex, leading to the formation of camptothecin-trapped cleavage complexes (TOP1cc). The effect was potentiated by rottlerin. To determine DNA repair capability, the time-related γH 2A.X formation was examined after camptothecin removal. Consequently, rottlerin significantly inhibited camptothecin removal-mediated decline of γH 2A.X formation at S phase, indicating the impairment of DNA repair activity in the presence of rottlerin. The combinatory treatment of camptothecin and rottlerin induced conformational change and activation of Bax and formation of truncated Bad, suggesting the contribution of mitochondria stress to apoptosis. In summary, the data suggest that rottlerin-mediated camptothecin sensitization is through the augmented stabilization of TOP1cc, leading to an increase of DNA damage stress and, possibly, an impairment of DNA repair capability. Subsequently, mitochondria-involved apoptosis is triggered through Bax activation and truncated Bad formation. The novel discovery may provide an anticancer approach of combinatory use between rottlerin and camptothecin for the treatment of HRPCs. ? 2012 Elsevier Inc.
SDGs
Other Subjects
ATM protein; camptothecin; DNA topoisomerase; protein BAD; protein Bax; protein kinase C delta; rottlerin; serine; small interfering RNA; article; cell cycle S phase; cell stress; chemosensitization; complex formation; conformational transition; controlled study; cytotoxicity; DNA cleavage; DNA fragmentation; DNA repair; drug potentiation; gene silencing; human; human cell; male; mitochondrial membrane potential; mitochondrion; priority journal; prostate cancer; protein phosphorylation; signal transduction; Acetophenones; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Benzopyrans; Blotting, Western; Camptothecin; Cell Culture Techniques; Cell Line, Tumor; Cell Survival; DNA Cleavage; DNA Topoisomerases, Type I; Drug Synergism; Flow Cytometry; Humans; In Situ Nick-End Labeling; Male; Neoplasms, Hormone-Dependent; Prostatic Neoplasms; Protein Kinase C-delta; RNA, Small Interfering; Topoisomerase I Inhibitors; Transfection
Type
journal article