title: 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.
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 Ser1981. The effect was correlated to apoptosis (r2 = 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 γH2A.X formation was examined after camptothecin removal. Consequently, rottlerin significantly inhibited camptothecin removal-mediated decline of γH2A.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.
authors.affiliation: School of Pharmacy, College of Medicine, National Taiwan University, No. 1, Section 1, Jen-Ai Road, Taipei 100, Taiwan.
authors.forename: Jui-Ling
authors.initials: JL
authors.lastname: Hsu
authors.forename: Yunn-Fang
authors.initials: YF
authors.lastname: Ho
authors.forename: Tsai-Kun
authors.initials: TK
authors.lastname: Li
authors.forename: Ching-Shih
authors.initials: CS
authors.lastname: Chen
authors.forename: Lih-Ching
authors.initials: LC
authors.lastname: Hsu
authors.forename: Jih-Hwa
authors.initials: JH
authors.lastname: Guh
mesh_terms: D000098:Acetophenones / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D001578:Benzopyrans / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D015153:Blotting, Western; D002166:Camptothecin / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D018929:Cell Culture Techniques; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D053837:DNA Cleavage / Q000187:drug effects*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004357:Drug Synergism; D005434:Flow Cytometry; D006801:Humans; D020287:In Situ Nick-End Labeling; D008297:Male; D009376:Neoplasms, Hormone-Dependent / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D011471:Prostatic Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D051745:Protein Kinase C-delta / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D059004:Topoisomerase I Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000627:therapeutic use; D014162:Transfection
chemical_list: D000098:Acetophenones; D001578:Benzopyrans; D034741:RNA, Small Interfering; D059004:Topoisomerase I Inhibitors; C085746:rottlerin; D051745:Protein Kinase C-delta; D004264:DNA Topoisomerases, Type I; C528909:TOP1 protein, human; D002166:Camptothecin