title: Mechanistic evaluation of the signaling events regulating curcumin-mediated chemosensitization of breast cancer cells to 5-fluorouracil.
abstract: 5-Fluorouracil (5-FU) is the first rationally designed antimetabolite, which achieves its therapeutic efficacy through inhibition of the enzyme thymidylate synthase (TS), which is essential for the synthesis and repair of DNA. However, prolonged exposure to 5-FU induces TS overexpression, which leads to 5-FU resistance in cancer cells. Several studies have identified curcumin as a potent chemosensitizer against chemoresistance induced by various chemotherapeutic drugs. In this study, we report for the first time, with mechanism-based evidences, that curcumin can effectively chemosensitize breast cancer cells to 5-FU, thereby reducing the toxicity and drug resistance. We found that 10 μM 5-FU and 10 μM curcumin induces a synergistic cytotoxic effect in different breast cancer cells, independent of their receptor status, through the enhancement of apoptosis. Curcumin was found to sensitize the breast cancer cells to 5-FU through TS-dependent downregulation of nuclear factor-κB (NF-κB), and this observation was confirmed by silencing TS and inactivating NF-κB, both of which reduced the chemosensitizing efficacy of curcumin. Silencing of TS suppressed 5-FU-induced NF-κB activation, whereas inactivation of NF-κB did not affect 5-FU-induced TS upregulation, confirming that TS is upstream of NF-κB and regulates the activation of NF-κB in 5-FU-induced signaling pathway. Although Akt/PI3kinase and mitogen-activated protein kinase pathways are activated by 5-FU and downregulated by curcumin, they do not have any role in regulating the synergism. As curcumin is a pharmacologically safe and cost-effective compound, its use in combination with 5-FU may improve the therapeutic index of 5-FU, if corroborated by in vivo studies and clinical trials.
authors: Cancer Research Program, Division of Cancer Research, Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, Kerala 695014, India.
authors: B S
authors: BS
authors: Vinod
authors: J
authors: J
authors: Antony
authors: H H
authors: HH
authors: Nair
authors: V T
authors: VT
authors: Puliyappadamba
authors: M
authors: M
authors: Saikia
authors: S Shyam
authors: SS
authors: Narayanan
authors: A
authors: A
authors: Bevin
authors: R John
authors: RJ
authors: Anto
mesh_terms: D017304:Annexin A5 / Q000378:metabolism; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D003474:Curcumin / Q000494:pharmacology* / Q000627:therapeutic use; D053938:DNA Fragmentation / Q000187:drug effects; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004357:Drug Synergism; D005260:Female; D005472:Fluorouracil / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D061986:MCF-7 Cells; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013940:Thymidylate Synthase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D017304:Annexin A5; D000970:Antineoplastic Agents; D016328:NF-kappa B; D034741:RNA, Small Interfering; D013940:Thymidylate Synthase; D011065:Poly(ADP-ribose) Polymerases; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases; D020169:Caspases; D003474:Curcumin; D005472:Fluorouracil