title: Mechanistic studies on the synergistic cytotoxicity of the nucleoside analogs gemcitabine and clofarabine in multiple myeloma: relevance of p53 and its clinical implications.
abstract: Hematopoietic stem cell transplantation (HSCT) is an established treatment for multiple myeloma (MM), a plasma cell malignancy. To identify an improved pretransplant conditioning regimen, we investigated the cytotoxicity of gemcitabine (Gem) and clofarabine (Clo) combinations toward MM cell lines and patient cell samples. A strong synergism of the two nucleoside analogs, when combined at their approximate IC10 concentrations, was observed. This synergism could be partly due to the observed Gem-mediated phosphorylation and activation of deoxycytidine kinase, resulting in enhanced phosphorylation of Gem and Clo. Their cytotoxicity correlated with a robust activation of the DNA damage response pathway. [Gem+Clo] decreased the mitochondrial membrane potential with a concomitant release of proapoptotic factors into the cytoplasm and nucleus and the activation of apoptosis. Exposure of MM cells to [Gem+Clo] also decreased the level of ribosomal RNA (rRNA), which might have resulted in nucleolar stress, as reported previously, and caused a p53-dependent cell death. A reduction by approximately 50% in the cytotoxicity of Gem and Clo was observed in the presence of pifithrin α, a p53 inhibitor. Furthermore, MM cell lines with mutant p53 exhibited greater resistance to Gem and Clo, supporting a role for the p53 protein in these cytotoxic responses. Our results provide a rationale for clinical trials incorporating [Gem+Clo] combinations as part of conditioning therapy for high-risk patients with MM undergoing HSCT.
authors: Departments of Stem Cell Transplantation and Cellular Therapy, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA. bvaldez@mdanderson.org
authors: Benigno C
authors: BC
authors: Valdez
authors: Guiyun
authors: G
authors: Wang
authors: David
authors: D
authors: Murray
authors: Yago
authors: Y
authors: Nieto
authors: Yang
authors: Y
authors: Li
authors: Jatin
authors: J
authors: Shah
authors: Francesco
authors: F
authors: Turturro
authors: Michael
authors: M
authors: Wang
authors: Donna M
authors: DM
authors: Weber
authors: Richard E
authors: RE
authors: Champlin
authors: Muzaffar H
authors: MH
authors: Qazilbash
authors: Borje S
authors: BS
authors: Andersson
mesh_terms: D000227:Adenine Nucleotides / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology / Q000627:therapeutic use*; D001087:Arabinonucleosides / Q000008:administration & dosage; D001483:Base Sequence; D045744:Cell Line, Tumor; D000077866:Clofarabine; D004249:DNA Damage; D017931:DNA Primers; D004260:DNA Repair; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism; D004357:Drug Synergism; D018380:Hematopoietic Stem Cell Transplantation; D006801:Humans; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000235:genetics / Q000601:surgery; D010766:Phosphorylation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D016159:Tumor Suppressor Protein p53 / Q000502:physiology*; D000093542:Gemcitabine
chemical_list: D000227:Adenine Nucleotides; D001087:Arabinonucleosides; D017931:DNA Primers; D016159:Tumor Suppressor Protein p53; D003841:Deoxycytidine; D000077866:Clofarabine; D000093542:Gemcitabine
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