Gene expression profiles of NCI-H929 cells after knockdown of RRM1 and RRM2

Purpose: Overexpression or polymorphisms of ribonucleotide reductase (RR) are described in many solid tumors, and its expression is highly correlated with survival. However, the biologic significance in multiple myeloma (MM) has not yet been elucidated. Here, we identify the role of RR in MM pathogenesis. Experimental Design: Here we studied the potential utility of RRM1 knockdown effect in multitple myeloma in vitro and in vivo. Results: Knockdown of RRM1 (large subunit) triggered significant growth inhibition, associated with apoptotic cells death, in MM cells, regardless of the existence of bone marrow microcnrivonment. To validate the role of RRM1 of xenograft model, tumor growth was significantly reduced in RRM1-knocked-down MM cells versus control MM cells. Gene expression profiling showed that p53 regulated genes were upregulated after RRM1 knockdown. Immunoblot and QRT-PCR validated that p53 pathways were acviated as well. Clofarabine (CLO), a purine nucleoside analog which inhibits both DNA polymerases and RRM1, is a potential therapeutic agent in MM. CLO induced growth arrest in p53 wild-type cell lines, but not in p53 mutant or null cells. Moreover, CLO treatment with combined with DNA damaging agents triggered synergetic cell death even in p53 mutant MM cells. Conclusions: Our results therefore demonstrate that RRM1 is a novel therapeutic target in patients with MM, and provide the basis for clinical evaluation of RRM1 inhibitor, alone or in combination with DNA damaging agents, to improve patient outcome. Myeloma cell line (NCI-H929) was transduced with either siRNAs targeting RRM1, RRM2 or scramble (control) in duplicate. The gene expression profiles of RRM1 and RRM2 knockdown cells were compared with that of control cells. A total of 6 RNA samples (2 RRM1 knockdown, 2 RRM2 knockdown, and 2 control) were analyzed.