Abstract
Drug-resistance is a major problem preventing a cure in patients with multiple myeloma (MM). Previously, we demonstrated that activated-leukocyte-cell-adhesion-molecule (ALCAM) is a prognostic factor in MM and inhibits EGF/EGFR-initiated MM clonogenicity. In this study, we further showed that the ALCAM-EGF/EGFR axis regulated the MM side population (SP)-mediated drug-resistance. ALCAM-knockdown MM cells displayed an enhanced ratio of SP cells in the presence of bone marrow stromal cells (BMSCs) or with the supplement of recombinant EGF. SP MM cells were resistant to chemotherapeutics melphalan or bortezomib. Drug treatment stimulated SP-genesis. Mechanistically, EGFR, primed with EGF, activated the hedgehog pathway and promoted the SP ratio; meanwhile, ALCAM inhibited EGFR downstream pro-MM cell signaling. Further, SP MM cells exhibited an increased number of mitochondria compared to the main population. Interference of the mitochondria function strongly inhibited SP-genesis. Animal studies showed that combination therapy with both an anti-MM agent and EGFR inhibitor gefitinib achieved prolonged MM-bearing mice survival. Hence, our work identifies ALCAM as a novel negative regulator of MM drug-resistance, and EGFR inhibitors may be used to improve MM therapeutic efficacy.
Highlights
Multiple myeloma (MM) is the second most common hematologic malignancy in the US [1]
Hoechst staining is often used to separate MM cells into a side population (SP) and a main population (MP), and the SP MM cells are believed to contribute to MM clonogenesis; SP MM cells are considered to have “stemness.”
MATERIALS AND METHODS Primary myeloma samples Bone marrow (BM) aspirations from newly diagnosed MM patients were provided by the tissue bank of the Department of Hematology, West China Hospital, Sichuan University, and processed as previously described [12]
Summary
Multiple myeloma (MM) is the second most common hematologic malignancy in the US [1]. Drug-resistance widely exists, in some newly diagnosed high-risk MM patients or relapsed/refractory MM patients [3]. A small population of MM cells, usually
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