IntroductionMultiple myeloma (MM), a malignancy hallmarked by accumulation of malignant plasma cells in the bone marrow, remains largely incurable despite the use of conventional and novel therapies. 1 The bone marrow (BM) microenvironment promotes tumor cell growth, survival, and confers drug resistance against conventional agents. 2 Although currently available anti-MM strategies have been effective in targeting the bulk of tumor cells, it has been postulated that a tumor-initiating subpopulation or cancer stem cell persists, which may be responsible for eventual relapses. 3 Side population (SP) cells are an enriched source of cancer-initiating cells with stem cell properties, which have been identified in solid tumors, as well as in hematopoietic malignancies. [4][5][6][7][8] The SP cells show a distinct ''low-staining pattern" with the Hoechst 33342 dye. 9 Importantly, SP cells possess the ability to generate non-SP cells both in vitro and in vivo, and are associated with chemoresistance and tumorigenicity in vivo. 4,10 The prevalence and biologic function of SP cells in MM are not fully defined.In the late 1990s, thalidomide was introduced to the treatment of relapsed/refractory MM; however, its effect in patients is associated with dose-and duration-dependent side effects. 11,12 Since then, more potent immunomodulatory drugs (IMiDs), such as lenalidomide, have been introduced. Lenalidomide has been approved for the treatment of both myelodysplasia with deletion of chromosome 5q and for relapsed MM, specifically in combination with dexamethasone. 12,13 Although IMiDs act directly on tumor cells, block adherence to bone marrow stromal cells (BMSCs), modulate angiogenesis and cytokines, and up-regulate host antitumor immunity, the molecular mechanism for their action remains largely undefined, and it is unclear whether they target SP cells in MM. [14][15][16][17][18] In this study, we identified SP cells in MM cell lines as well as in primary MM tumor cells by flow cytometry-based Hoechst 33342 staining, and showed heterogeneity in the percentage of SP cells, as well as the lack of strict correlation between SP fraction and CD138 Ϫ status. SP cells exhibited clonogenic and tumorigenic potential; and importantly, lenalidomide significantly decreased the percentage and clonogenicity of SP cells at clinically relevant concentrations. Moreover, lenalidomide only slightly altered expression of drug-resistant transporter ABCG2 with no effect on functional activity of BCRP1 efflux pump. Modulation of diverse signaling cascades in SP cells by lenalidomide, including changes in Akt, GSK-3␣/␤, MEK1, c-Jun, p53, and p70S6K phosphorylation was observed. Adherence to BMSCs increased the percentage, viability, and proliferation potential of SP cells. Interestingly, both lenalidomide and thalidomide attenuated this stimulatory effect of BMSCs by significantly decreasing SP cell percentages. Therefore, our studies provide insight toward developing novel strategies Submitted February 5, 2010; accepted October 10, 2010. Prepub...

Malignant cells have a higher nicotinamide adenine dinucleotide (NAD ؉) IntroductionMultiple myeloma (MM) is a clonal B-cell malignancy characterized by excessive bone marrow plasma cells in association with monoclonal protein. 1 The therapeutics currently available improve patients' survival and quality of life, but resistance to therapy and disease progression remain unsolved issues. Therefore, the definition of new aspects of MM biology that can be targeted and exploited from a therapeutic perspective remains a major basic and clinical research goal.Autophagy is a conserved process of normal cell turnover by regulating degradation of its components, which is characterized by the formation of autophagosomes, double-membrane cytoplasmic vesicles engulfing intracellular material including protein, lipids, as well as organelles, such as mitochondria and endoplasmic reticulum. Subsequently autophagosomes fuse with lysosomes, and their contents are degradated by lysosomal enzymes. 2 This selfcannibalization event is a highly conserved response to metabolic stress, in which cellular components are degraded for the maintenance of homeostasis. 3 Intriguingly, the waste removal function of autophagy appears as to be a double-edged sword, because it can either lead to cell survival or death. 4 A series of molecular mechanisms coordinate the autophagy machinery. Specifically, the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) is the major intracellular hub for integrating autophagy-related signals. 5 Upstream of mTORC1 is the cellular energy-sensing pathway. 6 Regulation of autophagy also occurs through the transcription factors EB (TFEB) and forkhead box (FOXO), whose activation leads to transcription of Atg genes. 7,8 Although apoptosis induction has been the major focus of research in novel MM therapies, a recent study documented a pivotal role for autophagy as a prosurvival mechanism in MM cells, suggesting its potential as an additional target for novel therapeutics. 9,10 Intracellular nicotinamide adenine nucleotide (NAD ϩ ) plays a major role in the regulation of several cellular processes. 11,12 In mammals, NAD ϩ is replenished from nicotinamide (Nam), tryptophan or nicotinic acid (NA), with Nam as the most important and widely available precursor. 13 Nicotinamide phosphoribosyltransferase (NAMPT), pre-B colony enhancing factor, is the ratelimiting enzyme in NAD ϩ synthesis from Nam. 14 The expression of this enzyme is up-regulated in activated immune cells, 15 in differentiated myeloid cells, 16 during the circadian clock, 17 in glucose-restriction impaired skeletal myoblast differentiation, 18 and during cytokine production in immune cells. 19 Importantly, Nampt is also overexpressed in cancer cells, which exhibit a significant dependence on NAD ϩ to support their rapid cell proliferation. 20 Importantly, a specific chemical inhibitor of Nampt FK866, also called APO866 or WK175, exhibits a broad antitumor activity both in vitro and in vivo against cell lines derived from several tumors, with a favorabl...

Background Previously, we validated capability of human adipose tissuederived mesenchymal stem cells (AT-MSC) to serve as cellular vehicles for gene-directed enzyme prodrug molecular chemotherapy. Yeast fusion cytosine deaminase : uracil phosphoribosyltransferase expressing AT-MSC (CD y -AT-MSC) combined with systemic 5-fluorocytosine (5FC) significantly inhibited growth of human colon cancer xenografts. We aimed to determine the cytotoxic efficiency to other tumour cells both in vitro and in vivo.