title: Lactate, a putative survival factor for myeloma cells, is incorporated by myeloma cells through monocarboxylate transporters 1.
abstract: BACKGROUND
  Lactate levels within tumors are correlated with metastases, tumor recurrence, and radioresistance, thus apparently contributing to poor outcomes in patients with various cancers. We previously reported that high-level production of lactate by multiple myeloma (MM) cell lines is associated with high-level LDH activity within such MM cells. However, the kinetics of lactate remains to be studied. In the present study, we attempted to elucidate the mechanism of lactate incorporation into MM cells.
  
  
  METHODS
  Six MM cell lines and stromal cells obtained through long-term culture of bone marrow samples from MM patients were employed. Incorporation of lactate was quantified using C(14)-labeled lactate. The role of MCT1, a member of the monocarboxylate transporters (MCTs), expressed on MM cells, was examined in the presence of its inhibitor (α-cyano-4-hydroxycinnamic acid: CHC) and by using gene-silencing technique.
  
  
  RESULTS
  MM cell lines as well as stromal cells were found to produce lactate. Incorporation of C(14)-labeled lactate into MM cells occurred in all 6 MM cell lines analyzed. Inhibition of MCT1 by using CHC or MCT1-targeting siRNA reduced lactate incorporation and caused apoptosis in MM cells. This apoptosis was enhanced when the activity of pyruvate dehydrogenase kinase was blocked by dichroloacetate. Survival of normal peripheral blood mononuclear cells was not influenced by MCT1 inhibition.
  
  
  CONCLUSIONS
  The present data suggest that lactate is produced by MM cell lines and stromal cells, and contributes to the survival of such MM cells in autocrine or paracrine manners. Suppression of lactate incorporation by targeting MCT1 may provide a novel therapeutic strategy for MM which may be applicable for other B-cell neoplasms.
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Shiho
authors.initials: S
authors.lastname: Fujiwara
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Naoko
authors.initials: N
authors.lastname: Wada
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Yawara
authors.initials: Y
authors.lastname: Kawano
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Okuno
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Kikukawa
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Endo
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Nao
authors.initials: N
authors.lastname: Nishimura
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Nina
authors.initials: N
authors.lastname: Ueno
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Mitsuya
authors.affiliation: Department of Hematology, Kumamoto University School of Medicine, 1-1-1, Honjo, Chu-ouku, Kumamoto city, Kumamoto 860-8556 Japan ; Graduate School of Health Sciences, Faculty of Medical Sciences, Division of Informative Clinical Sciences, Kumamoto University School of Medicine, 4-24-1 Kuhonji, Kumamoto, 862-0976 Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hata
keywords: Glucose; Lactate; Monocarboxylate transporters; Multiple myeloma