Hiromichi Yuki

PDK1 inhibition is a novel therapeutic target in multiple myeloma

Background:Cancer cells utilise the glycolytic pathway even when adequate oxygen is present, a phenomenon known as the Warburg effect. We examined whether this system is operative in multiple myeloma (MM) cells and whether glycolysis inhibition is a potential therapeutic modality.Methods:The MM cells were purified from 59 patients using CD138-immunomagnetic beads. The expression levels of genes associated with glycolysis, c-MYC, GLUT1, LDHA, HIF1A and pyruvate dehydrogenase kinase-1 (PDK1) were determined by real-time PCR. Glucose consumption and lactate production by MM cell lines were analysed. Oxamate, an LDH inhibitor, and dichloroacetate (DCA), a PDK1 inhibitor, were employed. Inhibition of PDK1 expression was achieved using a siRNA.Results:High LDHA expression was found to be an indicator of poor prognosis. It was also positively correlated with the expression of PDK1, c-MYC and GLUT1. Greater glucose consumption and lactate production in MM cells was associated with higher LDHA expression. All the glycolysis inhibitors (oxamate, DCA and PDK1 siRNA) induced apoptosis in MM cells. DCA combined with bortezomib showed additive cytotoxic effects.Conclusion:The present data suggest that the Warburg effect is operative in MM cells. As PDK1 is not overexpressed in normal tissues, PDK1 inhibition could serve as a novel therapeutic approach.

Multiple myeloma cells expressing low levels of CD138 have an immature phenotype and reduced sensitivity to lenalidomide

CD138 expression is a hallmark of plasma cells and multiple myeloma cells. However, decreased expression of CD138 is frequently observed in plasma cells of myeloma patients, although the clinical significance of this is unclear. To evaluate the significance of low expression of CD138 in MM, we examined the phenotypes of MM cells expressing low levels of CD138. Flow cytometric analysis of primary MM cells revealed a significant decrease in CD138 expression in patients with relapsed/progressive disease compared with untreated MM patients. Patients with low levels of CD138 had a worse overall survival compared with patients with high levels of CD138, in newly diagnosed patients and patients receiving high-dose chemotherapy followed by autologous stem-cell transplantation. Two MM cell lines, KYMM-1 (CD138− low) and KYMM-2 (CD138− high), were established from a single MM patient with decreased CD138 expression. High expression of BCL6 and PAX5, and downregulation of IRF4, PRDM1 and XBP1 was observed in KYMM-1 compared with KYMM-2 cells, indicative of the immature phenotype of KYMM-1. KYMM-1 was less sensitive to lenalidomide than KYMM-2, while no difference in sensitivity to bortezomib was observed. KYMM-2 cells were further divided in CD138+ and CD138− fractions using anti-CD138-coated magnetic beads. CD138− cells sorted from the KYMM-2 cell line also showed high BCL6, low IRF4 expression and decreased sensitivity to lenalidomide compared with CD138+ cells. Our observations suggest that low CD138 expression relates to i) poor prognosis, ii) immature phenotype and iii) low sensitivity to lenalidomide. The observed distinct characteristics of CD138 low MM cells, suggest this should be recognized as a new clinical entity. Establishment of a treatment strategy for MM cells expressing low levels of CD138 is needed to improve their poor outcome.

PU.1 is a potent tumor suppressor in classical Hodgkin lymphoma cells

PU.1 has previously been shown to be down-regulated in classical Hodgkin lymphoma (cHL) cells via promoter methylation. We performed bisulfite sequencing and proved that the promoter region and the -17 kb upstream regulatory element of the PU.1 gene were highly methylated. To evaluate whether down-regulation of PU.1 is essential for the growth of cHL cells, we conditionally expressed PU.1 in 2 cHL cell lines, L428 and KM-H2. Overexpression of PU.1 induced complete growth arrest and apoptosis in both cell lines. Furthermore, in a Hodgkin lymphoma tumor xenograft model using L428 and KM-H2 cell lines, overexpression of PU.1 led to tumor regression or stable disease. Lentiviral transduction of PU.1 into primary cHL cells also induced apoptosis. DNA microarray analysis revealed that among genes related to cell cycle and apoptosis, p21 (CDKN1A) was highly up-regulated in L428 cells after PU.1 induction. Stable knockdown of p21 rescued PU.1-induced growth arrest in L428 cells, suggesting that the growth arrest and apoptosis observed are at least partially dependent on p21 up-regulation. These data strongly suggest that PU.1 is a potent tumor suppressor in cHL and that induction of PU.1 with demethylation agents and/or histone deacetylase inhibitors is worth exploring as a possible therapeutic option for patients with cHL.

TRAIL produced from multiple myeloma cells is associated with osteolytic markers

Skeletal complications represent major clinical problems in multiple myeloma (MM). MM cells are known to induce differentiation of osteoclasts and inhibit osteoblasts. Receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) are key molecules for osteoclastogenesis. Although OPG interacts with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), the contribution of TRAIL to skeletal-related events (SRE) remains a matter of debate. In the present study, we examined the role of TRAIL in MM bone lesions. Myeloma cells were purified from 56 MM patients by CD138-immunomagnetic beads. TRAIL, DKK-1 and MIP1α RNA expression in purified MM cells was analyzed by real-time PCR. Immunohistochemistry of TRAIL was performed on paraffin-embedded plasmacytoma tissue sections. The concentration of TRAIL in the serum and bone marrow plasma from MM patients was analyzed by ELISA. TRAIL expression was significantly higher in MM cells than in plasma cells from patients with monoclonal gammopathy of undetermined significance (MGUS). TRAIL staining was detected in the cytoplasm of myeloma cells. TRAIL expression in MM cells correlated with bone marrow plasma TRAIL concentration. TRAIL expression had a positive correlation with osteolytic markers, such as serum calcium and urinary deoxypyridinoline. These results suggest that TRAIL, produced from myeloma cells, may play an important role in bone resorption of MM patients. Inhibition of this pathway may lead to development of a new therapeutic approach preventing bone resorption in MM.

Rituximab Monotherapy and Rituximab-Containing Chemotherapy Were Effective for Paraneoplastic Pemphigus Accompanying Follicular Lymphoma, but not for Subsequent Bronchiolitis Obliterans

A 60-year-old male patient suffered from mild exertional dyspnea, wheezing, and systemic blisters. He was diagnosed with paraneoplastic pemphigus (PNP) with follicular lymphoma in the pancreas head and pelvic cavity. He was first treated with eight cycles of rituximab; his blisters and erosions gradually improved and highly elevated levels of auto-antibodies related to PNP gradually decreased to normal levels. However, obstructive and restrictive respiratory failure still progressed. Computed tomography of the inspiratory and expiratory phases revealed obstructive pulmonary disorder, leading to a diagnosis of bronchiolitis obliterans (BO). The patient underwent plasma exchange and was repeatedly treated with rituximab monotherapy and rituximab-containing chemotherapies, but died 7 months after the diagnosis of BO. Early introduction of rituximab-containing regimens may be necessary to prevent the development of BO accompanying PNP. However, when a diagnosis of PNP-related BO is made, lung transplantation may also be considered for patients in whom rituximab-containing regimens are effective for PNP.