Multiple myeloma (MM) is a largely incurable plasma cell malignancy with a poorly understood and heterogeneous clinical course. To identify potential, functionally relevant somatic mutations in MM, we performed whole-exome sequencing of five primary MM, corresponding germline DNA and six MM cell lines, and developed a bioinformatics strategy that also integrated published mutational data of 38 MM patients. Our analysis confirms that identical, recurrent mutations of single genes are infrequent in MM, but highlights that mutations cluster in important cellular pathways. Specifically, we show enrichment of mutations in adhesion molecules of MM cells, emphasizing the important role for the interaction of the MM cells with their microenvironment. We describe an increased rate of mutations in receptor tyrosine kinases (RTKs) and associated signaling effectors, for example, in EGFR, ERBB3, KRAS and MAP2K2, pointing to a role of aberrant RTK signaling in the development or progression of MM. The diversity of mutations affecting different nodes of a particular signaling network appears to be an intrinsic feature of individual MM samples, and the elucidation of intra- as well as interindividual redundancy in mutations that affect survival pathways will help to better tailor targeted therapeutic strategies to the specific needs of the MM patient.
multiple myeloma; somatic mutations; whole-exome sequencing; adhesion; receptor tyrosine kinases
Epigenetic silencing of the tumor suppressor gene p15Ink4b (CDKN2B) is a frequent event in blood disorders like acute myeloid leukemia and myelodysplastic syndromes. The molecular function of p15Ink4b in hematopoietic differentiation still remains to be elucidated. Our previous study demonstrated that loss of p15Ink4b in mice results in skewing of the differentiation pattern of the common myeloid progenitor towards the myeloid lineage. Here, we investigated a function of p15Ink4b tumor suppressor gene in driving erythroid lineage commitment in hematopoietic progenitors. It was found that p15Ink4b is expressed more highly in committed megakaryocyte–erythroid progenitors than granulocyte–macrophage progenitors. More importantly, mice lacking p15Ink4b have lower numbers of primitive red cell progenitors and a severely impaired response to 5-fluorouracil- and phenylhydrazine-induced hematopoietic stress. Introduction of p15Ink4b into multipotential progenitors produced changes at the molecular level, including activation of mitogen-activated protein kinase\extracellular signal-regulated kinase (MEK/ERK) signaling, increase GATA-1, erythropoietin receptor (EpoR) and decrease Pu1, GATA-2 expression. These changes rendered cells more permissive to erythroid commitment and less permissive to myeloid commitment, as demonstrated by an increase in early burst-forming unit-erythroid formation with concomitant decrease in myeloid colonies. Our results indicate that p15Ink4b functions in hematopoiesis, by maintaining proper lineage commitment of progenitors and assisting in rapid red blood cells replenishment following stress.
p15Ink4b; hematopoiesis; stem cell; cell fate; differentiation; erythropoiesis
Special attention has recently been drawn to the molecular network of different genes that are responsible for the development of erythroid cells. The aim of the present study was to establish in detail the immunophenotype of early erythroid cells and to compare the gene expression profile of freshly isolated early erythroid precursors with that of the CD34-positive (CD34+) compartment. Multiparameter flow cytometric analyses of human bone marrow mononuclear cell fractions (n=20) defined three distinct early erythroid stages. The gene expression profile of sorted early erythroid cells was analyzed by Affymetrix array technology. For 4524 genes, a differential regulation was found in CD105-positive erythroid cells as compared with the CD34+ progenitor compartment (2362 upregulated genes). A highly significant difference was observed in the expression level of genes involved in transcription, heme synthesis, iron and mitochondrial metabolism and transforming growth factor-β signaling. A comparison with recently published data showed over 1000 genes that as yet have not been reported to be upregulated in the early erythroid lineage. The gene expression level within distinct pathways could be illustrated directly by applying the Ingenuity software program. The results of gene expression analyses can be seen at the Gene Expression Omnibus repository.
Pediatric leukemia survival rates have improved dramatically over the past decades. However, current treatment protocols are still largely ineffective in cases of relapsed leukemia and are associated with a significant rate of chronic health conditions. Thus, there is a continued need for new therapeutic options. Here, we show that mer receptor tyrosine kinase (MerTK) was abnormally expressed in approximately one half of pediatric T-cell leukemia patient samples and T-cell acute lymphoblastic leukemia (T-ALL) cell lines. Stimulation of MerTK by the ligand Gas6 led to activation of the prosurvival proteins Erk 1/2 and Stat5, and MerTK-dependent activation of the STAT pathway in leukemia represents a novel finding. Furthermore, inhibition of MerTK expression increased the sensitivity of T-ALL cells to treatment with chemotherapeutic agents and decreased the oncogenic potential of the Jurkat T-ALL cell line in a methylcellulose colony-forming assay. Lastly, inhibition of MerTK expression significantly increased median survival in a xenograft mouse model of leukemia (30.5 days vs 60 days, P<0.0001). These results suggest that inhibition of MerTK is a promising therapeutic strategy for the treatment of leukemia and may allow for dose reduction of currently used chemotherapeutics resulting in decreased rates of therapy-associated toxicities.
MerTK; receptor tyrosine kinase; T-cell leukemia; xenograft mouse model
Bone marrow (BM) cells depend on their niche for growth and survival. However, the genes modulated by niche stimuli have not been discriminated yet. For this purpose, we investigated BM aspirations from patients with various hematological malignancies. Each aspirate was fractionated, and the various samples were fixed at different time points and analyzed by microarray. Identification of niche-modulated genes relied on sustained change in expression following loss of niche regulation. Compared with the reference (‘authentic') samples, which were fixed immediately following aspiration, the BM samples fixed after longer stay out-of-niche acquired numerous changes in gene-expression profile (GEP). The overall genes modulated included a common subset of functionally diverse genes displaying prompt and sustained ‘switch' in expression irrespective of the tumor type. Interestingly, the ‘switch' in GEP was reversible and turned ‘off-and-on' again in culture conditions, resuming cell–cell–matrix contact versus respread into suspension, respectively. Moreover, the resuming of contact prolonged the survival of tumor cells out-of-niche, and the regression of the ‘contactless switch' was followed by induction of a new set of genes, this time mainly encoding extracellular proteins including angiogenic factors and extracellular matrix proteins. Our data set, being unique in authentic expression design, uncovered niche-modulated and niche-modulating genes capable of controlling homing, expansion and angiogenesis.
gene-expression profile; myeloma; leukemia; contactless gene signature; niche-modulated genes; niche-modulating genes
A previous US study reported poorer survival in children with acute lymphoblastic leukemia (ALL) exposed to extremely low-frequency magnetic fields (ELF–MF) above 0.3 μT, but based on small numbers. Data from 3073 cases of childhood ALL were pooled from prospective studies conducted in Canada, Denmark, Germany, Japan, UK and US to determine death or relapse up to 10 years from diagnosis. Adjusting for known prognostic factors, we calculated hazard ratios (HRs) and 95% confidence intervals (CI) for overall survival and event-free survival for ELF–MF exposure categories and by 0.1 μT increases. The HRs by 0.1 μT increases were 1.00 (CI, 0.93–1.07) for event-free survival analysis and 1.04 (CI, 0.97–1.11) for overall survival. ALL cases exposed to >0.3 μT did not have a poorer event-free survival (HR=0.76; CI, 0.44–1.33) or overall survival (HR=0.96; CI, 0.49–1.89). HRs varied little by subtype of ALL. In conclusion, ELF–MF exposure has no impact on the survival probability or risk of relapse in children with ALL.
leukemia; children; survival; electromagnetic fields; adverse effects; pooled analyses
Small nucleolar RNAs (snoRNAs) and small Cajal body-specific RNAs (scaRNAs) are non-coding RNAs involved in the maturation of other RNA molecules and generally located in the introns of host genes. It is now emerging that altered sno/scaRNAs expression may have a pathological role in cancer. This study elucidates the patterns of sno/scaRNAs expression in multiple myeloma (MM) by profiling purified malignant plasma cells from 55 MMs, 8 secondary plasma cell leukemias (sPCLs) and 4 normal controls. Overall, a global sno/scaRNAs downregulation was found in MMs and, even more, in sPCLs compared with normal plasma cells. Whereas SCARNA22 resulted the only sno/scaRNA characterizing the translocation/cyclin D4 (TC4) MM, TC2 group displayed a distinct sno/scaRNA signature overexpressing members of SNORD115 and SNORD116 families located in a region finely regulated by an imprinting center at 15q11, which, however, resulted overall hypomethylated in MMs independently of the SNORD115 and SNORD116 expression levels. Finally, integrative analyses with available gene expression and genome-wide data revealed the occurrence of significant sno/scaRNAs/host genes co-expression and the putative influence of allelic imbalances on specific snoRNAs expression. Our data extend the current view of sno/scaRNAs deregulation in cancer and add novel information to the bio-molecular complexity of plasma cell dyscrasias.
ncRNA; snoRNA; multiple myeloma.
To select an appropriate prognostic model in the treatment of mature T- and natural killer (NK) -cell lymphoma (peripheral T-cell lymphoma (PTCL) and NK-/T-cell lymphoma (NKTCL)) is crucial. This study investigated the usefulness of Ann Arbor staging classification International prognostic index (IPI), prognostic index for T-cell lymphoma (PIT) and International peripheral T-cell lymphoma Project score (IPTCLP). Between 2000 and 2009, 176 patients (122 males) with PTCL and NKTCL were diagnosed and treated from a single institute in Taiwan. The correlation between complete response (CR) rate, 3-year overall survival (OS), early mortality rate and four prognostic models was analyzed. Thirty-one patients received hematopoietic stem cell transplantation (HSCT) and were analyzed separately. Three-year OS rate was 34.7%, and anaplastic large-cell lymphoma harbored better outcome than others. IPI score had the lowest Akaike information criterion value (1081.197) and was the best score in predicting OS and early mortality (P=0.009). Ann Arbor stage classification can predict CR rate more precisely (P=0.006). OS was significantly better in patients who received HSCT, even in patients with unfavorable features compared with chemotherapy alone. All prognostic models were useful to evaluate the outcome of patients with PTCL and NKTCL but IPI score did best in predicting OS in PTCL and PIT score in NKTCL. This study also supported the role of HSCT in patients with high-risk or refractory PTCL or NKTCL.
T-cell lymphoma; prognostic score; hematopoietic stem cell transplantation; Asian population
The outcomes for patients with chronic myeloid leukemia have improved dramatically with the development and availability of BCR–ABL1 tyrosine kinase inhibitors (TKIs) over the past decade. TKI therapy has a superior safety profile compared with the previous standard of care, interferon-α, and most adverse events (AEs) observed with front-line and second-line TKI treatment are managed with supportive care. However, some patients are intolerant to TKI therapy and experience AEs that cannot be managed through dose reduction or symptomatic treatment. Careful management of AEs helps patients to remain adherent with treatment and increases their chances for successful outcomes. Proactive vigilance for potential AEs and treatment strategies that reduce symptom burden will help to minimize patient intolerance. This review discusses the most common AEs associated with intolerance to TKI therapy and treatment strategies to help manage patients at risk for or experiencing these events.
chronic myeloid leukemia; dasatinib; imatinib; intolerance; nilotinib; tyrosine kinase inhibitors
Shwachman–Diamond syndrome (SDS) is a rare inherited disorder characterized by bone marrow (BM) dysfunction and exocrine pancreatic insufficiency. SDS patients have an increased risk for myelodisplastic syndrome and acute myeloid leukemia. Mesenchymal stem cells (MSCs) are the key component of the hematopoietic microenvironment and are relevant in inducing genetic mutations leading to leukemia. However, their role in SDS is still unexplored. We demonstrated that morphology, growth kinetics and expression of surface markers of MSCs from SDS patients (SDS-MSCs) were similar to normal MSCs. Moreover, SDS-MSCs were able to differentiate into mesengenic lineages and to inhibit the proliferation of mitogen-activated lymphocytes. We demonstrated in an in vitro coculture system that SDS-MSCs, significantly inhibited neutrophil apoptosis probably through interleukin-6 production. In a long-term coculture with CD34+-sorted cells, SDS-MSCs were able to sustain CD34+ cells survival and to preserve their stemness. Finally, SDS-MSCs had normal karyotype and did not show any chromosomal abnormality observed in the hematological components of the BM of SDS patients. Despite their pivotal role in the hematopoietic stem cell niche, our data suggest that MSC themselves do not seem to be responsible for the hematological defects typical of SDS patients.
Shwachman–Diamond syndrome; mesenchymal stem cells; bone marrow failure; SBDS
Light-chain amyloidosis (AL) is a plasma cell dyscrasia closely related to multiple myeloma. In multiple myeloma, the cancer-testis antigens (CTAs) CT7 (MAGE-C1), CT10 (MAGE-C2) and MAGE-A CTAs are expressed in up to 80% of cases. In this study, we investigated the expression and immunogenicity of several CTAs in patients with AL amyloidosis in a total of 38 bone marrow specimens by employing standard immunohistochemistry techniques on paraffin-embedded archival tissues. Plasma samples from 35 patients (27 with matched bone marrow samples) were also analyzed by ELISA for sero reactivity to a group of full-length CTA proteins. CT7 was present in 25/38 (66%) while CT10 was demonstrated in 3/38 and GAGE in 1/38 AL amyloid cases. The expression pattern was mostly focal. There were no significant differences with regard to organ involvement, response to treatment, or prognosis in CTA positive compared to negative cases. None of the specimens showed spontaneous humoral immunity to CT7, but sero reactivity was observed in individual patients to other CTAs. This study identifies CT7 as the prevalent CTA in plasma cells of patients with AL amyloidosis. Further analyses determining the biology of CTAs in AL amyloidosis and their value as potential targets for immunotherapy are warranted.
AL amyloidosis; cancer-testis antigens; stem cell transplantation
Waldenström's macroglobulinemia (WM) is a clonal B-cell lymphoproliferative disorder (LPD) of post-germinal center nature. Despite the fact that the precise molecular pathway(s) leading to WM remain(s) to be elucidated, a hallmark of the disease is the absence of the immunoglobulin heavy chain class switch recombination. Using two-dimensional gel electrophoresis, we compared proteomic profiles of WM cells with that of other LPDs. We were able to demonstrate that WM constitutes a unique proteomic entity as compared with chronic lymphocytic leukemia and marginal zone lymphoma. Statistical comparisons of protein expression levels revealed that a few proteins are distinctly expressed in WM in comparison with other LPDs. In particular we observed a major downregulation of the double strand repair protein Ku70 (XRCC6); confirmed at both the protein and RNA levels in an independent cohort of patients. Hence, we define a distinctive proteomic profile for WM where the downregulation of Ku70—a component of the non homologous end-joining pathway—might be relevant in disease pathophysiology.
Waldenström macroglobulinemia; proteomics; 2D-electrophoresis; XRCC6
Aberrant reactivation of hedgehog (Hh) signaling has been described in a wide variety of human cancers including cancer stem cells. However, involvement of the Hh-signaling system in the bone marrow (BM) microenvironment during the development of myeloid neoplasms is unknown. In this study, we assessed the expression of Hh-related genes in primary human CD34+ cells, CD34+ blastic cells and BM stromal cells. Both Indian Hh (Ihh) and its signal transducer, smoothened (SMO), were expressed in CD34+ acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS)-derived cells. However, Ihh expression was relatively low in BM stromal cells. Remarkably, expression of the intrinsic Hh-signaling inhibitor, human Hh-interacting protein (HHIP) in AML/MDS-derived stromal cells was markedly lower than in healthy donor-derived stromal cells. Moreover, HHIP expression levels in BM stromal cells highly correlated with their supporting activity for SMO+ leukemic cells. Knockdown of HHIP gene in stromal cells increased their supporting activity although control cells marginally supported SMO+ leukemic cell proliferation. The demethylating agent, 5-aza-2′-deoxycytidine rescued HHIP expression via demethylation of HHIP gene and reduced the leukemic cell-supporting activity of AML/MDS-derived stromal cells. This indicates that suppression of stromal HHIP could be associated with the proliferation of AML/MDS cells.
acute myeloid leukemia (AML); myelodysplastic syndrome (MDS); human hedgehog-interacting protein (HHIP); stromal cells
Multiple myeloma (MM) is a heterogeneous plasma cell disorder characterized by genetic abnormalities, including chromosomal translocations, deletions, duplications and genetic mutations. Translocations involving the immunoglobulin heavy chain region at chromosome 14q32 are observed in approximately 40% of patients with MM. Translocation of oncogenes into this region may lead to their increased expression, contributing to disease initiation, disease progression and therapeutic resistance. The t(4;14) translocation is associated with upregulation of the fibroblast growth factor receptor 3 (FGFR3) and the myeloma SET domain protein. Patients with t(4;14) demonstrate an overall poor prognosis that is only partially mitigated by the use of the novel agents bortezomib and lenalidomide; as such, an unmet medical need remains for patients with this aberration. Preclinical studies of inhibitors of FGFR3 have shown promise in t(4;14) MM, and these studies have led to the initiation of clinical trials. Data from these trials will help to determine the clinical utility of FGFR3 inhibitors for patients with t(4;14) MM and may pave the way for personalized medicine in patients with this incurable disease.
multiple myeloma; translocation; t(4;14); FGFR3; MMSET
In the adult mammal, normal haematopoiesis occurs predominantly in the bone marrow, where primitive haematopoietic stem cells (HSC) and their progeny reside in specialised microenvironments. The bone marrow microenvironment contains specific anatomical areas (termed niches) that are highly specialised for the development of certain blood cell types, for example HSCs. The HSC niche provides important cell–cell interactions and signalling molecules that regulate HSC self-renewal and differentiation processes. These same signals and interactions are also important in the progression of haematological malignancies, such as multiple myeloma (MM). This review provides an overview of the bone marrow microenvironment and its involvement in normal, physiological HSC maintenance and plasma cell growth throughout MM disease progression.
myeloma; niche; bone microenvironment; haematopoietic stem cells
Sox2 (sex-determining region Y-Box) is one of the master transcriptional factors that are important in maintaining the pluripotency of embryonic stem cells (ESCs). In line with this function, Sox2 expression is largely restricted to ESCs and somatic stem cells. We report that Sox2 is expressed in cell lines and tumor samples derived from ALK-positive anaplastic large cell lymphoma (ALK+ALCL), for which the normal cellular counterpart is believed to be mature T-cells. The expression of Sox2 in ALK+ALCL can be attributed to nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), the oncogenic fusion protein carrying a central pathogenetic role in these tumors. By confocal microscopy, Sox2 protein was detectable in virtually all cells in ALK+ALCL cell lines. However, the transcriptional activity of Sox2, as assessed using a Sox2-responsive reporter construct, was detectable only in a small proportion of cells. Importantly, downregulation of Sox2 using short interfering RNA in isolated Sox2active cells, but not Sox2inactive cells, resulted in a significant decrease in cell growth, invasiveness and tumorigenicity. To conclude, ALK+ALCL represents the first example of a hematologic malignancy that aberrantly expresses Sox2, which represents a novel mechanism by which NPM-ALK mediates tumorigenesis. We also found that the transcriptional activity and oncogenic effects of Sox2 can be heterogeneous in cancer cells.
Sox2; transcriptional activity; NPM-ALK; STAT3; tumorigenicity
Aberrantly expressed tyrosine kinases have emerged as promising targets for drug development in acute myeloid leukemia (AML). We report that AKN-028, a novel tyrosine kinase inhibitor (TKI), is a potent FMS-like receptor tyrosine kinase 3 (FLT3) inhibitor (IC50=6 nℳ), causing dose-dependent inhibition of FLT3 autophosphorylation. Inhibition of KIT autophosphorylation was shown in a human megakaryoblastic leukemia cell line overexpressing KIT. In a panel of 17 cell lines, AKN-028 showed cytotoxic activity in all five AML cell lines included. AKN-028 triggered apoptosis in MV4-11 by activation of caspase 3. In primary AML samples (n=15), AKN-028 induced a clear dose-dependent cytotoxic response (mean IC50 1 μℳ). However, no correlation between antileukemic activity and FLT3 mutation status, or to the quantitative expression of FLT3, was observed. Combination studies showed synergistic activity when cytarabine or daunorubicin was added simultaneously or 24 h before AKN-028. In mice, AKN-028 demonstrated high oral bioavailability and antileukemic effect in primary AML and MV4-11 cells, with no major toxicity observed in the experiment. In conclusion, AKN-028 is a novel TKI with significant preclinical antileukemic activity in AML. Possible sequence-dependent synergy with standard AML drugs and good oral bioavailability has made it a candidate drug for clinical trials (ongoing).
acute myeloid leukemia; drug development; tyrosine kinase inhibitor; signal transduction; FLT3
Epstein-Barr Virus (EBV) is a γ-herpesvirus that infects >90% of the human population. Although EBV persists in its latent form in healthy carriers, the virus is also associated with several human cancers. EBV is strongly associated with Burkitt lymphoma (BL), even though there is still no satisfactory explanation of how EBV participates in BL pathogenesis. However, new insights into the interplay between viruses and microRNAs (miRNAs) have recently been proposed. In particular, it has been shown that B-cell differentiation in EBV-positive BL is impaired at the post-transcriptional level by altered expression of hsa-miR-127. Here, we show that the overexpression of hsa-miR-127 is due to the presence of the EBV-encoded nuclear antigen 1 (EBNA1) and give evidence of a novel mechanism of direct regulation of the human miRNA by this viral product. Finally, we show that the combinatorial expression of EBNA1 and hsa-miR-127 affects the expression of master B-cell regulators in human memory B cells, confirming the scenario previously observed in EBV-positive BL primary tumors and cell lines. A good understanding of these mechanisms will help to clarify the complex regulatory networks between host and pathogen, and favor the design of more specific treatments for EBV-associated malignancies.
Epstein-Barr virus; microRNAs; Burkitt lymphoma
Modern management of leukemia and selection of optimal treatment approaches entails the analysis of multiple recurrent cytogenetic abnormalities with independent diagnostic or prognostic value. We report the first multicenter validation of a multiplex molecular assay for 12 relevant fusion transcripts relative to cytogenetic methods. Performance was evaluated using a set of 280 adult and pediatric acute or chronic leukemias representative of the variety of presentations and pre-analytical parameters encountered in the clinical setting. The positive, negative and overall agreements were >98.5% with high concordance at each of the four sites. Positive detection of cases with low blast count or at relapse was consistent with a method sensitivity of 1%. There was 98.7% qualitative agreement with independent reference molecular tests. Apparent false negatives corresponded to rare alternative splicing isoforms not included in the panel. We further demonstrate that clinical sensitivity can be increased by adding those rare variants and other relevant transcripts or submicroscopic abnormalities. We conclude that multiplex RT-PCR followed by liquid bead array detection is a rapid and flexible method attuned to the clinical laboratory workflow, complementing standard cytogenetic methods and generating additional information valuable for the accurate diagnosis, prognosis and subsequent molecular monitoring of leukemia.
leukemia; diagnosis; prognosis; molecular classification; RT-PCR; multiplex
We previously reported that children in the UKALL XI ALL trial with HLA-DP 1 and -DP 3 supertypes had significantly worse event-free survival (EFS) than children with other DP supertypes. As DP 1 and DP 3 share two of four key antigen-binding amino-acid polymorphisms (aspartic acid84–lysine69), we asked whether Asp84-Lys69 or Asp84 alone were independent prognostic indicators in childhood acute lymphoblastic leukemia (ALL). We analysed EFS in 798 UKALL XI patients, stratified by Asp84-Lys69 vs non-Asp84-Lys69, for a median follow-up of 12.5 years. Asp84-Lys69 was associated with a significantly worse EFS than non-Asp84-Lys69 (5-year EFS: Asp84-Lys69: 58.8% (95% CI (confidence of interval): 52.7–64.9%); non-Asp84-Lys69: 67.3% (63.4–71.2%); 2P=0.007). Post-relapse EFS was 10% less in Asp84-Lys69 than non-Asp84-Lys69 patients. EFS was significantly worse (P=0.03) and post-relapse EFS marginally worse (P=0.06) in patients with Asp84 compared with Gly84. These results suggest that Asp84-Lys69 predicted adverse EFS in the context of UKALL XI because of Asp84, and may have influenced post-relapse EFS. We speculate that this may be due to the recruitment of Asp84-Lys69-restricted regulatory T cells in the context of this regimen, leading to the re-emergence of residual disease. However, functional and molecular studies of the prognostic value of this and other HLA molecular signatures in other childhood ALL trials are needed.
childhood ALL; HLA-DP supertype; DP molecular signature; event-free survival; relapse
The IRE1α-XBP1 pathway, a key component of the endoplasmic reticulum (ER) stress response, is considered to be a critical regulator for survival of multiple myeloma (MM) cells. Therefore, the availability of small-molecule inhibitors targeting this pathway would offer a new chemotherapeutic strategy for MM. Here, we screened small-molecule inhibitors of ER stress-induced XBP1 activation, and identified toyocamycin from a culture broth of an Actinomycete strain. Toyocamycin was shown to suppress thapsigargin-, tunicamycin- and 2-deoxyglucose-induced XBP1 mRNA splicing in HeLa cells without affecting activating transcription factor 6 (ATF6) and PKR-like ER kinase (PERK) activation. Furthermore, although toyocamycin was unable to inhibit IRE1α phosphorylation, it prevented IRE1α-induced XBP1 mRNA cleavage in vitro. Thus, toyocamycin is an inhibitor of IRE1α-induced XBP1 mRNA cleavage. Toyocamycin inhibited not only ER stress-induced but also constitutive activation of XBP1 expression in MM lines as well as primary samples from patients. It showed synergistic effects with bortezomib, and induced apoptosis of MM cells including bortezomib-resistant cells at nanomolar levels in a dose-dependent manner. It also inhibited growth of xenografts in an in vivo model of human MM. Taken together, our results suggest toyocamycin as a lead compound for developing anti-MM therapy and XBP1 as an appropriate molecular target for anti-MM therapy.
multiple myeloma; ER stress; IRE1α; XBP1; toyocamycin; adenosine analog