Clinical impact of airflow obstruction after allogeneic hematopoietic stem cell transplantation.

Criteria for airflow obstruction (AFO) at one year after allogeneic hematopoietic stem cell transplantation (allo-HSCT) in pulmonary function tests (PFTs) are more stringent than the bronchiolitis obliterans syndrome (BOS) criteria of the National Institutes of Health. This single-center, retrospective cohort study evaluated the clinical impact of the AFO criteria at any time after transplantation. In 132 patients who underwent allo-HSCT from 2006 to 2016, the 2-year cumulative incidence of AFO was 35.0%, and the median time to diagnosis of AFO was 101 days after transplantation (range 35-716 days). Overall chronic graft-versus-host disease (cGVHD) incidence was significantly higher in patients with AFO than in those without AFO (80.4% vs. 47.7%, P < 0.01); notably, 37.0% of patients with AFO developed cGVHD after AFO diagnosis. AFO patients developed BOS with a 5-year cumulative incidence of 49.1% after AFO onset. The 5-year cumulative incidence of non-relapse mortality in the AFO group was higher than that in the non-AFO group (24.7% vs. 7.1%, P < 0.01). These results suggest that closely monitoring PFTs within two years after allo-HSCT, regardless of cGVHD status, is important for early detection of AFO and prevention of progression to BOS. (192words).

Survival impact of response within the first year in a multicenter prospective observational study of chronic GVHD in a Japanese cohort.

A prospective multicenter observational study of organ response was conducted in patients with chronic GVHD diagnosed by the NIH criteria. When response was assessed at 12 months (12 M) in 118 patients, 74.6% were classified as responders and 25.4% as non-responders. The skin and oral cavity were the most frequent organs used as the basis for determining overall response. The lungs, liver, and eyes were also used in 20% of patients. Non-response decisions at 12 M were most frequent in the lungs. A significantly higher percentage of responders than non-responders completed systemic treatment (24.3% vs. 3.3%, P = 0.02). Global scoring showed significant changes, with improvement in responders and worsening in non-responders throughout the observation period. Two-year transplant-related mortality, using the 12 M assessment as the landmark, was significantly worse in non-responders (28.5% vs. 2,7%, P = 0.0001), while the 2-year recurrence rate was equivalent (5.4% vs. 4.8%, P = 0.78). Consequently, the 2-year overall survival rate from the 12 M assessment was significantly better in responders than non-responders (95% vs. 65.3%, P = 0.0001). Our data suggests that patients who do not achieve a response within the first year should be candidates for clinical studies on chronic GVHD.

Rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone (R-CHOP) therapy decreases lean body mass and appendicular skeletal muscle mass index even until one year after the final treatment in patients with B-cell non-Hodgkin lymphoma.

Sarcopenia is an independent prognostic factor for several solid cancers, including B-cell non-Hodgkin lymphoma (B-NHL). However, previous reports have measured the parameters of loss of skeletal muscle as sarcopenia only once before chemotherapy and have predicted poor outcomes. In this study, changes in body composition were measured in patients who received rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone (R-CHOP) therapy for B-NHL using the InBody 720 analyzer throughout the therapy. Twenty-seven patients who achieved complete remission and survived for one year after the last cycle were included in the study. Body composition was evaluated immediately before initiation and fourth cycle, and one month and one year after the last cycle. Throughout the follow-up period, the lean body mass index (LBMI) and appendicular skeletal muscle mass index (ASMI) showed significant transient decreases even one year following the last cycle (p < 0.001, p = 0.002, respectively). Body fat index (BFI) and body fat percentage (BF%) decreased until one month after the last cycle; however, they reached levels higher than the baseline levels, +22.1% and +15.9%, respectively, at 1 year from the last cycle. The loss of skeletal muscle mass did not recover even one year after the last cycle. Interventions in nutritional management are needed to prevent sarcopenia in patients treated with R-CHOP therapy.

Nilotinib vs dasatinib in achieving MR4.5 for de novo chronic myeloid leukemia: the randomized JALSG CML212 study.

ABSTRACT: Deep molecular response (DMR) is a prerequite for treatment-free remission (TFR) in chronic myeloid leukemia in chronic phase (CML-CP). The JALSG (Japan Adult Leukemia Study Group) conducted a prospective randomized phase 3 CML212 study for de novo CML-CP to compare the cumulative achievement of molecular response 4.5 (MR4.5; international scale BCR::ABL1 ≤0.0032%) by 18 months between nilotinib and dasatinib treatment as a primary end point. A total of 454 patients were randomly assigned to the 300 mg nilotinib twice daily arm or to the 100 mg dasatinib daily arm (both n = 227). BCR::ABL1 messenger RNA levels were monitored every 3 months. Study treatment was stopped if the patients were judged as failure according to the European LekemiaNet 2009 criteria or showed intolerance. The cumulative achievement rates of MR4.5 by 18 months were 32.6% (95% confidence interval [CI], 26.5-39.1) in the nilotinib arm and 30.8% (95% CI, 24.9-37.3) in the dasatinib arm with no significant difference (P = .66). The cumulative achievement rates of early molecular response, complete cytogenetic response, and major molecular response by 12, 18, 24, and 36 months were almost the same between the 2 arms. There was no significant difference in progression-free survival (PFS) or overall survival (OS) between the 2 arms by log-rank tests (PFS, P = .58; OS, P = .64). These results suggest that nilotinib and dasatinib would be equally effective for patients with de novo CML-CP. This trial was registered in the University Hospital Medical Information Network Clinical Trials Registry as #UMIN000007909.

Detection of clonal plasma cells in POEMS syndrome using multiparameter flow cytometry.

POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, monoclonal protein [M-protein], and skin changes) is a rare systemic disorder characterized by various symptoms caused by underlying plasma cell (PC) dyscrasia. Detection of monoclonal PCs is mandatory for the diagnosis of POEMS syndrome; however, the usefulness of EuroFlow-based next-generation flow cytometry (EuroFlow-NGF) in POEMS syndrome for detecting monoclonal PCs in bone marrow (BM) and the gating strategy suitable for flow cytometry study of POEMS syndrome remain unknown. We employed EuroFlow-NGF-based single-tube eight-color multiparameter flow cytometry (MM-flow) and established a new gating strategy (POEMS-flow) to detect the monoclonal PCs in POEMS syndrome, gating CD38 broadly from dim to bright and CD45 narrowly from negative to dim compared to MM-flow. MM-flow detected monoclonal PCs in 9/25 (36.0%) cases, including 2/2 immunofixation electrophoresis (IFE)-negative cases (100%). However, POEMS-flow detected monoclonal PCs in 18/25 cases (72.0%), including 2/2 IFE-negative cases (100%). POEMS-flow detected monoclonal PCs with immunophenotypes of CD19- in 17/18 (94.4%). In six cases where post-treatment samples were available, the size of the clones was significantly reduced after the treatment (P = 0.031). POEMS-flow can enhance the identification rate of monoclonal PCs in POEMS syndrome and become a valuable tool for the diagnosis of POEMS syndrome.

Diagnostic Value of sLR11 and sIL-2R in the Cerebrospinal Fluid for Malignant Central Nervous System Lymphoma.

Objective We previously reported that patients with acute leukemia and malignant lymphoma (ML) demonstrated significantly increased serum soluble LR11 (sLR11) levels compared to normal controls. Accurately diagnosing ML of the central nervous system (CNS ML) using cytology is frequently difficult. Therefore, we evaluated the use of cerebrospinal fluid (CSF) sLR11 and soluble interleukin-2 receptor (sIL-2R) as diagnostic and treatment response markers for CNS ML. Methods We retrospectively evaluated the CSF results for CNS ML using clinical data at our institution, and then analyzed the usefulness of sLR11 and sIL-2R in CSF for both the diagnosis and as surrogate markers that reflect the therapeutic effect. Patients We enrolled patients with CNS ML who received intrathecal anticancer drugs between 2017 and 2023. We analyzed the sLR11 and sIL-2R levels in CSF and cytological malignant grades. We studied 22 patients, including 17 with central nervous system (CNS) clinical conditions and five who received prevention treatment. Results The CSF sLR11 levels were significantly and positively correlated with CSF sIL-2R levels. The CSF sLR11 and sIL-2R levels in patients with CNS ML were significantly higher than those in the prevention group. A receiver operating characteristic (ROC) curve analysis showed the cut-off value of sLR11 for CNS invasion to be 21.7 ng/mL. Moreover, the chemotherapy-responder group demonstrated significantly decreased CSF sLR11 and sIL-2R levels after treatment. Conclusion CSF sLR11 and sIL-2R of CSF were found to be useful biomarkers for the diagnostic and treatment response evaluation in patients with CNS ML.

Successful Treatment of Primary Mediastinal Large B-cell Lymphoma with DA-EPOCH-Rituximab Therapy in a Transgender Woman.

In recent years, lesbian, gay, bisexual, and transgender (LGBT) populations have been gaining acceptance in society. However, very few cases of malignancy in the LGBT population have been reported thus far. We herein report a transgender woman receiving estrogen supplementation who developed primary mediastinal large B-cell lymphoma (PMBCL) and was treated with dose-adjusted EPOCH-rituximab (DA-EPOCH-R) therapy. The patient achieved complete remission after the sixth course of DA-EPOCH-R therapy. To help this LGBT patient continue receiving chemotherapy smoothly on admission, adjusting the hospital environment, such as the allocation of rooms, was essential.

Treatment strategy at the decision for allogeneic transplantation in patients with myelodysplastic syndrome in the era of azacitidine: A KSGCT prospective study.

The optimal bridge strategy at the decision for allogeneic hematopoietic stem cell transplantation (HSCT) in patients with myelodysplastic syndrome (MDS) is unclear. We performed a prospective observational study in which 110 patients with MDS who were decided to undergo HSCT were enrolled. Among these 110 patients, 77 patients were enrolled in this study within 1 month from the decision for HSCT. Among these 77 patients, 13 patients had a human leukocyte antigen (HLA)-matched sibling, 54 patients started an unrelated donor search, and the other 10 patients directly selected cord blood (CB) at the decision for HSCT, and 13 (100%), 38 (70.4%), and 9 (90%) patients actually underwent HSCT within 1 year, respectively. The overall survival (OS) at 1 year from their enrollment was 70.9%, and the selection of azacitidine use at the decision for HSCT was not associated with OS. Among 60 of the 77 patients who actually underwent HSCT within a year from their enrollment, a lower relapse rate after HSCT was observed in those who selected CB at the decision to undergo HSCT. However, this preferable effect of CB selection disappeared when patients who were enrolled in this study in > 1 month from the decision for HSCT were additionally included in the analyses. In conclusion, the selection of bridge strategy at the decision for HSCT did not affect outcomes in patients with MDS. The immediate performance of HSCT may be associated with better outcomes.

A retrospective analysis of clinical features and treatment outcome in 21 patients with immunoglobulin M-related light-chain amyloidosis in Japan: a study from the Amyloidosis Research Committee.

We retrospectively gathered data of 21 patients (13 male and 8 female; median age 65 years) diagnosed with immunoglobulin M (IgM)-related light-chain (AL) amyloidosis in Japan to investigate characteristics of IgM-AL amyloidosis and its optimal treatment strategy. Median IgM and difference free light chain (FLC) at diagnosis were 1257 mg/dl and 34.3 mg/l, respectively. Organ involvement was observed in the heart in 7 patients (33%), kidneys in 15 (71%), and lymph nodes in 5 (24%). Initial treatments were melphalan/dexamethasone in 7 patients, bortezomib/cyclophosphamide/dexamethasone in 3, autologous stem cell transplantation in 3, rituximab/bendamustine in 1, other in 3, and none in 4. Hematological responses among 15 evaluable patients were as follows: 3 reached complete response (CR), 4 partial response (PR), and 1 very good PR (VGPR), making the overall response rate of PR or better 40%. Median overall survival (OS) was 14.0 months and 1-year OS was 71.4%. Prognosis was significantly poorer in patients with cardiac involvement than those with non-cardiac involvement (1-year OS 27.8% vs. 85.7%, p = 0.0468). The involved FLC value was low in several patients and therapeutic response was difficult to assess. Further study is necessary to determine the optimal treatment for IgM-AL amyloidosis.

UTX inactivation in germinal center B cells promotes the development of multiple myeloma with extramedullary disease.

UTX/KDM6A, a histone H3K27 demethylase and a key component of the COMPASS complex, is frequently lost or mutated in cancer; however, its tumor suppressor function remains largely uncharacterized in multiple myeloma (MM). Here, we show that the conditional deletion of the X-linked Utx in germinal center (GC) derived cells collaborates with the activating BrafV600E mutation and promotes induction of lethal GC/post-GC B cell malignancies with MM-like plasma cell neoplasms being the most frequent. Mice that developed MM-like neoplasms showed expansion of clonal plasma cells in the bone marrow and extramedullary organs, serum M proteins, and anemia. Add-back of either wild-type UTX or a series of mutants revealed that cIDR domain, that forms phase-separated liquid condensates, is largely responsible for the catalytic activity-independent tumor suppressor function of UTX in MM cells. Utx loss in concert with BrafV600E only slightly induced MM-like profiles of transcriptome, chromatin accessibility, and H3K27 acetylation, however, it allowed plasma cells to gradually undergo full transformation through activation of transcriptional networks specific to MM that induce high levels of Myc expression. Our results reveal a tumor suppressor function of UTX in MM and implicate its insufficiency in the transcriptional reprogramming of plasma cells in the pathogenesis of MM.

Outcomes of poor peripheral blood stem cell mobilizers with multiple myeloma at the first mobilization: A multicenter retrospective study in Japan.

Autologous stem cell transplantation (ASCT) remains an important therapeutic strategy for multiple myeloma; however, a proportion of patients fail to mobilize a sufficient number of peripheral blood stem cells (PBSCs) to proceed to ASCT. In the present study, we aimed to clarify the characteristics and outcomes of poor mobilizers. Clinical data on poorly mobilized patients who underwent PBSC harvest for almost 10 years were retrospectively collected from 44 institutions in the Japanese Society of Myeloma (JSM). Poor mobilizers were defined as patients with less than 2 × 106/kg of CD34+ cells harvested at the first mobilization. The proportion of poor mobilization was 15.1%. A sufficient dataset including overall survival (OS) was evaluable in 258 poor mobilizers. Overall, 92 out of 258 (35.7%) poor mobilizers did not subsequently undergo ASCT, mainly due to an insufficient number of PBSCs. Median OS from apheresis was longer for poor mobilizers who underwent ASCT than for those who did not (86.0 vs. 61.9 mon., p = 0.02). OS from the diagnosis of poor mobilizers who underwent ASCT in our cohort was similar to those who underwent ASCT in the JSM database (3y OS rate, 86.8% vs. 85.9%). In this cohort, one-third of poor mobilizers who did not undergo ASCT had relatively poor survival. In contrast, the OS improved in poor mobilizers who underwent ASCT. However, the OS of extremely poor mobilizers was short irrespective of ASCT.

Unraveling unique features of plasma cell clones in POEMS syndrome with single-cell analysis.

POEMS syndrome is a rare monoclonal plasma cell disorder, with unique symptoms distinct from those of other plasma cell neoplasms, including high serum VEGF levels. Because the prospective isolation of POEMS clones has not yet been successful, their real nature remains unclear. Herein, we performed single-cell RNA-Seq of BM plasma cells from patients with POEMS syndrome and identified POEMS clones that had Ig λ light chain (IGL) sequences (IGLV1-36, -40, -44, and -47) with amino acid changes specific to POEMS syndrome. The proportions of POEMS clones in plasma cells were markedly smaller than in patients with multiple myeloma (MM) and patients with monoclonal gammopathy of undetermined significance (MGUS). Single-cell transcriptomes revealed that POEMS clones were CD19+, CD138+, and MHC class IIlo, which allowed for their prospective isolation. POEMS clones expressed significantly lower levels of c-MYC and CCND1 than MM clones, accounting for their small size. VEGF mRNA was not upregulated in POEMS clones, directly indicating that VEGF is not produced by POEMS clones. These results reveal unique features of POEMS clones and enhance our understanding of the pathogenesis of POEMS syndrome.

Rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone (R-CHOP) therapy increases carotid intima-media thickness and plaque score with von Willebrand factor activity elevation in patients with malignant lymphoma.

An increased risk for atherosclerosis has been noted in cancer survivors; however, studies that focus on the risk of atherosclerosis in patients treated with chemotherapy are scarce. Therefore, we evaluated 32 patients who received rituximab, cyclophosphamide, doxorubicin, vincristine and prednisolone (R-CHOP) therapy for B-cell malignant lymphoma by analysing the changes in atherosclerosis. Just before each treatment course, plasma levels of von Willebrand Factor (vWF) activity were evaluated, and carotid ultrasonography was performed at baseline and after the final treatment. Throughout the follow-up period, plasma vWF levels showed significantly transient increased by approximately 20%-40%. Both mean carotid intima-media thickness (IMT) and plaque score (PS) significantly increased during the 36.6 ± 26.0 weeks of observation (mean IMT: 0.724 ± 0.118 to 0.767 ± 0.129 mm; PS: 4.31 ± 3.53 to 4.87 ± 3.88, P < 0.001). Our study suggests that R-CHOP therapy promotes atherosclerosis.

Successful allogeneic bone marrow transplantation after massive gastrointestinal bleeding in a patient with myelodysplastic syndrome associated with intestinal Behçet-like disease.

A 45-year-old woman was diagnosed with myelodysplastic syndrome (MDS) with trisomy 8 and Behçet-like disease (BLD) with multiple colorectal ulcers. Nonspecific inflammatory cells were infiltrated in the intestinal mucosa, whereas fluorescence in situ hybridization (FISH) analysis revealed only sporadic trisomy 8-positive cells. She presented massive lower gastrointestinal bleeding early after bone marrow transplantation but achieved long-term remission of both MDS and BLD. This is the first report of massive gastrointestinal bleeding after transplantation for MDS with BLD. Based on FISH analysis, dysregulation of systemic inflammation may be involved in BLD rather than direct invasion by trisomy 8-positive MDS clones.

Pharmacokinetically guided, once-daily intravenous busulfan in combination with fludarabine for elderly AML/MDS patients as a conditioning regimen for allogeneic stem cell transplantation.

The efficacy of pharmacokinetically (PK) guided, once-daily administration of busulfan (BU) was evaluated in elderly patients with acute myeloid leukemia/myelodysplastic syndrome (AML/MDS). Twenty-one patients (median age 61) received 30 mg/m2 fludarabine for 6 days and BU for 4 days, starting from 3.2 mg/m2 and subsequently adjusted to the target area under the curve (AUC) of 6000 µmol-min/L. The median AUC of day 1 (AUC1), AUC4, and their average were 4871.3, 6021.0, and 5368.1 µmol-min/L, respectively. Veno-occlusive disease/sinusoidal obstructive syndrome (VOD/SOS) occurred in five patients (24%) but all recovered well. Four patients (20%) had non-infectious pulmonary complications (NIPCs). Patients with high AUC1 had frequent gastrointestinal adverse events, but similar incidence of VOD/SOS and NIPCs. Two-year overall survival (OS), non-relapse mortality (NRM), and relapse rates were 44.4%, 28.6%, and 29.1%, respectively. Patients with high AUC1 had significantly high NRM (57.1% vs. 14.3%, P = 0.04) and inferior OS (14.3% vs. 60.1%, P = 0.002), while patients with high AUC4 had a significantly low relapse rate (8.3% vs. 55.6%, P = 0.02). In conclusion, once-daily BU and a PK-guided dose intensification were beneficial for reducing relapse in elderly patients with AML/MDS. However, caution should be exercised as rapid BU dose elevation may contribute to NRM.

Genetic subtype classification using a simplified algorithm and mutational characteristics of diffuse large B-cell lymphoma in a Japanese cohort.

Recent large-scale genetic studies have proposed a new genetic classification of diffuse large B-cell lymphoma (DLBCL), which is clinically and biologically heterogeneous. However, the classification methods were complicated to be introduced into clinical practice. Here we retrospectively evaluated the mutational status and copy number changes of 144 genes in 177 Japanese patients with DLBCL, using targeted DNA sequencing. We developed a simplified algorithm for classifying four genetic subtypes-MYD88, NOTCH2, BCL2, and SGK1-by assessing alterations in 18 representative genes and BCL2 and BCL6 rearrangement status, integrating the significant genes from previous studies. In our cohort and another validation cohort from published data, the classification results in our algorithm showed close agreement with the other established algorithm. A differential prognosis among the four groups was observed. The NOTCH2 group showed a particularly poorer outcome than similar groups in previous reports. Furthermore, our study revealed unreported genetic features in the DLBCL subtypes that are mainly reported in Japanese patients, such as CD5-positive DLBCL and methotrexate-associated lymphoproliferative disorders. These results indicate the utility of our simplified method for DLBCL genetic subtype classification, which can facilitate the optimisation of treatment strategies. In addition, our study highlights the genetic features of Japanese patients with DLBCL.

Identification of clonal immunoglobulin λ light-chain gene rearrangements in AL amyloidosis using next-generation sequencing.

Amyloid light-chain (AL) amyloidosis is caused by deposition of abnormally folded clonal immunoglobulin (Ig) light chains made by malignant plasma cells in the bone marrow (BM), leading to multiorgan dysfunction. However, little is known of the factors that regulate the organ tropism of amyloid deposition in this disease. We aimed to identify the clonal composition of Igλ light-chain variable region (IGLV) genes in BM cells in patients with AL amyloidosis using next-generation sequencing. Based on our definition of the clonal IGLV rearrangement (dominant clone >2.5%, dominant cluster >5%), we identified clonal IGLV in 33 of 38 patients with AL amyloidosis (86.8%), 6 of 9 with monoclonal gammopathy of undetermined significance (67%), and 7 of 7 with multiple myeloma (100%). The clones in AL amyloidosis were significantly smaller than those in multiple myeloma (p < 0.01) but comparable to those in monoclonal gammopathy of undetermined significance. Importantly, in patients with AL amyloidosis, the difference in involved and uninvolved free light chains was not correlated with the clonal size of BM plasma cells in our repertoire analysis using NGS. In summary, the clonal composition of IGLV genes in the BM was successfully identified in most patients with AL amyloidosis using NGS. The clonal size of plasma cells in the BM is small, and small malignant clones of plasma cells may secrete free light chi and cause light chain depositions in AL amyloidosis.

High presepsin concentrations in bile and its marked elevation in biliary tract diseases: A retrospective analysis.

BACKGROUND: Presepsin is a diagnostic and prognostic biomarker of both bacterial infection and sepsis; however, elevated presepsin levels have also been observed without sepsis. We conducted several analyses to evaluate the clinical laboratory parameters affecting presepsin levels. METHOD: We analyzed the association between sequential organ failure assessment (SOFA) scores and plasma presepsin levels and then analyzed clinical laboratory parameters in 567 patients with univariate and multivariate regression analysis and analysis of covariance (ANCOVA). We also determined presepsin in the bile of 11 patients and examined the presepsin immunostaining in liver. RESULTS: Spearman's rank correlation analysis with loge change revealed that presepsin levels were closely associated with loge-transformed SOFA score (ρ = 0.541), alkaline phosphatase (ALP); (ρ = 0.454) and gamma-glutamyl transferase; (ρ = 0.505). Multivariate regression analysis revealed that loge-transformed SOFA score (ß-coefficient = 0.316), ALP level (ß-coefficient = 0.380), and creatinine level (ß-coefficient = 0.290) independently and significantly affected loge presepsin levels. ANCOVA revealed that presepsin levels were significantly higher in patients with hepatobiliary disease. Patients who presented with dilatation of the bile ducts and elevated ALP levels or total bilirubin levels exhibited high presepsin levels in the bile. Presepsin production in liver Kupffer cells was also confirmed by immunostaining. CONCLUSION: Presepsin levels is correlated with the elevation of biliary enzymes in patients without renal dysfunction or sepsis. Additionally, presepsin exists with high concentrations in the bile and is positive in Kupffer cells.

The combination of the tubulin binding small molecule PTC596 and proteasome inhibitors suppresses the growth of myeloma cells.

The novel small molecule PTC596 inhibits microtubule polymerization and its clinical development has been initiated for some solid cancers. We herein investigated the preclinical efficacy of PTC596 alone and in combination with proteasome inhibitors in the treatment of multiple myeloma (MM). PTC596 inhibited the proliferation of MM cell lines as well as primary MM samples in vitro, and this was confirmed with MM cell lines in vivo. PTC596 synergized with bortezomib or carfilzomib to inhibit the growth of MM cells in vitro. The combination treatment of PTC596 with bortezomib exerted synergistic effects in a xenograft model of human MM cell lines in immunodeficient mice and exhibited acceptable tolerability. Mechanistically, treatment with PTC596 induced cell cycle arrest at G2/M phase followed by apoptotic cell death, associated with the inhibition of microtubule polymerization. RNA sequence analysis also revealed that PTC596 and the combination with bortezomib affected the cell cycle and apoptosis in MM cells. Importantly, endoplasmic reticulum stress induced by bortezomib was enhanced by PTC596, providing an underlying mechanism of action of the combination therapy. Our results indicate that PTC596 alone and in combination with proteasome inhibition are potential novel therapeutic options to improve outcomes in patients with MM.