Abstract: 7504 Background: No standard of care for elderly patients with aggressive adult T-cell leukemia/lymphoma (ATL) has been established yet. We assessed the efficacy of an anti-CCR4 antibody, mogamulizumab (Moga) combined with biweekly cyclophosphamide (CPA), doxorubicin (DXR), vincristine (VCR), and prednisone (PSL) (Moga-CHOP-14) for untreated elderly patients with aggressive ATL. Methods: In this phase 2 trial conducted at 21 centers in Japan, untreated CCR4-positive aggressive ATL patients aged 66 years or older and 56-65 years who were not candidates for allogeneic hematopoietic stem cell transplantation (allo-HSCT) received six cycles of Moga-CHOP-14, followed by two cycles of Moga monotherapy. The primary endpoint was 1-year progression-free survival (PFS), defined as the time from enrollment to the progression/relapse of ATL or death due to any cause, whichever occurred first. Secondary endpoints were complete response rate (CR), overall response rate (ORR), overall survival (OS), 1-year event-free survival (EFS), and the incidence of adverse events. The necessary number of patients calculated by setting the threshold 1-year PFS at 16% and the expected 1-year PFS at 31% using the exact method based on binomial distribution under the conditions of one-sided level of significance of 5% (α = 0.05) and power of 70% was 43. Results: A total of 50 patients were enrolled from October 2015, until September 2020. Among the 48 evaluable patients, the median age was 74 years (interquartile range [IQR], 70-78). ATL subtypes included 31, 9, and 8 patients for the acute, lymphoma, and unfavorable chronic type, respectively. ATL-PI included 9, 31, and 8 patients for high, intermediate, and low risk, respectively. With a median follow-up of 1.6 years (IQR, 0.7-2.4), 1-year PFS was 36.2% (90% confidence interval (CI), 24.9-47.6), and a median PFS was 0.7 years (95% CI, 0.5-1.0). CR and ORR were noted in 64.6% (95%CI, 49.5-77.8), and 91.7% (95% CI, 80.0-97.7), respectively. One-year OS was 66.0% (95% CI, 50.6-77.6) and median OS was 1.6 years (95%CI, 1.1-2.8). One-year EFS was 29.9% (95% CI, 17.6-43.2) and median EFS was 0.5 years (95%CI, 0.4-0.7). The most frequent adverse events grades 3/4, which occurred in 〉 10% of patients were lymphocytopenia (97.9%), leukopenia (93.8%), neutropenia (89.6%), febrile neutropenia (64.8%), anemia (58.3%), thrombocytopenia (45.8%), infection (27.1%), skin rash (20.8%), and hyperglycemia (20.8%). Relative dose intensity (RDI) was calculated for each drug: the mean RDI for Moga was 82.1%, for CPA 71.7%, for DXR 72.7%, for VCR 72.0%, and for PSL 77.3%. Conclusions: This study demonstrated that Moga-CHOP-14 significantly improved PFS in elderly patients with aggressive CCR4-positive ATL who were ineligible for allo-HSCT. Moga-CHOP-14 is now considered for the preferred first-line treatment in those patients. Clinical trial information: jRCTs041180130 .

Abstract: Background: Enhancer of zeste homolog 2 (EZH2) and its close homolog, EZH1, catalyze the attachment of 3 methyl groups to histone H3 at lysine 27 (H3K27me3). H3K27me3 is an epigenetic mark involved in downregulating gene expression associated with tumor suppression and cell differentiation. Recent evidence suggests that adult T-cell leukemia/lymphoma (ATL) can be driven by epigenetic dysregulation (Blood. 2016;127:1790-1802). Specifically, altered EZH2 expression has been implicated in the development and progression of ATL. Valemetostat tosylate (DS-3201b; valemetostat) is a novel, potent, and selective dual inhibitor of EZH2 and EZH1 that has demonstrated antitumor activity against hematologic malignancies, especially T-cell lymphoma, including relapsed or refractory (R/R) ATL in a phase 1 study (EHA 2021. Abstract S218). Here, we report the results from the primary analysis of a pivotal phase 2 study of valemetostat in Japanese patients (pts) with R/R ATL. Aims: This multicenter, single-arm, open-label, phase 2 study (NCT04102150) evaluated the efficacy and safety of single-agent valemetostat in pts with R/R ATL. The primary objective was to evaluate efficacy by central efficacy assessment committee (EAC)-assessed overall response rate (ORR), defined as the proportion of pts whose best response was complete remission (CR), uncertified CR, or partial remission using international consensus criteria (J Clin Oncol. 2009;27:453-59). The null hypothesis was an ORR of ≤5% (binomial test with a 1-sided significance level of 5%). Secondary outcome measures included CR rate, duration of response (DOR) per EAC, efficacy per investigator (INV) assessment, and the safety and pharmacokinetics of valemetostat. Methods: Pts ≥20 years of age with R/R ATL (acute, lymphomatous, or unfavorable chronic type) were enrolled from 24 sites in Japan. Pts must have had a positive antihuman T-cell leukemia virus type 1 antibody serum test and received prior therapy with mogamulizumab or ≥1 prior systemic therapy in the case of intolerance of, or contraindication for, mogamulizumab. Pts with prior allogeneic hematopoietic stem cell transplant were excluded. Valemetostat 200 mg was orally administered once daily in continuous 28-day cycles until disease progression or intolerance. The EAC-determined efficacy assessment was based on central evaluation of radiographic images and clinical data, including peripheral blood, skin, and bone marrow lesions (J Clin Oncol. 2009;27:453-59). Results: At the time of data cutoff (April 24, 2021), the study enrolled the planned 25 pts which included 16, 6, and 3 pts with acute, lymphomatous, or unfavorable chronic ATL subtypes, respectively. The median age was 69 years (range, 59-84 years). The median number of prior lines of therapy was 3 (range, 1-8). 24 pts (96.0%) had prior treatment with mogamulizumab. The study met its primary endpoint: with a median follow-up of 28 weeks (range, 14-71 weeks), valemetostat resulted in a 48% (12/25) ORR per EAC assessment (P & lt;.0001; 95% CI, 27.8%-68.7%), including a 20% CR rate. Primary efficacy data are summarized in the Table. The median DOR (n=12) was not reached (95% CI, 8.14 weeks-not reached). EAC- and INV-assessed results were similar. 8 of 25 pts (32%) remained on treatment. 25 pts (100%) experienced ≥1 treatment-emergent adverse event (TEAE). Grade ≥3 TEAEs occurred in 15 pts (60%), and grade ≥3 serious TEAEs occurred in 6 pts (24%); valemetostat was not associated with any deaths. Dose interruption or reduction due to TEAEs occurred in 5 (20%) and 2 (8%) pts, respectively. Two pts (8%) discontinued due to TEAEs. The most common TEAEs (≥30% of pts) were platelet count decreased (80%), dysgeusia (36%), anemia (48%), and alopecia (40%); grade ≥4 platelet count decreased occurred in 3 pts (12%). Summary/Conclusions: Valemetostat resulted in a high response rate and durable antitumor effect in Japanese pts with R/R ATL, the majority of whom were pretreated with mogamulizumab. Valemetostat's safety profile was manageable. These results are consistent with those observed in the phase 1 study conducted in Japan and the US, suggesting that valemetostat could be a new treatment option for pts with R/R ATL. Valemetostat is also being evaluated in a global phase 2 study in pts with R/R ATL and R/R peripheral T-cell lymphoma (NCT04703192). Figure 1 Figure 1. Disclosures Yoshimitsu: Sanofi: Honoraria; Takeda: Honoraria; Novartis: Honoraria. Izutsu: Kyowa Kirin: Honoraria, Research Funding; Incyte: Research Funding; Chugai: Honoraria, Research Funding; Bayer: Research Funding; Beigene: Research Funding; AstraZeneca: Honoraria, Research Funding; Yakult: Research Funding; AbbVie: Honoraria, Research Funding; Takeda Pharmaceutical: Honoraria, Research Funding; HUYA Bioscience International: Research Funding; Eisai: Honoraria, Research Funding; MSD: Research Funding; Janssen: Honoraria, Research Funding; Genmab: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Daiichi Sankyo: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; Ono: Honoraria, Research Funding; Pfizer: Research Funding; Symbio: Honoraria, Research Funding; Allergan Japan: Honoraria; FUJI FILM Toyama Chemical: Honoraria. Makita: Takeda: Consultancy, Honoraria; SymBio: Honoraria; Novartis: Honoraria; Eisai: Honoraria; Daiichi-Sankyo: Consultancy; CSL Behring: Honoraria; Chugai: Honoraria; BMS: Consultancy, Honoraria. Nosaka: Eisai Co., Ltd: Honoraria; Celgene K.K.: Honoraria; Kyowa Kirin Co., Ltd: Consultancy, Honoraria, Research Funding; Meiji Seika Parma Co., Ltd: Honoraria; Chugai Pharmaceutical Co., Ltd.: Research Funding; Janssen Pharmaceutical K.K.: Honoraria; Bristol Myers Squibb: Honoraria. Utsunomiya: Novartis Pharma: Honoraria; Kyowa Kirin: Honoraria; Daiichi Sankyo: Honoraria; Celgene: Honoraria; Pfizer: Honoraria; Janssen Pharmaceutical: Honoraria; JIMRO: Honoraria; Meiji Seika Pharma: Honoraria; Otsuka Medical Devices: Honoraria. Kusumoto: Daiichi Sankyo: Research Funding; Chugai: Honoraria, Research Funding; Kyowa Kirin: Honoraria. Tsukasaki: Solasia Pharma: Consultancy; Meiji Seika Pharma: Consultancy; Yakuruto: Consultancy; HUYABIO: Consultancy, Research Funding; Ono Pharma: Consultancy; Daiichi Sankyo: Consultancy, Research Funding; Takeda: Honoraria; Kyowa-hakko/Kirin: Honoraria, Research Funding; Eizai: Honoraria, Research Funding; Byer: Research Funding; Chugai Pharma: Honoraria, Research Funding; Celgene: Honoraria, Research Funding. Ono: Chugai Pharmaceutical Co., Ltd.: Honoraria, Research Funding; Eisai Co., Ltd.: Honoraria; Janssen Pharmaceutical K.K: Honoraria; DAIICHI SANKYO COMPANY, LIMITED.: Honoraria; Mundipharma K.K.: Honoraria; TAIHO PHARMACEUTICAL CO., LTD.: Research Funding; Merck Sharp & Dohme: Honoraria, Research Funding; Astellas Pharma Inc.: Honoraria; Bristol-Myers Squibb Company: Honoraria; Novartis Pharma KK: Honoraria; Pfizer Japan Inc.: Honoraria; Otsuka Pharmaceutical Co., Ltd.: Honoraria; ONO PHARMACEUTICAL CO., LTD.: Honoraria, Research Funding; Takeda Pharmaceutical Company Limited.: Honoraria; Kyowa Kirin Co., Ltd.: Honoraria, Research Funding; Celgene: Honoraria, Research Funding. Rai: Chugai Pharmaceutical: Speakers Bureau; Ono Pharmaceutical: Speakers Bureau; Janssen Pharmaceutical: Speakers Bureau. Yamada: Daiichi Sankyo: Current Employment. Kato: Bristol Myers Squibb: Current equity holder in publicly-traded company; Daiichi Sankyo: Current Employment. Tachibana: Daiichi Sankyo: Current Employment. Kakurai: Daiichi Sankyo: Current Employment. Adachi: Daiichi Sankyo: Current Employment. Tobinai: Celgene: Consultancy, Honoraria; Chugai Pharmaceutical: Honoraria; Eisai: Honoraria; Daiichi Sankyo: Consultancy, Honoraria; HUYA Bioscience International: Consultancy, Honoraria; Kyowa Kirin: Honoraria; Mundipharma: Consultancy, Honoraria; Ono Pharmaceutical: Consultancy, Honoraria; Solasia Pharma: Honoraria; Takeda Pharmaceutical: Consultancy, Honoraria; Yakult: Honoraria; Zenyaku Kogyo: Consultancy, Honoraria. Yonekura: AbbVie: Honoraria; Amgen: Honoraria; Celgene: Honoraria; Daiichi Sankyo: Honoraria; Eisai: Honoraria; Eli Lilly Japan: Honoraria; Janssen Pharmaceuticals: Honoraria; Kaken Pharmaceutical: Honoraria; Kyowa Kirin: Honoraria; Maruho: Honoraria; Minophagen Pharmaceutical: Honoraria; Novartis: Honoraria; Sanofi: Honoraria; Taiho Pharmaceutical: Honoraria; Torii Pharmaceutical: Honoraria; UCB Japan: Honoraria. Ishitsuka: Pfizer: Other: Personal fees; Astellas Pharma: Other: Personal fees, Research Funding; Genzyme: Other: Personal fees; Sumitomo Dainippon Pharma: Other: Personal fees, Research Funding; Eisai: Other: Personal fees, Research Funding; Novartis: Other: Personal fees; Janssen Pharmaceuticals: Other: Personal fees; Taiho Pharmaceuticals: Other: Personal fees, Research Funding; Mundipharma: Other: Personal fees; Takeda: Other: Personal fees, Research Funding; BMS: Other; Chugai Pharmaceutical: Honoraria, Other: Personal fees, Research Funding; Celgene: Honoraria, Other: Personal fees; Ono Pharmaceutical: Other: Personal fees, Research Funding; Kyowa Kirin: Other: Personal fees, Research Funding; Daiichi Sankyo: Consultancy, Other: Personal fees; Mochida: Other: Personal fees, Research Funding; Shire: Other; Otsuka Pharmaceutical: Other: Personal fees; Teijin Pharma: Research Funding; MSD: Research Funding; Asahi kasei: Research Funding; Eli Lilly: Research Funding; Huya Japan: Other: Personal fees.

Abstract: [Background] Multiple myeloma (MM) still remains an incurable disease even after the development of novel agents including immunomodulatory drugs and proteasome inhibitors, thus needs alternative agents especially for the refractory subtypes harboring t(4;14)(p16;q32). Since constitutive expression of topoisomerase I (TopoI) in MM cells and the efficacy of SN-38, an active metabolite of irinotecan (CPT-11), have been reported (Br J Haematol83:68, 1993; Cancer Res64: 8749, 2004), we investigated on the therapeutic potential of the CPT-11. [Method] Eight MM together with lymphoma cell lines were examined for cellular proliferation and viability in the presence of various concentrations of CPT-11 or SN-38 (gift from Yakult Inc., Tokyo) by means of 3H-thymidine uptake and MTS assays. Total RNA prepared from purified plasma cells derived from MM and reactive plasmacytosis patients was quantified for the mRNA levels of carboxylesterase-2(CE-2), CE-1, TopoI, UGT-1A and ABCG2, which had been reported to be associated with either sensitivity or toxicity to CPT-11. To ensure responsive roles of CE-2 in drug sensitivity, we established U266-derived stable transfectants overexpressing CE-2 (U266/CE-2) using hCE-2 cDNA kindly provided by Dr M.E. Dolan (Univ. of Chicago). To make sure in vivo effect, SCID mice were inoculated subcutaneously with 3×107 KMS-11 cells together with Matrigel. At the day of (prophylactic model) and at the 13 days after inoculation (therapeutic model), mice began to be treated by weekly intra-peritoneal injection with CPT-11 (25 mg/kg) or saline as control. Tumor size was validated until 28 days after treatment. Serum free-light-chain (FLC) levels were also measured on day 28. [Results and Discussion] CPT-11 and SN-38 inhibited DNA synthesis of most MM cells to & lt;15% and to & lt;10% with 2 μg/mL and 2 ng/mL, respectively. In 4/8 MM cell lines, IC50 was & lt;2 μg/mL for CPT-11 and & lt;2 ng/mL for SN-38. The efficacy of CPT-11 was observed in MM cells with any types of chromosomal translocations including t(4;14) or with resistance against any types of chemotherapeutic agents. Such efficacy was partly explained by expression level of CE-2, which plays a major role in catalyzing CPT-11 to its bioactive form, SN-38, being higher in MM than lymphoma cells. The highest CE-2 level was observed in reactive plasma cells, i.e., normal counterpart of the MM cells. IC50 for CPT-11 was 3.0 and 0.13 μg/mL for U266/mock and U266/CE-2 cells, respectively, indicating the importance of the CE-2 in terms of the sensitivity to CPT-11. On the other hand, expression level of CE-1, TopoI, UGT-1A and ABCG2 did not seem to be associated with its sensitivity in MM. In murine xenograft model, CPT-11 significantly reduced the tumor volume at day 26 when compared to the controls from 3,986±1,338 to 0±0 mm3 in prophylactic and from 10,397±2,881 to 5,375±3,594 mm3 in therapeutic models. Serum kappa FLC produced by KMS-11 cells was lower in the treatment group as well. Taken together, efficacy of the CPT-11 for MM can be validated in the clinical trial setting, as Cmax after 100 mg/m2 infusion reaches to 1.87 μg/mL, probably followed by efficient generation of intracellular SN-38 in MM cells by highly expressed CE-2.

Abstract: Bortezomib, a proteasome inhibitor, which was originally developed as an inhibitor of NF-kappaB pathways, is currently used for the treatment of multiple myeloma (MM) and mantle cell lymphoma (MCL). The mechanisms of action of this anti-tumor agent have been studied by several investigators. As bortezomib has been reported effective for a fraction of peripheral T-cell lymphomas including adult T-cell leukemia/lymphoma (ATLL) and cutaneous T-cell lymphoma (CTCL) at clinically achievable concentrations, it is expected to be applicable for these refractory T-cell malignancies. In this study, we have explored the underlying mechanisms of bortezomib-induced apoptosis in cell lines established from CTCL and ATLL together with those from MM by particularly focusing on the level of mitochondrial membrane injury. It was because the apoptosis induced by bortezomib in CTCL and ATLL cells accompanied the activation of caspase-3, -8, and -9, and the disturbance of mitochondrial membrane potential preceded the process of bortezomib-induced apoptosis when detected by DiIC1 and Annexin V staining. In 6 MM lines including KMS-12-PE, 2 CTCL lines including Hut78, and 7 ATLL lines including ATN1 and MT4, anti-apoptotic factors such as c-Flip and XIAP were down-regulated after exposure to bortezomib, probably via inhibition of NF-kappaB signaling. This reduction of c-Flip and XIAP was also confirmed in the primary tumor cells derived from the patients with ATLL after exposure to 20nM bortezomib. These findings indicate that the activation of both intrinsic and extrinsic apoptosis pathways led to activation of caspases via reduced expression of negative regulators of apoptosis. Among the members of the BH3-only family protein, up-regulation of Noxa was consistently seen at both the transcriptional and protein levels in a p53-independent and c-Myc-independent manner after exposure to bortezomib, whereas the expression of other BH3-only family proteins showed no consistent changes. Of anti-apoptotic Bcl-2 family proteins, accumulation of Mcl-1 and its cleaved form were observed, but no altered expression of other Bcl-2 family members was seen. Specific repression of Noxa by small interfering RNA partially rescued CTCL and ATLL cells from bortezomib–induced apoptosis, suggesting a crucial role of Noxa in bortezomib-induced apoptosis in these cell types as well as in MM cells. Immunoprecipitation assays indicated time-dependent binding of Noxa and Mcl-1 in all cell types, suggesting that functional repression of Mcl-1 led to the loss of mitochondrial outer membrane potential. Similar results showing transcriptional and translational up-regulation of Noxa followed by increased amount of the Mcl-1/Noxa complexes after exposure to 20nM bortezomib were also obtained in primary tumor cells derived from patients with ATLL. Taken together, we conclude that bortezomib-induced apoptosis in ATLL/CTCL cells at least partly depends on up-regulation of Noxa and functional repression of Mcl-1 in addition to the reduced amount of c-Flip and XIAP proteins, although the mechanisms leading to the transcriptional activation of Noxa after exposure to bortezomib remains to be clarified.

Abstract: Background: Bortezomib (BTZ), a proteasome inhibitor (PI), mainly targets the beta 5 subunit of the 20S proteasome, and is widely used in the treatment of multiple myeloma (MM). However, inhibitory effects on other subunits of the proteasome are not well understood. Therefore, we examined the anti-MM activity of novel syringolin analogs that inhibit the activity of both beta 5 and 2 subunits. After examination, we investigated the activity of compound 19a, developed as a syrbactin-class PI to improve cytotoxic activity and membrane permeability (Chiba T et al. Angew Chem Int Ed. 2014). Materials and method: First, the cytotoxic and inhibitory effects of compound 19a on 20S proteasomes of MM cells, including BTZ-resistant MM cells and primary samples derived from MM patients, were examined. The primary MM specimens were collected after obtaining written informed consent at Nagoya City University Hospital, and the mechanism of antitumor activity of compound 19a on MM cells was evaluated by focusing on the unfolded protein response and endoplasmic reticulum (ER) stress. Finally, to evaluate the toxicity of compound 19a, BALB/c mice were intraperitoneally injected with either 19a or BTZ and body weight change was analyzed. These in vivo experiments were performed in accordance with the United Kingdom Coordinating Committee on Cancer Research Guidelines for the Welfare of Animals in Experimental Neoplasia, Second Edition, and were approved by the Ethics Committee of the Center for Experimental Animal Science, Nagoya City University Graduate School of Medical Sciences. Results: The cytotoxic activity of compound 19a, observed in various MM cell lines at nanomolar concentrations, was found to be similar to the activity observed when BTZ-resistant MM and T-cell lymphoma cell lines were tested. More precisely, the two BTZ-resistant cell lines KMS-11/BTZ and OPM-2/BTZ showed 44.4-fold and 52.1-fold higher resistance, respectively, to BTZ than that shown by their parental cell lines KMS-11 and OPM-2. However, the two BTZ-resistant cells showed only 3.2-fold (IC50: 18.0 nM) and 4.3-fold (IC50: 5.1 nM) higher resistance to compound 19a than that shown by their parental cell lines KMS-11 (IC50: 5.7 nM) and OPM-2 (IC50: 1.2 nM), suggesting that compound 19a exhibits less cross-resistance to BTZ. Evaluation of 20S proteasome activity showed time-dependent inhibition of both beta 5 and 2 subunits in MM cells on treatment with compound 19a. Treatment with 10 nM 19a induced remarkable apoptosis of the MM cells, accompanied by elevated CHOP and NOXA expression, indicating excessive ER stress. A similar activity was also observed in primary MM samples derived from the patients. Furthermore, to clarify the effect of beta 2 inhibition on anti-MM activity, two MM cell lines, U266 and AMO1, and one T-cell lymphoma cell line, Hut78, were transfected with either siRNA-targeting PSMB7 encoding beta 2 subunit or control siRNA and were subjected to the analysis of cell growth and viability. Specific knocking down of PSMB7 was observed, which resulted in the progression of apoptosis of the two MM cell lines and Hut78 when compared with the control. In addition, knocking down of both PSMB7 and PSMB5 encoding beta 5 subunits triggered more potent apoptosis of U266 and Hut78 cells when compared with the knocking down of either PSMB7 or PSMB5 alone. This result suggests that dual-inhibitory activities of beta 5 and 2 subunits have an additive or a synergistic effect on cytotoxicity when compared with single inhibitory activity. Finally, to examine the toxicity of compound 19a, BALB/c mice were administrated with it in a dose-escalation manner and subjected to the analysis of alteration of body weight. No significant difference in loss of body weight was observed between 19a-treated and BTZ-treated mice when administered with the same dose. Study of in vivo cytotoxic activity of 19a on xenografted MM cells is currently underway. Conclusion: We demonstrated the cytotoxic activity of a syringolin analog on various MM cells at nanomolar levels, which was attributed to the dual inhibition of beta 5 and 2 subunits of the 20S proteasome. Compound 19a, as a dual inhibitor of beta 2 and 5, was observed to be a more potent PI than BTZ, and could overcome the acquired BTZ resistance. The findings provide new insight into the treatment of relapse and/or refractory MM. Table Table. Disclosures Ishida: Celgene KK: Research Funding; Kyowa Hakko Kirin, Co., Ltd.: Honoraria, Research Funding; Bayer Pharma AG: Research Funding. Iida:Janssen Pharmaceuticals: Honoraria, Research Funding; Celgene: Honoraria, Research Funding.

Abstract: Background: Several studies have demonstrated that aberrant expression of microRNAs in multiple myeloma (MM) cells is associated with the pathogenesis and development of MM. Recently, circulating serum microRNAs have been recognized as novel biomarkers in tumor biology and have predictive value in determining the efficacy of various drugs. However, little is known regarding the role of circulating serum microRNAs in patients with MM in terms of MM biology and the clinical efficacy of anti-MM drugs. In this study, we evaluated the expression levels of serum microRNAs in patients with MM, including newly diagnosed (ND) and relapsed and/or refractory (RR) cases. We also evaluated the correlation of the expression levels of serum microRNAs with the clinical efficacy of bortezomib (BTZ)-containing treatment. Materials & Methods: Fifteen serum samples from healthy donors and 62 from 10 patients with NDMM and 52 patients with RRMM were collected and subjected to comprehensive microRNA analysis using next-generation sequencing (NGS). First, we compared the microRNA expression levels between healthy donors and patients with MM. Next, using 52 serum samples collected from patients with NDMM and RRMM who received BTZ plus low-dose dexamethasone (Bd) therapy, the correlation between the response to Bd therapy and specific serum microRNA expression profiles was determined. Results: Approximately 150-250 microRNAs were detected by small RNA analysis of serum samples using NGS. The expression levels of 32 serum microRNAs were higher in MM than in healthy donors (Mann-Whitney U test, P 〈 0.05). Among them, 5 microRNAs (mir-10a, 10b, 92a, 378a, and 378d) had higher expression in RRMM than in NDMM. These microRNAs are involved in the biology and oncogenesis of several solid tumors, including MM. The mir-92a expression level has been associated with the response to chemotherapy and disease progression in MM. Regarding the correlation between microRNA expression levels and the clinical efficacy of Bd therapy, expression levels of 14 microRNAs were associated with progression-free survival (PFS) in Bd therapy (Spearmanfs rho 〈 -0.2, P 〈 0.05). Among them, 5 microRNAs (mir-22, 146a, 193b, 584, and 1307) showed high correlation with PFS (Spearmanfs rho 〈 -0.4, P 〈 0.002). These microRNAs are involved in angiogenesis, proliferation, and apoptosis in several solid tumors and MM. Next, we divided the 52 samples into two groups according to PFS: short ( 〈 6 months; n = 27) or long (≥6 months; n = 25). The short-PFS group showed lower expression of 5 microRNAs (mir-22, 146a, 193b, 320b, and 320c) than the long-PFS group did (Mann-Whitney U test, P 〈 0.01). Among them, mir-146a can regulate TRAF6, NF-kB, and TNF-axis, and is regulated by the c-Myc at the transcriptional level. c-Myc-mediated mir-146a overexpression can reduce CXCR4 expression. Several studies suggest that CXCR4 expression is an important factor for MM cells to migrate and interact with stromal cells; lower expression is recognized as a poor prognostic factor in the survival of patients with MM. Therefore, we hypothesized that BTZ-insensitive clone has high mir-146a expression along with low CXCR4 expression, suggesting that low dependence on stromal cells may contribute to the resistance to BTZ activity. Conclusion: We have demonstrated that the expression levels of several serum microRNAs are associated with the progression of MM and may serve as predictive markers in BTZ-containing therapies in MM. Further validation studies in a larger number of patients is needed and the origin of these serum microRNAs, together with the functional consequences of aberrant expression, must be pursued. Our findings can contribute in developing circulating microRNA analysis as a potential strategy in determining useful biomarkers for diagnosis and therapeutic outcomes in MM. Figure Figure. Disclosures Ishida: Celgene KK: Research Funding; Kyowa Hakko Kirin, Co., Ltd.: Honoraria, Research Funding; Bayer Pharma AG: Research Funding. Iida:Celgene: Honoraria, Research Funding; Janssen Pharmaceuticals: Honoraria, Research Funding.