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CD38 is highly and uniformly expressed on multiple myeloma (MM) cells, and at relatively low levels on normal lymphoid and myeloid cells, and in some tissues of nonhematopoietic origin. CD38 is a transmembrane glycoprotein with ectoenzymatic activity, and also functions as a receptor and adhesion molecule. Altogether, this has triggered the development of several CD38 antibodies including daratumumab (fully human), isatuximab (chimeric), and MOR202 (fully human). CD38 antibodies have pleiotropic mechanisms of action including Fc-dependent immune-effector mechanisms, direct apoptotic activity, and immunomodulatory effects by the elimination of CD381 immune-suppressor cells. CD38-targeting antibodies are generally well tolerated and induce partial response or better in ~30% of heavily pretreated MM patients as monotherapy. Based on their distinct mechanisms of action, favorable toxicity profile, and single-agent activity, CD38 antibodies are attractive partners in combination regimens. Indeed, deep responses and prolonged progression-free survival can be achieved in relapsed/refractory MM patients when CD38 antibodies are combined with immunomodulatory agents or proteasome inhibitors. Infusion-related reactions, which typically occur during the first infusion, are the most frequent adverse events. Attention should also be paid to the interference of CD38 antibodies with certain laboratory assays, which may complicate response evaluation and blood compatibility testing. Several studies are currently examining the role of CD38-based therapies in newly diagnosed and highrisk smoldering MM. Furthermore, CD38 antibodies are currently also under investigation in other hematologic malignancies, including acute lymphoblastic leukemia, natural killer/T-cell lymphoma, and acute myeloid leukemia, as well as in solid tumors. [ABSTRACT FROM AUTHOR]

Ixazomib is the first investigational oral proteasome inhibitor to be studied clinically. In this phase 1 trial, 60 patients with relapsed/refractory multiple myeloma (median of 4 prior lines of therapy; bortezomib, lenalidomide, thalidomide, and carfilzomib/marizomib in 88%, 88%, 62%, and 5%, respectively) received single-agent ixazomib 0.24 to 2.23 mg/m2 (days 1, 4, 8, 11; 21-day cycles). Two dose-limiting toxicities (grade 3 rash; grade 4 thrombocytopenia) occurred at 2.23 mg/m2. The maximum tolerated dose was 2.0 mg/m2, which 40 patients received in 4 expansion cohorts. Patients received a median of 4 cycles (range, 1-39); 18% received ⩾12 cycles. Eighty-eight percent had drug-related adverse events, including nausea (42%), thrombocytopenia (42%), fatigue (40%), and rash (40%); drug-related grade ⩾3 events included thrombocytopenia (37%) and neutropenia (17%). Grade 1/2 drug-related peripheral neuropathy occurred in 12% (no grade ⩾3). Two patients died on the study (both considered unrelated to treatment). The terminal half-life of ixazomib was 3.3 to 7.4 days; plasma exposure increased proportionally with dose (0.48-2.23 mg/m2). Among 55 response-evaluable patients, 15% achieved partial response or better (76% stable disease or better). These findings have informed the subsequent clinical development of ixazomib in multiple myeloma. [ABSTRACT FROM AUTHOR]

Proteasome inhibition has emerged as an important therapeutic strategy in multiple myeloma (MM). Since the publication of the first phase 1 trials of bortezomib 10 years ago, this first-in-class proteasome inhibitor (PI) has contributed substantially to the observed improvement in survival in MM patients over the past decade. Although first approved as a single agent in the relapsed setting, bortezomib is now predominantly used in combination regimens. Furthermore, the standard twice-weekly schedule may be replaced by weekly infusion, especially when bortezomib is used as part of combination regimens in frontline therapy. Indeed, bortezomib is an established component of induction therapy for patients eligible or ineligible for autologous stem cell transplantation. Bortezomib has also been incorporated into conditioning regimens before autologous stem cell transplantation, as well as into post-ASCT consolidation therapy, and in the maintenance setting. In addition, a new route of bortezomib administration, subcutaneous infusion, has recently been approved. Recently, several new agents have been introduced into the clinic, including carfilzomib, marizomib and MLN9708, and trials investigating these "second-generation" Pis in patients with relapsed/refractory MMs have demonstrated positive results. This review provides an overview of the role of Pis in the treatment of MM, focusing on developments over the past decade. (Blood. 2012;120(5):947-959) [ABSTRACT FROM AUTHOR]

Objectives: To evaluate the safety and efficacy of maintenance therapy with the oral proteasome inhibitor ixazomib in patients with newly diagnosed multiple myeloma (NDMM) not undergoing transplantation. Methods: Data were pooled from four NDMM phase I/II studies; patients received induction therapy with once‐ or twice‐weekly ixazomib plus lenalidomide‐dexamethasone (IRd), melphalan‐prednisone (IMP), or cyclophosphamide‐dexamethasone (ICd), followed by single‐agent ixazomib maintenance, given at the last tolerated dose during induction, until disease progression, death, or unacceptable toxicity. Results: A total of 121 patients achieved stable disease or better after induction (weekly IRd, n = 25; twice‐weekly IRd, n = 18; weekly or twice‐weekly IMP, n = 35; weekly ICd, n = 43) and received ≥ 1 dose of ixazomib maintenance. Grade ≥ 3 drug‐related adverse events occurred in 24% of patients during maintenance; each event was reported in ≤2% of patients. Rates of complete response were 22% after induction and 35% after maintenance. A total of 28 patients (23%) improved their response during maintenance. Conclusions: Ixazomib maintenance following ixazomib‐based induction is associated with deepening of responses and a positive safety profile with no cumulative toxicity in patients with NDMM not undergoing transplantation, suggesting that ixazomib is feasible for long‐term administration. Phase III investigation of ixazomib maintenance is ongoing. [ABSTRACT FROM AUTHOR]

Summary: For patients with newly diagnosed multiple myeloma, survival outcomes continue to improve significantly: however, nearly all patients will relapse following induction treatment. Optimisation of induction therapy is essential to provide longer term disease control and the current standard of care for most patients incorporates an immunomodulatory agent and proteasome inhibitor, most commonly lenalidomide and bortezomib in combination with dexamethasone (RVD), with maintenance until progression. Historically there has been limited access to RVD as an induction strategy outside of the United States; fortunately, there is now increasing access worldwide. This review discusses the rationale for use of RVD as induction therapy and aims to provide guidance in prescribing this regimen in order to optimise efficacy while minimising the toxicities of treatment. We also highlight the increasing evidence for the utility of addition of a monoclonal antibody to the RVD backbone to deepen responses and potentially provide longer disease control. [ABSTRACT FROM AUTHOR]

The treatment of multiple myeloma (MM) has gone through several major advances over the last 5 years with the introduction of next generation proteasome inhibitors (PI; carfilzomib, ixazomib) and immunomodulatory derivatives (IMiD; pomalidomide), with these new agents having a substantial impact on patient outcome. However, despite these advances, MM remains a highly resistant disease given its propensity for clonal heterogeneity and its complex interaction with the surrounding bone marrow microenvironment. Almost all patients eventually relapse despite therapeutic responses to a PI, IMiD or both. With the regulatory approval of the monoclonal antibodies Daratumumab and Elotuzumab in 2015, impressive and durable responses are being observed, even in heavily pre-treated patients who have exhausted other therapeutic options, suggesting immunological approaches in this setting have real merit. This review will focus on newer monoclonal antibodies and chimericantigen receptor (CAR) T cell strategies currently under investigation and in various stages of clinical development. [ABSTRACT FROM AUTHOR]

Multiple myeloma (MM) is the second most common haematological malignancy after non-Hodgkin lymphoma. Despite the improvement in outcomes over the last decade with the introduction of novel therapies, such as immunomodulatory agents (IMiDs) and proteasome inhibitors (PIs), MM remains an incurable disease. Patients who are both refractory to IMiDs and PIs carry a particularly dismal prognosis. The development of targeted therapy in the form of monoclonal antibodies has shifted the treatment paradigm of this disease, resulting in unprecedented response rates, even among the highest-risk patients. In this review, we will summarize the mechanism of action and provide an overview of the clinical trials that have led to the US Food and Drug Administration approval of Daratumumab and Elotuzumab, and their current use in the treatment of MM. [ABSTRACT FROM AUTHOR]

Summary: Patients with multiple myeloma (MM) have improved treatment options, including immunomodulatory drugs (IMiDs) and proteasome inhibitors (PIs). Despite their efficacy, increased rates of cardiovascular (CV) complications occur in patients exposed to some of these therapies. While previous research has focused on identifying the toxicities inherent to each specific agent, the CV side effects may be potentiated by the combination of PIs and IMiDs plus dexamethasone. We present a patient with MM with recurrent cardiotoxicity only when exposed to combination PI and IMiD‐based therapy. We also review the literature in this context, and propose a potential algorithm for cardiotoxicity prevention in this population. [ABSTRACT FROM AUTHOR]

Marizomib ( MRZ) is an irreversible, pan-subunit proteasome inhibitor ( PI) in clinical development for relapsed/refractory multiple myeloma ( RRMM) and glioma. This study analysed MRZ, pomalidomide ( POM) and low-dose dexamethasone (Lo- DEX) [ PMD] in RRMM to evaluate safety and determine the maximum tolerated dose ( MTD) and/or recommended Phase 2 dose ( RP2D). Intravenous MRZ (0·3-0·5 mg/m2) was administered over 2 h on days 1, 4, 8, 11; POM (3-4 mg) on days 1-21; and Lo- DEX (5 or 10 mg) on days 1, 2, 4, 5, 8, 9, 11, 12, 15, 16, 22 and 23 of every 28-day cycle. Thirty-eight patients were enrolled that had received a median of 4 (range 1-10) prior lines of therapy; all patients received prior lenalidomide and bortezomib. No dose-limiting toxicities ( DLTs) were observed and 0·5 mg/m2 MRZ was determined to be the RP2D. The most common treatment-related ≥Grade 3 adverse events were: neutropenia (11/38 patients: 29%), pneumonia (4/38 patients 11%), anaemia (4/38 patients; 11%) and thrombocytopenia (4/38 patients; 11%). The overall response rate and clinical benefit rate was 53% (19/36) and 64% (23/36), respectively. In conclusion, PMD was well tolerated and demonstrated promising activity in heavily pre-treated, high-risk RRMM patients. [ABSTRACT FROM AUTHOR]

The oral proteasome inhibitor ixazomib is approved in the United States, European Union and other countries, in combination with oral lenalidomide and dexamethasone (Rd), for the treatment of patients with multiple myeloma who have received at least one prior therapy. Approval was based on the global, randomised, double-blind, placebo-controlled Phase III TOURMALINE- MM1 study of ixazomib-Rd ( IRd) versus placebo-Rd in patients with relapsed/refractory multiple myeloma. IRd resulted in a significant improvement in progression-free survival versus placebo-Rd (median: 20·6 vs. 14·7 months; hazard ratio 0·74). Common toxicities observed more commonly with IRd versus placebo-Rd were thrombocytopenia, nausea, vomiting, diarrhoea, constipation, rash, peripheral neuropathy, peripheral oedema and back pain; these were generally grade 1/2 in severity except for thrombocytopenia (19% vs. 9% grade 3/4), which appeared manageable and reversible, with no differences between arms in significant bleeding or dose discontinuations. No cumulative toxicities were observed, indicating the potential feasibility of long-term IRd treatment. Safety data from TOURMALINE- MM1 are reviewed and guidance for managing clinically relevant adverse events associated with IRd is provided. Most toxicities were manageable with supportive care and dose delays or reductions as needed. Clinicians should be aware of and understand these potential side effects to optimise and prolong patient benefit. [ABSTRACT FROM AUTHOR]

Marizomib, a natural marine product, is an irreversible proteasome inhibitor currently under investigation in relapsed-refractory multiple myeloma ( RRMM) and malignant glioma. Central nervous system-multiple myeloma ( CNS- MM) is a rare manifestation of extra-medullary disease with few therapeutic options, highlighting the unmet clinical need in these patients. Marizomib demonstrated encouraging activity in RRMM and has emerging clinical activity in glioma, making it a potential CNS- MM therapeutic intervention. Herein, we present two patients with RRMM and CNS involvement who benefited from marizomib-based therapy. These cases provide the first proof of principle for further exploring marizomib in CNS- MM patients. [ABSTRACT FROM AUTHOR]

Multiple myeloma (MM) has proven clinically susceptible tomodulation of pathways of protein homeostasis. Blockade of proteasomal degradation of polyubiquitinated misfolded proteins by the proteasome inhibitor bortezomib (BTZ) achieves responses and prolongs survival in MM, but long-term treatment with BTZ leads to drug-resistant relapse in most patients. In a proof-of-concept study, we previously demonstrated that blocking aggresomal breakdown of polyubiquitinated misfolded proteins with the histone deacetylase 6 (HDAC6) inhibitor tubacin enhances BTZ-induced cytotoxicity in MM cells in vitro. However, these foundational studies were limited by the pharmacologic liabilities of tubacin as a chemical probe with only in vitro utility. Emerging from a focused library synthesis, a potent, selective, and bioavailable HDAC6 inhibitor, WT161, was created to study the mechanism of action of HDAC6 inhibition in MM alone and in combination with BTZ. WT161 in combination with BTZ triggers significant accumulation of polyubiquitinated proteins and cell stress, followed by caspase activation and apoptosis. More importantly, this combination treatment was effective in BTZ-resistant cells and in the presence of bone marrow stromal cells, which have been shown to mediate MM cell drug resistance. The activity of WT161 was confirmed in our human MM cell xenograft mouse model and established the framework for clinical trials of the combination treatment to improve patient outcomes in MM. [ABSTRACT FROM AUTHOR]

Proteasome inhibitors ( PIs) are highly active in multiple myeloma ( MM) but resistance is commonly observed. All clinical stage PIs effectively inhibit chymotrypsin-like ( CT-L) activity; one possible mechanism of resistance is compensatory hyperactivation of caspase-like (C-L) and trypsin-like (T-L) subunits, in response to CT-L blockade. Marizomib ( MRZ), an irreversible PI that potently inhibits all three 20S proteasome subunits with a specificity distinct from other PIs, is currently in development for treatment of MM and malignant glioma. The pan-proteasome pharmacodynamic activity in packed whole blood and peripheral blood mononuclear cells was measured in two studies in patients with advanced solid tumours and haematological malignancies. Functional inhibition of all proteasome subunits was achieved with once- or twice-weekly MRZ dosing; 100% inhibition of CT-L was frequently achieved within one cycle at therapeutic doses. Concomitantly, C-L and T-L activities were either unaffected or increased, suggesting compensatory hyperactivation of these subunits. Importantly, this response was overcome by continued administration of MRZ, with robust inhibition of T-L and C-L (up to 80% and 50%, respectively) by the end of Cycle 2 and maintained thereafter. This enhanced proteasome inhibition was independent of tumour type and may underlie the clinical activity of MRZ in patients resistant to other PIs. [ABSTRACT FROM AUTHOR]

The efficacy and favorable safety profile of daratumumab monotherapy in multiple myeloma (MM) was previously reported. An updated pooled analysis of 148 patients treated with daratumumab 16 mg/kg is presented. Data were combined from part 2 of a "first-in-human," phase 1/2 study of patients who relapsed after or were refractory to ⩾2 prior therapies and a phase 2 study of patients previously treated with ⩾3 prior lines of therapy (including a proteasome inhibitor [PI] and immunomodulatory drug [IMiD]) or were double refractory. Among the pooled population, patients received a median (range) of 5 (2-14) prior lines of therapy, and 86.5% were double refractory to a PI and IMID. Overall response rate was 31.1%, including 13 very good partial responses, 4 complete responses, and 3 stringent complete responses. The median duration of response was 7.6 months (95% confidence interval [CI], 5.6-not evaluable [NE]). The median progression-free survival (PFS) and overall survival (OS) was 4.0 months (95% CI, 2.8-5.6) and 20.1 months (95% CI, 16.6-NE), respectively. When stratified by responders versus stable disease/minimal response versus progressive disease/NE, median PFS was 15.0 months (95% CI, 7.4-NE) versus 3.0 months (95% CI, 2.8-3.7) versus 0.9 months (95% CI, 0.9-1.0), respectively, and median OS was NE (95% CI, NE-NE) versus 18.5 months (95% CI, 15.1-22.4) versus 3.7 months (95% CI, 1.7-7.6), respectively. No new safety signals were identified. In this pooled dataset, daratumumab 16 mg/kg monotherapy demonstrated rapid, deep, and durable responses, with a clinical benefit that extended to patients with stable disease or better. [ABSTRACT FROM AUTHOR]

The proteasome inhibitor bortezomib is an effective therapy for the treatment of relapsed and refractory multiple myeloma (RRMM); however, prolonged treatment can be associated with toxicity, peripheral neuropathy and drug resistance. Our earlier studies showed that the novel proteasome inhibitor marizomib is distinct from bortezomib in its chemical structure, mechanisms of action and effects on proteasomal activities, and that it can overcome bortezomib resistance. Pomalidomide, like lenalidomide, has potent immunomodulatory activity and has been approved by the US Food and Drug Administration for the treatment of RRMM. Here, we demonstrate that combining low concentrations of marizomib with pomalidomide induces synergistic anti-MM activity. Marizomib plus pomalidomide-induced apoptosis is associated with: (i) activation of caspase-8, caspase-9, caspase-3 and PARP cleavage, (ii) downregulation of cereblon (CRBN), IRF4, MYC and MCL1, and (iii) suppression of chymotrypsin-like, caspaselike, and trypsin-like proteasome activities. CRBN-siRNA attenuates marizomib plus pomalidomide-induced MM cells death. Furthermore, marizomib plus pomalidomide inhibits the migration of MM cells and tumour-associated angiogenesis, as well as overcomes cytoprotective effects of bone marrow microenvironment. In human MM xenograft model studies, the combination of marizomib and pomalidomide is well tolerated, inhibits tumour growth and prolongs survival. These preclinical studies provide the rationale for on-going clinical trials of combined marizomib and pomalidomide to improve outcome in patients with RRMM. [ABSTRACT FROM AUTHOR]

Proteasome inhibitors ( PI) and immunomodulatory agents ( IMIDs) have improved the overall survival (OS) of patients with multiple myeloma ( MM), but concerns have been raised about increased incidence of extramedullary disease ( EMD) after the combined use of PIs and IMIDs for upfront therapy. We evaluated whether the addition of lenalidomide to bortezomib-based front-line regimens precipitated earlier development of EMD. We reviewed the charts of 117 MM patients (median follow-up from diagnosis 6·1 years; range 0·1-10·2 years) enrolled in eight clinical trials of first-line treatment with bortezomib-based regimens, with or without lenalidomide. We assessed development of EMD as extraosseous (distant from bone) or osseous (originating from bone) plasmacytomas. The primary endpoint was time from diagnosis until development of EMD, based on imaging, biopsy and/or physical examination. Any form of EMD at progression was observed in 40 (34·2%) patients, including 21 (18%) osseous, 8 (7%) extraosseous and 11 (9%) both osseous and extraosseous. Median OS was 0·9 years (range 0·1-4·8 years) after extraosseous EMD development. Sensitivity analyses with follow-up times truncated at 5 years detected no statistically significant difference in rates of any EMD form between the two groups ( P > 0·2 for each comparison). Therefore, we observed no evidence that bortezomib-lenalidomide-based front-line therapy precipitates earlier EMD. [ABSTRACT FROM AUTHOR]

Summary Background The combination of bortezomib, lenalidomide, and dexamethasone is a highly effective therapy for newly diagnosed multiple myeloma. Ixazomib is an investigational, oral, proteasome inhibitor with promising anti-myeloma effects and low rates of peripheral neuropathy. In a phase 1/2 trial we aimed to assess the safety, tolerability, and activity of ixazomib in combination with lenalidomide and dexamethasone in newly diagnosed multiple myeloma. Methods We enrolled patients newly diagnosed with multiple myeloma aged 18 years or older with measurable disease, Eastern Cooperative Oncology Group performance status 0–2, and no grade 2 or higher peripheral neuropathy, and treated them with oral ixazomib (days 1, 8, 15) plus lenalidomide 25 mg (days 1–21) and dexamethasone 40 mg (days 1, 8, 15, 22) for up to 12 28-day cycles, followed by maintenance therapy with ixazomib alone. In phase 1, we gave patients escalating doses of ixazomib (1·68–3·95 mg/m 2 ) to establish the recommended dose for phase 2. The primary endpoints were maximum tolerated dose for phase 1, and the rate of very good partial response or better for phase 2. Safety analyses were done in all patients who received at least one dose of study drug; efficacy analyses were done in all patients who received at least one dose of study drug at the phase 2 dose, had measurable disease at baseline, and had at least one post-baseline response assessment. This study is registered at ClinicalTrials.gov , number NCT01217957 . Findings Between Nov 22, 2010, and Feb 28, 2012, we enrolled 65 patients (15 to phase 1 and 50 to phase 2). Four dose-limiting toxic events were noted in phase 1: one at a dose of ixazomib of 2·97 mg/m 2 and three at 3·95 mg/m 2 . The maximum tolerated dose of ixazomib was established as 2·97 mg/m 2 and the recommended phase 2 dose was 2·23 mg/m 2 , which was converted to a 4·0 mg fixed dose based on population pharmacokinetic results. Grade 3 or higher adverse events related to any drug were reported in 41 (63%) patients, including skin and subcutaneous tissue disorders (11 patients, 17%), neutropenia (eight patients, 12%), and thrombocytopenia (five patients, 8%); drug-related peripheral neuropathy of grade 3 or higher occurred in four (6%) patients. Five patients discontinued because of adverse events. In 64 response-evaluable patients, 37 (58%, 95% CI 45–70) had a very good partial response or better. Interpretation The all-oral combination of weekly ixazomib plus lenalidomide and dexamethasone was generally well tolerated and appeared active in newly diagnosed multiple myeloma. These results support the phase 3 trial development of this combination for multiple myeloma. Funding Millennium Pharmaceuticals, a wholly owned subsidiary of Takeda Pharmaceutical International Company. [ABSTRACT FROM AUTHOR]

Proteasome inhibitors have demonstrated that targeting protein degradation is effective therapy in multiple myeloma (MM). Here we show that deubiquitylating enzymes (DUBs) USP14 and UCHL5 are more highly expressed in MM cells than in normal plasma cells. USP14 and UCHL5 short interfering RNA knockdown decreases MM cell viability. A novel 19S regulatory particle inhibitor b-AP15 selectively blocks deubiquitylating activity of USP14 and UCHL5 without inhibiting proteasome activity. b-AP15 decreases viability in MM cell lines and patient MM cells, inhibits proliferation of MM cells even in the presence of bone marrow stroma cells, and overcomes bortezomib resistance. Anti-MM activity of b-AP15 is associated with growth arrest via downregulation of CDC25C, CDC2, and cyclin B1 as well as induction of caspase-dependent apoptosis and activation of unfolded protein response. In vivo studies using distinct human MM xenograft models show that b-AP15 is well tolerated, inhibits tumor growth, and prolongs survival. Combining b-AP15 with suberoylanilide hydroxamic acid, lenalidomide, or dexamethasone induces synergistic anti-MM activity. Our preclinical data showing efficacy of b-AP15 in MM disease models validates targeting DUBs in the ubiquitin proteasomal cascade to overcome proteasome inhibitor resistance and provides the framework for clinical evaluation of USP14/UCHL5 inhibitors to improve patient outcome in MM. [ABSTRACT FROM AUTHOR]

Purpose: Bortezomib is an important agent in multiple myeloma treatment, but resistance in cell lines and patients has been described. The main mechanisms of resistance described in cancer fall into one of two categories, pharmacokinetic resistance (PK), e.g. over expression of drug efflux pumps and pharmacodynamic resistance, e.g. apoptosis resistance or altered survival pathways, where the agent reaches an appropriate concentration, but this fails to propagate an appropriate cell death response. Of the known pump mechanisms, P-glycoprotein (P-gp) is the best studied and considered to be the most important in contributing to general PK drug resistance. Resistance to bortezomib is multifactorial and there are conflicting indications that cellular overexpression of P-gp may contribute to resistance agent. Hence, better characterization of the interactions of this drug with classical resistance mechanisms should identify improved treatment applications. Methods: Cell lines with different P-gp expression levels were used to determine the relationship between bortezomib and P-gp. Coculture system with stromal cells was used to determine the effect of the local microenvironment on the bortezomib-elacridar combination. To further assess P-gp function, intracellular accumulation of P-gp probe rhodamine-123 was utilised. Results: In the present study, we show that bortezomib is a substrate for P-gp, but not for the other drug efflux transporters. Bortezomib activity is affected by P-gp expression and conversely, the expression of P-gp affect bortezomib's ability to act as a P-gp substrate. The local microenvironment did not alter the cellular response to bortezomib. We also demonstrate that bortezomib directly affects the expression and function of P-gp. Conclusions: Our findings strongly support a role for P-gp in bortezomib resistance and, therefore, suggest that combination of a P-gp inhibitor and bortezomib in P-gp positive myeloma would be a reasonable treatment combination to extend efficacy of this important drug. [ABSTRACT FROM AUTHOR]

Variations within proteasome β (PSMB) genes, which encode the β subunits of the 20S proteasome, may affect proteasome function, assembly, and/or binding of proteasome inhibitors. To investigate the potential association between PSMB gene variants and treatment-emergent resistance to bortezomib and/or long-term outcomes, in the present study, PSMB gene sequence variation was characterized in tumor DNA samples from patients who participated in the phase 3 Assess ment of Proteasome Inhibition for Extending Remissions (APEX) study of bortezomib versus high-dose dexamethasone for treatment of relapsed multiple myeloma. Twelve new PSMB variants were identified. No associations were found between PSMB single nucleotide polymorphism genotype frequency and clinical response to bortezomib or dexamethasone treatment or between PSMB single nucleotide polymorphism allelic frequency and pooled overall survival or time to progression. Although specific PSMB5 variants have been identified previously in preclinical models of bortezomib resistance, these variants were not detected in patient tumor samples collected after clinical relapse from bortezomib, which suggests that alternative mechanisms underlie bortezomib insensi-tivity [ABSTRACT FROM AUTHOR]

miRs play a critical role In tumor patho-genesis as either oncogenes or tumor-suppressor genes. However, the role of miRs and their regulation in response to proteasome inhibitors in multiple my-eloma (MM) Is unclear. In the current study, miR profiling in proteasome inhibi-tor MLN2238-treated MM.1S MM cells shows up-regulation of miR33b. Mecha-nistic studies indicate that the induction of miR33b is predominantly via transcrip-tional regulation. Examination of miR33b in patient MM cells showed a constitutively low expression. Overexpression of miR33b decreased MM cell viability, migra-tion, colony formation, and increased ap-optosis and sensitivity of MM cells to MLN2238 treatment. In addition, overex-pression of miR33b or MLN2238 expo-sure negatively regulated oncogene PIM-1 and blocked PIM-1 wild-type, but not PIM-1 mutant, luciferase activity. Moreover, PIM-1 overexpression led to significant abrogation of miR33b- or MLN2238-induced cell death. SGI-1776, a biochemi-cal inhibitor of PIM-1, triggered apoptosis in MM. Finally, overexpression of miR33b Inhibited tumor growth and prolonged survival In both subcutaneous and dis-seminated human MM xenograft models. Our results show that miR33b is a tumor suppressor that plays a role during MLN2238-induced apoptotic signaling in MM cells, and these data provide the basis for novel therapeutic strategies targeting miR33b In MM. [ABSTRACT FROM AUTHOR]

• In ICARIA-MM, isatuximab-pomalidomide-dexamethasone (Isa-Pd) improved PFS in RRMM. • We assessed Isa-Pd versus Pd in RRMM by prior lines of therapy/refractory status. • Isa-Pd improved PFS in RRMM regardless of prior lines of therapy/refractory status. • Isa-Pd improved ORR in RRMM regardless of prior lines of therapy/refractory status. • Overall safety profile of Isa-Pd is manageable in RRMM patients. Patients with relapsed/refractory multiple myeloma (RRMM) experience several relapses, and become refractory to successive therapies. In the ICARIA-MM trial (NCT02990338), isatuximab plus pomalidomide-dexamethasone prolonged median progression-free survival (PFS) in patients with RRMM. This subgroup analysis of ICARIA-MM assessed the treatment benefit of isatuximab by prior lines of therapy and refractory status. A total of 307 patients were randomized to isatuximab-pomalidomide-dexamethasone (n = 154) or pomalidomide-dexamethasone (n = 153). Isatuximab (10 mg/kg intravenously) was given weekly in the first 28-day cycle, then every other week. Standard pomalidomide-dexamethasone doses were given. PFS was assessed by prior lines and refractory status. Overall, 102 (66 %) patients receiving isatuximab-pomalidomide-dexamethasone and 101 (66 %) patients receiving pomalidomide-dexamethasone had received 2–3 prior lines; 52 (34 %) and 52 (34 %) had received >3 prior lines, respectively. Median PFS was higher with isatuximab-pomalidomide-dexamethasone versus pomalidomide-dexamethasone for patients who received 2–3 prior lines of therapy (12.3 vs. 7.8 months) and >3 prior lines of therapy (9.4 vs. 4.3 months). Median PFS was higher with isatuximab-pomalidomide-dexamethasone versus pomalidomide-dexamethasone for patients who were lenalidomide-refractory (11.4 vs. 5.6 months), lenalidomide-refractory at last line (11.6 vs. 5.7 months), refractory to a proteasome inhibitor (PI) (11.4 vs. 5.6 months), and double-refractory (11.2 vs. 4.8 months). Overall response rate (ORR) in patients receiving isatuximab-pomalidomide-dexamethasone versus pomalidomide-dexamethasone was 59.0 % versus 31.4 % in lenalidomide-refractory; 60.2 % versus 32.2 % in PI-refractory; and 58.6 % versus 29.9 % in double-refractory patients. Isatuximab-pomalidomide-dexamethasone improved PFS and ORR regardless of prior lines of therapy or refractory status, consistent with the benefit in the overall population. [ABSTRACT FROM AUTHOR]